JPS59142427A - Heat sensor - Google Patents

Abstract

PURPOSE:To enable stable heat sensing by combination of both functions of a constant temp. type and a differential type without mulfunction by detecting both of temp. and temp. rising rate with a pyroelectric element provided with an impedance conversion circuit. CONSTITUTION:An FET2 of an impedance conversion circuit connecting to an output resistance 4 is connected to a pyroelectric element 1 which is an insulator connected with an input resistor 3 and detects the IR corresponding to a temp. of high resistance. The DC bias voltage of the FET2 changes according to the change rate of ambient temp. and the AC signal superposed on a DC bias by the radiation IR energy of an object to be measured of temp. chopped through an IR transmission window is taken out from said FET. Both of the temp. rising rate and the temp. are detected by such DC bias signal and AC signal. The stable heat detection is thus accomplished by the combination of both functions of a constnat temp. type and a differential type without malfunction.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a compensated spot type heat sensor that combines the performance of both constant temperature and differential types.

Conventional structure and problems There are three types of conventional heat sensors: constant temperature type, differential type, and compensation type. Among them, there are constant temperature type and differential type with various operating principles, but the only known compensation type is the combined air/metal expansion type. When it comes to fire outbreaks, the differential type is advantageous in the combustion state, and the constant temperature type is advantageous in the smoldering state, but the compensation type, which compensates for the drawbacks of both, allows fires to be detected more reliably. By combining functions in this way, it is possible to more reliably discover malfunctions or problems that could not be detected using a single function.

Purpose of the Invention The present invention provides a compensating type heat sensor that detects both multiple temperatures and temperature change rates with a simple configuration, and has both a constant temperature type and a differential type, a temperature control sensor that operates stably, etc. The purpose of this study is to provide a new heat sensor to realize this.

DESCRIPTION OF THE INVENTION The present invention is a heat sensor that detects both ambient temperature and temperature rise rate based on fluctuations in the DC voltage level of a pyroelectric element that has undergone impedance conversion.

Description of examples The present invention will be described in detail below based on examples.

A pyroelectric infrared detector uses a pyroelectric element to receive infrared energy from an object to be measured, converts the resulting temperature rise into voltage, and reads it out. Since the pyroelectric element is an insulator and has a high resistance, it is difficult to handle, so as shown in Figure 1, an impedance conversion circuit using FET2 is connected to the pyroelectric element IK, and this circuit is connected to the header or cap of To-S etc. Incorporate. Here, 3 is an input resistance, and 4 is an output resistance. If 12V is added to the applied voltage vG to put the FET 2 into operation, the DC bias voltage Vo (To) will be approximately 1V at room temperature To. At this time, To
The output is taken out as an AC signal superimposed on (To). Here, Vo(T) changes as the ambient temperature (T) changes, and becomes less sensitive as the temperature rises.

The situation is shown in Figure 2. The way this rises depends on the type of FET2. Then, the applied voltage VC is reached near the upper limit of the operating temperature of the FET 2, and the FET 2 enters a launch-up state and stops operating. In this way, Vo(T) changes depending on the ambient temperature, so if the temperature is set so that it operates with a constant voltage, it becomes a constant temperature type heat sensor.

In this pyroelectric infrared detector, when the ambient temperature changes at a constant temperature change rate, the DC bias voltage changes by a constant amount.

2 mM X 2 am PbTiO3 on the substrate
FIG. 3 shows a configuration in which the element 2 and the input resistor 3 of 10Ω are placed in a TO-5 type container.

This is explained as follows. Polarization is P, pyroelectric coefficient is ′p
゛, temperature is T, time is t, element area is A, pyroelectric current ip,
Let α be the temperature change rate dT/dt. Therefore, ip = Aα・p...
(2), and the voltage vp generated at the gate of the FET is as follows, assuming that the value of the input resistor 3 is R1: Vp = 1p-R+ = Ap-R, ・a
・・・・・・(3) Hail. Therefore, the temperature change rate α is proportional to the pyrovoltage vpH caused by the temperature change. p
= :2.5X 10 coul/c4-0K (
PbTiO3), A-4-1R, = 10 Ω, then from equation (3), Vp: 1.67α [v/℃/rainbow n,)...
...(4). The output voltage V depends on the FIT characteristics.

From the twist of the intersection of the FET ID-vc, s curve and the load straight line that depends on the value R2 of the output resistor 4. Then, v-I
Indicated by DO'R2. Here, IDO changes depending on vp, and as vp increases, IDO increases. FI
Since the ID VG8 curve of CT is not a straight line, strictly speaking, V is not linearly proportional to vp, but experimentally, a straight line is a sufficient approximation. This seems to be because gm does not seem to change at all from the temperature dependence of the ID ves curve. When the ID yGs curve is linearly approximated, it becomes. In general, it is taken so that gmR2)1, so V≠vp
-vT (6) is approximated, and the output voltage V is linearly proportional to vp.

Here, vT is the pinch-off voltage of FIICT.

The actual measured value is V-Vo(T)≠1.3 a (V/C/min,') from Figure 3.
----(7) shows good agreement with equation (4). In this way, when the temperature change rate is several degrees centigrade/m1n1 or more, it is experimentally linear, so the temperature change rate can be determined by capturing the fluctuations in the output voltage V. From equation (7), if an applied voltage vCK of 12V is used, it will latch at α≠9°C/min, and will not operate at a temperature change rate of 1° to 15°C/min, which is the operating test condition for the fire detector. Therefore, in order to change the slope of this straight line, Vp is changed by changing the element area A or the input resistance value R1, as can be seen from equation (3). In addition, by increasing the heat capacity of the case so that changes in the outside ambient temperature are not directly transmitted to the element, the slope of the straight line becomes smaller, and it is easy to make it about 0.3 V/C/min.

In this way, the amount of DC bias voltage fluctuation with respect to the temperature change rate can be satisfied by designing the element and case and selecting the input resistance. With a set level at a constant voltage, temperature and/or temperature change can be sensed. In this case, the rate of temperature change that can be sensed when the ambient temperature is high is smaller than the rate of temperature change that can be sensed when the ambient temperature is low. If you want to avoid this phenomenon and detect a constant rate of temperature change, you can memorize the voltage level just before a sudden rate of temperature change occurs and perform electrical processing to use that value as a reference. good. In this way, the sensing function and level can be easily changed depending on the purpose.

In addition to using only this DC bias voltage, it is also possible to use the original effect of the infrared detector. For example, the radiant energy of a flame can be detected using an infrared optical filter that extracts only specific wavelengths. In this way, flame detection and temperature! It becomes a more reliable fire detector that can detect the rate of temperature change at the same time. Furthermore, this heat sensor is designed to have an arbitrary sensitivity value, and has the advantage of being able to easily change the set value, so it is expected that it will be used not only for fire detection but also for many consumer devices. For example, since it is used as a temperature sensor for an air conditioner to detect ambient temperature or a rapid rate of temperature change, this function can be used to control the temperature. Temperature control using this heat sensor is not so-called 0N10FF control, but corresponds to PID type temperature control, so that smooth temperature control with less ripple can be performed without the need for a complicated configuration. If infrared energy detection is not particularly necessary, you can seal it off by camping without windows.

Incidentally, since the reason for enclosing the pyroelectric element in the case is to accurately obtain the slope shown in FIG. 3, methods other than enclosing the pyroelectric element in the case may be used as long as it has a shielding effect.

In addition to heat radiation, the present invention can also be used in cases where heat conduction is used.

Effects of the Invention As described above, the present invention detects fluctuations in the DC bias voltage of a pyroelectric heat detector using a pyroelectric element that has undergone impedance conversion, and detects both the ambient temperature and the rate of temperature rise. It is possible to detect both temperature and rate of temperature change at the same time, and as a fire detector, it can be used as a compensated heat sensor that combines constant temperature type and differential type. This is a new heat sensor that operates stably and reliably and can also be used as a temperature control sensor.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram showing the configuration of a pyroelectric heat sensor according to the present invention, Fig. 2 is a characteristic diagram showing the temperature dependence of the DC bias voltage in the heat sensor of Fig. 1, and Fig. 3 is a diagram showing the temperature dependence of the DC bias voltage in the heat sensor of Fig. 1. FIG. 3 is a characteristic diagram showing the temperature change rate dependence of the DC bias voltage shown in FIG. 1...Pyroelectric element, 2...FICT, 3
...Input resistance, 4...Output resistance.

Claims (1)

[Claims] A heat sensor characterized in that it detects both an ambient temperature and a rate of temperature rise by detecting a DC voltage of a pyroelectric detector having a pyroelectric element equipped with an impedance conversion circuit.