Emerson’s Laurie Ben, director of control system modernization, shared some tips on how to manage your control system modernization projects.
Laurie opened with what a migration project looks like when it goes wild. A common issue the wrong form of PID control being configured. There are various algorithms associated with PID control. The DeltaV system uses a standard PID form by default. Other systems used the classical or series form. Put the loop in manual and chance the PID settings for the form. If you don’t use the derivative action in the PID algorithm, then series and standard action are the same.
Some legacy systems have up to five different forms of PID control. Laurie highlighted documentation available on how to configure the loop tuning parameters based upon the form used.
Another area that can cause problems is matching the correct units for the PID gain, rate, process variable (PV) filter and reset terms. Verify the units used on your existing system and the DeltaV system and convert to the same units to avoid bad parameter settings.
First thing to do is export your existing database and don’t make system wide assumptions. Make sure to verify all critical loops. Laurie and the Modernization team have conversion tools available tools to manage all settings for the loops.
Another common problem is the PV never getting to setpoint (SP). The problem is typically the anti-reset windup (ARW) settings incorrectly converted. Set the ARW limits to the output limits.
Another issue is that control system suppliers use different terminology for the PID forms. Sometimes you have to go into the math of what’s described to see if it is Series or Standard form.
Power supplies and capacitors are the two biggest area of failure for legacy systems, no matter who the supplier is. Firmware is another issue to know exactly what you have and what you need. Many times spares are no good because the firmware revisions are not what they need to be to operate with the legacy system. According to an ARC report, up to 1/3 or more of the spare parts are not serviceable. It’s not a long-term strategy to rely on spare parts to keep a legacy control system running.
Contact Laurie for additional information on the PID form conversions and other tips.