JPH0151135B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly sensitive quartz temperature sensor that exhibits linear frequency-temperature characteristics over a wide temperature range.

It has long been thought to make thermometers by exploiting the temperature dependence of crystal oscillators. Quartz is an anisotropic hexagonal crystal that is physically very stable.
Moreover, it exhibits various characteristics depending on the direction in which it is cut out.

If a cutting direction with highly accurate linear frequency-temperature characteristics and high sensitivity to temperature can be found, it will become an excellent temperature sensor.

The requirements for a crystal temperature sensor as a temperature-sensitive element are: 1. High temperature dependence of characteristics, that is, high sensitivity.

2. Small variations in characteristics and changes over time 3. Insensitive to physical quantities other than temperature 4. Appropriate size 5. Output characteristics and quantities that are easy to detect 6. Mechanically, chemically, and thermally Strong 7. Frequency-temperature characteristics exhibit linearity over a wide temperature range. Among these, characteristics 2, 3, 4, 5, and 6 of the crystal resonator are all covered by the conventional technology. Crystal temperature sensors currently in practical use do not have sufficient linearity over a wide range of frequency-temperature characteristics. For example, the linearity of the frequency-temperature characteristic of a crystal temperature sensor called 5°Y cut is 0~
3% in the range of 100°C, the sensitivity is 94PPm/°C.
The linearity of the frequency-temperature characteristic of LC Cut's crystal temperature sensor is 0.05% in the range of -40 to 230°C, and the sensitivity is 36ppm/°C. For this reason, thermometers using these crystal temperature sensors had to be corrected by a microcomputer.

The present invention has been made in view of the above drawbacks. The crystal piece of the crystal temperature sensor in the present invention is cut out in a direction of double rotation. This was discovered and applied through calculations based on Atsushi vibration theory.

In thickness vibration, there are a longitudinal wave called a mode and two transverse waves called b mode and c mode. Of these, b mode and c mode have a frequency of -
Shows good linearity in temperature characteristics.

In a thin crystal plate, the frequency of the thickness vibration mode is given by the following equation.

In the above equation, ρ is the density, y ₀ is the thickness of the crystal piece, and c is the eigenvalue. The above equation can be expanded as follows with respect to the temperature T for the cut in any direction. _(T) = _(T0) {1+a(T-T ₀ ) +1/2β(T-T ₀ ) ² +1/6γ(T-T ₀ ) ³ } In the above equation, _(T) is the frequency at temperature T. T ₀ is the reference temperature. α, β, γ are each 1
It is the second-order, second-order, and third-order temperature coefficient, and is defined by the following formula.

α=[1/(T)・∂(T)/∂T]T ₀ β=[1/(T)・∂(T)/∂T ² ]T ₀ γ=[1/(T)・∂( T)/∂T ³ ]T ₀ FIG. 1 is a diagram for explaining the cut angle of a crystal, and the X-axis, Y-axis, and Z-axis are the electrical axis, mechanical axis, and optical axis of the crystal, respectively. A plate parallel to a plane perpendicular to the Y-axis (Y-plate) is rotated by an angle φ around the Z-axis, and then rotated by an angle θ around the newly created X'-axis.

In each case, those rotating counterclockwise are positive.

Figure 2 shows the locus of the points where α=0, β=0, and γ=0 in the C-mode vibration of the vibration generated in the crystal piece, expressed by the relationship between the angle φ and the angle θ. It was calculated by As can be seen from Figure 2, the locus of β = 0 and the locus of γ = 0 intersect near θ = 0°, φ = 4° and at θ = 0°, φ =
-4°, and the locus of β = 0 and γ = 0 are very close to each other near θ = 31°, φ = 19° and in the vicinity of θ = 31°, φ = -19°. It is. It is a characteristic of crystal that it is symmetrical about φ=0°, and it is assumed to be 3-fold symmetrical about the Z axis. That is, in the description of the present invention, only one angle will be explained, but the part shifted by 120 degrees with respect to φ is the same as the present invention.

The area around θ=0° and φ=4° will be called the NL-O cut. When θ=-0゜20' and φ=4゜16' as typical cut angles of NL-O cut, the temperature coefficient is α=
6.492444×10 ^-5 /℃ β＝7.670672×10 ^-13 /℃ ²
γ=9.241893×10 ^-17 /℃ ³ .

The LC cut of the conventional crystal temperature sensor is α=3.748539×10 ^-5 /℃ β=−1.064300×10 ^-9 /℃ γ=3.035529×10 ^-10 /℃ ³⁵ °Y cut is α≒9.2×10 ^{- 5} /℃ β≒8.6×10 ^-8 /℃ ² γ≒4.4×10 ^-10 /℃ Compared to the temperature coefficient of ³ , the NL-O cut has a lower β and γ than the LC cut and the 5°Y cut. It turns out to be extremely small. This simply means that the NL-O cut exhibits good linearity.

The area around θ=31° and φ=19° will be called the NL-3 cut. When θ=31° and φ=19°24′ as typical cut angles for NL-3 cut, the temperature coefficient is α=8.987716×10 ^-6 /℃ β=4.127429×10 ^-11 /℃ ² γ=1.533113× 10 ^-11 /℃ ³ .

A sensor with zero β and γ and a large α is suitable as a temperature sensor. Compared to the LC cut, the NL-O cut has α 1.7 times, β 1/1400, and γ
is 1/3284532, and in the NL-3 cut, α is small at 1/4, but β is 1/26 and γ is 1/20.

Therefore, it can be seen that both NL-0 cut and NL-3 cut exhibit much better performance than conventional crystal temperature sensors. Also, the temperature range in which both show linearity is -
Temperature measurements can be made accurately over a wide range of 200 to 300 degrees Celsius even without a linearizer.

Figure 3 is a graph of the frequency-temperature characteristics of the 5°Y cut, LC cut, NL-0 cut, and NL-3 cut.

The advantages of the present invention are NL-0 cut,
Since both NL-3 cuts are near β=0 and γ=0,
This means that even if the cut angle slightly deviates, the characteristics do not change. For general temperature measurement, θ=4.5±1°, φ=−2°±6° for NL-0 cut, θ31.4°+2°−3°, φ=19.4°+3.5 for NL-3 cut A cut angle of -1.5° provided sufficient accuracy.

[Brief explanation of drawings]

Figure 1 is a diagram to explain the cut angle of crystal.
Figure 2 shows C mode vibration α=0, β=0, γ=0
Figure 3 shows the trajectory of 5゜Y cut, LC cut, NL
It is a graph of frequency-temperature characteristics of -0 cut and NL-3 cut.

Claims (1)

[Claims] 1 In a crystal temperature sensor, the crystal piece serving as the sensor rotates a plate perpendicular to the Y axis (mechanical axis) counterclockwise by 4.5° ± 1° with the Z axis (optical axis) as the rotation axis, and then This rotation created a new
A crystal temperature sensor that is obtained by rotating -2°±6° counterclockwise around the X′ axis.