C135 PCS 7 (PCS7)
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Activating and Controlling Equipment Modules (EM) via Interconnections in PCS 7

Activating and Controlling Equipment Modules (EM) via Interconnections in PCS 7

To activate and command an Equipment Module (EM / SFC Type)—such as commanding Start, Stop, Hold, Abort, or Complete—via programmatic signal interconnections in SIMATIC PCS 7, connect control signals to the dedicated interconnected command inputs: 'START_LI', 'STOP_LI', 'HOLD_LI', 'ABORT_LI', 'COMP_LI', and 'RESUME_LI'. The EM must be switched to Automatic mode ('AUTOMA_L := 1'), and operational enable permissions ('ENSTART', 'ENRESET', 'ENABORT') must be asserted. Interconnected commands are evaluated on signal rising edges, allowing higher-level plant logic to coordinate equipment phases programmatically.

Table of Contents

Executive Summary

In modular automation and recipe execution according to ISA-88, plant equipment is structured into Equipment Modules (EM) containing SFC Types that govern physical operations (e.g., 'Reactor_Dosing' or 'Filter_Backwash'). While operators can control EMs manually from WinCC faceplates, automated plant coordination requires supervisory charts, interlocks, or upstream recipe modules to command EMs programmatically. This article details the linked command interface (_LI) of SFC Types, operating mode selection, command edge detection, and interlocking rules.

Architecture and Fundamental Mechanics

Equipment Module Linked Command Architecture in SFC Types:

  • Operating Mode Authority (Auto vs Manual):
  • Manual Mode (MAN): The operator controls the EM via the WinCC faceplate. Interconnected command inputs (_LI) are ignored by the state machine.
  • Automatic Mode (AUTO): Interconnected inputs (_LI) have full command authority. Faceplate operator buttons are locked/disabled.
  • Mode Switching Pins: Force Automatic mode programmatically by asserting AUTOMA_L := 1 and AUTOMA_OP := 0.
  • Linked Command Inputs (_LI):
  • START_LI: Initiates sequence start (transitions Ready to start -> Starting -> Run).
  • HOLD_LI: Initiates sequence hold (transitions Run -> Holding -> Held).
  • RESUME_LI: Resumes sequence from hold (transitions Held -> Resuming -> Run).
  • STOP_LI: Controlled shutdown (transitions Run -> Stopping -> Stopped).
  • ABORT_LI: Emergency termination (transitions any active state -> Aborting -> Aborted).
  • RESET_LI: Resets completed/aborted sequence back to Ready to start.
  • Enable and Permission Pins:
  • ENSTART: Master enable for start. If ENSTART = 0, START_LI pulses are rejected.

Step-by-Step Implementation Procedure

Procedure to Wire and Command an Equipment Module via Interconnections:

  1. Instantiate Equipment Module (SFC Type) in CFC:
    - Place the SFC Type instance into the supervisory CFC chart.
  2. Configure Automatic Operating Mode:
    - Connect a static TRUE (or automated mode selector) to input AUTOMA_L.
    - Set input ENAUT := TRUE to permit automatic mode operation.
  3. Wire Linked Commands from Higher-Level Logic:
    - Connect the start trigger pulse (e.g., from an upstream batch completion block) to START_LI.
    - Connect process safety trip interlocks to ABORT_LI or HOLD_LI.
    - Connect sequence completion handshakes to COMP_LI (if manual phase completion is parameterized).
    - Connect reset logic to RESET_LI to return the unit to Ready to start.
  4. Ensure Operating Enables are Asserted:
    - Verify ENSTART := TRUE, ENHOLD := TRUE, ENABORT := TRUE, and ENRESET := TRUE.
  5. Compile and Test:
    - Compile CFC changes and download to the automation station.
    - Monitor the block online in CFC test mode.

Verification

To verify linked command execution:
1. In CFC test mode, confirm the SFC instance is in Automatic mode (QMAN_ACT = 0, QAUTO_ACT = 1) and Ready to start (QIDLE = 1).
2. Generate a 1-cycle rising edge on START_LI; verify the SFC advances immediately into Starting and then Run (QRUN = 1).
3. Pulse HOLD_LI; confirm the SFC transitions to Held.
4. Pulse RESUME_LI; confirm the SFC transitions back to Run.

Limitations and Operational Precautions

Operational precautions:
- Linked commands (_LI) require a 0-to-1 rising edge; maintaining START_LI continuously at TRUE can block subsequent state transitions or cause continuous restart attempts.
- In plants managed by SIMATIC BATCH, batch recipe phases are commanded via the SIMATIC BATCH interface; do not interconnect external _LI pins to BATCH-allocated phases without arbitration.
- Always prioritize ABORT_LI over operational commands for safety interlocks.

Engineer FAQ

Why does my SFC Type ignore pulses on START_LI?

Because the SFC is in Manual mode, ENSTART is FALSE, or the SFC is not in the 'Ready to start' state.

How do I force an SFC Type into Automatic mode via CFC?

Set AUTOMA_L := 1 and ensure ENAUT := 1.

Should linked command inputs be pulsed or maintained?

Linked commands are edge-triggered and should be asserted as pulses (e.g., for 1-2 scan cycles).

What is the difference between STOP_LI and ABORT_LI?

STOP_LI executes a controlled shutdown sequence; ABORT_LI executes an immediate emergency abort.

Can an operator override linked commands from the faceplate?

Only if the operator switches the block to Manual mode (and ENMAN permits manual intervention).

Technical References

Related Articles

Related Tags

  • Equipment Module
  • SFC Type
  • START_LI
  • Linked Commands
  • Auto Mode
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