JPH0353569B2 - - Google Patents

Description

[Detailed description of the invention] Industrial applications The present invention relates to an infrared detection device.

Conventional configurations and their problems Conventional infrared detection devices include thermal type and photon type. Among these, for measuring living space temperature,
Thermal detection devices are used, which have relatively high sensitivity in the long wavelength region (5 μm or more) and are inexpensive. A typical example is a pyroelectric element used in microwave ovens, security devices, and other applications. Other examples include thermistor bolometers and thermopiles. However, all of these devices or elements obtain analog output,
There is a problem with noise resistance. Therefore, there has been a desire for an infrared detection device with digital output.

On the other hand, with the development of microcomputers, there is a desire for an element that can directly input digital signals to the microcomputer.

OBJECTS OF THE INVENTION The present invention satisfies these demands and aims to provide a highly sensitive and inexpensive thermal infrared detection device that generates a digital output signal.

Configuration of the Invention The infrared detection device according to the present invention includes an infrared detector having a feedback oscillator composed of an acoustic wave element and an amplifier, a shutter for intermittent infrared rays to be irradiated to the acoustic wave element, and a shutter for intermittent infrared rays to be irradiated to the acoustic wave element. The number of closing time output pulses from the infrared detector in the time from a predetermined time before the shutter opening time to the opening time, and the number of closing time output pulses from the infrared detector in the time from a predetermined time before the shutter closing time to the closing time. It is equipped with a counter that counts the number of open time output pulses and the difference between the number of output pulses of the closed time and the number of output pulses of the open time, and from the output of the counter, infrared rays or infrared rays irradiated to the elastic wave element. It measures and detects the temperature of an object that emits radiation. According to this device, an output pulse corresponding to the measured detected temperature can be obtained, so it is suitable for directly digitally processing the output signal.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the apparatus of the present invention will be described with reference to the drawings.

FIG. 1 shows the basic configuration of the present invention. In the figure, reference numeral 1 denotes a substrate made of a piezoelectric material such as lithium niobate, and a transducer 2 for transmitting acoustic waves and a transducer 3 for receiving waves are formed on the polished surface of the piezoelectric substrate 1 by a method such as vapor deposition. The elastic wave element is configured by being attached by. An output end and an input end of an amplifier 4 are connected to the transducers 2 and 3, respectively, thereby forming a feedback oscillator 5.

When the elastic wave propagation surface of the piezoelectric substrate 1 is irradiated with infrared rays, the temperature of the piezoelectric substrate 1 increases. The temperature rise of the piezoelectric substrate 1 at this time is 70
When an object (not shown) at ℃ is placed 7 cm from its surface, the temperature is approximately 1/1000℃. This 1/10
A minute temperature increase of 00°C is an amount that is difficult to measure by ordinary thermal expansion measurements.

Due to this temperature increase, the speed of the elastic wave in the piezoelectric substrate 1 changes, and this change in the speed of the elastic wave causes the elastic wave (for example, surface acoustic wave) propagating from the transducer 2 to the transducer 3 to
The phase upon arrival at the transducer 3 changes, and the frequency of the output signal from the oscillator 5 changes by the amount of the phase change. This output signal is taken out from the output terminal 7 through the capacitor 6.

The change in frequency at this time is equivalent to 70°C for an object at 70°C.
When placed at a distance of cm, the oscillation frequency of oscillator 5 is
At 176MHz, it was approximately 700Hz. This frequency change increases as the frequency of the oscillator 5 becomes higher and as the temperature coefficient of the piezoelectric substrate 1 increases. That is, the frequency change amount Δ is given by the following equation. (Japan Society for the Promotion of Science 131st Committee Materials 1972)
October 23, 2015 (Sendai)).

Δ=1/3a...Ql ² /k where a is the temperature coefficient of the piezoelectric substrate 1, is the oscillation frequency of the oscillator 5, k is the thermal conductivity of the piezoelectric substrate 1, and l is the distance between the transducers 2 and 3. 1/2 of the distance,
Q represents the infrared energy given to the piezoelectric substrate 1. According to the above equation, if a configuration using a piezoelectric substrate 1 with large values a, , Q, and l and a small value of k is used, the frequency change due to infrared irradiation becomes large. At this time, the higher the temperature of the object that irradiates the piezoelectric substrate 1 with infrared rays compared to that of the piezoelectric substrate 1, the larger the frequency change becomes. That is, for an object having a temperature similar to that of the piezoelectric substrate 1, the change in the oscillation frequency will be small, making it difficult to detect the change in frequency. This corresponds, for example, to detecting human body temperature (about 30 degrees Celsius) at room temperature (about 25 degrees Celsius).

The present invention makes it possible to increase the change in oscillation frequency when the temperature difference between the piezoelectric body of the infrared detector and the object to be detected is small, thereby increasing the infrared detection sensitivity.

FIG. 2 shows an apparatus having the configuration shown in FIG.
This shows how the frequency changes when infrared rays are irradiated intermittently using a shutter. In the figure, curves 11 and 13 show changes in oscillation frequency when the shutter is opened, and curve 12 shows changes in frequency when the shutter is closed. ₀ is 171MHz, n is the minimum value at which the oscillation frequency changes (decreases) when the shutter is opened, and t ₁
indicates the time interval between shutter opening and closing. That is, when t<0, the oscillator 5 oscillates at a frequency of ₀ , that is, 171 MHz. When the shutter is opened at t=0, the piezoelectric substrate 1 is irradiated with infrared rays, and the oscillation frequency of the oscillator 5 gradually decreases. And t=t ₁
Then, the oscillation frequency changes by ( ₀ − n) from the beginning. The state of attenuation of the oscillation frequency at this time is curve 1
This is shown in 1. When the shutter is closed when t = t ₁ , the piezoelectric substrate 1 is no longer irradiated with infrared rays, and the oscillation frequency becomes ₀ =
Increases to 171MHz. This state is shown by curve 12.
When the shutter is opened again at t= _2t1 , the oscillation frequency decreases and follows curve 13 in the same manner as described above.
This is repeated as the infrared rays are interrupted. At this time, a signal obtained by pulsing the oscillation output signal from the oscillator 5 only during the period between time 14 and time t ₁ , which is a time t ₂ from the time t ₁ when the shutter is closed;
On the other hand, an up-down counter measures the difference between the pulsed oscillation output signal and the time ₁₅ , which also goes back by time _t2 , from the time 2t1 when the shutter is opened. The count signal from this up-down counter, that is, the difference in the number of pulses between the two pulse signals described above, changes depending on the temperature of the object that radiates infrared rays. Conversely, by measuring this count signal, the temperature of the object to be measured can be measured.

FIG. 3 shows an example of a configuration diagram of the measurement circuit. In the figure, 31 is the feedback oscillator 5 of FIG.
This shows an infrared detector composed of. The output of this surface acoustic wave oscillator 31 is guided to a pulse generator 32 and pulsed. On the other hand, infrared radiation from an object to be measured is incident from in front of the infrared detector 31, and a shutter 33 is provided in the middle of the infrared radiation. This shutter 33 is driven by a shutter opening/closing drive circuit 34. The output of the pulsing circuit 32 is input to an up-down counter 35, and the timing signals from the shutter opening/closing drive circuit 34, that is, times t ₁ , 2t ₁ , 3t ₁ , 14, 14, in FIG.
The output pulses from the pulse forming circuit 32 are counted using a timing signal according to the timing signal 15 or the like. This up-down counter 35 generates a pulse signal (number of closing time output pulses) from time 15 to _2t1 as shown in FIG.
and the pulse signal (opening time output pulse number) in the time from time 14 to _t1 is measured. This measurement output is led to a microcomputer 36, where it is subjected to arithmetic processing, and the result is displayed on a display 37. The microcomputer 36 has
A timing signal from the shutter opening/closing drive circuit 34 may be input. If this timing signal is input, the time change in the number of output measurement pulses of the up-down counter 35 can be stored in the microcomputer 36 and used for various controls. I can do it. For example, when used in a food heating cooker, the temperature of the food is detected by an infrared detector 31, the change in the number of output pulses over time is measured by a microcomputer, and when a certain number of pulses is reached, heating is stopped. It is used for such purposes.

FIG. 4 further shows a schematic diagram of an improved device in which the oscillation output frequency does not change due to temperature rise of the infrared detector itself. In the figure, 41
indicates an infrared detector having the same configuration as above, and 42
indicates a feedback oscillator having the same configuration as this infrared detector 41. The infrared rays are incident only on the infrared detector 41 via the shutter 43. Feedback oscillator 42
is used to offset the influence of ambient temperature fluctuations on the characteristics of the infrared detector 41. The output signals from the infrared detector 41 and the feedback oscillator 42 are
The signals are input to a mixer 46 through buffer amplifiers 44 and 45, respectively. In addition, the buffer amplifier 4
4 and 45 may be provided as needed, and are not always necessary. mixer 46
Then, a frequency difference signal between the output signals from the infrared detector 41 and the feedback oscillator 42 is extracted. Since the infrared detector 41 and the feedback oscillator 42 have the same configuration as described above, they generate substantially the same frequency signals. Therefore, the output signal frequency of mixer 46 is considerably lower than both output frequencies. In the experiment, an infrared detector 41,
The output of the feedback oscillators 42 was approximately 171 MHz, and the output of the mixer 46 was approximately 130 KHz.
The output signal of the mixer 46 is converted into a pulse signal by a pulse forming circuit 47. On the other hand, shutter 43
is driven by a shutter opening/closing drive circuit 48. At the same time, it includes an up-down counter that counts the pulse signal from the pulsing circuit 47 in accordance with the timing signal (at times t ₁ , 2t ₁ , 3t ₁ , 14, 15, etc.) from the shutter opening/closing drive circuit 48; The output of the pulsing circuit 47 is monitored by the microcomputer 48 (of course, the operation of the shutter opening/closing drive circuit 48 may be controlled by commands from the microcomputer 48). The number of pulses counted by the microcomputer 48 is displayed on the display 49. Alternatively, an object to be controlled, such as a heating cooker, can be controlled by the microcomputer 48 if necessary.

FIG. 5 shows how the number of counted pulses changes with respect to the temperature change of the object to be measured in the above apparatus. In addition, here, O~t ₁ in Fig. 2
was set to 2 seconds, and t ₂ was set to 1 second. From this, it is possible to accurately measure the temperature of the object to be measured from the number of counted pulses. In the figure, the negative sign attached to the number of counted pulses corresponds to the difference in the number of input pulses of the up-down counter 35.

Effects of the Invention As explained above, the infrared detection device according to the present invention configures a feedback oscillator with an acoustic wave element and an amplifier, and intermittents the infrared rays irradiated to the acoustic wave element with a shutter. , the frequency of each signal obtained from the feedback oscillator during the time from a predetermined time before the shutter opening time to the opening time, and from the time from a predetermined time before the shutter closing time to the closing time. It is configured to measure the temperature of the object to be measured by measuring the difference between the corresponding number of pulses (opening time output pulse number and closing time output pulse number), so it has an extremely high detection sensitivity. Furthermore, since the output signal is a pulse, it has the advantage of very good noise resistance. Since the frequency change corresponds to infrared energy, the temperature of the object to be measured can be measured without touching the object. Furthermore, higher sensitivity can be achieved by setting the pulse counting time due to opening and closing of the shutter to an appropriate value in accordance with the thermal time constant of the acoustic wave element.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the basic structure of an infrared detection device according to the present invention. Fig. 2 is a diagram for explaining the principle of the infrared detection device according to the present invention, Figs. 3 and 4 are block diagrams showing the configuration of one embodiment thereof, and Fig. 5 shows the temperature and temperature of the object to be measured. It is a figure which shows an example of the relationship with an output. DESCRIPTION OF SYMBOLS 1... Piezoelectric substrate, 2, 3... Transducer, 4... Amplifier, 5... Feedback type oscillator, 31...
...Infrared detector, 32...Pulsing circuit, 33...
...Shutter, 34...Shutter opening/closing drive circuit, 3
5...Up-down counter, 36...Microcomputer, 37...Display device, 41...Infrared detector, 42...Feedback type oscillator, 43...Shutter, 44, 45...Buffer amplifier, 46...Mixer , 47...Pulsing circuit, 48...Microcomputer including up-down counter, 49
……display.

Claims (1)

[Claims] 1. An infrared detector having a feedback oscillator composed of an acoustic wave element and an amplifier; a shutter for intermittent infrared rays to be irradiated to the acoustic wave element; The number of closing time output pulses from the infrared detector in the time period up to the opening time, and the number of opening time output pulses from the infrared detector in the time period from the predetermined period of time before the shutter closing time to the closing time. and a counter that counts the difference between the closed time output pulse number and the open time output pulse number, and irradiates the acoustic wave element with infrared rays or infrared rays from the output of the counter. An infrared detection device characterized by measuring and detecting the temperature of an object.