Displaying and Configuring Timer Setpoints in PCS 7 SFC Type Faceplates

To display and operate timer setpoints on an SFC Type faceplate in SIMATIC PCS 7, define a Setpoint characteristic (of data type TIME or REAL) within the SFC Type Characteristics editor rather than relying solely on internal step timers (T1 to T8). When a Setpoint characteristic is configured with Operator Control and Monitoring (OCM) enabled, the system automatically generates the runtime interface pins—including '_SP' for default setpoints and '_AI' for actual process time. In the SFC sequence, step actions read the setpoint value to drive phase duration, and the SFC Visualization faceplate displays the configured setpoint alongside the counting actual value in the Setpoints view.

Executive Summary

Sequential Function Chart (SFC) Types in SIMATIC PCS 7 represent reusable technological state machines for batch and continuous processes. During sequence development, engineers frequently utilize internal step timers to govern phase durations, mixing cycles, or reaction intervals. A recurring requirement is exposing these timer durations on the OS runtime faceplate so operators can view the configured setpoint and observe elapsed or remaining batch time. Because internal step timers (T_MIN, T_MAX, and T1) are step-scoped variables not automatically exposed as top-level faceplate setpoints, standard SFC instances appear to lack visible timer targets. This article details the configuration of technological setpoint characteristics, explains the runtime signal interconnects, and provides the verified workflow to display timer setpoints in SFC faceplates.

Architecture and Fundamental Mechanics

SFC Type Technological Characteristics, Parameter Generation, and OS Faceplate Integration:

Step-Scoped Timers vs. Technological Characteristics:
Inside an SFC Type step, internal timers (e.g. T_MIN, T_MAX, and step runtime T_RUN) monitor step execution locally.
These internal timer values belong to the step data block structure and are not exposed as technological setpoints in the standard SFC faceplate Setpoints tab (@pg_@sfc_type_actual.pdl / @pg_@sfc_type_overview.pdl).
To make a timer duration visible, editable, or trackable as an official recipe or operator parameter, it must be defined in the Characteristics (Merkmale) view of the SFC Type editor under the Setpoints (Sollwerte) branch.
Characteristic Definition and Autogenerated Interface Pins:
When a Setpoint named MixTimer of type TIME (or REAL with unit s) is created in the Characteristics view:
- MixTimer_SP: Setpoint input (used in Automatic mode, connected to SIMATIC BATCH or master logic).
- MixTimer_OP: Operator setpoint input (used in Manual mode from the faceplate).
- MixTimer_Q: Effective setpoint output delivered by the SFC Type arbitration logic.
- MixTimer_AI: Actual value input, reflecting the current elapsed or remaining time from the field or internal logic.
- MixTimer_AO: Actual value output, routed to external displays or archives.
The attribute OCM (Operator Control and Monitoring) must be selected to ensure OS compilation transfers the tag structures to the WinCC Tag Management database.
Linking Effective Setpoints to Step Transitions and Actions:
In the Step Actions tab, step timers can be assigned the value of MixTimer_Q.
For elapsed time display, the output of a run-time timer block (e.g. TIMER_P or internal step time T_ACT) is interconnected to MixTimer_AI. The SFC faceplate then renders both the configured setpoint and the active countdown simultaneously.

Step-by-Step Implementation Procedure

Open the SFC Type Characteristics Editor:
* In SIMATIC Manager, navigate to the Master Data Library or project S7 Program.
* Double-click the SFC Type to open the SFC Editor.
* Select menu View > Characteristics (or click the Characteristics icon on the toolbar).
Define the Timer Setpoint Characteristic:
* In the left tree, right-click Setpoints and select New > Setpoint.
* Assign a technological name (e.g. AgitTime or PhaseDuration).
* Select the Data Type: choose TIME (or REAL if using seconds with floating-point display).
* Set the High Limit and Low Limit (e.g. T#0s to T#2h).
* Set the Default Value (e.g. T#5m).
* Verify that the checkbox Operator Control and Monitoring is checked.
Configure Step Execution and Actual Value Feedback:
* Switch to the SFC topology view and double-click the step requiring timer control.
* In the Step Properties Actions tab, use the effective setpoint: assign the target parameter or internal variable using AgitTime_Q.
* In the Step Transition, evaluate whether elapsed time is greater than or equal to AgitTime_Q.
* Route the actual elapsed time back to the input pin AgitTime_AI in CFC or through internal assignment.
Compile SFC and Charts:
* In the SFC Editor, click Options > Compile to regenerate the SFC block type.
* Open the CFC chart hosting the SFC instance; select Options > Block Types, select the SFC Type, and click New Version to update instances.
* Compile CFC charts with 'Changes only'.
Compile and Download the OS:
* In SIMATIC Manager, right-click the OS project and select Compile.
* Verify that the new setpoint tags appear under the SFC instance tag group.
* Download changes to the Operator Station.

Verification

Open WinCC Runtime on the Operator Station.
Click the SFC Type block icon to open the SFC faceplate.
Navigate to the Setpoints tab (or Actual Values tab in standard APL layout).
Verify that the configured timer setpoint (e.g. AgitTime) is clearly displayed with its unit and configured target value.
Switch the SFC to Manual mode; modify the setpoint from the faceplate and verify that the SFC instance adopts the new duration.

Limitations and Operational Precautions

Internal step timers (T_MIN, T_MAX) configured directly inside the step properties dialog cannot be altered from WinCC faceplates at runtime unless mapped to technological characteristics. Data types between CFC timer blocks and SFC characteristics must match: interconnecting a REAL duration to a TIME parameter requires explicit conversion blocks (e.g. TIME_TCK or R_TO_TIME) to avoid compilation type mismatch errors.