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Why Does Control Loop Performance Change Over Time? What is Time Variant Behavior?

By Control Guru | January 28, 2015

You visit a doctor annually for a physical examination.  Your car gets an oil change every 3,000 miles.  Your company assesses profit versus loss every 3 months.  The list of routine “check ups” goes on and on.  Why?  Because such things are important and they change over time.  It’s valuable both to appraise their relative health and to determine what adjustments may be necessary.  As the foundation for regulatory control at most production facilities, PID control loops are no different.

How Do I Detect Valve Issues and Prevent Failures?

By Control Guru | January 22, 2015

It’s generally known that the behavior of final control elements (FCEs) (valves, air handlers, etc.) change over time. Like most things the dynamics of FCEs are different from the time they’re first installed to the time they’re serviced and ultimately replaced. Sometimes the change in dynamic behavior is subtle. Other times the change is dramatic. Unfortunately that’s the nature of things, and that’s the primary reason why monitoring for valve issues is beneficial.

What is the Process Time Constant? How Do I Calculate the Time Constant of A Process?

By Control Guru | January 13, 2015

Party hosts often cringe when guests arrive early or late. Seemingly subtle shifts in timing can throw off planned details that are of importance to the host and utterly lost on guests. So too the timing of a PID control loop’s response is important. Premature or delayed responses negatively impact the controller’s performance. Previously the calculation of Process Gain – the “how far” variable – was covered. The Process Time Constant is equally important to process modeling and PID controller tuning. As with most things, timing is everything.

How Should Control Loop Performance Issues Be Prioritized?

By Control Guru | January 7, 2015

There are many paths to Heaven or so the saying goes. With a growing array of automation technologies, such a philosophical expression can be applied to process control and plant-wide optimization. Whether the goal is focused on uptime, throughput, or quality, control loop monitoring and diagnostic solutions provide meaningful insight into a facility’s performance. The insights gained from these technologies enable practitioners to proactively address bothersome issues before they become costly problems, and lead somewhere other than Heaven.