JPS62259026A - Vibration type temperature sensor - Google Patents

Abstract

PURPOSE:To obtain a sensor suitable to a digital system by measuring the frequency or period of counting operation through the counting operation. CONSTITUTION:A vibrating piece 1 is formed by joining plates 11 and 12 made of materials having different coefficients of heat expansion with each other and its one end is joined with holders 3 and 4 and fixed to a base 2. Further, a weight 5 is fitted to the other end of the vibrating piece 1. Further, a piezoelectric element 6 for driving and a piezoelectric element 7 for detection are provided. Vibrations of the vibrating piece 1 are detected by the element 7 and converted into an electric signal, which is amplified 8; and the output of the amplification is applied to the element 6 to drive the vibrating piece 1. This feedback allows the vibrating piece 1 to oscillate continuously at its resonance frequency. The output voltage signal of the amplifier 8, on the other hand, is led out and its frequency or period is measured by a counter, so that temperature is known from the measured value.

Description

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, the cross-sectional shape of a bimetallic diaphragm obtained by joining plates with different coefficients of thermal expansion curves depending on the temperature, and as a result, the resonant frequency of the diaphragm increases. This relates to a vibration-type temperature sensor that utilizes changes in temperature.

Sensors that convert the measured quantity into pulse frequency and time width and output them are compatible with digital signal processing devices, so various types of sensors are being developed recently, but this type of temperature sensor is There aren't many things. So-called digital thermometers currently on the market use conventional temperature sensors such as thermistors and thermocouples to convert temperature into analog electrical signals, which are then converted into digital quantities using voltage-frequency converters, etc. Most of them are through indirect methods. A crystal thermometer that directly converts temperature into frequency is a crystal thermometer that uses the temperature coefficient of a crystal oscillator, but the rate of change in frequency due to temperature is originally small, so a constant temperature bath or the like is used to detect the frequency change. This method has the disadvantage that the entire system becomes large and expensive, such as requiring a separate precision crystal oscillator.

The temperature sensor of the present invention also directly converts temperature into frequency, but it uses a bimetallic diaphragm, and the cross-sectional shape of the diaphragm bends due to temperature changes, causing its second moment of area to change. This is a sensor based on a completely new principle that utilizes the phenomenon that the resonant frequency of the diaphragm changes.

The object of the invention is firstly to provide a temperature sensor suitable for digital systems.

This is because the output form of the sensor of the present invention is frequency.
This is because by measuring the frequency or period through a counting operation, it can be easily converted into a digital quantity.

The second objective is to provide a highly sensitive frequency output type temperature sensor. This is an effect using the new principle described above. In the sensor of the present invention, it is easy to scale the frequency change rate by 10% or more with respect to full-scale temperature change, and therefore, the clock accuracy of a normal digital computing device is sufficient for counting and measuring the frequency. , does not require a particularly precise crystal oscillator.

Thirdly, a temperature sensor with a simple structure and small size can be provided, which is also one of the advantages of using a new operating principle. Furthermore, the parts used in the sensor of the present invention are universal, such as bimetal and piezoelectric elements, and do not require precision machining, and therefore can be manufactured at extremely low cost. This is also one of the features of the sensor of the present invention.

In Figure 1, 1 has a coefficient of thermal expansion of C1 and C, respectively.
It is a bimetallic vibrating piece made by joining plates 11 and 12 of two materials, and one end thereof is joined to holders 3 and 4, thereby fixing it to base 2. A weight 5 is attached to the other end of the vibrating piece l, so that it can freely vibrate in the direction of the arrow in the figure. In actual use, a protection tube 10 as shown by the dotted line is attached, and is attached to the measurement point using an attachment port 9 provided on the base 2.

When measuring the temperature, the tube 10 has several small ventilation holes around it, but when measuring the temperature of a liquid, it has a sealed structure so that the entire sensor is immersed in the liquid. . The reason why the holder 3.4 is made into an elongated shape to hold the vicinity of the center line of the vibrating element l is to prevent as much as possible the curvature of the cross-sectional shape of the vibrating element due to temperature, which will be described later. .

The curvature of the bimetallic vibrating piece l changes as the temperature changes, but for the sake of simplicity, the thickness of the plates 11 and 12 will be expressed as hl and 'h2, respectively, and the thickness of the vibrating piece l will be expressed as h.
When expressed as 1t1=712=h/2 (1)
, and when the longitudinal elastic modulus of the material in 11.12 is expressed by Ex and E2, respectively, Ex = E2 = E
Assuming that (2) is true, the relationship between the radius of curvature R of the vibrating element l and the temperature T is as follows.

R=2h/3Δc T (3) However, T is the temperature based on the temperature θ0°C when the vibrating piece 1 becomes flat, and if the temperature of the vibrating piece 1 is 0°C, then T=θ−θo (4 ). In addition, ΔC is the difference in thermal expansion coefficient, Δc=c2−C1(
5).

As is clear from equation (3), the radius of curvature R changes in inverse proportion to the temperature T, which causes the weight 5 at the tip of the vibrating element 1 to displace, but at the same time, as shown in FIG. ,1
The shape of the cross section perpendicular to the length direction of the vibrating element 1 is also curved with a curvature of half 1xB, and as a result, the cross-sectional moment of inertia I of 1 changes. It is detected as a change in the resonant wave number.

The primary resonance frequency f1 of the transverse vibration of the vibrating element 1 is expressed as follows.

Here, l is the effective length of the vibrating part of 1, 1M, and the mass of the tip of the tip, 1m, is the mass of the vibrating part of l. The relationship between the second moment of area I and the radius of curvature R of the vibrating piece l is 4
Assuming that the thickness h of l is sufficiently small, it can be approximately expressed as follows.

1=a5h/720R" (7) Substituting equation (3) into the above equation) -a5Δc2T2/3207z (8) Therefore, the resonant frequency f1 changes approximately in proportion to the temperature T. Note that vibration The radius of curvature in the length direction of piece 1 is f
Since it has little to do with l, it can be freely set independently of the radius of curvature R of the cross section perpendicular to the length direction, and for example, a vibrating piece shaped like an arc in the length direction can also be used. .

There are various methods for detecting changes in the resonant frequency of the vibrating element 1, but the most reliable and simplest method is to construct an oscillation system including the vibrating element and oscillate at the resonant frequency. That is, in FIG. 1, 6 and 7 are piezoelectric elements for driving and detection, respectively, and the vibration of the vibrating element l is detected at 7 and becomes an electric signal, which is amplified by amplifier 8, and its output voltage is and drives the vibrating piece 1. This feedback causes l to oscillate continuously at its resonant frequency. The output voltage signal of the amplifier 8 is also led to the outside, and its frequency or period is measured by a counter or the like, from which the temperature T can be determined.

Here, considering the rate of change ΔR/R of the radius of curvature R when the temperature T changes by ΔT, the following relationship can be obtained from equation (3).

ΔR/R=-3ΔcRΔT/2h (10) Bimetals include combinations of various metals, including those bonded with non-metallic materials such as plastics, but here we will focus on the most common types. Assuming that brass-amber bimetal is used, Δc = 2X10-'/deg
and 71=0.511111, R=501,
If ΔT = 1100de, ΔR/R= -0,
Get 3. That is, when T changes by 1100 de in the initial state of R=50 mI11, R changes by about 30%. Therefore, according to (7), the second moment of area I is 6
Therefore, also by equation (6), it can be seen that the resonant frequency ht changes by 30%. As described above, compared to conventional crystal oscillator thermometers, the temperature sensor of the present invention has a much larger rate of change in frequency, and this is due to the principle of utilizing changes in the cross-sectional shape of the bimetal vibrating piece. . Note that if Δc<O, then T<O, and in this case, as the temperature rises, 17''l decreases, so the resonance frequency f1 can be made to decrease as the temperature rises.

The knob 5 attached to the tip of the vibrating piece 1 is not necessarily necessary in the present invention. The resonant frequency of the vibrating piece l without the weight 5 is given by M=O in equation (6). However, at the stage of manufacturing the sensor of the present invention, it is convenient to adjust the mass M of the weight 5 in order to adjust the resonance frequency of the vibrating element.

In the above description, the vibration of the lowest-order resonance frequency f1 of the vibrating element l has been described, but it is also possible to utilize higher-order resonance of the vibrating element.

The higher-order resonance frequency of the vibrating piece l is a constant multiple of fl, and (
6) is expressed in exactly the same format as Eq. Therefore, the above theory regarding the rate of change of fl due to temperature, etc. holds true even when using higher-order resonance frequencies, and the above theory is for simply explaining the principle of the present invention. (1) Although this is simplified by setting constraints for Equation and Equation (2), in reality, in the case of h1 arrow h2, or E1
The case of NE2 is common. Furthermore, three different metals may be joined to form a bimetal. However, it goes without saying that the sensor of the present invention can be constructed even in these cases.In these cases, it is important to understand how the radius of curvature of the vibrating element l is expressed as a function of temperature, or how the resonance frequency #j! , f1, etc. are explained in detail in specialized books and the like, and are already well known. Even in these cases, there is no change in the wood quality of the present invention in that the cross-sectional shape of the vibrating piece is bent by temperature, the moment of inertia of the area changes, and as a result, the resonant frequency of the vibrating piece changes.

The vibrating piece used in the sensor of the present invention is not limited to the one shown in FIG. 1. In FIG. This is an example in which the holder 23 is joined to 24 holders 23 in the shape of a tuning fork.

25 is a driving piezoelectric element, and 26 is a detection piezoelectric element, which constitute an oscillation system together with an electronic circuit (not shown) such as an amplifier or a phase-locked loop (PLL). And what is its oscillation frequency?

It changes in response to changes in the curvature of the cross-sectional shapes of 21 and 22 due to temperature. The advantages of such a tuning fork type vibrator are:
Since the vibrating pieces 21 and 22 vibrate in opposite phases to each other, and the forces due to their vibrations cancel each other out in the holder 23, the vibration energy dissipated from the base 24 to the outside via the mounting port 27 is small, and therefore oscillation can be performed with low power. It is something that can be sustained. In addition, 28 is a protection tube.

In FIG. 3, a current is passed directly to a bimetal vibrating element 31 through terminals 33 and 34, and the curvature of its cross section changes due to the temperature rise due to the heat generated in the vibrating element itself. This directly detects the temperature of the vibrating element, but since that temperature is determined by the magnitude of the current flowing through the vibrating element, it can be used to indirectly measure the magnitude of this current. can. FIG. 3 also shows an embodiment in which the vibrating piece is held at two points, unlike the previous two examples where one end of the vibrating piece is fixed and held.

In this case, the vibrating piece 31 bends and vibrates in a direction perpendicular to its surface, but if the length of the vibrating piece 31 is l, then at the primary resonance frequency, the vibration is at a position 0.2241 from both ends of the vibrating piece 31. Since a knot occurs, the stem 35.3 is placed around it.
Try to hold it at 6.

In this case, since the temperature of the vibrating element 31 becomes considerably high, the piezoelectric element is not used, and instead the reflective optical sensor 3 is used.
7 is used to detect the vibration displacement of the vibrating piece 31. Further, driving is also performed by attracting an iron piece 39 bonded to the vibrating piece 31 with an electromagnet 38. An electronic circuit (not shown) such as an amplifier or a PLL circuit is connected between 37 and 38, so that the vibrating piece continues to vibrate at its resonant frequency. The temperature can be determined by measuring the frequency or period with a counter or the like, as in the previous two examples. These elements are mounted on a base 32 having mounting holes 41 and 42, and are protected by a protective cover 40.

The diaphragm used in the temperature sensor of the present invention is not limited to the rectangular vibrating piece as in the above example. FIG. 4 shows an embodiment using a vibrating disk.

Reference numeral 51 denotes a vibrating disk having a radius r, which is made by stacking and joining two plates having different coefficients of thermal expansion, and its center portion is fixed to a stem 53, which is further fixed to a base 52.

When the vibrating disk 51 is flat, its lowest order resonance frequency f1 is expressed as under the conditions of equations (1) and (2). Here, m is the mass of the vibrating disk 51.

When the temperature changes from this state, the cross section of the vibrating disk 51 curves with a radius of curvature R given by equation (3), as shown by the dotted line in FIG. That is, the vibrating disk 51 has a radius R
forms part of the spherical shell of Depending on the direction of temperature change and the sign/negative of the difference in thermal expansion coefficients ΔC, there are cases where the curve bends downward, contrary to the figure, but in any case, as the radius of curvature R becomes smaller, the resonance frequency f1 becomes larger.

54 is a piezoelectric element for driving, which drives the vibrating disk 51 via the stem 53. Reference numeral 55 denotes an annular detection piezoelectric element, which is attached to the center of the vibrating disk 51.
A resilient plastic piezoelectric element is used to prevent it from peeling off even when bent. The output voltage of 55 is then amplified by an electronic circuit 56 and fed back to 54. As a result, the vibrating disk 51 continues to vibrate at the resonance frequency f1, and the temperature T can be determined from the frequency or period. It goes without saying that a diaphragm can also be used.

In summary, the wood of the present invention deforms the cross section of the diaphragm due to the difference in thermal expansion when the temperature changes in a diaphragm obtained by stacking and bonding plates made of materials with different coefficients of thermal expansion. This method utilizes the phenomenon that the resonant frequency of the diaphragm changes due to the change in the resonance frequency of the diaphragm, and by this method, it is possible to realize a frequency output type temperature sensor with a simple structure and high sensitivity.

[Brief explanation of drawings]

Figure 1 shows an example of the present invention, Figure 2 shows an example of the present invention using two vibrating pieces, and Figure 3 shows a case where the temperature of the vibrating piece is detected when a current is passed directly through the vibrating piece. Examples of the present invention,
FIG. 4 shows an embodiment of the invention using a vibrating disk. 1----1 vibrating piece, 2-11 base, 3.4----
Holder, 5---One weight, 6---Piezoelectric element for drive, 7---Piezoelectric element for detection, 8-111 amplifier, 9-111 mounting bolt, 10---1 protection tube , 11.12---
Plates with different coefficients of thermal expansion, 21.22---One vibrating piece, 23-One holder, 24---Base, 25
-----Piezoelectric element for driving, 26---Piezoelectric element for detection, 27--Mounting bolt, 28---Protection tube,
31---One vibrating piece, 32---Base, 33.
34---One terminal, 35.36---Stem,
37---Reflective optical sensor, 38---1 magnet, 39---1 iron piece, 40---protective cover, 41.
42---One mounting hole, 51--m-Vibrating disk, 52--
--- Base, 53 --- Stem, 54 --- Piezoelectric element for driving, 55 --- Piezoelectric element for detection. 56---Electronic circuit, 57---Protective cover, 58
゜59.60.61 --- One mounting hole.

Claims (1)

[Claims] It has one or more diaphragms obtained by stacking and bonding plates made of materials with different coefficients of thermal expansion, and means for detecting the resonant frequency of the diaphragm, and has a means for detecting the resonance frequency of the diaphragm. A vibration-type temperature sensor characterized in that the temperature of the diaphragm is determined by a change in the resonant frequency of the diaphragm caused by the deformation.