Control Talk Blog
The threshold sensitivity and resolution of measurements (smallest incremental change) has improved dramatically to better than 0.05% with new sensor technology and smart compensation of extraneous effects of operating conditions. The response of the air-actuated control valve has improved, but the smallest incremental change in position varies widely depending upon...
The value of a key PID feature is increasingly becoming apparent. I got a preview of the importance when I found the 1980s vintage DCS required a fix for override control that was inherently addressed in the next generation of DCS by this feature.
The questions submitted by the 10 worldwide participants in ISA Mentor program are refreshing and cause one to stand back and think about how we do things and how can we convey knowledge we take for granted.
We conclude this series with a look at control schemes that can increase process efficiency for distillation control, compressor control, and neutralizer control. These control schemes can inherently reduce process variability and controller tuning difficulty and for compressors increase onstream time.
What configuration changes to control strategies can readily take advantage of improvements in measurements and final control elements? Control strategies can inherently improve production rate by maximizing feed and efficiency by enforcing material and energy balances.
Process efficiency can be increased by eliminating the excess use of reactants, reagents, and energy, eliminating the production of waste and off-spec material, and taking advantage of low energy and raw material sources. Not well recognized is effect of sensor drift and location, missing measurements, abnormal operation, process understanding, control...
When we saw an increase in production rate needed during opportunity assessments at Monsanto and Solutia, we would salivate. Impressive results could be obtained in a matter of a few days by a simple change in setpoint, tuning, and/or configuration.
The best wireless settings provide an effective compromise between the need to maximize battery life and meet loop performance objectives. Since power consumption is greatest in transmitting an update, battery life can be significantly extended by reducing unnecessary updates.
Temperature loops benefit more than most loops from the use of derivative action. The rate time can be 1/2 of the total loop deadtime or larger by the use of a wireless smart transmitter, the enhanced PID for wireless, and a proper installation location and thermowell design.
A transmitter damping setting or signal filter setting that is too slow can not only degrade performance but also cause trips. Less understood is that a large filter setting can mislead operations into thinking the filter has helped rather than hurt the process.