Examine this P&ID for a level control system in a vessel where two different fluids (Feed A and Feed B) are mixed together:
Determine the effect on the control system’s regulation of liquid level inside the vessel if an instrument technician accidently mis-calibrates the control valve such that it opens 2% more than it should (e.g. when the controller sends a 50% signal to the valve, it actually opens to 52% stem travel). Assume all other loop components are properly configured and that the controller is well-tuned.
There will be no adverse effect resulting from this mis-calibration, unless the valve is unable to achieve a full-closed position when required. In such a case, the liquid level will slowly fall below setpoint.