What is the classification of the temperature controller, temperature controller types: snap action thermostat, liquid up type thermostat, pressure type thermostat, electronic temperature controller, digital temperature controller, digital and electronic thermostat now also not subdivided, the above several for mechanical temperature controller, the application is not particularly common, as long as the special place will apply, the following two is electronic, is our common temperature control instrument. Electronic thermostat: electronic temperature controller is using thermal resistance method to measure, common use white gold, copper, tungsten and thermal resistor as temperature resistance, the resistance have their defects. The most common household air conditioning use thermistor type. Electronic temperature control with stability, the advantages of small volume, now used in a growing number of categories. Intelligent temperature controller in the temperature control circuit, the thermostat for temperature sensor for temperature signal, the time will get to the set temperature using pulse type temperature control, so the temperature control is very precise, internal can set the heating characteristics, such as P ( Proportional band) I（ Integral action) D（ Differential action) , this is the job characteristics of PID control instrument.