CA1156853A - Length and temperature measuring apparatus for tank installations - Google Patents
Length and temperature measuring apparatus for tank installationsInfo
- Publication number
- CA1156853A CA1156853A CA000376410A CA376410A CA1156853A CA 1156853 A CA1156853 A CA 1156853A CA 000376410 A CA000376410 A CA 000376410A CA 376410 A CA376410 A CA 376410A CA 1156853 A CA1156853 A CA 1156853A
- Authority
- CA
- Canada
- Prior art keywords
- length
- measuring
- tube
- resistance
- temperature
- 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
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
- G01F23/30—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 floats
- G01F23/64—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 floats of the free float type without mechanical transmission elements
- G01F23/68—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 floats of the free float type without mechanical transmission elements using electrically actuated indicating means
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K3/00—Thermometers giving results other than momentary value of temperature
- G01K3/02—Thermometers giving results other than momentary value of temperature giving means values; giving integrated values
- G01K3/06—Thermometers giving results other than momentary value of temperature giving means values; giving integrated values in respect of space
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- Measurement Of Resistance Or Impedance (AREA)
- Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
- Arrangements For Transmission Of Measured Signals (AREA)
- Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)
- Level Indicators Using A Float (AREA)
Abstract
Abstract:
The invention provides length and temperature mea-suring apparatus for tank installations, by means of which the depth of fluid in a tank can be conveniently and accurately measured. The apparatus has a measuring tube located in the tank and a float element surrounding the tube. The float causes a slider within the tube to follow its movements, e.g. by magnetic means. The slider has a sliding contact which engages at least one resist-ance element located longitudinally within the tube. A
reference voltage is applied to the resistance element and the partial voltage determined by the position of the sliding contact on the resistance element is measured.
From this, the position of the slider (and hence the fluid level) can be determined. If the partial resistance is also measured, this provides an indication of the average temperature of the resistance element below the fluid level, since the temperature can be calculated from the determined position of the slider and information known about the resistance material.
The invention provides length and temperature mea-suring apparatus for tank installations, by means of which the depth of fluid in a tank can be conveniently and accurately measured. The apparatus has a measuring tube located in the tank and a float element surrounding the tube. The float causes a slider within the tube to follow its movements, e.g. by magnetic means. The slider has a sliding contact which engages at least one resist-ance element located longitudinally within the tube. A
reference voltage is applied to the resistance element and the partial voltage determined by the position of the sliding contact on the resistance element is measured.
From this, the position of the slider (and hence the fluid level) can be determined. If the partial resistance is also measured, this provides an indication of the average temperature of the resistance element below the fluid level, since the temperature can be calculated from the determined position of the slider and information known about the resistance material.
Description
Length and te~ J~ n~
apparatus for tank installations The invention relates to a length and temperature measuring apparatus for tank installations, having a measuring tube and a movable element surrounding the measuring tube for causing movement of a slider located within the measuring tube.
Such an apparatus is already known and measures the propagation time required for ultrasonic waves to travel Erom an upper ultrasonic generator/receiver to the slider, which is formed as a reflector and then back to the ultra-sonic generator/receiver. From the propagation time thusmeasured, the propagation distance, i.e. the actual posi-tion of the slider, can be calculated as a measure of -the actual fluid level within the tank, provided the tempera~
ture prevailing in the propagation path is approximately known as this exerts an influence on the speed of propagation. Alternatively, an average temperature prevailing within the measuring tube can be determlned from a propagation path of known length~
The temperature in the measuring tube is however sub-jected to considerable variations from time to time andalso from place to place depending upon the tank contents and the particular fluid level, so that the assumption of constant predetermined temperature at all times leads to .~, .
apparatus for tank installations The invention relates to a length and temperature measuring apparatus for tank installations, having a measuring tube and a movable element surrounding the measuring tube for causing movement of a slider located within the measuring tube.
Such an apparatus is already known and measures the propagation time required for ultrasonic waves to travel Erom an upper ultrasonic generator/receiver to the slider, which is formed as a reflector and then back to the ultra-sonic generator/receiver. From the propagation time thusmeasured, the propagation distance, i.e. the actual posi-tion of the slider, can be calculated as a measure of -the actual fluid level within the tank, provided the tempera~
ture prevailing in the propagation path is approximately known as this exerts an influence on the speed of propagation. Alternatively, an average temperature prevailing within the measuring tube can be determlned from a propagation path of known length~
The temperature in the measuring tube is however sub-jected to considerable variations from time to time andalso from place to place depending upon the tank contents and the particular fluid level, so that the assumption of constant predetermined temperature at all times leads to .~, .
- 2 ~
incorrect results in the length measurement. This known apparatus permits the determination of an unknown, i.e.
either the fluid level or the average temperature. Since, however, in general the fluid level cannot be determined in another way, this known apparatus is as a rule exclu-sively used for measurement of the fluid level.
In view of this, an object of the invention is to provide a measuring apparatus of the above mentioned type that makes possible an accurate distance measurement, especially of the depths of fluids in tanks or the like, and in addition enables an accurate measurement of the average temperature in a simple and dependable way.
According to the invention there is provided a length and temperature measuring apparatus for tank installa-tions, comprising: a measuring tube having a measuring span embracing the lengths to be measured; first and second resistance elements longitudinally located within the measuring tube over the entire measuring span thereof, said elements having terminals at each end thereof; a slider located within the measuring tube, ~aid slider having first and second sliding contacts sliding along said first and second resistance elements, respectively;
a movable element surrounding said measuring tube for causing movement of said slider located within the measur-ing tube; a reference voltage source; an electrical measuring unit; and circuitry enabling, in a first step, said reference voltage source to be connected to the terminals of the first resistance element and the electrical measuring unit to be connected to one of said terminals and to said first sliding contact for measuring the partial voltage between said terminal and said contact and hence the length between said terminal and said contact; and said circuitry, in a second step, enabling both said reference voltage source and said electrical measuring unit to be connected to one of said terminals of the second resistance element and said second sliding 5;3 - 2a -contact to measure the resistance value and hence the average temperature of the second resistance element therebetween.
The advantage of the invention in particular lies in that, in a first measuring step, a partial voltage of the reference voltage applied to a resistance element is measured at a point where the sliding contact of the slider, which taps the partial voltage, contacts the resistance element, said point being at exactly the level of the fluid. The partial voltage, which is drawn from i : .
,
incorrect results in the length measurement. This known apparatus permits the determination of an unknown, i.e.
either the fluid level or the average temperature. Since, however, in general the fluid level cannot be determined in another way, this known apparatus is as a rule exclu-sively used for measurement of the fluid level.
In view of this, an object of the invention is to provide a measuring apparatus of the above mentioned type that makes possible an accurate distance measurement, especially of the depths of fluids in tanks or the like, and in addition enables an accurate measurement of the average temperature in a simple and dependable way.
According to the invention there is provided a length and temperature measuring apparatus for tank installa-tions, comprising: a measuring tube having a measuring span embracing the lengths to be measured; first and second resistance elements longitudinally located within the measuring tube over the entire measuring span thereof, said elements having terminals at each end thereof; a slider located within the measuring tube, ~aid slider having first and second sliding contacts sliding along said first and second resistance elements, respectively;
a movable element surrounding said measuring tube for causing movement of said slider located within the measur-ing tube; a reference voltage source; an electrical measuring unit; and circuitry enabling, in a first step, said reference voltage source to be connected to the terminals of the first resistance element and the electrical measuring unit to be connected to one of said terminals and to said first sliding contact for measuring the partial voltage between said terminal and said contact and hence the length between said terminal and said contact; and said circuitry, in a second step, enabling both said reference voltage source and said electrical measuring unit to be connected to one of said terminals of the second resistance element and said second sliding 5;3 - 2a -contact to measure the resistance value and hence the average temperature of the second resistance element therebetween.
The advantage of the invention in particular lies in that, in a first measuring step, a partial voltage of the reference voltage applied to a resistance element is measured at a point where the sliding contact of the slider, which taps the partial voltage, contacts the resistance element, said point being at exactly the level of the fluid. The partial voltage, which is drawn from i : .
,
3 -the reEerence voltage, thereby directly reproduces thefluid leve] or measured length oE the total length of the resistance element. The average temperature within the measuring tube has no influence on the measurement of the fluid depth.
Preferably the measuring tube contains a second longitudinally extending resistance element. The lower terminal of the second resistance element is likewise guided out of the measuring tube, while the upper ter-10 minal terminates within the tube. The slider has asecond sliding contact which engages the second resist~
ance element and has a terminal which extends to the outside. In a second method step, the reference voltage is applied between the second sliding contact and the 15 lower terminal of the second resistance element, and then the resistance of the part of the second resistance element therebetween is measured. From this partial resistance, the average temperature of that part of the resistance element can be determined from known data for 20 the resistance material employed.
Al-ternatively, in the second measuring step, the reference voltage may be applied between the first slid-ing contact of the slider and the lower terminal of the first resistance element, and the thereby-produced par-25 tial resistance measured by the measuring device and theaverage temperature in the region therebetween determined Erom the measured value by use of the previously deter-mined fluid depth. The use of a second resistance element can then be avoided.
According to the invention, the measurement of the fluid depth, or some other length determined by the position of the slider is based on -the measurement of a partial voltage, and further the determination of the average temperature in the filled zone is made by 35 measurement of a partial resistance, whereby a great degree of accuracy and dependability can be obtained for comparatively low cost. The determined fluid depth is not dependent upon the average temperature in the mea-suring tube and is therefore relatively accurate. This accurate value of the liquid depth is employed in the followiny partial resistance measurement. From the measured partial resistance, the average temperature prevailing in that zone of the measuring tube in which the partial resistance is located can be concluded directly, i.e. without further corrections.
Preferably, the resistance elemen-ts are each formed of resistance wire which is stretched by a tensioning spring at one end. Particularly preferably, the re-sistance wire is helically wrapped around a strip of insulating material, and the strip of insulating material is stretched by the tensionlng spriny. Thereby, the useful length of the resistance wire is sukstantially increased, so that a very precise determination of the measured potential can be obtained.
Preferably, the lower terminals of the resistance 20 elements are guided to the top of the tube by means of a common guideway, e.g. between the two resistance elements, and through the upper cap of the tubeO The utilizable volume of the tank is in this way left free of the measuring equipment.
The temperature distribution present in the measuring tube is as a rule characterized in that the ~luid tank contents in the lower region of the measuring tube and the gaseous atmosphere in the upper regions of the measuring tube each have a definite temperature. The high heat 30 conductivity of the measuring tube guarantees that the temperature of the tank contents also essentially prevails in the corresponding submerged zone of the measuring tube. Thereabove, with a gradual transition, the zone of the measuring tube above the submerged zone takes on 35 the temperature of the atmosphere material. An homo-geneous temperature division is thereby located within 5;3 the measuring tube, whereby the accuracy of the first measuring step, namely the determination of the fluid depth, is improved, because then the voltage drop over a single division of the resistance element better ful-fills the hypothesis on which the effec-t is based that the partial voltage is proportional to the length of the part of the resistance elemen-t being measured.
Alternatively, the measuring tube may be made from a material of low heat conductivity. This is for example advatangeo~s if the tank employed is relatively small and is quickly filled or emptied, as then based on the heat insulating properties oE the measuring tube the same homogeneous temperature distribution is obtained in the measuring tube, directly after the Eil:ling or emptying of lS the tank as was present before the filling or emptying, and this is advantageous for the determination of the fluid ~evel of the full tank or the mostly empty tank.
If the accuracy of the system has to be increased, there may be provided, according to the invenkion, a temperature sensor with an accompanying temperature measuring circuit at one end of the measuring tube, in order to measure the ]ocal temperature at this end of the tube. Additionally, the resistance of the full length of a resistance element may be measured e.g. in a measuring step preceding the main measurements, and thereby the average temperature in the measuring tube determined.
With these values obtained from the local temperature sensor and for the average temperature within the tube, the measurement of the fluid level may then be corrected -perhaps by reference to a corresponding positionvariational function of the specific resistance of the resistance element. In order to carry out such a correction it is also possible to locate a temperature sensor having a temperature measuring circuit on the slider.
If the measuring tube is made of metal, the slider - , ., may be provided with a third sliding contact which slides along the inner wall oE the tube ancl is electrically connected to the ~irst and second sliding contac-ts. The wa]l of the tube then serves as the lead to the first and second sliding contacts, so that additiona] moving leads within the tube can be avoided.
Further advantages of the invention are apparent from the following description.
A preferred embodiment of the invention is explained in detail below with reference to the drawings, in which:
FigO 1 shows a side view in cross-section of the measuring tube of the apparatus of the invention; and Fig. 2 shows a block circuit diagram of the apparatus of the invention.
lS Fig. 1 shows a side view in cross-section of a mea-suring tube 2 of a measuring apparatus according to the invention. The measuring tube 2 is located vertically in a tank 1~. ~ magnet float 1~, 16 encircles the measuring tube 2 and is provided with a sleeve 15 which is integral with the float body 16. A magnet 14 is provided on the sleeve 15 at the immersion level of the Eloat body, the magnet projecting into the interior of the body. A
cylindrical slider 20 made of a magnetized or magnetizable material is slidah:ly mounted within the measuring tube 20 and is continuously held at the surface level within the tank by the magne-ts 14 of the magnet float 14, 16.
The measuring tube 2 has a circular cross section.
The slider 2 has the shape of a circular cylinder, the cylindrical surface of which is slidable along the inner wall of the measuring tube 2 with only a small clearance.
The measuring tube 2 is sealed from the atmosphere by a lower cap 10 and an upper cap 12. Two resistance elements 2~1, 26 are stretched along the central axis of the measur-ing tube between the lower cap 10 and the upper cap 12 by means of a spring 27 anchored to the upper cap 12a The lower contacts 30, 32 of the resistance elements are guided by means of a guideway 35 to the top of the tube and then through the upper cap 12 to the outside. The upper contact of the first resistance element 24 is also guided through the upper cap 12 via the spring 27. The upper end of the second resistance element 26 ends within the measuring tube.
The slider 20 has a central bore or recess 22, through which the resistance elements 2~, 26 extend. A first sliding contact 31 is provided in the slider 20, which 10 engages the first resistance element 24. Further, a second sliding contact 33 engages the second resistance element 26. The sliding contacts 31, 33 are arranged in a horizontaL plane correspondlng to the surface level of the fluid in the tank.
A third sliding contact 34 is attached to the slider 20 for engaging the inner wa]l of the measuring tube 2 and is electrically connected to the first and second sliding contacts 31, 33. The wall of the measuring tube 2 forms the circuit for the first and second sliding contacts 31, 20 33 via the third sliding contact 34, and has a correspond-ing terminal 36 at the top of the measuring tube. Variable conductors are thus provided within the measuring tube 2 and are connected to the outside via sliding contacts 31, 33.
The resistance elernents are formed of resistance wire closely wound on a strip of insulating materialO This allows a precise determination of the partial voltages encountered and consequently provides a high measurement accuracy.
A temperature sensor 50 is provided at the upper end of the measuring tube and is connected to a temperature sensing circuit 52. If for any reason a greater degree of accuracy o~ the apparatus according to the invention is desired, the temperature at the upper end of the 35 measuring tube may be measured locally by the sensor 50. Subsequently, the entire resistance of a resistance .
.. ..
- 8 ~ S~
element is determined, e.g. in a preparatory measurement step, and the average temperature in the whole Measuring tube ascertained. From the local temperature at the upper end of the measuring tu~e and the average tempera-ture within the measuring tube, a linear temperat~redistribution as a function of position, and thereby a corresponding linear function of the specific resistances relative to position, can be calculated. This linear function of the specific resistances according to position can then ~e used to correct the determination of the li-quid depth x in the Eirst method step. From the partial voltage, measured in the first method step, the liquid depth is obtained after a corrsponding correction, as the measured partial voltage is no longer proportional to the liquid depth x because of the positional variation of the specific voltages. In practice, however, such a correction can be omitted in most cases.
Fig. 2 shows a block circuit diagram of the appara-tus according to the invention. A reference voltage is applied/ during the first method step, to the two ter-minals 28, 30 of the first resistance element 24 from a reference voltage source 40 by closing a switch 41. A
partial voltage is generated between the first sliding contact 31, provided on the slider 20 (not shown in Fig.
2, but see Fig. l), and the lower terminal 30 and this is applied to the voltage measuring terminal 43 of a measuring device 42. The measuring device 42 sends a signal identi~ying the measured voltage to an analog/
digital transducer 46, which ~orwards a suitable signal containing the measured information to a calculator 48.
The calculator 48 determines the li~uid depth x from the measured voltage value and known total length l and transmits a corresponding signal to a monitor 5Q.
In a second method step, the switch 41 is thrown, so that the reference voltage is now applied to the lower terminal 32 of the second resistance element 26. The ~.5~53 electrical circuit continues through lower partial re-sistance Rx of the second resistance element 26 to the second sliding contact 33, which is located at the same height as the first sliding contact. Then the circuit continues to the resistance measurement terminal 44 of the measuring device 42, which determines the value of the partial resistance Rx. The measuring device 42 delivers a corresponding signal to the analog/digi-tal transducer 46 which forwards a corresponding digital signal containing the information to the calculator 48.
The calculator 48 calculates resistance Rx from the known information for the resistance element 26, as well as the previousl.y stored liquid depth x and from this the average temperature within the filled zone which the measured resistance Rx revea:Ls, is subsequently calculated.
Preferably the measuring tube contains a second longitudinally extending resistance element. The lower terminal of the second resistance element is likewise guided out of the measuring tube, while the upper ter-10 minal terminates within the tube. The slider has asecond sliding contact which engages the second resist~
ance element and has a terminal which extends to the outside. In a second method step, the reference voltage is applied between the second sliding contact and the 15 lower terminal of the second resistance element, and then the resistance of the part of the second resistance element therebetween is measured. From this partial resistance, the average temperature of that part of the resistance element can be determined from known data for 20 the resistance material employed.
Al-ternatively, in the second measuring step, the reference voltage may be applied between the first slid-ing contact of the slider and the lower terminal of the first resistance element, and the thereby-produced par-25 tial resistance measured by the measuring device and theaverage temperature in the region therebetween determined Erom the measured value by use of the previously deter-mined fluid depth. The use of a second resistance element can then be avoided.
According to the invention, the measurement of the fluid depth, or some other length determined by the position of the slider is based on -the measurement of a partial voltage, and further the determination of the average temperature in the filled zone is made by 35 measurement of a partial resistance, whereby a great degree of accuracy and dependability can be obtained for comparatively low cost. The determined fluid depth is not dependent upon the average temperature in the mea-suring tube and is therefore relatively accurate. This accurate value of the liquid depth is employed in the followiny partial resistance measurement. From the measured partial resistance, the average temperature prevailing in that zone of the measuring tube in which the partial resistance is located can be concluded directly, i.e. without further corrections.
Preferably, the resistance elemen-ts are each formed of resistance wire which is stretched by a tensioning spring at one end. Particularly preferably, the re-sistance wire is helically wrapped around a strip of insulating material, and the strip of insulating material is stretched by the tensionlng spriny. Thereby, the useful length of the resistance wire is sukstantially increased, so that a very precise determination of the measured potential can be obtained.
Preferably, the lower terminals of the resistance 20 elements are guided to the top of the tube by means of a common guideway, e.g. between the two resistance elements, and through the upper cap of the tubeO The utilizable volume of the tank is in this way left free of the measuring equipment.
The temperature distribution present in the measuring tube is as a rule characterized in that the ~luid tank contents in the lower region of the measuring tube and the gaseous atmosphere in the upper regions of the measuring tube each have a definite temperature. The high heat 30 conductivity of the measuring tube guarantees that the temperature of the tank contents also essentially prevails in the corresponding submerged zone of the measuring tube. Thereabove, with a gradual transition, the zone of the measuring tube above the submerged zone takes on 35 the temperature of the atmosphere material. An homo-geneous temperature division is thereby located within 5;3 the measuring tube, whereby the accuracy of the first measuring step, namely the determination of the fluid depth, is improved, because then the voltage drop over a single division of the resistance element better ful-fills the hypothesis on which the effec-t is based that the partial voltage is proportional to the length of the part of the resistance elemen-t being measured.
Alternatively, the measuring tube may be made from a material of low heat conductivity. This is for example advatangeo~s if the tank employed is relatively small and is quickly filled or emptied, as then based on the heat insulating properties oE the measuring tube the same homogeneous temperature distribution is obtained in the measuring tube, directly after the Eil:ling or emptying of lS the tank as was present before the filling or emptying, and this is advantageous for the determination of the fluid ~evel of the full tank or the mostly empty tank.
If the accuracy of the system has to be increased, there may be provided, according to the invenkion, a temperature sensor with an accompanying temperature measuring circuit at one end of the measuring tube, in order to measure the ]ocal temperature at this end of the tube. Additionally, the resistance of the full length of a resistance element may be measured e.g. in a measuring step preceding the main measurements, and thereby the average temperature in the measuring tube determined.
With these values obtained from the local temperature sensor and for the average temperature within the tube, the measurement of the fluid level may then be corrected -perhaps by reference to a corresponding positionvariational function of the specific resistance of the resistance element. In order to carry out such a correction it is also possible to locate a temperature sensor having a temperature measuring circuit on the slider.
If the measuring tube is made of metal, the slider - , ., may be provided with a third sliding contact which slides along the inner wall oE the tube ancl is electrically connected to the ~irst and second sliding contac-ts. The wa]l of the tube then serves as the lead to the first and second sliding contacts, so that additiona] moving leads within the tube can be avoided.
Further advantages of the invention are apparent from the following description.
A preferred embodiment of the invention is explained in detail below with reference to the drawings, in which:
FigO 1 shows a side view in cross-section of the measuring tube of the apparatus of the invention; and Fig. 2 shows a block circuit diagram of the apparatus of the invention.
lS Fig. 1 shows a side view in cross-section of a mea-suring tube 2 of a measuring apparatus according to the invention. The measuring tube 2 is located vertically in a tank 1~. ~ magnet float 1~, 16 encircles the measuring tube 2 and is provided with a sleeve 15 which is integral with the float body 16. A magnet 14 is provided on the sleeve 15 at the immersion level of the Eloat body, the magnet projecting into the interior of the body. A
cylindrical slider 20 made of a magnetized or magnetizable material is slidah:ly mounted within the measuring tube 20 and is continuously held at the surface level within the tank by the magne-ts 14 of the magnet float 14, 16.
The measuring tube 2 has a circular cross section.
The slider 2 has the shape of a circular cylinder, the cylindrical surface of which is slidable along the inner wall of the measuring tube 2 with only a small clearance.
The measuring tube 2 is sealed from the atmosphere by a lower cap 10 and an upper cap 12. Two resistance elements 2~1, 26 are stretched along the central axis of the measur-ing tube between the lower cap 10 and the upper cap 12 by means of a spring 27 anchored to the upper cap 12a The lower contacts 30, 32 of the resistance elements are guided by means of a guideway 35 to the top of the tube and then through the upper cap 12 to the outside. The upper contact of the first resistance element 24 is also guided through the upper cap 12 via the spring 27. The upper end of the second resistance element 26 ends within the measuring tube.
The slider 20 has a central bore or recess 22, through which the resistance elements 2~, 26 extend. A first sliding contact 31 is provided in the slider 20, which 10 engages the first resistance element 24. Further, a second sliding contact 33 engages the second resistance element 26. The sliding contacts 31, 33 are arranged in a horizontaL plane correspondlng to the surface level of the fluid in the tank.
A third sliding contact 34 is attached to the slider 20 for engaging the inner wa]l of the measuring tube 2 and is electrically connected to the first and second sliding contacts 31, 33. The wall of the measuring tube 2 forms the circuit for the first and second sliding contacts 31, 20 33 via the third sliding contact 34, and has a correspond-ing terminal 36 at the top of the measuring tube. Variable conductors are thus provided within the measuring tube 2 and are connected to the outside via sliding contacts 31, 33.
The resistance elernents are formed of resistance wire closely wound on a strip of insulating materialO This allows a precise determination of the partial voltages encountered and consequently provides a high measurement accuracy.
A temperature sensor 50 is provided at the upper end of the measuring tube and is connected to a temperature sensing circuit 52. If for any reason a greater degree of accuracy o~ the apparatus according to the invention is desired, the temperature at the upper end of the 35 measuring tube may be measured locally by the sensor 50. Subsequently, the entire resistance of a resistance .
.. ..
- 8 ~ S~
element is determined, e.g. in a preparatory measurement step, and the average temperature in the whole Measuring tube ascertained. From the local temperature at the upper end of the measuring tu~e and the average tempera-ture within the measuring tube, a linear temperat~redistribution as a function of position, and thereby a corresponding linear function of the specific resistances relative to position, can be calculated. This linear function of the specific resistances according to position can then ~e used to correct the determination of the li-quid depth x in the Eirst method step. From the partial voltage, measured in the first method step, the liquid depth is obtained after a corrsponding correction, as the measured partial voltage is no longer proportional to the liquid depth x because of the positional variation of the specific voltages. In practice, however, such a correction can be omitted in most cases.
Fig. 2 shows a block circuit diagram of the appara-tus according to the invention. A reference voltage is applied/ during the first method step, to the two ter-minals 28, 30 of the first resistance element 24 from a reference voltage source 40 by closing a switch 41. A
partial voltage is generated between the first sliding contact 31, provided on the slider 20 (not shown in Fig.
2, but see Fig. l), and the lower terminal 30 and this is applied to the voltage measuring terminal 43 of a measuring device 42. The measuring device 42 sends a signal identi~ying the measured voltage to an analog/
digital transducer 46, which ~orwards a suitable signal containing the measured information to a calculator 48.
The calculator 48 determines the li~uid depth x from the measured voltage value and known total length l and transmits a corresponding signal to a monitor 5Q.
In a second method step, the switch 41 is thrown, so that the reference voltage is now applied to the lower terminal 32 of the second resistance element 26. The ~.5~53 electrical circuit continues through lower partial re-sistance Rx of the second resistance element 26 to the second sliding contact 33, which is located at the same height as the first sliding contact. Then the circuit continues to the resistance measurement terminal 44 of the measuring device 42, which determines the value of the partial resistance Rx. The measuring device 42 delivers a corresponding signal to the analog/digi-tal transducer 46 which forwards a corresponding digital signal containing the information to the calculator 48.
The calculator 48 calculates resistance Rx from the known information for the resistance element 26, as well as the previousl.y stored liquid depth x and from this the average temperature within the filled zone which the measured resistance Rx revea:Ls, is subsequently calculated.
Claims (13)
1. Length and temperature measuring apparatus for tank installations, comprising:
a measuring tube having a measuring span embracing the lengths to be measured;
first and second resistance elements longitudinally located within the measuring tube over the entire measuring span thereof, said elements having terminals at each end thereof;
a slider located within the measuring tube, said slider having first and second sliding contacts sliding along said first and second resistance elements, respectively;
a movable element surrounding said measuring tube for causing movement of said slider located within the measur-ing tube;
a reference voltage source;
an electrical measuring unit; and circuitry enabling, in a first step, said reference voltage source to be connected to the terminals of the first resistance element and the electrical measuring unit to be connected to one of said terminals and to said first sliding contact for measuring the partial voltage between said terminal and said contact and hence the length between said terminal and said contact; and said circuitry, in a second step, enabling both said reference voltage source and said electrical measuring unit to be connected to one of said terminals of the second resistance element and said second sliding contact to measure the resistance value and hence the average temperature of the second resistance element therebetween.
a measuring tube having a measuring span embracing the lengths to be measured;
first and second resistance elements longitudinally located within the measuring tube over the entire measuring span thereof, said elements having terminals at each end thereof;
a slider located within the measuring tube, said slider having first and second sliding contacts sliding along said first and second resistance elements, respectively;
a movable element surrounding said measuring tube for causing movement of said slider located within the measur-ing tube;
a reference voltage source;
an electrical measuring unit; and circuitry enabling, in a first step, said reference voltage source to be connected to the terminals of the first resistance element and the electrical measuring unit to be connected to one of said terminals and to said first sliding contact for measuring the partial voltage between said terminal and said contact and hence the length between said terminal and said contact; and said circuitry, in a second step, enabling both said reference voltage source and said electrical measuring unit to be connected to one of said terminals of the second resistance element and said second sliding contact to measure the resistance value and hence the average temperature of the second resistance element therebetween.
2. Length and temperature measuring apparatus according to claim 1, wherein the resistance elements each comprise resistance wire stretched by a spring.
3. Length and temperature measuring apparatus according to claim 2, wherein the resistance wire is helically wound on a strip of insulating material.
4. Length and temperature measuring apparatus according to claim 1, claim 2 or claim 3, wherein the resistance elements are vertical and lower terminals of the resistance elements are guided to the top of the tube by means of a common guideway and through an upper cap of the measuring tube.
5. Length and temperature measuring apparatus according to claim 1, wherein the measuring tube is made of a metal of high heat conductivity.
6. Length and temperature measuring apparatus according to claim 5, wherein the sliding contacts which engage the resistance elements are connected to a third sliding con-tact which slides along the inner wall of the measuring tube.
7. Length and temperature measuring apparatus according to claim 1, claim 2 or claim 3, wherein the first and second resistance elements consist of a single element, and wherein the first and second sliding contacts consist of a single contact, said circuitry making each of said element and contact function in different ways during said first and second steps.
8. Length and temperature measuring apparatus according to claim 1, claim 2 or claim 3, wherein a calculating device is provided which receives a first signal from the measuring unit, which signal characterizes the partial voltage measured in the first step, and from this calcul-ates the actual position of the slider and records and stores the same, and which receives a second signal from the measuring device which characterizes the partial resis-tance measured in the second step, and from this calculates said average temperature by use of the determined actual position of the slider.
9. Length and temperature measuring apparatus according to claim 1, claim 2 or claim 3, wherein the measuring tube is vertically located in a tank, the movable element is formed as a magnetic float around the measuring tube, and the slider is made of magnetic material and is caused to follow the surface of the fluid by the magnet of the magnetic float.
10. Length and temperature measuring apparatus according to claim 1, claim 2 or claim 3, wherein the measuring tube is formed with a double wall structure and has an insulat-ing material located between the inner and outer walls.
11. Length and temperature measuring apparatus according to claim 1, claim 2 or claim 3, wherein a temperature sensor having an associated temperature measuring circuit is provided at one end of the measuring tube.
12. Length and temperature measuring apparatus according to claim 1, claim 2 or claim 3, wherein a temperature sensor is provided on the slider and is connected to a temperature measuring circuit.
13. Length and temperature measuring apparatus according to claim 1, claim 2 or claim 3, wherein the measuring tube is gas tight.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3016690.6 | 1980-04-28 | ||
| DE3016690A DE3016690C2 (en) | 1980-04-28 | 1980-04-28 | Length and temperature measuring device for tank systems |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1156853A true CA1156853A (en) | 1983-11-15 |
Family
ID=6101365
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000376410A Expired CA1156853A (en) | 1980-04-28 | 1981-04-28 | Length and temperature measuring apparatus for tank installations |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0039420B1 (en) |
| AT (1) | ATE17784T1 (en) |
| CA (1) | CA1156853A (en) |
| DE (1) | DE3016690C2 (en) |
| ZA (1) | ZA812753B (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3124875C2 (en) * | 1981-06-25 | 1983-04-28 | Manfred Ing.(grad.) 4630 Bochum Templin | "Measuring probe" |
| FR2548362B1 (en) * | 1983-06-29 | 1985-11-29 | Jaeger | LIQUID LEVEL ALARM DEVICE WITH RESISTIVE SENSOR |
| ES285250Y (en) * | 1985-02-25 | 1986-04-01 | Jaeger Iberica, S.A. | A TRANSMITTING DEVICE FOR THE LIQUID LEVEL ELECTRICAL SIGNAL IN TANKS |
| AT394273B (en) * | 1985-12-30 | 1992-02-25 | Enfo Grundlagen Forschungs Ag | MEASURING DEVICE FOR A COMPONENT MOVABLE IN A HOUSING |
| FR2601772B1 (en) * | 1986-07-21 | 1991-05-10 | Unimess Messtech Geraete | TEMPERATURE MEASURING PROBE |
| US4726226A (en) * | 1986-09-03 | 1988-02-23 | Mts Systems Corporation | Distance and temperature measuring system for remote locations |
| DE3926552A1 (en) * | 1989-08-11 | 1991-02-14 | Bayerische Motoren Werke Ag | FUEL LEVEL SENSOR FOR FUEL TANK |
| WO1998017974A1 (en) * | 1996-10-18 | 1998-04-30 | Data Instruments, Inc. | Position sensor with magnetic coupling |
| DE102004046780B4 (en) * | 2004-09-27 | 2007-04-26 | Siemens Ag | Method for functional tester of a level sensor |
| CN102901547A (en) * | 2012-09-19 | 2013-01-30 | 樊荣 | Electrical contacted type liquid level meter |
| CN111256033A (en) * | 2020-01-20 | 2020-06-09 | 北京航天试验技术研究所 | Unfolding mechanism for measuring temperature field in liquid hydrogen storage tank |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1182875B (en) * | 1958-03-04 | 1964-12-03 | British Petroleum Co | Temperature measuring device for determining the mean temperature in a liquid tank |
| DE1548903B1 (en) * | 1965-12-02 | 1970-05-06 | Bertram Fab Ernst & Wilhelm | Device for measuring a liquid in a container |
| US3653262A (en) * | 1970-10-22 | 1972-04-04 | Metritake Inc | Temperature and level sensor |
| DE2353171A1 (en) * | 1973-10-24 | 1975-05-07 | Oskar Luehn | Remote acting level indicator for steam generators etc. - has float following magnets contacting resistance wire |
| US4158964A (en) * | 1978-05-10 | 1979-06-26 | The Foxboro Company | Method and apparatus for determining liquid level |
-
1980
- 1980-04-28 DE DE3016690A patent/DE3016690C2/en not_active Expired
-
1981
- 1981-04-09 EP EP81102681A patent/EP0039420B1/en not_active Expired
- 1981-04-09 AT AT81102681T patent/ATE17784T1/en active
- 1981-04-27 ZA ZA00812753A patent/ZA812753B/en unknown
- 1981-04-28 CA CA000376410A patent/CA1156853A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0039420B1 (en) | 1986-01-29 |
| DE3016690A1 (en) | 1981-11-05 |
| ZA812753B (en) | 1982-04-28 |
| ATE17784T1 (en) | 1986-02-15 |
| EP0039420A2 (en) | 1981-11-11 |
| DE3016690C2 (en) | 1986-01-09 |
| EP0039420A3 (en) | 1983-02-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |