Digital temperature sensor

• US 4,448,546 A
• Filed: 11/28/1980
• Issued: 05/15/1984
• Est. Priority Date: 11/28/1980
• Status: Expired due to Term

• Current Assignee: Weigh-Tronix, Inc. (Illinois Tool Works Inc.)
• Original Assignee: Novex Corp. (Thermo Fisher Scientific Incorporated)
• Inventors: Paros, Jerome M.
• Primary Examiner(s): YASICH, DANIEL
• Application Number:
  US06/211,126
• Time in Patent Office: 1,264 Days
• Field of Search: 73/339 A, 73/778, 73/16, 73/579, 73/DIG. 1, 73/32 A, 73/702, 73/703, 73/704, 310/9.5, 310/361, 374/117, 374/118, 374/188
• US Class Current: 374/117
• CPC Class Codes: G01K 7/32 using change of resonant frequency of a crystal
• CPC Class Codes: Y10S 73/01 Vibration

Abstract

A temperature sensor is formed by mounting a force-sensitive resonator on a resilient or non-resilient base structure, preferably in an enclosure such that thermally induced expansions or contractions of the base structure apply a stress to the resonator. The resonant frequency of the resonator is measured to provide an indication of the temperature of the base structure and resonator.

Claims

1. A temperature sensor comprising a load-sensitive resonator having at least a pair of spaced-apart mounts which are secured to a base and which isolates said resonator from external forces, said base having a coefficient of thermal expansion which is different from that of said resonator such that said base applies a thermally induced stress to said resonator, said resonator having a resonant frequency and being unstressed at a first temperature in a preselected operating range of said temperature sensor so that said resonator is compressed at temperatures differing from said first temperature so as to vary the resonant frequency by one polarity and tensioned at temperatures differing from said first temperature so as to vary the resonant frequency in the opposite polarity, thereby changing the resonant frequency of said resonator solely in accordance with changes in the temperature of said resonator and base.

2. A temperature sensor according to claim 1 wherein the resonator is fabricated from quartz crystal.

3. A temperature sensor according to claim 1 wherein the resonator is a closed-end tuning fork having a pair of tines extending between said mounts.

4. A method of measuring temperature change, comprising:

exposing a temperature sensor to the temperature to be measured, said temperature sensor including a load-sensitive resonator having a pair of spaced-apart mounts secured to a temperature sensing member through a plurality of connections, said sensing member having a coefficient of thermal expansion which is different from that of said resonator such that the thermally induced stress applied to said resonator by said sensing member changes in accordance with said temperature change, said resonator having a resonator frequency and being unstressed at a first temperature in a preselected operating range of said temperature sensor so that said resonator is compressed at temperatures differing from said first temperature so as to vary the resonant frequency by one polarity and tensioned at temperatures differing from said first temperature so as to vary the resonant frequency in the opposite polarity, and

measuring the change in resonant frequency of said resonator due solely to said thermally induced stress, thereby providing an indication of said temperature change.

5. The method of claim 4 wherein said temperature sensing member is a base on which said resonator is mounted.

6. The temperature sensor of claim 4 wherein said temperature sensing member is a resilient bellows.

7. The temperature sensor of claim 6 wherein the mounts of said resonator are connected directly to respective ends of said bellows such that said resonator and bellows are connected in parallel.

8. The temperature sensor of claim 7 wherein said bellows encapsulates said load-sensitive resonator and isolates said resonator from an external environment.

9. The temperature sensor of claim 6 wherein said bellows and resonator are connected in series with each other along a common axis with one mount of said resonator connected directly to one end of said bellows and the other mount of said resonator indirectly connected to the other end of said bellows through a force-transmitting structure.

10. The temperature sensor of claim 9 wherein said force-transmitting structure is an enclosure encapsulating said bellows and resonator to isolate said resonator from an external environment.

11. The temperature sensor of claim 10 wherein said bellows is filled with a fluid such that thermally induced volumetric expansions or contractions of said fluid, in combination with thermally induced expansions or contractions of said bellows and enclosure, stress said resonator to change the resonant frequency of said resonator.

12. The temperature sensor of claim 6 wherein said bellows is filled with a fluid such that thermally induced volumetric expansions or contractions of said fluid, in combination with thermally induced expansions or contractions of said bellows, stress said resonator to change the resonant frequency of said resonator.

13. The temperature sensor of claim 6 wherein said temperature sensing member is a spring.

14. The temperature sensor of claim 13 wherein the mounts of said resonator are connected directly to respective ends of said spring such that said resonator and spring are connected in parallel.

15. The temperature sensor of claim 13 wherein said spring and resonator are connected in series with each other along a common axis with one mount of said resonator connected directly to one end of said spring and the other mount of said resonator indirectly connected to the other end of said spring through a force-transmitting structure.

16. The temperature sensor of claim 15 wherein said force-transmitting structure is an enclosure encapsulating said spring and resonator to isolate said resonator from an external environment.

17. The method of claim 4 wherein said temperature sensing member is a resilient spring.

18. The method of claim 17 wherein said resonator and spring are connected to each other in parallel with the mounts of said resonator connected to respective ends of said spring.

19. The method of claim 4 wherein said temperature sensing member is a resilient bellows.

20. The method of claim 19 wherein said resonator and bellows are connected to each other in parallel with the mounts of said resonator connected to respective ends of said bellows and said bellows encapsulating said resonator to isolate said resonator from an external environment.

21. The method of claim 19 wherein said bellows and resonator are connected in series with each other along a common axis with one mount of said resonator connected to one end of said bellows, the other mount of said resonator connected to an internal surface of an enclosure and the other end of said bellows connected to an opposite internal surface of said enclosure, said enclosure encapsulating said bellows and resonator to isolate said resonator from an external environment wherein said resonator is stressed solely by expansions and contractions of said bellows and enclosure.

22. The method of claim 21 wherein said bellows is filled with a fluid such that thermally induced volumetric expansions or contractions of said fluid, in combination with thermally induced expansions or contractions of said bellows and enclosure, stress said resonator to change the resonant frequency of said resonator.

23. The method of claim 19 wherein said spring and resonator are connected in series with each other along a common axis with one mount of said resonator connected to one end of said spring, the other mount of said resonator connected to an internal surface of an enclosure and the other end of said spring connected to an opposite internal surface of said enclosure, said enclosure encapsulating said spring and resonator to isolate said resonator from an external environment wherein said resonator is stressed solely by expansions and contractions of said spring and enclosure.