Temperature control system is a recycle process of “ Temperature detectors detect temperature→ Thermostats compare temperature→ Thermostats calculate the deviation→Control heating/cooling system working value” . Thermostat control method are mainly ON/OFF and PID two kinds.   1. ON/OFF control   ON means open, OFF means close. For example, if set (temperature) value to be 50 degree, RVSA, if present value is 48 degree, it will turn on to start heating; if present value is 50 degree, it will turn off to stop heating. ON/OFF control method can not make the temperature stably at the set value, it will oscillate up and down around the set value. So this is suitable for the occasion of not so strict control requirements.       2. PID Control   Combine three or two advantages of Proportional control (fast adjust) Integral control (automatic correct deviation ) Derivative control(fast response) to form a control method. Etop’s Thermostats & controllers adopt Proportional controls and Integral controls to form the control method.