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KB83813
Unusually large change in PID Output or Integral
Revision:  2.0
Published:  12/18/2015
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
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.)

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Ultimate I/O is a mature product and is no longer being updated.

Relevant Downloads
No relevant downloads have been specified.
Questions? Contact Opto 22 Product Support.
Phone: 800-835-6786 or 951-695-3080
Email: support@opto22.com

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This Opto 22 Knowledge Base ('OptoKB') article is intended to provide general technical information on a particular subject or subjects and is not an exhaustive treatment of such subjects. Accordingly, the information in this OptoKB article is not intended to constitute application, design, software, or other professional engineering advice or services. Opto 22 may modify the OptoKB articles at any time. Before making any decision or taking any action which might affect your equipment, you should consult a qualified professional.

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