C135 PCS 7 (PCS7)
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Configuring Operating-State-Dependent Alarm Suppression on APL Blocks in PCS 7

Configuring Operating-State-Dependent Alarm Suppression on APL Blocks in PCS 7

In SIMATIC PCS 7 APL, dynamically enabling pressure transmitter high alarms (PV_AH_En and PV_WH_En) only when a pump is running—and suppressing them when the pump is stopped—can be accomplished via chart-level parameter interconnection or Smart Alarm Hiding. The most direct, reliable method is to interconnect the run feedback output (FbkRunOut.Value) of the pump motor block (MotL FB1850) to the alarm enable inputs (PV_AH_En and PV_WH_En) of the analog monitoring block (MonAnL FB1845), optionally adding an on-delay timer (TimerP) to prevent nuisance alarms during pressure ramp-up. Alternatively, connect inverted pump running status to MonAnL's MsgLock input to suppress all messages, or configure WinCC Smart Alarm Hiding based on Plant State variables.

Table of Contents

Executive Summary

In process automation facilities, operating equipment state changes often generate nuisance alarms. For example, when a discharge pump is stopped, line pressure drops to zero; conversely, when the pump starts, downstream pressure surges, potentially triggering false high alarms before reaching steady state. Process engineers frequently request that High Alarm and High Warning limits on pressure transmitters be active exclusively when the pump is operating, and cleanly suppressed when offline. This technical guide outlines the three primary implementation strategies available in PCS 7 APL—direct parameter enabling, alarm message locking (MsgLock), and WinCC Smart Alarm Hiding—evaluating their engineering trade-offs and providing complete implementation procedures.

Architecture and Fundamental Mechanics

The alarm management architecture of the PCS 7 Advanced Process Library (APL) provides multiple independent layers for alarm gating and suppression:
1. Dedicated Alarm Enable Inputs (PV_xx_En):
- Technological blocks such as MonAnL (FB1845) feature dedicated boolean enable inputs for each alarm tier:
- PV_AH_En: Process Value Alarm High Enable
- PV_WH_En: Process Value Warning High Enable
- PV_WL_En: Process Value Warning Low Enable
- PV_AL_En: Process Value Alarm Low Enable
- Setting PV_AH_En = 0 completely disables evaluation of the high alarm limit. The block will neither generate an ALARM_8P event nor display the high alarm visual icon on WinCC faceplates.
2. Startup Ramp-Up Dynamics and Alarm Delay (AlarmDelay):
- Immediately energizing PV_AH_En when a pump starts can cause false alarms during transient pressure surges.
- APL provides built-in alarm delay parameters (PV_AH_DS / PV_WH_DS - Delay for Incoming Alarms in seconds) or external timer logic (TimerP) to delay alarm activation until steady-state operation is achieved.
3. Message Locking (MsgLock):
- When MsgLock = 1, all alarm and warning messages from the block are suppressed, though limit thresholds continue to be evaluated visually on faceplates.
4. WinCC Smart Alarm Hiding:
- Operates at the OS layer: alarms are hidden or shown dynamically based on Plant State tags without modifying CFC logic.

Step-by-Step Implementation Procedure

  1. Open CFC Chart Containing Pump and Pressure Monitoring Blocks:
    a. Open SIMATIC Manager and navigate to the Plant Hierarchy folder containing the pump unit.
    b. Open the CFC chart displaying the motor block (MotL FB1850) and analog monitoring block (MonAnL FB1845).

  2. Expose Alarm Enable Parameters on MonAnL:
    a. Right-click the MonAnL block and select Object Properties -> I/Os.
    b. In the parameter list, locate PV_AH_En (High Alarm Enable) and PV_WH_En (High Warning Enable).
    c. Check the 'Visible' checkbox for both parameters so their connection pins appear on the block symbol.

  3. Connect Pump Running Status to Alarm Enables:
    a. If immediate activation upon pump run is acceptable:

    • Drag a connection line from MotL.FbkRunOut.Value (active pump run feedback) to MonAnL.PV_AH_En.
    • Drag a second connection line from MotL.FbkRunOut.Value to MonAnL.PV_WH_En.

  4. Add Startup Delay Timer to Prevent Transient Alarms (Recommended):
    a. Insert an instance of TimerP (FB1884) between MotL and MonAnL.
    b. Connect MotL.FbkRunOut.Value to TimerP.In.
    c. Set TimerP.Ti to the desired stabilization delay (e.g., 10.0 seconds for line pressurization).
    d. Set TimerP.Mode = 0 (On-delay mode).
    e. Connect TimerP.Out to MonAnL.PV_AH_En and MonAnL.PV_WH_En.

  5. Alternative Method: Complete Message Suppression via MsgLock:
    a. If all alarms (including Low Alarms) must be suppressed when the pump is stopped:

    • Invert the pump running signal using a Not01 block (In = MotL.FbkRunOut.Value).
    • Connect Not01.Out to MonAnL.MsgLock.Value.

  6. Compile and Download Changes in RUN:
    a. Execute Chart -> Compile -> Changes only.
    b. Execute PLC -> Download -> Changes only in RUN mode.

Verification

  1. With the pump stopped (FbkRunOut = 0): verify in CFC online that MonAnL.PV_AH_En = 0. Artificially simulate line pressure exceeding the high limit: confirm no high alarm is generated in the WinCC Alarm banner.
  2. Start the pump: observe that after the 10-second stabilization timer elapses, PV_AH_En and PV_WH_En become 1.
  3. Increase line pressure above the high limit while running: confirm the high alarm fires promptly and appears on the WinCC operator screen.
  4. Stop the pump: verify that the high alarm clears immediately as PV_AH_En drops to 0.

Limitations and Operational Precautions

Directly disabling alarms via PV_AH_En = 0 completely prevents alarm logging. If regulatory compliance mandates that pressure excursions must still be archived in historical records even when equipment is offline, use WinCC Smart Alarm Hiding instead.

Engineer FAQ

What block parameters enable high alarms on MonAnL?

The inputs PV_AH_En (Process Value High Alarm Enable) and PV_WH_En (High Warning Enable).

Why should a timer be placed between the pump run signal and alarm enable?

To prevent nuisance alarms caused by transient pressure spikes while the pump ramps up to operating speed.

What is the difference between PV_AH_En and MsgLock?

PV_AH_En disables specific limit evaluations. MsgLock suppresses all message transmissions to WinCC while maintaining limit status on faceplates.

Can alarms be suppressed at the WinCC OS level without changing CFCs?

Yes, using WinCC Smart Alarm Hiding, which filters alarms dynamically based on Plant State tags.

Does changing PV_AH_En require an AS STOP download?

No. Connecting or changing parameter values in CFC can be downloaded in RUN using 'Changes only'.

Technical References

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Related Tags

  • Alarm Suppression
  • MonAnL
  • MotL
  • PV_AH_En
  • Smart Alarm Hiding
  • APL Alarms
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