How to Configure Hold-to-Run (WhilePressing) Control for APL Valve Blocks in PCS 7

In SIMATIC PCS 7 APL, standard faceplates do not natively support physical 'WhilePressing' (hold-to-run / jogging) operations due to two-step operator confirmation safeguards and Terminal Bus network latency risks. However, hold-to-run behavior can be achieved by utilizing APL Feature.Bit3 (Enabling resetting of commands for the control settings) or Feature.Bit4 (Switch mode vs Button mode), combined with custom WinCC graphic buttons utilizing 'Press Left' (set bit) and 'Release Left' (reset bit) events. Paired with controller-side off-delay timers (such as TIMER_P) to prevent runaway commands during communication dropouts, this delivers safe hold-to-run operation.

Standard APL Operator Control Philosophy vs Hold-to-Run

In industrial process automation, standard operating procedures enforce deterministic, latching commands: an operator clicks 'Open', the controller initiates travel, and internal monitoring timers supervise the stroke until limit switches confirm completion. Standard APL faceplates for valves (VlvL, Vlv2WayL) incorporate two-step operator control (Select -> Execute) to eliminate accidental commands.

However, specific mechanical operations—such as manual jogging of diverter valves, gate alignment, or valve unseating—require Hold-to-Run ('WhilePressing') behavior:
* While the operator holds down the mouse button or touchscreen button, the valve moves toward the selected position.
* As soon as the button is released, the command immediately drops to zero, halting movement.

Attempting to implement this directly on standard faceplate buttons without architectural safeguards introduces severe safety risks: if the network drops while the button is held, the controller might never receive the 'Release' event.

Feature Bits Governing Control Command Resetting (Bits 3 and 4)

The Advanced Process Library provides specific Feature bits designed to manage automatic command clearing in Vlv2WayL, VlvL, and MotL:

`Feature.Bit3`: Enabling Resetting of Commands for the Control Settings

When Feature.Bit3 = 1: The block algorithm automatically resets the control settings (Pos0Man, Pos1Man, Pos2Man) back to 0 when an interconnected reset condition occurs, or after executing a step.

`Feature.Bit4`: Button Mode (0) vs Switch Mode (1)

When Feature.Bit4 = 0 (Button Mode): Separate commands are required to open and close. A command pulse sets the state, which remains latched until an opposing command or trip occurs.
When Feature.Bit4 = 1 (Switch Mode): The block operates like a maintained electrical switch. For example, setting Pos1Man = 1 commands the valve to Position 1; setting Pos1Man = 0 immediately de-energizes the command, allowing the valve to return to its default failsafe position (Pos0).

Step-by-Step Implementation of Hold-to-Run Commands

To implement safe, reliable hold-to-run functionality without compromising standard faceplates:

Step 1: Configure Feature Bits in CFC

In CFC Editor, open the chart containing Vlv2WayL (or VlvL).
Open the block properties for parameter Feature:
* Set Feature.Bit3 = 1 (Enables command resetting).
* Set Feature.Bit4 = 1 (Enables Switch mode if default return is desired).

Step 2: Configure Safety Dead-Man Timer in CFC

To prevent a runaway valve if an operator client loses network connection while holding the mouse button:
1. Instantiate a TIMER_P block in the CFC chart.
2. Connect the HMI command bit to the timer input.
3. Set the timer to Pulse Mode with a maximum hold limit (e.g., TI := T#5s).
4. Connect the timer output to the manual command input (Pos1Man) of the valve block. If the release event is lost over the network, the timer guarantees command cutoff after 5 seconds.

Step 3: Configure WinCC Graphics Button Events

In Graphics Designer, place a standard Button object on the process picture.
In the Button Object Properties -> Events -> Mouse:
* Press Left: Attach a Direct Connection or C-Script:
c SetTagBit("Plant/Area/Chart/Vlv2WayL.Pos1Man", 1);
* Release Left: Attach a Direct Connection or C-Script:
c SetTagBit("Plant/Area/Chart/Vlv2WayL.Pos1Man", 0);
Ensure the button properties disable focus retention and context menu popups.

Control Mode and Feature Bit Configuration Matrix

The following table outlines the operational differences between standard latching control and hold-to-run configurations in APL valve blocks:

Control PhilosophyFeature.Bit3Feature.Bit4WinCC Event TriggerOperational BehaviorStandard APL Latching00Standard Faceplate ClickCommand latches until opposite command or limit reachedSwitch Mode (Maintained)01Faceplate Switch ToggleActive while tag = 1; auto-resets when tag = 0Hold-to-Run (Jogging)11Press Left / Release LeftActive ONLY while pressed; drops to 0 on releaseAuto-Reset Pulse10Single Faceplate ClickIssues single-cycle pulse and auto-clears command

Employing a controller-side dead-man watchdog timer is mandatory for all hold-to-run implementations.

Verification

To verify hold-to-run operation:
1. In WinCC Runtime, navigate to the test picture with the configured hold-to-run button.
2. Click and hold the mouse button down on the 'Jog Position 1' button.
3. Observe in CFC Editor Test Mode: verify that Pos1Man transitions to 1 and the valve actuator output energizes.
4. Release the mouse button: verify that Pos1Man immediately transitions to 0 and actuator motion ceases.
5. Click and hold continuously for >5 seconds; verify that the controller watchdog timer de-energizes the output to prove fail-safe protection.

Limitations and Operational Precautions

Never implement hold-to-run operations over high-latency remote connections (e.g., Web Navigator over cellular or satellite links), as packet delays can cause significant movement overshoots.
Standard APL faceplates (@PG_Vlv2WayL_Standard.pdl) should not be globally modified to replace standard two-step control, as this violates plant safety standards across unmonitored valves.
Always ensure hardwired emergency stop circuits and physical travel limit switches remain fully active independent of software jogging commands.
Ensure monitoring times (MonTiDynamic) are adjusted so intermittent jogging does not trigger nuisance transit time alarms.

Engineer FAQ

Can I use 'WhilePressing' on standard APL faceplate buttons?

Standard faceplate buttons use complex C-scripts with operator authorization dialogs that do not support raw mouse-down/mouse-up events. Hold-to-run is best implemented via dedicated process picture buttons.

What does `Feature.Bit4` do on valve blocks?

Feature.Bit4 toggles between Button mode (0) and Switch mode (1). In Switch mode, setting the open command to 0 automatically closes the valve without requiring an explicit close command.

Why is a dead-man timer necessary for hold-to-run commands?

If an operator holds down a button and the client PC crashes, freezes, or loses network connection, the 'Release' event is never sent. A controller timer ensures the command auto-resets.

Technical References

Related Tags

Vlv2WayL
Hold_To_Run
Feature_Bit4
WhilePressing
WinCC_Buttons

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How to Configure Hold-to-Run (WhilePressing) Control for APL Valve Blocks in PCS 7