Multi-wire mineral insulated cable thermocouple reference junction

• US 4,624,582 A
• Filed: 02/29/1984
• Issued: 11/25/1986
• Est. Priority Date: 02/29/1984
• Status: Expired due to Fees

• Current Assignee: Combustion Engineering Incorporated (ABB Limited)
• Original Assignee: Combustion Engineering Incorporated (ABB Limited)
• Inventors: Devon, Thomas J., Banda, Lionel A.
• Primary Examiner(s): Yasich, Daniel N.
• Application Number:
  US06/584,840
• Time in Patent Office: 1,000 Days
• Field of Search: 374/181, 374/179, 374/137, 374/171, 374/112, 374/115, 374/208, 374/182, 374/165, 374/172, 374/169, 174/35 C, 174/71 R, 174/11 R
• US Class Current: 374/181
• CPC Class Codes: G01K 7/13 Circuits for cold-junction compensation

Abstract

Apparatus for making a transition from leads (12-26) of a temperature measuring thermocouple to extension wires (44-58) within a hermetically sealed cable sheath (60) of small diameter. The interior of the cable sheath (60) is shielded from electromagnetic radiation by an electrically conductive liner (62). A thermally conductive, electrically insulating material (66) surrounds the intermediate junctions (28-42). The temperature of the intermediate junctions (28-42) is measured (64) providing a signal to compensate the voltage generated by the temperature measuring thermocouples due to the thermoelectric effect of the intermediate junctions (28-42).

Claims

1. Cable means for making a transition from leads of a temperature measuring means to extension wires that conduct a signal indicative of the temperature measured by the temperature measuring means to signal processing electronics, comprising:

(a) a cable sheath;

(b) a low resistance, electrically conductive liner means disposed coaxially within the sheath for defining a shielded region within the interior of the liner means and for shielding the interior region from electromagnetic radiation;

(c) a pair of leads extending from a temperature measuring means to within the shielded region within the interior of the liner means;

(d) a pair of extension wires extending from within the shielded region within the interior of the liner means to signal processing electronics;

(e) a plurality of intermediate junctions disposed in the shielded region and formed at the juncture of the leads of the temperature measuring means and the extension wires;

(f) thermally conductive, electrically insulating means for filling the shielded region at least through the region of the intermediate junctions and for conducting thermal energy from the conductive liner means throughout the thermally conductive, electrically insulating means in the region of the intermediate junctions such that no temperature gradient exists across the radius of the liner means; and

(g) a compensating temperature measuring means having leads, the compensating temperature measuring means disposed within the sheath in the region of the intermediate junctions for measuring the temperature of the intermediate junctions and for generating a signal indicative of the temperature of the intermediate junctions, said signal impressed on the leads thereof, whereby the signal indicative of the temperature of the intermediate junctions generated by the compensating temperature means is available to compensate a signal indicative of the temperature measured by the temperature measuring means as conducted on the extension wires due to the thermoelectric effect of the intermediate junctions.

2. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 1 wherein the cable sheath comprises a hermetically sealed cable sheath.

3. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 1 wherein the compensating temperature measuring means is disposed within the shielded region.

4. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 1 further comprising a thermal dampening means surrounding the cable sheath in the region of the transition for dampening the effects of thermal transients.

5. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 1 wherein the leads of the compensating temperature measuring means are disposed within the cable sheath.

6. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 1 wherein the compensating temperature means is comprised of a thermocouple.

7. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 1 wherein the compensating temperature means is comprised of a resistance temperature detector.

8. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 1 wherein the low resistance, electrically conductive liner means is comprised of a copper containing liner.

9. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 1 wherein the sheath is comprised of a stainless steel containing sheath.

10. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 1 wherein the thermally conductive, electrically insulating means is comprised of an inorganic insulation.

11. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 1 wherein the thermally conductive, electrically insulating means is comprised of a silicon dioxide.

12. Cable means for making a transition from leads of a temperature measuring thermocouple to extension wires that conduct a signal indicative of the temperature measured by the temperature measuring thermocouple to signal processing electronics, the transition being as close to the temperature measuring thermocouple as practical, comprising:

(a) a first cable sheath;

(b) a low resistance, electrically conductive liner means disposed coaxially within the sheath for defining a shielded region within the interior of the liner means and for shielding the interior region from electromagnetic radiation;

(c) a pair of leads extending from a temperature measuring thermocouple to within the shielded region within the interior of the liner means;

(d) a pair of extension wires extending from within the shielded region within the interior of the liner means to signal processing electronics;

(e) a plurality of intermediate junctions disposed in the shielded region and formed at the juncture of the temperature measuring thermocouple leads and the extension wires;

(f) thermally conductive, electrically insulating means for filling the shielded region at least through the region of the intermediate junctions and for conducting thermal energy;

(g) a compensating temperature measuring means disposed in the region of the intermediate junctions and having leads extending therefrom away from the region of the intermediate junctions to signal processing electronics;

(h) a second cable sheath, the interior of the second cable sheath in communication with the interior of the first cable sheath in the region of the intermediate junctions, the second sheath branching from the first sheath to house the leads of the compensating temperature measuring means; and

(i) a low resistance, electrically conductive liner means within the second cable sheath, the liner means within the second cable sheath electrically conductive with the liner means within the first cable sheath, for defining a shielded region within the interior of the liner means within the second cable sheath and for shielding the interior region within the second sheath from electromagnetic radiation.

13. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 12 wherein the leads of the compensating temperature measuring means are disposed within the second cable sheath.

14. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 12 wherein the compensating temperature measuring means is disposed within the first cable sheath.

15. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 12 wherein the compensating temperature measuring means is disposed within the second cable sheath.

16. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 12 wherein the low resistance, electrically conductive liner within the second sheath is comprised of copper.

17. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 12 wherein the second cable sheath is comprised of stainless steel.

18. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 12 further comprising a thermal dampening means surrounding at least the first cable sheath in the region of the transition for dampening the effects of thermal transients.

19. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 12 wherein the second cable sheath is sealed to the first cable sheath at the juncture thereof.

20. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 19 wherein the seal between the first cable sheath and the second cable sheath is a weld seam circumscribing the second cable sheath at the juncture.

21. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 19 wherein the seal between the first cable sheath and the second cable sheath is a braze seam circumscribing the second cable sheath at the juncture.

22. Apparatus for making a transition within a cable from leads of a temperature measuring means to extension wires as recited in claim 12 wherein the combination of the thermal conductivity of the thermally conductive, electrically insulating means and the radius of the liner means is such that no temperature gradient exists across the radius of the liner means in the region of the intermediate junctions.

23. Apparatus for measuring a temperature gradient, comprising:

(a) a cable sheath closed at one end having an active length adjacent the closed end for measuring a temperature gradient;

(b) a low resistance, electrically conductive liner means within the sheath for defining a shielded region within the interior of the liner means and for shielding the shielded region from electromagnetic radiation;

(c) means for measuring temperature, disposed within the sheath adjacent the closed end and having leads extending therefrom away from the closed end of the sheath within the sheath;

(d) extension wires disposed within the cable sheath joining with the leads of the temperature measuring means forming the intermediate junctions within the active length of the cable sheath;

(e) a compensating temperature measuring means having leads extending therefrom away from the closed end of the cable sheath, the compensating temperature measuring means disposed within the cable sheath in the region of at least one of the intermediate junctions for measuring the temperature of the intermediate junction; and

(f) thermally conductive, electrically insulating means for filling the shielded region at least in the region of the temperature measuring means and the compensating temperature measuring means, and for conducting thermal energy from the conductive liner means throughout the thermally conductive, electrically insulating means in the region of the temperature measuring means and the compensating temperature measuring means such that no temperature gradient exists across the radius of the liner means, whereby the temperature of at least two points along the active length of the cable sheath are measured with the temperature of one of the points being simultaneously the temperature along the active length of the cable sheath and the temperature of an intermediate junction.

24. Apparatus for measuring a temperature gradient as recited in claim 23 wherein the compensating temperature measuring means comprised of a resistance temperature detector.

25. Apparatus for measuring a temperature gradient as recited in claim 23 wherein the low resistance, electrically conductive liner means is comprised of copper.

26. Apparatus for measuring a temperature gradient as recited in claim 23 wherein the cable sheath is comprised of stainless steel.

27. Apparatus for measuring a temperature gradient as recited in claim 23 wherein the thermally conductive, electrically insulating means is comprised of an inorganic insulation.

28. Apparatus for measuring a temperature gradient as recited in claim 23 wherein the thermally conductive, electrically insulating means is comprised of silicon dioxide.

29. Apparatus for measuring a temperature gradient as recited in claim 23 wherein the compensating temperature measuring means is comprised of a thermocouple.