C135 PCS 7 (PCS7)
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Enabling Test Mode in SFC and Distinguishing SFC Types from SFC Instances in PCS 7

Enabling Test Mode in SFC and Distinguishing SFC Types from SFC Instances in PCS 7

In SIMATIC PCS 7, the 'Test Mode' button (glasses icon) is permanently disabled when viewing an SFC Type definition because an SFC Type is a reusable class template without allocated runtime memory or a physical instance data block. To test and monitor sequential logic online, you must open an SFC Instance from within its host CFC chart. In the SFC Instance window, the Test Mode button is enabled, allowing real-time step execution monitoring, manual transition triggering, and condition evaluation.

Table of Contents

Executive Summary

The Sequential Function Chart (SFC) system in SIMATIC PCS 7 (V8.0 through V9.1) supports two distinct sequential control paradigms: standalone SFCs and object-oriented SFC Types with SFC Instances (frequently utilized for Equipment Phases / EPHs and Equipment Modules / EMs). During commissioning and testing, engineers frequently report that the 'Test Mode' button (online monitoring) is greyed out and inactive, even after compiling and downloading changes to the automation controller. This article clarifies the fundamental distinction between SFC Types and SFC Instances, explains why template definitions cannot be monitored online, and provides the step-by-step procedure to test and commission SFC instances.

Architecture and Fundamental Mechanics

Architectural Mechanics: SFC Types vs. SFC Instances in SIMATIC PCS 7:

  • SFC Type (The Class Template):
  • Defined in the SIMATIC Manager Component View or Master Data Library.
  • Represents a reusable technological template (e.g. standard reactor phase, CIP cleaning sequence, dosing phase).
  • Contains sequence topologies, steps, transitions, setpoint definitions, and technological parameters.
  • Crucial Architectural Principle: An SFC Type possesses no execution memory and no assigned instance Data Block (DB) in the controller. It cannot be executed or monitored directly because it represents code metadata, not a running process entity.

  • Consequently, when an engineer opens an SFC Type directly from SIMATIC Manager, the Test Mode button (Debug -> Test Mode or glasses icon) is permanently disabled by system design.

  • SFC Instance (The Executable Object):

  • Created by dragging an SFC Type from the library onto a Continuous Function Chart (CFC).
  • The CFC compiler assigns a dedicated instance Data Block (DB) in the controller's work memory to each SFC Instance.
  • The SFC Instance executes cyclically in the designated priority class (e.g. OB35 / 100ms) and processes live field I/O connections.

  • When an engineer opens the SFC Instance from the CFC chart, the window title explicitly indicates the instance path. In this window, Test Mode is fully functional, enabling real-time step tracking, condition evaluation, and manual overrides.

  • Other Causes of Disabled Test Mode:

  • Target AS Offline or Unreachable: The engineering station cannot establish an S7 connection to the controller.
  • Timestamp Inconsistency: The offline chart database differs from the program loaded in the CPU. Downloading changes restores synchronization.
  • CPU Operating State: If the CPU is in STOP mode, step advancement and online execution monitoring are disabled.

Step-by-Step Implementation Procedure

Step-by-Step Procedure to Test and Monitor SFC Sequential Logic:

  1. Verify Object Type in SIMATIC Manager:
    - Inspect the title bar of your open SFC window.
    - If the title bar reads SFC Type: [Name] (e.g. SFC Type: EPHT), you are inside the template editor where Test Mode is permanently disabled.
    - Close the SFC Type window.
  2. Locate the SFC Instance in the Plant Hierarchy / CFC:
    - In SIMATIC Manager Plant View, navigate to the target process cell, unit, or equipment module (e.g. Area01 -> Unit01 -> EPH_Dosing).
    - Open the host CFC chart where the SFC Type was instantiated.
    - Locate the SFC block symbol on the chart sheet.
  3. Open the SFC Instance:
    - Double-click the SFC block instance on the CFC chart (or right-click the block -> select Open).
    - The SFC editor opens. Verify the title bar now displays the full technological instance path (e.g. SFC: PlantHierarchy/Area01/Unit01/CFC_Dosing/EPH1).
  4. Activate Online Test Mode:
    - Click the Test Mode button (glasses icon) on the toolbar, or select menu Debug -> Test Mode (Ctrl+T).
    - The editor connects online to the CPU instance DB. The active step illuminates with a green/yellow execution halo.
  5. Execute Testing and Diagnostics:
    - Open the SFC Control panel to switch operating modes (Manual, Auto, or Simulation).
    - Double-click any active transition to open the condition evaluation window; verify boolean states of interlocks and process criteria in real time.
    - Use manual step advancement controls or force transition conditions to validate phase logic safety responses.

Verification

Verification Procedure:
1. Online Status Verification: In the SFC Instance window, confirm the title bar shows 'Test Mode' and the CPU operating state indicates 'RUN'.
2. Transition Diagnostics: Double-click an active transition icon. Confirm that condition logic expressions display dynamic live values (e.g. TT_101.PV_Out.Value > 65.0 = TRUE highlighted in green).
3. HMI Synchronization: In WinCC Runtime, open the corresponding SFC faceplate. Confirm that phase status, active step name, and operating mode match the online CFC/SFC Instance view exactly.

Limitations and Operational Precautions

Operational Precautions and Safety Guardrails:
- Forcing Transitions: Forcing transition conditions in SFC Test Mode bypasses programmed process interlocks. Always verify that physical plant equipment, pumps, and valves are in a safe state before forcing transitions on live processes.
- Editing Restrictions in Test Mode: An SFC Instance is read-only regarding structure; you cannot add steps or modify transition logic in the instance editor. Structural modifications must be made in the master SFC Type definition, followed by compiling and updating block types.
- Type Change in RUN (TCiR): Updating an SFC Type modifies block interfaces. To avoid an AS STOP download on running plants, use the CPU 410-5H TCiR mechanism under strict engineering guidelines.

Engineer FAQ

Why is the Test Mode button disabled in my SFC editor?

You have opened the SFC Type definition instead of an SFC Instance. SFC Types are code templates without runtime memory; you must open an SFC Instance from a CFC chart to test online.

How do I distinguish an SFC Type window from an SFC Instance window?

Check the window title bar: an SFC Type displays SFC Type: [Name], whereas an SFC Instance displays the full chart path SFC: [Plant Hierarchy/Chart/Instance].

Can I modify transition conditions while online in an SFC Instance?

No. Structural logic changes must be made in the master SFC Type definition in the library or component view, followed by recompilation and type updating.

What does a green transition condition indicate in Test Mode?

A green condition indicates that the boolean logic expression currently evaluates to TRUE (fulfilled).

Can I control an SFC Instance from both the ES and the OS simultaneously?

Yes. Operating modes (Manual/Auto) and step commands can be executed from the ES SFC Instance test panel or the WinCC OS faceplate.

Technical References

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Related Tags

  • SFC Test Mode
  • SFC Type
  • SFC Instance
  • Sequential Control
  • Equipment Phase
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