Architectural Differences Between SIMATIC PCS 7 SFC and TIA Portal S7-GRAPH

While both SIMATIC PCS 7 SFC (Sequential Function Chart) and TIA Portal S7-GRAPH execute sequential state logic based on steps and transitions according to IEC 61131-3, they serve fundamentally different automation paradigms. S7-GRAPH generates standalone function blocks (FBs) for machine-level discrete manufacturing in STEP 7 and TIA Portal. In contrast, PCS 7 SFC is deeply integrated with Continuous Function Charts (CFC) and the Plant Hierarchy, supports reusable SFC Types controlling technological blocks, generates native WinCC faceplates automatically, and integrates natively with SIMATIC BATCH for ISA-88 recipe execution.

Executive Summary

Sequential state control is a cornerstone of modern industrial automation, orchestrating complex machinery through distinct operational phases, permissive checks, and timed state transitions. Automation engineers transitioning between machine-level automation (SIMATIC S7-1500 / S7-300 in TIA Portal) and process plant control (SIMATIC S7-400 / CPU 410-5H in PCS 7) frequently evaluate the technological differences between S7-GRAPH and SIMATIC PCS 7 SFC. While both languages draw visual inspiration from Grafcet and IEC 61131-3 sequential function charts, their underlying operating system integration, memory models, operator visualization, and recipe batch capabilities diverge significantly. This technical guide outlines the architectural differences and practical engineering boundaries between the two tools.

Sequential Control Paradigms: Continuous Process vs Discrete Machine Logic

The two engineering systems address distinct industry domains:

Discrete Machine Automation (S7-GRAPH): Tailored for high-speed assembly lines, packaging machines, pick-and-place robots, and mechanical presses. Sequences execute cyclically in OB1 or fast cyclic interrupts, focusing on interlocking mechanical cylinders, pneumatic slides, and servo axes.
Process Industry Operations (PCS 7 SFC): Tailored for batch chemical reactors, CIP (clean-in-place) skids, brewing phases, and furnace temperature profiles. Sequences govern fluid transfer, thermal ramp-soak profiles, and recipe execution according to ISA-88 / IEC 61512 standards.

S7-GRAPH Architecture in TIA Portal and Classic STEP 7

In TIA Portal and STEP 7, S7-GRAPH compiles into a standard S7 block container:

Generates a standard Function Block (FB) with an associated Instance Data Block (DB).
Internal execution relies on a dedicated S7-GRAPH runtime sequencer engine loaded into controller memory.
HMI integration requires manual graphic configuration or deploying pre-packaged ProDiag / Graph overview controls in WinCC Comfort/Advanced.

SIMATIC PCS 7 SFC Architecture: SFC Charts and SFC Types

In SIMATIC PCS 7, SFC is deeply woven into the technological DCS framework:

CFC Interaction: Steps and transitions interact directly with Continuous Function Chart (CFC) blocks. An engineer can drag block outputs directly into transition logic and block inputs into step actions.
SFC Types & Instances: Reusable technological types defined in the Master Data Library (MDL). Instantiating an SFC Type creates a technological block (e.g. Dosing_Phase) with automatic AS-OS message generation.
SIMATIC BATCH Native Integration: SFC Types act as Equipment Phases (EPH) that interface directly with SIMATIC BATCH recipe servers for automated recipe execution.
Standardized Operating States: Implements standardized state machines (Ready, Starting, Running, Holding, Held, Pausing, Aborting, Completed) compliant with NAMUR NE33.

SFC vs S7-GRAPH Architectural Comparison Matrix

The following table compares architectural and operational features between PCS 7 SFC and TIA Portal S7-GRAPH:

Engineering FeatureSIMATIC PCS 7 SFCTIA Portal S7-GRAPHOperational DifferenceTarget ControllersS7-400 / CPU 410-5HS7-1500, S7-300, S7-400PCS 7 is optimized for high-end DCS processors.CFC IntegrationDirect Graphical InterconnectionStandalone Block CallsSFC steps read/write CFC block pins natively.Type / Instance ConceptSupported (SFC Type in MDL)Limited to FB multi-instancesSFC Types support bulk engineering and IEA.ISA-88 Batch InterfaceNative SIMATIC BATCH CouplingManual Interface LogicSFC Types expose batch recipe control pins.WinCC Faceplate GenerationFully Automated (@PG_SFC.pdl)ProDiag / Custom FaceplatesZero manual HMI drawing in PCS 7.State Machine StandardNAMUR NE33 / ISA-88 Built-inUser-Defined LogicPCS 7 enforces standardized process states.Alarm System IntegrationAutomated via ALARM_8PProDiag / Program AlarmsChronological alarm generation with timestamps.

Step-by-Step Procedure to Implement Reusable State Sequences in PCS 7

Method: Authoring an SFC Type in Master Data Library

In SIMATIC Manager, open the Master Data Library (MDL).
In the Charts folder, select Insert > SFC Type.
Double-click the SFC Type to launch the SFC Editor.
In the characteristics editor, define phase parameters, setpoints, and control strategies (e.g. Heating_Rate, Target_Temp).
Design the sequential topology: insert steps (e.g. START, RAMP_UP, SOAK, COOL, COMPLETE) and transitions.
In step actions, assign technological commands to block inputs (e.g. TC_01.SP_Ext = Target_Temp).
In transitions, assign boolean conditions (e.g. TC_01.PV_Out >= Target_Temp).
Save and compile the SFC Type. SIMATIC Manager generates the technological FB and symbol.
Instantiate the SFC Type into project CFC charts across identical plant units (e.g. 10 identical fermenters).
Compile the OS project (Options > OS > Compile); WinCC automatically generates @SFC_Type.pdl block icons and faceplates.

Verification

To verify sequential control functionality in PCS 7:

Compilation Check: In the SFC Editor, select SFC > Compile. Confirm that compilation completes with 0 errors.
Online Monitoring: Download the program to S7-PLCSIM or physical AS. Open the SFC chart in Test Mode; confirm active step highlighting in green.
WinCC Faceplate Operation: In WinCC Runtime, click the SFC block icon. In the generated faceplate, test mode transitions (Manual, Auto), start sequence execution, and confirm step timer progression.

Limitations and Operational Precautions

Memory Consumption: SFC Types consume substantial S7-400 work memory; avoid creating monolithic sequences containing hundreds of steps; decompose complex processes into modular unit phases.
Do Not Mix Methodologies: Avoid implementing S7-GRAPH blocks inside a PCS 7 project; S7-GRAPH bypasses the PCS 7 OS Project Editor and cannot communicate with SIMATIC BATCH.
Licensing Requirements: Engineering and monitoring SFCs in PCS 7 requires active SFC Engineering and SFC Visualization licenses in Automation License Manager.

Engineer FAQ

Can S7-GRAPH be installed on a PCS 7 Engineering Station?

While the STEP 7 optional package S7-GRAPH can be installed, it is not supported for PCS 7 process control operations.

Can an SFC chart be modified online while the sequence is executing?

Yes, PCS 7 supports online step and transition modifications; however, extensive structural changes require an SFC download in STOP.

How does SIMATIC BATCH communicate with an SFC Type?

SIMATIC BATCH commands the SFC Type using standardized status words (BA_STATE, BA_CONTROL) transferred cyclically over S7 connections.

Technical References

Related Tags

https://industrialautomation.net/search?query=simatic-pcs7
https://industrialautomation.net/search?query=sfc-editor
https://industrialautomation.net/search?query=s7-graph
https://industrialautomation.net/search?query=tia-portal

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Architectural Differences Between SIMATIC PCS 7 SFC and TIA Portal S7-GRAPH