February 1, 2012

Monitoring Control Loop Performance

By Jacques F. Smuts, OptiControls Inc.; John N. Sorge, Dale Evely, and Mark Faurot, Southern Company; and Aaron Hussey, Electric Power Research Instit

Benefits of Loop Performance Assessment Software

Although it might be difficult to establish a dollar value for the return on investment, many benefits are associated with the information, analysis, and diagnoses provided by control loop performance-monitoring software.

For example, as older, experienced workers retire, they are inevitably replaced by younger workers who have less experience. CLPM software can be useful to less-experienced process control engineers and technicians by helping them differentiate between good and poor loop performance and helping them diagnose the causes of poor loop performance.

There are several additional ways in which loop performance assessment software can improve work processes, raise efficiency, and save time. These are described in more detail below.

Assessing Loop Performance Automatically. A typical coal-fired power plant has several hundred control loops. CLPM software assesses the performance of hundreds or thousands of control loops without the need for human intervention. The software can identify poorly performing control loops so that these can be attended to.

Prioritizing Bad Actors. A loop may be performing poorly, but if it is not an important control loop, it should not be worked on if more important loops are also performing poorly. Loops that are important and also performing poorly should be worked on first. When CLPM software considers both the performance and the importance of control loops, it can provide a prioritized list of poorly performing loops.

Diagnosing Control Problems. CLPM software not only indicates which loops have poor performance, but it also attempts to give a diagnosis of why the performance is poor.

Providing Guidance on Problem Resolution. CLPM software can provide steps for validating the diagnosis and resolving the problem. This is vital information for the non-expert.

Maintaining Performance and Tuning History. CLPM software can maintain history related to several aspects of control loop performance and controller tuning settings. These settings can be trended over time to see the effect of tuning changes on loop performance. It is helpful to see at what point in time the tuning settings were changed, what the old values were, what they were changed to, and what effect the changes had on loop performance, loop stability, and standard deviation in error.

An Aid in Boosting Loop Performance

CLPM software can be tricky to install, connect, and configure, so obtaining support from the vendor or an agent is advisable. The tweaking of loop assessment criteria is required to take into account the specific objectives and operating constraints of each loop.

Once the system has been properly configured, however, it can draw attention to poorly performing loops to help support a loop optimization program.

Pilot installation of the software is valuable in that it helps to identify potential value and problems, thus enabling more informed decisions before broader deployment.