CA1192418A - Temperature controlled pressure transducer - Google Patents
Temperature controlled pressure transducerInfo
- Publication number
- CA1192418A CA1192418A CA000416032A CA416032A CA1192418A CA 1192418 A CA1192418 A CA 1192418A CA 000416032 A CA000416032 A CA 000416032A CA 416032 A CA416032 A CA 416032A CA 1192418 A CA1192418 A CA 1192418A
- Authority
- CA
- Canada
- Prior art keywords
- temperature
- pressure
- fluid
- control means
- pressure sensing
- 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.)
- Expired
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01G—WEIGHING
- G01G5/00—Weighing apparatus wherein the balancing is effected by fluid action
- G01G5/04—Weighing apparatus wherein the balancing is effected by fluid action with means for measuring the pressure imposed by the load on a liquid
- G01G5/06—Weighing apparatus wherein the balancing is effected by fluid action with means for measuring the pressure imposed by the load on a liquid with electrical indicating means
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01G—WEIGHING
- G01G23/00—Auxiliary devices for weighing apparatus
- G01G23/48—Temperature-compensating arrangements
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L19/00—Details of, or accessories for, apparatus for measuring steady or quasi-steady pressure of a fluent medium insofar as such details or accessories are not special to particular types of pressure gauges
- G01L19/04—Means for compensating for effects of changes of temperature, i.e. other than electric compensation
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measuring Fluid Pressure (AREA)
Abstract
TEMPERATURE CONTROLLED PRESSURE TRANSDUCER
ABSTRACT
Apparatus for measuring the pressure in a confined fluid. A pressure transducer senses the fluid pressure and produces an output signal representative of the fluid pressure. Temperature control means are provided to maintain the temperature of the pressure transducer near a selected temperature. The temperature control means includes means for raising and lowering the temperature of the pressure transducer. Preferably, the temperature control means comprises a Peltier effect device. The apparatus may also be used to determine the weight of a load supported by a confined fluid since the fluid pressure is representative of the weight of the load.
ABSTRACT
Apparatus for measuring the pressure in a confined fluid. A pressure transducer senses the fluid pressure and produces an output signal representative of the fluid pressure. Temperature control means are provided to maintain the temperature of the pressure transducer near a selected temperature. The temperature control means includes means for raising and lowering the temperature of the pressure transducer. Preferably, the temperature control means comprises a Peltier effect device. The apparatus may also be used to determine the weight of a load supported by a confined fluid since the fluid pressure is representative of the weight of the load.
Description
TEMPERATURE CONT~OLLED PRESSURE TRANSDUCER
Field of the Invention This invention relates to apparatus for measuring the pressure in a confined fluid and, in particular, to temperature controlled apparatus for measuring the pressure in a confined fluid. The inven-tion further relates to apparatus for measuring weight supported by a confined fluid and, in particular, to apparatus for providing a temperature independent measurement of such weight.
~escription of the Prior Art Measurement of the pressure in a confined fluid (the "fluid" may be a gas such as a pneumatic fluid confined within a pneumatic circuit, or it may be a liquid such as a hydraulic fluid confined within a hydraulic circuit) has conventionally been effected by means of a fluid pressure gauge coupled directly to a line containing the pressurized fluid. However, pressure gauges are typically only capable of approxi-mating the actual fluid pressure. In an effort toobtain more accurate pressure measurements, load cells which provide an electrical output signal representative of the fluid pressure have been substituted for pressure gauges. However, the mere substitution of a load cell for a pressure gauge will not of itself significantly improve the accuracy of the pressure readings obtained because the load cell output signal will fluctuate with the temperature of the transducer which is used to measure pressure. Pressure transducers such as those used in load cells are inherently temperature sensitive.
- 1- `~' Many attem~ts have been made to compensate ~or tem~erature-induced errors which affect pressure readings obtained from a load cell. Although such compensation methods enable reasonably accurate pressure measurements -to be made over a narrow temperature range, they do not o~er accuracies of, say, 1% over an environmental temperature range.
The environmental temperature range of a confined hydraulic fluid (i.e. the range of operating temperatures to which the fluid may be exposed) may typically vary from about -50 F to about +200 F.
Accurate measurement of the pressure in a confined fluid is important if, for example, a reliable indication of the weight supported by the confined fluid is to be lS obtained by mathematical conversion of the fluid pressure~ If an accurate measurement of the weight of a load supported by a fluid confined within a hydraulic circuit can be obtained, then the weight of the load itself can be determined.
Summary of the Invention The present invention provides an active means for con-trolling the temperature of a pressure transducer to maintain that temperature within a prescribed temper-ature range. By maintaining the temperature of the pressure transducer constant, one provides an accurate basis for comparing individual pressure readings obtained from the transducer. The procedure used to correct such measurements to eliminate temperature-induced errors may be simplified since one need only deal wi~h a single temperature rather than a range oE
temperatures~
In accordance with the present invention, there is provided new and improved apparatus for measur-ing the pressure in a confined fluid. The apparatuscomprises pressure sensing means for sensing the fluid pressure and producing a Eirst output signal representa-tive of such pressure; and, temperature control means for maintaining the temperature of the pressure sensing means near a selected temperature. The temperature control means includes means for raising and lowering the temperature of the pressure sensin~ means. The apparatus includes temperature sensing means for sensing the temperature of the pressure sensing means and producing a second output signal representative of such temperature.
The apparatus may also include signal processing means for comparing the second output signal to a reference signal representative of the selected temperature, for actuating the temperature control means to raise the temperature of the pressure sensing means when the temperature falls below the selected tempera-ture and for actuating the temperature control means to lower the temperature of the pressure sensing means when the temperature rises above the selected temperature.
Preferably, the temperature con-trol means is a Peltier Effect device.
The confined fluid may be a hydraulic fluid or a pneumatic fluid.
Preferably, the driving signal which actuates the temperature control means is varied in inverse proportion to the rate at which the temperature of the pressure sensing means changes with respect to the selected temperature.
The invention also provides new and improved apparatus ~or weighing a load supported by a confined fluid. The apparatus comprises pressure sensing means for sensing the pressure in the confined 1uid and producing a first output signal representative o~ such pressure and of the weight of the load; and, temperature control means for maintaining the temperature of the pressure sensing means near a selected temperature, the temperature control means including means for raising and lowering the temperature of the pressure sensing means .
Brief Description of the Drawings Figure 1 is a block diagram of a system for measuring the pressure in a confined fluid in accordance with the invention.
Figure 2 is a cross-sectional view depicting the mounting of a pressure transducer, temperature sensor and temperature controller for measuring pressure in a fluid confined within a hydraulic circuit.
Figure 3 is a schematic diagram of the ; preferred embodiment of an electrical circuit for controlling the temperature of the pressure sensing means.
Figure 4 is a schematic diagram oE the preferred embodiment of a temperature sensor amplifier.
Figure 5 is a schematic diagram of the preEerred embodiment oE a pressure sensing means amplifier.
Description of the Preferred Embodiment Figure 1 depicts in block diagram form a system or measuring the pressure in a confined fluid.
The system may also be used for measuring the weight supported by the confined fluid if the pressure readings obtained are converted mathematically. The fluid may be either a hydraulic or a pneumatic fluid. If the fluid is a hydraulic fluid then it will typically be confined within a hydraulic circuitO The hydraulic circuit may be of the type commonly provided in heavy machinery used Eor moving or supporting loads; for example, hydraul-ically operated log yarding machines, fork lift trucks or excavators, to name but a few.
As shown in Figure 1, the system includes a "pressure interface" 1 comprising a temperature sensor
Field of the Invention This invention relates to apparatus for measuring the pressure in a confined fluid and, in particular, to temperature controlled apparatus for measuring the pressure in a confined fluid. The inven-tion further relates to apparatus for measuring weight supported by a confined fluid and, in particular, to apparatus for providing a temperature independent measurement of such weight.
~escription of the Prior Art Measurement of the pressure in a confined fluid (the "fluid" may be a gas such as a pneumatic fluid confined within a pneumatic circuit, or it may be a liquid such as a hydraulic fluid confined within a hydraulic circuit) has conventionally been effected by means of a fluid pressure gauge coupled directly to a line containing the pressurized fluid. However, pressure gauges are typically only capable of approxi-mating the actual fluid pressure. In an effort toobtain more accurate pressure measurements, load cells which provide an electrical output signal representative of the fluid pressure have been substituted for pressure gauges. However, the mere substitution of a load cell for a pressure gauge will not of itself significantly improve the accuracy of the pressure readings obtained because the load cell output signal will fluctuate with the temperature of the transducer which is used to measure pressure. Pressure transducers such as those used in load cells are inherently temperature sensitive.
- 1- `~' Many attem~ts have been made to compensate ~or tem~erature-induced errors which affect pressure readings obtained from a load cell. Although such compensation methods enable reasonably accurate pressure measurements -to be made over a narrow temperature range, they do not o~er accuracies of, say, 1% over an environmental temperature range.
The environmental temperature range of a confined hydraulic fluid (i.e. the range of operating temperatures to which the fluid may be exposed) may typically vary from about -50 F to about +200 F.
Accurate measurement of the pressure in a confined fluid is important if, for example, a reliable indication of the weight supported by the confined fluid is to be lS obtained by mathematical conversion of the fluid pressure~ If an accurate measurement of the weight of a load supported by a fluid confined within a hydraulic circuit can be obtained, then the weight of the load itself can be determined.
Summary of the Invention The present invention provides an active means for con-trolling the temperature of a pressure transducer to maintain that temperature within a prescribed temper-ature range. By maintaining the temperature of the pressure transducer constant, one provides an accurate basis for comparing individual pressure readings obtained from the transducer. The procedure used to correct such measurements to eliminate temperature-induced errors may be simplified since one need only deal wi~h a single temperature rather than a range oE
temperatures~
In accordance with the present invention, there is provided new and improved apparatus for measur-ing the pressure in a confined fluid. The apparatuscomprises pressure sensing means for sensing the fluid pressure and producing a Eirst output signal representa-tive of such pressure; and, temperature control means for maintaining the temperature of the pressure sensing means near a selected temperature. The temperature control means includes means for raising and lowering the temperature of the pressure sensin~ means. The apparatus includes temperature sensing means for sensing the temperature of the pressure sensing means and producing a second output signal representative of such temperature.
The apparatus may also include signal processing means for comparing the second output signal to a reference signal representative of the selected temperature, for actuating the temperature control means to raise the temperature of the pressure sensing means when the temperature falls below the selected tempera-ture and for actuating the temperature control means to lower the temperature of the pressure sensing means when the temperature rises above the selected temperature.
Preferably, the temperature con-trol means is a Peltier Effect device.
The confined fluid may be a hydraulic fluid or a pneumatic fluid.
Preferably, the driving signal which actuates the temperature control means is varied in inverse proportion to the rate at which the temperature of the pressure sensing means changes with respect to the selected temperature.
The invention also provides new and improved apparatus ~or weighing a load supported by a confined fluid. The apparatus comprises pressure sensing means for sensing the pressure in the confined 1uid and producing a first output signal representative o~ such pressure and of the weight of the load; and, temperature control means for maintaining the temperature of the pressure sensing means near a selected temperature, the temperature control means including means for raising and lowering the temperature of the pressure sensing means .
Brief Description of the Drawings Figure 1 is a block diagram of a system for measuring the pressure in a confined fluid in accordance with the invention.
Figure 2 is a cross-sectional view depicting the mounting of a pressure transducer, temperature sensor and temperature controller for measuring pressure in a fluid confined within a hydraulic circuit.
Figure 3 is a schematic diagram of the ; preferred embodiment of an electrical circuit for controlling the temperature of the pressure sensing means.
Figure 4 is a schematic diagram oE the preferred embodiment of a temperature sensor amplifier.
Figure 5 is a schematic diagram of the preEerred embodiment oE a pressure sensing means amplifier.
Description of the Preferred Embodiment Figure 1 depicts in block diagram form a system or measuring the pressure in a confined fluid.
The system may also be used for measuring the weight supported by the confined fluid if the pressure readings obtained are converted mathematically. The fluid may be either a hydraulic or a pneumatic fluid. If the fluid is a hydraulic fluid then it will typically be confined within a hydraulic circuitO The hydraulic circuit may be of the type commonly provided in heavy machinery used Eor moving or supporting loads; for example, hydraul-ically operated log yarding machines, fork lift trucks or excavators, to name but a few.
As shown in Figure 1, the system includes a "pressure interface" 1 comprising a temperature sensor
2, pressure sensing means 3 and temperature controller 4. Pressure sensing means 3 produces a first electrical output signal at 5 which is an analog repre-sentation of the pressure in the confined fluid.
Temperature sensor 2 produces a second electrical output signal at 6 which is an analog representation of the temperature of pressure sensing means 3. Temperature controller 4 is used to selectably raise or lower the temperature of pressure sensing means 3 to maintain its temperature near a selected temperature.
Signal processing means 7 are provided to compare the second output signal to a reference signal representative of the selected temperature oE pressure sensing means 3. When the temperature of pressure sens-ing means 3 falls below the selected temperature, temperature controller 4 is activated - as hereinafter described - to raise the temperature of pressure sensing means 3. When the temperature of pressure sensing means
Temperature sensor 2 produces a second electrical output signal at 6 which is an analog representation of the temperature of pressure sensing means 3. Temperature controller 4 is used to selectably raise or lower the temperature of pressure sensing means 3 to maintain its temperature near a selected temperature.
Signal processing means 7 are provided to compare the second output signal to a reference signal representative of the selected temperature oE pressure sensing means 3. When the temperature of pressure sens-ing means 3 falls below the selected temperature, temperature controller 4 is activated - as hereinafter described - to raise the temperature of pressure sensing means 3. When the temperature of pressure sensing means
3 rises above the selected temperature, temperature controller 4 is ac-tivated to lower the temperature oE
pressure sensing means 3. Signal processing means 7 includes a master control device 8 such as a micropro-cessor or computer, capable of analyzing the various signals aforesaid and producing suitable signals to actuate temperature controller 4. Signal processing means 7 also includes a multiplexer 9 (for alternately presenting either the first or the second output signal to master control device 8) and an analog-digital converter 11 for converting the first and second output signals (typically measured in volts) to digital repre-sentations convenient for manipulation by master control device 8. Signal processing means 7 also includes a suitable interface 13 for presentation of the analog-digital converter output signal to master control device 8 and for presentation of output signals from master control device 8 to temperature controller 4.
Master control device 8 may be programmed by conventional known techniques to monitor the temperature of pressure sensing means 3 and to actuate temperature controller 4 as required to maintain the temperature of pressure sensing means 3 at or near the selected temper-ature. Similarly, master control device 8 may be programmed to convert the first output signal produced by pres~ure sensing means 3 to provide a direc-t readin~
of the pressure in the confined fluid (in units such as pounds per square inch). The master control device program may include steps for "correcting" the pressure readings to account Eor the temperature of pressure sensing means 3. Pressure readings so obtained may also be mathematically converted by master control device 8 to provide a representation of the weight supported by the confined fluid. Visual representations of pressure or weight may be presented either on alpha-numeric type display 15 or on hard~copy printer 17. A keyboard 19 may be provided to permit the system operator to enter commands to master control device 8, to select informa-tion for presentation on display 15 or printer 17~ etc.
Pressure sensing means 3 is maintained at ornear a pre-selected temperature so -that all pressure readings are taken at substantially the same temper-ature. An appropriate algorithm may then be used to mathematically "correct" all such pressure readings to eliminate any temperature-induced error component.
Figure 2 is a cross-sectional illustration of one way in which pressure sensiny means 3 (hereinafter referred to as a "pressure transducer"), temperature sensor 2 and temperature controller 4 may be mounted for measuring the pressure in a fluid con-fined within a hydraulic circuit. Pressure transducer 3 is rigidly mounted on metal plate lO in close thermal contact therewith. Pressure transducer fluid inlet port 12 protrudes through plate 10 and through metal plate 14 for connection to hose 18 which couples pressurized hydraulic :Eluid to pressure transducer 3. Metal plates 14, 15, 16 and 17 form an enclosure for pressure trans-ducer 3. Plate 14 includes a plurality of fins 19 for conveying heat to or from plate 14 as hereinafter described. The enclosure is filled with a fibre type insulating material 20 to thermally isolate pressure transducer 3. Electrical leads for temperature sensor 2 and pressure transducer 3 are also passed through plates 10 and 14 to emerge at 21.
Temperature controller 4 includes three indiv idual temperature control devices 24 which are rigidly affixed, for example, by gluing, between metal plates 10 and 14 so as to maximize thermal conductivity between fins 19, plate 14, devices 24 plate 10 and pressure transducer 3. Temperature control devices 24 are "Peltier Effect" devices. A Peltier Effect device is a two port electrical component which will "pump" heat one way when a current passes through the device in one direction and which will "pump" heat the other way when a current passes through the device in the opposite direction. Peltier Effect devices 24 are electrically connected in series so that a current applied to devices 24 in one direction will cause them to "pumpl' heat from fins 19 and plate 14 to plate 10 and pressure transducer 3 (thus raising the temperature of pressure transducer 3) and so that a current applied in the opposite direction will cause devices 24 to l'pump" heat from pressure transducer 3 and plate 10 to plate 14 and fins 19 (thus lowering the temperature of pressure transducer 3). Electric leads from Peltier Effect ~evices 24 protrude throu~h plate 14 a-t 21.
Temperature sensor 2 is insert~d into plate 10 near pressure transducer 3. A suitable adhesive such as epoxy is used to seal temperature sensor 2 in plate 10 to provide good thermal conductivity between temper-ature sensor 2 and pressure transducer 3. Preferably, temperature sensor 2 is not positioned directly between any of Peltier Effect devices 24 and pressure transducer 3; the object being to minimize the effect of Peltier E~fect devices 2~ on temperature readings taken by temperature sensor 2 so that temperature sensor 2 provides a reliable indication of the temperature of pressure transducer 3.
Figure 3 is an electrical circuit schematic diagram o:E a tempera-ture controller for controlling ~eltier Effect devices 24 to selectably raise or lower the temperature of pressure transducer 3. An input signal comprising two binary digits is applied by master control device 8 (via interface 13) to input terminals Ao and Al of the temperature contro].ler.
If a logic "low" signal is applied to both input -terminals Ao and Al, then the output of each logical '~nand" gate Nl and N2 will be "high"O These "high" signals are applied to the base of each of trans-istors Ql and Q2 via resistors Rl and R2 respec-tively, causing each of transistors Ql and Q2 to turn "on"~ The collector voltayes of transistors Ql and Q2 will therefore be "low", causing each of transistors Q3 and Q~ to turn "off". The collector g _ voltages o:E transistors Q3 ancl Q~ will then be "high" and thelr emitter voltages will be "low". Hence, each of Darlington power transistor pairs Q5, Q6~
Q7 and Q~ will be "off", and no current will Elow in Peltier Effect device Pl. Similarly, i a logic "high" signal is presented at input terminal Ao and a logic "low" signal is presented at input terminal Al then the output of both nand gates Nl and N2 will be "high" and again no current will flow in Peltier Effect device Pl.
If master control device 8 determines that the temperature of pressure transducer 3 is equal to a pre-determined selected temperature, no action need be taken to raise or lower the temperature of pressure transducer 3. Accordingly, no current need be passed through Peltier Effect device Pl. This may be achieved by holding input terminal Al of the temperature controller "low" so that Pel-tier Effect device P
remains "off".
If a logic 'llow" signal is presented at input terminal Ao and a logic "high" signal presented at input terminal Al, then the output of nand gate Nl will be "low" (due to presence of logical inverter Il). The output of nand gate N2 will remain "high", thus power transistor stages Q6 and Q8 will remain "oEf" as described above. However, the "low' signal at the base of transistor Ql will turn Ql "off", resulting in the coupling of a "high" signal to the base of transistor Q3 causing it to turn "on".
The voltage at the collector of -transistor Q3 then drops to enable the flow of emitter-base ~urrent in power translstor stage Q5 thereby driving Q5 to an "on" condltion. When Q5 is "on" the source voltage of 30 volts (less tlle emitter-collector drop across Q5) ls applied to right hand terrninal "~" (as viewed in Figure 3) of Peltier Effect device P1. Similarly, the voltage at the emitter of transistor Q3 rises to enable the flow of a base-emitter curren-t in power transistor stage Q7 thereby drivin~ Q7 to an "on"
condi-tion. This action applies electrical ground reference (plus the collector-emitter drop across Q7) to the left hand terminal "-" (as viewed in Figure 3) of Peltier Effect device Pl Accordingly, a current path is established from the 30 volt source, through Q5 and Peltier Effect device Pl to ground via Q7. Current will thus flow through Peltier effect device Pl from the "+" to the "-" terminals (as viewed in Figure 3).
In the preferred embodiment, Peltier effect device P
pumps heat away Erom pressure transducer 3 when a current passes from the "+" to the "-" terminals oE the Peltier effect device.
It may similarly be determined tha-t current will Llow in the opposi-te direction through Peltier Effect device Pl frorn the "-" to the "-~" termina~s (as viewed in Figure 3) which in turn means that heat is pumped towards pressure transducer 3 in the preEerred embodiment, if a "high" signal is presented at each of input terminals Ao and Al. The output of nand gate Nl will then be "high" causing power transistor s-tages Qs and Q7 to remain "off" as explained above.
However, the output of nand gate N2 will be "low"
causin~ transistor Q2 to turn "off" and transistor Q4 to turn "on" due to the presence o~ a "hicJh" signal at its base. The "high" voltage present at the collector and emitter oE conducting transistor Q~ will cause power transistor stages Q6 and Q8 to turn "on'l, thus causing a current to flow rom ~6 through Peltier Effect device Pl to yround via Q8.
Figure 4 is an electronic circuit schematic diagram of a differential amplifier for comparing the output signal of temperature sensor 2 with a reference signal representative of the selected temperature of pressure transducer 3. The temperature sensor used in the preferred embodiment is a National Semiconductor LM135 precision temperature sensor which operates as a two terminal zener diode, shown in Figure 4 as D2.
Because the vol-tage drop across zener diode D2 varies with temperature, the voltage presented at input terminal X2 of amplifier Al will vary with the tempera-ture of pressure transducer 3 (because temper-ature sensor 2 is placed in thermal conductivity with pressure transducer 3).
Regulator Ul provides an accurate, temper-ature independent reference voltage for amplifier A1.
Resistor Rf and capacitor Cf shift and scale the output of amplifier Al into the 0-5 volt range which is suitable for input to analog-digital converter 11.
To calibrate the difEerential amplifier, diode D2 is heated to the selected -temperature of pressure trans-ducer 3 and potentiometer R18 is then adjusted so that the output voltage o:E ampli:Eier ~l is 2.5 volts ~the midpoint o:E the 0-5 volt amp:Lifier output voltage range).
If the temperature of pressure transducer 3 is less than the selected temperature, then the output voltage o~ amplifer ~l will be less than 2.5 volts.
The difference between the amplifier output voltage and 2.5 volts will represent the difference between the selected temperature of pressure transducer 3 and i~s actual temperature. If the temperature of pressure transducer 3 is grea-ter than its selected temperature, then the output voltage of ampliEier Al will be greater than 2.5 volts - the magnitude of the difference in voltages representing the difference between the actual and selected temperatures of pressure transducer 3. The analo~ output voltage signal produced by amplifier Al is converted into a digital represen-tation by analog-digital converter ll or presentati.on to master control device 8. By sensing whether the amplifier output voltage is greater than 2.5 volts, less than 2.5 volts, or equal to 2.5 volts, master control device 8 may determine whether the temperature of pressure transducer 3 is too high (greater than the selected temperature) or too low (lower than the selected temperature) or "correct" (equal to the selected temperature). If the temperature of pressure transducer 3 is too high, then -temperature controller may be activated as described above to lower the temperature of pressure transducer 3. Conversely, if the temperature of pressure transducer 3 is too low, then temperat~lre controller 4 rnay be activated as described above to raise the temperature of pressure transducer 3. If master control device 8 detects that the temperature of the pressure transducer 3 is equal to the selected temperature, then temperature controller 4 may be turned "off".
Preferably, the drive signal for Peltier effect devices 24 includes two components. The Eirst, as just described above, is directly dependent upon the temperature of pressure transducer 3. To avoid "over-shooting" the selected tempera-ture of pressure trans-ducer 3 or perhaps causing the pressure transducer temperature to "oscillate" about -the selected temper-ature, a second drive signal component is preferably used to drive Peltier Effect devices 24 in inverse proportion to the rate of -temperature change which is considered appropriate to change the actual temperature of pressure transducer 3 to the selected temperature.
For example, if the temperature of pressure transducer 3 is 20C below its selected temperature, then it will likely be desirable to apply a maximum drive signal to Peltier Effect devices 24 to "pump" heat toward pressure transducer 3 in order to raise its temperature as quickly as possible. However, as the temperature of pressure -transducer 3 approaches the selected temper-ature, the driving signal for Peltier Effect devices 24 should be reduced so as to reduce the amount of heat "pumped" toward pressure transducer 3. (If this is not done then pressure transducer 3 may be heated well above the selected temperature and will therefore have to be -- 1'1 --cooled.) The drive signal Eor Peltier EfEect devic2s 24 may there~ore be continually changed in response to the changing temperature of pressure transducer 3. It may even be appropriate in some cases to drive Peltier Ef~ect devices 24 so as to "pump'; heat away from pressure transducer 3 even thouyh the temperature of pressure transducer 3 is below the selected temperature.
This would occur, for example, iE Peltier Effect devices 24 had been driven to "pump" heat toward pressure trans-ducer 3~ raising its temperature near the selected temp-erature. As the pressure transducer temperature approaches the selected temperature, heat is pumped away to avoid overshooting the selected temperature. Similar "proportional control" of the driving signal for Peltier Effect devices 24 should be used when the pressure -transducer temperature exceeds the selected temperature.
An appropriate algorithm for driving Peltier Effect devices 24 in response to changing temperatures of pressure transducer 3 may be programmed into master control device 8.
Figure 5 is an electronic circuit schematic diagram of an amplifier for the analog voltage output signal produced by pressure transducer 3~ The pressure transducer is represented in Figure 5 as Px~
Potentiome-ter R20 may be adjusted to select the amplifier gain. Potentiometer R23 may be adjusted to provide an offset voltage to compensate Eor variations in output voltage ranges between different pressure transducers. For example, the pressure trans-ducer used in the preferred embodiment has an output voltage range of 0 - 5 volts (representing pressures of 0 psi through 3,000 psi respectively).
In operation, a hose containing pressurized hydraulic fluid is coupled to pressure transducer 3.
Pressure transclucer 3 produces a first electrical output signal which is representative of the pressure in the confined fluid. The first output signal is amplified as described above for presentation to master control device 8 via multiplexer 9 and analog-digital converter ll. Temperature sensor 2 produces a second electrical output signal which is representative of the temperature of pressure transducer 3. As described above, the second output signal is compared by temperature sensor amplifier ~l with a reference signal representative of the selected temperature of pressure transducer 3. The temperature sensor amplifier output signal is presented to master control device 8 via multiplexer 9 and analog-digital converter ll. Temperature controller 4 is activated by master control device 8 (preferably, by means of "proportional control" as decribed above) to pump heat toward or away from pressure transducer 3 in order to raise or lower its temperature., depending upon tlle actual temperature oE the pressure transducer relative to its selected temperature, and the desired rate of temperature change.
Thus, the temperature of pressure transducer 3 may be actively controlled to hold it at or near a selected temperature at which the digital representa~ion of the :Eirst output signal representative of the fluid pressure may be reliably converted by master control w devlce 8 to yield a measure of the Eluid pressure, a measure oE the wei(3ht supported by the con~ined fluid, etc.
The following table includes specifications for components which have been used in the preEerred embodiment:
pressure transducer Gulton Industries Inc.
GSH series high pressure transducer temperature sensor (D2) National semiconductor LM135 precision temperature sensor Peltier Effect devices Melcor Materials Electronic Products Corporation Model No. CP 1~4~71-lOL
R1 - R2r ~16 ~ R17 lOK ohm R3 - R4, R7 - Rlo lK ohm Rs - R6, Rll - R14, R17~ R19 4.7K ohm R18 ~ R20 J R23 lOK ohm po R21 - R22 lOOK ohm Ql ~ Q4 2N3904 Q5 ~ Q6 TIP 125 Q7 ~ Q8 TIP 120 Ul, Al National Semiconductor A2 National Semiconductor LMll l 7400 Mul-tiplexer Motorola MC 14051B
Analog to Digital Converter Philbrick 8703 It will be readily apparent to those skilled in the art that master control device ~ may be programmed to utilize the accurate pressure represen-ta-tions obtainable through use of the invention in a number oE ways. As one example, a temperature controlled pressure transducer may be inserted into a hydraulic line used to drive the hydraulic cylinders which raise or lower the Eorks of a ~arding machine used for loacling logs onto logging trucks. By means of a suitably programmed algorithm, master control device 8 may be used to convert pressure signals derived from the temperature controlled pressure transducer into a representation of the weight of a log or logs suspended in the forks of -the yarding machine. Master control device 8 may be interfaced in known fashion as shown in Figure 1 to a display and/or printer which may be used to present the operator of the yarding machine with a display and/or print-out representative of the weight of the load supported in the forks of the machine. The operator will then be able to determine the weight of the load he is placin~ upon a logging truck or other transportation or storage means. Master control device 8 may also accumulate the weight of all loads suspended in the forks of the machine since a given reference time. For example, the operator may "initialize" master control device 8 (typically, by striking a key on a keyboard console) to indicate that he is about to begin loading logs onto a truck. As each load is placed upon the truck, the operator may be presented by master control device 8 with a display or print-out to indicate the weight of that load and the weight of all loads previously placed upon the particular truck. Hence the operator will be able to "adjust" the total load placed upon the truck 50 that the truck carries a required payload without exceeding any applicable weight restrictions~
It will be readily apparent to those skilled in the art that the temperature controlled pressure transducer hereinbefore described may be included in ~-irtually any hydraulic or pneumatic circuit to provide a reliable indication of the pressure o~ con~ined fluid in the system or, iE desired, an accurate representation of the weiyh~ suppor~ed by the conEined fluid.
Modifications falling within the scope o~ the in~ention will also occur to those s~illed in the art.
As one example, it might in some cases be more expedient to control the temperature of the fluid surrounding the pressure transducer than to control the temperature of the transducer itself. This could be accomplished by applying Peltier Effect devices to the housing oE a load cell which contains both pressurized fluid and a pres-sure transducer for sensing the fluid pressure. The Peltier Efect devices could be controlled as herein-beEore described to maintain the temperature of fluid within the load cell housing near a selected tempera-ture; thus ensuring that pressure readings obtained from - the transducer are taken at a substantially uniform temperature and independen-tly of ambient temperature fluctuations.
pressure sensing means 3. Signal processing means 7 includes a master control device 8 such as a micropro-cessor or computer, capable of analyzing the various signals aforesaid and producing suitable signals to actuate temperature controller 4. Signal processing means 7 also includes a multiplexer 9 (for alternately presenting either the first or the second output signal to master control device 8) and an analog-digital converter 11 for converting the first and second output signals (typically measured in volts) to digital repre-sentations convenient for manipulation by master control device 8. Signal processing means 7 also includes a suitable interface 13 for presentation of the analog-digital converter output signal to master control device 8 and for presentation of output signals from master control device 8 to temperature controller 4.
Master control device 8 may be programmed by conventional known techniques to monitor the temperature of pressure sensing means 3 and to actuate temperature controller 4 as required to maintain the temperature of pressure sensing means 3 at or near the selected temper-ature. Similarly, master control device 8 may be programmed to convert the first output signal produced by pres~ure sensing means 3 to provide a direc-t readin~
of the pressure in the confined fluid (in units such as pounds per square inch). The master control device program may include steps for "correcting" the pressure readings to account Eor the temperature of pressure sensing means 3. Pressure readings so obtained may also be mathematically converted by master control device 8 to provide a representation of the weight supported by the confined fluid. Visual representations of pressure or weight may be presented either on alpha-numeric type display 15 or on hard~copy printer 17. A keyboard 19 may be provided to permit the system operator to enter commands to master control device 8, to select informa-tion for presentation on display 15 or printer 17~ etc.
Pressure sensing means 3 is maintained at ornear a pre-selected temperature so -that all pressure readings are taken at substantially the same temper-ature. An appropriate algorithm may then be used to mathematically "correct" all such pressure readings to eliminate any temperature-induced error component.
Figure 2 is a cross-sectional illustration of one way in which pressure sensiny means 3 (hereinafter referred to as a "pressure transducer"), temperature sensor 2 and temperature controller 4 may be mounted for measuring the pressure in a fluid con-fined within a hydraulic circuit. Pressure transducer 3 is rigidly mounted on metal plate lO in close thermal contact therewith. Pressure transducer fluid inlet port 12 protrudes through plate 10 and through metal plate 14 for connection to hose 18 which couples pressurized hydraulic :Eluid to pressure transducer 3. Metal plates 14, 15, 16 and 17 form an enclosure for pressure trans-ducer 3. Plate 14 includes a plurality of fins 19 for conveying heat to or from plate 14 as hereinafter described. The enclosure is filled with a fibre type insulating material 20 to thermally isolate pressure transducer 3. Electrical leads for temperature sensor 2 and pressure transducer 3 are also passed through plates 10 and 14 to emerge at 21.
Temperature controller 4 includes three indiv idual temperature control devices 24 which are rigidly affixed, for example, by gluing, between metal plates 10 and 14 so as to maximize thermal conductivity between fins 19, plate 14, devices 24 plate 10 and pressure transducer 3. Temperature control devices 24 are "Peltier Effect" devices. A Peltier Effect device is a two port electrical component which will "pump" heat one way when a current passes through the device in one direction and which will "pump" heat the other way when a current passes through the device in the opposite direction. Peltier Effect devices 24 are electrically connected in series so that a current applied to devices 24 in one direction will cause them to "pumpl' heat from fins 19 and plate 14 to plate 10 and pressure transducer 3 (thus raising the temperature of pressure transducer 3) and so that a current applied in the opposite direction will cause devices 24 to l'pump" heat from pressure transducer 3 and plate 10 to plate 14 and fins 19 (thus lowering the temperature of pressure transducer 3). Electric leads from Peltier Effect ~evices 24 protrude throu~h plate 14 a-t 21.
Temperature sensor 2 is insert~d into plate 10 near pressure transducer 3. A suitable adhesive such as epoxy is used to seal temperature sensor 2 in plate 10 to provide good thermal conductivity between temper-ature sensor 2 and pressure transducer 3. Preferably, temperature sensor 2 is not positioned directly between any of Peltier Effect devices 24 and pressure transducer 3; the object being to minimize the effect of Peltier E~fect devices 2~ on temperature readings taken by temperature sensor 2 so that temperature sensor 2 provides a reliable indication of the temperature of pressure transducer 3.
Figure 3 is an electrical circuit schematic diagram o:E a tempera-ture controller for controlling ~eltier Effect devices 24 to selectably raise or lower the temperature of pressure transducer 3. An input signal comprising two binary digits is applied by master control device 8 (via interface 13) to input terminals Ao and Al of the temperature contro].ler.
If a logic "low" signal is applied to both input -terminals Ao and Al, then the output of each logical '~nand" gate Nl and N2 will be "high"O These "high" signals are applied to the base of each of trans-istors Ql and Q2 via resistors Rl and R2 respec-tively, causing each of transistors Ql and Q2 to turn "on"~ The collector voltayes of transistors Ql and Q2 will therefore be "low", causing each of transistors Q3 and Q~ to turn "off". The collector g _ voltages o:E transistors Q3 ancl Q~ will then be "high" and thelr emitter voltages will be "low". Hence, each of Darlington power transistor pairs Q5, Q6~
Q7 and Q~ will be "off", and no current will Elow in Peltier Effect device Pl. Similarly, i a logic "high" signal is presented at input terminal Ao and a logic "low" signal is presented at input terminal Al then the output of both nand gates Nl and N2 will be "high" and again no current will flow in Peltier Effect device Pl.
If master control device 8 determines that the temperature of pressure transducer 3 is equal to a pre-determined selected temperature, no action need be taken to raise or lower the temperature of pressure transducer 3. Accordingly, no current need be passed through Peltier Effect device Pl. This may be achieved by holding input terminal Al of the temperature controller "low" so that Pel-tier Effect device P
remains "off".
If a logic 'llow" signal is presented at input terminal Ao and a logic "high" signal presented at input terminal Al, then the output of nand gate Nl will be "low" (due to presence of logical inverter Il). The output of nand gate N2 will remain "high", thus power transistor stages Q6 and Q8 will remain "oEf" as described above. However, the "low' signal at the base of transistor Ql will turn Ql "off", resulting in the coupling of a "high" signal to the base of transistor Q3 causing it to turn "on".
The voltage at the collector of -transistor Q3 then drops to enable the flow of emitter-base ~urrent in power translstor stage Q5 thereby driving Q5 to an "on" condltion. When Q5 is "on" the source voltage of 30 volts (less tlle emitter-collector drop across Q5) ls applied to right hand terrninal "~" (as viewed in Figure 3) of Peltier Effect device P1. Similarly, the voltage at the emitter of transistor Q3 rises to enable the flow of a base-emitter curren-t in power transistor stage Q7 thereby drivin~ Q7 to an "on"
condi-tion. This action applies electrical ground reference (plus the collector-emitter drop across Q7) to the left hand terminal "-" (as viewed in Figure 3) of Peltier Effect device Pl Accordingly, a current path is established from the 30 volt source, through Q5 and Peltier Effect device Pl to ground via Q7. Current will thus flow through Peltier effect device Pl from the "+" to the "-" terminals (as viewed in Figure 3).
In the preferred embodiment, Peltier effect device P
pumps heat away Erom pressure transducer 3 when a current passes from the "+" to the "-" terminals oE the Peltier effect device.
It may similarly be determined tha-t current will Llow in the opposi-te direction through Peltier Effect device Pl frorn the "-" to the "-~" termina~s (as viewed in Figure 3) which in turn means that heat is pumped towards pressure transducer 3 in the preEerred embodiment, if a "high" signal is presented at each of input terminals Ao and Al. The output of nand gate Nl will then be "high" causing power transistor s-tages Qs and Q7 to remain "off" as explained above.
However, the output of nand gate N2 will be "low"
causin~ transistor Q2 to turn "off" and transistor Q4 to turn "on" due to the presence o~ a "hicJh" signal at its base. The "high" voltage present at the collector and emitter oE conducting transistor Q~ will cause power transistor stages Q6 and Q8 to turn "on'l, thus causing a current to flow rom ~6 through Peltier Effect device Pl to yround via Q8.
Figure 4 is an electronic circuit schematic diagram of a differential amplifier for comparing the output signal of temperature sensor 2 with a reference signal representative of the selected temperature of pressure transducer 3. The temperature sensor used in the preferred embodiment is a National Semiconductor LM135 precision temperature sensor which operates as a two terminal zener diode, shown in Figure 4 as D2.
Because the vol-tage drop across zener diode D2 varies with temperature, the voltage presented at input terminal X2 of amplifier Al will vary with the tempera-ture of pressure transducer 3 (because temper-ature sensor 2 is placed in thermal conductivity with pressure transducer 3).
Regulator Ul provides an accurate, temper-ature independent reference voltage for amplifier A1.
Resistor Rf and capacitor Cf shift and scale the output of amplifier Al into the 0-5 volt range which is suitable for input to analog-digital converter 11.
To calibrate the difEerential amplifier, diode D2 is heated to the selected -temperature of pressure trans-ducer 3 and potentiometer R18 is then adjusted so that the output voltage o:E ampli:Eier ~l is 2.5 volts ~the midpoint o:E the 0-5 volt amp:Lifier output voltage range).
If the temperature of pressure transducer 3 is less than the selected temperature, then the output voltage o~ amplifer ~l will be less than 2.5 volts.
The difference between the amplifier output voltage and 2.5 volts will represent the difference between the selected temperature of pressure transducer 3 and i~s actual temperature. If the temperature of pressure transducer 3 is grea-ter than its selected temperature, then the output voltage of ampliEier Al will be greater than 2.5 volts - the magnitude of the difference in voltages representing the difference between the actual and selected temperatures of pressure transducer 3. The analo~ output voltage signal produced by amplifier Al is converted into a digital represen-tation by analog-digital converter ll or presentati.on to master control device 8. By sensing whether the amplifier output voltage is greater than 2.5 volts, less than 2.5 volts, or equal to 2.5 volts, master control device 8 may determine whether the temperature of pressure transducer 3 is too high (greater than the selected temperature) or too low (lower than the selected temperature) or "correct" (equal to the selected temperature). If the temperature of pressure transducer 3 is too high, then -temperature controller may be activated as described above to lower the temperature of pressure transducer 3. Conversely, if the temperature of pressure transducer 3 is too low, then temperat~lre controller 4 rnay be activated as described above to raise the temperature of pressure transducer 3. If master control device 8 detects that the temperature of the pressure transducer 3 is equal to the selected temperature, then temperature controller 4 may be turned "off".
Preferably, the drive signal for Peltier effect devices 24 includes two components. The Eirst, as just described above, is directly dependent upon the temperature of pressure transducer 3. To avoid "over-shooting" the selected tempera-ture of pressure trans-ducer 3 or perhaps causing the pressure transducer temperature to "oscillate" about -the selected temper-ature, a second drive signal component is preferably used to drive Peltier Effect devices 24 in inverse proportion to the rate of -temperature change which is considered appropriate to change the actual temperature of pressure transducer 3 to the selected temperature.
For example, if the temperature of pressure transducer 3 is 20C below its selected temperature, then it will likely be desirable to apply a maximum drive signal to Peltier Effect devices 24 to "pump" heat toward pressure transducer 3 in order to raise its temperature as quickly as possible. However, as the temperature of pressure -transducer 3 approaches the selected temper-ature, the driving signal for Peltier Effect devices 24 should be reduced so as to reduce the amount of heat "pumped" toward pressure transducer 3. (If this is not done then pressure transducer 3 may be heated well above the selected temperature and will therefore have to be -- 1'1 --cooled.) The drive signal Eor Peltier EfEect devic2s 24 may there~ore be continually changed in response to the changing temperature of pressure transducer 3. It may even be appropriate in some cases to drive Peltier Ef~ect devices 24 so as to "pump'; heat away from pressure transducer 3 even thouyh the temperature of pressure transducer 3 is below the selected temperature.
This would occur, for example, iE Peltier Effect devices 24 had been driven to "pump" heat toward pressure trans-ducer 3~ raising its temperature near the selected temp-erature. As the pressure transducer temperature approaches the selected temperature, heat is pumped away to avoid overshooting the selected temperature. Similar "proportional control" of the driving signal for Peltier Effect devices 24 should be used when the pressure -transducer temperature exceeds the selected temperature.
An appropriate algorithm for driving Peltier Effect devices 24 in response to changing temperatures of pressure transducer 3 may be programmed into master control device 8.
Figure 5 is an electronic circuit schematic diagram of an amplifier for the analog voltage output signal produced by pressure transducer 3~ The pressure transducer is represented in Figure 5 as Px~
Potentiome-ter R20 may be adjusted to select the amplifier gain. Potentiometer R23 may be adjusted to provide an offset voltage to compensate Eor variations in output voltage ranges between different pressure transducers. For example, the pressure trans-ducer used in the preferred embodiment has an output voltage range of 0 - 5 volts (representing pressures of 0 psi through 3,000 psi respectively).
In operation, a hose containing pressurized hydraulic fluid is coupled to pressure transducer 3.
Pressure transclucer 3 produces a first electrical output signal which is representative of the pressure in the confined fluid. The first output signal is amplified as described above for presentation to master control device 8 via multiplexer 9 and analog-digital converter ll. Temperature sensor 2 produces a second electrical output signal which is representative of the temperature of pressure transducer 3. As described above, the second output signal is compared by temperature sensor amplifier ~l with a reference signal representative of the selected temperature of pressure transducer 3. The temperature sensor amplifier output signal is presented to master control device 8 via multiplexer 9 and analog-digital converter ll. Temperature controller 4 is activated by master control device 8 (preferably, by means of "proportional control" as decribed above) to pump heat toward or away from pressure transducer 3 in order to raise or lower its temperature., depending upon tlle actual temperature oE the pressure transducer relative to its selected temperature, and the desired rate of temperature change.
Thus, the temperature of pressure transducer 3 may be actively controlled to hold it at or near a selected temperature at which the digital representa~ion of the :Eirst output signal representative of the fluid pressure may be reliably converted by master control w devlce 8 to yield a measure of the Eluid pressure, a measure oE the wei(3ht supported by the con~ined fluid, etc.
The following table includes specifications for components which have been used in the preEerred embodiment:
pressure transducer Gulton Industries Inc.
GSH series high pressure transducer temperature sensor (D2) National semiconductor LM135 precision temperature sensor Peltier Effect devices Melcor Materials Electronic Products Corporation Model No. CP 1~4~71-lOL
R1 - R2r ~16 ~ R17 lOK ohm R3 - R4, R7 - Rlo lK ohm Rs - R6, Rll - R14, R17~ R19 4.7K ohm R18 ~ R20 J R23 lOK ohm po R21 - R22 lOOK ohm Ql ~ Q4 2N3904 Q5 ~ Q6 TIP 125 Q7 ~ Q8 TIP 120 Ul, Al National Semiconductor A2 National Semiconductor LMll l 7400 Mul-tiplexer Motorola MC 14051B
Analog to Digital Converter Philbrick 8703 It will be readily apparent to those skilled in the art that master control device ~ may be programmed to utilize the accurate pressure represen-ta-tions obtainable through use of the invention in a number oE ways. As one example, a temperature controlled pressure transducer may be inserted into a hydraulic line used to drive the hydraulic cylinders which raise or lower the Eorks of a ~arding machine used for loacling logs onto logging trucks. By means of a suitably programmed algorithm, master control device 8 may be used to convert pressure signals derived from the temperature controlled pressure transducer into a representation of the weight of a log or logs suspended in the forks of -the yarding machine. Master control device 8 may be interfaced in known fashion as shown in Figure 1 to a display and/or printer which may be used to present the operator of the yarding machine with a display and/or print-out representative of the weight of the load supported in the forks of the machine. The operator will then be able to determine the weight of the load he is placin~ upon a logging truck or other transportation or storage means. Master control device 8 may also accumulate the weight of all loads suspended in the forks of the machine since a given reference time. For example, the operator may "initialize" master control device 8 (typically, by striking a key on a keyboard console) to indicate that he is about to begin loading logs onto a truck. As each load is placed upon the truck, the operator may be presented by master control device 8 with a display or print-out to indicate the weight of that load and the weight of all loads previously placed upon the particular truck. Hence the operator will be able to "adjust" the total load placed upon the truck 50 that the truck carries a required payload without exceeding any applicable weight restrictions~
It will be readily apparent to those skilled in the art that the temperature controlled pressure transducer hereinbefore described may be included in ~-irtually any hydraulic or pneumatic circuit to provide a reliable indication of the pressure o~ con~ined fluid in the system or, iE desired, an accurate representation of the weiyh~ suppor~ed by the conEined fluid.
Modifications falling within the scope o~ the in~ention will also occur to those s~illed in the art.
As one example, it might in some cases be more expedient to control the temperature of the fluid surrounding the pressure transducer than to control the temperature of the transducer itself. This could be accomplished by applying Peltier Effect devices to the housing oE a load cell which contains both pressurized fluid and a pres-sure transducer for sensing the fluid pressure. The Peltier Efect devices could be controlled as herein-beEore described to maintain the temperature of fluid within the load cell housing near a selected tempera-ture; thus ensuring that pressure readings obtained from - the transducer are taken at a substantially uniform temperature and independen-tly of ambient temperature fluctuations.
Claims (24)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Apparatus for measuring the pressure in a confined fluid, said apparatus comprising:
(a) pressure sensing means for sensing said fluid pressure and producing a first output signal representative of such pressure; and, (b) temperature control means for maintaining the temperature of said pressure sensing means near a selected temperature, said temperature control means including means for raising and lowering the temperature of said pressure sensing means.
(a) pressure sensing means for sensing said fluid pressure and producing a first output signal representative of such pressure; and, (b) temperature control means for maintaining the temperature of said pressure sensing means near a selected temperature, said temperature control means including means for raising and lowering the temperature of said pressure sensing means.
2. Apparatus as defined in Claim 1, further comprising temperature sensing means for sensing the temperature of said pressure sensing means and producing a second output signal representative of such temper-ature.
3. Apparatus as defined in Claim 2, further comprising signal processing means for comparing said second output signal to a reference signal represent-ative of said selected temperature, for actuating said temperature control means to raise the temperature of said pressure sensing means when said temperature falls below said selected temperature and for actuating said temperature control means to lower the temperature of said pressure sensing means when said temperature rises above said selected temperature.
- Page 1 of Claims -
- Page 1 of Claims -
4. Apparatus as defined in Claim 1, 2, or 3, wherein said confined fluid is a hydraulic fluid.
5. Apparatus as defined in Claim 1, 2, or 3, wherein said confined fluid is a pneumatic fluid.
6. Apparatus as defined in Claim 1, 2, or 3, wherein said temperature control means comprises a Peltier Effect device.
7. Apparatus as defined in Claim 3, wherein said confined fluid is a hydraulic fluid and said temperature control means comprises a Peltier Effect device.
8. Apparatus as defined in Claim 3, wherein said confined fluid is a pneumatic fluid and said temperature control means comprises a Peltier Effect device.
9. A method for measuring the pressure in a confined fluid comprising sensing said fluid pressure while maintaining the temperature of the pressure sensing means near a selected temperature.
10. Apparatus as defined in Claim 3, wherein the driving signal for actuating said temperature control means is varied in inverse proportion to the rate of change of temperature of said pressure sensing means with respect to said selected temperature.
11. Apparatus for weighing a load supported by a confined fluid, said apparatus comprising:
(a) pressure sensing means for sensing the pressure in said confined fluid and and producing an output signal representative of such pressure and of the weight of said load; and, - Page 2 of Claims -(b) temperature control means for maintaining the temperature of said pressure sensing means near a selected temperature, said temperature control means including means for raising and lowering the temperature of said pressure sensing means.
(a) pressure sensing means for sensing the pressure in said confined fluid and and producing an output signal representative of such pressure and of the weight of said load; and, - Page 2 of Claims -(b) temperature control means for maintaining the temperature of said pressure sensing means near a selected temperature, said temperature control means including means for raising and lowering the temperature of said pressure sensing means.
12. Apparatus as defined in Claim 11, further comprising temperature sensing means for sensing the temperature of said pressure sensing means and producing a second output signal representative of such temper-ature.
13. Apparatus as defined in Claim 12, further comprising signal processing means for comparing said second output signal to a reference signal represent-ative of said selected temperature, for actuating said temperature control means to raise the temperature of said pressure sensing means when said temperature falls below said selected temperature and for actuating said temperature control means to lower the temperature of said pressure sensing means when said temperature rises above said selected temperature.
14. Apparatus as defined in Claim 13, wherein said confined fluid is a hydraulic fluid.
15. Apparatus as defined in Claims 11, 12, or 13, wherein said temperature control means comprises a Peltier Effect device.
16. Apparatus as defined in Claim 14, wherein said temperature control means comprises a Peltier Effect device.
-Page 3 of Claims -
-Page 3 of Claims -
17. Apparatus as defined in Claim 13, wherein the driving signal for actuating said temperature control means is varied in inverse proportion to the rate of change of temperature of said pressure sensing means with respect to said selected temperature.
18. A method for measuring the pressure in a con-fined fluid comprising sensing said fluid pressure while maintaining the temperature of the fluid surrounding the pressure sensing means near a selected temperature.
19. The method as defined in claim 9 wherein said step of maintaining the temperature of said pressure sensing means near a selected temperature comprises the further steps of:
a) Sensing the temperature of said pressure sensing means;
b) Producing a signal representative of said temperature;
c) Comparing said signal to a reference signal representative of said selected temperature;
and d) Actuating a temperature control means to raise the temperature of said pressure sensing means when said temperature falls below said selected temperature and to lower the tem-perature of said pressure sensing means when said temperature rises above said selected temperature.
- Page 4 of Claims -
a) Sensing the temperature of said pressure sensing means;
b) Producing a signal representative of said temperature;
c) Comparing said signal to a reference signal representative of said selected temperature;
and d) Actuating a temperature control means to raise the temperature of said pressure sensing means when said temperature falls below said selected temperature and to lower the tem-perature of said pressure sensing means when said temperature rises above said selected temperature.
- Page 4 of Claims -
20. The method of claim 19 wherein said temperature control means comprises a Peltier Effect device.
21. The method of claim 19 wherein the driving signal for actuating said temperature control means is varied in inverse proportion to the rate of change of temperature of said pressure sensing means with respect to said selected temperature.
22. The method as defined in claim 18 wherein said step of maintaining the temperature of the fluid surrounding the pressure sensing means near a selected temperature comprises the further steps of:
a) Sensing the temperature of said fluid;
b) Producing a signal representative of said temperature;
c) Comparing said signal to a reference signal representative of said selected temperature;
and d) Actuating a temperature control means to raise the temperature of said fluid when said temperature falls below said selected temperature and to lower the temperature of said fluid when said temperature rises above said selected temperature.
a) Sensing the temperature of said fluid;
b) Producing a signal representative of said temperature;
c) Comparing said signal to a reference signal representative of said selected temperature;
and d) Actuating a temperature control means to raise the temperature of said fluid when said temperature falls below said selected temperature and to lower the temperature of said fluid when said temperature rises above said selected temperature.
23. The method of claim 22 wherein said tempera-ture control means comprises a Peltier Effect device.
24. The method of claim 22 wherein the driving signal for actuating said temperature control means is varied in inverse proportions to the rate of change of temperature of said fluid with respect to said selected temperature.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000416032A CA1192418A (en) | 1982-11-19 | 1982-11-19 | Temperature controlled pressure transducer |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000416032A CA1192418A (en) | 1982-11-19 | 1982-11-19 | Temperature controlled pressure transducer |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1192418A true CA1192418A (en) | 1985-08-27 |
Family
ID=4123988
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000416032A Expired CA1192418A (en) | 1982-11-19 | 1982-11-19 | Temperature controlled pressure transducer |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1192418A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1925922A1 (en) * | 2006-11-24 | 2008-05-28 | Mettler-Toledo AG | Temperature controlled multiple weighing device |
| WO2016048424A3 (en) * | 2014-09-23 | 2016-08-11 | Rosemount Inc. | Cooling for industrial process variable transmitters |
| US9752947B2 (en) | 2014-09-23 | 2017-09-05 | P I Components Corp. | Thermoelectric heating, cooling and power generation for direct mount and dual compartment fill remote seal systems |
| US9772246B2 (en) | 2014-09-30 | 2017-09-26 | Rosemount Inc. | Fill fluid thermal management |
-
1982
- 1982-11-19 CA CA000416032A patent/CA1192418A/en not_active Expired
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1925922A1 (en) * | 2006-11-24 | 2008-05-28 | Mettler-Toledo AG | Temperature controlled multiple weighing device |
| US7686507B2 (en) | 2006-11-24 | 2010-03-30 | Mettler-Toledo Ag | Multi-module weighing system with temperature control |
| WO2016048424A3 (en) * | 2014-09-23 | 2016-08-11 | Rosemount Inc. | Cooling for industrial process variable transmitters |
| US9752947B2 (en) | 2014-09-23 | 2017-09-05 | P I Components Corp. | Thermoelectric heating, cooling and power generation for direct mount and dual compartment fill remote seal systems |
| US9752946B2 (en) | 2014-09-23 | 2017-09-05 | Rosemount Inc. | Cooling for industrial process variable transmitters |
| US9772246B2 (en) | 2014-09-30 | 2017-09-26 | Rosemount Inc. | Fill fluid thermal management |
| US11313747B2 (en) | 2014-09-30 | 2022-04-26 | Rosemount Inc. | Fill fluid thermal management |
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