If the system must remain online, one tuning method is to first set K_{i}} K_{i} and K_{d}} K_{d} values to zero. Increase the K_{p}} K_{p} until the output of the loop oscillates, then the K_{p}} K_{p} should be set to approximately half of that value for a “quarter amplitude decay” type response. Then increase K_{i}} K_{i} until any offset is corrected in sufficient time for the process. However, too much K_{i}} K_{i} will cause instability.
Finally, increase K_{d}} K_{d}, if required, until the loop is acceptably quick to reach its reference after a load disturbance. However, too much K_{d}} K_{d} will cause excessive response and overshoot. A fast PID loop tuning usually overshoots slightly to reach the setpoint more quickly; however, some systems cannot accept overshoot, in which case an overdamped closed-loop system is required, which will require a K_{p}} K_{p} setting significantly less than half that of the K_{p}} K_{p} setting that was causing oscillation.
