As shown in the figure, the warehouse temperature measurement alarm circuit. The device is composed of a non-inverting amplifier IC1, a comparison amplifier IC2, a low-frequency multivibrator IC3, a multivibrator IC4 with controllable oscillation frequency, a bridge measurement network, a speaker Y, a power supply circuit and the like. The bridge measurement network consists of the PN junction of the temperature sensor BY (the tube 3AX31), the resistors R1 to R4, and the potentiometer W1. IC1 (F033) and some RC components form a non-inverting amplifier. The reference voltage of the comparison amplifier composed of IC2 (F007) is connected to the inverting terminal of IC2. IC3 and the RC component form a low frequency oscillator of about 1 Hz, which in turn controls the oscillation frequency of the multivibrator IC4.
The adjustable potentiometer W1 in the circuit makes the bridge in equilibrium at 0 °C, correspondingly the output of IC1 is about 0V, and then the zero is adjusted by the micro-ampere table CB. Potentiometer W2 is used to adjust the gain of the amplifier so that the microampere scale reaches approximately 0.1V/°C. Potentiometer W3 is used to adjust the balance of the amplifier so that the indication of the micro-ampere table CB is zero. The potentiometer W4 is used to adjust the reference comparison voltage of the amplifier IC2, and the high temperature can be determined according to the seasonal variation and the room temperature requirement to turn on the power of the alarm circuit to make an alarm sound. In addition, the power contact J1-1 of the alarm circuit is controlled by the relay at the output of IC2. When the voltage at the non-inverting terminal 3 of IC2 is higher than the voltage at the inverting terminal 2, the output of IC2 is a positive voltage, so that D2 is turned on, and the coil of the relay is attracted by the current flowing to the J1-1 contact.
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