PID

Manual Setpoint mapping

PID.Opr.Param[1].CP.Value = 45

  • [CM_PROC_WRAP]
  • PID.Opr.Param[1].CP.Value -> CVoper
  • CM.ST.CO -> CO
  • CM.C.CV -> CV.Value
  • CVcm.C.CV -> CO -> CM.ST.CO 0
  • CVcm.PCmd.Own.CV -> CV.Value 0
  • CV.Value -> CVout 0
  • If NOT Override AND NOT AUTO AND OPERATOR Move CVoper -> Cvout 45
  • CVout -> CV.Value -> CM.C.CV 45

[CM_PIDE]

  • CV.Value or 0 (off) -> CVProg
  • CVEU -> CM.C.CV -> CV.Value -> CVout

cmPID.CVOut -> cv.Value -> CM.C.CV -> CM.ST.CO -> cvCM.PCmd.CV -> PID.CV 0

[CM_PARAM]

  • PID.Opr.Param[1] -> Param
  • {only set if in program or auto mode} CM.C.CV -> CP -> Param.CP.Value 45 changed to 0
  • CM.ST.CO -> RP -> Param.RP.Value

Abnormal PID Conditions 

Triggers abnormal Condition: PV Not Settled (Custom Process #4)

CV Oscillation Limit                        Raise Condition if CV PP exceeds this range (0 = disabled, eng units)

Oscillation Zero Crossing Limit     Number of times PV crosses SP before arming Oscillation

NOTE: This may need a grace oscillation count so that it can delay alarming if an upset occurs.  Perhaps it should always re-apply the Zero Crossing limit anytime it is within the limit.

Triggers abnormal Condition: Max Deviation (Custom Process #3) 

PV Deviation High Limit                 High PV Limit Offset from SP (0 = disabled)

PV Deviation Low Limit                  Low PV Limit Offset from SP (0 = disabled, must be negative)

Deviation Zero Crossing Limit       Number of times PV crosses SP before arming Deviation

Deviation Timeout Time                Trigger Deviation Condition Timeout (ms) before zero crossing

Triggers abnormal Condition: Slow Response (Custom Process #2) 

Slow Response PV Rate                  Weighted Minimum PV Rate of Change Condition

Slow Response Timeout                 Timeout (ms) before raising Slow Response

The CV Oscillation limit is the maximum Peak to Peak range the CV is allowed to fluctuate in after the PV has crossed the zero point (or setpoint) more than the amount specified by the Oscillation Zero Crossing limit parameter.

For example:

The PV crosses the zero point 8 times and the CV Peak to Peak ranges from 80% down to 15%.

If the oscillation limit is 30 and the zero crossing limit is 4 then this would trigger the condition at the 4th crossing and up until the pp<30 around the 6th crossing.

If the zero crossing limit is increased to 6 then this oscillation condition would never be triggered because the CV PP value never exceed 30 after the 6th crossing.

The zero crossing setting is to allow the process time to settle out before checking for oscillation.  The zero crossing count is reset when the PID is not in Auto, SP changes or the CM Clear Failures is pressed.

 

 

Updated on January 7, 2019

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