Fiber optic thermal anemometer

• US 4,621,929 A
• Filed: 10/12/1983
• Issued: 11/11/1986
• Est. Priority Date: 10/12/1983
• Status: Expired due to Fees

• Current Assignee: Luxtron Corp. (Advanced Energy Industries, Inc. (China))
• Original Assignee: Luxtron Corp. (Advanced Energy Industries, Inc. (China))
• Inventors: Phillips, Stephen R.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Scanlon, Patrick R.
• Application Number:
  US06/541,384
• Time in Patent Office: 1,126 Days
• Field of Search: 374/43, 374/44, 374/45, 374/54, 374/130, 374/131, 374/141, 374/142, 374/143, 374/164, 374/17-20, 356/43, 356/44, 250/458.1, 250/461.1, 250/337, 250/227, 250/356.1, 250/357.1, 250/361 R, 73/861.05, 73/861.22, 73/292, 73/295, 73/700, 73/714, 219/553, 219/10.55 R, 219/10.55 A, 34/4, 165/154, 165/155
• US Class Current: 374/43
• CPC Class Codes: A61B 5/028 by thermo-dilution
• CPC Class Codes: G01F 1/3273 for detecting fluid speed oscillations by thermal sensors
• CPC Class Codes: G01F 1/68 by using thermal effects
• CPC Class Codes: G01F 1/6884 making use of temperature dependence of optical properties
• CPC Class Codes: G01F 1/6986 with pulsed heating, e.g. dynamic methods
• CPC Class Codes: G01F 23/22 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 involving the use of floats G01F23/30
• CPC Class Codes: G01K 11/3213 using changes in luminescence, e.g. at the distal end of the fibres
• CPC Class Codes: G01L 11/002 by thermal means, e.g. hypsometer
• CPC Class Codes: G01L 21/10 by measuring variations in the heat conductivity of the medium, the pressure of which is to be measured
• CPC Class Codes: G01N 25/18 by investigating thermal conductivity by calorimetry G01N25/20; by measuring change of resistance of an electrically-heated body G01N27/18

Abstract

To measure the heat transfer coefficient of a sample, an element with temperature sensitive optical properties is placed in contact or implanted in the sample. The element is heated or cooled. The temperature difference between the element and the unheated sample and the rate of heating or cooling indicate the heat transfer coefficient of the sample. In one embodiment, the element is heated or cooled at a constant rate. The heat transfer coefficient of the sample is then inversely related to the difference in temperature between the element and the unheated sample. Alternatively, the element may be heated or cooled at such a rate that the temperature difference between the element and the unheated sample remains substantially constant. The heat transfer coefficient of the sample then varies directly with the rate of heating or cooling. The heat transfer coefficient of a sample is a measure of its composition and other physical properties. The composition of gasses, liquids, the presence of bubbles in a liquid, and fluid levels can be detected by the optical technique. Pressure and flow rates of fluids can also be detected. The technique can be used also to more accurately measure the thermal conductivity and temperature of small objects with small heat capacities.

Claims

1. An apparatus for testing the heat transfer coefficient of a sample in an environment comprising:

an element having temperature sensitive optical properties and being adapted to contact or to be implanted in the sample;

radiation heat transfer means for directly supplying heat to the element;

means for transmitting electromagnetic radiation to said element; and

means for optically detecting said temperature sensitive optical properties of the element to test the heat transfer coefficient of the sample, whereby the difference between the temperature of the element and that of the environment is an indication of the heat transfer coefficient of the sample.

2. The apparatus of claim 1, further comprising a length of optical fiber having a first and a second end, wherein said element is held at the first end of said fiber and wherein said transmitting means and detecting means are held at the second end of the fiber.

4. The apparatus of claims 1 or 3, wherein the radiation heat transfer means supplies heat at a substantially constant rate from said sample so that the heat transfer coefficient of the sample is inversely related to the difference between the temperature of the element and the ambient temperature.

6. The apparatus of claims 1 or 3, wherein the radiation heat transfer means supplies heat at such rate that the difference between the temperature of the element in contact with the sample and the ambient temperature is substantially constant, so that the heat transfer coefficient of the sample is proportional to the rate of heating.

7. The apparatus of claim 6, wherein the heat capacity of the sample is much greater than that of the element and the rate of heating of the sample is such that the ambient temperature of the sample is substantially unaltered thereby so that when such ambient temperature remains substantially constant, the temperature of the element is maintained substantially constant.

8. The apparatus of claims 1 or 3 wherein the temperature sensitive element includes a luminescent material in its composition.

9. The apparatus of claim 8, further comprising means for detecting the intensities of radiation at two distinct wavelengths from the luminescent material in said element to determine the temperature of the temperature sensitive element.

10. The apparatus of claim 8, further comprising means for detecting the luminescent response of the luminescent material in said element over time to determine the temperature of the temperature sensitive element.

11. The apparatus of claim 10, wherein said luminescent response detecting means detects a parameter indicative of the luminescent decay time of the luminescent material.

12. The apparatus of claims 1 or 3 wherein the temperature sensitive element is a liquid crystal sensor whose light reflectance is a function of its temperature.

13. The apparatus of claims 1 or 3 wherein the temperature sensitive element includes a semiconductor material which absorbs light energy as a function of temperature.

14. The apparatus of claims 1 or 3 wherein the temperature sensitive element includes a luminescent material and wherein said radiation heat transfer means comprises:

an optical filter that absorbs electromagnetic radiation, said filter placed in heat conductive relationship with the element; and

source for supplying electromagnetic radiation to said filter for heating the elements by heating the optical filter.

15. The apparatus of claim 14 wherein the optical filter absorbs electromagnetic radiation in a manner that does not interfere substantially with the transmission of electromagnetic radiation by the transmitting means to said element.

16. The apparatus of claim 14 wherein the optical filter and the temperature sensitive element is one member comprising a heat absorbing medium into which a temperature sensitive material is dispersed.

17. The apparatus of claim 16 wherein the temperature sensitive material is phosphor.

18. The apparatus of claims 2 or 3 wherein the temperature sensitive element includes a luminescent material and wherein said radiation heat transfer means comprises:

an optical filter that absorbs light in a manner which does not interfere substantially with the transmission of electromagnetic radiation to said element by the transmitting means and with the optical detection of the temperature of the element, said filter placed between said first end and the element and in heat conductive relationship with the element; and

source for supplying light to said second end, said light being transmitted by the optical fiber to its first end for heating the element by heating the optical filter.

19. The apparatus of claim 18 wherein the optical filter absorbs light within a frequency range which does not overlap with the frequencies of radiation emitted by the element and of radiation transmitted by the transmitting means.

20. The apparatus of claim 19 wherein the optical filter absorbs infrared light.

21. The apparatus of claims 2 or 3 wherein the temperature sensitive element includes phosphor in its composition and wherein said radiation heat transfer means comprises a source for supplying ultraviolet light to said second end which is then transmitted by the optical fiber to the phosphor in the temperature sensitive element to heat the element.

22. The apparatus of claims 1 or 3 wherein said radiation heat transfer means comprises:

a heating member which absorbs radio frequency electromagnetic waves, said heating member being placed in heat conductive relationship with said element; and

means for supplying radio frequency electromagnetic waves to said heating member to supply heat to said element.

23. The apparatus of claims 1 or 3 wherein said radiation heat transfer means comprises:

a heating member which absorbs ultrasonic waves, said heating member being placed in heat conductive relationship with said element; and

a source for supplying ultrasonic waves to said heating member.

24. The apparatus of claims 1 or 3 wherein said radiation heat transfer means comprises means for supplying heat to a medium surrounding the element.

3. A probe apparatus for testing the heat transfer coefficient of a sample in an environment, comprising:

a length of optical fiber having a first and a second end; and

an element held in optical communication with the first end of said optical fiber, said element having temperature sensitive optical properties and being adapted to contact or to be implanted in the sample, wherein the second end of the optical fiber is adapted to be connected to (a) a radiation heat transfer means for directly heating the element, (b) means for transmitting electromagnetic radiation to said element and (c) means for detecting the temperature of the element optically, in order to test the heat transfer coefficient of the sample whereby the difference between the temperature of the element and that of the environment is an indication of the heat transfer coefficient.

5. The apparatus of claim 3, wherein the heat capacity of the sample is much greater than that of the element and the rate of heating of the sample is such that the ambient temperature of a large portion of the sample is substantially unaltered thereby.

25. A probe apparatus for testing the heat transfer coefficient of a sample in an environment, comprising:

a length of optical fiber;

an element held in optical communication with a first end of said optical fiber, said element having temperature sensitive optical properties and being adapted to contact or to be implanted in the sample; and

radiation heat transfer means for directly supplying heat to the element to test the heat transfer coefficient of the sample whereby the difference between the temperature of the element and that of the environment is an indication of the heat transfer coefficient of the sample.

69. The apparatus of claims 25, 30, 34, 38, 42, 48, 51, 55, 57 or 66 wherein the temperature sensitive element includes phosphor in its composition.

70. The apparatus of claim 69 further comprising means for detecting the intensities of radiation at two distinct wavelengths from the phosphor in said element to determine the temperature of the temperature sensitive element.

71. The apparatus of claim 69 further comprising means for detecting the luminescent response of the phosphor in said element over time to determine the temperature of the temperature sensitive element.

72. The apparatus of claim 71, wherein said luminescent response detecting means detects a parameter related to the luminescent decay time of the phorphor.

73. The apparatus of claims 25, 30, 34, 42, 48, 51, 55, 57 or 66 wherein the temperature sensitive element includes phosphor in its composition and wherein said radiation heat transfer means comprises:

an optical filter that absorbs infrared light but transmits light emitted by the phosphor upon excitation, said filter placed between said first end and the element and in heat conductive relationship with the element; and

infrared light source for supplying infrared light to said second end which is then transmitted by the optic fiber to its first end for heating the element by heating the optical filter.

78. The probe apparatus of claim 25 further comprises means at the second end of the optic fiber for exciting said temperature sensitive element.

26. An apparatus for testing the heat transfer coefficient of a sample in an environment comprising:

a length of optical fiber;

an element held in optical communication with one end of said fiber, said element having temperature sensitive optical properties and being adapted to contact or to be implanted in the sample;

radiation heat transfer means for directly supplying heat to the element;

means at the other end of the fiber for transmitting electromagnetic radiation to said element; and

means at the other end of the fiber for optically detecting said temperature sensitive optical properties of the element to test the heat transfer coefficient of the sample whereby the difference between the temperature of the element and that of the environment is an indication of the heat transfer coefficient of the sample.

27. An apparatus for testing the thermal heat transfer coefficient of a sample in an environment comprising:

a first length of optical fiber;

a temperature sensitive element held at a first end of said optical fiber, said element having temperature sensitive luminescent properties and being adapted to contact or to be implanted in the sample;

radiation heat transfer means for directly supplying heat to the element;

means at the second end of the optical fiber for exciting said temperature sensitive element; and

means at said second end of the optical fiber for optically detecting the temperature sensitive luminescent properties of said element to test the heat transfer coefficient of the sample whereby the difference between the temperature of the element and that of the environment is an indication of the heat transfer coefficient of the sample.

28. The apparatus of claim 27 wherein said element includes phosphor in its composition and wherein said means for exciting said temperature sensitive element comprises a source of ultraviolet light.

29. The apparatus of claim 28, wherein said radiation heat transfer means comprises an infrared light source, said apparatus further comprising four additional optical fibers in optical communication with said first length of optical fiber, the four additional lengths of optical fibers being so spatially oriented that a first additional optic fiber is used to transmit ultraviolet light from the exciting means to said element, a second additional optical fiber transmits infrared light from the infrared light source to said element, a third and a fourth additional optical fiber for transmitting the electromagnetic transmission from said element to detectors for detecting the intensities of radiation at two distinct wavelengths from the phosphor in said element.

30. An apparatus for measuring the flow rate of a fluid comprising:

a length of optical fiber;

a temperature sensitive element held at a first end of said optical fiber, said element having temperature sensitive luminescent properties and being adapted to be placed in the flowing fluid;

radiation heat transfer means for directly supplying heat to the element;

means at the second end of the optical fiber for exciting said temperature sensitive element; and

means at the second end of the optical fiber for detecting electromagnetic radiation emitted by said element to indicate the flow rate of the fluid whereby the difference between the temperature of the element and that of the unheated fluid is an indication of the flow rate.

31. The apparatus of claim 30 wherein the radiation heat transfer means supplies heat to the element at a substantially constant rate so that the flow rate of the fluid varies inversely with the difference in temperature between the element and the fluid thermally unaffected by the radiation heat transfer means.

32. The apparatus of claim 30 wherein the radiation heat transfer means supplies heat at such a rate that the difference in temperature between the element and the fluid thermally unaffected by the radiation heat transfer means remains substantially constant so that the flow rate of the fluid varies directly with the rate of heating of the element.

59. The apparatus of claims 31, 35, 43, 49, 52 or 58 further comprising means for measuring the temperature of the thermally unaffected fluid.

60. The apparatus of claim 59 wherein said temperature measuring means comprises:

a length of a second optical fiber;

a second element held at one end of said second optical fiber, said second element having temperature sensitive luminescent properties and being adapted to be placed in the fluid at a location substantially unaffected by the heating by the radiation heat transfer means;

means at the other end of the optical fiber for exciting said second element; and

means at said other end of the fiber for detecting the electromagnetic radiation emitted by said second element to determine the temperature of the thermally unaffected fluid.

61. The apparatus of claims 31, 35, 43, 49, 52 or 58 further comprising means for turning the radiation heat transfer means on and off periodically, so that the radiation detected by the detecting means at a time during which the radiation heat transfer means is on indicates the temperature of the element when it is heated, and the radiation detected at a selected time after the radiation heat transfer means is turned off indicates the temperature of the thermally unaffected fluid at such time.

62. The apparatus of claim 61 wherein said means for turning on and off the radiation heat transfer means is adapted to turn on and off the radiation heat transfer means at a selected rate that corresponds to the rapidity of temperature variations of the fluid thermally unaffected by the radiation heat transfer means.

64. The apparatus of claims 32, 36, 44, 50 or 63 wherein the radiation heat transfer means includes a control means comprising:

means for measuring the temperature of the thermally unaffected fluid; and

means responsive to the difference between the temperature of the element and that of the thermally unaffected fluid for changing, when required, the rate of heating so that such difference remains substantially constant.

74. The apparatus of claims 30, 34, 38, 42, 48, 51, 55, 66 or 68 wherein said element includes phosphor in its composition and wherein said means for exciting said temperature sensitive element comprises a source of ultraviolet light.

75. The apparatus of claim 74, wherein said radiation heat transfer means comprises an infrared light source, said apparatus further comprising four additional lengths of optical fibers in optical communication with said length of optical fiber, the four additional lengths of optical fibers being so spatially oriented that a first additional optical fiber is used to transmit ultraviolet or visible light from the exciting means to said element, a second additional optical fiber transmits infrared light from the infrared light source to said optical filter, a third and a fourth additional optical fiber for transmitting the electromagnetic transmission from said element to detectors for detecting the intensities of radiation at two distinct wavelengths from the phosphor in said element.

33. A method for measuring the flow rate of a fluid by means of an element having temperature sensitive luminescent properties, said method comprising:

placing the temperature sensitive element in the flowing fluid;

directly supplying heat to the element;

exciting said temperature sensitive element to luminescence;

detecting the electromagnetic radiation emitted by said element to detect the temperature of the element; and

detecting the temperature of the unheated fluid so that the difference between the temperature of the element and that of the unheated fluid is an indication of the flow rate of the fluid.

34. An apparatus for measuring the flow rate of a fluid comprising:

a length of optical fiber;

a temperature sensitive element held at one end of said fiber optic, said element having temperature sensitive luminescent properties and being adapted to be placed in the flowing fluid;

a vortex generating element also placed in the flowing fluid but at a location upstream relative to said element so that vortices generated thereby will come into contact with the element;

radiation heat transfer means for directly supplying heat to the element;

means at a second end of the optical fiber for exciting said temperature sensitive element; and

means at a second end of the optical fiber for detecting electromagnetic radiation emitted by said element to determine the frequency of generation of vortices which indicates the flow rate of the fluid.

35. The apparatus of claim 34 wherein the radiation heat transfer means supplies heat to the element at a substantially constant rate so that when the vortex comes into contact with the first end of said fiber, the higher flow rate of the vortex will cause the temperature of said element to fluctuate so that the frequency of such temperature fluctuations will indicate the frequency of generation of the vortices.

36. The apparatus of claim 34 wherein the radiation heat transfer means supplies heat at such a rate that the difference in temperature between the element and the fluid thermally unaffected by the radiation heat transfer means remains substantially constant so that when a vortex reaches the first end of said fiber, the high flow rate of the fluid at the vortic will cause the rate of heat supplied to the element to increase momentarily so that the frequency of such momentary increases in the heat transfer rate will indicate the frequency of generation of the vortices.

37. A method for measuring the flow rate of a fluid by means of an element having temperature sensitive luminescent properties and a vortex generating element, said method comprising:

placing the temperature sensitive element in the flowing fluid;

placing the vortex generating element in the flowing fluid at a location upstream relative to said element so that vortices generated thereby will come into contact with the element;

directly supplying heat to the element;

exciting said temperature sensitive element to luminescence; and

detecting the electromagnetic radiation emitted by said element to determine the frequency of generation of vortices which indicates the flow rate of the fluid.

38. An apparatus for measuring the flow rate of a fluid comprising:

a length of optical fiber;

a temperature sensitive element held at one end of said fiber, said element having temperature sensitive luminescent properties and being adapted to be placed in the flowing fluid;

radiation heat transfer means for supplying heat to a bolus of fluid at a known distance upstream from said element;

means at a second end of the optical fiber for exciting said temperature sensitive element; and

means at said second end of the optical fiber for detecting electromagnetic radiation emitted by said element to determine the time of arrival and temperature differences of said bolus of fluid at the element thereby also determining the flow rate of the fluid wherein the radiation heat transfer means comprises means for heating a portion of the optical fiber between the first and second ends, said portion being placed upstream and at a known distance from said element.

39. The apparatus of claim 38 wherein said means for heating a portion of the optical fiber comprises:

an optical filter that absorbs electromagnetic radiation but transmits at least some light emitted by said element upon excitation, said filter placed between said first and second ends of the optical fiber; and

source for supplying electromagnetic radiation to said second end of the fiber for heating the optical filter.

40. An apparatus for measuring the flow rate of a fluid comprising:

a length of optical fiber;

a temperature sensitive element held at one end or said fiber, said element having temperature sensitive luminescent properties and being adapted to be placed in the flowing fluid;

a radiation heat transfer means for supplying heat to a bolus of fluid at a known distance upstream from said element;

means at a second end of the optical fiber for exciting said temperature sensitive element and;

means at said second end of the optical fiber for detecting electromagnetic radiation emitted by said element to determine the time of arrival and temperature differences of said bolus of fluid at the element thereby also determining the flow rate of the fluid, wherein said radiation transfer means comprises;

a length of a second optical fiber adapted to be placed in the fluid upstream from said element;

an optical filter that absorbs electromagnetic radiation, said filter being implanted in said second optic fiber so that heating of the filter will cause heat to be transferred between the filter and the fluid surrounding the second optical fiber; and

source for supplying a pulse of electromagnetic radiation to said second optical fiber for heating the filter momentarily so that the bolus of fluid surrounding the filter will be heated before it reaches said element.

41. A method for measuring the flow rate of a fluid by means of a length of optical fiber and an element having temperature sensitive luminescent properties placed at one end of the optical fiber, said method comprising:

placing the temperature sensitive element and said one end of the optical fiber in the flowing fluid;

directly supplying heat to a portion of the optical fiber for heating a bolus of fluid at a known distance upstream from said element;

exciting said temperature sensitive element to luminescence; and

detecting the electromagnetic radiation emitted by said element to determine the time of travel and temperature differences of said bolus of fluid thereby also determining the flow rate of the fluid.

42. An apparatus for detecting the presence of a first fluid in a second fluid, said two fluids being immiscible and having different thermal properties, said apparatus comprising:

a length of optical fiber a first end of which is adapted to be inserted into the second fluid;

a temperature sensitive element held at the first end of said fiber, said element having temperature sensitive luminescent properties;

radiation heat transfer means for directly supplying heat to the element;

means at a second end of the optical fiber for exciting said temperature sensitive element; and

means at a second end of the optical fiber for detecting electromagnetic radiation emitted by said element to detect the temperature of the element and the presence of the first fluid whereby such presence is indicated by a change in temperature of the element.

43. The apparatus of claim 42 wherein the radiation heat transfer means supplies heat to the element at a substantially constant rate so that the presence of the first fluid is indicated by a change in temperature of said element.

44. The apparatus of claim 42 wherein the radiation heat transfer means supplies heat to the element at such rate that the difference in temperature between the element and the second fluid thermally unaffected by the radiation heat transfer means remains substantially constant so that the presence of the first fluid is indicated by a change in the rate of heat supplied or withdrawn from the element.

45. The apparatus of claim 42 wherein said first fluid is a gas and said second fluid is a liquid.

46. The apparatus of claim 45 wherein the liquid is blood and the gas to be detected is air embolism.

47. A method for detecting the presence of a first fluid in a second fluid said two fluids being immiscible and having different thermal properties by means of an element having temperature sensitive luminescent properties, said method comprising:

placing the temperature sensitive element in the second fluid;

directly supplying heat to the element;

exciting said temperature sensitive element to luminescence; and

detecting the electromagnetic radiation emitted by said element to detect the temperature of the element and the presence of the first fluid in the second fluid whereby such presence is indicated by a change in temperature of the element.

48. An apparatus for determining the composition of a mixture of fluids having different heat capacities and conductivities, comprising:

a length of optical fiber;

a temperature sensitive element held at a first end of said optical fiber, said element having temperature sensitive luminescent properties and being adapted to be placed in the fluid mixture;

radiation heat transfer means for directly supplying heat to the element;

means at a second end of the optical fiber for exciting said temperature sensitive element; and

means at a second end of the optical fiber for detecting electromagnetic radiation emitted by said element to indicate the temperature of the element and the composition of the fluid mixture whereby the temperature of the element is an indication of the composition of the fluid mixture.

49. The apparatus of claim 48 wherein the radiation heat transfer means supplies heat to the element at a substantially constant rate so that the proportion of a fluid in the fluid mixture with a lower thermal capacity and conductivity varies inversely with a difference in temperature between the element and the fluid mixture thermally unaffected by the radiation heat transfer means.

50. The apparatus of claim 48 wherein the radiation heat transfer means supplies heat at such a rate that the difference in temperature between the element and the fluid mixture thermally unaffected by the heat transfer means remains substantially constant so that the proportion of the fluid in the mixture with a smaller heat capacity and heat conductance varies directly with the rate of heating of the element.

51. An apparatus for measuring the pressure of a fluid comprising:

a length of optical fiber;

a temperature sensitive element held at a first end of said optical fiber, said element having temperature sensitive luminescent properties and being adapted to be placed in the fluid;

radiation heat transfer means for directly supplying heat to the element;

means at the second end of the optical fiber for exciting said temperature sensitive element; and

means at the second end of the optical fiber for detecting electromagnetic radiation emitted by said element to detect the temperature of the element and the pressure of the fluid whereby the temperature of the element is an indication of the pressure of the fluid.

52. The apparatus of claim 51 wherein the radiation heat transfer means supplies heat to the element at a substantially constant rate so that the pressure of the fluid varies inversely with a difference in temperature between the elements and the fluid thermally unaffected by the radiation heat transfer means.

53. The apparatus of claim 51 wherein the radiation heat transfer means supplies heat at such a rate that the difference in temperature between the element and the fluid thermally unaffected by the radiation heat transfer means remains substantially constant so that the pressure of the fluid varies directly with the rate of heating or cooling of the element.

54. A method for measuring the pressure of a fluid by means of an element having temperature sensitive luminescent properties, said method comprising:

placing the temperature sensitive element in the fluid;

directly supplying heat to the element;

exciting said temperature sensitive element to luminescence; and

detecting the electromagnetic radiation emitted by said element to detect the temperature of the element, said temperature being an indication of the pressure of the fluid.

55. An apparatus for measuring the pressure of a gas above a liquid comprising:

a length of optical fiber;

a temperature sensitive element held at a first end of said optical fiber, said element having temperature sensitive luminescent properties and being adapted to be placed in the gas at a location immediately above the surface of the liquid;

means for heating the liquid to boiling state;

means at the second end of the optical fiber for exciting said temperature sensitive element; and

means at a second end of the optical fiber for detecting electromagnetic radiation emitted by said element to determine the temperature of the vapor from the boiling liquid said temperature being an indication of the pressure of the gas.

56. A method for measuring the pressure of a gas above a liquid by means of an element having temperature sensitive luminescent properties, said method comprising:

placing the temperature sensitive element in the gas at a location immediately above the surface of the liquid;

heating the liquid to a boiling state;

exciting said temperature sensitive element to luminescence; and

detecting the electromagnetic radiation emitted by said element to determine the temperature of the vapor from the boiling liquid said temperature being an indication of the pressure of the gas.

57. An apparatus for determining levels between immiscible fluids having different thermal capacities and conductivities, said apparatus comprising:

a plurality of optical fibers, each fiber being placed with its first end placed at a desired location in one of the fluids for determining the level between said fluid and the fluid immediately above;

a temperature sensitive element held at each of the first ends of said plurality of optical fibers, said element having temperature sensitive luminescent properties and being adapted to be placed in the corresponding fluid;

radiation heat transfer means for directly supplying heat to each of the elements;

means at the second end of each optical fiber for exciting the temperature sensitive element held at the first end of such fiber; and

means at the second end of each optical fiber for detecting electromagnetic radiation emitted by the element held to such fiber to detect the temperature of each element, said temperature being an indication of the levels between the fluids.

58. The apparatus of claim 57 wherein the radiation heat transfer means supplies heat to each element at a substantially constant rate so that when the level between the fluid in which the element is placed and the fluid immediately above falls below the level of said element, such change in level is indicated by a change in temperature of such element.

63. The apparatus of claim 57 wherein the radiation heat transfer means supplies heat to each element at such rate that the difference in temperature between such element and the portion of the fluid thermally unaffected by the radiation heat transfer means remains substantially constant so that when the level between the fluid into which such element is placed and the fluid immediately above falls below the level of such element such change in level is indicated by a rise in the rate of heat supplied to the element.

79. The apparatus of claim 57 wherein said element includes phosphor in its composition and wherein said means for exciting said temperature sensitive element comprises a source of ultraviolet light.

65. A method for determining the level between two immiscible fluids having different thermal properties as the level changes, with an element having temperature sensitive luminescent properties, said method comprising:

placing the temperature sensitive element at a desired location in the fluid with the lower altitude for determining the level between said fluid and the fluid above;

directly supplying heat to the element;

exciting the temperature sensitive element to luminescence; and

detecting the electromagnetic radiation emitted by the element to detect the temperature of the element, said temperature being an indication of the level between the fluids as it changes.

66. An apparatus for measuring the thermal conductivity of a solid sample comprising:

a length of optical fiber;

a temperature sensitive element held at a first end of said optical fiber, said element having temperature sensitive luminescent properties and being adapted to contact one side of the solid sample;

a radiation heat transfer means for directly supplying heat to the element;

means at a second end of the optical fiber for exciting said temperature sensitive element; and

means at said second end of the optical fiber for detecting electromagnetic radiation emitted by said element to detect the temperature of the element which indicates the thermal conductivity of the solid sample.

67. The apparatus of claim 66 further comprising a heat sink adapted to contact a solid sample on a side opposite to that in contact with said element so that a steady temperature gradient may be maintained in the sample for measuring its thermal conductivity.

68. The apparatus of claim 66 wherein the thermal capacity of said element is much smaller than that of the solid sample and wherein the radiation heat transfer means is such that the heat supplied to the solid sample through the element does not significantly change the temperature of most of the solid, so that the temperature of the phosphor element is an indication of the thermal conductivity of the material of which the sample is composed.

76. A method for measuring the thermal conductivity of a solid sample with an element having temperature sensitive luminescent properties, said method comprising:

contacting one side of the solid sample with the element;

directly supplying heat to the element;

exciting said temperature sensitive element to luminescence; and

detecting the electromagnetic radiation emitted by said element to detect the temperature of the element, said temperature being an indication of the thermal conductivity of the solid sample.

77. A method for improving the accuracy of temperature measurement wherein the measurement apparatus comprises a temperature probe housing, a temperature sensitive element held at the probe tip of said housing and means for determining the temperature of said element when said element is held in contact with a sample the temperature of which is to be measured, said method comprising:

determining the approximate temperature of the sample;

directly heating, through radiation, the probe tip and the temperature sensitive element to a temperature substantially equal to the approximate temperature of the sample to reduce the heat transfer between the probe tip and the element when they are placed in contact; and

bringing said element into contact with the sample and measuring the temperature of the sample.