7.1.4 Integral Term ti

In a proportional only controller, an error between setpoint and PV must exist for the controller to deliver power. Integral is used to achieve zero steady state control error.

 

The integral term slowly shifts the output level as a result of an error between setpoint and measured value. If the measured value is below setpoint the integral action gradually increases the output in an attempt to correct the error. If it is above setpoint integral action gradually decreases the output or increases the cooling power to correct the error.

 

The diagram below shows the result of introducing integral action.

 

 

The units for the integral term are measured in time (1 to 9999 seconds). The longer the integral time constant, the more slowly the output is shifted and results in a sluggish response. Too small an integral time will cause the process to overshoot and even oscillate. The integral action may be disabled by setting its value to OFF.