Patent US5111692A successfully refreshed from Google Patents.
US5111692A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Temperature compensated liquid level and fluid flow sensor
Assignee: Fluid Components International LLC
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Filing: 1991-02-14
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Granted: 1992-05-12
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Expires: 2011-02-14
Abstract
Abstract A temperature compensated, self-heating, resistance thermal detector in a sensor circuit for determining fluid level or fluid flow. A resistor in shunt with the detector provides the temperature compensation. The resistor and the thermal detector are connected between electrical input and output lines. Alternative embodiments include a speed enhancing lead network and a fully automated circuit under microprocessor control.
Inventors
- 👤 Malcolm M. McQueen
- 👤 David J. Allen
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 14:06
CPC Classifications
G; G01; G01F; G01F1/00; G01F1/68; G01F1/696; G01F1/698; G01F1/6986; G01F23/00; G01F23/22; G01F23/24; G01F23/246; G01F23/247
Claims Analysis
Total Claims: 33
Claim 1
Independent Claim
273 words
A method for detecting liquid level and fluid flow employing a circuit comprising an electrical input line and an electrical output line, a resistance temperature detector (RTD) having a variable resistance related to temperature connected between the input and output lines, a fixed value temperature compensating resistor connected between the input and output lines in parallel with the RTD, the parallel combination being selectively coupled through the input line to a constant current source through a selectively actuable switch, and voltage sensing means connected between the input and output lines across the parallel combination, said method comprising the steps of: closing the switch and taking a reference voltage reading at initial process temperature; self heating the RTD for a first predetermined period of time with current from the constant current source; shunting increasing amounts of current through the fixed value temperature compensating resistor as the resistance of the RTD increases with temperature, thereby reducing the amount of power dissipated in the RTD in relation to the total power dissipated in the parallel combination; taking a measurement temperature voltage reading at the end of the first predetermined period; comparing the reference voltage with the measurement temperature voltage, a large temperature differential within a predetermined differential range indicated that the liquid level has not reached the RTD or that there is no or low fluid flow, a relatively smaller temperature differential within a second predetermined differential range indicating that the liquid level has reached the RTD or that there is significant fluid flow; and opening the switch to remove heating current from the RTD and to allow the RTD to return to a reference temperature.
Claim 2
Independent Claim
273 words
A method for detecting liquid level and fluid flow employing a circuit comprising an electrical input line and an electrical output line, a resistance temperature detector (RTD) having a variable resistance related to temperature connected between the input and output lines, a fixed value temperature compensating resistor connected between the input and output lines in parallel with the RTD, the parallel combination being selectively coupled through the input line to a constant current source through a selectively actuable switch, and voltage sensing means connected between the input and output lines across the parallel combination, said method comprising the steps of: closing the switch and taking a reference voltage reading at initial process temperature; self heating the RTD for a first predetermined period of time with current from the constant current source; shunting increasing amounts of current through the fixed value temperature compensating resistor as the resistance of the RTD increases with temperature, thereby reducing the amount of power dissipated in the RTD in relation to the total power dissipated in the parallel combination; taking a measurement temperature voltage reading at the end of the first predetermined period; comparing the reference voltage with the measurement temperature voltage, a large temperature differential within a predetermined differential range indicated that the liquid level has not reached the RTD or that there is no or low fluid flow, a relatively smaller temperature differential within a second predetermined differential range indicating that the liquid level has reached the RTD or that there is significant fluid flow; and opening the switch to remove heating current from the RTD and to allow the RTD to return to a reference temperature.
Claim 3
Dependent Claim
37 words
The method recited in claim 1, and comprising the further step of periodically monitoring the liquid level or fluid flow by repeatedly closing the switch for the predetermined period of time and taking the comparison voltage readings.
Claim 4
Dependent Claim
105 words
A sensor for detecting liquid level and fluid flow, said sensor comprising: an electrical input line; an electrical output line; a resistance component having a variable resistance related to temperature connected between said input and output lines; a temperature stable, temperature compensating resistor of fixed resistance value connected between said input and output lines in parallel with said resistance component; a constant current source for applying current to said parallel combination of said resistance component and said compensating resistor through said input line; and switch means for selectively coupling said constant current source to said parallel combination and causing self heating of said resistance component.
Claim 5
Dependent Claim
105 words
A sensor for detecting liquid level and fluid flow, said sensor comprising: an electrical input line; an electrical output line; a resistance component having a variable resistance related to temperature connected between said input and output lines; a temperature stable, temperature compensating resistor of fixed resistance value connected between said input and output lines in parallel with said resistance component; a constant current source for applying current to said parallel combination of said resistance component and said compensating resistor through said input line; and switch means for selectively coupling said constant current source to said parallel combination and causing self heating of said resistance component.
Claim 6
Dependent Claim
31 words
The sensor recited in claim 3, wherein said compensating resistor has a resistance value at least an order of magnitude greater than the resistance of said resistance component at calibration temperature.
Claim 7
Dependent Claim
32 words
The sensor recited in claim 3, wherein said compensating resistor has a resistance value in the range of six to ten times that of said resistance component at its maximum resistance value.
Claim 8
Dependent Claim
22 words
The sensor recited in claim 3, and further comprising means for providing an indication representative of the voltage across said parallel combination.
Claim 9
Dependent Claim
16 words
The sensor recited in claim 3, wherein said resistance component is a resistance temperature detector (RTD).
Claim 10
Dependent Claim
13 words
The sensor recited in claim 7, herein said RTD comprises a point sensor.
Claim 11
Dependent Claim
15 words
The sensor recited in claim 7, wherein said RTD comprises a plurality of point sensors.
Claim 12
Dependent Claim
14 words
The sensor recited in claim 7, wherein said RTD comprises an elongated continuous sensor.
Claim 13
Dependent Claim
141 words
A sensor for detecting liquid level and fluid flow, said sensor comprising: an electrical input line; an electrical output line; a resistance temperature detector (RTD) having a variable resistance related to temperature connected between said input and output lines; a temperature stable, temperature compensating resistor of fixed resistance value connected between said input and output lines in parallel with said RTD, said compensating resistor having a resistance value at least an order of magnitude greater than the resistance of said RTD at calibration temperature; a constant current source for applying current through said input line to said parallel combination of said RTD and said compensating resistor and causing self heating of said RTD; switch means for selectively coupling said constant current source to said parallel combination; and means for providing an electrical signal representative of the voltage across said parallel combination.
Claim 14
Dependent Claim
141 words
A sensor for detecting liquid level and fluid flow, said sensor comprising: an electrical input line; an electrical output line; a resistance temperature detector (RTD) having a variable resistance related to temperature connected between said input and output lines; a temperature stable, temperature compensating resistor of fixed resistance value connected between said input and output lines in parallel with said RTD, said compensating resistor having a resistance value at least an order of magnitude greater than the resistance of said RTD at calibration temperature; a constant current source for applying current through said input line to said parallel combination of said RTD and said compensating resistor and causing self heating of said RTD; switch means for selectively coupling said constant current source to said parallel combination; and means for providing an electrical signal representative of the voltage across said parallel combination.
Claim 15
Dependent Claim
267 words
A sensor for detecting liquid level and fluid flow, said sensor comprising: an electrical input line; an electrical output line; a resistance temperature detector (RTD) having a variable resistance related to temperature connected between said input and output lines; a temperature stable, temperature compensating resistor of fixed resistance value connected between said input and output lines in parallel with said RTD; a constant current source for applying current to said parallel combination of said RTD and said compensating resistor; means for selectively connecting said constant current source to said parallel combination and causing self heating of said RTD; first sample and hold circuit means having an output and being connected to said RTD to detect initial voltage thereon; amplifier means having an output; means for connecting the output of said first sample and hold circuit means for said amplifier means; comparator means having an output and having an input connected to said output of said amplifier means; means for applying a reference voltage to said comparator means with which the output from said amplifier means in compared; second sample and hold circuit means connected to said output of said comparator means to detect the difference between the initial voltage and the voltage on said RTD at a time after said RTD is heated and subjected to the fluid being sensed; indicator means coupled to said output of said second sample and hold circuit means; and control means for controlling the timing of the operation of said first and second sample and hold means and said selective connecting means, and for providing said reference voltage to said comparator.
Claim 16
Dependent Claim
267 words
A sensor for detecting liquid level and fluid flow, said sensor comprising: an electrical input line; an electrical output line; a resistance temperature detector (RTD) having a variable resistance related to temperature connected between said input and output lines; a temperature stable, temperature compensating resistor of fixed resistance value connected between said input and output lines in parallel with said RTD; a constant current source for applying current to said parallel combination of said RTD and said compensating resistor; means for selectively connecting said constant current source to said parallel combination and causing self heating of said RTD; first sample and hold circuit means having an output and being connected to said RTD to detect initial voltage thereon; amplifier means having an output; means for connecting the output of said first sample and hold circuit means for said amplifier means; comparator means having an output and having an input connected to said output of said amplifier means; means for applying a reference voltage to said comparator means with which the output from said amplifier means in compared; second sample and hold circuit means connected to said output of said comparator means to detect the difference between the initial voltage and the voltage on said RTD at a time after said RTD is heated and subjected to the fluid being sensed; indicator means coupled to said output of said second sample and hold circuit means; and control means for controlling the timing of the operation of said first and second sample and hold means and said selective connecting means, and for providing said reference voltage to said comparator.
Claim 17
Dependent Claim
30 words
The sensor recited in claim 12, wherein said compensating resistor has a resistance value at least an order of magnitude greater than the resistance of said RTD at calibration temperature.
Claim 18
Dependent Claim
31 words
The sensor recited in claim 12, wherein said compensating resistor has a resistance value in the range of six to ten times that of said RTD at its maximum resistance value.
Claim 19
Dependent Claim
22 words
The sensor recited in claim 12, and further comprising means for providing an indication representative of the voltage across said parallel combination.
Claim 20
Dependent Claim
13 words
The sensor recited in claim 12, wherein said RTD comprises a point sensor.
Claim 21
Dependent Claim
15 words
The sensor recited in claim 12, wherein said RTD comprises a plurality of point sensors.
Claim 22
Dependent Claim
14 words
The sensor recited in claim 12, wherein said RTD comprises an elongated continuous sensor.
Claim 23
Dependent Claim
86 words
The sensor recited in claim 12, and further comprising a lead network connected between said amplifier means and said comparator means, said lead network comprising: second amplifier means having at least one input and an output; voltage divider means connected to one said input of said second amplifier means, said voltage divider means comprising at least two legs; and capacitor means connected across one leg of said voltage divider means, the output of said second amplifier means being connected to an input of said comparator means.
Claim 24
Dependent Claim
38 words
The sensor recited in claim 19, wherein the gain of said second amplifier means is configured to equal the attenuation of said voltage divider means so that at DC the net gain of said lead network is unity.
Claim 25
Dependent Claim
137 words
A sensor for detecting liquid level and fluid flow, said sensor comprising: an electrical input line; an electrical output line; a source of electrical power; a resistance component having a variable resistance related to temperature connected between said input and output lines in circuit with said source of electrical power; a fixed resistance value resistor connector in combination with said resistance component between said input and output lines with said source of electrical power in a manner to function as a temperature compensating resistor; and switch means for selectively coupling said source of power to said resistance component and said resistor and causing self heating of said resistance component, excess power caused by said self heating being dissipated by said resistor so that said resistance component can give readings accurately relating to liquid level and fluid flow.
Claim 26
Dependent Claim
137 words
A sensor for detecting liquid level and fluid flow, said sensor comprising: an electrical input line; an electrical output line; a source of electrical power; a resistance component having a variable resistance related to temperature connected between said input and output lines in circuit with said source of electrical power; a fixed resistance value resistor connector in combination with said resistance component between said input and output lines with said source of electrical power in a manner to function as a temperature compensating resistor; and switch means for selectively coupling said source of power to said resistance component and said resistor and causing self heating of said resistance component, excess power caused by said self heating being dissipated by said resistor so that said resistance component can give readings accurately relating to liquid level and fluid flow.
Claim 27
Dependent Claim
29 words
The sensor recited in claim 21, wherein: said temperature compensating resistor is connected in parallel with said resistance component; and said source of power is a constant current source.
Claim 28
Dependent Claim
238 words
A sensor for detecting fluid flow, said sensor comprising: an electrical input line; an electrical output line; a resistance temperature detector (RTD) having a variable resistance related to temperature connected between said input and output lines; a constant current source for applying current to said RTD through said input line; means for selectively connecting said constant current source to said RTD and causing self heating of said RTD; first sample and hold circuit means having an output and being connected to said RTD to detect initial voltage thereon; amplifier means having an output; means for connecting the output of said first sample and hold circuit means to said amplifier means; comparator means having an output and having an input connected to said output of said amplifier means; means for applying a reference voltage to said comparator means with which the output from said amplifier means is compared; second sample and hold circuit means connected to said output of said comparator means to detect the difference between the initial voltage and the voltage on said RTD at a time after said RTD is heated and subjected to the fluid flow being sensed; indicator means coupled to said output of said second sample and hold circuit means; and control means for controlling the timing of the operation of said first and second sample and hold means and said selective connecting means and for providing said reference voltage to said comparator.
Claim 29
Dependent Claim
238 words
A sensor for detecting fluid flow, said sensor comprising: an electrical input line; an electrical output line; a resistance temperature detector (RTD) having a variable resistance related to temperature connected between said input and output lines; a constant current source for applying current to said RTD through said input line; means for selectively connecting said constant current source to said RTD and causing self heating of said RTD; first sample and hold circuit means having an output and being connected to said RTD to detect initial voltage thereon; amplifier means having an output; means for connecting the output of said first sample and hold circuit means to said amplifier means; comparator means having an output and having an input connected to said output of said amplifier means; means for applying a reference voltage to said comparator means with which the output from said amplifier means is compared; second sample and hold circuit means connected to said output of said comparator means to detect the difference between the initial voltage and the voltage on said RTD at a time after said RTD is heated and subjected to the fluid flow being sensed; indicator means coupled to said output of said second sample and hold circuit means; and control means for controlling the timing of the operation of said first and second sample and hold means and said selective connecting means and for providing said reference voltage to said comparator.
Claim 30
Dependent Claim
21 words
The sensor recited in claim 23, and further comprising means for providing an indication representative of the voltage across said RTD.
Claim 31
Dependent Claim
13 words
The sensor recited in claim 23, wherein said RTD comprises a point sensor.
Claim 32
Dependent Claim
15 words
The sensor recited in claim 23, wherein said RTD comprises a plurality of point sensors.
Claim 33
Dependent Claim
14 words
The sensor recited in claim 23, wherein said RTD comprises an elongated continuous sensor.
References Cited (Backward Citations)
US3111031A
Cited
US3372590A
Cited
US3485100A
Cited
US3479875A
Cited
US3719083A
Cited
US3803913A
Cited
US3745827A
Cited
US3891391A
Cited
US4053874A
Cited
US4163391A
Cited
US4116045A
Cited
US4356728A
Cited
US4361037A
Cited
US4326199A
Cited
US4513616A
Cited
GB2120482A
Cited
US4525850A
Cited
JPS59104515A
Cited
US4513615A
Cited
US4494406A
Cited
US4532799A
Cited
US4619140A
Cited
US4633491A
Cited
US4640127A
Cited
US4825383A
Cited
US4853637A
Cited
US4854167A
Cited
US5031126A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1995-05-12 | 1995-11-11 | 1996-05-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1999-05-12 | 1999-11-11 | 2000-05-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2003-05-12 | 2003-11-11 | 2004-05-12 | $7700.00 | Window Closed / Lapsed |