C135 PCS 7 (PCS7)
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Implementing Technological Actions and Step Execution in PCS 7 SFC Types

Implementing Technological Actions and Step Execution in PCS 7 SFC Types

In SIMATIC PCS 7 SFC Types, Technological Actions are reusable, high-level control instructions defined in the Characteristics editor that encapsulate multi-variable commands (e.g., 'Dosing_Valve.Open' or 'Agitator.Start_Fast'). When assigned to a sequencer step, standard actions execute cyclically on every CPU scan cycle while the step is active, whereas Initialization actions execute once on entry and Termination actions execute once on exit. Technological Actions abstract raw boolean assignments, allowing recipe authors to assign clear operational commands to steps while the SFC type engine manages underlying parameter routing.

Table of Contents

Executive Summary

When creating equipment phases and unit recipes in PCS 7, automation engineers choose between elementary step assignments (writing values directly to individual block inputs) and Technological Actions. Technological Actions—introduced in modern PCS 7 releases—standardize procedural code by linking step logic to predefined technological parameters. However, engineers frequently question how frequently these actions execute, whether they consume cycle time on every scan, and how to structure setpoints versus pulsed commands. This article explores the architecture, configuration, and execution timing of Technological Actions in SFC Types.

Architecture and Fundamental Mechanics

Technological Action Architecture and Execution Mechanics:

  • Concept of Technological Actions:
  • Defined in the SFC Type Characteristics view under 'Actions'.
  • An Action links one or more target block inputs (e.g., Motor.SpdExt, Valve.OpenAut) to specific predefined constants or recipe setpoint variables.
  • Reusability: An action like 'Flush_System' can be assigned to multiple steps across different sequencers without re-typing variable names.
  • Execution Timing Within Steps:
  • Initialization Tab (Init): Actions execute once during the first CPU cycle when entering the step. Best for initiating single-pulse triggers or resetting accumulators.
  • Processing Tab (Run): Actions execute cyclically every scan (e.g., every 100ms in OB35). Essential for continuous setpoint tracking, temperature ramping, and maintaining run commands against timeout monitors.
  • Termination Tab (Term): Actions execute once on the final scan cycle after the transition evaluates to TRUE, prior to advancing to the next step. Used for de-energizing actuators and clearing commands.

Step-by-Step Implementation Procedure

Step-by-Step Configuration of Technological Actions in SFC Types:

  1. Open SFC Type in SIMATIC Manager:
    - Open the Master Data Library -> open the target SFC Type in the SFC Editor.
  2. Define Technological Actions in Characteristics:
    - In the left tree view, click Actions.
    - Insert a new action row (e.g., ACT_CHARGE_ACID).
    - In the detail table, specify the technological assignment:
    • Target: Acid_Valve.OpenAut := TRUE;
    • Target: Acid_Pump.StartAut := TRUE;
  3. Assign Action to Sequencer Steps:
    - Switch to the Sequencer view tab.
    - Double-click the charging step (STEP_CHARGE).
    - Under the Processing tab, click 'Insert Action' -> select ACT_CHARGE_ACID from the dropdown.
  4. Configure Termination / Reset Action:
    - In Characteristics -> Actions, define ACT_STOP_ACID:
    • Target: Acid_Pump.StartAut := FALSE;
    • Target: Acid_Valve.OpenAut := FALSE;
    • In the step's Termination tab, assign ACT_STOP_ACID.
  5. Compile and Download:
    - Compile the SFC Type and execute an online delta download to the AS.

Verification

To verify action execution:
1. In CFC test mode, open the SFC chart instance online.
2. Trigger the sequence into STEP_CHARGE.
3. Verify that Acid_Valve.OpenAut asserts TRUE immediately upon entry.
4. Fulfill the step transition condition (e.g., target weight reached); observe that upon leaving the step, the Termination action executes and Acid_Pump.StartAut drops to FALSE.

Limitations and Operational Precautions

Operational precautions:
- Do not assign contradictory actions across overlapping parallel branches in an SFC Type, which causes alternating output flickers within the same scan cycle.
- Actions assigned in Processing execute on every scan cycle; avoid placing resource-intensive math or edge-triggered function calls in continuous processing actions.
- Ensure that emergency stop or holding sequencers explicitly contain termination or reset actions for all physical equipment energized by primary steps.

Engineer FAQ

What is the primary benefit of Technological Actions in SFC Types?

They provide standardized, reusable operational commands with clear textual descriptions, improving code readability and reducing assignment errors.

Do actions in the Processing tab execute on every cycle?

Yes, actions placed in the Processing (Run) tab execute continuously on every CPU scan cycle while the step is active.

How do I execute an action only once when a step starts?

Assign the action in the step's Initialization (Init) tab.

Can an action modify multiple block inputs simultaneously?

Yes, a single Technological Action can group multiple assignments across different technological blocks.

Where do I configure Technological Actions?

In the SFC Type Characteristics editor under the 'Actions' folder.

Technical References

Related Articles

Related Tags

  • Technological Actions
  • SFC Type
  • Step Execution
  • Characteristics
  • Sequencer Timing
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