Reduce valve stiction for better control

Source: ExperTune, Inc.
A control loop fighting a sticky valve will often push the loop into a cycle that can permeate through an entire plant, causing havoc and off-spec product.

A new version of ExperTune's PID Loop Analyzer includes a stiction check wizard that provides a simple way of measuring the stiction in the control loop. ExperTune's wizard works on the installed valve, giving a true measure of the in-service valve stiction. Measuring the in-service stiction is much more significant than measuring it when the valve is not in use.

Expertune software determines the extent of valve stiction so you can decide how to repair or replace the valve.

If the measured stiction is larger than 1%, then repairing the valve can result in the much better performance and increased product quality. Reducing stiction may eliminate a troublesome cycle, resulting in product made closer to specification with less energy.

Checking a valve for stiction is the third of 5 steps to completely optimize the loop. The complete optimization steps are:

  1. Statistical analysis and diagnosis from normal operating data.
  2. Power Spectral Density analysis to check for hidden cycles.
  3. Check and correct valve problems: stiction, hysteresis and sizing.
  4. Test for and characterize non-linearities. Apply a characterizer to linearize the loop.
  5. Find optimal PID Tuning parameters.

ExperTune includes all the tools needed to make completing the optimization steps simple. ExperTune creates a full loop report including stiction analysis in Microsoft Word.

For more information: Glenn Lovensheimer, ExperTune Inc., 4734 Sonseeahray, Hubertus, WI 53033. Tel: 262-628-0088.

Edited by Angelo DePalma
Managing Editor, Pharmaceutical Online and Drug Discovery Online
Email: adepalma@vertical.net