Commissioning in the field of industrial automation is the process of assuring that all systems and components of an industrial plant are designed, installed, tested, operated, and maintained according to the operational requirements of the final client.
So, suppose a plant is controlled from a PLC, the initial phase of programming would mostly be completed at the office and rather at the plant. After a generic verification from the client, the program is approved. PLC would be installed in the panel and shall be dispatched to the plant.
Now, once the panel reaches the plant/site, probably one of the technician does the basic wiring and connects it to the main supply. Any PLC will have inputs and outputs, these have to be connected to the appropraite site equipments. Here, an engineer/site commissioner comes into play. He makes sure that all the signals recieved at the PLC inputs are as per the design specification and this is of utmost importance, else the logic wouldn’t work as per the requirement. After this, based on the plant condition, the program in the PLC has to be edited. Reasons for change are plenty, for example: certain motor shall be eliminated and the group sequence must run without it; a new system of interlocks are required based on the site conditions. Also, PLC commissioning involves appropraite scaling of analog values and proper tuning of PID parameters.
All the above mentioned are performed at the site by the PLC programmers or commissioners. The program has to be customised according to the plant’s current situation. After successful trials, which tests the logic cretated, the clearance is given by the PLC team to kick-start the plant. Thus, the plant is said to be commissioned.