Automatic humidity controller. Encyclopedia of radio electronics and electrical engineering
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The automatic humidity controller makes it possible to maintain air humidity in the ranges of 20...55 and 50...90% with an accuracy of 1,5 and 1%, respectively, when the supply voltage deviates by no more than -20% from the nominal value. It is advisable to use such sensors in vegetable and granaries, livestock farms, in everyday life and medical institutions.
The regulator consists of a hygrometric sensor - a hygristor R1, a threshold device - a Schmitt trigger on transistors V2-V4, an amplifying stage V7 and a power supply. With increasing humidity, the resistance of the hygristor decreases, and the negative voltage at the base of transistor V2 increases. When the threshold voltage on the base of V2 is reached, equal to the voltage on the diode V5, the trigger switches and the transistor V4 closes. This will cause an increase in the base current of the transistor V7, due to which it will open, the relay K1 will work and turn on the humidifier actuator with its contacts K1.2.
In this case, the contacts of the relay K1.1 are closed by the limiting resistor R9, and the signal lamp H1 will start to glow brighter.
Details. Relay K1 type RPU-2 or RPG for voltage 24 V; transformer T1 is made on the magnetic circuit ShL12 x 16: winding I contains 5300 turns of wire PEV-1 0,1, winding II - 480 turns of wire PEV-1 0,21; signal lamp H1 type KM for 24 V and 35 mA. Humidity sensor - hygristor is made of one-sided foil fiberglass 1 mm thick. The design of the sensor is shown in the figure.
After etching an insulating groove 1 mm wide, the sensor electrodes are tinned, degreased, covered with a saturated solution of lithium chloride or sodium chloride and dried. The resistance of the sensor with a change in humidity of 20...55% is 120...30 kOhm. At high humidity of 50...95%, the sensor is made of double-sided fiberglass without subsequent coating with sodium chloride solution. Connect the sensor to the regulator with a shielded wire. Establishing the regulator comes down to setting the limits of the scale of the resistor R3 by selecting the resistor R2.
To calibrate the scale of the resistor R3, an industrial psychrometer is used, which is placed together with the sensor in a chamber with varying humidity. At different humidity, determined using a psychrometer, the position of the potentiometer R3 slider is fixed, at which relay K.1 is activated. When operating the humidity controller, the hygristor board is mounted vertically. In this case, moisture condensation on the board should be avoided.
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