JPS5811822A - Temperature detecting circuit - Google Patents

Abstract

PURPOSE:To remove a noise component without delaying a signal by separating the noise component from the detection voltage of a thermocouple through a high-pass filter, and processing the separated noise component and detection voltage together. CONSTITUTION:A heater 3 heats up by the application of an alternating current 2 phase-controlled through a triac 1, and the electromotive force of a thermocouple 4 coupled thermally and electrically with the heater 3 is amplified by a differential amplifier 5. The output of the amplifier 5 is passed through a high- pass filter 10 to separate its noise component, which is applied to a differential amplifier 12 through a buffer amplifier 11. The differential amplifier 12 amplifiers the separated noise component and the output of the differential amplifier 5 to output a detection output free of a noise component.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature detection circuit having a circuit for removing noise induced in a thermocouple.

As shown in Fig. 1, a conventional temperature detection circuit has a heater 3 to which AC 2 whose phase is controlled by a tritic IK is applied.
A differential amplifier 5 removes common mode noise from the electromotive voltage of the thermocouple 4 which is thermally and electrically coupled to the detection voltage 8. Ideally, similar noise should be induced in both wires of the thermal lightning pair 4 by the AC waveform 7 applied to the heater 3, so the common mode noise can be completely removed by the differential amplifier 5. . However, in reality, due to the length and arrangement of the electric wires, unbalance of the differential amplifier 5, circuit components, etc.
), (b) [As shown, since the AC waveform 7 applied to the heater 3 is included as noise in the detected voltage waveform 8, highly accurate and stable temperature detection cannot be performed. If a low-pass filter 6 is added to remove the noise from the octopus, Figure 2 (
As shown in c>, the detection voltage 9 has a disadvantage in that it changes with a lag behind the actual temperature change.

The present invention eliminates these drawbacks, and its purpose is to detect temperature stably with high accuracy.

Another purpose of the detector is to detect changes in temperature with as little delay as possible.

An embodiment of the present invention will be explained based on FIGS. 5 and 4. 1, 2, 3, and 4.5 are the same as those explained in FIG. pair 4 and differential amplifier 5. 10 is a high-pass filter, 11 is a buffer amplifier, and 12 is a second differential amplifier. In the above configuration, the electromotive force of the heat pair 4 is generated by the tenth differential amplifier 517i7.
Therefore, as described in the conventional method, a certain amount of common mode noise is removed, resulting in a voltage waveform 131C containing noise as shown in FIG. 4(a). The output of the first differential amplifier 5 is filtered by a high-pass filter 10 to form a voltage waveform as shown in FIG. Only the noise components shown at 14 are separated and then buffered and amplified by the buffer amplifier 11. Here, the detected voltage 13 containing the noise and the separated noise 14 are differentially amplified by the second differential amplifier 12, and the noise component is removed, so that the voltage waveform shown in FIG. 4(c) is obtained. Only the temperature detection voltage will be used.

As described above, according to the present invention, the detection voltage output from the first differential amplifier and the noise component separated from this detection voltage by the high-pass filter are differentially amplified by the second differential amplifier. By eliminating noise, it is possible to detect temperature changes without delay even in cases that are highly susceptible to noise, such as temperature detection of a heater to which phase-controlled alternating current is applied.
It can be detected accurately and stably, and has great effects in controlling temperature and miscarriages.

[Brief explanation of the drawing]

FIG. 1 shows a conventional temperature detection circuit. Figure 2 (a) shows the AC voltage waveform applied to the heater in a conventional temperature detection circuit, (b) the output waveform of the differential amplifier, and the output waveform of the low-pass filter (c>), that is, the conventional temperature detection circuit. FIG. 3 shows a temperature detection circuit according to an embodiment of the present invention. FIG. 4(a) shows a waveform of an AC voltage applied to a heater in an embodiment of the present invention. b) is the noise component separated by the high-pass filter, and (c) is the detected voltage waveform. 1. Triac 2. AC power supply 3. Heater 4. Thermocouple 5. Differential amplifier 6. -Low pass filter 7...AC voltage waveform applied to the heater 8...Output voltage waveform of the differential amplifier 9...Output voltage waveform of the low pass filter 10...High pass filter 11...Buffer amplifier 12 ...Second differential amplifier 13...Detection voltage containing noise from the first differential amplifier 14...Separated noise component 15...Second differential amplifier output voltage, that is, temperature detection voltage Person Shuwa Seikosha Co., Ltd. Agent Patent Attorney Tsutomu Mogami 5- (b) (C) Figure 2

Claims (1)

[Claims] A humidity detection circuit that uses the electromotive force of a thermocouple thermally and electrically coupled to an AC heater as a detection voltage includes a high-pass filter that separates noise components from the detection voltage, and a second filter that removes the separated noise components. A temperature detection circuit comprising a differential amplifier.