Resonator temperature transducer

• US 4,592,663 A
• Filed: 05/10/1984
• Issued: 06/03/1986
• Est. Priority Date: 05/10/1984
• Status: Expired due to Term

• Current Assignee: Weigh-Tronix, Inc. (Illinois Tool Works Inc.)
• Original Assignee: Quartex Incorporated
• Inventors: EerNisse, Errol P., Wiggins, Robert B.
• Primary Examiner(s): Smith, Robert I.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/608,857
• Time in Patent Office: 754 Days
• Field of Search: 374/117, 374/118, 374/119, 73/579, 310/370, 310/367
• US Class Current: 374/117
• CPC Class Codes: G01K 7/32 using change of resonant frequency of a crystal

Abstract

A vibratory temperature transducer includes a pair of elongate, generally parallel bars coupled together at one end in a type of tuning fork arrangement. The bars each have a thickness of t, a width of w and a length between free and fixed ends of L. The distance between the free end and the point where the bars are coupled together is m. Apparatus is provided to cause the bars to vibrate in torsional opposition, where the frequency of vibration is generally a function of temperature. Apparatus is also provided for determining the frequency of vibration of the bars so that when the bars are subjected to a change in temperature, the temperature can be readily determined by simply determining the magnitude of the frequency change. By careful determination of the dimensions L, m, t and w, spurious modes of oscillation of the transducer, which cause a reduction in the mechanical Q and thus an erroneous reading of temperature, are avoided.

Claims

1. A resonator temperature transducer comprising

a pair of elongate, spaced-apart, generally parallel bars coupled together at one end, said bars each having a thickness t and width w, with the distance from the location at which the bars are coupled together to the free ends of the bars being m, and said bars being made of a material so that when the bars are caused to vibrate in the torsional mode, the frequency of vibration varies as a function of temperature,

an enlarged mounting section formed integral with the bars at said one end, with the distance from the mounting section to the free ends of the bar being L,

means for causing said bars to vibrate in the torsional mode 180°

out of phase at a frequency f_T, and

wherein t, w, m and L are selected so that ##EQU5## where A_an =3.05, 18.99, 51.92 for n=1, 2 and 3

A_bn =8.57, 41.82, 96.97 for n=1, 2 and 3

A_pn =3.91, 22.12, 59.09, 114.1, 189.9, 281.8 for n=1, 2, 3, 4, 5 and 6

A_wn =4.96, 30.91, 71.82, 89.80, 143.4, 180.8 for n=1, 2, 3, 4, 5 and 6 ##EQU6## f_an, f_pn, f_bn and f_wn are the frequencies of vibration of spurious modes of the transducer, where n is the order of the mode, P is the density of the material and S₅₅ and S₆₆ are shear compliances and E is Young'"'"'s Modulus of the material.

2. A resonator temperature transducer as in claim 1 wherein t, w, m and L are further selected so that

3. A resonator temperature transducer as in claim 2 wherein m and L are further selected so that 1.1≦

L/m≦

1.5.

4. A resonator temperature transducer as in claim 3 wherein t, w, m and L are further selected so that 0.1≦

t/w≦

1, and 4≦

m/w≦

25.

5. A resonator temperature transducer as in claim 2 wherein said vibration causing means includes an oscillator means which provides an oscillatory signal which follows the frequency of vibration of the bars.

6. A resonator temperature transducer as in claim 5 further comprising means coupled to said oscillator means and responsive to the oscillatory signal for providing a read out of the temperature indicated by the frequency of vibration of the bars.

7. Resonator temperature measuring apparatus comprising

a pair of elongate, spaced-apart generally parallel bars coupled together at one end, each having a thickness t and width w, with the distance from the location at which the bars are coupled together to the free ends of the bars being m, said bars comprised of piezoelectric material with the crystallographic axes oriented such that when the bars are stimulated to vibrate in the torsional mode 180 degrees out of phase, the frequency of vibration varies as a function of the temperature to which the bars are exposed,

a support structure to which the joined ends of the bars are attached, where the distance from the support structure to the free ends of the bars is L,

electrodes placed on the bars and responsive to oscillatory signals for causing the bars to resonate in the torsional mode 180 degress out of phase,

means for applying oscillatory signals to said electrodes to cause the bars to resonate in the torsional mode at a frequency f_T,

means for producing an oscillatory signal having frequencies which follow the frequency of vibration of the bars, and

wherein t, w, m and L are selected so that the following representations do not approach within about three percent of equaling one or two:

##EQU7## where A_an =3.05, 18.99, 51.92 for n=1, 2 and 3

A_bn =8.57, 41.82, 96.97 for n=1, 2 and 3

A_pn =3.91, 22.12, 59.09, 114.1, 189.9, 281.8 for n=1, 2, 3, 4, 5 and 6

A_wn =4.96, 30.91, 71.82, 89.80, 143.4, 180.8 for n=1, 2, 3, 4, 5 and 6 ##EQU8## f_an, f_pn, f_bn and f_wn are the frequencies of vibration of spurious modes of the transducer, where n is the order of the mode, P is the density of the material and S₅₅ and S₆₆ are shear compliances and E is Young'"'"'s Modulus of the material.

8. Apparatus as in claim 7 wherein said bars include an enlarged mounting section at the end where the bars are joined, and where the distance from the mounting section to the free ends of the bars is L.

9. Apparatus as in claim 8 wherein L and m are selected so that 1.1≦

L/m≦

1.5.

10. A resonator temperature transducer comprising

a pair of elongated, generally parallel bars coupled together at one end, said bars each having a thickness t and width w, with the distance from the location at which the bars are coupled together to the free ends of the bars being m, and said bars being made of quartz crystal with the crystallographic axes oriented so that when the bars are caused to vibrate in the torsional mode, the frequency of vibration varies as a function of temperature,

an enlarged mounting section joined to the bars at said one end, with the distance from the mounting section to the free ends of the bars being L,

means for causing said bars to vibrate in the torsional mode 180°

out of phase at a frequency f_T, and

wherein t, w, m and L are selected so that

space="preserve" listing-type="equation">0.2≦

t/w≦

0.5,

space="preserve" listing-type="equation">10≦

m/w≦

16

space="preserve" listing-type="equation">1.35≦

L/m≦

1.45, and

space="preserve" listing-type="equation">f.sub.T /f.sub.p4 ≠

1, f.sub.T /f.sub.a2 ≠

1, f.sub.T /f.sub.w5 ≠

1,

where ##EQU9## E is Young'"'"'s Modulus of the material, and P is the density of the material.

11. A resonator temperature transducer as in claim 10 wherein t, w, m, and L are further selected so that

12. The resonator temperature transducer comprising

a pair of elongated, generally parallel bars coupled together at one end, said bars each having a thickness t and width w, with the distance from the location at which the bars are coupled together to the free ends of the bars being m, and said bars being made of quartz crystal with the crystallographic axes oriented so that when the bars are caused to vibrate in the torsional mode, the frequency of vibration varies as a function of temperature,

an enlarged mounting section joined to the bars at said one end, with the distance from the mounting section to the free ends of the bars being L,

means for causing said bars to vibrate in the torsional mode 180°

out of phase at a frequency f_T, and

wherein t, w, m and L are selected so that

space="preserve" listing-type="equation">0.4≦

t/w≦

0.8,

space="preserve" listing-type="equation">12≦

m/w≦

18,

space="preserve" listing-type="equation">1.35≦

L/m≦

1.45, and

space="preserve" listing-type="equation">f.sub.T /f.sub.p4 ≠

1, f.sub.T /f.sub.a3 ≠

1, f.sub.T /f.sub.b3 ≠

1,

where ##EQU11## E is Young'"'"'s Modulus of the material, and P is the density of the material.

13. A resonator temperature transducer as in claim 12 wherein t, w, m, and L are further limited so that

14. Resonator temperature measuring apparatus comprising

a pair of elongate, spaced-apart, generally parallel bars coupled together at one end, said bars each having a thickness t and width w, with the distance from the location at which the bars are coupled together to the free ends of the bars being m, said bars comprised of a piezoelectric material with the crystallographic axes oriented so that when the bars are caused to vibrate in the torsional mode, the frequency of vibration varies as a function of temperature,

an enlarged mounting section formed integral with the bars at said one end, with the distance from the mounting section to the free ends of the bars being L,

means for causing said bars to vibrate in the torsional mode 180°

out of phase at a frequency f_T,

means for providing an indication of the frequency of vibration of th bars,

wherein t, w, m and L are selected so that the following ratios do not approach with about three percent of equaling one or two;

f_T /f_an, f_T /f_pn, f_T /f_bn, and f_T /f_wn, and wherein m and L are further selected so that 1.1≦

L/m≦

1.5,

where ##EQU13## A_an =3.05, 18.99, 51.92 for n=1, 2 and 3 A_bn =8.57, 41.82, 96.97 for n=1, 2 and 3

A_pn =3.91, 22.12, 59.09, 114.1, 189.9, 281.8 for n=1, 2, 3, 4, 5 and 6

A_wn =4.96, 30.91, 71.82, 89.80, 143.4, 180.8 for n=1, 2, 3, 4, 5 and 6 ##EQU14## f_an, f_pn, f_bn and f_wn are the frequencies of vibration of spurious modes of the transducer, where n is the order of the mode, P is the density of the material and S₅₅ and S₆₆ are shear compliances and E is Young'"'"'s Modulus of the material.