PPID formula values

Use the
General
tab on the
PPID Properties
 dialog box to monitor and enter formula values for Process Proportional + Integral + Derivative (PPID) instructions.
To monitor and enter formula values for PPID instructions
  1. On the instruction in the routine, perform one of these actions:
    • On the Ladder or FBD instruction, select .
    • In the Structured Text editor, right-click the tag name and select
      Configure <tag name>
      .
  2. Monitor these parameters:
    • Device state
      . When the
      Logix Designer
       application is online with the controller, displays the current device state, such as
      SP ramping
       or
      CV held
      .
    • Device issues
      . When the
      Logix Designer
       application is online with the controller, displays fault conditions, such as
      PV uncertain
      ,
      SP fail
      , or
      Configuration error
      .
    • Device mode
      . When the
      Logix Designer
       application is online with the controller, displays the current device mode:
      • Manual
      • Auto
      • Cascade (no Ratio)
      • Ratio
    • Current SP
      . Displays the setpoint value Val_SP provided as the setpoint input to the Proportional + Integral + Derivative (PID) formula. The setpoint value is displayed in PV engineering units. Check the
      SP
       tab for the source of origin and to see modifications to the setpoint value before it enters the PID formula. Use the
      HMI
       tab to assign a value label to PV engineering units.
    • Input PV
      . Displays the process variable value Inp_PV provided as the PV input to the PID formula. PV value is displayed in PV engineering units.
    • Error
      . Displays the loop error Val_E and Val_EPercent. Val_E is displayed in PV engineering units, and Val_EPercent in percent of PV span. 100% is Cfg_PVEUMax-Cfg_PVEUMin. The loop error is calculated as SP-PV if Cfg_CtrlAction is set to False. Loop error is calculated as PV-SP if Cfg_CtrlAction is set to True.
    • Control action
      . Displays the control action configured for CV and PV. Select the control action on the
      Advanced
      tab. Control action can be set to:
      • Reverse: SP - PV for reverse control, in which the CV decreases as the PV increases.
      • Direct: PV - SP for direct control, in which the CV increases as the PV increases.
    • PID gains format
      . Displays the gains format configured for the PID formula. Select the gains format on the
      Advanced
      tab.
      These gains are available in Independent mode:
      • Kp – proportional gain, unitless
      • Ki – integral gain, 1/minute
      • Kd – derivative gain, minutes
      • Kt – CV tracking gain, 1/minute
        These gains are available in Dependent mode:
      • Kc – overall gain, unitless
      • Ti – integral time constant, reset time, minutes
      • Td – derivative time constant, rate time, minutes
      • Tt – CV tracking time constant, minutes
    • Feed forward
      . Displays the value from feedforward input. Feedforward is displayed in CV engineering units. Assign a label for CV engineering units on the
      HMI
      tab.
    • Previous feed forward
      . Displays the feedforward value from the past sample that the velocity algorithm of PID uses to calculate change in feedforward over one sample. The previous value is not in use if the PPID instruction is configured for PD algorithm without bumpless transfer from Manual to Auto or Cascade (Cfg_PositionBump=1). Past feedforward is displayed in CV engineering units.
    • CV target
      . Displays the CV value before ramping. The CV target is displayed in CV engineering units. The
      CV target
       tab displays CV target source processing.
    • CV output
      . Two displays indicate the CV value provided by the PPID instruction after ramping. Ramping is skipped if the PPID instruction is in Manual loop mode and Cfg_SkipCVManRoC is set to 1. Val_CVOut is displayed in CV engineering units, and Val_CVPercent in percent of CV span. 100% is Cfg_CVEUMax, 0% is Cfg_CVEUMin. The
      CV output
       tab displays how the CV output is derived from the CV target, CV track input, and CV hand feedback or initial value.
    • CV track
      . Displays the value provided from input Inp_CVTrack. CV output mirrors this value if the PPID instruction is configured to do so, or if the PPID instruction is placed in the outer loop and the inner loop in cascade is not available or not following the CV provided by the outer loop. The outer loop typically provides the SP for the inner loop or actuator target position. CV track value is displayed in CV engineering units.
  3. Configure or monitor these parameters:
    • P gain
      . Enter or monitor the Cfg_PGain parameter used in the PID formula. The parameter does not contain units.
      • When the PID formula is configured for independent gains, the P gain is the Kp gain used in proportional action.
      • When the PID formula is configured for dependent gains, the P gain is the overall gain Kc applied to all three terms.
    • P SP weight b
      . Enter or monitor the Cfg_PSPWeight parameter used in the two degrees of freedom PID formula. The weight b (beta) is the factor with which the SP enters loop error calculation for proportional term, Cfg_PSPWeight × Val_SP.
    • I gain
      . Enter or monitor the Cfg_IGain parameter used in the PID formula.
      • When the PID formula is configured for independent gains, the I gain is the Ki gain used in integral action. Ki is in repeats/minute.
      • When the PID formula is configured for dependent gains, the I gain is the integral time constant Ti, reset time. Ti is in minutes.
        TIP: Ki = Kc/Ti.
    • I CV tracking gain
      . Enter or monitor the Cfg_CVTrackGain parameter used in the PID formula to allow for tracking external CV.
      • When the PID formula is configured for independent gains, the Cfg_CVTrackGain parameter is the Kt gain used in integral action to act on CV tracking error (CV to track – loop CV calculated). Kt is in repeats/minute.
      • When the PID formula is configured for dependent gains, the Cfg_CVTrackGain parameter is the tracking time constant Tt used in integral action to act on CV tracking error (CV to track – loop CV calculated). Tt is in minutes.
        TIP: Kt = 1/Tt.
    • I CV tracking
      . Select to enable CV tracking, enabling tracking error calculation in the PID formula.
    • D gain
      . Enter or monitor the Cfg_DGain parameter used in the PID formula.
      • When the PID formula is configured for independent gains, the Cfg_DGain parameter is the Kd gain used in derivative action. Kd is in minutes.
      • When the PID formula is configured for dependent gains, the Cfg_DGain parameter is the derivative time constant Td, rate time. Td is in minutes.
        TIP: Kd = Kc×Td.
    • D SP weight c
      . Enter or monitor the Cfg_DSPWeight parameter used in the two degrees of freedom PID formula. The weight c (gamma) is the factor with which the SP enters loop error calculation for derivative term, Cfg_DSPWeight × Val_SP.
    • D smoothing
      . Select to enable derivative smoothing. When set, the derivative action is limited at high frequencies.
  4. When online with the controller, select these commands. The action is immediate if the command request does not need to be confirmed by the operator. If the command request requires a signature, this will enforce security from the HMI and disable the command from the Logix Designer dialog.
    TIP: Visibility of the command buttons is dynamic based on the configuration of the device.
    • On-line loop mode request: Auto
      . Enables Auto mode for this PPID loop.
    • On-line loop mode request: Cascade
      . Enables Cascade mode for this PPID loop.
    • On-line loop mode request: Manual
      . Enables Manual mode for this PPID loop.
  5. Select
    Apply
    .
Provide Feedback
Have questions or feedback about this documentation? Please submit your feedback here.