When the utilization of a control loop is found to be low during normal plant operation, the measurement or control problems that prevent the control loop from functioning in its normal (designed) mode of operation should be further explored. In Chapter 3 of Advanced Control Foundation – Tools, Techniques, and Applications we outline the steps involved in resolving problems that impact control utilization as illustrated below. To achieve full utilization, effective communication between maintenance and operations is important.
When a control loop is routinely not operated in normal mode (which is most often automatic mode), further investigation is needed to determine the cause of the poor control utilization. Some of the most common problems that can impact control loop operation in automatic mode are:
- Measurement health, i.e., quality of the measurement
- Incorrect tuning
- Valve/actuator malfunction
- Changing process gain
- Split range setup
- Process gain
- Process dynamics
- Loop interaction
Control performance tools provide information that guides the user in solving the performance problem. However, where there is no clear indication of the source of the problem, it may be necessary to test and observe the loop operation in both manual and automatic modes.