Temperature control device

In refrigeration and air conditioning system there are two type of temperature control device or thermostat; Mechanical and electric or digital types. 

Electric temperature controller

An electronic temperature controller, electronic thermostat or digital thermostat is a device that is used to control a cooler, heater or other equipment by comparing a sensor signal with a set point and performing calculations according to the deviation between those values. An electronic thermostat or digital thermostat is included one or more analogue inputs, digital outputs or relays and depends on models’ digital inputs and analogue outputs and is able to perform controlling in on/off, proportional or PID controls.

Mechanical temperature controller

A mechanical temperature controller or mechanical thermostat are electric circuit control devices which open or close an electric contact depending on temperature changes at the bulb. The position of contacts can be different according to function of contacts The application range of this type of thermostats is mainly determined by the charge in the bulb and various bulb sizes and shapes are needed. 

Functions of mechanical thermostat contacts 

Mechanical thermostat contacts can be active on temperature rise above or temperature drop below the setting. It can be manual or automatic reset. Anyway, some functions of the mechanical thermostat contacts are as follows:

• Function of contacts SPDT

On temperature rise above setting, 1-2 opens and 1-4 closes. On temperature drop below setting 1-2 closes and 1-4 opens. 

• Function of contacts SPDT with manual reset Max.

On temperature rise above setting, 1-2 opens and 1-4 closes and latches. The switch can be manually reset when the temperature has dropped below setting. 

• Function of contacts SPDT with manual reset Min.

On temperature drop below setting, 1-2 closes and 1-4 opens and latches. The switch can be manually reset when the temperature has risen above setting.