Designing and Operating SIMATIC PCS 7 SFC Types Without Control Strategies

You can design and operate a SIMATIC PCS 7 SFC Type without defining any Control Strategies (CS) if the equipment unit performs a single, unvarying procedural sequence (such as a standard Filter Backwash, CIP Cycle, or Reactor Purge). In this configuration, the SFC Type contains only a default Sequencer whose Start Condition evaluates simply as 'RUNNING', eliminating the need to parameterize or handshake strategy inputs ('CS', 'CS_LL'). SIMATIC BATCH seamlessly supports SFC Types without control strategies, representing the equipment phase as a single recipe phase with no strategy selection parameter.

Executive Summary

Control Strategies in SIMATIC PCS 7 SFC Types offer flexibility by allowing up to 32 different operating procedures within a single block instance. However, for many dedicated plant units, multiple strategies introduce unnecessary engineering complexity, bloated faceplate menus, and redundant handshaking logic. Engineers frequently ask whether omitting Control Strategies is officially supported, how it impacts ISA-88 state behavior, and how SIMATIC BATCH interacts with strategy-less SFC Types. This article explores the architecture, benefits, step-by-step creation, and integration of SFC Types designed without Control Strategies.

Architecture and Fundamental Mechanics

Architecture of Strategy-Less SFC Types:

Role of Control Strategies (CS):
Control Strategies exist to multiplex multiple operational sequences (e.g., 'Fast Agitation' vs 'Slow Agitation') within a single technological equipment type.
When Control Strategies are defined, each sequencer must explicitly validate CS = n in its start conditions, and the operator or recipe must select a strategy before starting.
Architecture Without Control Strategies:
The 'Control Strategies' folder in the SFC Type Characteristics remains empty.
The SFC Type contains one or more sequencers governed strictly by state conditions (e.g., a main sequence for RUNNING, an alternate branch for HOLDING, and an abort sequence for ABORTING).
The start condition for the primary sequencer simplifies to: RUNNING.
Faceplate Impact: In WinCC Runtime, the 'Strategy' drop-down selector on the SFC faceplate is automatically hidden or disabled, streamlining operator interaction.
SIMATIC BATCH Integration:
When Batch compiles the equipment phase from a strategy-less SFC Type, it maps the phase directly to an Equipment Phase (EPH) with no CS parameter required in the recipe editor.

Step-by-Step Implementation Procedure

Creating an SFC Type Without Control Strategies:

Create a New SFC Type in SIMATIC Manager:
- Open the Master Data Library -> right-click 'Blocks' or 'SFC' -> Insert New Object -> SFC Type.
- Assign a name (e.g., FB2010 - Filter_Flush).
Configure Characteristics:
- Open the SFC Type editor.
- In the tree view on the left, click 'Control Strategies'.
- Leave the table completely empty; do not add any strategy rows.
Configure the Default Sequencer:
- Click the 'Sequencer' tab.
- Select the default sequencer (or rename it SEQ_RUN).
- Open Sequencer Properties -> Start Condition:
- Set Start Condition to simply: RUNNING (or leave default).
Program Operational Steps and Transitions:
- Insert initialization steps, action steps (e.g., open flush valve, run pump), and completion transitions.
- If emergency handling is needed, create specialized sequencers for HOLDING or ABORTING with start conditions HOLDING and ABORTING respectively.
Instantiate in CFC and Test:
- Drag the SFC Type into a CFC chart.
- Note that strategy inputs (CS_LL, CS_LI) are inactive or omitted.
- Compile CFC and OS, then verify in WinCC faceplate.

Verification

To verify the strategy-less SFC Type:
1. Open the SFC faceplate in WinCC Runtime.
2. Observe that the 'Control Strategy' combo box is absent or grayed out.
3. Click 'Start'; verify the sequencer transitions directly into step 1 without demanding a strategy selection.
4. In SIMATIC BATCH, open the recipe editor; insert the phase and confirm that the recipe step executes without requiring strategy configuration.

Limitations and Operational Precautions

Operational precautions:
- If an equipment unit is expected to gain alternative operational procedures in future project phases, defining a single control strategy from the beginning makes adding future strategies simpler without modifying SIMATIC BATCH recipe templates.
- Ensure that auxiliary sequencers (such as Holding or Stopping) do not have conflicting start conditions that compete with the main sequence.
- Always verify that ENSTART and operating mode interlocks are wired properly in CFC regardless of whether strategies are used.

Engineer FAQ

Is it mandatory to use Control Strategies in PCS 7 SFC Types?

No. Control Strategies are entirely optional. SFC Types work perfectly for single-procedure equipment without any strategies defined.

How does SIMATIC BATCH handle an SFC Type with no Control Strategies?

SIMATIC BATCH treats the SFC Type as a single equipment phase (EPH) with no strategy selection parameter required in the recipe.

What should the sequencer Start Condition be when no strategies are used?

The Start Condition should simply be RUNNING for the main operational sequence.

Can I add Control Strategies later if the plant requirements change?

Yes, but adding strategies later changes the block interface, requiring a library update, block compilation, and potentially stopping the CPU for download if memory boundaries shift.

Does omitting Control Strategies save CPU memory?

Yes, omitting unused strategies slightly reduces DB instance data storage and simplifies faceplate runtime communications.

Technical References

Related Tags

SFC Type
Control Strategy
Batch Recipe
ISA-88 State Logic
SIMATIC BATCH

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Designing and Operating SIMATIC PCS 7 SFC Types Without Control Strategies