How to use wireless for control

PIDPlus is a modification of PID to accommodate slow and varying update rates, as well as lost communications

Terry Blevins and Neil Peterson
CG1505 Wireless

As plants have gained experience using wireless measurements to monitor process operations, they have found the transmitters to be reliable and are now looking at how to incorporate these wireless measurements into closed-loop control. The natural choice for implementing feedback control is the proportional, integral, derivative (PID) algorithm, since it is the dominant control technique in the process industry. However, the slow sample rate and delay that are characteristic of wireless measurement present new technical challenges in implementing control in some applications. A new control approach is required to achieve effective control using a wireless measurement.

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Timeless Resources

Beginner's guide to differential pressure level transmitters

By David W. Spitzer

The importance of level measurement cannot be overstated. Incorrect or inappropriate measurements can cause  levels in vessels to be excessively higher or lower than their measured values. Low levels can cause pumping problems and damage the pump, while high levels can cause vessels to overflow and potentially create safety and environmental problems. Vessels operating at incorrect intermediate levels can result in poor operating conditions and affect the accounting of material. Learn more.

Controllers: Direct vs. reverse-acting control

By Bela Liptak

Valve failure position is determined by safety considerations. If, in case of failure, you want your column to go on full reflux, your selection where the reflux control valve is fail-open, and net overhead control valve is fail-close, is right. Assuming that the valve actuators are spring-operated pneumatic ones, and assuming that you define "failure" as the loss of air supply, the spring will act to open a fail-open (FO) valve and to close a fail-closed (FC) valve, regardless what the controller actions are. Read more.

Voices: Ask The Experts

What's wrong with my thermocouple? How do I know my RTD measurement is accurate?

Our experts tackle these not-so-simple problems

By Bela Liptak

Q: Thermocouple Diagnosis Our Type K thermocouple at 25 ºC generates 1.0 mV. It has a long TC cable which does not show continuity, but 130 ohms resistance. Can you explain why this is occurring and how it can be fixed? Ashish Garg A: One of the problems associated with…

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Control Talk Blog

Essential Feedforward Control and Operator Interface Tips

All feedforward control systems can be reduced to a common form that enables a better understanding and recognition that leads to the best performance and the best interface for the operator. For “smart controls” to be fully appreciated and utilized, the operator needs to know what is going on and how to participate. Here we show how to make the advantages of feedforward control more achievable and recognizable.

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