C135 PCS 7 (PCS7)
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How to Configure Time-Delayed Flow Alarms and Resolve WinCC Tag Synchronization in PCS 7 CFC and APL

How to Configure Time-Delayed Flow Alarms and Resolve WinCC Tag Synchronization in PCS 7 CFC and APL

To configure a 10-minute delayed flow alarm in PCS 7, use the native limit delay capabilities of the Advanced Process Library (APL) analog monitoring block (MonAnL) by setting the high alarm limit PV_AH_Lim to 140.0 and configuring the alarm delay parameter PV_AH_DC to 600.0 seconds. Alternatively, connect a comparator block (CMP_R) to an on-delay timer (TimerP, Mode 0) feeding an EventTs alarm block. If newly configured tags do not appear in WinCC Dynamic Wizard, ensure the block output possesses attribute S7_m_c := 'true', execute an OS Compilation ('Changes only') from SIMATIC Manager, and confirm the OS server communication driver is active.

Table of Contents

Methods for Implementing Time-Delayed Alarms in PCS 7

In process automation plants, transient flow surges caused by pump start-ups, valve stroke transitions, or pressure pulsations can cause flow measurements to cross alarm thresholds momentarily. Generating alarms immediately upon threshold crossing results in operator alarm flooding.

In SIMATIC PCS 7, engineers can implement sustained threshold alarming (e.g., flow exceeding 140 m³/h for at least 10 minutes continuously) using two primary architectural approaches:
1. Native APL Block Delay (Recommended): Standard APL analog monitoring blocks such as MonAnL (FB1845) include built-in, parameterizable alarm delay counters and hysteresis controls. This requires no additional CFC blocks, minimizing memory footprint and CPU execution cycle overhead.
2. Auxiliary CFC Logic (Comparator + Timer + Event Block): Comparing the analog value using a floating-point comparator (CMP_R), gating the result through an on-delay timer (TimerP), and triggering an alarm message block (EventTs or Event). This method is useful when integrating legacy library blocks (such as MeasPP) that lack native multi-stage timers.

Implementing Native Limit Delays in APL MonAnL

The most elegant and standardized method in PCS 7 V7.1, V8.x, and V9.x is configuring the standard APL block MonAnL:

  1. Place MonAnL in CFC:
    * Open the target CFC chart and insert MonAnL from the APL library.
    * Interconnect the analog input driver (Pcs7AnIn.PV_Out) to MonAnL.PV.
  2. Configure Limits and Alarm Delays:
    * Set PV_AH_Lim = 140.0 (High Alarm Limit).
    * Set PV_AH_DC = 600.0 (Delay Count in seconds, corresponding to 10 minutes).
    * Set PV_Hyst = 2.0 (e.g., 2% hysteresis to prevent alarm flutter upon falling back).
  3. Configure Message Characteristics:
    * In MonAnL properties, click Messages. Confirm that the PV_AH_Alarm message is assigned to the appropriate alarm class (e.g., Alarm High).
    * When the process value exceeds 140.0, the internal timer increments. If the flow remains above 140.0 for 600 consecutive seconds, the block triggers the alarm and generates an operator message in WinCC.

Alternative Implementation Using CMP_R and TimerP with EventTs

When working with custom libraries, legacy blocks, or when the timer must be dynamically reset by external operational conditions:

[Flow Transmitter PV] 
        |
        v
+------------------+
|      CMP_R       |
| In1 = PV         |----(Out: GT)---->+-------------------+
| In2 = 140.0      |                  |      TimerP       |
+------------------+                  | Mode = 0 (On-Dly) |----(Q)---->+-------------------+
                                      | Ti   = T#10m      |            |      EventTs      |
                                      +-------------------+            | In1 = Timer.Q     |
                                                                       +-------------------+
  • CMP_R (FC353): Compares In1 (Flow PV) with In2 (140.0). Output GT becomes TRUE when Flow > 140.0.
  • TimerP (FB5): Configured in Mode 0 (On-Delay). When GT stays TRUE continuously for duration Ti = 600s, output Q becomes TRUE. If GT drops FALSE even momentarily, the internal timer resets to zero.
  • EventTs (FB1817): High-resolution timestamped alarm block. Connect TimerP.Q to In1. When Q goes TRUE, EventTs generates an alarm message sent directly to the WinCC alarm logging system.

Resolving WinCC Tag Visibility and OS Compilation Discrepancies

A common issue encountered after creating new CFC measurement blocks is that the WinCC Dynamic Wizard cannot find the tag (e.g., FT823/PV), or the tag appears on Server 01 but is absent on Server 02:

  • S7_m_c Attribute: Confirm that the block and its output pins have the attribute S7_m_c := 'true'. In CFC, double-click the block, select I/O Properties, and ensure the OCM (Operator Control and Monitoring) checkbox is enabled.
  • Perform OS Compilation: Tags created in CFC are not automatically visible in WinCC until an OS Compilation is executed:
  • In SIMATIC Manager Component View, right-click the OS Server object and select Compile.
  • Choose Changes Only (or Entire OS).
  • Ensure the AS chart containing FT823 is selected in the scope of compilation.
  • Redundant Server Tag Sync: If Server 01 contains the tag but Server 02 does not, the OS download to Server 02 was skipped or failed. Download the compiled OS project to both servers.
  • Simulation Mode in Tag Management: Verify in WinCC Tag Management on the runtime server that the PLC driver connection is not stuck in simulation mode.

Managing Engineering Units and Text Library Unit Codes

When assigning engineering units (e.g., liters per minute l/min), PCS 7 utilizes standardized numeric unit codes based on IEC 61987 / PROFIBUS PA profile:
* Unit code 1352 corresponds to l/min (or L/min).
* If entering 1352 into the block parameter PV_Unit (or PV_Out.ST) does not render the text string l/min on the WinCC faceplate:
1. Open the WinCC project and check the Text Library.
2. Verify that the numeric ID 1352 is mapped to l/min across all installed languages (English, German, French).
3. If using an industry-specific library (such as Paper and Pulp, Minerals, or Cement), ensure the domain library's unit XML table was imported into the Master Data Library.

Comparison of Alarm Delay Implementations

The table below compares the two primary implementation strategies for time-delayed threshold alarming in SIMATIC PCS 7.

Feature / CriteriaNative APL MonAnL DelayAuxiliary Logic (CMP_R + TimerP + EventTs)Block CountSingle block (MonAnL)3 blocks (CMP_R, TimerP, EventTs)AS Memory / PO Usage1 Process Object (PO)Multiple blocks; consumes additional PO count if EventTs is usedExecution Cycle OverheadExtremely low (internal integer counter)Higher (multiple block calls in OB35/OB32)Standard Faceplate IntegrationAutomatic integration with standard APL faceplateRequires custom faceplate or separate alarm interconnectionDelay Modification in RuntimeModifiable online via faceplate parameter viewRequires CFC online edit or interconnected parameter tagFailsafe HandlingIntegrated sensor quality / bad status suppressionRequires manual interlocking of quality code bits

Verification

To confirm proper operation of the delayed flow alarm:
1. In CFC, open the chart online and monitor MonAnL (or the TimerP network).
2. Force or simulate the flow transmitter input above 140.0 m³/h.
3. Verify that the alarm is not generated immediately. Start a stopwatch and observe that the alarm output remains FALSE during the first 9 minutes.
4. Keep the simulated flow above 140.0 m³/h past 10 minutes (600 seconds). Confirm that the high alarm activates and generates a flashing alarm on the WinCC alarm banner.
5. In WinCC Graphics Designer, open the dynamic wizard or tag selection dialog and confirm that FT823/PV is fully selectable under the Named Connections hierarchy.

Limitations and Operational Precautions

  • Do not configure excessively small alarm delay times (e.g., less than the cyclic execution period of the OB task), as this causes timer rounding inaccuracies.
  • If the flow signal drops below the threshold for even one execution cycle before the 10 minutes elapse, the delay timer resets to zero.
  • Ensure that the Engineering Station is used as the single source of truth for OS compilation; never configure WinCC tags directly on an individual OS Server when running redundant multi-station projects.
  • Verify that the selected engineering unit code is recognized by both the AS block library and the WinCC Text Library to avoid blank unit displays.

Engineer FAQ

Why did the WinCC Dynamic Wizard fail to find my newly created flow tag?

The Dynamic Wizard queries the WinCC Tag Management database. If a new block is added in CFC, its tags exist only in the AS until an OS Compilation is executed from SIMATIC Manager. Furthermore, the block's S7_m_c attribute must be set to true for its I/O to be mapped to the OS.

Can the 10-minute alarm delay be changed from WinCC Runtime by operators?

Yes, if using APL MonAnL. The alarm delay parameter PV_AH_DC has the S7_m_c := 'true' attribute and is accessible in the APL faceplate parameter view, provided the logged-in user possesses the required authorization level.

What happens to the alarm delay if the sensor signal status goes Bad?

In standard APL blocks, if PV receives a Bad signal status (e.g., wire break 16#00), limit evaluation is automatically suppressed or directed to a separate bad-quality alarm, preventing false limit alarms during sensor failure.

Technical References

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Related Tags

  • MonAnL
  • TimerP
  • Alarm Delay
  • CFC
  • OS Compilation
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