JPH03180730A - Temperature measuring instrument - Google Patents

Abstract

PURPOSE:To detect temperature in a constant range according to infrared rays without using any chopper mechanism by making the temperature of a pyroelectric infrared detecting element varies when the infrared rays are supplied from outside and detecting the variation by a temperature detecting means. CONSTITUTION:A C/F converter 7, a frequency measuring circuit 8, and an output transistor(TR) 9 constitute the temperature detecting means 12 which detects temperature according to variation in the capacity of the pyroelectric infrared detecting element 2. Then the temperature measuring instrument is arranged by oppositing a body whose temperature is to be detected and then the infrared rays are made incident on the element 2 through a Fresnel lens 1. Therefore, when the temperature of an object to be detected is about 48 deg.C e.g. 50 deg.C, the temperature of the element 2 itself rises as well and the electrostatic capacity of a capacitor C is decreased. Further, when the temperature of the object is lower than 48 deg.C, the temperature of the element 2 itself is lowered and the electrostatic capacity of the capacity C is increased. Therefore, the temperature of the object which is about 48 deg.C, e.g. 40 - 53 deg.C can be measured according to the output of the converter 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for measuring the temperature of a heat source that emits infrared rays, and particularly to a temperature measuring device using a pyroelectric infrared detecting element.

[Conventional technology]

Since a pyroelectric infrared detection element can only detect temperature changes, this detection element has conventionally been used to detect moving heat sources. In order to detect the amount of infrared rays, a mechanical chopper mechanism is provided in front of the pyroelectric infrared detection element, and the amount of infrared rays is detected by cutting off the incident infrared rays.

[Problems to be Solved by the Invention] Therefore, the conventional temperature measuring device requires a drive section for a chopper mechanism, which has the drawback of making the configuration large and complicated. Furthermore, the drive section of the chopper mechanism has a short lifespan, and the shortcomings are that the heat source cannot be switched on and off very quickly and the response speed cannot be increased.

The present invention has been made in view of the problems of the conventional temperature measuring device that uses a pyroelectric infrared detection element as a sensor and uses a mechanical chopper mechanism. The technical challenge is to be able to measure the temperature of objects using infrared rays.

[Means for Solving the Problems] The present invention includes a pyroelectric infrared detection element, a heating means for heating the pyroelectric infrared detection element to a predetermined temperature, and a frequency component of the resonance frequency of the pyroelectric infrared detection element. The device is characterized in that it includes voltage application means for applying an alternating current voltage, and temperature detection means for detecting temperature based on a change in capacitance of a pyroelectric infrared detection element.

[Effect]

According to the present invention having such characteristics, by heating the pyroelectric infrared detecting element to a predetermined temperature and applying an alternating current voltage having a frequency component corresponding to its resonant frequency, infrared light obtained from the outside can be detected. The operating point where the capacitance changes due to infrared light is selected. When infrared rays are applied from the outside, the temperature of the pyroelectric infrared detection element changes, and the temperature change appears as a change in capacitance.

Therefore, this capacitance change is detected by the temperature detection means.

〔Example〕

FIG. 1 is a diagram showing the overall configuration of a temperature measuring device according to an embodiment of the present invention. The temperature measuring device of this embodiment has a Fresnel lens 1 for focusing infrared rays on an object that generates infrared rays, and a pyroelectric infrared detecting element 2 is provided at the focal point of the Fresnel lens 1. The equivalent circuit of the pyroelectric infrared detection element 2 is expressed as a parallel connection of a resistor R and a capacitor C as shown in the figure. This pyroelectric infrared detection element 2 is housed in a heater block 3 as shown.

Heater block 3 is heated by heating device 4 .

A predetermined power is supplied to the heating device 4 so that the pyroelectric infrared detecting element 2 is kept at a predetermined temperature, for example, 48° C. in this embodiment. Now, the capacitor C shown in the equivalent circuit of the pyroelectric infrared detection element 2 has frequency characteristics having a plurality of resonance points. Fig. 2(a) shows the frequency characteristics of the capacitance of capacitor C. Fig. 2(b) shows the frequency characteristics of the admittance, which in this example is about 1.04M.
It resonates at a frequency of Hz. Here, the oscillation frequency of the oscillator 5 is selected to be equal to this resonant frequency, and is applied to the pyroelectric infrared detection element 2 via the DC power supply 6 superimposed on this DC voltage. Here, the DC bias power supply is set to -35V, for example, and the frequency of the oscillator 5 is 1.0V.
The frequency is 4MHz and the amplitude is 0.45V. Additionally, a C/F converter 7 is connected to both ends of the pyroelectric infrared detection element 2. C
The /F converter 7 oscillates a frequency corresponding to the capacitance of the capacitor C shown in the equivalent circuit, and its output is given to the frequency measuring circuit 8. The frequency measurement circuit 8 has a comparator to which a predetermined dark value is set, and provides an output to the outside via an output transistor 9 when the frequency exceeds the dark value due to a frequency change based on a change in capacitance. It is. Here, heater block 3 and heating device 4
constitutes a heating means IO that heats the pyroelectric infrared detection element 2 to a predetermined temperature, and the oscillator 5 and the DC amount ag6 are voltages that apply an AC voltage having a resonance frequency component of the pyroelectric infrared detection element. It constitutes the application means 11. Also C,
/F converter 71, frequency measuring circuit 8, and output transistor 9 constitute temperature detecting means 12 that detects temperature based on a change in capacitance of a pyroelectric infrared detecting element.

FIG. 3 is a diagram showing the capacitance of the capacitor C in the equivalent circuit of the pyroelectric infrared detection element 2 and its temperature change. In this figure, the temperature of the pyroelectric infrared detection element 2 in the heater block 3 is maintained at 48° C. by the heating device 4. When this temperature measuring device is placed facing the object whose temperature is to be detected, infrared rays are incident on the pyroelectric infrared detecting element 2 through the Fresnel lens (2). Therefore, if the temperature of the object to be detected is in the vicinity of this temperature, for example 50° C., the temperature of the pyroelectric infrared detection element 2 itself will also rise, thereby reducing the capacitance of the capacitor C. Further, if the temperature of the object to be detected is lower than 48° C., the temperature of the pyroelectric infrared detection element 2 itself also becomes low, and thereby the capacitance of the capacitor C increases as shown in the figure. Therefore, based on the output of the C/F converter 7, the temperature around 48°C of the object whose temperature is to be detected, for example, in this embodiment, the temperature in the range of 40°C to 53°C is measured and the output is obtained. I can do it.

In this embodiment, as mentioned above, the DC power supply 6 receives -35V.
It gives a bias voltage of . FIG. 4 shows the change in capacitance C when the pie-sumi pressure is changed. As shown in this figure, it can be seen that when a bias voltage exceeding 20 V is applied, the capacitance of the capacitor C hardly changes. Also, as the frequency of the AC power applied to the pyroelectric infrared detection element 2, a frequency other than the resonance point, for example, 4M
When Hz is selected, the capacitance of capacitor C with respect to temperature changes is shown as shown in FIG. In this case, the capacitance hardly changes with respect to temperature changes, making it impossible to perform sufficient temperature detection. Therefore, as shown in FIG. 2, it is necessary to select the resonance point frequency as the frequency of the AC power source.

In this embodiment, the oscillator 5 whose oscillation frequency is manually changed is used to select this frequency, but the oscillation frequency may be automatically made to follow the resonant frequency.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to construct a temperature measuring device that can detect temperature within a certain range based on infrared rays without using a mechanical chopper mechanism. Furthermore, since it can be configured without using a mechanical chopper, it is also possible to downsize the entire device.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of a temperature measuring device according to an embodiment of the present invention, FIG. b) is a diagram showing changes in equivalent admittance with respect to temperature, Figure 3 is a diagram showing changes in capacitance with respect to temperature of the heater block, Figure 4 is a diagram showing changes in capacitance with respect to DC bias voltage, and Figure 5 is a diagram showing changes in capacitance with respect to DC bias voltage. The figure is a graph showing the characteristics of capacitance with respect to temperature changes at frequencies other than the resonant frequency. Fresnel lens 2 --- Pyroelectric infrared detection 3 ---
・Heater block 4...--Heating 5--
-Oscillator 6-・-DC power supply 7C/F converter
8------Frequency measurement circuit---Output transistor ■0------1 Heating means 1---1 Voltage application means 12---Temperature detection means output element device No. figure? 2 2 -------1 Jiao, Den? ! , twoto a kidahi Izuki↓
Preliminary 10----Ichikaro Sad 8a 11---- tJEel'1o-8!12----
---, Detection-8t Figure (a) (M day 2) Figure (b) □□□'r-4z)

Claims (1)

[Claims] (1) A pyroelectric infrared detection element, a heating means for heating the pyroelectric infrared detection element to a predetermined temperature, and a voltage application for applying an alternating current voltage having a frequency component of the resonance frequency of the pyroelectric infrared detection element. A temperature measuring device comprising: a temperature detecting means for detecting temperature based on a change in capacitance of the pyroelectric infrared detecting element.