Distributed RTD

An RTD (resistance temperature sensor or detector) sensing device which is a long, thin, unitary device adapted to be distributed across an extended field for the continuous, uninterrupted sensing or interrogation of such field, avoiding the inaccuracy, unreliability, and excessive expense of conventional "point" RTD and thermocouple sensors currently employed for this purpose. According to the invention, a very long, thin, ductile protective metal outer sheath houses a coextensive body of insulation material, which in turn supports and electrically insulates one or more coextensive RTD filaments and in most forms of the invention one or more heater filaments. Distributed RTDs of the invention may, along their lengths, have continuous linear function sensitivity, continuous variable function sensitivity, or step function sensitivity. Distributed RTDs of the invention have particular utility for gauging liquid level, measuring average mass flow velocity of fluids in large ducts, and sensing the average temperature of an extended nonisothermal field.

 

I claim:

1. Distributed RTD sensing means comprising a pair of distributed RTD sensing devices each of which is suitable for interrogating physical phenomena in an extended field and producing a signal output in response thereto, each said sensing devices comprising:

an elongated, thin, tubular outer protective sheath;

an elongated body of electrical insulation material contained within said sheath and extending longitudinally generally coextensively with said sheath;

elongated RTD filament means supported within said insulation body and extending longitudinally within said insulation body and said sheath;

said RTD filament means along its length being physically separated and electrically insulated from said sheath by said insulation body;

said RTD filament means having end means electrically connectable to a source of electrical current and to detection circuitry from at least one end of said sheath; and

means for heating said RTD filament means;

said pair of RTD sensing devices being arranged in a spaced, generally parallel array and deployed over the extending field having nonuniform thermal response characteristics, one of said sensing devices having its said heating means normally unenergized so that it serves as a thermal reference, and the other of said sensing devices having its said heating means energized when interrogating the physical phenomena in the extended field so as to be response to such thermal response characteristics with a signal output which, when compared with the signal output of said unenergized sensing device, provides physical information about said field.

2. Distributed RTD sensing means comprising at least one RTD sensing device suitable for interrogating physical phenomena in an extended field, said sensing means comprising:

an elongated, thin, tubular outer protective sheath;

an elongated body of electrical insulation material contained within said sheath and extending longitudinally generally coextensively with said sheath;

elongated RTD filament means supported within said insulation body and extending longitudinally within said insulation body and said sheath;

said RTD filament means along its length being physically separated and electrically insulated from said sheath by said insulation body;

said RTD filament means having end means which is electrically connectable to a source of electrical current and to detection circuitry from at least one end of said sheath; and

means for heating said RTD filament means;

said distributed RTD sensing means being deployed across the inside of a fluid flow duct having nonuniform flow rate distribution, and said distributed RTD sensing means being employed to provide information as to mass flow rate of fluid through said duct.

3. An RTD sensing device suitable for interrogating physical phenomena in an extended field, said sensing device comprising:

an elongated, thin, tubular outer protective sheath;

an elongated body of electrical insulation material contained within said sheath and extending longitudinally generally coextensively with said sheath; and

elongated RTD filament means supported within said insulation body and extending longitudinally within said insulation body and said sheath;

said RTD filament means along its length being physically separated and electrically insulated from said sheath by said insulation body;

said RTD filament means having end means which is electrically connectable to a source of electrical current and to detection circuitry from at least one end of said sheath;

said RTD filament means comprising a single RTD filament.

4. An RTD sensing device as defined in claim 3, wherein at least one end of said insulation body is hermetically sealed.

5. An RTD sensing device as defined in claim 3, wherein both ends of said insulation body are hermetically sealed.

6. An RTD sensing device as defined in claim 3, wherein said electrical insulation material is mineral insulation material.

7. An RTD sensing device as defined in claim 6, wherein said mineral insulation material is alumina.

8. An RTD sensing device as defined in claim 6, wherein said mineral insulation material is magnesia.

9. An RTD sensing device as defined in claim 3, wherein said outer sheath is metal.

10. An RTD sensing device as defined in claim 9, wherein said metal is stainless steel.

11. An RTD sensing device as defined in claim 3, wherein said outer sheath is plastic.

12. A plurality of sensing devices as defined in claim 3, arranged in a parallel, generally longitudinally registering array, and a tubular outer protective sheath engaged peripherally about said array and extending longitudinally generally coextensively with said array, said array sheath holding said array tightly together along the length of the array.

13. An RTD sensing device suitable for interrogating physical phenomena in an extended field, said sensing device comprising:

an elongated, thin, tubular outer protective sheath;

an elongated body of electrical insulation material contained within said sheath and extending longitudinally generally coextensively with said sheath; and

elongated RTD filament means supported within said insulation body and extending longitudinally within said insulation body and said sheath;

said RTD filament means along its length being physically separated and electrically insulated from said sheath by said insulation body;

said RTD filament means having end means which is electrically connectable to a source of electrical current and to detection circuitry from at least one end of said sheath;

said RTD filament means comprising a plurality of separate RTD filaments which are physically separated and electrically insulated from each other along their length by said insulation body.

14. An RTD sensing device as defined in claim 13, wherein said RTD filaments are electrically connected in series by series connection means.

15. An RTD sensing device as defined in claim 14, wherein said series connection means between said RTD filaments is disposed within said insulation body.

16. An RTD sensing device as defined in claim 13, wherein said RTD filament means comprises an even number of said RTD filaments, and said end means comprises two end portions of said RTD filament means which are electrically connectable to detection circuitry from the same end of said sheath.

17. An RTD sensing device as defined in claim 16, wherein said RTD filament means comprises two of said RTD filaments.

18. An RTD sensing device as defined in claim 16, wherein said RTD filament means comprises four of said RTD filaments.

19. An RTD sensing device as defined in claim 16, which comprises elongated, electrically energizable heater means extending longitudinally generally coextensively with said RTD filaments,

said heater means along its length being transversely physically separated and electrically insulated by said insulation body from said RTD filaments, and

said heater means having end means which is electrically energizable from at least one end of said sheath.

20. An RTD sensing device as defined in claim 19, wherein said heater means comprises heater filament means supported within said insulation body so as to be physically separated and electrically insulated by said insulation body from said RTD filaments and said sheath.

21. An RTD sensing device as defined in claim 16, which further comprises heater means comprising an even number plurality of electrically energizable heater filaments each of which extends longitudinally generally coextensively with said RTD filament means,

said heater filaments along their lengths being transversely separated and electrically insulated by said insulation body from each other, from said RTD filaments means, and from said sheath,

said heater filaments having two end portions which are electrically energizable from the same end of said sheath as said RTD filaments are connectable.

22. An RTD sensing device as defined in claim 21, wherein said RTD filament means comprises two of said RTD filaments, and said heater filament means comprises two of said heater filaments.

23. An RTD sensing device suitable for interrogating physical phenomena in an extended field, said sensing device comprising:

an elongated, thin, tubular outer protective sheath;

an elongated body of electrical insulation material contained within said sheath and extending longitudinally generally coextensively with said sheath;

elongated RTD filament means supported within said insulation body and extending longitudinally within said insulation body and said sheath;

said RTD filament means along its length being physically separated and electrically insulated from said sheath by said insulation body;

said RTD filament means having end means which is electrically connectable to a source of electrical current and to detection circuitry from at least one end of said sheath; and

elongated, electrically energizable heater means extending longitudinally generally coextensively with said RTD filament means;

said heater means along its length being transversely physically separated and electrically insulated by said insulation body from said RTD filament means;

said heater means having end means which is electrically connectable to an electric power source for energizing said heater means.

24. An RTD sensing device as defined in claim 23, wherein said heater means comprises heater filament means supported within said insulation body so as to be physically separated and electrically insulated by said insulation body from said RTD filament means and said sheath.

25. An RTD sensing device as defined in claim 24, wherein said heater filament means comprises a single heater filament.

26. An RTD sensing device as defined in claim 24, wherein said heater filament means comprises a plurality of separate heater filaments,

said heater filaments being physically separated and electrically insulated from each other along their lengths by said insulation body.

27. An RTD sensing device as defined in claim 26, wherein said heater filaments are electrically connected in series by series connection means.

28. An RTD sensing device as defined in claim 27, wherein said heater filament means comprises an even number of said heater filaments, and said heater end means comprises two end portions of said heater means which are electrically energizable from the same end of said sheath.

29. An RTD sensing device as defined in claim 23, wherein said sheath serves as said heater means.

30. An RTD sensing device as defined in claim 23, wherein said heater means is segmented along its length into alternate high resistance and low resistance sections, said high resistance sections providing high sensitivity for sections of said RTD filament means that are substantially coextensive therewith, said low resistance sections providing low sensitivity for sections of said RTD filaments means that are substantially coextensive therewith, so as to provide step function sensitivity of the sensing device along its length.

31. An RTD sensing device as defined in claim 23, wherein said RTD filament means is a segmented along its length into alternate sections of high resistance temperature sensitivity and sections of low or no resistance temperature sensitivity, so as to provide step function sensitivity of the sensing device along its length.

32. An RTD sensing device as defined in claim 23, wherein said body of insulation material is segmented along its length into alternate sections of relatively high thermal conductivity for relatively good thermal coupled with and heating of sections of said RTD filaments means that are substantially coextensive therewith, and sections of relatively low thermal conductivity for relatively poor thermal coupling with and heating of sections of said RTD filament means that are substantially coextensive therewith, so as to provide step function sensitivity of said RTD sensing device along its length.

33. A pair of distributed RTD sensing devices as defined in claim 23, each of which is suitable for interrogating an extended field and comprises said pair of RTD sensing devices being arranged in a spaced, generally parallel array and deployed over an extended field having nonuniform thermal response characteristics, one of said sensing devices having its said heater means unenergized so that it serves as a thermal reference, and the other of said sensing devices having its said heater means energized so as to be responsive to such characteristics with a signal output which, when compared with the signal output of said unenergized sensing device, provides physical information about said field.

34. Distributed RTD sensing means comprising at least one RTD sensing device as defined in claim 23 deployed through an extended field having nonuniform thermal response characteristics so as to produce a signal output providing physical information about said field.

35. The distributed RTD sensing means deployment as defined in claim 34, wherein said field has a phase change interface, and said distributed RTD sensing means is oriented to extend across such interface so as to provide information as to the location of such interface.

36. The distributed RTD sensing means deployment as defined in claim 35, wherein said phase change is defined by liquid level in a vessel, and said distributed RTD sensing means is oriented generally vertically in the vessel so as to gauge liquid level in the vessel.

37. The distributed RTD sensing means deployment as defined in claim 36, wherein said distributed RTD sensing means is substantially enclosed in a still well to prevent signal output errors from fluid circulation in the vessel.

38. The distributed RTD sensing means deployment as defined in claim 34, wherein said distributed RTD sensing means has substantially continuous, linear function sensitivity along its length.

39. The distributed RTD sensing means deployment as defined in claim 35, wherein said distributed RTD sensing means has variable function sensitivity along its length.

40. The distributed RTD sensing means deployment as defined in claim 35, wherein said distributed RTD sensing means has step function sensitivity along its length.

41. The distributed RTD sensing means deployment as defined in claim 34, wherein said distributed RTD sensing means is deployed across the inside of a fluid flow duct having nonuniform flow rate distribution, and said distributed RTD sensing means is employed to provide information as to mass flow rate of fluid through said duct.

42. The distributed RTD sensing means deployment as defined in claim 41, wherein said distributed RTD sensing means is enclosed in a perforated shroud to avoid signal output saturation from relatively high mass flow rates.

43. The distributed RTD sensing means deployment as defined in claim 41, wherein said distributed RTD sensing means has substantially continuous, linear function sensitivity along its length.

44. The distributed RTD sensing means deployment as defined in claim 41, wherein said distributed RTD sensing means is deployed in said duct in a nonlinear configuration.

45. The distributed RTD sensing means deployment as defined in claim 44, wherein said nonlinear configuration places substantially equal lengths of said distributed RTD sensing means across substantially equal cross-sectional flow areas of said duct.

46. The distributed RTD sensing means deployment as defined in claim 45, wherein said distributed RTD sensing means is arranged generally diametrically across said duct, and said nonlinear configuration is a variable sinuous configuration.

47. The distributed RTD sensing means deployment as defined in claim 45, wherein said distributed RTD sensing means is arranged generally radially in said duct, and said nonlinear configuration is a spiral configuration.

48. The distributed RTD sensing means deployment as defined in claim 47, wherein said spiral configuration comprises a plurality of substantially regularly angularly spaced spiral arms.

49. The distributed RTD sensing means deployment as defined in claim 48, wherein said spiral configuration comprises at least four substantially regularly spaced spiral arms.

50. The distributed RTD sensing means deployment as defined in claim 44, wherein said nonlinear configuration places relatively greater lengths of said distributed RTD sensing means across zones of relatively slower fluid flow rates in said duct so as to provide an overall increase in sensitivity of said distributed RTD sensing means to mass flow rate of the fluid through said duct.

51. The distributed RTD sensing means deployment as defined in claim 44, wherein said nonlinear configuration places relatively lesser lengths of said distributed RTD sensing means across zones of relatively slower fluid flow rates in said duct so as to provide increased accuracy in sensing the average mass flow rate of fluid through said duct.

52. The distributed RTD sensing means deployment as defined in claim 34, which comprises elongated, tubular support means substantially coextensive with and substantially enclosing said sensing device,

said support means comprising a series of support devices spaced along said support means, each of said support devices supporting said sensing device with substantially point contact to minimize heat transfer away from said sensing device.

53. An RTD sensing device suitable for interrogating physical phenomena in an extended field, said sensing device comprising:

an elongated, thin, tubular outer protective sheath;

an elongated body of electrical insulation material contained within said sheath and extending longitudinally generally coextensively with said sheath;

elongated RTD filament means support within said insulation body and extending longitudinally within said insulation body and said sheath;

said RTD filament means along its length being physically separated and electrically insulated from said sheath by said insulation body;

said RTD filament means having end means which is electrically connectable to a source of electrical current and to detection circuitry from at least one end of said sheath, said ends means being at one end of said RTD filament means; and

elongated, thin electrical conductor means for electrically connecting said RTD filament means to detection circuitry and having one end thereof electrically connected to said end means;

said outer sheath and insulation body comprising extension portions which extend continuously beyond said RTD filament end means so as to form an elongate, thin housing for at least a portion of said conductor means;

said portion of said conductor means along its length being physically separated and electrically insulated from said sheath by said insulation body.

54. An RTD sensing device as defined in claim 53, which comprises elongated, electrically energizable heater filament means extending longitudinally generally coextensively with said RTD filament means,

said heater filament means along its length being transversely physically separated and electrically insulated by said insulation body from said RTD filament means and from said sheath,

said heater filament means having electrically energizable end means at the end of said heater filament means that generally registers with said RTD filament end means, and

second elongated, thin electrical conductor means for electrically connecting said heater filament means to a source of electrical power and having one end thereof electrically connected to said energizable end means,

at least a portion of said second conductor means along its length being housed by said extension portions of said outer sheath and insulation body,

said portion of said second conductor means along its length being physically separated and electrically insulated from said sheath and said first-mentioned conductor means by said insulation body.

55. An RTD sensing device as defined in claim 53, wherein said RTD filament means comprises a plurality of RTD filaments which are physically separated and electrically insulated from each other along their lengths by said insulation body, and

said conductor means comprises a like plurality of conductor elements which are physically separated and electrically insulated from each other along said portion of said conductor means by said insulation body extension,

each of said conductor elements being electrically connected to a separate one of said RTD filaments.

56. An RTD sensing device as defined in claim 55, which comprises elongated, electrically energizable heater filament means extending longitudinally generally coextensively with said RTD filament means,

said heater filament means along its length being transversely physically separated and electrically insulated by said insulation body from said RTD filaments and from said sheath,

said heater filament means having electrically energizable end means at the end of said heater filament means that generally registers with said RTD filament end means, and

second elongated, thin electrical conductor means for electrically connecting said heater filament means to a source of electrical power and having one end thereof electrically connected to said electrically energizable end means,

at least a portion of said second conductor means along its length being physically separated and electrically insulated from said sheath and said RTD conductor elements by said insulation body extension.

57. An RTD sensing device as defined in claim 56, wherein said heater filament means comprises a plurality of heater filaments which are physically separated and electrically insulated from each other along their lengths by said insulation body, and

said second conductor means comprises a like plurality of conductor elements which are physically separated and electrically insulated from each other along said portion of said second conductor means by said insulation body extension,

each of said second conductor elements being electrically connected to a separate one of said heater filaments.

58. Distributed RTD sensing means comprising a pair of distributed RTD sensing devices, each of which is suitable for interrogating physical phenomena in an extended field and producing a signal output in response thereto, each said sensing device comprising:

an elongated, thin, tubular outer protective sheath;

an elongated body of electrical insulation material contained within said sheath and extending longitudinally generally coextensively with said sheath;

elongated RTD filament means supported within said insulation body and extending longitudinally within said insulation body and said sheath; and

means for heating said RTD filament means;

said RTD filament means along its length being physically separated and electrically insulated from said sheath by said insulation body;

said RTD filament means having end means which is electrically connectable to a source of electrical current and to detection circuitry from at least one end of said sheath;

said pair of RTD sensing devices being arranged in a space, generally parallel array and deployed over the extended field having nonuniform thermal response characteristics, one of said sensing devices having its said heating means normally unenergized so that it serves as a thermal reference, and the other of said sensing devices having its heating means energized when interrogating the physical field phenomena in the extended field so as to be responsive to such thermal response characteristics with a signal output which, when compared with the signal output of said unenergized sensing device, provides physical information about said field.

59. An RTD sensing device suitable for interrogating physical phenomena in an extending field, said sensing device comprising:

an elongated, thin, tubular outer protective sheath;

an elongated body of electrical insulation material contained within said sheath and extending longitudinally generally coextensively with said sheath; and

elongated RTD filament means supported within said insulation body and extending longitudinally within said insulation body and said sheath;

said RTD filament means along its length being physically separated and electrically insulating from said sheath by said insulation body;

said RTD filament means having end means which is electrically connectable to a source of electrical current and to detection circuitry from at least one end of said sheath;

said RTD sensing means comprising at least one RTD sensing device adapted to be deployed through the extended field having nonuniform thermal response characteristics so as to produce a signal output providing physical information about said field.

60. The distributed RTD sensing means deployment as defined in claim 59, wherein said field has a phase change interface, and said distributed RTD sensing means is oriented to extend across such interface so as to provide information as to the location of such interface.

61. The distributed RTD sensing means deployment as defined in claim 60, wherein said phase change is defined by liquid level in a vessel, and said distributed RTD sensing means is oriented generally vertically in the vessel so as to gauge liquid level in the vessel.

62. The distributed RTD sensing means deployment as defined in claim 61, wherein said distributed RTD sensing means is substantially enclosed in a still well to prevent signal output errors from fluid circulation in the vessel.

63. The distributed RTD sensing means deployment as defined in claim 60, wherein said distributed RTD sensing means has substantially continuous, linear function sensitivity along its length.

64. The distributed RTD sensing means deployment as defined in claim 60, wherein said distributed RTD sensing means has a variable function sensitivity along its length.

65. The distributed RTD sensing means deployment as defined in claim 60, wherein said distributed RTD sensing means has step function sensitivity along its length.

66. The distributed RTD sensing means deployment as defined in claim 59, wherein said distributed RTD sensing means is deployed across the inside of a fluid flow duct having nonuniform flow rate distribution, and said distributed RTD sensing means is employed to provide information as to mass flow rate of fluid through said duct.

67. The distributed RTD sensing means deployment as defined in claim 66, herein said distributed RTD sensing means is enclosed in a perforated shroud to avoid signal output saturation from relatively high mass flow rates.

68. The distributed RTD sensing means deployment as defined in claim 66, wherein said distributed RTD sensing means has substantially continuous, linear function sensitivity along its length.

69. The distributed RTD sensing means deployment as defined in claim 66, wherein said distributed RTD sensing means is deployed in said duct in a nonlinear configuration.

70. The distributed RTD sensing means deployment as defined in claim 69, wherein said nonlinear configuration places substantially equal lengths of said distributed RTD sensing means across substantially equal cross-sectional flow areas of said duct.

71. The distributed RTD sensing means deployment as defined in claim 10, wherein said distributed RTD sensing means is arranged generally diametrically across said duct, and said nonlinear configuration is a variable sinuous configuration.

72. The distributed RTD sensing means deployment as defined in claim 69, wherein said nonlinear configuration places relatively greater lengths of said distributed RTD sensing means across zones of relatively slower fluid flow rates in said duct so as to provide an overall increase in sensitivity of said distributed RTD sensing means to mass flow rate of the fluid through said duct.

73. The distributed RTD sensing means deployment as defined in claim 69, wherein said nonlinear configuration places relatively lesser lengths of said distributed RTD sensing means across zones of relatively slower fluid flow rates in said duct so as to provide increased accuracy in sensing the average mass flow rate of fluid through said duct.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electrical resistance temperature sensors or detectors (RTDs), and it relates more particuarly to a long, slender, continuous RTD capable of sensing continuously over an extended field.

2. Description of the Prior Art

Both thermocouples and resistance temperature sensors (RTDs) are in widespread use for sensing temperature and providing an electrical output representative of the temperature sensed. Thermocouples, by their nature, are point sensors because they thermoelectrically produce an e.m.f. at a specific junction between two different metals. RTDs employ a wire sensing element which has a resistance that varies according to temperature. Present RTDs are designed to concentrate the electrical resistance at a small point or in the smallest possible volume, with miniaturization being a principal feature so that RTDs are, like thermocouples, essentially point sensors. Because of this point sensing feature of both thermocouples and RTDs, wherever an extended field is to be interrogated with the use of either thermocouples or RTDs, it has heretofore been necessary to distribute a multiplicity of thermocouples or RTDs at selected points in the field.

No matter how many point sensing thermocouples or RTDs are distributed in a field, they still are unable to provide an accurate analog representation of the information to be determined from the field, because they are still only sensing specific points in the field, and determining the best points to interrogate, installing the individual thermocouples or RTDs. Making the numerous required individual electrical connections to the point sensing thermocouples and RTDs as is currently done is cumbersome and expensive.

One type of sensing of an extended field by the point sensing thermocouples and RTDs is sensing of the average temperature of a field. It will be apparent that the larger such a thermal field is, and the more varied the temperatures across the thermal field, the more point sensing thermocouples or RTDs are required to obtain an average readout which is fairly representative of the average temperature of the field.

Another type of extended field interrogation currently made with thermocouples or RTDs involves gauging of the level or location of a phase change interface, such as the liquid level, or interface between liquid and gas, in a tank. Such liquid level gauging is currently accomplished with thermocouples and RTDs by arranging a series of spaced thermocouples or RTDs along the height of the tank, i.e., at vertically separated points in the field being interrogated. Where RTDs are employed for this purpose, a series of heated RTDs and companion reference RTDs are employed along the height of the tank. As liquid reaches each RTD point sensor, the sensor reports that it is wet when it becomes cooled by the higher thermal dispersion rate of the liquid than the air above it. However, the operator is unable with such point sensing to determine whether the liquid level is just at that particular point or at any level between that point and just below the next higher RTD sensing point. Further filling of the tank will result in discrete reports from the sequentially higher RTDs, while lowering of the liquid level in the tank will cause successive discrete reports from successively lower RTDs as they are uncovered from the liquid. For example, if ten sensing points are employed along the height of the tank each with an individual heated RTD sensor and a reference RTD sensor, the gauging can only be performed at ten individual stepped points, with total uncertainty of where the liquid level is between the points. The only way to reduce such uncertainty is to increase the number of sensing points, at correspondingly increased expense. A liquid level sensing system of this type is disclosed in applicant's U.S. Pat. No. 4,449,403, issued May 22, 1984 for "Guide Tube Inserted Liquid Level Sensor."

Accurate liquid level sensing is of critical importance in liquid storage vessels and reactor buildings and in the reactor vessels themselves of nuclear power plants to avoid accidents such as that at the Three Mile Island plant, where liquid level was misinterpreted. Where a series of vertically arrayed point sensing thermocouples or RTDs is employed to determine liquid level, not only is there a lack of desired accuracy by not knowing where the liquid level is between the sensing points, but liquid level changes may not be immediately sensed, since there can be a considerable change in liquid level prior to detection, so that a developing problem may not be immediately detected, and therefore mitigating action to suppress the problem would not be promptly taken by the operator.

Since each of the vertical sequence of thermocouples or RTDs in such present liquid level gauging systems requires its own separate electrical connections to the detection circuitry, the required large number of electrical joints or splices results in undesirably low reliability, which could be dangerous in the nuclear power plant environment. As an illustration of how serious this problem can be, applicant is familiar with one point-sensing RTD system for gauging water level in a nuclear reactor building which has as many as fifty RTD sensors arrayed over a vertical height of approximately sixty feet.

RTDs are generally preferred for some purpose over thermocouples for most uses because they can be made much more sensitive, being able to provide an output signal many times greater than thermocouples. This is because RTDs operate with an external electrical power source, which can provide as high a voltage or current as is self-generated junction e.m.f., which inherently has a very low output voltage level as well as other inaccuracies. Nevertheless, for sensing some extended fields, such as the inside of a nuclear reactor vessel, access may be difficult, and best achieved by encasing a series of the sensors in a long, slender tubular probe. Such a probe can readily be inserted in an existing reactor vessel instrument guide tube. While it would be desirable to have RTDs so packaged because of their high output, and hence sensitivity, current state of the art RTDs are not suitable for such packaging, being much too bulky, and having a ceramic or glass insulator too brittle to allow them to be deformed as would be required for packaging them in such a long, slender tubular probe. Thermocouples, on the other hand, have been known to be packaged inside a metal casing as small as 0.010 inch in diameter, and a series of such encased thermocouples and the required electrical leads placed inside a tube and encased by drawing or swaging the tube down around the thermocouples and leads to produce a long, slender probe suitable for gaining access to constricted regions inside a nuclear reactor vessel. However, such thermocouple probes have serious disadvantages. First, the thermocouples are delicate and are easily subject to breakage during the manufacture of such probes or upon accidental impacting. Also, because of their inherent point sensing, the thermocouple-type probes necessarily have a step function output, rather than a continuous output, so liquid level cannot be accurately determined. Further, the electrical output of the thermocouples is so small that performance is grainy and resolution and accuracy are poor. Also, individual wire leads are required for each of the thermocouples, so that numerous wires must extend along the tube of the probe, which seriously limits how small the outside diameter of the tubular probe can be, and of course the larger the number of thermocouples placed along the probe in an attempt to increase resolution, the greater the number of leads. The large number of leads also seriously reduces the reliability of such thermocouple-type probes. Such thermocouple-type probes are also quite expensive to make, and it is even more expensive to provide leads, connections and electronic cooperating devices for thermocouple-type probes.

Another type of extended field which has been interrogated by a multiplicity of RTDs or thermocouples is a large duct having a nonuniform flow profile, where it is sought to obtain an average reading of the flow velocity in the duct. Such nonuniform flow distributions exist, for example, in air ducts where diameters are large and fittings such as tees, elbows, transitions, bends, section changes, louvers, dampers, and the like cause flow disturbances. Nonuniform flow distributions also typically occur in the input air ducts and combustion output ducts of fossil fuel power plants. In such cases, a multiplicity of point sensing RTD or thermocouple sensors are placed at what are considered to be strategic locations across the air or gas flow path, but only a rough approximation of the flow velocity can be obtained by use of such discrete, point sensing locations. Again, these individual RTD point sensors suffer from high costs of leads, connectors, and mating electronic devices that cooperate in interpreting the individual signals.

SUMMARY OF THE INVENTION

In view of these and other problems in the art, it is a general object of the present invention to provide an RTD of very long, thin configuration suitable for interrogating an extended field.

Another general object of the invention is to provide a long, thin RTD which, disposed along or across an extended field, is capable of serving the same sensing function as a multiplicity of point sensing-type RTDs or thermocouples distributed over the field, and which therefore may be considered as a unitary distributed RTD.

Another object of the invention is to provide a long, thin distributed RTD which is capable of providing infinitessimally continuous, uninterrupted sensing, as compared to the discontinuous, interrupted, step function-type sensing of conventional point sensing RTDs and thermocouples.

Another object of the invention is to provide a distributed RTD which has a high degree of sensitivity and has an output with excellent resolution.

Another object of the invention is to provide a long, thin distributed RTD which may be made as long as desired for spanning any particular field to be sensed.

Another object of the invention is to provide a long, thin distributed RTD of the character described which is flexible such that it can be rolled up for convenience of storage, shipping, and installation in cramped quarters.

A further object of the invention is to provide a distributed RTD capable of providing an accurate analog representation of information sensed in an extended field, as compared to an averaging of specific finite points in the field or a step function output of the level or location of a phase change interface such as the liquid level in a tank.

A further object of the invention is to provide a long, slender distributed RTD which is capable of accurately sensing the average temperature of an extended field.

A further object of the invention is to provide a distributed RTD of the character described, which, when deployed as a matched pair along the vertical height of a tank, is capable of accurately gauging the liquid level in the tank on a continuous, uninterrupted basis.

A still further object of the invention is to provide a distributed RTD of the character described which is capable, deployed as a matched pair, of measuring the average mass flow velocity of gas flow in an irregular region of a large duct where there is nonuniform flow velocity distribution.

Yet another object of the invention is to provide, for the first time, RTD packaging which is long, thin, and continuous, and which can be made even thinner than multiple channel thermocouple probes for sensing in fields normally difficult to access such as inside a nuclear reactor vessel, yet which has the high sensitivity and resolution capability of RTD sensors.

Another object of the invention is to provide a distributed RTD sensor capable of sensing over an extended field, yet which has a high degree of reliability because it requires only a minimum number of electrical connections, and because its operative filaments are well protected in a strong outer metal casing or sheath. The outer casing may be provided with springlike flexibility and toughness which avoids likelihood of impact damage to the RTD and heater filaments or of sharp bends or kinks being formed therein from handling, and enables the long, thin distributed RTD to be rolled up for convenience of storage, shipping, and installation in cramped quarters.

A further object of the invention is to provide a distributed RTD of the character described which is relatively inexpensive to manufacture, and which is particularly inexpensive to install because it does not require the numerous attachments and many electrical connections and junctions associated with point sensing thermocouples and RTDs distributed about an extended field.

A still further object of the invention is to provide a distributed RTD of the character described wherein RTD filament material may be nonlinearly arranged along its length so as to accommodate or compensate for a nonlinear field.

A still further object of the invention is to provide a long, thin distributed RTD of the character described wherein portions thereof may be so arranged as to provide a step function output.

Another object of the invention is to provide a distributed RTD sensor of the character described in which the conductors connecting the RTD and heater filaments of the sensor to remote detection circuitry are housed in the same continuous outer sheath as the sensor filaments to avoid any junctions near the region being sensed.

Yet another object of the invention is to provide a method of increasing sensitivity of distributed RTD devices of the invention to mass fluid flow which involves utilizing relatively larger amounts of the RTD material in regions of relatively slower fluid flow.

An additional object of the invention is to provide configurations and methods for correlating equal incremental lengths of the distributed RTDs of the invention with equal areas in ducts to provide a signal output truly representative of average mass flow rates through the ducts.

According to the invention, an RTD sensing device is provided in a long, thin, linear configuration capable of spanning and interrogating an extended field. The basic structure of the invention in its simplest form consists of an elongated, thin, tubular outer sheath preferably made of a ductile metal such as stainless steel or other suitable metal, or made of other tough material such as plastic, that is capable of being drawn out from a relatively short, thick starting stage to the final long, thin configuration. An elongated body of electrical insulation material, preferably mineral insulation material such as alumina or magnesia, is contained within the outer metal sheath and extends longitudinally generally coextensively with the sheath. At least one long, thin filament of RTD material is supported within the insulation body and extends longitudinally generally coextensively with the insulation body and the sheath, the RTD filament along its length being transversely physically separated from and electrically insulated from the sheath by the insulation body. Electrical connections are made to end portions of the RTD filament for connection to detection circuitry, which may be of either the constant voltage type or the constant current type. A simplified form of RTD according to the invention does not include a heater filament as a companion to the RTD filament, and this form has utility as a linear thermometer adapted to have its length disposed across or along an extended nonisothermal temperature field for sensing the average temperature of the field, as compared to the conventional costly deployment of a multiplicity of point sensing RTDs or thermocouples.

A distributed RTD of the invention which does not have an internal heater filament may be made as a heated distributed RTD by making the outer sheath out of a high resistance ductile metal, and electrically energizing the sheath so that it will serve as a heater.

The other forms of the invention include one or more electrically energizable heater filaments generally coextensive with one or more RTD filaments, the heater filament or filaments being supported in the insulation body so as to be thermally coupled with the RTD filament or filaments but physically separated and electrically insulated from the RTD filament or filaments. The heater-type distributed RTDs of the invention are particularly useful for gauging liquid level on a continuous, linear, nonstepped basis, and for measuring the average mass flow velocity of gas flowing in an irregular region of a large duct where the irregularity causes nonuniform flow velocity distribution. For such uses of the heater-type distributed RTDs of the invention, they are preferably deployed in matched parallel pairs, with the heater filament or filaments of one of a matched pair being energized, while the heater filament or filaments of the other is left unenergized, the unheated distributed RTD serving as a thermal reference.

In preferred forms of the invention, a plurality of RTD filaments each extend the length of the distributed RTD, and are electrically connected preferably in series so as to multiply the sensitivity and resolution of the distributed RTD. By utilizing an even number of such series-connected filaments, both of the outside electrical connections are enabled to be made at one end of the distributed RTD, which makes connection to detection circuitry much more convenient than if connections must be made from both ends of the very long distributed RTD.

All of the long, thin, linear forms of the invention are made by initially providing the outer sheath, insulation body, and RTD and heater filaments in relatively short, thick form, assembling them in such form, and then swaging and/or drawing the assembly as a unit in a series of passes out to its final very long, thin configuration, and during such swaging and/or drawing the parts remain in their same relative proportions and locations.

In some forms of the invention, the effective length of RTD filament is greatly increased for increase of sensitivity and resolution by arranging the RTD filaments in a long, thin, helical array. This is accomplished by employing one or more extremely long linear forms of the invention helically coiled along a thin tubular mandrel which preferably houses the heater filaments.

For most purposes, it is desired to have a sensitivity of the distributed RTD which is linear along its length. However, the helical form of distributed RTD may have its coils wound nonlinearly so as to provide any desired nonlinear sensitivity along the length of the helical distributed RTD. Similarly, a step function may be provided along the length of the helical-type distributed RTD of the invention by having a series of helical clusters regularly or irregularly spaced along the length of the helical RTD, the clusters providing high sensitivity steps, with the clusters being interconnected by straight, axial RTD sections of relatively low sensitivity.

The step function may alternatively be accomplished in distributed RTDs of the invention by employing one or more heater filaments that are segmented into alternate high resistance and low resistance sections, the high resistance sections providing high sensitivity for the coextensive sections of RTD filament, and the low resistance sections providing regions of low sensitivity for the coextensive sections of RTD filament. A similar step function can be provided by employing one or more RTD filaments that are segmented into alternate RTD and non-RTD sections, or alternate sections of high and low RTD sensitivity. A step function can also be accomplished by employing alternating sections of insulation material having high and low thermal conductivity.

A form of the invention which is particularly useful in atomic power plants has the conductors connecting the RTD and heater filaments of the sensor to remote detection circuitry housed in the same continuous outer sheath as the sensor filaments to avoid junction boxes or other connecting devices in sensitive areas.

All forms of the present invention may be made very long and very thin. Thus, linear or nonhelical forms of the invention can be made with an outside diameter as small as from approximately 0.010 inch to approximately 0.030 inch, and can be made as long as several hundred feet if desired. A helical form of the invention with a single helix layer can be made with an outside diameter as small as approximately 1/8 inch, and in lengths of sixty feet or more if desired.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects of the invention will become more apparent when taken in conjunction with the drawings, wherein:

FIG. 1 is a diametrically enlarged, fragmentary perspective view of a form of the invention which has a single RTD filament and does not include a heater filament;

FIG. 2 is a greatly enlarged transverse sectional view taken on the line 2--2 in FIG. 1;

FIG. 3 is a fragmentary axial section, partly in elevation, taken on line 3--3 and the scale of FIG. 2, showing the distributed RTD of FIGS. 1 and 2;

FIG. 4 is a billet-like starting assembly which is to be swaged and/or drawn to produce the distributed RTD of FIGS. 1-3;

FIG. 5 is a view similar to FIG. 1, but illustrating a distributed RTD of the invention having both an RTD filament and a heater filament;

FIG. 6 is a greatly enlarged transverse sectional view taken on the line 6--6 in FIG. 5;

FIG. 7 is a fragmentary axial sectional view, partly in elevation, taken on the line 7--7 in FIG. 6 and having the same scale as FIG. 6;

FIG. 8 is a greatly enlarged, fragmentary axial sectional view, partly in elevation, illustrating another form of the invention which has a pair of RTD filaments electrically connected in series, and a single heater filament;

FIG. 9 is a transverse sectional view taken on the line 9--9 in FIG. 8 and having the same scale as FIG. 8;

FIG. 10 is a greatly enlarged, fragmentary perspective view which is axially sectional with portions in elevation, illustrating a further form of the invention which has four RTD filaments electrically connected in series, and a single heater filament;

FIG. 11 is a view similar to FIG. 10, but illustrating another form of the invention which has a pair of RTD filaments electrically connected in series, and a pair of heater filaments electrically connected in series;

FIG. 12 is a greatly enlarged, fragmentary axial sectional view, with portions in elevation, illustrating a helical form of the invention having a linear distributed RTD of the invention helically coiled in a single layer, and with phantom lines indicating the great length of the helically coiled distributed RTD relative to its diameter;

FIG. 13 is a still further enlarged, fragmentary axial sectional view, partly in elevation, taken on the line 13--13 in FIG. 12, showing the closed end portion of the linear distributed RTD which is helically coiled in the helical distributed RTD of FIG. 12;

FIG. 14 is a greatly enlarged, fragmentary axial section, partly in elevation, taken on the same scale as FIG. 12, showing another helical form of the invention in which the helically coiled linear RTD element is encased in a potting or other filler material for protection of the coil;

FIG. 15 is a greatly enlarged, fragmentary axial section, partly in elevation, similar to FIG. 12 but on a somewhat smaller scale, illustrating a double helical form of the invention having two linear RTDs helically coiled in two layers along the length of the helical RTD;

FIG. 16 is a fragmentary vertical section, partly in elevation, illustrating a tank with a matched, parallel pair of distributed RTDs of the invention vertically deployed along a wall of the tank for liquid level gauging;

FIG. 17 is a side elevational view, with a portion broken away, illustrating a duct elbow with a matched pair of distributed RTDs of the invention deployed across it;

FIG. 18 is a transverse sectional view, with portions shown in elevation, taken on the line 18--18 in FIG. 17, with the diameters of the distributed RTDs exaggerated relative to their lengths for illustrative purposes;

FIG. 19 is a transverse vertical section, partly in elevation, illustrating a right circular cylindrical tank laid on its side, with a matched pair of the helically coiled form of distributed RTDs of the invention vertically deployed in the tank, the pair of distributed RTDs being diagramatically illustrated as having the coils of the helical winding variably separated along their lengths with the winding variations characterized to represent the curvature of the tank so as to provide a linear output representing liquid quantity in the tank;

FIG. 20 is a fragmentary vertical sectional view, partly in elevation, illustrating a tank with a vertically deployed matched pair of diagramatically illustrated distributed RTDs of the invention having alternating helical and straight RTD sections for providing a step function output with linear output between the steps;

FIG. 21 is a greatly enlarged, fragmentary axial section, partly in elevation, illustrating another step function form of the invention in which the heater filament has alternating high resistance and low resistance sections;

FIG. 22 is a view similar to FIG. 21, illustrating a still further step function form of the invention in which the insulation body has alternating sections of relatively high thermal conductivity and relatively low thermal conductivity;

FIG. 23 is a block diagram illustrating a constant current circuit which may be utilized in connection with any of the forms of the present invention;

FIG. 24 is a view similar to FIG. 16, but with the distributed RTDs disposed within a still well to mitigate the effects of fluid turbulence;

FIG. 25 is an enlarged, fragmentary, horizontal sectional view taken on the line 25--25 in FIG. 24;

FIG. 26 is a view similar to FIG. 18, but with the distributed RTDs disposed within a perforated shroud to prevent signal saturation by high fluid flow velocities through the duct;

FIG. 27 is an enlarged, fragmentary sectional view taken on the line 27--27 in FIG. 26;

FIG. 28 is a diagrammatic cross-sectional view of duct illustrating linear RTD means of the invention diametrically deployed across the duct and variably sinuously configured to provide a variable function response corresponding to the variable diametrical area function of fluid flow symmetrical about its diametrical axis;

FIG. 29 is a diagrammatic cross-sectional view of a duct illustrating linear RTD means of the invention arrayed in a spiral configuration to provide a variable function response corresponding to the variable radial area function of fluid flow symmetrical about the center axis of the duct; and

FIG. 30 is a greatly enlarged fragmentary axial sectional view, with portions in elevation and p