Direct Acting Thermostat Definition

Direct acting thermostat an instrument which activates a control circuit when a predetermined temperature is reached.

Direct acting thermostat definition.

Direct acting and reverse acting my comments the terms direct and reverse are frequently used when discussing control valves positioners and controllers while writing the control narratives for the complex loops though the definitions of direct and reverse seem pretty straightforward. On the other hand the reverse acting pneumatic thermostat or ra is responsible for decreasing the pressure in the branch line as temperature is increased. A direct acting da pneumatic thermostat increases branch line pressure as temperature increases. A the process under control mainly flow or pressure applications b the process controller that initiates control action to the control valve.

For example an air conditioner or a refrigerator. A reverse acting ra pneumatic thermostat decreases branch line pressure as temperature increases. Direct and reverse the direct acting pneumatic thermostat or da is responsible for increasing the pressure in the branch line as temperature is increased. As i understand it if the controller output increases when the measurement value rises it is a direct acting controller and if controller output decreases when the measurement rises it is a reverse acting controller.

A controller serves as the connection between the pressure tube the thermostat and the. For example if we have two controllers on a distillation column reflux. This week s podcast covered the difference between direct acting and reverse acting thermostats and controllers. Direct acting types of thermostats increase the pressure in the tube in proportion to the rise in temperature.

In a reverse acting pneumatic thermostat the pressure lowers when the temperature increases while rises in pressure occur as it gets cooler. The opposite to this is a direct acting thermostat which energises equipment as the set point is reached. The thermostat that controls a typical house furnace is reverse acting since it switches the furnace off or de energises as the set point is reached.