Handling Faults and Resuming SFC Types Under SIMATIC BATCH Control in PCS 7

Handling Faults and Resuming SFC Types Under SIMATIC BATCH Control in PCS 7

When an SFC Type controlled by SIMATIC BATCH encounters a process interlock or equipment fault, the SFC state machine automatically transitions from 'Run' to 'Holding' and then 'Held'. All recipe parameters, target setpoints, and step execution timers are preserved in the instance data block and SIMATIC BATCH runtime database. To resume execution after rectifying the physical fault, the operator or supervisor must issue a 'Resume' command directly within BatchCC (or via the SFC faceplate if released to manual mode), which transitions the sequence through 'Resuming' back to 'Run', continuing precisely from the interrupted step.

Table of Contents

• Executive Summary
• Architecture and Fundamental Mechanics
• Step-by-Step Implementation Procedure
• Verification
• Limitations and Operational Precautions
• Engineer FAQ
• Technical References
• Related Articles
• Related Tags

Executive Summary

In automated chemical, pharmaceutical, and food-and-beverage plants running SIMATIC BATCH, process interruptions—such as high vessel pressure, loss of cooling water, or pump trips—frequently halt batch recipes. Plant operators and recipe authors often fear that an equipment trip requires aborting the recipe and discarding expensive materials. In PCS 7, the ISA-88 state architecture preserves complete recipe context during hold conditions. This article details the coordination mechanics between SIMATIC BATCH and SFC Types during holding states, parameter retention rules, operator handshakes, and step-by-step recovery procedures.

Architecture and Fundamental Mechanics

SIMATIC BATCH and SFC Type Handshaking and State Machine Interaction:

• ISA-88 State Transition Coordination:
• SIMATIC BATCH communicates with the SFC Type via a dedicated interface block (BAP / Batch Interface).
• Normal Run: Ready to start -> Starting -> Run.
• Interlock Trip / Fault: When an interlock input de-asserts, the SFC transitions: Run -> Holding -> Held.
• Parameter Retention in the Instance DB:
• Recipe setpoints (target temperature, dosing volumes, agitator speeds) written by BATCH during phase allocation remain stored in the SFC Type instance Data Block (DB).
• Dynamic values, such as step elapsed time (QSTEP_TIME) and accumulated dosing weights, are frozen and not reset while in the Held state.
• Mode Handover and Command Authority:
• In Automatic (Batch) Mode: Commands must originate from SIMATIC BATCH Control Center (BatchCC). The faceplate command buttons are disabled to prevent operator conflicts.
• Manual Takeover: If troubleshooting requires manual operator intervention, the operator can switch the SFC to 'Manual' mode via ENMAN. The operator can jog valves or clear lines, but must return the SFC to 'Automatic' mode before BatchCC can resume the recipe.

Step-by-Step Implementation Procedure

Standard Operating Procedure for Recovering from a Batch Hold:

1. Diagnose the Root Cause of the Hold:
   - Open the SFC faceplate in WinCC Runtime.
   - Check the 'Interlocks' and 'Messages' tabs to identify which trip condition asserted (e.g., LockAct, Intlock, or high temperature trip).
   - In BatchCC, check the Batch Control Center message log for the active unit and phase.
2. Clear the Physical Plant Condition:
   - Acknowledge alarms in WinCC.
   - Reset field hardware (e.g., reset overload relay, open manual supply valve).
   - Ensure that technological interlock signals on the SFC block return to 1 (OK).
3. Resume the Batch Sequence:
   - If operating in Automatic Batch Mode:
   • In BatchCC, select the active batch in the recipe monitor.
   • Right-click the held phase -> select 'Resume' (or click the green Resume button on the toolbar).
   • BatchCC sends the resume command to the SFC Type block in the AS.
   • If operating via Operator Intervention:
   • Switch the SFC faceplate to Manual mode if line flushing is needed.
   • Complete manual adjustments.
   • Return SFC mode to 'Auto' -> in BatchCC, issue the 'Resume' command.
4. Monitor Phase Completion:
   - Verify that the SFC transitions: Held -> Resuming -> Run.
   - Confirm that step timers resume counting from their frozen values, rather than resetting to zero.
   - Observe successful transition to Completing -> Completed, allowing BatchCC to proceed to the subsequent recipe step.

Verification

To verify proper batch fault handling and recovery:
1. In a staging environment, run a test batch in BatchCC and simulate a field interlock trip while in the heating step.
2. Verify that the SFC faceplate indicates state 'Held' (yellow/orange state banner) and that BatchCC displays the step in a held state.
3. Confirm that recipe setpoints in the SFC instance DB match the batch recipe quantities.
4. Clear the simulated trip and click 'Resume' in BatchCC; verify the SFC transitions to 'Resuming', executes the resuming sequencer, and returns to 'Run' at the identical step position.

Limitations and Operational Precautions

Operational precautions:
- Never abort a batch in BatchCC unless materials must be scrapped; an 'Abort' command terminates the entire recipe and cannot be resumed.
- If manual steps are taken to adjust physical product while an SFC is in 'Held', verify that actual physical levels match the SFC internal accumulators before resuming.
- Do not force SFC state variables directly in the CPU variable table (VAT); state forcing bypasses BatchCC synchronization and can cause recipe deadlock.

Engineer FAQ

Do recipe parameters get lost when an SFC Type goes into the 'Held' state?

No. All setpoint parameters, material dosing values, and accumulated runtimes are preserved in the instance DB and in the SIMATIC BATCH database.

Can an operator click 'Resume' directly on the WinCC SFC faceplate during an active batch?

Only if BatchCC has released command authority or the SFC is switched to manual mode; normally, BatchCC holds master command authorization.

What happens if a plant operator resets the SFC while SIMATIC BATCH is running?

Resetting an active phase out from under SIMATIC BATCH generates a synchronization fault in BatchCC, putting the batch recipe into an error state.

What is the difference between 'Holding' and 'Held' in SFC state logic?

'Holding' is the transitional state during which clean-up actions execute; 'Held' is the stable steady state waiting for a Resume or Abort command.

Can an SFC Type have a specialized 'Resuming' sequence?

Yes. In the SFC Type editor, you can program a distinct sequencer that executes only during the transition from 'Held' back to 'Run'.

Technical References

• SIMATIC Process Control System PCS 7 SIMATIC BATCH Manual
• SIMATIC Process Control System PCS 7 SFC for SIMATIC S7
• SIMATIC Process Control System PCS 7 Advanced Process Library (APL)

Related Articles

• Understanding ISA-88 Operating State Logic and Sequencer Architecture in PCS 7 SFC Types
• Understanding Internal Commands, Acquisition Logic, and State Execution in PCS 7 SFC Types
• Designing and Operating SIMATIC PCS 7 SFC Types Without Control Strategies

Related Tags

• SIMATIC BATCH
• SFC Type
• ISA-88 State Logic
• Batch Recovery
• Held State