Resonator transducer system with temperature compensation

• US 4,535,638 A
• Filed: 10/03/1983
• Issued: 08/20/1985
• Est. Priority Date: 10/03/1983
• Status: Expired due to Term

• Current Assignee: Quartztronics, Inc.
• Original Assignee: Quartztronics, Inc.
• Inventors: EerNisse, Errol P., Ward, Roger W.
• Primary Examiner(s): Ruehl, Charles A.
• Application Number:
  US06/538,171
• Time in Patent Office: 687 Days
• Field of Search: 73/DIG.1, 73/DIG.4, 73/702, 73/703, 73/862.59, 73/581, 374/117, 310/338, 310/366, 331/37, 331/163
• US Class Current: 73/862.59
• CPC Class Codes: G01D 3/032 affecting incoming signal, e.g. by averaging; gating undesired signals
• CPC Class Codes: G01K 7/32 using change of resonant frequency of a crystal
• CPC Class Codes: G01L 1/10 by measuring variations of frequency of stressed vibrating elements, e.g. of stressed strings using resistance strain gauges G01L1/22
• CPC Class Codes: G01L 1/106 Constructional details
• CPC Class Codes: G01L 1/162 using piezoelectric resonators
• CPC Class Codes: Y10S 73/04 Piezoelectric

Abstract

A method and apparatus for measuring force or other parameters and temperature. The apparatus includes an oscillator and a vibratory element, such as a quartz crystal, which is caused to resonate by the oscillator at two frequencies f₁ and f₂ selected from the fundamental frequency and its overtone frequencies of the vibratory element. The vibratory element is selected so that the two frequencies f₁ and f₂ both vary with variation in force (or other parameter) applied to the element and with variation in temperature of the element, and so that the magnitude or scale factor of variation for frequency f₁ is different from that for frequency f₂. The apparatus also includes a detection device for detecting the frequencies f₁ and f₂ and for producing signals representing the frequency variation of the two frequencies relative to a reference frequency, and a processor for processing the signals produced by the detector device for determining the force (or other parameter) and temperature to which the vibratory element is subjected.

Claims

1. A resonator transducer system comprising a single vibratory element which is responsive to an oscillatory electrical signal for resonating at frequencies f₁ and f₂, selected from the fundamental frequency and overtone frequencies of the vibratory element, where the two frequencies vary with variation in force or other parameter applied to the vibratory element and with variation in temperature to which the vibratory element is exposed, with the magnitude of variation due to the change in temperature for frequency f₁ being different from that for frequency f₂,

means for applying an oscillatory signal to the vibratory element to cause the vibratory element to resonate and for producing a vibratory signal having a frequency f₁ and a frequency f₂ which follow the selected frequencies f₁ and f₂ respectively of the vibratory element, and

processing means responsive to the frequencies f₁ and f₂ of the vibratory signal produced by the oscillator means for producing a first signal representing the force or other parameter applied to the vibratory element, and a second signal representing the temperature to which the vibratory element is subjected.

2. A resonator transducer system as in claim 1 wherein said vibratory element is caused to resonate in modes substantially free of activity dips.

3. A resonator transducer system as in claim 1 wherein the vibrating element is a quartz crystal.

4. A resonator transducer system as in claim 3 wherein said crystal is caused to resonate in thickness shear modes.

5. A resonator transducer system as in claim 4 wherein said crystal is an SC-cut quartz crystal.

6. A resonator transducer system as in claim 4 wherein said crystal is an AT-cut quartz crystal.

7. A resonator transducer system as in claim 4 wherein said crystal is a BT-cut quartz crystal.

8. A resonator transducer system as in claim 3 wherein said crystal is a double-bar, double-ended resonator which vibrates in flexure modes.

9. A resonator transducer system as in claim 3 wherein said crystal is a double-bar, single-ended resonator which vibrates in flexure modes.

10. A resonator transducer system as in claim 1 further including a first filter means and second filter means connected in parallel with each other between the vibratory element and the oscillator means, said first filter means being adapted to pass oscillatory signals having frequencies in a band generally centered about the frequency f₁, and said second filter means being adapted to pass oscillatory signals having frequencies in a band generally centered about the frequency f₂.

11. A resonator transducer system as in claim 10 wherein said frequency f₁ is the fundamental frequency of vibration of the vibratory element and said frequency f₂ is the third overtone of the fundamental frequency.

12. A resonator transducer system as in claim 10 wherein said frequency f₁ is the fundamental frequency of vibration of the vibratory element, and said frequency f₂ is the fifth overtone of the fundamental frequency.

13. A resonator transducer system as in claim 10 wherein said frequency f₁ is the third overtone of the fundamental frequency of vibration of the vibratory element, and said frequency f₂ is the fifth overtone of the fundamental frequency.

14. A resonator transducer system as in claim 10 further including third filter means and fourth filter means connected in parallel with each other between the oscillator means and the processing means, said third filter means being adapted to pass oscillatory signals having frequencies in a band generally centered about the frequency f₁, and said second filter means being adapted to pass oscillatory signals having frequencies in a band generally centered about the frequency f₂.

15. A resonator transducer system as in claim 14 wherein said processing means includes

first counting means coupled to the third filter means for producing a first signal s₁ indicative of the frequency change relative to a reference frequency of the oscillatory signal received from the third filter means,

second counting means coupled to the fourth filter means for producing a second signal s₂ indicative of the frequency change relative to a reference frequency of the oscillatory signal received from the fourth filter means, and

means for producing signals ##EQU2## where a_F, b_F, c_F, d_F, e_F, f_F and g_F are predetermined constant force or other parameter coefficients, and where a_T, b_T, C_T, d_T, e_T, f_T and g_T are predetermined constant temperature coefficients.

16. A resonator force transducer system with temperature self-compensation comprising

a vibratory element which resonates at a first selected frequency f₁ and a second selected frequency f₂ in response to an oscillatory electrical signal, said frequencies varying by different scale factors with variation in force applied to the vibratory element and variation in temperature to which the vibratory element is exposed,

means for causing said vibratory element to resonate at the frequencies f₁ and f₂,

means for detecting the frequency f₁ and frequency f₂ of resonance of the vibratory element and for producing a signal ##EQU3## and a signal ##EQU4## where f₀₁ is the first selected frequency of vibration of the vibratory element at a predetermined reference force F₀ and reference temperature T₀, and where f₀₂ is the second selected frequency of vibration of the vibratory element at the reference force and temperature, and

processing means responsive to signals s₁ and s₂ for producing a signal F representing the change in force applied to the vibratory element from the reference force, corrected for temperature variations.

17. A resonator system as in claim 16 wherein the vibratory element is a quartz crystal.

18. A resonator force transducer system as in claim 17 wherein said resonation causing means comprises an oscillator.

19. A resonator force transducer system as in claim 18 further including a first filter means and second filter means connected in parallel with each other between the crystal and the oscillator, said first filter means being adapted to pass oscillatory signals having frequencies in a band generally centered about the frequency f₁, and said second filter means being adapted to pass oscillatory signals having frequencies in a band generally centered about the frequency f₂.

20. A resonator force transducer system as in claim 19 wherein said processing means includes means for producing signals ##EQU5## where a_F, b_F,c_F, d_F, e_F, f_F and g_F are predetermined constant force coefficients, where a_T, b_T, c_T, d_T, e_T, f_T and g_T are predetermined constant temperature coefficients, and where T is the change in temperture from the reference temperature T₀.

21. A resonator force transducer system as in claim 17 wherein said resonation causing means comprises a first oscillator coupled to the crystal for causing the crystal to resonate at the frequency f₁, and a second oscillator coupled to the crystal for causing the crystal to resonate at the frequency f₂.

22. A resonator force transducer system as in claim 21 further including a first filter means coupled between the first oscillator and the crystal, said first filter means being adapted to pass oscillatory signals having frequencies in a band generally centered about the frequency f₁, and a second filter means coupled between the second oscillator and the crystal, said second filter means being adapted to pass oscillatory signals having frequencies in a band generally centered about the frequency f₂.

23. A resonator force transducer system as in claim 22 wherein said first and second oscillators cause said crystal to oscillate in thickness shear modes.

24. A resonator force transducer system as in claim 23 wherein said crystal is selected from a group consisting of SC-cut, AT-cut and BT-cut quartz crystals.

25. A resonator force transducer system as in claim 24 wherein said processing means includes means for producing signals ##EQU6## where a_F, b_F, c_F, d_F, e_F, f_F, and g_F are predetermined constant force coefficients, where a_T, b_T, c_T, d_T, e_T, f_T and g_T are predetermined constant temperature coefficients, and where T is the change in temperature from the reference temperature T_O.

26. A resonator force transducer as in claim 22 wherein said crystal is a double-bar, double-ended resonator configuration, and wherein said first and second oscillators cause said crystal to oscillate in flexure modes.

27. A resonator force transducer as in claim 22 wherein said crystal is a double-bar, single-ended resonator configuration, and wherein said first and second oscillators cause said crystal to oscillate in flexure modes.

28. A resonator transducer system for determining force or other parameter and temperature comprising

a single vibratory element which is responsive to an oscillatory electrical signal for resonating at frequencies f₁ and f₂, with the frequencies being selected from the group of frequencies consisting of the fundamental and overtone frequencies of the vibratory element, where the two frequencies vary with variation in force or other parameter applied to the vibratory element and with variation in temperature to which the vibratory element is exposed, with the magnitude of variation of frequency f₁ due to the change in force or other parameter or the change in temperature being different from that for frequency f₂,

means for applying an oscillatory signal to the vibratory element to cause the vibratory element to resonate and for producing a vibratory signal having frequencies f₁ and f₂ which follow the selected frequencies of resonance f₁ and f₂ respectively of the vibratory element, and

processing means responsive to the frequencies f₁ and f₂ of the vibratory signal for producing a first signal representing the force or other parameter applied to the vibratory element and a second signal representing the temperature to which the vibratory element is subjected.

29. A resonator transducer system as in claim 28 wherein the vibratory element is caused to resonate in modes substantially free of activity dips.

30. A resonator transducer system as in claim 29 wherein the vibratory element is a quartz crystal.

31. A resonator transducer system as in claim 30 wherein the crystal is selected from the group of crystals consisting of SC-cut, AT-cut and BT-cut quartz crystals.

32. A resonator transducer system as in claim 30 wherein the crystal is selected from the group consisting of a double-bar, double-ended resonator configuration or a double-bar, single-ended configuration, and wherein the crystal is caused to resonate in flexure modes.