EP0070893A1

EP0070893A1 - Gravimetric diluter

Info

Publication number: EP0070893A1
Application number: EP82900871A
Authority: EP
Inventors: Jeptha E. Campbell; Samuel Schalkowsky; Donald Whitley; James E. Gilchrist
Original assignee: Spiral Systems Inc
Current assignee: Spiral Systems Inc
Priority date: 1981-02-09
Filing date: 1982-02-04
Publication date: 1983-02-09
Also published as: JPH0442619B2; WO1982002696A1; GB2108288A; DE3231634T1; EP0070893A4; JPS58500337A; GB2108288B

Abstract

Dispositif (10) permettant d'obtenir des dilutions d'un echantillon (11) avec un diluant (36) jusqu'a concurrence d'un facteur de dilution f predetermine en poids du diluant. Une balance (12) pourvue d'une fonction TARE produit un signal de sortie du poids W d'un echantillon a l'interieur d'un recipient (20) en soustrayant le poids du recipient, Une commande (24) de facteur de dilution est prevue pour determiner le facteur de dilution f predetermine. Des blocs (218 et 220) sont prevus pour calculer et stocker la valeur TW = W/f qui est egale au poids total de l'echantillon plus le poids du diluant necessaire pour diluer l'echantillon jusqu'a concurrence du facteur de dilution f predetermine. Une pompe (42) est connectee entre un reservoir (38) de diluant et le recipient pour l'echantillon et sert a pomper dans le recipient la quantite de diluant necessaire pour diluer l'echantillon jusqu'a concurrence du facteur de dilution f en poids predetermine. La balance fournit une sortie continue du poids W de l'echantillon et du diluant a l'interieur du recipient a chaque instant. Un point de decision (256) est prevu pour determiner le moment ou TW - W = 0. Dans un mode de realisation, l'ecoulement du diluant vers le recipient est arrete par la fermeture d'une paire de vannes (34 et 46) situees entre la pompe et le recipient lorsque TW - W = 0.Device (10) for obtaining dilutions of a sample (11) with a diluent (36) up to a predetermined dilution factor f by weight of the diluent. A balance (12) provided with a TARE function produces an output signal of the weight W of a sample inside a container (20) by subtracting the weight of the container, A dilution factor control (24) is planned to determine the predetermined dilution factor f. Blocks (218 and 220) are provided for calculating and storing the value TW = W / f which is equal to the total weight of the sample plus the weight of the diluent necessary to dilute the sample up to the dilution factor f predetermined. A pump (42) is connected between a diluent reservoir (38) and the sample container and is used to pump into the container the amount of diluent necessary to dilute the sample up to the dilution factor f by weight predetermined. The balance provides a continuous output of the weight W of the sample and of the diluent inside the container at all times. A decision point (256) is provided to determine the moment when TW - W = 0. In one embodiment, the flow of diluent to the container is stopped by closing a pair of valves (34 and 46) located between the pump and the container when TW - W = 0.

Description

GRAVIMETRIC DILUTER Background of the Invention

The invention relates to apparatus for making dilutions of samples of any weight with a diluent to a predetermined weight percentage of diluent.

Description of the Prior Art

In the fields of microbiology, biochemistry and chemistry it is often necessary to dilute liquid or solid samples with a diluent to a predetermined concentration by weight. In the case of solid samples, the liquid diluent may be used to make a slurry of the solid in the liquid. Bacterial density in solid food or fruit juices is determined by analysis of dilutions of these samples. In certain areas such as clinical laboratories or quality control laboratories it is necessary to make dilutions of large numbers of samples. While it is possible to manually dilute samples with diluents to a predetermined percentage by weight or volume, the amount of time required can be great where high accuracy or large numbers of dilutions are required.

Summary of the Invention

The invention is an apparatus for diluting liquid or solid samples to a predetermined concentration by weight of a diluent. The invention has means for measuring the weight of the container; means for specifying a predetermined dilution factor f by weight of a diluent in a sample; means for calculating TW - W, fluid conducting means disposed between a reservoir of diluent and the container for permitting the diluent to flow from the reservoir to the container for the purpose of diluting a sample within the container to the predetermined concentration by weight of diluent f; and selectively closeable valve means in fluid communication with the fluid conducting means which is disposed between the reservoir and the container for interrupting the flow of diluent between the reservoir and the container, said valve means. being coupled to the means for calculating TW - W and being closed when TW - W = 0 and open when TW>W. The valve means is pulsed on and off when TW - W<1 to prevent overshoot in the amount of diluent added to the sample for any value of f. The invention also includes means for specifying a maximum weight limit UL of the combined weight of sample and diluent which is acceptable for a given dilution factor f and means for specifying a minimum weight limit LL of the combined weight of sample and diluent which is acceptable for a given dilution factor f. Brief Description of the Drawings

Figure 1 is a system schematic of one embodiment of the present invention.

Figure 2 is a flow chart of the preferred form of a microprocessor control for the embodiment of Figure 1.

Figure 3 is a system schematic of another embodiment of the presentinvention.

Description of the Embodiments

Figure 1 is a general system schematic of the present invention 10 which functions to automatically dilute a sample 11 contained within a container 20 to a predetermined weight dilution factor f of a diluent 36. In accordance with the invention, dilutions of samples 11 are made without requiring measurement of the sample weight prior to placement in the container 20. The dilutions made by the present invention are by weight percentage of the diluent in the sample 11. The dilution factor f of the present invention is defined by the equation: For example, a 100 gram solution of ethanol which has been diluted with 100 grams of water is diluted to a weight dilution factor f = 0.5 which equals a 50% dilution by weight of diluent. In accordance with the invention, a scale 12 with a TARE control lh is provided which has an output line 16 on which is continually produced a signal of the weight placed on the pan 18 in binary coded decimal (BCD) format. In accordance with the invention, the TARE control 14 is activated is activated to produce a zero weight BCD output signal on line 16 when the pan 18 has a container 20 resting on it within which a sample 11 will be placed which is to be diluted by diluent 36. Scales are commercially available having TARE capability and a BCD output which may be used with the present invention is a model PS15 which is manufactured by the Mettler Instrument Corporation of Hightstown, New Jersey.

The controller 22 of the present invention includes a plurality of controls which include a dilution factor selector control 24, an automatic dispenser switch 26, a rapid manual dispenser switch 32 which is used to manually open a first rapid dispense valve 34 to the flow of diluent 36 from reservoir 38 through conduit 40, under the power of pump 42, a slow dispense switch 44 which is used to manually open a second valve 46 to the flow of diluent 36 from a reservoir 38 through conduit 40 under the power of pump 42, a ready light 46A, an expensive sample indicator light 48, an insufficient sample indicator light 50, a power on indicator light 52, maximum weight control 53 and minimum weight control 55. The maximum weight control 53 specifies the maximum weight of sample plus diluent which is permissible for the dilution of a sample to a specified dilution factor f. The minimum weight control 55 specifies the minimum weight of sample plus diluent which is permissible for the dilution of a sample to a specified dilution factor f . The rapid manual dispense switch 32 and the slow manual dispense switch 44 may be used to manually override the automatic control of valves 34 and 46 by the controller 22 to permit selective flow control of diluent into container 20. The first valve 34 has a rated flow rate for a given pressure which is 10 times greater than the flow rate of the second valve 46. The controller 22 has an interlock line 54 which is coupled to a switch 54A and attached to the chassis of the scale 12 which allows valves 34 and 46 attached to the horizontal member 76 to operate when the stanchion 74 is rotated so that switch 54A is closed and valve 34 and valve 46 are over the container 20, a power line 56 which provides suitable electrical power for the scale 12 and a pump activation line 58 which controls the activation of pump 42 for pumping diluent 36 from reservoir 38 through conduit 40, through either the first valve 34 or the second valve 46 into container 20 in a manner to be hereinafter described. The power line for the controller 22 has been omitted. The conduit 40 contains a T section having an input which is coupled to the pump 42 and first and second valves 34 and 36. Valve control line 64 is connected between the controller 22 and the first valve 34 for selectively controlling the flow of diluent 36 from the pump 42 through the first valve in a manner to be hereinafter explained in conjunction with Figure 2. Valve control line 66 is connected between the controller 22 and the second valve 46 for selectively controlling the flow of diluent 36 from the pump 42 through the second valve 46 in a manner to be hereinafter explained in conjunction with Figure 2. The vavles 34 and 46 may have solenoids which are activated under the control of activation signals from the controller 22 over control lines 64 and 66. Valves 34 and 46 may be model V5 valves sold by Skinner Precision Industries, Inc. of New Britain, Connecticut. Bacterial filters 68 may be coupled between the outputs 70 and 72 of the first and second valves 34 and 46 to filter the diluent 36 prior to discharge into container 20. The valves 34 and 46 are supported above container 20 by a metallic stanchion 74 and a horizontal member 76. Figure 2 illustrates a flow chart of the preferred form of implementation of the controller 22 for the invention which utilizes a microprocessor to control the system operation. A the starting point 200 of the microprocessor control program, it is assumed the following sequence of events has occured: maximum and minimum weight UL and LL of samples and diluent have been entered; the dilution factor f has been set; the power has been turned on; a sample container 20 has been placed on the pan 18; the TARE control 14 has been depressed, a sample 11 has been placed in the container 20; and the automatic dispense switch 26 has been depressed. The program proceeds to block 202 where the ready light on the controller is turned off to signify entry into a dilution of a sample. The program proceeds to block 204 where the weight W of the sample to 0.1g in BCD format is read from the scale 12. The program proceeds to block 206 where the weight W is stored in memory. The program then proceeds to block 208 where the dilution factor f is read from the dilution input factor control 24 within the controller 22. The program then proceeds to block 210 where the dilution factor f is stored in memory. The program then proceeds to block 212 where the maximum weight limit UL of the sample and diluent is read from the maximum weight control 53 in the controller 22. The range of the maximum weight linit is 0<.UL-49999 grams. The program then proceeds to block 214 where the maximum weight UL is stored in memory. The program then proceeds to block 216 where the minimum weight limit LL of sample and diluent is read from the minimum weight control 55 in the controller 22. The range of the minimum weight limit is 0 < LL < 9999 grams. The program proceeds to block 218 where the minimum weight LL is stored in memory. The program then proceeds to block 220 where the calculated weight TW = W/f is calculated and rounded to the nearest 0.1g. The program then proceeds to block 222 where TW> is stored in memory. The program then proceeds to the decision point 224 where a determination is made if TW> UL. If the answer is "yes" the program branches to block 226 where an overweight light 48 in the controller 22 is turned on to indicate that the weight of the sample plus the diluent for achieving the previously set dilution factor f is greater than the. specified maximum weight which has been set with the maximum weight control 53. The program then proceeds to block 228 where the memory elements are reset with switch 38 in the controller 22 to prepare the system for another dilution. The program then proceeds to stopping point 230 which terminates all activity in the program. If the answer is "no" at decision point 224, the program branches to block 234 where the insufficient indicator light 50 in the controller 22 is turned on to indicate that the weight of the sample plus the diluent for achieving the previously set dilution factor f is less than the specified minimum weight which has been set with the minimum weight control 55. The program then proceeds to block 236 where the memory elements in the controller 22 are reset with switch 28 to prepare the system for another dilution. The program then proceeds to stopping point 238 which terminates all activity in the program. If the answer is "no" at decision point 232 the program proceeds to block 240 where the pump 42 is turned on and the valve 34 opened. At this point, the pump is pumping diluent 36 into the container at the higher rate of flow permitted by valve 34 than is possible with valve 46. The program then proceeds to block 242 where the BCD output from scale 12 of the combined weight of diluent and sample is read. The program then proceeds to decision point 244 where a determination is made if TW - W >10. If the answer is "no" the program loops back to block 242 and to decision point 244 where the calculation TW - W≥10 is made. As long as TW - W>10, valve number 34 is open and the highest flow rate of diluent into the container takes place. The program continues to loop until TW - W = 10 at which point the program branches to block 246 where valve 34 is closed and valve 46 is opened. At this point the flow rate into the container 20 has been reduced by a factor of 10 as a consequence of the lower rated flow capacity of valve 46 in comparison with valve 34. The program then proceeds to block 248 where the weight W of sample plus diluent is read from the scale 12. The program then proceeds to decision point 250 where a determination is made if TW - W≤1. If the answer is "no", the program loops back to block 248. If the answer is "yes", the program proceeds to block 252 where the valve is pulsed to be on for 0.2 seconds and pulsed off for 1.8 seconds. The program proceeds to block 254 where the weight of the sample plus diluent is read from scale 12. The program then proceeds to decision point 256 where a determination is made if TW = W. If the answer is "no", the program loops back to block 252 where the valve 46 is again pulsed. The program continues to loop until TW = W at which time the program proceeds to block 258 where valve 46 is closed and valve 34 is maintained in its previously closed state. At this point in time, the predetermined weight dilution factor f of diluent has been achieved and the combined weight of sample plus diluent equals TW. The program then proceeds to block 260 where the pump 42 is turned off, the ready light in the controller 22 is lit and the memory elements of the controller are reset. The program then proceeds to stopping point 262 where no further program action occurs. Figure 3 is a general system schematic of the second embodiment 300 of the present invention. The second embodiment is identical to the first embodiment of the present invention which is illustrated in Figure 1 with the exception that the apparatus for controlling the flow of diluent is different. Identical parts in Figures 1 and 4 are identified by identical reference numerals. In the second embodiment of the invention, the flow of diluent between the reservoir and the container is controlled by the starting and stopping of a pump 302 without the first and second valves 34 and 46 of Figure 1. The pump may be any type of pump which stops the pumping of fluid immediately when a stop command is applied thereto on lines 304 and/or 306 from controller 22. There are many types of pumps which have this capability. The preferred type of pump is a peristaltic pump which may be a model Master Flex Pump C-7500-00 manufactured by the Cole-Parmer Corporation of Chicago, Illinois. The peristaltic pump is preferred because it may be controlled to immediately cease the pumping of fluid. The present invention requires the immediate ceasing of fluid flow into container 20 when TW - W = 0 in order to achieve accurate dilutions which are very close to the predetermined dilution factor f. In this embodiment, reciprocating pumps, centrifugal pumps, rotary pumps, or other types of pumps which have a relatively high inertia during pumping would not be useful unless they contained valving which permitted the immediate stopping of the flow of liquid upon the application of the stop command from the controller 22. Without valving to immediately stop the flow of diluent, the inertia of the operating pump would result in the continued pumping of diluent after the application of the stop command which would result in a dilution to a greater dilution factor than the factor f.

The second embodiment may include a pump 302 which may be controlled to pump at two different flow rates which are used such that the higher flow rate is used when the quantity TW - W >10 and the lower flow rate is used when

0<TW - W<10 in a manner analogous to the two valve mechanisms of the first embodiment. A microprocessor flow chart like the one illustrated in Figure 2 may be used with the second embodiment. The only difference between the first embodiment and the second embodiment is that in the second embodiment the valves 34 and 36 are omitted and the signals for controlling the flow of diluent are applied directly to the pump 302.

Operation

The operation of the invention to make a dilution of a sample of ethanol with a 50% solution by weight (f =

0.5) of water is summarized as follows. The maximum and minimum weights UL and LL have been previously set by the maximum and minimum weight controls 53 and 55 of the controller 22 and are assumed to not warrant system shutdown. The dilution factor f is set at 0.5 by the dilution factor selector control 24. The TARE control

14 is activated to zero the BCD output of the scale 12 after the container 20 has been placed on the pan 18.

The sample of ethanol is then placed in the container 20 and the automatic dispenser switch 26 -is depressed. The

BCD output from the scale specifies that the sample is

100 grams. The means for calculating TW: reflects that the combined weight of ethanol and water. to achieve an 0.5 dilution factor is 200 grams. The pump 42 is immediately activated and rapid dispense valve 34 is opened. The pump then proceeds to pump water into the container 20 through valve 34 until the combined weight of the water plus ethanol reaches 190 grams at which point the program causes rapid dispense valve 34 to close and slow dispense valve 46 is opened to reduce the rate of introduction of water into the container 20. When the weight of ethanol plus water W equals 199 grams, the valve 46 is repeatedly pulsed on for 0.2 seconds and off for 1.8 seconds. The pump 42 continues to pump water into the container through the pulsating valve 46 until the weight of the water plus ethanol equals 200 grams which is equal to the previously calculated TW. The pump 42 is then shut off and valve 46 is closed to complete the dilution.

Claims

We Claim 1. An apparatus for diluting a sample within a container to a dilution factor f by weight of diluent comprising: a) means for repeatedly measuring the weight W of the sample plus any diluent within the container; b) means for choosing a dilution factor f by weight of a diluent to be used for diluting the sample; c) means for calculating TW wherein TW = W/f and W is the weight of the sample within the container prior to the addition of diluent; d) means for calculating TW-W; e) fluid conducting means disposed between a reservoir of diluent and the container for permitting the diluent to flow from the reservoir to the container for the purpose of diluting the sample within the container to the selected dilution factor f; and f) valve means in fluid communication with the fluid conducting means and coupled to the means for calculating TW-W for interrupting the flow of diluent between the reservoir and the container when TW - W = 0 and permitting diluent to flow between the reservoir and the container when TW = W.

2. An apparatus for diluting a sample within a container to a dilution factor f by weight of diluent comprising: a) means for repeatedly measuring the weight W of the sample plus any diluent within the container; b) means for choosing a dilution factor f by weight of a diluent to be used for diluting the sample; c) means for calculating TW wherein TW = W/f and W is the weight of the sample within the container prior to the addition of diluent; d) means for calculating TW-W; e) fluid conducting means disposed between a reservoir of diluent and the container for permitting the diluent to flow from the reservoir to the container for the purpose of diluting the sample within the container to the selected dilution factor f; and f) means responsive to the means for calculating

TW-W for controlling the flow of diluent between the reservoir and the container to cause diluent to flow between the container and the reservoir when TW>W and to stop the flow of diluent when TW = W.