FR2526159A1 - DEVICE FOR MEASURING ENTIRELY STATIC LEVELS - Google Patents

Abstract

FULLY STATIC LEVEL MEASURING DEVICE INCLUDING A PLURALITY OF THERMISTORS AND RESISTORS MOUNTED IN SERIES ON AN INSULATING PLATE, WHICH IS INCLUDED IN A CONTAINER COMMUNICATING WITH THE EXTERIOR THROUGH A CALIBRATED HOLE. THE VARIATION IN RESISTANCE BETWEEN THE OUTPUT CONDUCTIVE WIRE AND THE EARTH OBTAINED BY IMMERSION OR EMERSION OF THE THERMISTORS BY APPLYING TO THE PROBE TERMINALS EITHER A CONSTANT CURRENT OR A CONSTANT VOLTAGE WITH A RESISTANCE IN SERIES. THE VOLTAGE LEVELS OBTAINED AT THE TERMINALS OF THE SENSOR THUS CONSTITUTED ARE REPRESENTATIVE OF THE LEVEL OF LIQUID INSIDE THE TANK. A CHANGE IN THE VOLTAGE RESULTS IN THE INITIALIZATION OF A FUEL QUANTITY REGISTER AT THE DESIRED VALUE. A FLOWMETER ENSURES THE CONTINUITY OF THE INFORMATION BY DECOUNTING THE SAME REGISTER BETWEEN TWO PRECISE RESETS, AND A DIFFERENTIATION SYSTEM TAKES INTO ACCOUNT THE DIRECTION OF THE MOVEMENT OF THE LIQUID LEVEL, TO INDEX THE REGISTER AT THE RIGHT VALUE.

Description

1 2526159

  The invention relates to a liquid level detector in a tank, which can contain, for example, the fuel

  necessary for the operation of an engine.

  Many systems are known for measuring the level in a tank. Most use the principle of the float, which is maintained by a system of rods or slides, carries a slider which rubs on a resistive element thus modifying its shape. resistance in

function of the level.

  These devices have many drawbacks and

  usually that of having a rubbing contact and therefore subject to wear and tear The mechanics, without being very complicated, can however take the game or get stuck On the other hand, their accuracy is mostly insufficient, which is particularly troublesome especially when they are associated with on-board computers giving hourly or mileage consumption as well as

than autonomy.

  We also know more precise devices, but whose price is far above what is possible to admit, for very large series manufacturing (capacitive systems, pneumatic, etc.) There are also systems allowing to locate a point level using a non-zero temperature coefficient resistance, crossed by a current, whose resistance changes when it

  is, or not, immersed in the liquid.

  The device according to the invention is essentially static

  and has a plurality of elements providing thermal contacts

  connected in series, powered by one or more control wires.

  Each element delimits a particular level inside

  of the reservoir Between two precise levels, the measurement of the quantity of

  used is performed by a flowmeter.

  This is, in fact, essential to provide the on-board computer

  the elements needed to determine the instantaneous consumption

  born, autonomy, etc. Its use therefore brings no extra charge

cost.

  Different features and advantages of the invention

  will appear on reading the following detailed description, as well as

  in the accompanying drawings, in which: FIG. 1 represents a level measurement probe

according to the invention.

  Figure 2 gives the diagram of another probe, also

according to the invention.

2 2526159

  FIG. 3 is a sectional view of the fuel tank

  tible. Figure 4 is a graph showing, as a function of

  time, some practical cases of resetting and resetting

fuel consumed.

  Figure 5 is a system flow diagram of the system.

  FIG. 6 gives the block diagram of the electronic device

than realized.

  FIG. 7 is a flowchart describing a mode of ob-

  lottion of an alert in case of incomplete filling of the tank.

  FIG. 1 represents a level measurement probe. This comprises, by way of example, four measuring devices each consisting of a resistor

  4 and a temperature-sensitive therio resistance (PTC) with a temperature coefficient of

  Positive erasure Different embodiments are possible.

  fixed cores can be probed, or deposited in a thin layer or thick layer on a substrate 2 of insulating material (ceramic, glass, etc.) The "CTP" are soldered across the fixed resistors and all the assembly is optionally covered with a hydrocarbon resistant varnish The assemblies consisting of resistors 4 and 5 are connected in series and thus joined together by a conductor 6 which is fixed by one of its

  ends at the bottom of the tank and thus electrically connected to the ground.

  The other end comes out of the tank to be connected to a resistor

  7, which is itself connected to a positive potential V. The plate thus constituting

  is located inside a tube of any material 1,

  at its lower part a calibrated hole 3,

  nication of the inner part of the tube with the reservoir, which makes it possible, thanks to the delay effect thus produced, to obtain inside the tube a level

less disturbed than outside.

  FIG. 3 shows the implantation of such a probe in a tank 8, comprising a liquid suction outlet 12 in the path of which a flowmeter 11 is located. This tank is closed.

  by a plug 10 actuating a contact 9 whose utility will be demonstrated-

further.

  The operation of the probe shown in Figure 1 is the

following.

  When the tank is empty, the thermistors "CTP" 5 and the resistors 4, are fed via the resistor 7 The "CTP" heating up, their resistance is very large, and we have:

3 2 5 2 6 1 5 9

  E r V (R 41 + R 42 + R 43 + R 4 n) R 7 + R 41 + R 42 + R 43 + R 4 n

  if the resistors R 4 are chosen such that R 4 R 5 in the hot state.

  If this probe is supplied with constant current we have more simply: E ^, I (R 41 + R 42 + R 43 + R 4 n). When an assembly R 4 R 5 is covered by the liquid, R 5 cools and

  its value becomes very small compared to that of R 4, which decreases the

sion E.

  Examination of the latter by a simple electronic device makes it possible to

  the precise moment when the liquid covers or discovers a thermistor-

  this and therefore according to their distribution within the reservoir of determination.

  level, and as a result, the amount of liquid

of the probe.

  By way of example, FIG.

  realized tronic which comprises a microprocessor 4 which receives on the one hand pulses from a flow meter II and secondly from

  logic signals ABCD supplied by 4 voltage comparators (T 1 to 4)

  which switches when the voltage E at the terminals of the probe is greater than a reference voltage fixed by a resistance bridge which is

clean.

  It is assumed in this example, that, the tank being full, the voltage E is minimal and the liquid has reached the level 400 by covering the entire probe, the other three levels being located at 300, 200 and If the level goes down slightly, the probe SI is no longer covered by the liquid and the increasing voltage E makes the comparator T 1 switch

  which goes to "1". If the level increases slightly, this compares to

  go to "o", the level remaining the mnme at Sprès Thus, for the same

  indication, the comparator under consideration (here T 1) may be at "1" or "O"

  the direction of moving the level The table below shows the

  3 Of the different comparators at different levels, the arrows

the meaning of variation.

A B C D H F A B C D I H F

  400% OOO OO or 1 OOOIO 300 OOOO 1 or 1 10 O 1 O 200 1 1 OOO l or 1 O o 20110 001 o ilioi Q 11 O 1 or 1 1 1 1 1 O It is thus seen that same combination exists to indicate

  2 different levels For example: "1000" appears twice in the table.

  for 300 and 400 depending on the direction of liquid level displacement.

  To distinguish them, we use 4 differentiators DI to D 4 associated with 4 inverters I 1 to I 4 to obtain at the output H or F of one of the 2 doors '1 01' 1 and 2, a positive "puls" , depending on the signal at the output

  a comparator T changes from "O" to "1" or "1" to "0".

  This "then" applied to a microprocessor input will trigger a request to interrupt the current program. In the table above, the state of the two outputs E and F, according to the direction of movement of the level, has been indicated. Each transient signal "1" determines the progress of a particular program, once the request has been made.

  interrupted by the microprocessor The two organizations

  Corresponding Iograms are shown in Figures 5-1 and 5-2.

  The states 100 and 200 respectively characterize the start of interrupt programs 1 and 2. Steps 101, 102, 104, 106, 108 and 201, 202, 204, 206, 208 correspond to the test of inputs A, B, C and D. and determine according to the answer either the passage to the next test or

  151 'indexation of the fuel quantity register to the desired number.

  (This register, R fig 6, can possibly be outside P, but

  in any case its content is non-volatile).

  If the result of the test is always negative, it means that the correct combination has not been found and that one of the comparators

does not work anymore.

  In this case, an alarm is triggered (states 110 and 210) and the interrupt return made (111 and 211). A third flowchart is shown in FIG. 5-3. The state 300 corresponds to the start of an interrupt triggered by a impulse flowmeter, which leads, in step 301, to the countdown of a

  unit in the quantity register, then the interrupt return to 302.

  It can thus be seen that outside the periods when a number of

  the register of quantity is regularly counted by the 3 O pulses coming from the flowmeter. This implies that at any moment, the number in the register is the exact representation of the quantity of

liquid included in the tank.

  This is true even when the engine stops because the contents of the register are then transferred to permanent memory (either an EEPROM or

  a RAM with autonomous power supply).

  Difficulties may arise during the filling of the tank, since it is generally carried out at engine stop and therefore without

  power supply on the microprocessor.

  Solutions according to the invention are given in cases 4 opreci (presented in FIG. 4) that may arise during the use of the vehicle Q 1, Q 2, Q 3 and Q 4 represent the 4 levels.

  the register is systematically recalibrated. These are material-

  on the graph with circled dots The crosses indicate

  stances and departures with filling or not.

  At time to, the register memerizes an amount Q 34, then, the fuel decreasing, the register is reset to the level Q 3 Then stop Then start with a quantity Q 23, resetting to Q 2, finally stop with

  a quantity Q 12 and then filling at time tl.

  Referring to Figure 3, and Figure 6, we see

  that there is a normally open contact 9 which closes when the

  This is to supply the micropro-

  to give him a signal indicating that the fuel cap

see was removed.

  This logical level "o" is also applied by the

  a relay L whose other end is connected to the + battery This relay then glues and self-energizes on the contact C 2 and the resistor R1 The contact C1 then supplies the power supply.

  the microprocessor The contact C 3 represents the ignition key

  R1 and R2 are of the same order of magnitude as the relay resistance,

  this sticky for a voltage of 6 'The resistance R 2 is intended to e-

  avoid a short circuit if, by chance, the tank cap is removed and the ignition key in the closed position The filling is done, at time tl, until full The quantity register then contains the

  quantity Q 4, after two successive readjustments to Q 2 and Q 3.

  At time t 2, after resetting to 100, the full is not done completely and the last indexation takes place at Q 3 Referring to the

  FIG. 7 shows the utility of the signal Y in the represented flowchart.

  This subroutine is located in one of the main loops of the micro-

  processor and comprises a start step 400, then a test of the signal Y in

  30401 If not present, return to the main program.

  If the tank is open, the signal Y exists and the following test at 402, relates to the state of the comparators. If the tank is not full, ABCD # 0000, a flashing alert or a buzzer (AI fig 6)

  is triggered in step 404 then return of subroutine If, by

  the tank is full ABCD = 0000, the alert is stopped in step 403.

  This is to warn the driver that if the fuel is not

  killed, he must himself intervene on the calculator to enter manual-

  the quantity indicated at the pump, which will come in addition

  the quantity previously included in the quantity register.

6 2526159

  It will be noted in this flowchart, that the alarm once engaged will not be stopped when the tank cap is delivered

  in place, which forces the driver to intervene.

  Indeed, as seen in Figure 6, the contact 9 is open (tank cap in place) the signal goes back to "1"

  via the resistor R 2, the relay L and the microprocessor

  remaining powered, one by his self-maintenance contact C 2 and the other

by the contact C 1.

  When the ignition switch C 3 closes; the relay L

  falls back, -because it is no longer powered C 1 and C 2 open, the microproces-

  It is powered by C 3 which keeps the alarm system under control.

  until the user enters the quantity

displayed at the pump.

  Another solution, also in the context of the invention,

  In the case of partial filling, do not warn the user that

  to manually enter the quantity displayed at the pump, but to temporarily suspend the calculations involving the quantity

  until an automatic resetting occurs.

  This has the advantage of simplicity since no

  User intervention is necessary.

  This is achieved simply by removing the devices

  alarm AI of Figure 6 and using the control signal for in-

hiber the stones.

  Step 404 of Figure 7 becomes: "Inhibition calculations"

  and step 403: 'narret inhibition'.

  Step 111 of Figure S1 changes to: "stop

  inhibition ", the" interrupt return "being carried forward to the next step.

  Finally, FIG. 2 shows the diagram of another probe also according to the invention, comprising several thermistors

  One of their ends is connected to the earth and the other is connected

  resistors 71, 72, 73, 7 n, themselves connected to the + bat-

  crocheted. The voltage existing between the point of junction CTP, resistance and the mass

  is noted El, E 2, E 3, In this one is weak when the thermistor-

  it is cooled inside the liquid and raised when it is at the

TER AL.

  The operating diagram is the same as that of the figure

  re 6 The voltages El, E 2, E 3, En are applied to the inputs of the com-

  parators T 1, T 2, T 3, Tn the reference voltage between Emin and

Emax is the same for everyone.

7 2526159

Claims (7)

R E V E N D I C A T IO N S   1 static level measuring device comprising resistors with a non-zero temperature coefficient,   Characterized by the presence on an insulating plate   vertically from a plurality of them at pre-existing heights   said plate being fixed inside a shaped container   any communication with the outside through an ori-   calibrated fielder located at the bottom, the assembly thus realized being placed in the of a tank.   2 Device according to claim 1,   Characterized by the fact that each thermistor is   in parallel with a fixed resistance and that each assembly thus con-   titué is placed in series in such a way that only one   The probe can be powered at constant voltage with a resistance   "ad hoc" or constant current series.   3 Device according to claim 1,   Characterized by the fact that each thermistor is self-   and that there are as many output leads as levels   Each can be powered at constant voltage with a resistance   suitable series or constant current series.   4 Device according to claim 2 or 3, characterized by the presence of a flow meter that associated   point measurements can be used to count down a quantity register.   which is ystematically recalibrated when moving to a specific level.   Device according to claim 4,   Characterized by the presence of differentiator for detecting   ter the direction of variation of the level, thus making it possible to overcome the errors that can appear when the liquid covers and discovers one of the   detector assemblies without the level having varied significantly.   6 Device according to claim 5, characterized by the addition of a device ensuring a   change of state, activated by the absence of the tank cap, allows   so much to obtain, if the full is not done, a particular signal forcing the user to manually enter the device the number of liters indicated at the pump.   7 Device according to claim 5, characterized in that the opening of the reservoir cap determines an inhibition of calculations, the latter being lifted only 8 2526159   by filling the tank completely or by automatic resetting of the quantity register when the liquid level drops inside. of the tank.