JPS6326853B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a quartz thermometer, and more particularly to a quartz thermometer using a quartz crystal resonator whose sensor exhibits linear frequency-temperature characteristics over a wide temperature range.

Conventionally, it has been considered to make a thermometer by utilizing the temperature dependence of the vibration frequency of a crystal resonator. Quartz is an anisotropic hexagonal crystal whose properties vary greatly depending on the cutting angle, but the physical properties of the quartz crystal itself are extremely stable, and its frequency-temperature characteristics exhibit linearity over a wide temperature range. If the cutting angle can be found, it can be used as an excellent temperature measurement element. Crystal thermometers currently in practical use do not exhibit linearity in the frequency-temperature characteristics of the crystal oscillator that serves as the sensor, so they must be corrected using a microcomputer, and even after correction, the temperature range that can be measured is narrow. It was hot. -50℃ with a vibrator called Ys cut
The temperature was ~+120℃, and even the LC cut was around -80℃~+250℃. Additionally, thermometers have become expensive due to the use of microcontrollers.

The present invention has been made in view of the above drawbacks. The crystal cut used in the present invention was discovered through calculations based on thickness vibration theory, and obtained by double rotation. This vibrator has two transverse waves: a longitudinal wave called "a" mode and two transverse waves called "b" mode and "c" mode. Among them, the "b" mode and the "c" mode exhibit excellent linearity in frequency-temperature characteristics over a wide temperature range.

The frequency formula for the thickness vibration mode of a thin crystal plate is: is given by ρ and y _p are the density and thickness of the quartz plate, respectively, and C is the eigenvalue.

The frequency of a crystal plate of any cut angle can be Taylor expanded with respect to temperature T. Using equation (1), approximately (T) (T _p ) {1−α(T−T _p ) +1/2β(T−T _p ) ² +1/6γ(T−T _p ) ³ }− (2
). Here, T _p is the reference temperature, and the coefficients α, β, and γ are α≡(1/(T)δ(T)/δT)T _p β≡(1/(T)δ ² (T)/δT ² ) T _p γ≡(1/(T) δ ³ (T)/δT ³ ) T _p is defined.

α, β, and γ are the primary, secondary, and tertiary temperature coefficients of crystal, respectively.

Figure 1 is a diagram to explain the cut angle of the crystal, and the X, Y, and Z axes are the electric axis of the crystal, and
These are the mechanical axis and the optical axis. A plate parallel to the plane perpendicular to the Y-axis (Y plate) is rotated by an angle φ around the Z-axis, and then rotated θ around the newly created X'-axis. Each,
Counterclockwise rotation is positive.

Figure 2 shows the locus of the points where α=0, β=0, and γ=0 in the C-mode vibration generated in the crystal plate, expressed by the relationship between angle φ and angle θ, and is calculated using thickness vibration theory. This is what I did.

When using a crystal oscillator as a thermometer sensor, the following requirements are required for the crystal oscillator: 1. Characteristics should have high temperature dependence. 2. Characteristic variations and changes over time should be small. 3. Insensitivity to physical quantities other than temperature. 4. Appropriate size 5. Output characteristics and quantity that are easy to detect 6. Mechanically, chemically, and thermally strong 7. Mass production possible and low price 8. Frequency temperature in a wide temperature range The characteristics are linear, etc.

Among these, characteristics 2, 3, 4, 5, and 6 of the crystal resonator are already covered by the conventional technology. To satisfy requirements 1 and 8,
It is sufficient that β and γ are zero and α is large. In order to satisfy the requirement 7, it is sufficient that the cut angle has a wide allowable range and that the size can be reduced.

As can be seen from Fig. 2, at the point where both β and γ become zero, there is a point near θ=5°, φ=5°, and around θ=5°, φ
In the vicinity of =-5° (hereinafter referred to as 5°-5° cut), β and γ are close to each other, and it is far from the locus of α zero. In this vicinity, it has been calculated that the influence of β and γ on α is about 0.01% and can be ignored. Figure 4 is a graph showing the frequency-temperature characteristics of a 5°-5° cut crystal resonator manufactured using a 12 m x 14.7 mm rectangular crystal.

Shows excellent linearity from -200℃ to +250℃,
Both the fundamental wave and the tertiary wave are about 60PPm/℃, and there is no big difference. Which one to use may be determined by considering the need for measurement accuracy and the workability of the crystal piece.

Regarding the linearity of frequency-temperature characteristics, the allowable range of cut angle for use with an accuracy of 0.01℃ is θ=
5° and φ=5°, each has a width of ±3°, which is 60 times the machining accuracy of ±3′ during mass production of crystals, so the cutting angle of the crystal can be achieved without any problems.

FIG. 3 is a block diagram of the thermometer, in which 11 is a sensor oscillation circuit, 12 is a beat detection section, 13 is a converter for temperature display, 14 is a display section, and 15 is a reference oscillation circuit. 16 is controlled by a thermometer. The frequency ₀ of the reference oscillation circuit 15 and the frequency _T of the sensor oscillation circuit 11 are measured by a beat detector and _T - ₀ = △ is obtained. Beat △ converter 13
Although the configuration is such that the temperature is converted into a temperature and displayed on the display unit 14, various methods can be considered for the configuration itself, and this is not the gist of the present invention.

According to the present invention, the frequency-temperature characteristics of the crystal oscillator can be used as is, and there is no need for correction, so the configuration of the crystal thermometer is simplified, measurement can be performed over a wide temperature range, and it is inexpensive and high-performance. Accurate crystal thermometers can be manufactured.

[Brief explanation of drawings]

Figure 1 is a diagram to explain the cut angle of the crystal, and the X, Y, and Z axes are the electric axis of the crystal, and
These are the mechanical axis and the optical axis. Figure 2 shows the temperature coefficient (α,
Figure 3 is a block diagram of the thermometer of the present invention, where 11 is a sensor oscillation circuit, 12 is a beat detector, and 13 is a block diagram of the thermometer of the present invention. is a converter for temperature display. 14
1 is a display section, and 15 is a reference oscillation circuit. FIG. 4 is a graph showing the frequency-temperature characteristics of the 5°-5° cut crystal resonator used in the present invention.

Claims (1)

[Claims] 1. In a crystal thermometer that uses a crystal oscillator as a sensor, the crystal vibrating piece used for the crystal oscillator is
The plate (Y plate) perpendicular to the Y axis (mechanical axis) of the crystal is rotated counterclockwise by φ = 5° ± 3° with the Z axis (optical axis) as the rotation axis, and then the newly created X' axis (electrical A crystal thermometer characterized in that it is a crystal plate obtained by rotating the crystal plate counterclockwise by θ=5°±3° with the axis of rotation as the rotation axis.