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电子体温表电路
电子体温表电路如图所示。它由中增益运算放大器Fc3、负温度系数的热敏电阻Rt、VD1～VD4二极管桥式整流和VT1、VT2开关电路等组成。
当热敏电阻Rt的阻值随所测物体的温度发生变化，A、B两点就会有差值信号输出，此信号经Fc3运算放大器放大．vD1～VD4二极管桥式整流后加到晶体管VT1的基极，当差值信号达到一定值时，晶体管VT1导通、VT2截止，小灯泡HL不亮；这时旋动电位器RP．使A、B两点间无差值信号输出，则晶体管vT1截止、VT2导通,小灯泡就亮。如果电位器RP旋转角度记以温度刻度，那么就可以在灯泡亮时，读出所测物体的温度了。
Rt可采用20"C时阻值为10kΩ的热敏电阻，它作为感温嚣放在金属管内，用两根引线从金属管内引出。使用时，将感温器放在被测部位，旋动RP，指示灯最亮时，指针所指的温度刻度即为被测的温度。
google translate:
Electronic thermometer circuit as shown. It consists of medium-gain op amp Fc3, negative temperature coefficient thermistor Rt, VD1 ~ VD4 diode bridge rectifier and VT1, VT2 switching circuit and other components.
When the thermistor resistance value Rt of the temperature with the measured changes in the object, A, B will have two points difference signal output, this signal by Fc3 operational amplifier. vD1 ~ VD4 diode bridge rectifier added after the base of the transistor VT1, when the difference signal reaches a certain value, the transistor conduction VT1, VT2 end, do not light a small bulb HL; then rotating potentiometer RP. So that A, B no difference between the two signal output, the transistor vT1 end, VT2 conduction, small light bulb to light. RP if the potentiometer rotation in mind the temperature calibration, then you can light bulb, the reading out the temperature of the measured object.
Rt 20 ℃, can be used for the 10kΩ thermistor resistance, as a sensing device on the metal tube, with two wire leads from the metal tube. When used, the sensing device on the measured position, rotating RP, the brightest light, the pointer shall be measured within the meaning of the temperature of the temperature scale.
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