Thermostat with temperature and light sensors. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Thermostat with temperature and light sensors. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers

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A thermostat with temperature and light sensors allows you to maintain a constant temperature in the range from 15 to 50 ° C with an accuracy of 0,4 ° C and change it stepwise within 12 ° C from the set value, depending on the level of illumination, which can also be changed within 500 ...2500 lx.

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The device consists of a temperature control unit, including thermistor R14, transistors V6, V8, V10, relay K.1, and a temperature correction unit made on the photoresistor R1 and transistors V2 and V4. Both blocks are based on Schmitt triggers. The illumination level, determined by the threshold for the operation of the correction block, is set by resistor R2, and the temperature threshold of the second block is set by resistor RJ5. The value of the temperature increment is set by resistor R12, and the sign of the increment is selected by switch S1.

Details. Transistors type MP40-MP42 (V10 type P213-P216); thermistor R14 types MMT-6, MMT-4 or KMT-4; variable resistors type SP3; relay type RPU-2 or another that operates at a voltage of 24 V and provides the required switching current of the heater; the transformer is made on the SHL20 x 16 magnetic circuit: winding I contains 3300 turns of PEV-2 0,1 wire, winding II - 350 turns of PEV-2 0 47, winding III - 100 turns of PEV-2 0,21; switches S1 and S2 type P2K. The temperature and light sensors are connected to the controller with a shielded wire. Resistors R2, R12, R15 are calibrated using a reference thermometer and a light meter.

Author: V.Savykin

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