Emerson Exchange 365

Pressure Spikes Causing DP alarms

I received a call today from a DeltaV customer who was looking to see if anyone had a control strategies to deal with pressure spikes causing DP measurement alarms in their system. I said I'd pose it to the DeltaV community. I unfortunately didn't get any more detail on if it is a gas or liquid being measured.

I was in a meeting with Greg McMillan and bounced the question off him. He provided a couple of ideas, plus a copy of his presentation for the upcoming Emerson Exchange conference in Anaheim.

He first suggested that if possible, resolve the source of pressure pulses. Sometimes improper tuning contributes to these pulses. Next, it you can measure the source and have enough time to react to the disturbance, feedforward control can be applied.

If the first two cases don't apply, the he suggests using a deadtime block to calculate the rate of change of the pressure (PVnew -PVold). When a large change in PV is measured, change the controller mode to output tracking and open the downstream valve enough for a period of 1 reset time (per the integral action of the loop). After this time, release the loop back to feedback control.

The open loop backup to deal with incredibly fast unmeasured disturbances in on slides 32-37. Also see slides 25-28 on feedforward in his presentation.

If anyone has clarifying questions or other suggestions, please share!

Emerson-Exchange-2012-Effective-Use-of-PID-Features-for-Loop-Perfromance-and-Optimization.pdf

• feedforward
• deadtime
• pressure spike
• open loop backup

Jim Cahill

• 21 Sep 2012 7:29 PM
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4 Replies

• Anonymous

  

  • 22 Sep 2012 7:49 PM

  Nice hints from a real guru, I would say  if it's a simple loop just tune for least overshoot

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• Paul Ambler

  

  • 24 Apr 2015 8:09 PM

  In reply to Anonymous:

  We have a low pressure (4" WC) system that includes a baghouse. The pulse jet bag cleaners introduce pressure pulses that influence the system pressure controller. Is there a way to filter out these pulses?

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• Ben Bishop

  

  • 24 Apr 2015 8:26 PM

  In reply to Paul Ambler:

  I read the question a bit differently. It seemed to me the poster wanted to find a method to prevent the process alarms from triggering when a short jet burst. If the issue is "nuisance" alarming, then adding an on delay to the alarm configuration might work. A short high (or low) DP wouldn't cause an alarm, but if the condition persisted then the alarm would become active. If the issue is the reaction of the pressure controller and its output, then you couldn't ask for a better resource than Greg.

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• DBacker

  

  • 24 Apr 2015 8:54 PM

  In reply to Paul Ambler:

  I would try setting the PID loop to ROUT at the current % output for a fixed amount of time based on knowing when the system will blowback. This will be easiest if the DeltaV actually initiates the blowback. If the blowback is in a PLC, I would wire (or otherwise communicate) from the PLC to deltaV. I would have this output as true for a few seconds before the baghouse blows back. Once DeltaV gets this signal, it changes the controller to ROUT at the current output for a changeable amount of time and then goes back into the previous mode. This essentially disregards the pressure spike from the blowback. If the blowback is hardwired in a local timer relay, I have no suggestion.

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