JPH0331376B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a temperature detection device using an oscillator whose oscillation frequency changes depending on temperature, and particularly to a temperature detection device that is easy to calibrate.

[Technical background of the invention and its problems]

As an oscillator-type temperature detection device, devices using a crystal oscillator or a surface acoustic wave oscillator are conventionally known. This is because, in principle, the resonance frequency of a crystal resonator or surface acoustic wave element can be expressed as a function of temperature _.
The temperature is detected by using an oscillator configured with a surface acoustic wave resonator made of a crystal resonator (cut thickness shear vibration) or a LiNbO ₃ crystal substrate with a large temperature coefficient as a temperature sensor, and counting the oscillation frequency with a frequency counter. It is.

FIG. 1 shows an example of a conventional temperature detection device using a crystal oscillator. In FIG. 1, a temperature sensor 1 is constituted by an oscillator 3 equipped with a crystal oscillator 2, and generates an output at a frequency depending on the temperature.

This output is amplified by an amplifier 4 and mixed with a reference frequency signal from a local oscillator 6 in a mixer 5 to obtain a frequency difference signal. This is amplified in an amplifier 7, further ANDed with a time base 9 in an AND circuit 8, and this output is counted by a counter 10 to detect the temperature and display it on a display 11.

Moreover, what is shown in FIG. 2 is an example of a conventional temperature detection device using a surface acoustic wave oscillator. Second
The temperature detection device shown in the figure uses an oscillator 23 with an elastic surface resonator 22 as the temperature sensor 21, separates the temperature detection side (transmitter) and the display side (receiver), and connects the antenna 24a between the amplifiers 4a and 4b. , 24b for transmission and reception, the configuration is the same as that shown in FIG. 1, and the same parts are indicated by the same reference numerals.

The relationship between the frequency and temperature of the crystal oscillator 2 and surface acoustic wave resonator 22 used in these temperature detection devices can be approximated by the following cubic equation.

f _T −f _T0 = f _T0 {1+A(T−T ₀ ) +B(T−T ₀ ) ² +C(T−T ₀ ) ³ } …(1) f _T : Frequency at T°C f _T0 : T ₀ °C Frequency T: arbitrary temperature T ₀ : arbitrary reference temperature A, B, C: first-order, second-order, third-order temperature coefficients Note that the value of ABC varies greatly depending on the crystal material used. For example, Y cut Z propagation
In the case of a surface acoustic wave resonator using a LiNbO ₃ substrate, the values are approximately as shown below.

A=-88.7× ^10-6 , B=5.6× ^10-9 , C=112.7×
10 ^-12 Therefore, the temperature can be detected by performing the calculation shown in the following equation.

T=T ₀ + {(f _T −f _T0 )/f _T0 }/A...(2) In addition, if the second-order and third-order temperature coefficients B and C cannot be ignored, calculations to correct them should be performed. It is also possible to improve measurement accuracy by

(For Y-cut Z-propagation LiNbO ₃ , linearity is good and ±10°C to +60°C temperature range without correction.
A non-linear error of 0.1°C has been reported. ) However, in order to achieve and maintain this accuracy, the oscillation frequency f _T0 at an arbitrary reference temperature T ₀ must be finely adjusted.
It is necessary to calibrate it so that it can detect temperature correctly. Also, when used for a long time, the oscillation frequency f _T0 changes over time, causing temperature errors.
The original performance cannot be obtained. Therefore, in order to deal with this, it becomes necessary to periodically check whether the temperature display is correct and perform appropriate calibration.

This calibration is performed in an atmosphere where the temperature is conventionally maintained accurately, and in the case of Fig. 2, the temperature sensor 21
This is done by adjusting the oscillation frequency of the oscillator 23 that constitutes the. FIG. 3 is a block diagram showing more specifically an example of the transmitter on the temperature detection side of FIG. 2, and parts corresponding to those in FIG. 2 are indicated by the same reference numerals.

In the figure, Tr ₁ is an oscillation transistor, Tr ₂ is an amplification transistor, 25 is a bias stabilization circuit, 2
6 is the power supply, 27 is the trimmer capacitor, 28-3
1 is a resistor, 32 and 33 are capacitors, and the oscillator 23 is constructed as a Colpitts type.

In such an oscillator 23, frequency adjustment for temperature calibration is performed by finely adjusting the trimmer capacitor 27. However, fine adjustment of the trimmer capacitor 27 is a troublesome task that requires skill, and has the disadvantage that accurate adjustment is difficult.

[Purpose of the invention]

SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned drawbacks, and to provide a temperature detection device that can be easily and accurately calibrated without requiring any skill, and can perform highly accurate measurements.

[Summary of the invention]

This invention uses a temperature-sensitive and stable oscillator such as a crystal oscillator with a large temperature coefficient or a surface acoustic wave oscillator to detect temperature, and combines the output of this oscillator with a reference frequency signal from a stable local oscillator. The device is characterized in that the temperature is detected by obtaining a difference frequency signal and counting this with a counter, and also has a function of externally changing the oscillation frequency of the local oscillator, thereby calibrating the temperature.

[Effects of the Invention] According to the present invention, since calibration is performed by adjusting the oscillation frequency of the reference local oscillator based on data from the calculation section, temperature calibration is easy. Highly accurate temperature measurement is always possible.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

In the figure, a temperature sensor 41 is composed of a surface acoustic wave oscillator 43 equipped with a surface acoustic wave resonator 42, and has an oscillation frequency output depending on the temperature (for example, 25°C
It generates a frequency of 75.235 MHz (temperature change: 6.6 KHz/°C), and after power amplifying this output via an amplifier 44, it is radiated into the air from an antenna 45.

On the other hand, the receiving section receives this radio wave with an antenna 46, amplifies the received signal with a high frequency amplifier 47, and then supplies it to a first mixer 48. A first local oscillator 49 is connected to the mixer 48, and the mixer 48 mixes the output of the high frequency amplifier 47 and the stable local oscillation output to obtain an intermediate frequency output (for example, 10.7 MHz).

The local oscillator 49 is configured as a voltage controlled oscillator, and uses a prescaler 50, a PLL circuit 51, a crystal oscillator 52, and a low-pass filter 53 as a frequency synthesizer that can change the local oscillation frequency based on a predetermined program.

The intermediate frequency output of the mixer 48 is transmitted to the intermediate frequency amplifier 5.
4 and then supplied to the second mixer 55. A second local oscillator 56 is connected to the mixer 55, and the mixer 55 mixes the output of the intermediate frequency amplifier 54 with a local oscillation output (for example, 10.522 MHz) that is stable and corresponds to the intermediate frequency at 0°C. , only the change in the oscillation frequency that changes depending on the temperature of the temperature sensor 41 is extracted.

After this signal is amplified by a low frequency amplifier 57, an AND circuit 58 performs an AND operation with a reference signal having a frequency of 66 Hz that changes at 0.01° C. supplied from a time base 59, and supplies the result to a counter 60. At this time, the frequency value input to the counter 60 is the temperature itself. Therefore, the microcomputer 61 as a calculation means uses this temperature signal.
temperature indicator 63 consisting of an LED, for example.
display the temperature.

In this embodiment, data D is input to the microcomputer 61 and a control signal CS is output, so that critical temperature control is possible. That is, data can be outputted from the microcomputer 61, which is a calculation means, to the PLL circuit 51, and temperature control can be performed by changing the oscillation frequency of the local oscillator 49 according to this data.

If you want to perform temperature calibration now, as shown in the lower left of FIG. The input is made through the key input 62 of the microcomputer 61.

In this way, the microcomputer 61
Data is output to the PLL circuit 51, the oscillation frequency of the local oscillator 49 is finely adjusted, and control is performed so that the temperature display of the reference thermometer 64 and the display of the temperature display 63 become equal, and temperature calibration is completed. Therefore, calibration can be carried out easily and accurately without requiring the skill required to adjust the trimmer capacitor on the conventional temperature sensor side.

FIG. 5 shows another embodiment of the invention. In the embodiment shown in FIG. 4, the displayed value of the reference thermometer 64 is inputted as the key input 62 of the microcomputer 61, but in this embodiment, this is inputted directly to the microcomputer 61. Since the other configurations are the same as those shown in FIG. 4, the same parts are denoted by the same reference numerals and the explanation thereof will be omitted.

In this embodiment as well, the computer 61 performs calculations so that the display of the reference thermometer 64 and the display of the temperature display 63 are equal, and the resulting data output is added to the PLL circuit 51. Temperature calibration can be performed in the same way as in the case of .

Next, Fig. 6 shows a case where there are multiple transmitters including temperature sensors, and for ease of understanding, each component on the transmitter side is designated by the same number with a suffix of a, b, c...n attached to the corresponding part. It is displayed.

In this embodiment, each temperature sensor 41a, 4
The oscillation frequencies of 1b, 41c, . . . , 41n are shifted from each other. When receiving a temperature signal, the oscillation frequency of the local oscillator 49 on the receiving side is changed by a signal from the microcomputer 61.
The temperature detectors 41a, 41b, 41c, . . . , 41n can detect the temperature at each location. In this case as well, the reference thermometer 64 is placed at each position, and the local oscillator 49 is set so that the display of the reference thermometer 64 and the display of the temperature display 63 are equal.
The temperature can be calibrated by finely adjusting the oscillation frequency.

Note that the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications without changing the gist.

For example, in each of the above embodiments, the reference thermometer 64 is provided separately from the receiver, but it can also be provided inside the receiver, which makes it extremely easy to handle as a temperature detection device with a built-in calibration function. This makes it possible to easily and accurately measure the thermometer.

Furthermore, although the above embodiment uses two local oscillators on the receiving side to adopt a so-called double superheterodyne reception system, in some cases, the detection device of the present invention may be constructed using one local oscillator. You can also do it.

Further, in the above embodiment, the detection side and the reception side are separated and signals are transmitted and received using an antenna, but the present invention uses a configuration in which the detection side and the reception side are not separated, as shown in FIG. can also be implemented. As the oscillator for temperature detection, in addition to the surface acoustic wave oscillator, an oscillator whose oscillation frequency changes greatly depending on the temperature, such as a crystal oscillator, can be appropriately selected and used.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an example of a conventional temperature detection device using a crystal oscillator, Fig. 2 is a block diagram of an example of a conventional temperature detection device using a surface acoustic wave oscillator, and Fig. 3 is a block diagram of an example of a conventional temperature detection device using a surface acoustic wave oscillator. FIG. 4 is a block diagram of one embodiment of the present invention, FIG. 5 is a block diagram of another embodiment of the present invention, and FIG. 6 is a block diagram of the detector. FIG. 3 is a block diagram showing still another embodiment of the present invention, which includes a plurality of . 1...Temperature detector, 2...Crystal oscillator, 3...
Oscillator, 4, 4a, 4b...amplifier, 5...mixer, 6...local oscillator, 7...amplifier, 8...AND circuit, 9...time base, 10...counter, 11...indicator , 21...temperature detector, 22
... Surface acoustic wave resonator, 23 ... Oscillator, 24
a, 24b... Antenna, Tr ₁ ... Transistor for oscillation, Tr ₂ ... Transistor for amplification, 25
...Bias stabilization circuit, 26...Power supply, 27...
Trimmer capacitor, 28-31...Resistance, 3
2, 33... Capacitor, 41... Temperature detector,
42... Surface acoustic wave resonator, 43... Surface acoustic wave oscillator, 44... Amplifier, 45, 46... Antenna, 47... High frequency amplifier, 48... First mixer, 49... First Local oscillator, 50... Prescaler, 51... PLL circuit, 52... Crystal resonator, 53... Reduction filter, 54... Intermediate frequency amplifier, 55... Second mixer, 56... Second local section Oscillator, 57...Low frequency amplifier, 58...AND circuit, 59...Time base, 60...Counter, 61...Microcomputer, 62...Key input, 63...Temperature display, 64...Reference temperature Total, 65...prologue.

Claims (1)

[Claims] 1. A temperature sensor having an oscillator whose oscillation frequency changes depending on the temperature, a local oscillator that generates a reference frequency signal, and a temperature sensor that mixes the output of the temperature sensor with the reference frequency signal to generate a frequency. a mixer for obtaining a difference signal; a means for detecting temperature based on the frequency difference signal obtained by the mixer; a reference thermometer placed in the same temperature atmosphere as the temperature sensor; 1. A temperature detection device comprising: arithmetic means for outputting data such that a temperature display of the meter and a temperature display obtained by the temperature sensor are equal, and varying a reference frequency signal of the local oscillator. 2. The temperature detection device according to claim 1, wherein a surface acoustic wave oscillator is used as the oscillator for temperature detection. 3. Claim 1, characterized in that a crystal oscillator is used as the oscillator for temperature detection.
Temperature detection device described in section. 4. The temperature detection device according to any one of claims 1 to 3, wherein the output of the reference thermometer is inputted as a key input to the calculation means. 5. The temperature detection device according to any one of claims 1 to 3, wherein the output of the reference thermometer is directly input to the calculation means. 6. Temperature detection according to any one of claims 1 to 5, characterized in that the transmitter on the temperature detection side and the receiver on the display side are separated and the temperature signal is transmitted and received through a pair of antennas. Device. 7. The temperature detection device according to any one of claims 1 to 6, characterized in that a plurality of the temperature detectors are provided, and the oscillation frequencies of the respective oscillators are different from each other.