The temperature control circuit described in this article is good in use. The circuit is shown in figure(a).
Circuit working principle
(Take artificial hatching turtle for example, the temperature is about 33 °C), Turn off the switch S in Figure (a) and then the circuit is connected. At this time, if the temperature in the incubator is lower than 33 °C set by W1 , W1 is disconnected, the relay KM1 loses power, its normally open contact is disconnected, and KA loses power, its normally closed contact is closure, ac contractor K is power on, its normally open contact is closure, and the load (such as electric furnace) is electrically heated. At the same time, the normally open assist contact of K is closed, and the indicator light H is bright.
When the temperature in the incubator rises to the temperature of W1 set by 33 °C, W1 is closed, KM1 is energized, its normally open contact is closed, KA is energized, its normally closed contact is open, K loses power, and its normally closed contact is closure. And then the load loses power to stop heating. The indicator light, meanwhile, is off. After a period of time, the circuit repeats the above process when the temperature in the incubator drops below 33 °C.
Selection of main circuit components: W1 and W2 are WCG type adjustable electric contact glass mercury thermometer, -58-+30°C; Contact voltage ≤36V, work current <20mA. KM1 and KM2 are JRX-13F small DC electromagnetic relays with voltage of 24V and pickup current of 9.5mA. KA is the intermediate relay JZ13, DC 24V. K is AC contactor CJ10-20, 220V. H is the indicator light XD13, 220V. S is the power switch. F is the fuse RC1A-30/20. Regulated power supplies are available in the market.