GB2105476A - Electrical measurement of the level of liquid in a container - Google Patents
Electrical measurement of the level of liquid in a container Download PDFInfo
- Publication number
- GB2105476A GB2105476A GB08224812A GB8224812A GB2105476A GB 2105476 A GB2105476 A GB 2105476A GB 08224812 A GB08224812 A GB 08224812A GB 8224812 A GB8224812 A GB 8224812A GB 2105476 A GB2105476 A GB 2105476A
- Authority
- GB
- United Kingdom
- Prior art keywords
- liquid
- level
- resistor
- compensation
- container
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
- G01F23/24—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid
- G01F23/246—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid thermal devices
- G01F23/247—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid thermal devices for discrete levels
Landscapes
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
Abstract
An arrangement for continuous measurement of the level of liquid in a container or tank, e.g. a fuel tank, uses the series-connection of a heatable measuring resistor RM which is generally partially immersed in the liquid, and a compensation resistor RK which is immersed in the liquid even at the minimum level thereof, and an evaluating circuit V1 which processes the incoming measurement signal and the compensation signal to form a differential signal. A constant current supply STK for the measuring resistor RM and the compensation resistor RK is controlled to a limited value via a feedback circuit, d. <IMAGE>
Description
SPECIFICATION
A circuit arrangement for the continuous measurement of the level of liquid in a tank or container at least partially filled therewith
This invention relates to a circuit arrangement for the continuous measurement of the level of liquid in a tank or a container at least partially filled therewith, having the features of the preamble to claim 1.
In addition to indication of the level of fuel in the fuel tank, motor vehicles are increasingly required to have an analog display of the levels of cooling water and oil. In comparison with transmitters which operate by switching, e.g. to indicate when the level falls below a minimum value, analog displays give the opportunity of faults being found and refilling carried out much earlier.
Analog level measuring systems which utilize the change in the resistance of a heated resistance sensor having a high temperature coefficient and disposed between the minimum and maximum levels, are generally known.
German Offenlegungsschrift 1473 132, 2455198,27 18295 and German
Auslegeschrift 21 40 963 and 28 41 889 disclose systems consisting of two resistors, only one of which at any time is heated, depending upon the level, to a temperature above that of the surrounding medium, while the second resistor is used to detect the liquid temperature and provide compensation of the liquid level signal. If the level of liquid is to be detected at varying temperatures, such compensation is absolutely essential, since the temperature of the measuring resistor is the resultant of the liquid temperature and the excess temperature. For example, a single-resistor system without a compensation resistor may have the same resultant resistance at both low liquid temperature and low level and high temperature and high level.To obviate this ambiguity, a sensor with a compensation resistor is absolutely essential.
German Offenlegungsschrift 24 55 198, 14 73 132 and German Auslegeschrift 21 40 963,28 41 889 describe circuit arrangements for forming a level signal with maximum compensation, suitable amplified signal voltages being related to, or subtracted from, one another. With these known evaluating methods, however, there is still a considerable temperature dependence particularly in respect of the level signal at low level, i.e. when the measuring sensor is exposed. The reason for this is that it is not just the measuring and compensation parts of the sensor that have a temperature-dependent resistance; the thermal resistance of the exposed measuring part of the sensor is also temperaturedependent.
German Auslegeschrift 28 41 889 describes a variation in the heating/measuring currents in opposition to the temperature above the liquid, for a sensor comprising resistors disposed in parallel. The control circuit provided controls the current of the power supply to the sensor in dependence on the temperature above the level of liquid. The control of the current as described is exactly the opposite to an oil/water sensor, in which, for example, an 0.1 mm diameter nickel iron wire is brought to an approx. I 000C excess temperature for reasons of accuracy and in order to obtain a high efficiency.
For reasons of costs it is also desirable not to have to use an extra control circuit.
The object of the invention is to improve the circuit arrangement according to German
Auslegeschrift 28 41 889 so that it can be of simpler and hence cheaperconstruction and yet operate more accurately.
The invention solves this problem with the characterising features of the invention disclosed in claim 1.
The invention advantageously makes use of the divided sensor operated with a constant current and using subtraction evaluation. A sensor arrangement of this kind results in a temperature-dependent residual error sllch that the level signal for a low level of liquid (with the measuring resistor partially or fully exposed) decreases with increasing temperature. The reason for this is that the thermal resistance of the exposed part of the measuring resistor influenced by the surrounding air (gaseous medium) falls with increasing temperature. Thus at high ambient temperature a higher heating current has to be used than at a lower ambient temperature in order to obtain an excess temperature which provides the same AU8 effect at a given level.This can be embodied cheaply and accurately by means of an adjustable feedback of the UK signal to the (originally constant) heating current for the sensor such that a UK signal of correspondingly higher temperature results in an adjusted increase in the heating current so that constant Ua=UsVKUK are obtained throughout the temperature range for identical liquid levels.
The invention will be explained in detail hereinafter with reference to one exemplified embodiment illustrated in the drawing wherein:
Fig. 1 is a block schematic of the measuring system and
Fig. 2 is a circuit diagram.
The system for continuously measuring the level of liquid in a tank or container comprises a sensor S disposed in the tank and formed by two series-connected resistors RM and RK. The measuring resistor RM is immersed in the liquid. In these conditions the level may vary between "max" and "min". At "max" level the resistor RM is fully immersed. At the level "min" the resistor is exposed, i.e., no longer surrounded by liquid.
The series-connected compensating resistor RK is fuily immersed in the liquid.
One sensor S in a practical embodiment consists of 0.1-0.2 mm diameter nickel or nickel iron resistance wire. Depending upon the required impedance and level characteristic, the sensor element may be in the form of a rod or arranged as a coil around a former.
The sensor S is fed by a constant power supply
STK. This supply delivers a current I at a constant value as.long as the temperature of the liquid in the tank is at a constant value. The value of the current i is independent of the level of liquid in the tank.
The current i has a value such that the resistors R M and R -which both have a relatively high temperature coefficient-are heated. In a practical embodiment of an oil/water sensor heating was to a temperature of about 1000C above the temperature of the gaseous medium present in the tank when the level of liquid had fallen.
A measurement signal Us, which is fed to the positive input of a differential amplifier V1 via a lead a, is obtained at the sensor S having the resistance R5=R K+RM.
The compensation signal U K is obtained across the compensating resistor RK and is fed to the input of an amplifier V2 via a lead b. The output of this amplifier V2 is connected to the negative input of the differential amplifier V, via a lead c.
The output of the differential amplifier V, delivers the display signal U 8=U sVKXUK, where R5 RM+RK
VK= = RK RK In order to compensate for any variations in the temperature of the liquid, the output of the amplifier V2 is connected to the constant power supply STK via a lead d. The constant power supply STK is so controlled via this feedback, which is preferably a positive feedback, that a UK signal corresponding to higher liquid temperature results in an adjusted increase in the heating current Iso that constant values Ua=USVKXUK are obtained throughout the temperature range for identical liquid levels.
The adjustable feedback compensates for the temperature relationship between the thermal resistance of the RM resistor no longer immersed in the liquid, and the gaseous medium (air) situated above the liquid.
The gaseous medium is saturated with vaporized liquid to a greater or lesser degree. This in turn makes the thermal resistance dependent upon the liquid. Consequently, the sensor output signals are different, for example, in the case of water and oil. Thus different degrees of feedback are required and are adjustable for inexpensive and accurate level measurement.
There may additionally be a temperature display, for which purpose the lead b at which the compensation signal UK occurs is connected via a lead e to an amplifier, V3, whose output delivers a temperature display signal UTfor a display (not shown).
The practical embodiment of a circuit shown in
Fig. 2 consists of publicly known and readily constructed stages such as a voltage stabilizer, power supply, amplifiers, and does not therefore require too detailed a description. The constant power supply STK of Fig. 1 comprises a transistor
T, and an operational amplifier B,. An accurate controlled power supply is obtained with its peripheral components. The operational amplifier
B, provides a controlled accurate feed voltage at
R1. An accurate current iwhich flows to the sensor S is thus obtained across an accurate
resistor R1.
The reference voltage produced by the cascaded resistors R4, R5 and Zener diodes D, and
D2 gives a reference value which is stable across wide battery voltage and temperature ranges. The base bias for the transistor T, is produced across the voltage divider resistors R2, R 3. The positive input of the operational amplifier B, is obtained at the voltage divider formed by the resistors R,, Re, this divider being at the reference voltage. The negative input of the operational amplifier B, is fed via resistor R5 by the feed voltage across the resistor R1. The peripheral circuit also contains the resistor R,2.
The output of the operational amplifier B, is connected via resistor R9 to the base of the transistor T,.
Feedback of the temperature-dependent compensation signal UK is via the resistors R10 and R".
Together with its peripheral components, the operational amplifier B2 forms an amplifier for the
UK signal. It operates with the required amplification: R +R
M K VK= .
RK
The UK signal is fed to the positive input via the resistor R2, and the resistor R22. The negative input is connected to the resistors R23 and R24. Its output is connected to the base of the transistor
T2, the emitter of which is connected to the resistor R25. The collector feeds the amplified UK signal to the resistors R10, R . This circuit gives a relatively non-reactive coupling of other stages and feedback of the VKXUK signal to the power supply against the positive lead.
The differential amplifier is formed by the operational amplifier B3 with its peripheral components. It is used to obtain the required operation US VKXUK It amplifies the differential signal in accordance with R29/R27=R28/R26 so that the resulting level signal Uh utilizes a great part of the battery voltage range.
The sensor signal Us is fed to the positive input of the operational amplifier B3 via the resistor R28 while its negative input is connected to the emitter of the transistor R2 via the resistor R27.
Resistor R29 is connected from the negative input to the output.
Together with its peripheral components the operational amplifier B4 forms an amplifier which allows temperature display of a specific part of the compensating signal UK in expanded form. To this end, the positive input is connected to the transistorT2 via the resistor R30. The resistor R3, is connected to the negative battery fed voltage line.
R33 and R34 are connected to the negative input of the operational amplifier. The voltage UT for the temperature display can be taken off at the output.
The transistors T3 and T4 together with their peripheral components, resistors R13, R14, R,5, R18,
R,7, R8, R19 and R20, and diode D4, form a voltage regulator which produces accurate reference voltages required for adjustment of the amplifier operating point.
The capacitor C, and the diode D3 as peripheral components with the resistor R,2 form an overvoltage protection for the supply voltage for the operational amplifier B1B4.
Parts list
TK=1 00 ppm
TK=temp. coefficient
R1 10
R2 1,6 KQ+5% R3 1,3 KQ+5% R4 270 #5% R5 620 #5% R6 1,8 K#5% R7 ca. 3,2 K#5% R8 10 K#5% R9 6,8 KQ+5% R10 ca. 20 KQ+5% R11 ca. 700 #5% R,2 15 #5% 1 watt wire R,3 300 #5% Ra4 1 KQ+5% R,5 Balancing about 0.1 K# Rie 4,3 kS?t1% R17 5,6 K#1% RIB 6,2 K#1% R19 2,4 K#1% R20 1,5
R2, 20
R22 100 K#1% R23 20 K#1% R24 100 K#1% R25 1 KQ+1% R28 10 K#1% R27 10 KQ+ 1% R28 62 R29 62 K#1% R30 10 K#1% R31 51 KQ~1% R33 51 KQ+1% R34 10 KQ+1% C, 100,uF D1 ZPD 8,2
D2 ZPD 5,1
D3 ZY20
D4 ZPD 5,1
T, BD 876
T2 BC 237
T3 BC 635
T4 BC 237
B, 1 LM 2902
B2 1 LM 2902
B3 1 LM 2902
B4 1 LM 2902
Claims (6)
1. A circuit arrangement for the continuous measurement of the level of liquid in a tank or container at least partially filled with said liquid, comprising a measuring resistor connected to and adapted to be heated by a constant power supply, said measuring resistor having a relatively high temperature coefficient and being disposed so as to be immersed in the liquid, a compensation resistor which is also connected to a constant power supply and which has a relatively high temperature coefficient and which is also immersed in the liquid, an evaluating circuit which processes the incoming measurement signal and the compensation signal to form a differential signal and produces a display corresponding to the level of liquid at any time, the current through the measuring resistor being controlled in dependence on the temperature above the level of liquid, characterised in that the compensation resistor (RK) is arranged to be immersed in the liquid even at minimum liquid level, the compensation resistor and the measuring resistor (RM) are connected in series and to a common constant power supply (STK) and an adjustable feedback circuit is provided between the constant power supply and the input of the evaluating circuit (V,) for the compensation signal (UK).
2. A system according to claim 1, wherein the compensation resistor (RK) is additionally connected to a temperature display (UT).
3. A circuit arrangement according to claim 1 or claim 2 wherein the tank is a fuel tank.
4. A circuit arrangement according to claim 1 or claim 2 wherein the container is an oil container.
5. A circuit arrangement according to any preceding claim wherein the tank or container is contained in a motor vehicle.
6. A circuit arrangement for the continuous measurement of the level of liquid in a tank or container substantially as described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19813134912 DE3134912C2 (en) | 1981-09-03 | 1981-09-03 | Circuit arrangement for continuous measurement of the fill level in a container at least partially filled with liquid |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2105476A true GB2105476A (en) | 1983-03-23 |
| GB2105476B GB2105476B (en) | 1985-07-17 |
Family
ID=6140791
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08224812A Expired GB2105476B (en) | 1981-09-03 | 1982-08-31 | Electrical measurement of the level of liquid in a container |
Country Status (3)
| Country | Link |
|---|---|
| DE (1) | DE3134912C2 (en) |
| FR (1) | FR2512201B1 (en) |
| GB (1) | GB2105476B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2128340A (en) * | 1982-10-06 | 1984-04-26 | Kliklok Corp | Hot liquid level control |
| GB2235538A (en) * | 1989-09-01 | 1991-03-06 | Yazaki Corp | Temperature compensated liquid level detecting apparatus. |
| GB2263551A (en) * | 1992-01-23 | 1993-07-28 | Imi Air Conditioning Ltd | Level control of fluid condensate in air conditioner |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3337779A1 (en) * | 1983-10-18 | 1985-04-25 | Vdo Adolf Schindling Ag, 6000 Frankfurt | CIRCUIT ARRANGEMENT FOR ELECTROTHERMIC LEVEL MEASUREMENT |
| FR2562244B1 (en) * | 1984-04-03 | 1988-10-07 | Renault | METHOD AND DEVICE FOR CONTROLLING THE LIQUID LEVEL IN A TANK |
| DE3421803A1 (en) * | 1984-06-12 | 1985-12-12 | Messer Griesheim Gmbh, 6000 Frankfurt | DEVICE FOR DETERMINING THE LEVEL IN CRYE CONTAINERS |
| DE3520126A1 (en) * | 1985-06-05 | 1986-12-11 | Vdo Adolf Schindling Ag, 6000 Frankfurt | DEVICE FOR ELECTRIC OIL LEVEL MONITORING, IN PARTICULAR IN MOTOR VEHICLE COMBUSTION ENGINES |
| DE3742783C2 (en) * | 1987-12-17 | 1994-07-21 | Hella Kg Hueck & Co | Device for measuring the liquid level in containers, in particular the oil level in internal combustion engines of motor vehicles |
| DE10357771B4 (en) * | 2003-12-10 | 2012-08-30 | Continental Automotive Gmbh | Control unit and control device with the control unit |
| DE10357772A1 (en) * | 2003-12-10 | 2005-07-14 | Siemens Ag | Control unit as for an oil level sensor in a motor vehicle comprises current mirror whose output current governs the voltage drop over a sensor resistance |
| DE102004026396B4 (en) * | 2004-05-29 | 2007-10-31 | Itw Automotive Products Gmbh & Co. Kg | Device for measuring the level height and / or the temperature in a container |
| DE102013105172A1 (en) | 2013-05-21 | 2014-11-27 | Khs Gmbh | Level sensor on a glue container and labeling unit |
| DE102013218065A1 (en) * | 2013-09-10 | 2015-03-12 | Robert Bosch Gmbh | Novel sensor arrangement for level measurement |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1349325A (en) * | 1962-12-03 | 1964-01-17 | Level measurement method by dissipation | |
| US3283576A (en) * | 1963-10-07 | 1966-11-08 | United Control Corp | Means for detecting change of heat transfer rate |
| US3302458A (en) * | 1963-10-09 | 1967-02-07 | American Radiator & Standard | Liquid level sensing device |
| DE2140963B2 (en) * | 1971-08-16 | 1977-12-29 | Robert Bosch Gmbh, 7000 Stuttgart | DEVICE FOR CHECKING THE LEVEL OF LIQUIDS |
| DE2455198A1 (en) * | 1974-11-21 | 1976-05-26 | Bernd Dipl Phys Volle | Liquid level measuring and displaying device - is esp. an oil level indicator for motor vehicles |
| DE2645743C2 (en) * | 1976-10-09 | 1985-11-07 | Vdo Adolf Schindling Ag, 6000 Frankfurt | Liquid level measuring device |
| DE2718295B2 (en) * | 1977-04-25 | 1981-07-09 | Hauser Verwaltungs-Gesellschaft Mbh, 6370 Oberursel | Device for measuring the oil level in the crankcase of internal combustion engines |
| DE2841889B2 (en) * | 1978-09-26 | 1980-09-25 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Device for continuous measurement of the filling level in a container at least partially filled with liquid |
| US4251809A (en) * | 1979-02-16 | 1981-02-17 | Alco Standard Corporation | Method and apparatus for detecting the presence of water in oil |
| DE2946585A1 (en) * | 1979-11-19 | 1981-05-27 | Vdo Adolf Schindling Ag, 6000 Frankfurt | DEVICE FOR ELECTRICALLY MONITORING THE LEVEL OF A LIQUID CONTAINED IN A CONTAINER |
-
1981
- 1981-09-03 DE DE19813134912 patent/DE3134912C2/en not_active Expired
-
1982
- 1982-08-31 GB GB08224812A patent/GB2105476B/en not_active Expired
- 1982-09-03 FR FR8215066A patent/FR2512201B1/en not_active Expired
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2128340A (en) * | 1982-10-06 | 1984-04-26 | Kliklok Corp | Hot liquid level control |
| GB2235538A (en) * | 1989-09-01 | 1991-03-06 | Yazaki Corp | Temperature compensated liquid level detecting apparatus. |
| GB2235538B (en) * | 1989-09-01 | 1994-06-01 | Yazaki Corp | Liquid level detecting apparatus |
| GB2263551A (en) * | 1992-01-23 | 1993-07-28 | Imi Air Conditioning Ltd | Level control of fluid condensate in air conditioner |
| US5323620A (en) * | 1992-01-23 | 1994-06-28 | Imi Air Conditioning Limited | Air conditioners |
| GB2263551B (en) * | 1992-01-23 | 1995-02-08 | Imi Air Conditioning Ltd | Improvments relating to air conditioners |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3134912A1 (en) | 1983-03-17 |
| FR2512201B1 (en) | 1986-06-06 |
| FR2512201A1 (en) | 1983-03-04 |
| GB2105476B (en) | 1985-07-17 |
| DE3134912C2 (en) | 1984-05-10 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |