Fix Missing VlvL Feedback in a PCS 7 Training Simulation

A VlvL feedback error in a PCS 7 training simulation can occur because the simulated valve has no source for its open and closed position inputs. A command from WinCC does not establish that the corresponding input feedback has been supplied. Trace the Pcs7DiIn connections and provide the intended simulator or model response. For an isolated block-only test, APL V9.0 also documents internal simulation through SimLiOp and SimOn, but that mode does not validate the input-channel path or normal feedback monitoring.

Follow the Command and Feedback Paths

In a real installation, the AS command reaches the valve through an output channel, while independent position contacts return through input channels such as Pcs7DiIn. A symbolic input address identifies where the program reads feedback; it does not generate the valve's physical response.

For APL V9.0 VlvL, the relevant feedbacks are FbkOpen and FbkClose. Inspect their actual value and quality, along with the current command and monitoring settings. Do not confuse the valve's command output with proof of its position. The correct electrical polarity and any inversion must come from the engineered channel path, not from a generic instruction to set the closed feedback to zero.

Distinguish Dynamic and Static Feedback Errors

Siemens documents MonTiDynamic for feedback monitoring after a control change and MonTiStatic for monitoring compliance with position. The corresponding VlvL outputs distinguish MonDynErr, feedback error due to a control change, from MonStaErr, feedback error due to an unexpected feedback change.

In the training case, the final explanation was that the simulator needed an explicit feedback source; the valve's simulated position did not arrive automatically at the mapped input. Inspect the actual error type before increasing a monitoring time or suppressing an alarm. APL manual, pp. 1338 and 1350

Method 1 — Supply the Input Through the Simulation Model

Use this project-specific approach when the purpose is to test the channel and feedback path.

Trace the actual open and closed feedback connections from the VlvL inputs through Pcs7DiIn to their configured input addresses.
Identify what supplies those addresses in the test: manually controlled simulator inputs or a connected process model.
Begin with a coherent initial position, then issue an approved open or close command.
Provide the corresponding end-position response through the selected simulation input path within the reviewed monitoring time.
Observe the input channel, VlvL feedback and alarm state, including the opposite end-position behavior.

The exact simulator editing dialog depends on the installed simulator release and is not invented here. A SIMIT model is one possible external source, not an established requirement of every training exercise. Determine which simulation package the exercise actually supplies.

Method 2 — Use Documented Block-Internal Simulation

For an isolated APL V9.0 VlvL functional test, Siemens documents internal signal simulation:

Preserve the existing settings and confirm that the test is isolated from real outputs.
Inspect SimLiOp. With SimLiOp = 0, the faceplate's parameter view controls SimOn.
Activate SimOn through the authorized faceplate.
Exercise the intended open/close behavior and observe the simulation indication and block feedback.
End simulation after testing and verify the return to the intended operating configuration.

With SimLiOp = 1, simulation is instead controlled through SimOnLi. Internal simulation is not equivalent to providing real input-channel feedback: Siemens describes corrected feedback without normal monitoring being active. Use Method 1 when validating the feedback channel or missing-feedback detection. APL manual, pp. 58–59, 1339 and 1348

Verification

For the external-input method, observe the actual mapped input, Pcs7DiIn output and VlvL feedback in sequence. Test open and closed positions, then deliberately withhold a feedback in the isolated test to confirm that the configured monitoring still detects the intended fault.

For internal simulation, verify that simulation is indicated and that it is disabled afterward. A disappearing alarm in this mode does not prove that the physical or simulated input path is correct.

Limitations and Operational Precautions

The verified block behavior is APL V9.0. The exact installed simulator, exercise configuration and wiring polarity were not established.

Do not connect command outputs directly to feedback inputs or disable Monitor as a production repair. Such shortcuts remove independent position evidence. Do not apply a generic voltage to a field input without the actual module's electrical requirements. Retain monitoring values and test overrides in the rollback record, and remove all simulation states before returning equipment to service.

Engineer FAQ

Does WinCC create valve feedback when I press Open?
No automatic feedback source is established by that operator action. The test must provide external feedback or deliberately use the documented internal simulation mode.

Does internal simulation verify the Pcs7DiIn path?
No. It tests a narrower block behavior and must not be accepted as an I/O-channel test.

Technical References

Siemens — Advanced Process Library V9.0 Function Manual, March 2017, A5E39147331-AA — signal simulation, pp. 58–59; VlvL monitoring and simulation, pp. 1338–1339; simulation inputs, p. 1348; diagnostic outputs, p. 1350.

PCS 7 valve simulation

Fix Missing VlvL Feedback in a PCS 7 Training Simulation