WO1999000647A1 - Apparatus for detecting a level of a liquid - Google Patents

Apparatus for detecting a level of a liquid Download PDF

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Publication number
WO1999000647A1
WO1999000647A1 PCT/US1998/004543 US9804543W WO9900647A1 WO 1999000647 A1 WO1999000647 A1 WO 1999000647A1 US 9804543 W US9804543 W US 9804543W WO 9900647 A1 WO9900647 A1 WO 9900647A1
Authority
WO
WIPO (PCT)
Prior art keywords
conductive region
liquid
temperature
level
electrical signal
Prior art date
Application number
PCT/US1998/004543
Other languages
French (fr)
Inventor
Kurt A. Estes
Morris B. Bowers
Original Assignee
Motorola Inc.
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Motorola Inc. filed Critical Motorola Inc.
Priority to AU65459/98A priority Critical patent/AU6545998A/en
Publication of WO1999000647A1 publication Critical patent/WO1999000647A1/en

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/24—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid
    • G01F23/246—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid thermal devices
    • G01F23/247—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid thermal devices for discrete levels
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/24—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid
    • G01F23/241—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid for discrete levels
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/24—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid
    • G01F23/241—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid for discrete levels
    • G01F23/242—Mounting arrangements for electrodes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/24—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid
    • G01F23/246—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid thermal devices
    • G01F23/247—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid thermal devices for discrete levels
    • G01F23/248—Constructional details; Mounting of probes

Definitions

  • This invention relates generally to sensors, and, more particularly, to an apparatus and method for detecting a level of a liquid.
  • Electronic modules such as multi-chip modules and electronic hybrid assemblies such as power amplifiers, as well as other electronic devices, may contain heat sources which require cooling during normal operation. It is known to dispose electronic devices on substrates such as printed circuit boards, which may be flexible or rigid, and immerse the devices in a dielectric liquid such as FluorinertTM perfluorocarbon fluid to keep the heat sources cool.
  • a dielectric liquid such as FluorinertTM perfluorocarbon fluid
  • Float sensors are typically large mechanical devices which may be prone to corrosion or mechanical failure, and are not ideally suited for electronics applications.
  • Optical sensors may also be large, typically expensive relative to other types of sensors, and may not be used with all types of liquids.
  • Liquid conduction sensors are generally reliable only in liquids which conduct electricity, and may not be useful to detect levels of dielectric fluids such as perfluorocarbon fluids .
  • Liquid conduction sensors also may be prohibitively large, and relatively expensive, for widespread use in electronics applications.
  • an apparatus for detecting a level of a liquid which includes a conductive region having a resistance which varies as a function of a temperature of the conductive region, where the conductive region is configured to receive an electrical signal; and a sensor in communication with the conductive region.
  • the sensor is responsive to a change in the resistance to detect a change in the temperature.
  • the conductive region is immersed in the liquid, the electrical signal is applied to the conductive region, the resistance has a first value and the sensor detects a first temperature of the conductive region.
  • the conductive region In a second state, the conductive region is not immersed in the liquid, the electrical signal is applied to the conductive region, the resistance has a second value and the sensor detects a second temperature of the conductive region.
  • the second temperature is greater than the first temperature.
  • FIG. 1 is a two-dimensional view of a liquid-level sensing device in accordance with one embodiment of the present invention.
  • FIG. 2 is a two-dimensional view of a liquid-level sensing device in accordance with another embodiment of the present invention.
  • FIG. 1 is a two-dimensional view of a liquid level sensing device 10 according to one embodiment of the present invention.
  • Device 10 includes a substrate 12 having one or more conductive regions 14 disposed thereon (one conductive region 14 is shown) .
  • Substrate 12 may be a flexible material such as a KaptonTM flexible sheet available from DuPont .
  • Other suitable flexible materials include NomexTM and MylarTM materials, available from DuPont, as well as other materials such as silicone rubber or Teflon.
  • substrate 12 may be rigid, composed, for example, of plastic or ceramic.
  • substrate 12 may include printed wiring and other electronics thereon.
  • device 10 is inside container 20 and conductive region 14 is immersed in a liquid 16 having a first level 18.
  • Liquid 16 may be a perfluorocarbon fluid such as FluorinertTM perfluorocarbon fluid, available from 3M Corp., or may be another dielectric coolant or any other liquid such as water or antifreeze.
  • Conductive region 14 may be a material such as copper or another conductive material having a resistance which varies as a function of a temperature of region 14. Region 14 is preferably in communication with a device 22 supplying an electrical signal, and with a sensor 24. Conductive region 14 may be sized to produce a heat flux that will induce boiling of liquid 16. The heat flux required to produce boiling on a particular surface will depend on an amount of power dissipated by conductive region 14 and by a boiling point of liquid 16, and may be determined using well- known heat transfer equations. A thermally conductive substantially dielectric material such as an epoxy may also be disposed on conductive region 14 if, for example, fluid 16 is conductive.
  • electronic modules 45 which may include one or more heat sources such as NPN silicon radio frequency (RF) power transistors available from RF.
  • RF radio frequency
  • Electronic modules 45 are shown disposed on substrate 12 and also disposed on another substrate 13.
  • Substrate 13 may be constructed of similar materials as substrate 12, and may include printed wiring and other electronics thereon.
  • an electrical signal which is preferably a small constant amount of direct current (or voltage) , but may be a periodic signal or another type of signal, is passed through conductive region 14.
  • the heat generated by conductive region 14 is dissipated by the surroundings of region 14, which is liquid 16 when liquid 16 is at first level 18.
  • conductive region 14 will be cooled by a change in phase associated with boiling when region 14 is sized to produce a heat flux that will induce boiling.
  • a temperature of region 14 will be approximately the boiling point of liquid 16.
  • a conductive region having dimensions of 0.5 millimeters by 5.0 millimeters dissipating 0.2 Watts of heat has been measured to have a temperature difference of 280 degrees Celsius between a first level and a second level of FluorinertTM perfluorocarbon liquid, where at the first level the conductive region is completely immersed in the liquid and at the second level the conductive region is not immersed in the liquid.
  • sensor 24 may be an ammeter or a voltmeter in communication with a general purpose computer, which may be programmed to generate an alarm (not shown) upon detecting a change in voltage (or current) meeting a predetermined threshold.
  • a separate computer may not be necessary, as any processor or other device capable of comparison and/or detection, including devices being cooled by liquid 16, may be used.
  • Alarms may be visible or audible or a combination of visible and audible.
  • electronic modules 45 may be shut down.
  • FIG. 2 is a liquid level sensing device 10 constructed according to another aspect of the present invention.
  • conductive region 14 is serpentine-shaped, although other shapes are possible.
  • a small constant amount of current (or voltage) is preferably passed through conductive region 14 via electrical signal supply 22.
  • electrical signal supply 22 At first level 18, a particular an amount of heat generated by the immersed area of conductive region
  • sensor 24 may be similar in construction and operation to sensor 24 described in connection with FIG. 1.
  • sensor 24 may generate an alarm, which may be visible or audible or a combination of visible and audible.
  • electronic module 45 may be shut down.
  • the serpentine shape of region 45 may allow multiple alarms to be triggered and/or provide a more precise measurement of the level of liquid 16.
  • the various aspects of the apparatuses and methods described herein may be used to monitor a level of a liquid without moving parts .
  • the apparatuses may be mounted directly to a substrate containing electronic devices to be cooled by the liquid, and combining fluid cooling with electronics may reduce cost and complexity often associated with fluid delivery systems.
  • the aspects of the present invention described herein also result in an inexpensive, robust apparatus having a compact size which is sensitive to small differences in liquid levels.
  • any conventional means for providing flow of a coolant may be used in conjunction with the described embodiments of the present invention, and that more than one apparatus may be connected to a single source of coolant or that one or more sources of coolant may be connected to a single apparatus, for example, for redundancy purposes. It is also contemplated that either an open-loop or a closed-loop fluid flow may be used with the various aspects of the present invention, and that the conductive region may be cooled via two-phase or single-phase heat transfer.
  • the various embodiments of the present invention may also be used in other applications not related to the cooling of electronic devices, such as in fuel tanks, washing machines, dishwashers and other applications where monitoring of a liquid level is desirable. It is contemplated that wherever sealing and/or fastening may be required, numerous methods and materials may be used. For example, fasteners such as screws, compliant gaskets, ultrasonic welding, brazing, soldering or swaging may be utilized. And it will be understood that any combination of the aspects of the present invention may be used together on a substrate.

Landscapes

  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)

Abstract

The apparatus includes a conductive region (14) configured to receive an electrical signal (22) and a sensor (24) in communication with the conductive region. The sensor is responsive to a change in a temperature of the conductive region. In a first state, theconductive region is immersed in the liquid (16) to a first level (18), the electrical signal is applied to the conductive region and the temperature has a first value based on the first level. In a second state, the conductive region is immersed in the liquid to a second level (19), the electrical signal is applied to the conductive region and the temperature has a second value based on the second level.

Description

APPARATUS FOR DETECTING A LEVEL OF A LIQUID
Field of the Invention
This invention relates generally to sensors, and, more particularly, to an apparatus and method for detecting a level of a liquid.
Background of the Invention
Electronic modules such as multi-chip modules and electronic hybrid assemblies such as power amplifiers, as well as other electronic devices, may contain heat sources which require cooling during normal operation. It is known to dispose electronic devices on substrates such as printed circuit boards, which may be flexible or rigid, and immerse the devices in a dielectric liquid such as Fluorinert™ perfluorocarbon fluid to keep the heat sources cool. One example of an immersion cooling technique for electronics which uses a perfluorocarbon fluid is described in U.S. Patent No. 4,590,538.
It may be desirable to monitor a level of the liquid in which electronic devices are immersed and to be able to quickly detect changes in the liquid level to prevent serious damage to electronic devices. Various well-known techniques and devices are available for measuring liquid levels, including but not limited to float sensors, optical sensors and liquid conduction sensors. Float sensors are typically large mechanical devices which may be prone to corrosion or mechanical failure, and are not ideally suited for electronics applications. Optical sensors may also be large, typically expensive relative to other types of sensors, and may not be used with all types of liquids. Liquid conduction sensors are generally reliable only in liquids which conduct electricity, and may not be useful to detect levels of dielectric fluids such as perfluorocarbon fluids .
Liquid conduction sensors also may be prohibitively large, and relatively expensive, for widespread use in electronics applications.
There is therefore a need for an apparatus and method for detecting a level of a liquid which is compact, which has no moving parts, which is sensitive to small differences in liquid levels, which may be integrated into a circuit board and which is simple and inexpensive to manufacture.
Summary of the Invention
According to an aspect of the present invention, the foregoing needs are addressed by an apparatus for detecting a level of a liquid which includes a conductive region having a resistance which varies as a function of a temperature of the conductive region, where the conductive region is configured to receive an electrical signal; and a sensor in communication with the conductive region. The sensor is responsive to a change in the resistance to detect a change in the temperature. In a first state, the conductive region is immersed in the liquid, the electrical signal is applied to the conductive region, the resistance has a first value and the sensor detects a first temperature of the conductive region. In a second state, the conductive region is not immersed in the liquid, the electrical signal is applied to the conductive region, the resistance has a second value and the sensor detects a second temperature of the conductive region. The second temperature is greater than the first temperature. Advantages of the present invention will become readily apparent to those skilled in the art from the following description of the preferred embodiment (s) of the invention which have been shown and described by way of illustration. As will be realized, the invention is capable of other and different embodiments, and its details are capable of modifications in various respects . Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
Brief Description of the Drawings
FIG. 1 is a two-dimensional view of a liquid-level sensing device in accordance with one embodiment of the present invention.
FIG. 2 is a two-dimensional view of a liquid-level sensing device in accordance with another embodiment of the present invention.
Detailed Description of the Preferred Embodiments
Turning now to the drawings, wherein like numerals designate like components, FIG. 1 is a two-dimensional view of a liquid level sensing device 10 according to one embodiment of the present invention.
Device 10 includes a substrate 12 having one or more conductive regions 14 disposed thereon (one conductive region 14 is shown) . Substrate 12 may be a flexible material such as a Kapton™ flexible sheet available from DuPont . Other suitable flexible materials include Nomex™ and Mylar™ materials, available from DuPont, as well as other materials such as silicone rubber or Teflon. Alternatively, substrate 12 may be rigid, composed, for example, of plastic or ceramic. In addition, substrate 12 may include printed wiring and other electronics thereon. As shown, device 10 is inside container 20 and conductive region 14 is immersed in a liquid 16 having a first level 18. Liquid 16 may be a perfluorocarbon fluid such as Fluorinert™ perfluorocarbon fluid, available from 3M Corp., or may be another dielectric coolant or any other liquid such as water or antifreeze.
Conductive region 14 may be a material such as copper or another conductive material having a resistance which varies as a function of a temperature of region 14. Region 14 is preferably in communication with a device 22 supplying an electrical signal, and with a sensor 24. Conductive region 14 may be sized to produce a heat flux that will induce boiling of liquid 16. The heat flux required to produce boiling on a particular surface will depend on an amount of power dissipated by conductive region 14 and by a boiling point of liquid 16, and may be determined using well- known heat transfer equations. A thermally conductive substantially dielectric material such as an epoxy may also be disposed on conductive region 14 if, for example, fluid 16 is conductive.
Also shown within container 20 and immersed in liquid 16 are electronic modules 45, which may include one or more heat sources such as NPN silicon radio frequency (RF) power transistors available from
Motorola. Of course, other heat sources may be present, such as differently-configured power transistors and completely different electronic components, including but not limited to passive components, all types of integrated circuits, multi-chip modules and hybrid circuits. Electronic modules 45 are shown disposed on substrate 12 and also disposed on another substrate 13. Substrate 13 may be constructed of similar materials as substrate 12, and may include printed wiring and other electronics thereon. During operation of device 10, an electrical signal, which is preferably a small constant amount of direct current (or voltage) , but may be a periodic signal or another type of signal, is passed through conductive region 14. The heat generated by conductive region 14 is dissipated by the surroundings of region 14, which is liquid 16 when liquid 16 is at first level 18. At first level 18, conductive region 14 will be cooled by a change in phase associated with boiling when region 14 is sized to produce a heat flux that will induce boiling. Thus, at first level 18, a temperature of region 14 will be approximately the boiling point of liquid 16.
As level 18 of liquid 16 goes down to level 19, due to leakage, for example, conductive region 14 will no longer be completely immersed in liquid 16. Then, the heat generated by region 14 will be dissipated by natural convection and radiation. Because phase change heat transfer is more efficient than natural convection and radiation, region 14 ' s temperature will rise when it is no longer completely immersed in liquid 16.
For example, a conductive region having dimensions of 0.5 millimeters by 5.0 millimeters dissipating 0.2 Watts of heat has been measured to have a temperature difference of 280 degrees Celsius between a first level and a second level of Fluorinert™ perfluorocarbon liquid, where at the first level the conductive region is completely immersed in the liquid and at the second level the conductive region is not immersed in the liquid.
The temperature change of region 14 caused by liquid 16 moving from first level 18 to second level 19 may be detected by sensor 24. Because the temperature increase changes the resistance of conductive region 14, and consequently the voltage (or current) necessary to maintain the constant current (or voltage) , sensor 24 may be an ammeter or a voltmeter in communication with a general purpose computer, which may be programmed to generate an alarm (not shown) upon detecting a change in voltage (or current) meeting a predetermined threshold. Of course, a separate computer may not be necessary, as any processor or other device capable of comparison and/or detection, including devices being cooled by liquid 16, may be used. Alarms may be visible or audible or a combination of visible and audible. In response to one or more alarms, electronic modules 45 may be shut down.
FIG. 2 is a liquid level sensing device 10 constructed according to another aspect of the present invention. As shown, conductive region 14 is serpentine-shaped, although other shapes are possible. During operation of device 10, a small constant amount of current (or voltage) is preferably passed through conductive region 14 via electrical signal supply 22. At first level 18, a particular an amount of heat generated by the immersed area of conductive region
14 is dissipated by liquid 16, and another amount of heat generated by the exposed area of conductive region 14 is dissipated by natural convection and radiation. As liquid 16 goes down to level 19, less of conductive region 14 will be immersed in liquid 16. Then, more the heat generated by exposed areas of region 14 will be dissipated by natural convection and radiation, and region 14 ' s temperature, and therefore the resistance over the exposed portion of region 14, will rise by a detectable amount.
The temperature change of region 14 caused by liquid 16 moving from first level 18 to second level 19 is detected by sensor 24, which may be similar in construction and operation to sensor 24 described in connection with FIG. 1. Upon detecting a predetermined temperature change, sensor 24 may generate an alarm, which may be visible or audible or a combination of visible and audible. In response to one or more alarms, electronic module 45 may be shut down. The serpentine shape of region 45 may allow multiple alarms to be triggered and/or provide a more precise measurement of the level of liquid 16.
Thus, the various aspects of the apparatuses and methods described herein may be used to monitor a level of a liquid without moving parts . The apparatuses may be mounted directly to a substrate containing electronic devices to be cooled by the liquid, and combining fluid cooling with electronics may reduce cost and complexity often associated with fluid delivery systems. The aspects of the present invention described herein also result in an inexpensive, robust apparatus having a compact size which is sensitive to small differences in liquid levels.
It is contemplated that any conventional means for providing flow of a coolant may be used in conjunction with the described embodiments of the present invention, and that more than one apparatus may be connected to a single source of coolant or that one or more sources of coolant may be connected to a single apparatus, for example, for redundancy purposes. It is also contemplated that either an open-loop or a closed-loop fluid flow may be used with the various aspects of the present invention, and that the conductive region may be cooled via two-phase or single-phase heat transfer.
The various embodiments of the present invention may also be used in other applications not related to the cooling of electronic devices, such as in fuel tanks, washing machines, dishwashers and other applications where monitoring of a liquid level is desirable. It is contemplated that wherever sealing and/or fastening may be required, numerous methods and materials may be used. For example, fasteners such as screws, compliant gaskets, ultrasonic welding, brazing, soldering or swaging may be utilized. And it will be understood that any combination of the aspects of the present invention may be used together on a substrate.
It will be apparent that other and further forms of the invention may be devised without departing from the spirit and scope of the appended claims and their equivalents, and it will be understood that this invention is not to be limited in any manner to the specific embodiments described above, but will only be governed by the following claims and their equivalents.

Claims

Clai sWe claim:
1. An apparatus for detecting a level of a liquid, the apparatus comprising: a conductive region having a resistance which varies as a function of a temperature of the conductive region, the conductive region configured to receive an electrical signal; and a sensor in communication with the conductive region, the sensor responsive to a change in the resistance to detect a change in the temperature, in a first state, the conductive region immersed in the liquid, the electrical signal applied to the conductive region, the resistance having a first value and the sensor detecting a first temperature of the conductive region, and in a second state, the conductive region not immersed in the liquid, the electrical signal applied to the conductive region, the resistance having a second value and the sensor detecting a second temperature of the conductive region, the second temperature greater than the first temperature.
2. The apparatus according to claim 1, wherein the electrical signal comprises one of a voltage and a current .
3. The apparatus according to claim 2, wherein the electrical signal is constant.
4. The apparatus according to claim 1, wherein the liquid comprises a dielectric liquid.
5. The apparatus according to claim 4, wherein the dielectric liquid comprises a perfluorocarbon liquid.
6. The apparatus according to claim 1, wherein in the first state, the liquid boils proximate the conductive region.
7. The apparatus according to claim 6, wherein the boiling of the liquid cools the conductive region.
8. The apparatus according to claim 6, wherein the first temperature is approximately a boiling point of the liquid.
9. The apparatus according to claim 1, wherein the conductive region comprises copper.
10. The apparatus according to claim 1, further comprising a thermally-conductive substantially- dielectric material at least partially covering the conductive region.
PCT/US1998/004543 1997-06-27 1998-03-09 Apparatus for detecting a level of a liquid WO1999000647A1 (en)

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Application Number Priority Date Filing Date Title
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US88397697A 1997-06-27 1997-06-27
US08/883,976 1997-06-27

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3308665A (en) * 1966-02-18 1967-03-14 Trans Sonics Inc Fluid depth indicator
US4129848A (en) * 1975-09-03 1978-12-12 Raytheon Company Platinum film resistor device
US4521373A (en) * 1982-08-23 1985-06-04 General Electric Company Liquid level sensor
US4567762A (en) * 1981-03-10 1986-02-04 Telefunken Electronic Gmbh Thermoelectric level detector and a method for its manufacture
US5201233A (en) * 1992-01-29 1993-04-13 General Motors Corporation Retainer assembly with dished retaining ring
US5552371A (en) * 1994-05-17 1996-09-03 Industrial Technology Research Institute YBA CUO-type superconducting material based apparatus for auto-filling liquid nitrogen
US5719332A (en) * 1994-09-28 1998-02-17 Vdo Adolf Schindling Ag Process and system for operating a level sensor

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3308665A (en) * 1966-02-18 1967-03-14 Trans Sonics Inc Fluid depth indicator
US4129848A (en) * 1975-09-03 1978-12-12 Raytheon Company Platinum film resistor device
US4567762A (en) * 1981-03-10 1986-02-04 Telefunken Electronic Gmbh Thermoelectric level detector and a method for its manufacture
US4521373A (en) * 1982-08-23 1985-06-04 General Electric Company Liquid level sensor
US5201233A (en) * 1992-01-29 1993-04-13 General Motors Corporation Retainer assembly with dished retaining ring
US5552371A (en) * 1994-05-17 1996-09-03 Industrial Technology Research Institute YBA CUO-type superconducting material based apparatus for auto-filling liquid nitrogen
US5719332A (en) * 1994-09-28 1998-02-17 Vdo Adolf Schindling Ag Process and system for operating a level sensor

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