T he PID Tuner was used to check the tuning of this loop. There were concerns by plant personnel that, during tuning, the gas pressure should not rise too much above setpoint, because of explosion risks.
The control task was excuted by an Allen Bradley PLC. The PID Tuner software was installed on the same Windows PC that was used to program the PLC. The PID Tuner communicated with the PLC via the OPC server of Rockwell Automation (RSLinx Classic OEM).
The PID Tuner was set up to execute its tuning in a safe way: the tick box PVmax was used to ensure that control would resume in feedback mode should the pressure exceed a predefined limit. A short step experiment was executed by the PID Tuner, followed by a retuning of the PID controller. The figure below shows the comparison of the closed loop response with the 'old' tuning and the 'optimised' tuning. Clearly, the 'old' tuning was indeed slow compared to what it could be. The new settings were downloaded to the PID controller and they worked out as expected: the pressure returned to setpoint at least a factor 5 faster.