CA1335513C

CA1335513C - Speed control system for pump motor

Info

Publication number: CA1335513C
Application number: CA000615873A
Authority: CA
Inventors: Robert W. Allington
Original assignee: Isco Inc
Current assignee: Teledyne Isco Inc
Priority date: 1986-03-10
Filing date: 1990-09-25
Publication date: 1995-05-09
Anticipated expiration: 2007-03-06

Abstract

To provide smooth constant flow, a liquid chromatographic system comprises: a chromatographic column having an inlet; a pump for supplying fluid to the inlet of the chromatographic column; a power means for a pump motor; a feedback loop means for controlling said power means; means for alternately energizing and de-energizing said positive and negative feedback control means; said negative feedback control means receiving a signal from said means for measuring flow rate and including means for comparing said signal with said corrected flow rate reference signal while said second feedback loop is energized to generate an error signal controlling said power means; and said positive feedback control means applying an acceleration voltage to said motor from a time a preset period after the initiation of a return stroke of said piston until after a timed duration.

Description

' I 1 33551 ~
BACKGROUND OF THE INVENTTON
This invention is a division of copending Ap~lication No. 53I,3~7.
This invention re].ates to reciprocating pumps and control circuits for them.
In one class of reciprocating pump, a piston continuously reciprocates in a cylinder to direct]y force a liquid from the cylinder, a].ternately pulling liquid into the cylinder through an inlet port from a reservoir and pushing it from the cylinder through an outlet port to the destination of the liquid.
In some uses of this class of pump, the pumps are designed to reduce pulsation in the flow of fluid. One such use is ~iquid chromatography. It is desirab]e in ].iquid chromatography that ].iquid which is pumped through a chromatographic column flow at a constant flow rate through the co]umn so that different molecular species in the effluent from the column are eluted at times that are reproducible from run to run.. Pulses in whi.ch the liquid flows at unpredictab]e rates reduce this reproducibility.
In one type of prior art pump of this class, the pressure at the out]et port of the pump is measured by a pressure sensor. A feedback signal from the pressure sensor controLs the speed of the pump motor to cause the pump motor to react to changes in pressure in the chromatographic column and thus maintain a more constant rate of ~low of the fluid. One pump of this type is described in United States patent 3,~5,467, issued October 12, 1976 to~ Peter ~efferson.
This type of pump has a disadvantage when used in liquid chromatography in that it maintains pressure constant against varying pressure loads but may cause the rate of f~ow of fluid through the chromatographic column to vary, even in applications where it is desirable to maintain the rate of flow of liquid constant.
In another type of prior art pump of this class, the piston is driven at a constant rate while expelling liquid from the pump into the chromatographic column, but when returning on a fi]l stroke to draw fluid into the pump from the reservoir, the motor is driven at an increased and substantially constant speed to draw the 1uid into the pump more rapidly.
During the forward stroke of the piston in this type of prior art pump, the piston moves at a higher than normal rate until the pressure in the pump cylinder equals the pressure that existed near the end of the liquid expelling foward stroke of the piston and just before the piston began a refill stroke. After the pressure in the cylinder reaches the pressure during constant ~low rate pumping before the start of the refill stroke, the outlet valve is opened and the piston continues foward at a constant rate. This type of pump is described in-United States patent 4,131,393 issued December 26, 1978, to ~aaken T. Magnussen Jr. and 4,18~,375 issued December 25, 1979 to ~aaken T. Magnussen Jr.
This type of pump has severa] disadvantages such as for example: (1) the opening of the valveat the pressure of the last part of the previous cycle results in an increased time during which no liquid leaves the out~et port over that time needed to fill the cylinder; and (2) the constant speed o the motor during refill and pump up does not reduce the time before fluid leaves the pump as soon as it could.

~ 33~5 1 3 Accordingly, the invention provides a feedback system for controlling a motor comprising:
apparatus driven by a motor at a plurality of preselected speeds correlated with positions of the apparatus;
power means having an output signal for driving the motor at a speed related to the power means output signal;
means for generating a signal representing the velocity of the motor;
means for detecting a position of the apparatus for a 0 change of speed;
a feedback loop having velocity negative feedback means and positive feedback means and means for connecting the velocity negative feedback means and positive feedback means into circuit with the power means;
the feedback loop including means for alternately controlling the output signal from the power means by an input signal which increases in power with time under the control of an increasing positive feedback signal from the motor and by an input signal which varies in power in relation to the difference between a relative constant motor speed and a preset motor speed;
means for storing a preset analog value of velocity having an amplitude representing the preset analog value of velocity;
the velocity negative feedback means having means for comparing the preset analog value of velocity with the signal JJ: 4 1 3355 t 3 representing the velocity of the moto~ to generate a velocity feedback error signal for controlling the power means for driving the motor with an input power related to the velocity feedback error signal;
means for storing the velocity feedback error signal when the output signal from the power means is controlled by an input signal which increases in power with time under the control of an increasing positive feedback signal from the motor;
the positive feedback means including means for applying a signal to the power mean~ related to a constant, whereby the motor accelerates at a predetermining rate; and timing means for timing a period of time for the output signal from the power means to be controlled by an input signal which increases in power with time under the control of an increasing positive feedback signal from the motor, which period of time is related to the amplitude of the preset analog signal.
In a second embodiment, the invention provides an improvement to a feedback system for controlling an apparatus driven by a motor at a plurality of preselected speeds correlated with positions of the apparatus and having drive means for supplying power to drive the motor; means for generating a signal representing the velocity of the motor;
means for detecting a position of the apparatus; means for storing a preset analog value of velocity; negative velocity feedback means for comparing the preset analog value of velocity JJ: 4a 1 33~5 1 3 with the signal representing the velocity of the motor and generating a velocity feedback error signal for controlling the drive means; the negative velocity feedback means including a negative feedback loop, whereby the drive means may drive the motor with an input power related to the velocity feedback error signal. This improvement comprises:
a positive feedback means;
means for alternately controlling the output signal from the power means by an input signal which increases in power with time under the control of an increasing positive feedback signal from the motor and by an input signal which varies in power in relation to the difference be;ween a relative constant motor speed and a preset motor speed;
the negative velocity feedback means including a comparator means for generating an error signal;
means for storing the velocity feedback error signal;
the positive feedback means applying a signal to the drive means related to the amplitude of the velocity feedback error signal, whereby the motor accelerates; and timing means for timing a period of time for the output signal from the power means to be controlled by an input signal which increases in power with time under the control of an increasing positive feedback signal from the motor, which period of time is related to the preset analog signal.
Advantageously, there is a control means for alternately energizing and de-energizing said positive and JJ: 4b negative feedback loops. The negative velocity feedback loop receives a signal from said means for measuring pump velocity and includes means for comparing said signal with said flow rate reference signal while said positive feedback loop is energized to generate an error signal for controlling said driver circuit.
The positive feedback loop applies and acceleration voltage to said motor from a time a JJ: 4c preset period after the ini.~iation of a return stroke of said piston until after a timed duration related to the preset constant speed of the pump.
The positive feedback loop may cause said means to accelerate said motor at a rate related to the amplitude of power to the driver ci.rcuit while said negative feedback loop is de-energi.zed. The system may inc~.ude a sample-and-hold circui.t which stores a value of the amplitude of a factor related to the prevention of cavitation, a multiplier and means for applying said stored value through said multiplier to said positive feedback loop, whereby an acceleration potential is obtained, and the time of acceleration under the control of said positive feedback loop is related to the preset rate of flow.
Advantageously, the system may include means for detecting a position of the piston in said pump to determine the time for a change of speed; and means for storing a preset analog value of ve~ocity to determine a period for acceleration; said velocity negative feedback loop having means for comparing said preset analog value of velocity with said signal representing the velocity of the motor to generate a velocity feedback error signal for controlling said driver circuit with an input power level related to said velocity feedback error signal during a portion of a pumpi.ng cycle.
It may further include means for disconnect~ng said connectable ve~ocity negative feedback loop from the driver circuit and connecting said connectable positi.ve feedback loop; and means ~or storing a velocity feedback analog signa~; sai.d connect~able positive feedback loop applying a signal to said motor driver circuit related to said amplitude of the stored analog signal, whereby the motor accelerates; and timing means for timing a period from a~ter said connection of said .pa connectable positive feedback means re~ated to said stored analog signa~.
Advantageously, there is included a velocity feedback signal to control the ve]ocity of the pump in a constant velocity mode and said apparatus includes a permanent velocity feedback control loop for periodica-ly correcting said ve~ocity feedback signal.
A method of operating a chromatograph in a constant flow rate mode according to the invention comprises the steps of selecting a rate of ~low of liquid into a column; representing the flow rate in a digital code in terms of a number of pulses for , 13355~3 each cycle of a reciprocating pump; measuring the rate of movement of a piston in the reciprocating pump only in the ~irection in which it is pumpi.ng liquid into a chromatographic column; filling the cylinder of the reciprocating pump .in a stroke in a return direction of the piston with influent to be pumped into the chromatographic column with the motion,~in the return direction being controlled by a motor which accelerates starting at a time during-the return cyc~e and ends at a time during a pumping stroke related to the preset rate of flow into the chromatographic column.

Advantageously, the method includes the steps of controlling the amount of acceleration from asample-and-hold circuit representing the motor current; adjusting the signal in the samp]e and hold circuit by a value set empirica].ly to avoid cavitation; controlling the signal applied to a motor driver circuit to acce].erate the motor for a predetermined time by a timer set by the rate of flow; and causing the flow from the pump to communicate with the inlet of a chromatographiC
column, whereby a re]atively smooth and constant flow of influent into the column is provided. It may also include the step of measuring the motor 8 ~ 3~5~ ~ 3 current; and terminating the motor operation when the motor current exceeds a predeterminea amount.
~his method may further inc]ude the steps of controlling the speed of the pump motor in a first time period by velocity negative feedback;
controlling the speed of the motor i.n a second time period by positive feedback which constantly accelerates the pump motor; controlling the speed of the motor in both the first and second time periods by second velocity feedback system which monitors the rate of flow and corrects the input signal to the first feedback loop.
Advantageously, the speed of the piston in the reciprocating pump is contro~.led by the shape of a cam driven by the motor to provide constant f~ow during one portion of the rotation of the cam, acceleration during a refi~.]. portion and decelaration and acceleration during another portion of the pumping stroke without cavitation.
Preferably, the method is used for applying a gradient to the pump and pumping at a high pressure, whereby gradient elution under high pressure is provided with a constant time base by the detection and recording system of the liquid chromatograPh-SUMMARY OF T~F DRAWINGS
The above noted and other eatures of the invention will be hetter understood from the ollowing detaile~ description when considered with reference to the accompanying drawings i.n whi.ch:
FIG. 1 is a block diagram of a chromatographic system utilizing an embodiment o the inventiOn;
FIG. 2 iS a b~.ock diagram o a con~rol system for a high pressure pump ~n the chromatographic 10system of FIG. 1 in accordance with an embodiment of the invention;
FIG. 3 iS a block diagram of a motor circuit for a pump in accor~ance with the embodiment of FIG.
2;
FIG. 4 is a schematic circuit diagram of a portion of the motor control circuit of FIG. 3:
FIG. 5 iS a schematic circuit diagram of another portion o the motor control circuit of FIG.

3;
20FIG. 6 is a schematic circuit ~iagram o still another portion of the motor control circuit of FIG.
3;

FIG. 7 is a schematic circuit diagram of still another portion of the motor control circuit of FIG.
3;

~ 3355 1 3 FIG. 8 is schematic circuit diagram of another portion of the motor contro3. c;rcuit of FIG. 3;
FIG. 9 is a block ~iagram of a portion of the circuit of FIG. 2;
FIG. 10 is a block circuit diagram of one portion of the block diagram of FIG. 9;
FI~G. 11 is a schematic circuit diagram of a portion of the block diagram of FIG. 10;
FIG. 12 is a schematic ci.rcuit diagram of another portion of the block diagram of FIG. 10;
FIG. 13 is a schematic circuit diagram of a portion of the block diagram o FIG. 9;
FIG. 14 is a schematic circuit diagram of stil~
another portion of the block ~iagram of FIG. 9;
FIG. l5 is a schematic circuit diagram of sti].1 another portion of the block diagram of FIG. 9;
FIG. 16 is a schematic circuit diagram of still another portion of the block diagram of FIG. 9;
FIG. 17 is a schematic circuit diagram of another portion of the embodiment of the motor control circuit of FIG. 2;
FIG. 18 is a block diagram of stil] another portion of the block diagram of FIG. 2;
FIG. 19 is a block diagram of another portion of the block diagram of FIG. 2;

FIG. 20 is a block diagram of a portion of the block diagram of FIG. 18;
FIG. 21 is a schematic circuit diagram o-~-another portion of the block diagram o~ FIG. 18;
FIG. 22 is a b].ock diagram of a portion of the block diagram of FIG. 20;
FIG. 23 is a schematic circuit diagram of aportion of the b]ock diagram of FIG. 22;
FIG. 24 is a schematic circuit diagram of another portion of the b]ock diagram of FIG. 22;
FIG. 25 is a schematic circuit diagram of still another portion of the block diagram of FIG. 20;
FIG. 26 is a block diagram of still another portion of the block diagram of FIG. 2;
FIG. 27 is a b~ock diagram-of still another portion of the block diagram of the motor control system of FIG. 2;
FIG. 28 is a schematic circuit diagram of a portion of the block diagram of FIG. 25;
FIG. 29 is a schematic circuit diagram of sti.ll another portion of the block diagram of FIG. 26;
FIG. 30 is a sectional view, partly schematic, of a pump in accordance with an embodiment of the invention; and 12 1 33~51 3 FIG. 31 is a schematic circuit ~iagram of an average rate of flow circuit.

DETAILED DESCRIPTIOM
In FIG. 1, there is shown a block diagram of a chromatographic system 10, having a low pressure system 12, a high pressure pumping system 14, a high pressure pump control system 15, a chromatographic column, an injector system 18 and a detector and, collector system 20. The high pressure pumping system 14 communicates with the low pressure system 12 to receive sol,vents therefrom and with the chromatographic column and injector 18 to suppl.y the influent thereto for detection and at times col].ection by the detector and collector system 20.
To control the hiqh pressure pumping system 14, the high pressure pump control system 16 is electrically connected to the low pressure system 12 from which it receives signals relating to the flow rate of the influent to the chromatographic column and injector system 18 and is electrically connected to the high pressure pumping system 14 to maintain that flow rate as constant as possible.

The low pressure system 12, the ehromatographie column and injeetor system 1~ and the detector an~
collector system 20 are not part of this invention except insofar as they cooperate with the h;gh pressure pumping system 14 and the high pressure pump control system 16 to provide a constant flow rate of solvents through the chromatographic column and injector system 18.
~he low pressure system 12 includes a low pressure pumping and mixing system 24 and a gener~l system control].er 22. ~he genera]. system control].er 22 contains flow rate information and, in some configurations, gradient information as well as information for injecting samples i.nto the chromatographic column or providing data acquisition and processing funetions in conjunction with the detector and eolleetor system 20. The general system controller 22 is not part of the invent;on except insofar as it provides signals to the high pressure pump control system 16 to control the f~ow rate from the high pressure pumping system 14.

In FIG. 2, there is shown a block diagram of the high pressure control system 16 having a motor circuit 30, a flow rate circuit 32, a first flow rate control system 3~, a second flow rate control system 36 and an average flow rate control loop circuit 47. The first 10w rate control system and the second flow rate control system each appl.y signals to the flow rate control circuit through conductors 62 and 64, one of them app].ying generally linear signals duri.ng at least a portion of each cycle 'of operation of the motor circuit and the 10other applying non].inear signals through conductor 64.
The linear an~ nonlinear signa3s control a pulse-width-modulator within the flow rate circuit 32 which ultimately controls the speed of the motor circuit 30 to maintain the f]ow rate of the fluid through the chromatographic column and injector system 18 (FIG. 1) as nearly constant as possible.
~he linear and nonlinear signals are related, with the nonlinear signat being larger or smaller in 20relation to the linear siqnal and for thi,s purpose the first flow rate control system and second flow rate control system are e3ectricaLly connecte~

through a conductor 556 in a manner to be descri.bed hereinafter, The average flow rate control l.oop 1 3355 t 3 circuit 47 periodically measures output liquid flow during each cycle of the pump and changes the signal on conductor 46 representing the preset flow rate to maintain an average flow rate equal to the preset flow rate.
To provide a substantially linear signal during at least a portion of the motor circuit 30, the first flow rate control system 34 inc]udes a linear flow rate control circuit 38 and a first compensati.on circuit 40. The first compensation circuit 40 receives signals ~rom the motor circuit 30 to provide certain correction signals to the linear flow rate control circuit 38 to which it is connected. The linear flow rate control circuit 38 receives signals from the system'controller 22 (FIG.
1) on a conductor 46 indicating the desired rate of flow and supplies a resu]ting signal to the flow rate circuit 32 which inc].udes corrections made in response to the motor circuit 30 and from the first comp~nsation circuit 40.
To provide a signal to the flow rate circuit 32 to accelerate the pump motor, the nonlinear flow rate control system 36 inc~,udes a non].inear flow rate control circuit 42 and a second and positive feedback compensation circuit 44 (hereinafter second compensation circuit). The nonlinear flow rate control circuit 42 receives signals from the motor circuit 30 to which it is electrically connected and applies signals through an electrical connection to the flow rate circuit 32 as modified by signals from the second compensation circuit 44.
~ith this arrangement, the high pressure pump, control system 16 maintains the flow rate through the column relatively constant at the pro~rammed ra~e to cause the time at which peaks are detected ~o be reproducible because o~ pulses of fluid of different rates occurring at different times in the column rather than constantly e~'uting the molecular species from the column. Generally, the high pressure pump control system 16 controls the pump motor through the motor circuit 30 in such a way as to maintain the average flow of fluid at the preset rate and to minimize rapid fluctuations in flow rate such as might be caused by a refill stroke of a piston pump or the like.

1 3355 t 3 In FIG. 3, there is shown a block diagram of the flow rate circuit 32 and the motor circuit 30.
The flow rate control circuit 32: (1) receives a signal on conductor 62 during a portion of a pump cycle which is the output o~ a servo loop ana has a substantially linear relationship with the desired pumping rate; and (2) a signal on conductor 6~ which is a ramp nonlinear~y corrected in slope to relate to the preset average flow rate, to the accelerating refill speed. Both signals contain some corrections which are directed to establishing a rate of pumping which permits a single piston reciprocating pump to approach constant flow through a chromatographic column across a period of time.
The ~low rate circuit 32 is electrically connected to the motor circuit 30 through a conductor 66 to apply to the motor circuit 30 periodic pulse-~idth-modulated signals in which the pulse width (duty cycle) is related to the speed at which the piston is intended to move to: (1) reduce flow rate pulsations in the chLomatographic column by ~.aintai.ning the average rate of flow of inf~uent to the column in as constant as possibl.e; and (2) changing the piston speed to reduce the time that the pump is not forcing f~ui~ through its outlet port. The speed of the piston is controlled to avoid cavitation or changes in the flow rate that are so sudden as to disrupt the rate of flow through the chromatographic column an~ injector system 18 (FIG. 1).
To provide a speed of piston movement for constant ~low rate of the influent to the chromato-graphic column and injector system 18 (FIG. 1), the motor circuit 30 includes a motor 50, a brake circuit S2, a refill inception detector circuit 54, a tachometer aisc and sensors system 58, and an overcurrent sensor circuit 60. The motor 50 is driven by power applied throug-h the conductor 66 from the flow rate control circuit 32 and drives the piston of the pump (not shown in FIG. 3~ through its outlet shaft 56.
To slow the pump, dynamLc braking is under some circumstances applied to the motor through the brake circuit 52 in response to control signals on a conductor 70 indicating the time of application of the braking. The brake circuit 52 transmits signals through a conductor 72 to the first compensation circuit 40 (FIG. 2) Which iS used to adjust the motor speed at the end of a motor acceleration portion of a cycle to reduce drive power to the motor.
To aid in coordinating the pump motor control circuit within the second compensation circuit 44 (FIG. 2) the refill inception detector circuit 54 transmi,ts a signal on conductor 76 for application to the first compensation circuit 40 (FIG. 2) at the end of a liquid delivery stroke to initiate a refi]l portion of a cycle. This signa~ aids in timing the start and termination of motor accelerati.on.
To generate signals indicating the volume of fluid pumped and motor speed, the tachometer ~isc and sensors system 58 generates signals for application through conductor 78 to the ~inear f~ow rate control circuit 38 (FIG. 2) and the average flow rate control loop circuit 47 (FIG. 2). The overcurrent sensor circuit 6Q detects currents which exceed a preset va]ue in the motor circuit, usually indicating binding or a bearing fault, so as to avoid damage to of the pump.

13355~3 In FIG. 4, there is shown a schematic circuit diagram of the flow rate circuit 32 having a comparator circuit shown generally at 80 and a drive circuit shown general]y at 8 , with the comparator circuit 80 receiving a ramp signal on conductor 64 from the second flow rate control system 36 (FIG.
2), a linear signal on conauctor 62 from the first ~low rate control circuit 34 (FIG. 2) and an over-current protection signal on conductor 84 from the second flow rate control system 36 (FIG. 2).
~hese signals result in a positive-going variable width 13 KHz (kilohertz) pulse train being applied by the comparator through a conductor to the driver circuit 82 inversely related to how steep the ramp circuit applied to conductor 64 is, directly related to the amplitude of the signa] applie~ to 62, which determines the duty factor of the pu]se train.
The motor driver circuit 82, during the time duration it receives the pulse train from the comparator 80, appLies a variable voltage across conductors 66A and 66B, resulting in power being applied to the motor 50 (FIG. 3) during a time controlled by the pulse-width-modulator 32 and consistent with the pulse train applied by the comparator 80.
To compare the ramp signal onconductor 64 with the servo input signal on conductor 62, the comparator circuit 80, .is a LM 311 voltage comparator sold by National Semiconductor, 2900 Semiconductor Drive, Santa Clara, California 25051, and described in its 198; catalogue "Linear Integrated Circuits", having pin 1 e].ectrica~].y connected to the driver circuit 82, pin 2 electrically connected to conductor 62 through a lOK
resistor 92 to receive the servo input signal, pin 3 electrically connected to conductor 64 to receive the ramp, pin 4 el.ectricall.y connected to a source 94 of a negative 12 volts and to the electrical common through a 1 uf (microfarad) capacitor 96, pin 6 electrically connected to conductor 84 to receive an overcurrent signal from the second flow rate control system 36 (FIG. 2) and pin 8 electrically connected to a source 98 of a positive -1 3355 f 3 12 volts. An equivalent circuit wou:ld be a simple comparator having an inverter on its output connected to one input of a two input NA~D gate an<~

conductor 84 connected to the other input.
The comparator 86 has its noninverting input terminal electrical ly connected to conductor ~2 through the resistor 92 and its inverting input terminal electrically connected to conductor 64. A
first -rail is electrically connected to the source 94 of a minus 12 volts and to electrical common through the capacitor 96 and its other rai l electrical ly connected to the source 98 of a positive 12 volts. The output of the comparator from pin 1 is electrical]y connected to the driver circuit 82 to apply a signal thereto corresponding to the time in which the ramp voltage applied on conductor 64 is less than the level on conductor 62.

The driver circuit 82, includes a MTP12NO5 MOSFET transistor 102, a MR2400F diode 104 (a] l manufactured by Motorola Corporation), and a source 106 of a positive 32 volts. The gate of the transistor 102 is electrically connected: (1) to the 23 1 33~

output of the comparator 86 through a 33 ohm resistor 108; (2) to a source 112 of a negative 8 volts through a 820 ohm resistor 110; (3) to the overcurrent sensor circuit 60 (FIG. 3) through the reverse resistance of a lN5245B Zener diode 114; and (4) to a source 98 of a positive 12 volts through the resistor 110.
T~e source of the transistor 102 is electrically connected to the overcurrent sensor circuit.60 (FIG. 3) through a conductor 1~8. To provide noise filtering for the comparator 86, the source 98 of a positive 12 volts is electrically connected to electrical common through two 1 uf capacitors 120 and 122 in parallel with each other and to the source 112 o~ a negative 8 vol ts through a 1 uf capacitor 116, with a source o negative volts 112 also being electrical]y connected to the gate through the resistor 110 to provide biasing directly to the gate. ~ 0.2 uf capacitor 174 is connected across conductors 66A an~ 66B to filter lower frequencies.

Conductor 118 is essentially grounded for power supply purposes and the drain ls electrica~ly connected through the forward resistance of the diode 104 to the source 106 of a posi.tive 32 volts -and to conductor 66A so that, the positive 32 volts is connected at all times to one end of the armature of the motor 50 (FIG. 3), conductor 66B on the other armature and being electrically connected through a current limiting inductor 124 to the anode of the diode 104 and the drain of the transistor 102. ~he capacitance across the motor is essentially 2 uf.

The mo~or is a Pitman 13000 series DC motor and the inductor is substantially 200 uh (mi.crohenries~. -With this circuit arrangement, when the transistor 102 is condeucting as a result of the positive pulse at its gate, current flows from thesource 106 of a positive 6 volts through the motor, the inductor 124 and the traqnsistor 102 to ground through conductor 118, and when the positive pu]se is not appli.ed, the current is maintalned by inductor 124 through diode 104 and, the motor and back through the inductor unless the motor is operating to generate current for dissipation in the brake circuit 52 (FIG. 3) to be descri.bed hereinafter.

With this arrangement, when the linear feedback circuit indicates tha~ the motor speed falls below its preset speed, the pulse width is increased linearly and when the nonlinear feeAback circuit 2~

1 3355 t 3 indicates the need for acceleration to equalize the flow, the width of the pulse i.s inc~eased provide a correction of motor speed in a velocity feedback loop during a portion of a pump cycle prior to re~ill. The nonlinear feedback circuit proviaes an acceleration signal prior to the constant flow portion of the delivery for a longer time as the flow ~ate during the last portion of delivery increaseS and a shorter time as it decreases.

In FIG. 5, there is shown a schematic circuit diagram of the brake circuit 52 (FIG. 3) having an input logic circuit 130, a drive circu~t 132, and a shunt circuit 134. ~he input logic circuit 130 receives a signal on conductor 70 from the second flow rate correction circuit 36 (FIG. 2) and causes the drive circuit 132 to form a conducting path in the shunt circuit 134 across the armature of the motor to provide dynamic braking. The input logic circuit 130 also app].ies output signals through conductor 72 to the second compensation circuit 44 (FIG. 2) and to conductor 62 to the flow rate control circuit 32 (FIG. 3).
To provide a signal causing dynamic braking, the input logic circuit 130 includes a .NAND gate 136, input conductor 70 and output conductors 72 and 62. The NAND gate 136 has one of its inputs eleetrically connected to a source 138 of a positive 8 volts and its other input eleetrieally conneeted to the input 70 through a 10 K resistor 1~0 to receive signals from the second flow rate eorreetion system 36 (FIG. 2) indicating a braking action. ~he output of the NAND gate 136 is eleetriea~ly eonneeted to eonduetor 72 to provide a positive output signal when braking aetion is to oeeur ana to conductor 62 through the lN5060 diode 142 to turn off drive pulses from the flow rate control elrcuit 32.
To energize the dynamic brake, the drive eireuit 132 ineludes first and seeond NPN
transistors lS0 and 152 a~d a diode 154. The anode of the diode 154 is electrica~ly conneeted to the output of the NAN~ gate 136 and its eathode is eleetrically connected ~o the base of the transistor lS0 through a 4.7 K (kilohm) resistor lS6 and to eléetrieal eommon through a 4.7 K resistor 158. The emitter of transistor 150 is eleetrieally eonneeted to the base of transistor 152 and to eleetrieal common through a 470 ohm resistor 160 and the emitter of transister 152 is direetly eonneeted to eleetrieal eommon. The collector of the transistors ~6 150 and 152 are each electrically connectecl to the input to the shunt circuit 134 through two 34 ohm resistors 162 and 164 electrical] y connected in series. rhe transistors 150 and ]52 are 2N3704 and D44C8 transistors manufactured by G.E. Corporation and described in the catalogue and the diode 154 is a type lN914 diode.
To form a conducting path for current generated by the pump motor when it is being driven by inertia and thus to provide dynamic braking, the shunt circuit 134 inc]udes a D4sH8 PNP transistor 170, and a lNS060 diode 172. The transistor 170 has its base electrically connected to the output of the drive circuit 132, its emitter ~lectrically connected to itS base through a 220 ohlr. pull-down resistor 173 and its collector electrically connected through the diode 172 to its emi tter and to conductor 74B
through a resistor 176.
The emitter of the transistor 170 is electrically connected to conductor 66A so that, when the motor operates as a generator for dynamic braking, a path is formed between conductors 66A and 66B through the motor and transistor 170 when transistor 170 is saturated and provides an open circuit when the motor is driven as a motor.

~ 3355 t 3 In FIG. 6, there is shown a schematic circuit diagram of the refill inception detection circuit 54 (FIG. 3), having an optical sensor 180, a rotatable flag 182 on the cam shaft, and a comparator 184.
The flag 182 shown in fragmentary schematic form, rotates with the cam shaft on it in a location to be detected by the optical sensor 180, which transmits a posi~tive going pulse in response to a signal indicating the start of the refill cycle to the noninverting input terminal of the comparator 184.
The comparator 184 signals the second flow rate control system 36 (FIG. 2) indicating the start of the refill cycle in response to the detected signal.

For this purpose, the comparator 184 has its noninverting input terminal e]ectrica31y connected to electrical common through a 2.2 K resistor 186 and to the output of the optica3 sensor 180. The inverting input terminal of the comparator 184 is electrically connected to conductor 76B, to electrical common through a 100 ohm resistor 188 and to a source 112 of a negative 8 volts through a l.SK

resistor 190 so that a reference potentia] ;s established, above which a signa] is provided through conductor 76A indicating a refill cycle.

The comparator 184 has positive and negative 8 volt rails at 138 and 112.
The optical sensor 180 has a light emitting diode, with its anode electrically connecte~ to electrical common and its cathode electrically connected to a source of negative 8 volts through a 1.5 K resistor 192 and has a light sensitive transistor therein with its collector electricallY
connected to the noninverting input terminal of the comparator 184 and its ~PN emitter junction electricall~ connected to the source 112 o~ a negative 8 volts.
In FIG. 7, there is shown a schematic circuit diagram of the overcurrent sensor circuit 60 (FIG.
3) having a current sensing network 202, a reference network 204 and a comparator circuit 206. The sensing network 202 senses the motor current ana the reference network 204 provides part of the reference with both values being compared in the comparator circuit 206 to provide an out~ut signa] disabling the average flow rate control circuit 32 (FIG. 3 and FIG. 4) when the motor current is too high indicating a jammed condition of the pump or the like.

.

To sense the current through the pump, the current sensing network 202 includes three 0.1 ohm resistors 210, 212, and 214 respectively connected in parallel between a conductor 216 and a conductor 218. Conductor 216 is electrically connected to conductor 118 to receive motor current and conductor 218 is electrically connecte~ to the electrical - common~so that the current flow through the motor on conductor 118 causes a voltage drop in the sensing 10network 202, which voltage drop occurs between conductors 216 and 218.
To provide a reference potential, the reference network 204 is electrically connected: (1) through 86.6 K resistor 240 to 4.7 K resistor 234 and thence to the source of a positive 8 vo~ts; (2) to conductors 216 and 218; and t3) to the comparator circuit 206 through conductors 220 and 222.
Conductor 216 is electrica~ly connected through a conductor 200 to the anode of the ~ener diode 114 20(FIG. 4) of the flow rate control circuit 32 (FIGS.

2, 3 and 4) to receive current therethrough and to conductor 220 through a 1 K reslstor 224.

Conductor 218 is electrically connected to conductor 222 through a 4.75 K resistor 226 and to a source -112 of a negative 8 volts potentia~ through a 309 K
resistor 228.
With this arrangement, conductor 222 is maintained at a potential above the eleetrical common by the sources of potential 138 and resistors 234 and 240.
To eompare the potential on conductors 220 and 222 fbr the purpose of in~icating an overcurrent, the comparator eircuit 206 includes the comparator 230 whieh is manuactured and sold by National Semi-conductor Corporation (2qO0 SemiconduCtor r~rive, Santa Clara, California 950Sl) type 311 having its inverting input terminal at pin 3 e].ectrieaJ ly connected to conductor 220 and its noninvertin9 input termi.nal at pin 2 electri.cal ly connected to conductor 222 to provide a comparlson of the voltages therein.
During an overcurrent, the output at pin 7 of the comparator goes from 8 to common potential. ~he removes positive potential from resistor 240 and negative potential from sources 112 through resistor 278 causes the comparator to latch up and disable the drive cireuit.
At the end o~ the pulse cycle, a reset pulse on pin 6 at 296 resets the comparator from a clock in the second positive feedback and compensation circuit 44 to enable the comparator and drive circuit 32.
The output of the comparator 230 at pin 7 is electrically connected to: (1) the source 138 through the resistor 234, (2) a conductor 84 through 680 ohm resistor 239; (3) the reverse resistance of the 8.2 IN5237 volt Zener diode 237 and the foreward resistance of diode 238; and (~) conductor 222 through a 86.6 K resistor 240. The conductor 84 (FIG. 4) is electrically connected to the pulse-width-modulator 86 (FIG. 4) so that conductor 84 provides signals to disable the f~.ow rate circuit 32 (FIG~. 2, 3 and 4) by de-energizing the comparator 86 upon a current overload condition.
In FIG. 8, there is shown a schematic circuit diagram of the tachometer disc and sensor system 58 (FIG. 3~ having a first and a second optical sensor 250 and 252 respectively, rotatab].e disc 254 and first and second 270 ohm resistors 258 and 260 respect;vely. The first and second optical sensors sense indicia indicati.ng the rotation of the pump on disc 254 which is mounted to the output shaft of the pump motor. The optical sensors 250 and 252 are located in quadrature with respect to the indicia so 33 l 3355 1 3 as to indicate the amount of rotation of the motor and its direction in a manner in the art.
With this arrangement, the optical sensors~ provide signals indicating the amount of rotation and direction of the motor by rotation of the disc in one direction as well as position of the piston in part of a delivery stroke by sensing indicia at equispaced distances along the disc 254.
To sense indicia on disc 254 the first optical sensor 250 includes a light emitting diode having its anode electrically connected to the electrical common and its cathode electrically connected to the source 112 of a negative 8 volts through the resistor 258. To provide electrical signals indicating the amount of electrical rotation of the disc 254, the first optical sensor 250 includes a light sensitive element separated from the light emitting diode by the disc 254 to have light blocked or transmitted to it as the disc 254 rotates.
The light sensitive element has its collector electrically connected to the linear flow rate control circuit 38 (FIG. 2) and non~.inear flow ra~e.
control circuit 42 (FIG. 2) and average f].ow rate control loop circuit 47 (FIG. 2) through a conductor 262 and has its emitter electrically connected to the source 112 of a negative 8 volts to provide electrical signa]s to conductor 262 indicating the amount of rotation of the pump.
The second light sensor 252 has a light emitting diode in it with its anode electrically connected to the electrical common and its cathode electrically connected to the source 112 of a negative ~ volts through the 270 ohm resistor 260.
It has a light sensitive element separated from the light emitting diode 252 by the rotatable disc 254 so as to sense indicia upon it.
The light sensitive e~ement has its collector electrically connected ~o the linear and nonlinear flow rate control circuit 38 and 42 (FIG. 2) through a conductor 264 and average ]ow rate control loop circuit 47 (FIG. 2) and has its emitter electrical~Y
connected to the source 112 of a negative 8 volts so as to provide electrical signals to conductor 264 indicating the amount of rotation of the disc 254 with the signals on conductors 262 and 264 indicating the amount o rotation and the direction of rotation.
In FIG. 9, there is shown a block diagram of the nonlinear flow rate control circuit 42 (FIG. 2) having a quadrature detector 270, a frequency to voltage converter 272, a multivibrator circuit 274, an exponential amplifier circuit 276 and a ramp generator 278. The quadrature detector 270 is electrically connected to conductors 262 and 264 to receive signals rom the tachometer disc and sensor system 58 (FIGS. 3 and 8~ and apply a signal indicating the amount of rotation in one direction to a conductor 2~0 to the frequency to voltage converter 272 which generates a.signal representing in amplitude the rate of rotation of the motor for application to a conductor 280.
Conductor 280 is electrically connected to the exponential amplifi.er circuit 276 and the output from the exponential amplifier circuit 276 and from the multivibrator circuit 274 are connected to the ramp generator 278 to generate a ramp which varies in slope in a manner related to the motor speed.
~o receive correcting signals, the second compensation circuit 44 (FIG. 2) is connected to the ramp generator 278 through a conductor 282 and to select the flow rate operating range of the frequency to voltage converter control signal is applied to the frequency to volta~e converter 272 from the linear flow rate control circuit 38 (FIG.
2) through a conductor 284 to select a flow rate range.
In FIG. 10, there is shown a block diagram of the quadrature detector 270 (FIG. 9~ having a pulse output conductor 290, a direction circuit 292 and a tachometer sensor input circuit 294. The tachometer sensor input circuit 294 is electrically connected to conductors 2~2 and 264 to receive signals from the first and second optical sensors 250 an~ 252 (FIG. 8) respectively, which sensors generate pulses at the same ~requency as the motor rotates but 90 degrees out of phase. The output of the tachometer sensor input circuit 294 applies both sets of pulses to the direction circuit 292 which selects only those pulses which indicate a forward movement of the pump piston or plunger for application to the output at conauctor 290. This circuit is explained in the aorementioned patent application.
The tachometer sensor input circuit 294 includes a first channel 2~6 and a second channel 298 with the first channel 296 being electrically . 37 1 33551 3 connected to the first optica~. sensor 250 through conductor 262 to receive signals therefrom and electrically connected to the direction ci.rcuit 292 through a conductor 300 and the second channel 298 being electrica31y connected to the second sensor 252 (FIG. 8~ through the conductor 264 to receive signals therefrom and to the direction circuit 292 through a conductor 302 to supp3y signals thereto.
The irst channel 296 is identical to the first channel 298 except that they receive signals ~rom different sources and supply to the direction circuit 292 through different conductors.
In FIG. 11, there is shown a schematic circuit diagram of the first channel 296 (FIG. 10) within the tachometer sensor input circuit 294 (FIG. 10) having a first operational amp3ifier 304 and a second operational amplifier 306. The amplifiers 304 and 306 are type LM3~3 amplifiers each having one rail connected to a source 138 of a positive 8 vol.ts and the other rail electrically connected to a source 112 of a negative 8 volts.
To provide amplification and low pass noise filtering, amplifier 304 has its noninverting input terminal electrically connected to the eLectrical common and its inverting input termina] electrically connected to: (1) conductor 262 through a 470 ohm resistor 308 and to a source 138 o~ a positive 8 volts through the resistor 308, a 27 K resistor 310 and a variable 50 K resistor 312 so as to permit adjustment of the input to operat.ing current of the light sensor connected to conductor 262. The output of amplifier 304 is electrically connected to: (1) its inverting input terminal through a 56 K resistOr 314 and a lS0 pf (picofarad) capacitor 316 electrically connected in para~.lel; and (2) to the noninverting input terminal o~ the amplifier 304 through a 47 R resistor 318.
To provide Schmidt Tragger action, amplifier 306 has its output electrically connected to: (1) conductor 300 through a 4.7 K resistor 320, a source 138 of a positive 8 volts through the resistor 320 and the forward resistance o a lN273 diode 322; (3) and the electrical common through the reverse resistance of a lN273 diode 324; (4) to its non-inverting input terminal through a 1.2M resi.stor 326 and to the electrical common through the resistor 326 and a 47 K resistor 328.
In FIG. 12, there is shown a schematic circuit diagram of the direction circuit 2~2 (FIG. 10) having a divide-by-two circuit 330, an up-down counter circuit 332 and an input gating circuit 334.

The input gating circuit 334 is electrically connected to conductors 300 and 302 to receive signals processed by channels 1 and 2 from the first and second sensors 250 and 2S2 respectively (FIG. 8) and has its output electrically connected to the up-down counter circuit 332 which caused by backward movement of counts pulses proportional the motor, by counting backwards from lS and requiring recounting of those pulses in the forward direction for application to the divide-by-two circuit 330 and eventually to output conductor 290 to the frequency to voltage converter 272 (FIG. 9).

The input gating circuit 334 includes four exclusive OR gates 336, 338, 340, and 342 and one NOR gate 344. Conductor 300 is electricallY
connected to one input of each of the exclusive OR

gates 338 and 342 and con~uctor 302 is electrically connected to another input of the two input exclusive OR gates 338 and 342 and to: (]) an input of the exclusive OR gate 342 through a lS0 K

resistor 34&; and (2) to the electrical common through the resistor 346 and a 120 pf capacitor 348.

The output of exclusive OR gate 338 is electrically connected to: (1) one of the two inputs of the exclusive OR gate 33G; (2) the input of the NOR gate 344 through a 27 ~ resistor 350; and (3) the electrical common through the resistor 350 and a 120pf capacitor 3S2.
The output o the exclusive OR gate 342 is electricall y connected to one of the two inputs of the exclusive OR gate 340, the other input being electrically connected to a source 138 of a positive 8 volts. The output of the exclusive OR gate 336 is electrical ly connected to the up-down counter circuit 332 through a conductor 3~4 and the output of the OR gate 340 is electrical]y connected to the up-down counter circuit 332 through a conductor 356 to proviae signals correspondirig to the first and second sensor thereto modified so that signals received from the first sensor before the second count up and signals received by the second sensor before the irst sensor count down.
The up-down counter circuit 332 includes a type 4029 up-down counter 360 and a type 4002B NOR gate 362. Conductor 354 is electrically connected to pin 15 of the counter 360 to cause it to count up and conductor 356 is electrically connected to pin 10 of the counter 360 to cause it to count down and to one of the our inputs o the NOR gate 362, the output 4'- 1 3355 t 3 of which is electrically connected to pin ~ to inhibit counting upon receiving a s~gnal on conductor 3~6 passing through the NOR gate 362.
Pins 2, 14, and 11 of the counter 360 are each electrically connected to (1) a different one of the other three inputs of the NOR gate 362; and (2) a different one of the 10 K resistor 364, 22 K
resistor 366 and 39 K resistor 368. The other end of the resistors 364, 366, and 368 are each electrically connected to: (1) pin 6 of the counter 360 through an 82 K resistor 370; and (2) the electrical common through a 1 K resistor 372. Pins 8 and 4 of the counter 360 are grounded and pins 16, 13, 12, 9 and 3 are electricaliy connected to the source 138 of a positive 8 volts to determine the output voltage of the counter. Pins 1 and 7 are electrically connected to conductors 374 and 376 to provide output positive 8 volt pulses as the counter counts in binary notation upwardly in response only to signals caused by rotation of the motor in the direction which enables the piston to force fluid from the cylinder of the pump. The counter counts downward]y in response to reverse rotation but is inhibited from counting past zero.

To divide the binary signals appl ied on conductors 374 and 376 in two, the divide-by-two circuit 330 includes a type 4013B divider 374 having pins 3 and 11 electrically connected to conauctor 376 and pin 13: (1) electrically connected to conductor 374 and to pin lO through a 2.7 K resistor 380; and (2) to the electrical common through resistor 380 and a .01 uf capacitor 382. Pins 9 and 14 of the divider 378 are each electrical ly connected to the source 138 of a positive 8 vo].ts, pin 1 is electrically connected to conductor 290 to provide a frequency output representing the rate of flow of effluent from the pump, pins 2 and 5 are electrically connected together-and pins 4, 6, 8 and 7 are each electrically connected to the electrical common.
In FIG. 13, there is shown a schematic circuit diagram of a frequency to voltage converter 272 (FIG. 9) having an analog switch ~90, an ~M2907 frequency to voltage converter 392 and a gain adjustment circuit 394.
The frequency to voltage converter may be any suitable type, many of which are known in the art but in the preferred embodiment it is an integrated circuit sold by ~ational Semiconductor under the 43 1 3355 t 3 designation LM2907. Pin 1 of that unit is electrically connected to conductor 290 to receive pulses from the tachometer disc and sensor system 58 (FIGS. 3 and 8) through a 22 K resistor 3~6. ~his cirçuit is part of a tachometer that produces an output voltage proportional to motor speed.
The conductor 290 is also electrically connected to the electrical common through the resistor 396 and a 22 K resistor 398 and to the system controller 22 (FIG. 1~ through a 10 K
resistor 402 and a conductor 400 where lt may be used by the system to indicate .he progress of the chromatographic run. The frequency to voltage converter 39~ has pin 11 electrically connected: (1) through a source 138 of a positive 8 volts and 47 K
resistor 404 for biasing; and (2) through a 0.47 uf capacitor 406 and a 15 K resistor 408 to the electrical common in parallel to short out noise.
Pins 7 and 12 are electrically connected to a source 112 of a negative 8 volts and to the electrica]
common through a 1 uf capacitor 410, pins 8 and 9 electrically connected to a source 138 of a positive 8 volts and to the electrical common through a 1 uf capacitor 412.
-4~ 1 3355 1 3 To accommodate changes in pumping speed, frequency to voltage converter 392 has pin 2electrically connected to (1) the etectrical common through an g20 p~ capacitor 414; and (2) one ]ead of 4016 analog switch 390 through an 820 pf capacitor 416. The gate o~ the ana~og switch 390 is connected to conductor 418 to receive a low range signal and the other level is electrically connected to the electrical common through a 33 K resistor 422~
T~le switch 390 doubles the gain of the frequency to voltage converter by doubling capacitance by switching capacitor 416 in parallel with 414 to provide low range operation at a high sca3.e with an addition multiplier to be described hereinafter upon receiving a signal on conductor 418.
To control the gain of the voltage conversion provided by frequency to voltage converter 392, the gain control circuit 394 includes a first 5 K

potentiometer 424 and a second 5 K potentiometer 42fi with the potentiometer 426 being connected at one end to a source 138 of a positive 8 volts and at the other end to a source 112 of a negative 8 volts, its variable tap being electrically connected through a 10 megaohm resistor 427 to: (1) pin 10 through a switch which may be opened or closed; (2) and pin 3 of the frequency to voltage converter 392; (3) pin 5 through a .022 uf capacitor 428 and a 0.33 uf capacitor 430, and (4) to the tap of the potentiometer 424 through a 30.9 K resistor 432.
The potentiometer 424 is electrically connected at one end ~co a conductor 280 and to pin 5 of the frequency to voltage converter 392 and at its other end to the electrical common through a 10 K resistor 436 and directly to pin 5 of the frequency to voltage converter and to pin S of the voltage to frequency converter through the capacitor 430.
Conductor 280 applies the voltage corresponding to the rate of f]ow of fluid to the exponential amplifier circuit 276 (FIG. 9) through conc~uctor 280 and to the first compensation circuit 40 (FIG. 2).
Conductor 280 is e~ectrically connected to the source 94 of a negative 12 volts through a 604 ohm resistor 440.
With this arrangement, the amplitude of the voltage output may be adjusted by potentiometer 424 and 426 to provide a voltage which varies in relation to the rate of flow of fluid as measured by the tachometer. This voltage is applied to the ~6 1 3355 1 3 first compensation circuit 40 (FIG. 2) for application to the linear flow rate control circuit 38 (FIG. 2) and to the exponential amplifier circuit 276 (FI~. 9) through conductor 280 to control the nonlinear flow control circuit 42 (FIG. 2).
In FIG. 14, there is shown a schematic circuit diagram of the multivibrator circuit 274 (FIG. 9) having a conventional astable multivibrator 450 which may be of any conventional designation but in the preferred embodiment is a National Semiconductor 55 multivibrator connected as shown to provide a suitable frequency during a portion of the time normally required for a full piston stroke of the pump. The function of the multivibrator circuit is to reset the overload circuit and the ramp generator.
To provide the proper frequency, the multivibrator circuit 274 includes: (~) 3 capacitors 452, 454, and 456 having values of 1 uf, .01 uf and 2200 pf respectively; (2) 2 resistors 458 and 460 having values of 680 ohms and 39.2 ohms respectively; and (3) a 10 K potentiometer 462 with pins 4 and 6 of the multivibrator 4S0 being electrically connected to one end of the potentiometer 462, pin 7 being electrically =~==~

connected to: (1) to the other end of the potentiometer 462 through the resistor 460; (2) to pins 6 and 2 of the multivibrator 4~0 through thé
resistor 458; and (3) to the electrical common through the capacitor 456. The electrical common is also electrically connected to pin 1, to pin 5 through the capacitor 4~4 and to pins 4 and 8 through the capacitor 452.
To provide a reset pulse to the ramp generator 278 (FIG. g~ and to the flow rate control circuit 32 (FIGS. 2, 3 and 4) pin 3, which is the output of the multivibrator 450, is electrically connected to conductor 470 to apply a positive pulse thereto for initiating a ramp circuit and providing an output pulse from the flow rate control circuit 32 (FIGS.
2, 3 and 4) through conductor 84. To provide a signal to the ramp circuit to initiate a ramp, the multivibrator 274 includes a source 112 of a negative 8 volts electrically connected to conductor 470 through a 3.~ K resistor 472 and a 1.82 K
resistor 474 with output conductor 476 being electrically connected to resistor 472 and 474 to change from a negative to a positive value upon receiving a signal from the multivibrator 450.
Conductor 476 is electrically connected to the ramp generator 278 (FIG. 9).
To provide a turn-off signal on conductor 84 to the flow rate control circui.t 32 (FIGS. 2, 3 and 4) conductor 84 is electrically connected to conductor 470 through a 680 ohm resistor 478, the reverse resistance of CR106 zener diode 480 and the forward resistance of a lN914 diode 482.
To reset the overcurrent sensor 60 (FIGS. 3 and 7), conductor 296 to the overcurrent sensor 60 is electrically connected through a 680 ohm resistor 484 and through the forward resistance of a ]N914 diode 486 to conductor 470 to apply a positive potential thereto, permitting the flow rate circuit 32 (FIGS. 2, 3 and 4) to operate;
In FIG. 15, there is shown a schematic circuit diagram of the exponential amplifier circuit 276 (FIG. 9) having a first PNP 2N3702 transistor 490, a second PNP 2N4061 transistor 492, an adjustment circuit 496 and a bias circuit 4~4. The transistor 490 has a lower input impedance than and conducts approximately ten times the current through transistor 492 causing transistor 492 to follow the potential on conductor 280, thus providing an exponential drop between the emitter and base of transistor 492. The two transistors cancel their temperature coefficients. The first transistor 4~0 receives an input signal from the requency to voltage converter 272 tFIGS. 9 and 13) on conductor 280 indicating the speed of pumping and var.ies the emitter bias of the transistor 492 to cause an exponential~ amplification of the signal from the frequency to voltage converter 272 for application through a conductor to the ramp generator circuit 278 (FIG. 9).
To provide emi.tter biasing to the first and second transistors 490 and 492, the emitters of each of these transistors is electrically connected to a source 98 of a positive 1~ volts through a ~.18 K
resistor 502 and to a second such source through the 1.18 K resistor 502 and a 33 ohm resistor 500.
To vary the emitter potential of the second transistor 490 in a manner related to the input amplitude on conductor 280 from the frequency to voltage converter 272 (FIGS. g and 13) so as to provide an exponential transfer function, the base of the transistor 490 is electrica~.ly connected to:
(1) the electrical common through a 47.5 ohm resistor 508; (2) to input conductor 280 through a 1.40 K resistor S04; and (3) to a source 106 of a positive 32 volts through a 45.3 K resistor S06.

The collector of the transistor 490 is electrically connected to a source 112 oE a negative 8 volts so that it will draw current through the emitter biasing circuit from the source 98 of a positive 12 volts and through the resistor 502 in proportion to the input signal on conductor 280 and thus cause a drop i~ the positive potential on the emitter of the transistor 492 as the current increases.
To provide a further adjustment on a sawtooth waveform to be controlled by the transistors 490 and 492, the adjustment circuit 496 includes a 1.18 K
resistor S10, a 100 K resistor S12 and a 5 K
potentiometer 514. To establish biasing, one end of the potentiometer 514 is electrically connected to a source 138 of a positive 8 volts and the other end is electrically connected to a source 112 of a negative 8 volts, with the movable tap being electrically connected to the base of the transistor 492 through a 100 K resistor 512. The base of the transistor 4~2 is also electrically connected to the electrical common through a 1.18 K resistor 510 to provide biasing. The collector of the transistor 492 is connected to conductor 520 to provide an exponentially decreasing amplification of the signa received on conductor 280.

1 3355~ 3 To provide a continuous bias on conductor S20, the bias circuit 4~4 includes 150 K resistor 516 and a 500 K potentiometer S18. The resistor 516 and potentiometer 518 are electrical.ly connected between a source 98 of a positive 12 volts and the conductor 520 to permit adjustment of the vo.ltage drop for application of a current to the ramp generator 278.
In FIG. 16, there i.s shown a schematic circuit-diagram of the ramp qenerator 278 (FIG. 9). To form a ramp which varies in slope in a manner related to the output from the exponential amplifier 276 (FIGS.
9 and lS) for application to the flow rate circuit 32 (FIGS. 2 and 4) the ramp generator circuit 278 includes a type TLOllC current.mirror 530 made and sold by Texas Instruments, a 2N3710 NPN transistor 532, a 2N4403 PNP transistor 534, and a 910 pf capacitor 536. The current mirror 530 has its input electrically connected to conductor S20 to receive the output of the exponential amplifier 276 (FIGS. 9 and 15) and its output electrica].ly connected to conductor 64 to apply current which decreases as the motor speed increases from a high output impedance source with a gain of 1 to draw current from capacitor S36 across to generate a negative going ramp from the capacitor.

The common of the current mirror 530 is electrically connected to the col~ector of aiode connected transistor 532 through which it conducts current. The emitter of the transister 532 is electrica]~y connected to a source 112 of a negati.ve 8 volts to control the bias on current mirror 530.
The ~.7 K resistor 538 keeps the voltage at its collector o~ the transistor 532 relatively constant at about 7.3 volts regardless of the operation of the current mirror 530.
To form a ramp from the output of the current mirror 530, conductor 64 is electrically connected to its output and to one plate of the capacitor 536, the other plate of which is electrically connected to the emitter of transistor 534. With this arrangement, the current flowing from the output of the current mirror 530 charges capacitor 536 to form a ramp potential on conductor 64.
To reset capacitor 536, the transistor 534 has its collector electrically connected to conductor 64 and its base electrically connected to the multivibrator circuit 274 (FIGS. 9 and 14) through conductor 476 so that when the multivibrator provides a negative pulse at the end of a ramp, transistor 534 becomes conducting to discharge capacitor 536. When transistor 534 becomes nonconducting at the end of tlle negative pulse at its input, the capacitor 536 receives a high impedance between one plate in conductor 64 and low impedance on the other to be in condition to charge and form a ramp potential on conductor 64 as current - flows through the current mirror 530.
The current mirror 530 may be any conventional circuit which results in a complementary current flow from its input. In the preferred embodiment this is a commercial integrated circuit designated TLOllC and sold by Texas Instruments.
In FI~. 17, there is shown a schematic circuit diagram of the linear flow rate control circuit 38 (FIG. 2) having a reference voltage to current converter 540, a summing no~e 54~, a switch 544, and a servoamplifier circuit 546. The reference vo~tage to current converter 540 receives a signal indicating the desired constant flow rate of the influent to the chromatographic column on conductor 46 and converts it to a current for application to the summing node 54~ where it is summed with a`
feedback signa.l.. Upon being gated by the gate 544, this signal is applied to the main servoamplifier circuit 546 where it is subtracted from certain other correction signals for application through conductor 62 to the flow rate circuit 32 (FIG. 2, 3 and 4).
To provide a feedback signal during the delivery portion of a pumping stroke, the summing node S42 receives: tl~ a current set to represent the desired flow rate from resistor and low pass filter S40; and (2) a current from conductor 548 fed back from the motor circuit 30 (FIG. 2) representng the effluellt as corrected by the first compensation circuit 40 (FIG. 2) in a manner to be ~escribea hereinafter.
~his current is gated by the analog gate 544 under the control of a signal -on conductor SS0 to the inverting termina~l of the servoamplifier 546 where it is summed with a signal from the first compensation circuit 40 (FIG. 2) through a conductor 598.
The main servoamplifier 546 receives a signal from the second compensation circuit 44 (FIG. 2) through a conductor 554 and the difference between the two signals is applied to con~uctor 62.
Conductor 62 at different times receives compensation circuits on conductors S56 to provide servogain and certain compensations such as for compressibility of the fluids, logic signals on conductor 558, a refill gain correction signal on conductor 560, and a gain from the braking circuit on conductor 562.
To process the set point voltage on conductor 46 and apply to summing node 542, the reference voltage to current converter S40 includes a 10 K
resistor 570, a 0.1 uf capacitor S72, and a 187 K
resistor 574. ~he resistor S7.0 is electrically connected at one end to conductor 46 and at its other end to the electrical common through the capacitor 572 ana the summing node 542 through the resistor 574.
The switch 544 is a typ.e 4016 integrated circuit switch sold by the aforementioned National Semiconductor although any suitable electronically operated switch may be used. The switch 544 is electrically connected to be controlled by the first compensation circuit 40 (FIG. 2).
To compare the signal on conductor 544 fed back from the motor tachometer, with the signal on conductor 46 indicating the desirable flow rate, the servoamp].ifier circuit 546 includes an LM ~53 differential amplifi.er 580 sold by National Semi-conductor, four resistors 582, 584, 586 and 590, a 22 pf capacitor 592, and a lN914 diode 594. ~he resistors are a 470 ohm resistor S82, a 10 K
resistor 584, a 47 K resistor 586 and a 220 ohm resistor 590O 'rhe resistor 582 is electricallY
connected at one end to the output of the switch 544 ana at its other end to: (1) the inverting input terminal of the amplifier 580 to supply a signal thereto representing the ~low rate error signa~; and (2) conductor 598 electrical ly connected to the first compensation circuit 40 (FIG 2); and (3) to the output of the differentia] amplifier 580 through the capacitor 592.
The output of the amplifier 580 is electrically connected to conductor 62 through the resistor 590 and the amplifier has a source 138 of a positive 8 volts connected as one rail at pin 8 and a source 112 of a negative 8 volts connected as a second rail at pin 4. The noninverting input terminal of the amplifier is electrically connected to: (1) the 2û electrical common through the res;stor S86; (2) conductor 554 to receive the feedback pumping rate signal; and (3) a conductor 596 through the forward resistance of the diode S94 and the resistor 584 for placing the pump in the stop mode. Conductor 596 -. 57 1 3355 1 3 receives a signal from a start circuit under the control of the system controller 22 (FIG. 1~.
In FIG. 18, there is shown a block diagram of the first compensation circuit ~0 (FIG. 2~ as it is electrically connected to the linear flow rate control circuit 38 (FIGS. 2 and 17). The first compensation circuit 40 (FIG. 2~ includes a summing node compensation circuit 600 and a servoamplifier compensation circuit ~02 each electrically connected to the linear flow rate control circuit 38 (FIGS. 2 & 173 at different locations, with the summing node compensation circuit 600 being electrically connected to the summing node 542 (FIG. 17) an~ the servoamplifier compensation circuit 602 being electrically connected to the servoamplifier inverting input at 5~8 and at its output as shown at 556, 558, 560 and 562 (FIG. 17).
l~ith this arrangement, the speed of the motor is corrected by the range of fluid that .is flowing, the measured average flow of the influent into the chromatographic column and for certain factors such as the braking gain, refill gain, servo gain ana l.iquid compensation or for braking val.ues at the input to the servoamplifier.

In FIG. 19, there is shown a schematic circuit diagram of the summing node compensation circuit 600 (FIG. 18) having a range selection circuit 608.and coupling circuit shown generally at 604. ~he range selection circuit 608 may energize either a high or low voltage levels current to be applied to the coupling circuit 604 which receives the variable amplit~ude voltage from the frequency to voltage converter 272 ~FI~,S. 9 and 13) on conductor 2~0 and converts. it to a current applied through conductor 548 to the ~summing node. ~he magnitude of the current depends on whether a high or low range is selected. While a switch 608 is shown connected to conductor 630, in the preerred embodi.ment, a signal from the microprocessor is used to energize the transistor 610 and open switch ~40. In this specification, a high signal is applied to terminals 628 to se].ect a one-tenth sca~e set point and corresponding feedback signals and terminals 626 or 418 from a low range in which the signa~s are subject to less attenuation by a factor of 10.
To provide a larger or smaller current depending on the selection of a high or low range, the range selection circuit 608 includes a 2N3704 NPN transistor 610, a 2N3704 NPN transistor 612 and .

-seven resistors which are respectively a 2.2 K
resistor 614, a 2.2 K resistor 61~, a 230 ohm resistor 618, a 2.43 K resistor 620, 1 K resistor 622, and a 22 K resistor 624.
To provide a low range current, the transistor 610 has its emitter electrica~ly connected to a source 112 of a negative 8 volts, its base electrically connected to: (]) a source ~4 of a negative 12 volts through the resistor 622; and (3) a source l38 of a positive 8 volts through resistors 618 and 620 in series and has its collector electrically connected to (1) a contact 626 within the range selection circuit 608 for a low ranqe current; (2) the base of transistor 612 through resistor 624; and (3) a source 138 of a positive 8 volts through the resistor 616.
The emitter of the transistor 612 is electrically connected to a source 112 of a negative 8 volts and its collector is electrically connected to a source ]38 of a positive 8 volts through the resistor 614. The range se]ection circuit 608 has a movable contact which connects a source o~ positive potential to either the low range switch 626 or the high range switch 628, the low range switch placing a voltage on conductor 630 and the high range switch plaeing a voltage on eonduetor 632.
The conduetor 630 is eleetrieally conneeted through eonduetor 418 to the frequeney to voltage.
eonverter 272 tFIGS. 9 and 13) to ground the eapaeitor 410 (FIG. 13), thus inereasing the amplitude of the output potential~
To eonvert potential to eurrent for app~ication to th~-summing node 542 (FIG. 17~ through conduetor S~8, the eoupling eireuit 604 ineludes an analog switeh 640, a 0.047 uf eapacitor 642, three resistors and a S K potentiometer 6S2. The three resistors are an 11.5 K resistor 646, a 49.9 K
resistor 648 and a 4.7 K resistor 650. Conduetor 280 from the output of the voltage to frequeney converter 272 (FIGS. 9 and 13) is electrical ly connected to: (1) the input o the switch 640 through the potentiometer 652 and the resistor 648;
and (2) eleetrieal eommon through the resistor 650 and the eapaeitor 642. The gate of switch 640 is electrically eonnected to eonductors 630 and 418 and its output is eleetrieally eonneeted to electrieal eommon through the resistor 448 and the capaeitor 642.

_ 61 1 3355 ~ 3 In FIG. 20, there is shown a block diagram of the servoamplifier compensation circuit 602 (FIG.
18), having a braking gain circuit 660, a refi]-l gain circuit 662, a servo gain and compensation circuit 664, a delivery logic circuit 666, and an acceleration time generator circuit 668. ~ach of these circuts generates signals relating to the timing of the acceleration of the pump motor and applies the signal to the linear flow rate control circuit 38 (FIGS. 2 and 17) through a plurality of analog switches. ~he analog switches are 670, 672, and 674.
For this purpose, the acceleration time generator circuit 668 applies signa~s to the delivery logic circuit 666 and to conductor 550 through one conductor and to the switch 672 through another conductor. The switch 670 is control]ed by a signal on con~uctor 72 from the brake circuit 52 (FIGS. 3 and 5) to apply a brake gain through conductor 560 and a servo gain from the servo gain and compensation circuit 664 through conductor 558 by opening switch 674. The refill gain is applied from the refill gain circuit 662 upon being opened by a signal from the acce~eration time generator circuit 668 indicating a refill cycle.

62 1 33551 ~

In FIG. 21, there is shown a schematic circuit diagram of the braking gain circuit 660, the refill gain circuit 662, and the servo gain a~d compensation circuit 664 and their associated switches 670, 672, and 674 (FIG. 20) The braking gain circuit 660 ;s controlled by switch 670, the refill gain circuit 662 is contro]led by switch 672 and th-e servo gain and compensation circuit 664 is controlled by the switch 674 to which they are connected to apply curren~s through conductor 5a8 to the flow rate control circuit 38 (FIGS. 2 and 17) to change the speed of the motor in accordance with corrections required for braking, refill and servo gain and compensation.
The braking gain circuit 660 includes a 4.7 M
resistor 680 electrically connected at one end to the output switch 670 an~ at its other end to conductor 598 to attenuate the signal on conductor 598 during a braking cycle. Switch 670 has its gate input electrically connected to conductor 72 from the brake circuit 52 (FIG. 3) and its input electrically connected to the conductor 558. ~he analog switch controls the gain and applies an attenuated voltage of the servo amplifier. The level of the set point signal on conductor 46 is -63 1 33~5 1 3 level shifted by the 7.5 K resistor 677, the negative source 112 and the 2.05 K resistor 675 to be applied to conductor 816 when switch 673 is opened.
. The reill gain circuit 662 (FIG. 20) includes a 68 K resistor 682 and a 1.2 M (megohm) resistor 684. The resistor 682 is electrically connected to the electrical common at one end and connected to the one lead of the switch 672 and the resistor 684-is electrically connected at one end to conductor 598 to apply a signal to the linear 1Ow rate control circuit 38 (FIG. 2 and 17). Switch 672 has its gate electrically connected to conductor 560 to the delivery logic circuit 666 (FIG. 20) and the second drain electrically connected through conductor 556 to the second compensation ci.rcuit 44 (FIG. 2).
To control servo gain and thus to provide servo stability, the servo gain and compensation circuit 664 includes an analog switch 688, two 3.3 M
resistors 690 and 692, a 180 K resistor 694, a 0.22 uf capacitor 696 and a 0.047 uf capacitor 698 One lead of the switch 688 is electrica]ly connected through the resistor 690 and the capaci.tor 696 in series to conductor 598 to apply a compensation 64 1 3 3 55 ~ ~
.

signal thereto. The other lead of the switeh 698 is electrically connected to~ the capacitor 696through resistor 690; (2) one lead of the switeh 674; (3) conductor Sg8 through the resistor 692 and the capacitor 698 in series.
To eontrol the servogain and compensation circuit, the switch 674 has its gate eleetrieally connected to the delivery logic cireuit 666 (FIG.
20) through eonduetor 700. With this arrangement,.
signals from the delivery logic circuit 666 are applied to the gate of switch 674 to e~ose this switch and carry signals from resistors 692 and 694 and switeh 688 providing the required compensations.
~.he refi~.l gain eireuit 662 (FIG. 20) upon receiving a signal on eonductor S56 from the acceleration time generator circuit 668 indieating a refill eyele provides a eedback path for the servo amplifier through a resistive network including resistors 682, 684, and 685 to eon~uctor 598 and the servo gain and eompensation eircuit 664 eloses an additional feedbaek path for the servo amplifier through a resistance network including a signal applied to switch 688 on eonductor 702.
In FIG. 22, there is shown a block diagram of the acceleration time generator circuit 668 (FIG.

-20) having an acceleration timer 710 and an acceleration timer output circuit 712. The acceleration timer 710 is electrically connected to conductor 76 to receive a refill inception signa], conductor 418 to receive a signal indicating the compressibility of the fluid being pumped and a signal on conductor 46 indicating the set flow rate.
The acceleration timer 710 processes these signals and applies a signal to the acceleration timer output circuit 712 and to conductors 550 and 556 to speed up the motor at the end of fluid delivery at an accelerating rate to make up for fluid flow that will be lost during a time period before delivery commences again.
The acceleration timer 7i0 receives a signal indicating the start of the refill cycle and causes a time limit on motor acceleration while there is no flow so that the cylinder will be fil~ed across the period of time control~ed by the timer. The motor may also be caused to accelerate in a forward stroke in a manner contolled by the acceleration timer 710 if the forward stroke starts during this time period. The time is increased as the flow rate increases.

In FIG. 23, there is shown a schematic circuit aiagram of the acceleration timer 710 having a monostable mu].tivibrator 714, a 2N4403 P-NP
transistor 716 and an analog switch 718. The multivibrator 714 is type ~5 sold by National - Semiconductor Corporation identified above but any monostable multivibrator may be usea provided it is designed to have satisfactory parameters in a manner known in the art.
To provi.de an output signal to conductor 724 related to the motor acceleration, the acceleration timer 710 has a time duration circuit 720, a connection to lead 418 which carries a signal indicating the compressibility.of the fluid being pumped and an output conductor 724, all of which are electrically connected to the multivibrator 714 so that the amplitude adjustment circuit 720 provides correction amplitude for high or ].ow range, calibration and compression of liquids.
To trigger the monostable multivibrator 714, conductor 76 from the output of the comparator 184 (FIG. 6~ drives conductor 724 high at inception of the refill stroke and goes low at the end of the signal and a short time later. It is differentiated by capacitor 762 to trigger the multivibrator to high and maintaining lead 724 high until the ti.mer drops low under the control of capacitor 150 and curren~ through transistor 716 to remove potential from conductor 724.
To permit aajustment of the signal on conductor 744 electrically connected to the colJector of the transistor 716, the emitter of the transistor is electrically connected to a source 138 of a positive 8 volts through a 16.S K resistor 746 and a 10 K
potentiometer 748. rrhe transistor 716 is a type 2N4403 and the adjustment of the potentiometer 748 adjusts the current applied to conductor 744 through its collector so as to permit adjustment of the acceleration time of the motor.
Conductor 744 is electrically connected to pins 6 and 7 and to the source 112 of a negative 8 volts through a 1 uf timing ramp capacitor 150, the source 112 being electrically connected to pin 1 and pins 4 and 8 being electrically connected to the source 138 of a positive 8 volts, whereby the time duration of the output pulse width from the muJ.tivibrator 714 is adjusted. Pin 5 of the multivibrator 714 is electrically connected to electrical common through a 0.01 uf capacitor 752 and pin 3 is electricallY
connected to conductor 724 through the forward resistance of a diode lN914 754 to apply the output to conductor 724. The multivibrator 714 is triggered on by the trailing edge of a signal applied through conductors 76A and 76B from the refill initiator.
To trigger the multivibra~or 714, the trigger circuit 722 includes a lN914 diode 760, a 0.22 uf capacitor 762, a lN273 diode 764, a 47 K resistor 766 and a 3.74 K resistor 768. Conductor 76B is electrically connectea to conductor 76A through the resistor 768 and to pin 2 of the multivibrator 714 through the capacitor 762. Pin 2 is also electrically connected to the source 138 of a positive 8 volts through the resistor 766 and the forward resistance of the diode 764. Conductor 76A
is electrically connected to conductor 724 through the forward resistance of diode 760 and to the cathode of the diode 754 so that, a pulse differentiated by capacitor 762 and resistor 766 triggers the mult.ivi.brator 714 to apply a potential to conductor 724.
In FIG. 24, there is shown a schematic circuit diagram of the acceleration timer output circuit 712 (FIG. 22) which receives a signal on conductor 724 to establish acceleration across a predetermined ` 1 3355 1 3 period of time and supplies signals to conductors 686 to close switch 672 (FIG. 21) and apply compensation from the ref;ll gain circuit 662 (FIGS.
20 and 21) and conauctor 55~ to open switch 544 (FIG
17) to disconnect potential from the summing node 542 (FIG. 17) to the servoamplifier 5B0 (FIG. 17).
To generate a signal for conductor 5S6, the output circuit includes a first LM 311 comparatOr 770 having its inverting input terminal electrically connected to conductor 724 and its noninverting input terminal electrically connected to: (1) electrical common through a 2.43 K resistor 772; and (2) to a source 112 of a negative 8 volts through a 4.7 R resistor 77~. The comparator 770 has one rail electrically connected to a source 138 of a positive 8 volts and the other rail electrically connected to a source 112 o~ a negative 8 volts. Its inverted output terminalis electrically connected to conductor 5S6 and to a source 112 of a negative 8 volts through a 10 K resistor 776.
To apply a signal to switch 544 (FIG. 17), the acceleration timer output circuit 712 (FIG. 22) includes a 2N3704 NPN transistor 780 having its base electrically connected to: (1) conductor 724 through a 15 K resistor 782; and (2) to a source 112 of a . 70 1 3355 1 3 negative 8 volts through a 2.2 K resistor 784. ~rhe emitter of the transistor 780 is el ectrical ly connected to the source 112 of a negative 8 volts and to a source 138 of a positive 8 volts through a 1 uf capacitor 786. The source 138 of a positive 8 volts is electrically connected to the collector of the transistor 780 through a 4.7 K resistor 788 and the collector o the transistor 780 is electrically connected to conductor 550 through a 22 K resistor 790. Conductor 550 is connected to electrical common through a 0.1 uf capacitor 7~2.
In FIG. 25, there is shown a schematic circuit diagram o the delivery logic circuit 666 (FIG. 20) having 3 NAND gates 800, 802, and 804, respectively, and a differential amplifier 806. The differential amplifier 806 has its noninverting input terminal electrically connected to conductor 556 to receive the output from the main servoamplifier 546 (FIG.
17) through a 10 K resistor 810 and a 68 K resistor 812 in series. The inverting input terminal of the differential amplifier 806 is electrically connected to: (1) conductor 816 to receive a level shifted set point signal during braking; and (2) the electrical common through a 47 K resistor 818 and through a 0.1 uf capacitor 820 in parallel to slow the motor when it is near its constant speed point.
The noninverting input terminal of the differential amplifier 806 is electrically connected to the electrical common through a 220 pf capacitor 822 and through the resistor 812 and a 0.1 uf capacitor 824. With this arrangement, the differential amplifier 806 transmi.ts a negative going signal to one input of the two-input NAND gate 804 during braking. ~he other input of the NAND
gate 804 and conductor 7Q0 are electrically connected to the output of a flip-f~op comprising NAND gate 802, one input of the NAND gate 802 being electrically connected to conductor 5~0 and its other input electrically connect;ed to the output of NAND gate 800.
Conductor ~50 goes to a low potential at the start of refill, setting the flip-flop composed of NAND gates 800 and 802. The output of NAND gate 802 is electrically connected to one input of the NAND
gate 800 and the other input is electrical ly connected to: (1) a source 138 of a positive 8 volts through a 4.7 K resistor 830 and the forwara resistance of a lN914 diode 832; (2) the source 138 of a positive 8 volts through the resistor 830 and a 220 R resistor 834; and (3) the output of differential amplifier 806 through the resistor 830, a 0.001 uf capacitor 838 and a 10 K resistor 840 in series in the order named. At the ena of the braking period, the servo amplifier output voltage on lead 556 drops below the level shifted setpoint voltage on lead 816. ~his produces a negative transition at the output of differentia]. amplifier 806 which resets flip flo~ 800 and 802 through resistor 840, capacitor 838 and resistor 830. The output of the differential amplifier 806 is electrically connected to one of the two inputs of the NAND gate 804 so as to provide a low output signal for bra'King only when the flip-flop including NAND gates 800 and 802 is set -and the output of differenti.a]. amplifier 806 is high.
In FIG. 26, there is shown a b~ock diagram of the second compensation circui~ 44 having a refill acceleration compensation circuit 85~, a sample and hold ampliier circuit 852 and a servo voltage multiplier and offset circuit 854. The refi].l acceleration compensation circuit 850 receives signals on conductor 46 indicating the flow rate and on conductor ~18 from the compensation circuit and applies a signal to the ramp generator 278 (FIGS. 9 and 16) through conductor 282 when a switch 856 is .

. 73 1 3355 1 3 closed by a signal on conductor 700.
To apply a speed-up signal to the servoamplifier, conductor 700 is electrica],l'y connected to gate 858 to open this gate and apply the servo gain and compensation to the servo voltage multiplier and offset circuit 854. Upon receiving a signal indicating fluid delivery on conductor 862 from t~e delivery logic circuit 666 (FIG. 20), the switch 864 is closed to store the servo feedback signal from the output of the servo amplifier in the sample and hold amplifier circuit 852. The sample and hoid amplifier circuit 852 is connected to the servo voltage multiplier and ofEset circuit 854 to be corrected and to apply the signal through gate 858 to the input 554 of the servoamplifier for acceleration.
In FIG. 27, there is shown a schematic circuit diagram of the refill acceleration compensation circuit 850 having a first analog switch 852, a second analog switch 854 and a 2N3704 NPN transistor 857. The transistor 857 applies a signal through switch 864 to conductor 282 to correct for the acceleration compensation with a compressibility correction being applied to its base. ~o apply an acceleration offset to the transistor 8S7, conductor 46 carrying set point signal is electrically connected to~ the base of transistor 857 through a 10 K resistor 868; (2~ to the analog switch -854 through the resistor 868; (3~ to a source 94 of a negative 12 volts through a 1 K potentiometer gate 870, a 500 ohm resistor 872 and a 1 K resistor 874 in series in the order named W~th this arrangement, the potentiometer gate 870 may ~e adjusted to provide different base current to the transistor 8S7. The emitter of the transistor 857 is electrically connected to a source of a negative 8 volts 112 ana its collector is electrically connected to the source of the switch 864 through a 46.4 K resistor 880 to provide a signal to the output conductor 282 upon receiving a signal on conductor 700. To provide compressibility compensation, conductor 418 is electrically connected to the switch 864 through a 1.8 M resistor 882.
To provide a signal to conductor 520 to modify the rate of acceleration which commences at the start of refil] when a low range signal is received on conductor 626 by the switches 852 and 854, conductor 46 is electrically connected to the source of the one levél of switch 852 through: (1) the resistor 858 and a 24.9 K resistor 884; (2) through the resistor 868, a 2.7 K resistor 886 and the resistor 884. Conductor 46 is connected to the electrical common through the resistor 868 and a 649 ohm resistor 888.
In FIG. 28, there is shown a schematic of.the sample and hold amplifier circui.t 852 having a switch 890, a storage capacitor 892 and an operational amplifier 894. The switch 890 is electrically connected to the output of the servo-amplifier through conductor 556 and to conductor 282 to receive a signal during the delivery portion of the pumping cycle. The switch 890 has one lead electrically connected to: (1) one plate of the ~.22 uf storage and noise filtering capacitor 892 through a 680 K resistor 896 and a 3.3 M resistor 898; (2) to the noninverting terminal of the ampli.fier 894 through the resistors 896 and 898; (3) to the electrical common through a 1 Uf storage and noise filtering capacltor 900; and (4) to a source 138 of a positive 8 vo]ts through the 22 M reslstor 902.
The capacitor 892 is a 0.22 uf capacitor having one of its plates connected to the output of the switch 890 and its other connected to electrical ground.
The capacitors 892 and 900 store a voltage representing the drive signal to the motor during the delivery portion of the pumping.
The output of the operational amplifier 894 ~s electrically connected to its inverting input terminal and to a conductor 904 from the servo voltage multiplier and offset circuit 854 (FIG. 26).
With this c.ircuit arrangement, a value of potential equivaient to the drive signal to the motor stored on capacitors 8g2 and 900 and applied with an offset to conductor 904 to the servo voltage multiplier and offset circuit 854.
In FIG. 29, there is shown a schematic circuit diagram of the servo vol~age multiplier and offset circuit 8S4 (FIG. 26) having an operational amplifier 910, a first potentiometer 912, an analog switch 914, and a second potentiometer 916. The potentiometer 9].6 is electrically connected at one end to a source 138 of a positive 8 volts and at the other end to a source 112 of a negative 8 volts to permit se]ection of a potential to be applied to the source of switch 914 and the potentiometer ~12 is e]ectrica].ly connected at one end to conductor 904 of the sample and hold amplifier circuit 852 (FIGS. 26 and 28) through a 1 K resistor 918.
The potentiometer 916 is a 10 K potentiometer .

and the potentiometer 912 is a 2 K potentiometer.
The other end of tlle potentiometer ~12 is electrically connected through a 6.19 K resistor 9~0 and a 100 K resistor 922 to the inverting input terminal of the operational amplifier 910. ~he ~ inverting input terminal of the operationa]
amplifier 910 is also electrically connected to conductor 558 through a 100 K resistor 924 to receive a signal from the output of the servo-amplifier.
'rhe output of the amplifier 910 is electricallyconnected through a 220 ohm resistor 926 to one side of the resistor 922 and through a 22 pf capacitor 928 to the other end of the resistor 922 and to the inverting input terminal of the amplifier 910. The noninverting input of the amplifier 910 is electrically connected to the electrical common so that the input signal from the output of the main servoamplifier on conductor ~58 is applied to the inverting input terminal of the amplifier 910. ~.he output of the amplifier 910 is applied to one end of the servo voltage multiplier where its magnitude is adjusted by the servo offset and servo voltage multiplier potentiometers and by the signal on conductor 904 for application through the switch 914 and conductor 554 to the input of the servoampiifier, thereby providing a feedback circuit which incorporates a sample and hold circuit and certain corrections.
When switch 914 closes and connects the wiper of potentiometer 912 to conductor 554, a negative signal from the sample and hold circuit at 904 is applied through the main servoamplifier 580 (FIG.
17) and inverted in amplifier 91Q. ~he signal is transmitted from conductor 904 on the output of the amplifier 894 (FIG. 28) in the sample and hold amplifier circuit 852 (FIG~. 26 and 28), through the potentiometer 912 and conductor 554 to the noninverting input of servoamplifier 580 (FIG. 17) and to the inverting input of operational amplifier 910. The amplifier 910 includes equal input and feedback resistors 922 and 924 establishing a potential at 927 on the output of the inverter 910 connecting resistors 920, 922 and 926 which is inverted but equal to the potentia] at 558.
The servo amplifier 580 (FIG. 17) is a high gain amplifier and causes the potential at 554 to be close to zero. Because amplifier 910 is a part of a negative 1 gain inverter, point 927 is the inverted value of the output of the servoamplifier at 558.

-79 1 3355 ~ 3 Since the potential at the wiper of potentiometer 912 is not far from zero volts, being not far from the potential at 554, the potential at 927 is -a multiple of the potentia~ at 904 established by the voltage diviaer including the resistance from the w~per to the point 9-27 and from the wiper to point 904. The voltage at 927 is a multiple of the sample and ho~d voltage which is equivalent to the motor drive signal during delivery and the output signal at 558 is the inverted value of the potential at 927 to represent a multiple of the motor drive signal during delivery.
During acceleration, 686 goes high to close 914 connecting it to potentiometer 916. The offset on 916 is set to cause the servo amplifier to go negative when switch 914 closes. ~roltage on 554 to servo amplifier, when switch 914 is closed, reaches a balance depending on potentiometer setting 912.
With this arrangement, the servoamplifier generates a signal to cause acceleration o~ the motor until terminated by the acceleration time generator circuit, causing the total volume of fluid per stroke to tend to equalize and thus reduce pulsations of current through the chromatographic column. The acceleration is related to the signal on conductor S58 reflecting the sample and hold voltage stored during delivery.
In FIG. 30, there is shown a schematic sectional view of a pump 14 (FIG. 1) having a cam 950, a cam follower 952, and a pump head 954. The cam 950 is mounfed to the output shaft of the motor 50 (FIG. 3) for rotation thereby. The cam follower 952 is mounted to move in the direction of the pump head 954 and the direction of the output shaft as the cam rotates to provide a reciprocating motion for a piston within the pump head 954.
The pump head 954 includes an outlet port 956 and an inlet port 958, closed by pressure-activated valves so that when the piston is moved inwardly in response to the cam follower 952, ~luid is drawn into the pump cylinder 960, the outlet port ~S6 being closed and the inlet port 958 being open.
Similarly when the piston is moved forwardly, fluid is forced from the outlet port 9S6 and fluid is blocked from entering or ~eaving the inlet port 9S8 by check valves therein. The high pressure pump itself and the electric motor are not part of the invention themselves except that the rotatable masses thereof are sufficient to provide a flywheel effect to the pump itself. This and other flywheel implements reduce the effect of friction and increases repeatability. Bearings are selected for low riction.
In FIG. 31, there is shown a schematic circuit diagram of a circuit 1000 for presetting a liquia - flow rate from the pump to adjust the amplitude of the current on conductor 46 having a keyboard 1002, a clock source 1004, an updating circuit 1006, and a current source 100~. The current 46, of course, may be set by any analog circuit including a manual potentiometer in a manner known in the art.
In the preferred embodiment, it is set by a software program utilizing an 8031 microcomputer of the type manufactured by Intel, containing 128 bytes of RAM, a serial port and two counter/timers. An EPROM in the unit contains instruction codes for controlling the pump. The software program for monitoring the current 46 to maintain a constant average flow rate as follows:

~ 1 33s5 1 3 ~CS-51 MACRO ASSEnBLER HPLC RECIP PUnP, 11.05q CRYSTAL AND SERIAL 02-20-85 LOC OBJ LINE SDURCE
03A4 C24F 70B TD MAIN: CLR START UP ;IF ~ADE IT THROUGH, IHEN IS STARTED UP
03A6 0201CB 70q LJMP MAIN

712 ; THE FOLLOUING SUBROUTINES ~OUASI INT,NO PRESS UPDA, LOADEROFXXX, AND
713 ; CALC ALL BELONG TO THE FLOU RAIE ALORIIHM. OUASI INT IS USED HHEN THE
714 ; INIERRUPIS HAVE BEEN DISABLED AND AFTER RENABLING, THE INTERRUPT BIT FOR
715 ; EXTERNAL IS SET. IT PULLS A "FAXE" INTERRUPT TO nAINTAIN THE ALGO.
716 ; ALSO, THE SUBROUTINES ADJUST REF,TAKE CARE HIGH, AND TAXE CARE LOU
717 ; aRE USED IN THE ALGORITHM AT DIFFERENT TI~ES
71~ ;
03Aq 20q605 71q OUASI INT: JB Pl.6,CALL CALCl 03AC D23C 720 SETB GATED ;CATE OFF PRESSURE
03AE D23A 721 SETB CATEDl jMESSAGE TO OTHER LOOPS TO
03~0 22 722 REI ;START INITIAL ALGORIIHM MOgE
03~1 61EA 723 CALL CALCl: AJMP CALC ;RETURN IS IN CALC

726 ; REAL INTERRUPTS FROM EXTERNAL JUnP TO THIS SPOI

03B3 20q606 728 NO PRESS UPDA: JB P1.6,CALL CALC
03B6 D23C 72q SETB GATED ;SET TO GATE OFF PRESSURE
03b8 D23A 730 SETB GATED1 ;USED IN MAIN, RAPID, AND AGAIN

03BC 71EA 732 CALL CALC: ACALL CALC ;NOT A REFILL PULSE BUT A TIMER PULSE
03BE DOa3 733 SKIDOO: POP DPH

73~ ;
737 ; THESE ROUTINES LOAD THE TACH COUNTER (C0 2) 73~ ;
73q 03C3 qO2002 740 LOADEROF300: MOV DPTR,UCO_2 03C6 742D 741 nov A,~2BH ;LOAD 29q SINCE FIRST PULSE LOADS IN
742 ; THE COUNT VALUE AND SO IS MISSED
03C8 FO 743 MOVX eDPTR,A
03cq 7401 744 MOV AruolH
03CB FO 745 MOVX eDPIR,A

03CD qO2002 747 LOADEROFIOO: no~ DplR~uco 2 03D0 7463 74a nov A,U063H jLOAD IN q9 FOR SAnE REASON AS 300 03D2 FO 74q MOVX QDPTR,A
03D3 7400 750 MOV A,#OOH
03D5 FO 751 MOVX QDPTR,A
03Db 22 752 RET
03D7 902000 153 LOAD OTHER COUNTS: MOV DPTR,UCO O
03DA 74EA 754 MOV A,#OEAH ;LOAD CO O UITH 17,aqa 03DC FO 755 MOVX QDPTR,A ;TInERS LINXED TO 32 BIIS
03DD 7445 756 HOV A,#45H
03DF FO 757 MOVX ~DPIR,A
03EO qO2001 75a LOAD OTHER COUNTSA: MOV DpTR~uco l 03E3 74FD 759 MOV A,~OFDH ;SO CO 1 COUNTS AT.OlSEC
03E5 FO 760 MOVX QDPTR,A ;DOWN FROM 65533 03E6 74FF 7kl nov A,UOFFH ;b5533 SINCE FIRST PULSE LOADS
03E8 FO 762 MOVX QDPTR,A ;VALUE AND IS MISSED AND SEE~S

A

MCS-51 nACRO ASSEMBLER HPLC RECIP PUMF, 11.05q CRYSTAL AND SERIAL 02-20-85 LOC OBJ LIME SOURCE
03E9 22 763 RET ;TO nlSS ONE IN TInlNG ALSO

765 ; CALCULATIONS FOR THE SECONbARY ADJUSTMENTS BASED ON TACH RATE
7b6 ; JU~PED TO BY INIERRUPT
767 ; BaSIC CONTROL EOUATIDN IS:
76b 76q ; DAC_ADJUSTl (DAC OLD~B33 3~Tl~E)/~PULSES~FLOU BlN) 770 ; DAC OLD DAC ADJUSIl OF LAST READINC

772 ; WHERE SOME ADDED CONVERSION FACIORS ARE NEEDED
773 ; AND PULSES IOO OR 300 AND TI~E IS ~EASURE, BUT NOT
774 ; ACTUALLY STORED IN A RECISTER
775 ; ADDITIONALLY, THE VhLUES ARE LI~ITED TO A ADJUSTnENS77b ; OF 2X aT .5 HL LINEARLY INCREASINC TO 25X AT .01 ML

03EA CO~O 77~ C~LC: PUSH PS~ ;PUSH RSO AND RSI ~ITH PS~

03EE D2D4 7el SETB RSl 03FO 902001 782 MOV DPTR,KCO 1 ;LOAD IN TInER VALUE
03F3 EO 7B3 MOVX A,~DPTR
03F4 FD 784 nov R5,A
03F5 EO 785 MOVX A,eDPtR
03F6 FE 78b MOV Rb,A
03F7 7F00 787 MOV R7,UOOH
03Fq qO0306 7B8 MOV DPTR,KNUnBER OF IInES
03FC EQ 789 MOVX A,eDPTR

03FE FO 791 MOVX eDPTR,A ;PUT NUMBER BACR
03FF 203805 7q2 JB AlOO PULSES,CHK 15 0402 B40507 7q3 CJNE A,U05H,KEEP COUNTINC
0405 8014 7q4 SJ~P RESET COUNIER
0407 B40F02 7q5 CHK 15: CJNE A,UOFHlKEEP_COUNTINC
040A 800F 7q6 SJMP RESET COUNTER
040C 203B06 7q7 KEEP COUNTING: JB AlOO PULSES,LOAD ONLY 100 040F 71E0 7~8 ACALL LOAD OTHER_COUNTSA
0411 71C3 7qq ACALL LOADEROF300 0413 900E 800 SJnP REEP COUNT
0415 71EO 801 LOAD ONLY IOO: ACALL LOAD OTHER COUNTSA

041q 800B B03 SJMP XEEP COUNT
041B 7400 804 RESET COUNIER: MOV A,KOOH
041D FO B05 novx ~DPTR,A
041E 121770 806 LCALL INII ADJUST ;LOCAIED RICHI AFTER KRUN
0421 AlBE 807 AJnP CLEAR OUT jCEI OUT OF HERE
0423 7AFF 808 8EEP COUNT: MOV R2,ROFFH ,LOAD IN 65535 ~FFFF) 0425 7BFF 80~ ~OV R3, uoFFH
0427 7COO 810 MOV R4,UOOH
042q BID4 811 ACALL BINSUB ;SUBT 65535-COUNT VALUE
042B AA20 812 MOV R2,20H
042D AB21 813 MOV R3,21H ;MULT BY 25bO
042F 7C00 814 nov R4,UOOH
0431 7DOO 815 MOV R5,UOOH
0433 7EGA 816 nov Rb,KOAH
0435 7F00 817 MOV R7,UOOH

.~ .

MCS-51 MACRO ASSEMBLER HPLC REGIP PUMP, 11.05q CRYSIAL AND SERIAL 02-20-85LOC ObJ LINE SOURCE
0437 BlE8 81a ACALL BINMUL
043q AA23 81q MOV R2,23H
043P AB24 a20 MOV R3,24H
043D AC25 a21 MOV R4,25H
043F 203816 a22 JB A100 PULSES,ONLY 100 0442 7D46 823 MOV R5,#46H ;ADD 1282 502H ~RNDING IN NEXI) 0444 7E05 824 HOV R6,N05H . ;12/2185 ADD 1350 546H
0446 7F00 825 HOV R7,#OOH
0448 ElCl 826 ACALL BINADD
044A AA20 827 MOV R2,20H
044C AB21 828 MOV R3,21H ;~f~12/2/a5 CNG REF TO 833.3 044E AC22 82q MOV R4,22H
0450 7D6C 830 MOV R5,NObCH ;DIVBY 2563 A03H ~300~7500/a78) 0452 7EOA a31 MOV R6,~0AH ;~HERE 7500 IS 2000UL REF ~ORD
0454 7F00 832 MOV R7,NOOH ;~12/2/85 (300~7500/833.3) 2700 0456 8014 833 S.IMP CALL DIVIDER ;2700 A8CH
0458 7DC2 a34 ONLY 100: ~OV R5,NOC2H ;ADD 427 FOR ROUNDINC ~854/2) 045A 7E01 835 MOV Rb,NOlH ;427 1ABH
045C 7F00 83~ MOV R7,NOOH ;~12/2/B5 450 1C2H ~qOO/2) 045E BlCl 837 ACALL BINADD
0460 AA20 83a MOV R2,20H
04b2 A~21 B3q ~OV R3,21H
0464 AC22 840 MOV R4,22H
0466 7D94 841 MOV R5,N084H
0468 7E03 842 MOV R6,N03H ;DIVBY 854 356H ~100~7500/B78) 046A 7FOO g43 MOV R7,NOOH ;i~12/2/a5 qOO 384H ~100~7500/833.3) 046C DlAD 844 CALL DIVIDER: ACALL BINDIV
046E hA20 B45 ~OV R2,20H ;GET RESULT
0470 AB21 846 nov R3,21H
0472 AC22 B47 MOV R4,22H
0474 205206 B48 JB CALIBRATED,DIVOIHER
0477 AD46 84q HOV R5,FLO~ BIN ;MULTIPLY BY FLO~RATE BINARY
FORM ~0 TO 1875 BINARY FOR O TO 500 UL/MIN) 0479 AE47 .850 MOV R6,FLO~ BIN~l 047B B004 R51 SJMP DIV NORn 047D AD5F 852 DIVOTHER: MOV R5,FLOU BIN CAL ;IF CALIBRATED, U5E THIS 3 047F AE60 853 MOV R6,FLO~ BIN CAL~l 04al 7F00 854 DIV NORM: MOV R7,~00H
0483 BlEa B55 ACALL BINMUL
0485 AA23 856 ~OV R2,23H ;ADD 50 FOR DIVISION ROUNDING
0487 AB24 857 MOV R3,24H
0489 AC25 85a MOV R4,25H
048B 7D32 859 MOV R5,#50 0480 7EOO 560 HOV R6,NOO
04aF 7F00 861 MOV R7,NOO
04ql BlCl 862 ACALL BINADD
04q3 AA20 863 MOV R2,20H ;DIVIDE BY 100 04q5 AB21 864 MOV R3,21H
0497 AC22 865 MOV R4,22H
049q 7D~4 866 . MOV R5,N064H
049B 7E00 867 MOV R6,uooH
04qD 7F00 868 MOV R7,NOOH
04qF DlAD 86q ACALL BINDIV
04Al AA20 870 MOV R2,20H
04A3 AB21 871 MOV R3,21H

-~

MCS-51 HACRO ASSE~BLER HPLC RECIP PUMP, 11.05q CRYSTAL AND SERIAL 02-20-85 LOC OBJ LINE SOURCE
04AS AC22 B72 ~OV R4,22H
04A7 AD5q 873 MOV R5,DAC ADJUSTl 04Aq AESA 874 ~OV R6,DAC ADJUSTI+l 04AB 7FOO B75 MOV R7,~00H
04AD blE8 876 ACALL BINMUL ;HULIIPLY OLD BY CURRENT~
04AF 7F00 877 MOV R7,~00H
04Bl AA23 B7B MOV R2,23H
04B3 AB24 B7~ MOV R3,24H
04B5 AC25 880 nov R4,25N
04B7 7DOO BBl nov R5,~00H
04B9 7E05 BB2 nov R6,~05H
04B~ 7F00 8B3 MOV R7,tl00H
04BD BICl 8B4 ACALL BINADD ;ADD 1280 FOR ROUNDING
04BF AA20 885 HOV R2,20H ,DIVIDE BY 2560 BY MOVING OVEfi 04Cl AB21 88b MOV R3,21H ;ONE BYTE WHEN STORING
04C3 AC22 887 MOV R4,22H
04C5 7DOO 88B ~OV R5,~OOH
04C7 7EOA BBq MOV R6,~0AH
04cq 7F00 890 MOV R7,~OOH
04C8 DlAD 8ql ACALL BINDIV
04CD AA20 5q2 MOV R2,20H
04CF AB21 893 MOV R3,21H
04Dl AC22 Bq4 ~OV R4,22H
04D3 qO0300 8q5 MOV DPTR,tlDAC OLD
04D6 E55q 8q6 MOV A,DAC ADJUSTl 04D8 FO 8q7 MOVX ~DPTR,a 04Di A3 8q8 INC DPTR
04Da E55A Bqq MOV A,DaC hDJUSTltl 04DC FO qOO MOVX eDPTR,A
04DD AD5q qOl HOV R5,DAC ADJUSIl 04DF AE5A qO2 ~0~ ~,DAC_AD~USTI~l 04E1 BA5q qO3 MOV DaC ~DJUSTl,R2 ;MOV NEW IN DAC ADJUST
04E3 ~B5A qO4 MOV DAC_ADJUSTltl,R3 04E5 BlD4 qO5 ACALL BINSUB ;SUBT NEW FRO~ OLD
04E7 4Dbq 90~ JC BEELOW ;CARRY THEN ADJUST IS BELOW REF
04Eq 7A75 qO7 MOV R2~u75H ;USE 102t885/FLOW BIN AS LI~II
04EB 7B03 908 MOU R3ltlo3H
04ED 7COO qOq MOV R4,ttOO
04EF AD46 qlO ~OV R5,FLO~ BIN
04Fl AE47 qll nov R6,FLOH BINtl 04F3 7FOO ql2 MOV R7,~00 04F5 1206AD ql3 LCALL BINDIV
04Ft AA20 ql4 ~OV R2,20H
04FA AB21 ql5 nov R3,21H
04FC AC22 916 MOV R4,22H
04FE 7Db6 ql7 HOV R5,~102 0500 7EOO 918 MOV R6,tloo 0502 7FOO 91q MO~ R7,~00 0504 1205Cl 920 LCALL BINADD
0507 AD20 921 MOV R5,20H
050q AE21 922 MO~ R6,21H
050B AF22 q23 MOV R7,22H
050D qO0300 q24 MOV DPTR,~DAC OLD
0510 EO 925 MO~X A,QDPTR ;LOAD OLD NUMBER TO HAKE 2Z LI~
0511 FA q26 MOV R2,A

.~

1 3355 ~ 3 MCS-51 HACRO ASSEM~LER HPLC fiECIP PUMP, 11 05q CRYSTAL AND SERIAL 02-20-85 LOC OBJ LINE SOUfiCE
0512 A3 q27 INC DPTR
0513 EO q28 ~O~X A,eDPIR
0514 FP 924 MO~ R3,A
0515 7C00 930 MO~ R4,#00H
0517 1205Ea q31 LCALL BINHUI
051A AA23 q32 ~0~ R2,23H ;DI~IDE BY 100 051C AP24 q33 ~~ R3,24H jADD 50 FIRST FOR ROUNDING
051E AC25 q34 HO~ R4,25H
0520 7D32 q35 MO~ R5~U50 0522 7E00 936 MO~ Rb,UOOH
0524 7F00 ~37 MO~ R7,UOOH
0526 PlCl q38 ACALL BINADD
0528 AA20 93~ HO~ R2,20H
052A aB21 940 MOV R3,21H
052C AC22 941 ~OV R4,22H
052E 7Db4 942 MO~ R5,#100 0530 7EOO q43 HO~ R6,800 0532 7FOO q44 MOV R7,UOO
0534 DIAD ~45 ACALL BINDIV
0536 A820 q46 MOU RO,20H ;STORE IN TWO PLACES
0539 A~21 q47 MOV Rl,21H
053A AA20 ~48 MO~ R2,20H
053C AP21 i4q MOV R3,21H
053E AC22 950 HO~ R4,22H
0540 AD5q q51 MO~ R5,DAC aDJUSTI
0542 AE5A 952 MO~ R6,DAC aDIUSTltl 0544 7FOO qS3 MO~ R7,UOOH
0546 BlD4 q54 ACALL BINSUD ;SUBTRACT NEW FROM 2~Z ~ALUE
054B 4002 qSS IC TIMES 102 ;IF CARRY THEN USE 2tZ ~ALUE
054A B06A 95b SJMP DACCY
054C 885q q57 TIHES 102: HO~ DAC ADIUSTI,RO
054E Bq5A 95B MO~ DAC ADJUSTltl,Rl ;LOAD IN 2~X VAL

0552 7A75 960 BEELOW: MO~ R2,~75H
0554 7P03 qbl MO~ R3,~03H
0556 7COO q62 MOV R4,UOOH
055~ AD4b qb3 MO~ R5,FLOW BIN
055A AE47 964 MO~ R6,FLO~ BlNtl 055C 7FOO 9b5 MOV R7,~00H
055E 1206AD q66 LCALL BINDI~
0561 AD20 qb7 MO~ RS,20H
0563 AE21 9b8 MO~ Rb,21H
05bS AF22 qbq MO~ R7,22H
0567 7Ab2 q70 HO~ R2,#qB
OSbq 7POO 971 MOV fi3,UoOH
056P 7COO q72 MOV R4,UOOH
056D 1205D4 q73 LCALL BINSUB
0570 AD20 q74 MO~ R5,20H ;MULT BY 9a-BB5/FLO~ BIN
0572 AE21 q75 MO~ Rb,21H ;UILL DI~IDE BY 100 TO GET A
0574 7FOO q76 MO~ R7,UOO ;2t PERCENT LIMIT TO CHECK WITH
0576 qO0300 q77 MO~ DPTR,UDAC OLb 057q EO 97B MOUX A,eDPTR
057A FA q7q MOV R2,A
057B A3 qao INC DPTR
057C EO qBl MOVX A,ODPTR

r ~ r~ .

~ 3355 1 3 MCS-51 MACRO ASSEMbLER HPLC RECIP PUMP, 11.05q CPYSTAL AND SERIAL 02-20-B5 LbC OEJLINE SOUhCE
057D F~ qB2 MOV R3,A
057E 7COOqB3 ~OV R4,NOOH
05BO BIE9qB4 ACALL bINHUL
0552 AA23 qBS MOV R2,23H ;DIVIDE BY 100 05B4 AB24 qB6 MOV R3,24H ;ADD SO FIRST FOR ROUNDING
05Bb AC25 qB7 MOV R4,25H
058B 7D32 qBB MOV R5,~50 OSBA 7EOO qBq MOV R6,~00H
05BC 7FOO qqO MOV R7,~00 05BE BICI q91 ACALL ~INADD
05qO AA20 q92 HO~ R2,20H
05q2 A~21 q93 MOV R3,21H
0594 AC22 994 MOV R4,22H
05q6 7D64 995 MOV R5,~100 OS9B 7E00 996 MOV R6,~00 05qA 7FOO qq7 MOV R7,~00 059C DlAb qqB ACALL BINDIV
Q5qE A820 qqq MOV RO,20H ;SSORE IN IWO PLACES05AO A921 1000 MOV Rl,21H
05A2 AA20 1001 MOV R2,20H
05A4 AB21 1002 MOV R3,21H
05A6 AC22 1003 MOV R4,22H
05A3 AD5q 1004 MOV R5,DAC ADJUSIl 05AA AE5A lOg5 HOV Rb,bAC ADlUSTltl 05AC 7F00 1006 MOV R7,~OOH
05AE ElD4 1007 ACALL ~INSUb ;SUbTRACT NE~ FROM 2X VALUE
05B0 4004 lOOB JC DACCY ;IF CARRY THEN USE OLD VALUE
05~2 8B5q lOOq MOV DAC AbJUSSl,RO
05B4 8q5A 1010 MOV DAC ADJUSTltl,Rl 05~b 795q 1011 DACCY: MOV Rl,#bAC ADJUSSl 05B~ 901000 1012 MO~ DPIR,~ANALOG_LO
05bB 1214DC 1013 LCALL DAC5 05BE DODO 1014 CLEAR OUT: POP PSU ;RETURN RBANK SELECTS
05C0 22 1015 RET ;RETURN TO INT HANDLE
1016 ;OR Ta CALLING SU~ROUTINE
1017 ;IF NOT AN ACTUAL INSERRUPTlOlB
lOlq 1023 ;~ DINARY NUMBER MATH ROUTINES ~ t 1025 ;~X Y ~-X Y ~/X YZ W~X YZ
102~ ;

05CI E51A 1023 BINADD: MOV A,OlAH
05C3 251D 102q ADD A,OlDH
05C5 F520 1030 MOV 20H,A
05C7 E51B 1031 MOV A,lBH
05cq 351E 1032 ADDC A,lEH
05CB F521 1033 MOV 21H,A
05CD E51C 1034 MOV ~,lCH
05CF 351F 1035 ADDC A,lFH
05Dl F522 1036 MOV 22H,A

MCS-51 ~ACRO ASSE~BLER HPLC RECIP PUMP~ 11.05q CRYSTAL AMD SERIAL 02-20-B5 LOC OBJ LINE SOURCE
1750 ADJUSTER: ;THIS SUBROUTINE PREPARES THE TI~ER ~8253) 1751 ;FOR THE NEXT PART OF THE CONTROL ALGORYTH~

OB38 7A40 1754 HOV R21~40H ;~AIJ 40tO00 CYCLES BEFORE CHECK
OB3A 7PqC 1755 nov R3t~qCH ;EOUIVALENT IO .08 SEC
OB3C DAFE 175b ZEROSA: DJNZ R2tZEROSA
OP3E DBFC 1757 DJNZ R3tZEROSA
OB40 30B311 1758 JNB P3.3tNOADJUST ;IF STILL GATED~ DISREGARD
OB43 C23A 175q CLR CATEDl jGATE INJERRUPJ HAS BEEN HANDLED
OBq5 20640C 1760 JB PREP HEADt NOADJUSJ ;NOADJUSTMENJS FOR PREP
OB4B 307DOq 17bl JNB nlCROLtNOADJUST ;OR FOR HIGH PLOWS
OB4P E531 1762 ~OV AtFLOU RATE~l OB4D B40502 1763 CJNE At~OSH~CHK FURTHER ;ADJUSTS UP TO 49q UL/~IN
OB50 B002 17k4 SJMP NOADJUST
OP52 4001 17b5 CHK FURTHERs JC OK
OB54 22 17bb NOADJUST: REJ
OB55 E531 17b7 OX: ~OV AtFLOU RATE+l ;READJUST FOR NEXT UPDAIES
OB57 B40103 17b8 CJNE At#OlHtIS LO~ER ,IS IT LESS THAN lOOUL?

OB5D 4004 1770 IS LOUER: JC SET IT Hl ;IF IS~ USE 100 FULSES
OB5F C23B 1771 NO SET: CLR A100 PULSES
OPbl BO10 1772 SJ~P LOAD 300 OBb3 D23B 1773 SET II HI: SETB AlOO PULSES
OBb5 1203D7 1774 LCALL LOAD OIHER COUNTS
OBb8 1203CD 1775 LCALL LOADEROF100 OPbB qO030b 177b HOV DPTRt~NU~BER OF TIMES
OBbE 7400 1777 MOV At~OOH ;CLEAR THIS
OP70 FO 1778 HOVX eDPTRtA
OP71 800C 1779 SJnP SEJ CLOCK COUNJ
OB73 1203D7 1780 LOAD 300: LCALL LOAD OJHER COUNTS

OP7q 900306 1782 MOV DPJRt~NU~BER OF TIMES
OB7C 7400 17B3 HOV At#OOH
OB7E FO 17B4 HOVX eDPTRth OB7F D2qb 17a5 SET CLOCK COUNT: SEJB Pl.6 OB81 22 17Bb RET

178q 17qO
17ql ; BRANCH ON KEYBOARD ENIRY
17q2 OBB2 121bBE 1793 KEYBD: LCALL BOP
ObB5 ~00801 17q4 ~OV DPTRt~DISPLAY CONJROL
OB88 7440 17q5 HOV ArK40H ;READ KEYBOARD
OBaA FO 17qb ~OVX QDPTRtA
OB8B A3 17q7 INC DPTR
OBBC EO 17q8 ~OVX At~DPTF;

OBBE 547E 1800 ANL A~KO111111OP ;nASK ACTIVE KEYS
OBqO F8 1801 nov RO~A ;SAVE COPY
OBql qOOPqD 1802 ~OV DPTR~ADTABLE
OBq4 04 lgO3 INC A
OP95 q3 1804 ~OVC A~IA~DPTR ;CREATE RETURN ADDRESS

.. ~ .

In addition to a source which may be aajusted by a potentiometer and the use of a computer as is aone in the pre~erred embodiment, a hardware circuit may be used as shown in FIG. 1 in which a keyboard 1002 initiates clock pulses from a source 1004 and a value into the updating circuit 1006. A source o~
pulses from the tachometer is applied through conductor 400 to the updating circuit and the number of tachometer pulses in one cycle of the pump are counted sequentially and compared with an idealized number, with the current source being increased if the number lags so that the computer averages the amount of flow across a cycle of the pump to maintain a constant average flow rate by adjusting the current source in addition to the other adjustments hereinbefore described.
To monitor the tachometer pulses, the updating circuit includes first and second counters 1010 and 1012, first and second digital-to-analog converters 1014 and 1016 and a comparator 1018. The counter 1010 has counted into it from the clock 1004 the clock pulses in a cycle of the pump before being reset and the clock rate is set to equal the number of tachometer pulses which should be received in one pump cycle. The counter 1012 is reset by the same 9~ 1 3355 1 3 pulse that re~ets the coun~er 1~10 ~t ~ount~ th~
taa~ometer pulses a~ thRy act~all~ c)ccur. r~igltal-t~-~nalog c~nverter 1014 generate~ ~n ~nalog voltage ~gui~alent t~, the ~oun~cs ln counter lO10 and dig~tal-to an~log ~onverter 101~ gene~ate~ an ~n~l~g ~i~nal equl~alent to t~e count~ of ~ounte~
'rhe ~o~parator 101~ aompares the analo~ outp~t~ from the ~igi~ to-an~l~g converter~ 1014 and 101~ ~nd ~d lu~ h~ ~urrent sourae 1~3 wi~h the ~gnal ~o as t~ mainta~n ~ ~ignal on ~nduato~ ~ wh~h wi~l co~pensate for de~iation~ ~f flow ~rom the pump fro~
cy~le to ~y~le~
B~fore oper~ting the pump, ~ t is cal~bra~ed to avol~ ~:av$tati~n while ~he motor acceler~es rom th~ ~tart of a re~ ycle to p~ll fluid into the pump until a pred~termined period of time ha~
el~pse~ ~ram the ~t~r~ of the ~eler~on. Thi~ is mplished by ~d~ustinq potentl~meter~ 91~ and ~1~
~ . 29~, S14 ~ . 15~ and 857 ~FI~ 27) wh~le pump~ng water and moni~oring the pressure output from str~e to ~troke t~ dete~t ca~itation. ~he v21ue~, whi~h a~fect ~he a~ae~er~tion, when properly ~et redu~e the cavitation and ~ari~t~on ~n flow rate wlth pre8sure V~a~ion~ and may be maintained for m~ximum operation of ~he pump.

-1 3355 ~ 3 Once the pump is calibrated, it is operated by setting a flow rate, priming the pump, filling its cylinder and expelling 1uid. In expelling the fluid, near an end portion of the stroke, the pump is run at a constant speed until it reaches the end of the expulsion stroke, at which time a réfill signal is generated and the piston begins a refill stroke~in a return direction. When it reaches a start of the re~ill stroke, the pump motor begins to-accelerate at the controlled rate and continues to accelerate for a predetermined amount of time related to the operating conditions, at which timeit slows to the preset rate for constant flow.

In setting a flow rate in the preferre~

embodiment, the flow rate is keyed into the keyboard and a software circuit retains it, generating a set point signal for application to an analog voltage generator of a conventional type. The analog set point signal controls the flow rate.

The preset flow rate is compared with tachometer pulses generated during the forward stroke of the piston of the pump and, if the average pumping rate is below that preset, the voltage on conductor 46 is increased.

Although a computer is used for this function in the preferred embodiment, it can be accomplished by a hardware circuit such as that shown in FIG. 1-in which a count representing an ideal tachometerrate is set into a counter 1010 (FIG. 31) and converted to a digital-to-analog signal in the digital-to-analog converter 1014. The tachometer pulses as they are counted on conductor 400 are also converted to an analog signal in digital-to-analog converter 1016 and the analog signals are compared to adjust the current source so that a basic linear feedback circuit related to liquid influent 10w into the chromatographic column and injector system 18 (FIG. 1) is provided.
Of course, the current for conductor 46 may be set by a simple source of potential and variable resistor or by any other technique in which a current directly proportional to the flow rate is provided. This current will, in general, control through a linear circuit the flow ràte regardless of how it is obtained and exert a tendency to maintain it constant as influent to the chromatographiC
co]umn.
During a refill cycle and the first part of the cycle forcing fluid out of the pump, the motor 50 ~2 (FIG. 3) receives a signal from the nonlinear flow rate control circuit a~2 (FIGS. 2 and 9) having a time duration controlled by a timer and initiated at a point during the refill cycle an~ continuing for a time therea~ter related to rate of flow which has been set ~or flow into the chromatographic column.
The time of acceleration is related to the charge on capacitor 150 (FIG. ~) which is modu~ ated by transistor 716 (FIG. 23) in response partly to the signal on conductor 46 (FIG. 23) from the set point value. The amount of acceleration is related to the closed loop servo signa' which was last driving the pump, that value being obtained by a sample and hold circuit electrically connected to the output of the servoamplifier to store the signal during the last part of a pumping cycle when the pump is pumping at a constant rate under closed loop control of a motor speed rotation signa]. The sampl e and ho~ d amplifier circuit 852 tFIG. 26 and 28) stores a signal on a capacitor 900 and 892 (FIG. 28). The rate of acceleration is adjusted by offset and multiplication values during calibration by adjusting potentiometers 916 and 912 (FIG. 29). The signal from potentiometer 912 is applied as a closed loop control signal to the amplifier 580 (FIG. 17) . 94 ~ 3355 1 3 in which the ~eedback signal has been closed by analog switch 914 and the amplifier 910.
With this arrangement, the pump is maintained during a portion of a pumping cycle at a constant speed under a tachometer feeaback circuit using analog circuitry and a digital control which adjusts the constant current control for the flow rate.
During the refill cycle, the motor is accelerated continuously while the piston is controlled by a cam to acce.ierate and decelerate to zero and then accelerate again, with the motor acceleration terminating at a time controlled by a timer to reduce pulsations in flow to a minimum.
From the above descri~tion, it can be understood that the pump o~ this invention has several advantages, such as: (1) the time during which no liquid is pumped through the outlet port is low; (2) the pump is relatively uncomplicated because the acceleration time of the motor is time-limited rather than distance-limited; (3~ the pump is able to accomodate a wider range of flow rates without cavitation; (4) the pump mai.ntains an accelerating velocity during the return portion while refilling coming to a stop at the end and accelerating upwardly under constant positive .

driving of a motor through a cam, with the motor receiving a continuous accelerating voltage so as to reduce noise which might otherwise be caused by inertial effects as the motor spee~ is changed; (5) the average flow rate is continuously monitored and adjusted by adjusting a current input signal representing the preset flow rate of fluid; and (6) the flow rate remains constant as pressure varies.
Although a preferred embodiment of the invention has been described with some particularity, many modifications and variations are possible in the preferred embodiment without deviating from the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practicefl other than as specifically described.

Claims

1. A feedback system for controlling a motor comprising:
apparatus driven by a motor at a plurality of preselected speeds correlated with positions of said apparatus;
power means having an output signal for driving said motor at a speed related to the power means output signal;
means for generating a signal representing the velocity of the motor;
means for detecting a position of said apparatus for a change of speed;
a feedback loop having velocity negative feedback means and positive feedback means and means for connecting the velocity negative feedback means and positive feedback means into circuit with said power means;
said feedback loop including means for alternately controlling the output signal from said power means by an input signal which increases in power with time under the control of an increasing positive feedback signal from said motor and by an input signal which varies in Claim 1 Cont'd.

power in relation to the difference between a relative constant motor speed and a preset motor speed;
means for storing a preset analog value of velocity having an amplitude representing said preset analog value of velocity;
said velocity negative feedback means having means for comparing said preset analog value of velocity with said signal representing the velocity of the motor to generate a velocity feedback error signal for controlling said power means for driving the motor with an input power related to said velocity feedback error signal, means for storing said velocity feedback error signal when said output signal from said power means is controlled by an input signal which increases in power with time under the control of an increasing positive feedback signal from said motor;
said positive feedback means including means for applying a signal to said power means related to a constant, whereby the motor accelerates at a predetermining rate; and timing means for timing a period of time for said output signal from said power means to be controlled by an input signal which increases in power with time under the control of an increasing positive feedback signal from said motor, which period of time is related to the amplitude of said preset analog signal.

2. In a feedback system for controlling an apparatus driven by a motor at a plurality of preselected speeds correlated with positions of said apparatus and having drive means for supplying power to drive said motor; means for generating a signal representing the velocity of the motor; means for detecting a position of said apparatus; means for storing a preset analog value of velocity; negative velocity feedback means for comparing said preset analog value of velocity with said signal representing the velocity of the motor and generating a velocity feedback error signal for controlling said drive means; said negative velocity feedback means including a negative feedback loop, whereby said drive means may drive said motor with an input power related to said velocity feedback error signal; the improvement of which comprises:
a positive feedback means;
means for alternately controlling the output signal from said power means by an input signal which increases in power with time under the control of an increasing positive feedback signal from said motor and by an input signal which varies in power in relation to the difference between a relative constant motor speed and a preset motor speed;
said negative velocity feedback means including a comparator means for generating an error signal;
means for storing said velocity feedback error signal;
said positive feedback means applying a signal to said drive means related to said amplitude of said velocity feedback error signal, whereby the motor accelerates; and timing means for timing a period of time for said output signal from said power means to be controlled by an input signal which increases in power with time under the control of an increasing positive feedback signal from said motor, which period of time is related to said preset analog signal.

3. In a feedback system according to claim 2:
a reciprocating pump having a piston;
said means for alternatetly controlling the output signal from said power means by an input signal which increases in power with time under the control of an increasing positive feedback signal from said motor and by an input signal which varies in power in relation to the difference between a relative constant motor speed and a preset motor speed; including means for measuring the rate of movement of said piston within said reciprocating pump in a direction which causes fluid to be expelled;
means for setting a flow rate in digital form;
comparison means for generating a first error signal at period intervals when the rate of flow as measured in said first loop deviates from the preset rate of flow; and said positive feedback means including means for applying an acceleration voltage to said motor from a time a preset period after the initiation of a return stroke of said piston.

4. Apparatus according to claim 3 in which said positive feedback control means causes said power means to accelerate said motor at a rate related to the stored error signal.