In most cases, control systems are not behind the curve in performance. Many systems boast detailed, well designed graphics and millisecond alarming capabilities. They offer fast and reliable processing and I/O control.
However, no matter how much performance you have in a control system, at the end of the day, a process is only as controlled as the measurements and final control elements that interact on the said process.
Keeping the previous in mind, the range of tasks during a single day for today’s control system engineer can range from network security to virtualization and server administration tasks to PLC programming to tuning control loops.
In my experience, the controls engineer cannot routinely monitor hundreds or thousands of system control loops for performance. Usually, an operational team member will bring a control loop with low performance to the engineer’s attention after it has caused production issues for some time.
Proactively monitoring control loops
With current technology, control teams have the capability to let control systems perform loop monitoring for them. Once implemented, a system can monitor all the control loops in a facility and bring to the attention of control engineers any loops that are not performing as needed by operations.
Getting started with identification and prioritization
The first step of implementing such a monitoring system would be to identify and prioritize all the control loops in a facility. This would likely be broken down into sub-areas for reporting clarity and ease of evaluation. Depending on process impact, some control loops will have higher standards for performance.
Control loop parameters
Next, parameters and alarms would then need to be evaluated and monitored as well. What mode should the loop be in? What is the Deviation High/Low that is acceptable? At this point, the system can monitor how many loops are operating in their correct mode and is the loop performance at an acceptable level.
The Action Plan
Does loop monitoring benefit my facility? I submit to you it depends on what you do with the data. If you’re monitoring control loops to check a box on your yearly performance goals, then that is the reward. However, if control loop monitoring is just the beginning of an action plan that brings said loops into a state of constant control, then the benefits can be significant.
Every loop that does not meet mode or acceptable deviation criteria must be looked at to determine the cause. Is the issue tuning related? Is the final control element (i.e. valve) sticking or have slack issues? Sometimes, control loops may not run in control system control simply due to operator preference.
Whatever the case, a schedule can then be made to perform bump tests during operation, final control element inspections and replacement, if necessary, during the next outage opportunity and finally follow up to ensure that repairs have the control loop operating within acceptable limits. Any loop not on control will find itself in an action plan that ensures a follow through commitment to determine the cause and repair the issue.
If you are experiencing a “firefighter” approach to control system loop performance, maybe it is time to move to a new phase of proactively monitoring performance and spending time with resolution of action plan items.
This shift in approach can benefit operations by ensuring stability, maintenance by planning and commitment to make repairs and the control systems group by optimizing the tasks that demand their attention.
Written by Brandon Cooper
Senior Controls Engineer and Freelance Writer