KB83813
Published: December 18, 2015
Revision: 2.0

Unusually large change in PID Output or Integral


Applies To:

SNAP-PAC-R1
SNAP-PAC-R1-FM
SNAP-PAC-R1-W
SNAP-PAC-R2
SNAP-PAC-R2-FM
SNAP-PAC-R2-W
SNAP-PAC-EB1
SNAP-PAC-EB1-FM
SNAP-PAC-EB1-W
SNAP-PAC-EB2
SNAP-PAC-EB2-FM
SNAP-PAC-EB2-W
SNAP-PAC-SB1
SNAP-PAC-SB2
SNAP-UP1-ADS
SNAP-UP1-M64
SNAP-UP1-D64

Versions Affected:

Problem affects versions: SNAP PAC: R8.0f through R9.4b
Problem affects versions: SNAP UIO: R7.2h and higher
Problem is fixed in version: SNAP PAC: R9.4c (See Resolution section.)

Resolved In Version:

Problem is fixed in version: SNAP PAC: R9.4c (See Resolution section.)


Symptoms:

You may see one or both of the following:

  • PID Output drops from 100% to 0% in one scan time or increases from 0% to 100% in one scan time.
  • Integral of PID changes by multiple orders of magnitude in one scan time. For example, a change from -1625 to 3282675.
This issue affects only ISA, Parallel, and Interacting PID algorithms. If the PID input is functioning correctly, this issue won't be triggered.  It is triggered only when ALL of the following conditions are met:
  1. The PID output is at the lower or upper clamp value.
  2. The PID input is configured to be an analog input point.
  3. The analog input module goes offline or resets.

Workaround:

Setting a Max Change to the output might help.

Resolution:

Opto 22 has resolved this issue in SNAP PAC firmware R9.4c. The fix isnot included in R9.4a or R9.4b.
Ultimate I/O is a mature product and is no longer being updated.

Questions?

Contact: Opto 22 Product Support.
Phone: 800-835-6786 or 951-695-3080
Email: support@opto22.com


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