Using a PID loop I have easily implemented controls that are controlled purely by the error signal, in that the controlled device is in position when the error signal is zero and the output of the PLC is zero. How do you implement control on a device that requires the output to be a say 50% when the error signal is zero. An example would be the control of a VSD on a conveyor. The conveyor speed (pv) matches the (sp) hence the error is zero but the output must be sitting constant say at 50 %. Do you just add the error signal to the input signal - this will causes oscillation. I hope someone can understand my question.