JPS60102532A - Temperature detecting method - Google Patents

Abstract

PURPOSE:To simplify the constitution of circuits, by providing a circuit, whose circuit constant can be changed, in a temperature measuring circuit in a chopper, which intermittently cuts infrared rays emitted from a body, and adjusting the offset of operation amplifiers by the regulation of said circuit constant. CONSTITUTION:Infrared rays emitted from an object A, whose temperature is to be measured, are intermittently cut by a chopper 2 and inputted to an integrating circuit 6 through an infrared-ray sensor 1, an amplifier 3, and a high-pass filter 4. The output of a photointerrupter 2b is imparted to an FET5, and the output of the filter 4 is synchronously rectified. The temperature of a disk 2a of the chopper 2 is detected by a diode 9. The signal corresponding to the temperature difference between the object A and the disk 2a is inputted to an amplifier 8. Variable resistors 4b and 6b for regulating the offset of operation amplifiers 4a and 6a can be omitted. The offset compensation is made by the adjustment of only a voltage dividing circuit 11 in the temperature measuring circuit of the disk 2a.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-contact temperature detection method using a pyroelectric element, and more specifically, it provides a temperature detection method that can simplify the circuit configuration of a detection device.

FIG. 1 is a schematic diagram showing the configuration of this type of temperature detection device used in microwave ovens and the like. The temperature measurement object A, such as the food to be cooked, emits infrared rays according to its surface temperature.
There is no way to detect it. Directly below the infrared sensor 1 is a chopper 2 that cuts off infrared rays. The chopper 2 uses a motor (not shown) to rotate a circle i2a in which infrared ray transmitting parts and infrared ray blocking parts are arranged alternately, so that the infrared rays emitted by the temperature measurement object A reach the infrared sensor 1 intermittently. be. In other words, the infrared sensor 1 alternately receives infrared rays from the temperature measurement object A and the chopper 20 disk 2a. This signal is applied to an amplifier 3, where it is amplified, and then applied to a bypass filter circuit 4 using an operational amplifier (hereinafter referred to as an operational amplifier) 4a. A photo ink converter 2b is provided in the rotation range of the disc 2a of the digisova 2 to obtain a signal synchronized with the infrared intermittent cycle of the chopper 2, and this is connected to the output terminal of the bypass filter circuit 4.
5, and the output of the filter circuit is synchronously rectified. The signal thus synchronously rectified is applied to an integrating circuit 6 using an operational amplifier 6a, and the signal integrated here is gain adjusted in a gain adjustment circuit 7 and applied to an amplifier 8. be. The output of the gain adjustment circuit 7 is a signal corresponding to the temperature difference between the temperature measurement circuit 8 and the infrared cutoff section of the disk 2a.

Diode 9 is the circle of chopper 2! It is used to measure the temperature of the infrared cutoff section of It2a, and is installed in a housing that houses the infrared sensor 1, chopper 2, etc. The output of this diode 9 is input to one terminal of the differential amplifier 1°, and the output of a voltage dividing circuit 11 consisting of a variable resistor and a fixed resistor is given to its child terminal. The output of the differential amplifier 10 is further amplified to an appropriate level.

The output of the chopper temperature measuring circuit 12 is applied to the amplifier 8 together with the output of the gain adjustment circuit 7. Note that the voltage dividing circuit 11 is for adjusting the output of the chopper temperature measuring circuit 12.

If the output of ζamplifier 8 is affected by dirt, the circle i2a of chopper 2
A signal corresponding to the sum of the temperature of the infrared cutoff 91 ( ) and the difference between this temperature and the surface temperature of the temperature measurement object A, that is, a signal corresponding to the surface temperature of the temperature measurement object A is obtained.

Now, in such a conventional device, the operational amplifier 4a
, 6a is indispensable, and the offset adjustment is performed by adjusting a variable resistor connected to an offset compensation circuit built in each. This is because if such adjustment is not performed, the output voltage will not be 0 even if the input voltage is 0, and a measurement error will occur.

An object of the present invention is to provide a temperature detection method that does not require such offset adjustment using an external resistor of an operational amplifier and can simplify the circuit configuration.

In the temperature detection method according to the present invention, infrared rays emitted by an object are intermittently made to enter an infrared sensor using a chopper, and the infrared sensor output is fed to an operational amplifier to measure the temperature difference between the object and the chopper. In the temperature detection method of determining the temperature of the object by measuring the temperature of the object, a temperature measuring circuit of the chopper is provided with a circuit whose circuit constant is variable, and by adjusting the circuit constant, the offset circuit of the operational amplifier is adjusted.
It is characterized by tidying up.

The present invention will be specifically explained below based on the drawings.

FIG. 2 is for explaining the measurement error due to the offset of the operational amplifier. If the offset voltage VO is not adjusted as shown by the broken line in FIG. ), the period during which the filter circuit output V4 is given to the integrator circuit 6 becomes longer than the A period, and it is integrated by the amount shown with hunting in FIG. 2 (b), and the integration result is As shown by the solid line in FIG.
(double-dashed line).

Now, the output error due to this offset voltage is constant regardless of the magnitude of the input signal, so even if the temperature of the temperature measurement object changes, the T4 characteristic that infrared radiation energy is proportional to the fourth power of the absolute temperature is It is thought that it will appear as if it were shifted by a certain amount. Figure 3 is a graph showing the relationship between the absolute temperature T and the output of the integrator circuit 6.The relationship between T Vc when there is no error due to off-cellar l- is shown by the two-dot chain line, and when there is an error, the relationship is shown by the solid line. This is an indication. And the difference α between the two is constant. Therefore, this difference α can be corrected by adjusting the temperature compensation circuit of the output of the chopper temperature measuring circuit 12, which is added to the output of the gain adjustment circuit 7 which inputs the integrating circuit output ■6, without adjusting the offset of the operational amplifiers 4a and 6a. is possible. This will be explained as follows based on the drawings.

Figure 4 shows that the offset voltage of operational amplifiers 4a and 6a is 0.
This shows the relationship between the absolute temperature (horizontal axis) and voltage (vertical axis) when the chopper temperature is measured correctly.
This shows the characteristics of the voltage (1)5 synchronously rectified by V5, and V5 becomes 0 when the temperature measurement target A is at room temperature Tc (-temperature of chopper 2).

FIG. 4(b) shows the characteristics of the output V2 of the chopper temperature measuring circuit 12, which becomes Vc when the room temperature is Tc. Fourth
Figure (c) shows the voltage V ADD that is the sum of these two. (Actually, the voltage ■ is integrated, the gain is adjusted, and it is added to V12).

FIG. 5 shows the relationship between absolute temperature and voltage when the offset voltage is not zero. Voltage V5 shown in Figure 5 (a)
The characteristic is similar to that shown in FIG. 3, and is shifted upward by α as shown by the solid line from the correct characteristic (double-dashed line) where V5=0 at room temperature Tc. FIG. 5(B) shows the characteristics of the output V12 of the chopper temperature measurement circuit. In the present invention, from the characteristics when the offset voltage = 0 (double-dashed line) when V12 = Vc at room temperature 'rc, the above In order to compensate for the upward shift of α, the output characteristic is adjusted by the voltage dividing circuit 11 so as to obtain the output characteristic shown by the solid line, which is shifted downward by α. As a result, the characteristic obtained by adding V5+V12 can be obtained as shown in FIG. 5(C), which is similar to that shown in FIG. 4(C).

FIG. 6 shows the configuration of a temperature measuring device for carrying out the method of the present invention. The difference from the circuit shown in FIG. 1 is that variable resistors 4b and 6b are omitted, and the others are given the same reference numerals and their explanation will be omitted. In other words, according to the present invention, this external resistor can be omitted, and the operational amplifier 4
As for a and 6a, it is possible to use inexpensive external terminals that do not have terminals. Furthermore, the present invention has excellent effects, such as eliminating the troublesome adjustment work because the voltage dividing circuit 11 is the only part of the circuit that needs to be adjusted.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a conventional temperature measuring device, Figures 2 and 3 are explanatory diagrams for explaining errors caused by offset voltage, and Figure 4
．． FIG. 5 is an explanatory diagram of the method of the present invention, and FIG. 6 is a schematic diagram of a temperature measuring device to which the method of the present invention is applied. ■...Infrared sensor 2...Chopper 4...Filter circuit 5...FliT 6...Integrator circuit 9
...Diode 12...Chopper temperature measurement circuit Applicant Sanyo Electric Co., Ltd. Agent Patent Attorney Noboru Kono (B) (C) ¥, S Figure

Claims (1)

[Claims] 1. Infrared rays emitted by an object are intermittently incident on an infrared sensor using a chopper, the infrared sensor output is fed to an operational amplifier to measure the temperature difference between the object and the chopper, and the temperature of the chopper is measured to The temperature detection method for measuring the temperature of an object is characterized in that the temperature measuring circuit of the chopper is provided with a circuit whose circuit constant is variable, and the offset 1-a of the operational amplifier is adjusted by adjusting the circuit constant. Temperature detection method.