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Ask The Experts"Ask The Experts" is moderated on ControlGlobal.com by noted process control authority and CONTROL Columnist Bela Liptak. Liptak either answers the questions himself, or brings in one or more experts from his cadre of co-authors that worked with him on the Instrument Engineers' Handbook, Fourth Edition. Save yourself the hefty consulting fees by getting the answers to your questions here.

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Ask the experts: How to determine open-loop gain?

What to do when the process overshoots the mark.

Nov 23, 2016

*Q: *This is for tuning a control valve on a pipeline. In an open-loop gain test, with a step increase applied to valve opening, the controlled parameter increases, then settles at a number. In this case, flow increased and then decreased to settle at x number. To calculate my Tc, should I use the peak value that PV (flow) reached or the final value that it settled at? If I use x, then 63% of PV happens much sooner.

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