C135 PCS 7 (PCS7)
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Disabling Automatic Message Suppression on ConPerMon Control Performance Monitor Blocks

Disabling Automatic Message Suppression on ConPerMon Control Performance Monitor Blocks

In the SIMATIC PCS 7 Advanced Process Library (APL) ConPerMon (Control Performance Monitor, FB1805) block, the message suppression indicator (check mark 4 in the Limit view) is forced active (CPI_Suppress = 1) whenever the monitored control loop is open or operating in manual mode (LoopClosed = 0 or ManAct = 1). The block automatically suppresses Control Performance Index (CPI) warning and alarm messages to prevent nuisance alarms during startup, manual tuning, or setpoint transitions. To clear CPI_Suppress, interconnect the LoopClosed output from the upstream PID controller (PIDConL / PIDConR) to ConPerMon.LoopClosed, ensure the loop operates in Automatic mode, and allow the settling time to elapse.

Table of Contents

Executive Summary

The Control Performance Monitor (ConPerMon, FB1805) block in the PCS 7 Advanced Process Library (APL V8.2 / V9.0) provides continuous statistical supervision of PID control loops, calculating control performance indices (CPI), settling times, and oscillation detection. Engineers implementing ConPerMon often observe that the faceplate Limit view displays an active message suppression indicator (check mark 4), with Status1 Bit 15 (CPI_Suppress) asserted high, even when global message suppression (MsgLock = 0) is inactive on the CFC chart and no suppression was commanded from the faceplate. This behavior is an intentional internal protective feature of APL. The block automatically forces CPI_Suppress = 1 while the control loop is open, in manual mode, or experiencing transient settling, preventing false performance alarms from flooding the operator alarm list.

Architecture and Fundamental Mechanics

The message suppression architecture of ConPerMon integrates statistical evaluation with operating mode awareness:

1. CPI Performance Evaluation Prerequisites

The ConPerMon algorithm assesses how well a PID controller maintains process variable (PV) at setpoint (SP). This calculation is mathematically valid only when:
- The controller is actively executing closed-loop feedback (LoopClosed = 1 and ManAct = 0).
- The process is not undergoing an operator-commanded setpoint step change (DiffSP settling phase).
- Actuator saturation (MV_HiLim or MV_LoLim) is not artificially preventing control action.

2. Automatic CPI_Suppress Evaluation Logic

Inside FB1805, the internal logic for CPI_Suppress evaluates:
$$\text{CPI_Suppress} = \text{MsgLock} \lor \text{CPI_Suppress_Op} \lor (\text{NOT } \text{LoopClosed}) \lor \text{ManAct} \lor \text{SettlingActive}$$
- When an engineer tests ConPerMon in isolation without connecting PIDConL.LoopClosed, the default input value of LoopClosed is 0 (False).
- As long as LoopClosed = 0, the block considers the loop disconnected or offline, asserting CPI_Suppress = 1 and lighting check mark 4 on the faceplate.
- Once LoopClosed transitions to 1 (Automatic closed-loop) and the internal learning buffer fills with steady-state data, CPI_Suppress clears to 0.

Step-by-Step Implementation Procedure

To properly configure ConPerMon and release message suppression:

Step 1: Interconnect Control Loop Status Signals in CFC

  1. Open the CFC chart containing ConPerMon and the associated PID controller (PIDConL or PIDConR).
  2. Establish the mandatory loop status connections:
    - Connect PIDConL.LoopClosed $\rightarrow$ ConPerMon.LoopClosed.
    - Connect PIDConL.ManAct $\rightarrow$ ConPerMon.ManAct.
    - Connect PIDConL.PV_Out $\rightarrow$ ConPerMon.PV.
    - Connect PIDConL.SP_Out $\rightarrow$ ConPerMon.SP.
    - Connect PIDConL.MV $\rightarrow$ ConPerMon.MV.
  3. Alternatively, utilize the pre-engineered APL template PIDConL_ConPerMon.

Step 2: Configure Message Enable Parameters

  1. In the Object Properties of ConPerMon, verify message enable inputs:
    - CPI_AL_En: Set to 1 (Enable CPI Alarm Limit messages).
    - CPI_WL_En: Set to 1 (Enable CPI Warning Limit messages).
    - MsgLock: Confirm set to 0 (General message lock inactive).

Step 3: Compile and Test in Automatic Mode

  1. Compile and download CFC changes to the Automation Station.
  2. Switch the PIDConL block to Automatic mode (AutModOp = 1 or via faceplate).
  3. Verify in CFC Test Mode that PIDConL.LoopClosed transitions to 1.
  4. Allow the loop to run at steady state through one statistical evaluation window (defined by parameter RefHorizon and MonTiDynamic).
  5. Observe that CPI_Suppress resets to 0, and check mark 4 clears on the WinCC faceplate.

Verification

To confirm that message suppression is disabled:

  1. CFC Status Bit Inspection:
    - In CFC online mode, monitor the Status1 word on ConPerMon.
    - Confirm that Bit 15 (CPI_Suppress) has transitioned from 1 to 0.

  2. Faceplate Limit View Verification:
    - Open the ConPerMon faceplate in WinCC Runtime and select the Limit view.
    - Verify that check mark 4 (suppression icon) is no longer illuminated beside the CPI alarm thresholds.

  3. Alarm Generation Test:
    - Artificially degrade loop tuning or tighten the CPI warning limit (CPI_WL).
    - Verify that when CPI drops below the limit, a genuine alarm appears in the WinCC Alarm List.

Limitations and Operational Precautions

Operational limitations and precautions:

  1. Statistical Learning Delay: ConPerMon requires an observation window to calculate baseline metrics. During initial startup, suppression remains active until sufficient valid process cycles have been recorded.
  2. Uncertain Signal Quality: If PV.ST or SP.ST has Bad quality ($16#00$), ConPerMon flags an 'Uncertain Process' state and forces suppression.
  3. Execution Scheduling: ConPerMon must be scheduled in the same cyclic interrupt OB (e.g., OB35) or an integer multiple of the associated PID block's scan cycle.
  4. Commercial Disclaimer: Verify all software libraries, APL versions, and APC options with an authorized Siemens distributor or the Siemens Industry Mall.

Engineer FAQ

Why is CPI_Suppress equal to 1 when MsgLock is 0?

ConPerMon automatically forces CPI_Suppress = 1 when the control loop is open (LoopClosed = 0), in manual mode (ManAct = 1), or during initial statistical learning.

What does check mark 4 signify in the ConPerMon Limit view?

Check mark 4 visually indicates that message suppression is currently active for the Control Performance Index (CPI) alarms.

How does ConPerMon know if the loop is closed?

It reads the boolean input parameter LoopClosed, which must be interconnected to PIDConL.LoopClosed.

Where can I find the pre-wired template for ConPerMon?

In the PCS 7 APL Templates library under Process Tag Types -> PIDConL_ConPerMon.

Does ConPerMon generate alarms if the process is in manual mode?

No. By design, performance monitoring alarms are suppressed in manual mode because the operator, not the PID algorithm, controls the output.

Technical References

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Related Tags

  • ConPerMon
  • Message Suppression
  • APL
  • PID Tuning
  • CPI_Suppress
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