How to Enable the Faceplate Reset Button and Clear Undefined States on APL Valve Blocks in PCS 7

In SIMATIC PCS 7 APL valve and motor blocks (such as VlvMotL and MotL), the faceplate 'Reset' button is enabled only when Feature.Bit31 (Activating reset of protection / error in manual mode) is set to 1, a latched error exists (RdyToReset = 1), and the initiating physical fault condition has been resolved. If a motor-driven valve becomes mechanically jammed in mid-travel, it enters an 'Undefined' state where both operational and maintenance commands are safety-locked. To restore operation from SCADA, operators cannot simply press Reset while the fault persists; engineers must either clear the mechanical jamming or temporarily force the limit switch feedback inputs to Open or Closed to exit the undefined state.

APL Fault Latching and Reset Mechanism

The SIMATIC PCS 7 Advanced Process Library (APL) implements strict deterministic safety and reset state machines for drive blocks (including VlvMotL, MotL, VlvL, and MotRevL).

When an actuator encounters an abnormal operational condition—such as a runtime monitoring error (MonDynErr), static limit feedback error (MonStaErr), thermal overload trip (Trip), or interlocking protection trip (Protect)—the block transitions to a faulted state and de-energizes control outputs to protect equipment.

The Role of `RdyToReset`

The APL faceplate does not present an unconstrained reset button. The button in the Standard View of the faceplate is dynamically governed by the internal block output parameter:
* RdyToReset (Ready to Reset):
The Reset push button on the WinCC faceplate is only active and clickable when RdyToReset = 1. If RdyToReset = 0, the button is greyed out and disabled.

Root Cause Analysis for Disabled Faceplate Reset Button

Engineers often attempt to modify block icon scripts or faceplate properties when the Reset button remains disabled. However, the button status is governed strictly by the following boolean conditions inside the AS block algorithm:

Condition 1: Feature Bit Configuration

Feature.Bit31: 'Activating reset of protection / error in manual mode'. If Feature.Bit31 = 0, faults automatically clear as soon as the initiating condition disappears; the block does not require or support manual faceplate reset. If Feature.Bit31 = 1, the block latches the fault and requires manual operator acknowledgment via the Reset button.

Condition 2: Elimination of the Initiating Cause

RdyToReset will never become 1 while the root cause of the error is still actively asserted!
* If a thermal overload (Trip = 0) is still tripped, Reset is disabled.
* If a protection interlock (Protect = 0) is active, Reset is disabled.
* If a motor-driven valve is stuck in mid-travel and the dynamic transit monitoring timer expired, the block detects that neither the Open limit switch (FbkOpen) nor the Closed limit switch (FbkClose) is reached. The block considers the feedback fault continuously active.

Handling Valves Stuck in Mid-Travel Undefined State

When a motor-driven valve (VlvMotL) is stuck between open and closed positions due to mechanical resistance or torque limiter tripping:
1. The Undefined State (Pos = 3): The block evaluates the position as 'Undefined' because both FbkOpen and FbkClose are false while movement has stopped.
2. Safety Lockout: In the Undefined state, the block locks both Open and Close commands, and even Service/Maintenance mode is inhibited to prevent driving a jammed mechanical assembly into destruction.
3. Reset Inability: Because neither limit switch is made, the monitoring fault cannot clear, keeping RdyToReset = 0.

Supported Engineering Workarounds from SCADA

To recover the valve remotely without local manual handwheel intervention:
* Temporary Feedback Simulation: In CFC, the block provides simulation inputs (SimOn, SimLiOp, SimFbkOpen, SimFbkClose). By enabling simulation from an authorized engineering view, the engineer can temporarily force SimFbkClose := 1 or SimFbkOpen := 1. This satisfies the feedback check, asserts RdyToReset := 1, enables the Reset button, and clears the undefined state. Once reset, the engineer disables simulation and issues a reverse travel command to unseat the valve.
* External Reset Signal: If Feature.Bit19 (Reset via input RstLi) is configured, a pulse can be applied via logic or automated recovery sequences.

APL Reset Feature Bits and Behavior Matrix

The following table outlines the configuration parameters governing reset behavior in APL drive blocks:

Parameter / Feature BitSettingOperational Behavior on FaultFaceplate Reset Button StateFeature.Bit310 (Default)Fault auto-clears when physical cause clearsPermanently Disabled (Not required)Feature.Bit311Fault latches; requires manual operator resetEnabled when cause clears (RdyToReset = 1)Feature.Bit191Enables reset via interconnected input RstLiOperates concurrently with faceplate resetFeature.Bit31First-in, first-out fault handling enabledGoverns multi-fault priority evaluationFault Cause ActiveAnyFault continuously asserted in fieldDisabled (RdyToReset = 0)Fault Cause ClearedFeature.Bit31 = 1Physical signal healthy, fault latchedEnabled (RdyToReset = 1)

Feature bits must be set offline in CFC or online via the block parameter view.

Verification

To verify proper operation of the faceplate Reset button:
1. Open the CFC chart containing VlvMotL and verify that Feature.Bit31 = 1.
2. In WinCC Runtime, open the faceplate for the valve.
3. Simulate or trigger a fault (e.g., trip an interlock or exceed monitoring time).
4. Verify that the valve indicates a fault and trips to its safe position.
5. Clear the simulated initiating fault condition (restore interlock to healthy).
6. Observe the faceplate: the Reset push button should immediately transition from greyed-out (disabled) to active (enabled).
7. Click Reset; verify that the fault clears and the valve becomes operable in Manual and Automatic modes.

Limitations and Operational Precautions

Never bypass mechanical torque trips or force limit switches remotely without confirming field safety; forcing a jammed valve can burn out the actuator motor or shear valve stems.
Modifying Feature bits in CFC requires compiling and downloading the AS program.
Do not attempt to modify WinCC @PG_VlvMotL_Standard.pdl faceplate scripts to bypass RdyToReset; faceplate scripting mirrors AS state and forcing the button in WinCC will be rejected by AS block security.
If a valve repeatedly jams in mid-travel, adjust MonTiDynamic (dynamic transit monitoring time) to accommodate slower stroke speeds before concluding that a fault exists.

Engineer FAQ

Why is the Reset button disabled even though Feature.Bit31 is set to 1?

Because the initiating fault signal is still actively asserted in the controller (e.g. limit switch feedback missing, interlock open, or thermal overload tripped). RdyToReset only becomes 1 after the root cause clears.

Can an operator reset a fault when the block is in Automatic mode?

By default, faceplate manual reset is only permitted in Manual mode. To allow reset in Automatic mode, configure Feature.Bit30 or interconnect the RstLi input to automation logic.

What does `Pos = 3` mean on `VlvMotL`?

Pos = 3 represents the 'Undefined' position, occurring when the actuator is between end positions and neither the Open nor Closed limit switch is made while movement has stopped.

Technical References

Related Tags

APL_VlvMotL
Feature_Bit31
Faceplate_Reset
RdyToReset
Motor_Valve

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How to Enable the Faceplate Reset Button and Clear Undefined States on APL Valve Blocks in PCS 7