The sensor picks up the lower temperature, feeds that back to the controller, the controller sees that the “temperature error” is not as great because the PV (temperature) has dropped and the air con is turned down a little. The air-con is switched on and the temperature drops. Let’s imagine the temperature PV in our house is higher than the SP. In our house this will either be cooling or heating depending on whether the PV is higher or lower than the SP respectively. However, if there is a disparity between the SP and the PV we have an error and corrective action is needed. It doesn’t have to do anything it will set its output remain same value. If the SP and the PV are the same – then the controller is a very happy little box. Back in our house, the box of electronics that is the PID controller in our Heating and cooling system looks at the value of the temperature sensor in the room and sees how close it is to 22☌. The PID controller looks at the setpoint and compares it with the actual value of the Process Variable (PV). “We want the heating and cooling process in our house to achieve a steady temperature of as close to 22☌ as possible” The Setpoint (SP) is the value that we want the process to be.įor example, the temperature control system in our house may have a SP of 22☌. Here is the classic block diagram of a process under PID Control.
