Why PCS 7 APL VlvL Shows a Feedback Error in Simulation

A PCS 7 APL VlvL reports a feedback error when its monitored valve command is not followed by the expected open or close feedback within the configured monitoring time. In a simulation, the output command does not by itself represent the valve's returned position: the project must provide feedback through real input modules or a configured simulation chart. Trace VlvL's FbkOpen and FbkClose inputs back to their Pcs7DiIn sources and confirm the simulation is generating those states.

What the Feedback Error Means

The APL V9.0 Function Manual describes feedback monitoring for valve travel. With monitoring enabled (Monitor = 1), the block expects a feedback value within its configured monitoring period, including MonTiDynamic for dynamic feedback behavior. When the expected feedback is absent after a command, the faceplate can show “Control error” and the block can enter its configured neutral or safe position. An alarm therefore points to a mismatch between command and feedback; it does not by itself identify whether the cause is wiring, I/O configuration, simulation logic or timing.

Trace the Valve Feedback Path

In a typical PCS 7 configuration, a VlvL command is sent toward the output driver, while returned open and closed limit-switch states reach FbkOpen and FbkClose through input drivers. Siemens' PCS 7 SMART V9.0 Getting Started example uses Pcs7DiIn blocks to provide the open/closed feedback to VlvL. For each affected valve, inspect the two input interconnections, driver/channel assignments and the live values visible at the block inputs. Check polarity as well: open and closed limit switches may have different normal states.

Diagnose Several Valves at Once

When many valves show the same alarm, compare their shared configuration first: whether their input drivers are connected, whether the simulation mode is active, and whether a common simulation chart or reset logic is absent. Then inspect one valve's command and return signals in order: VlvL command, output-driver value, simulated or physical switch response, input-driver value, and the corresponding FbkOpen or FbkClose input. The same alarm on all instances can result from a common missing feedback source, but verify each channel rather than assuming identical wiring.

Method 1: Simulate Valve Feedback with CFC Logic

Use this approach only in a project whose simulation architecture supports CFC-based process-tag simulation. Siemens' PCS 7 SMART V9.0 Getting Started - Part 2 documents a SIMV chart that models valve state and returns signals to the VlvL inputs.

Check whether the project already contains a valve simulation chart and a means of selecting CFC simulation versus physical I/O. Do not duplicate existing simulation logic.
In the documented Siemens SMART example, SIMV derives a state from the valve command, produces open and closed feedback values, and exposes them as chart I/Os.
The chart I/O names in the example are FBOPEN and FBCLOSE, described as feedback values for VALVE.FbkOpen and VALVE.FbkClose.
Confirm that the relevant simulation mode is selected and that the chart outputs reach the intended valve inputs. Confirm the observed feedback follows the simulated valve state after commands.
Reset any latched monitoring error only after the cause has been corrected, using the project's designed reset mechanism.

This is a documented PCS 7 SMART V9.0 example, not a universal plug-in procedure for every PCS 7 training project. Its block layout and simulation selection must match the installed project.

Method 2: Test the Feedback Inputs with PLCSIM

If the training project uses PLCSIM rather than a CFC simulation chart, provide the feedback states through the simulator's configured digital input addresses or tags. Identify the actual open and closed input assignments from HW Config and the CFC interconnections; do not assume an address such as I64.5 applies to another project. For a test, change the simulated input state in accordance with the project's documented switch polarity and check that FbkOpen or FbkClose changes at the APL block. Never use forcing as an operational workaround on a live plant; keep simulator testing isolated from physical I/O.

Check Monitoring and Reset Settings

Read the installed APL version's documentation and inspect the valve's monitoring inputs and times, including Monitor and MonTiDynamic where those parameters apply. Confirm that the expected signal transition can occur within the configured time. Do not lengthen the timeout or disable monitoring merely to hide a missing feedback source. Siemens documents Monitor = 0 as disabling feedback monitoring and resetting static and dynamic errors; it changes the alarm behavior, not the physical valve or missing input. Use it only where the design explicitly calls for operation without the relevant feedback and the project's safety and operating requirements permit it.

Verification

Issue an open and close command in the isolated simulation or approved test setup. Observe the VlvL command, the modeled or physical switch state, the digital input driver's value and FbkOpen/FbkClose at the valve block. Confirm that each transition matches the configured polarity and that the feedback error does not return after the configured monitoring interval. If the feedback values do not reach the block, continue tracing the I/O mapping or simulation connections; a cleared faceplate alarm alone does not prove correct valve-state indication.

Limitations and Operational Precautions

The source case describes a Siemens course simulation but does not identify the exact project build, APL release or simulation topology. Siemens' cited CFC-based simulation example is specifically for PCS 7 SMART V9.0; use it as a reference pattern only if the target project's components and chart structure match. In a real installation, do not jumper, force or bypass feedback alarms to suppress them. Confirm switch polarity, fail position, interlocks and commissioning authorization before changing logic or monitoring parameters.

Engineer FAQ

Does the feedback error mean the valve hardware is defective? No. It means monitored feedback did not match the expected response in time; the cause can be in the field device, wiring, I/O mapping or simulation.

Will WinCC generate the feedback automatically when I click Open? No. The command path and the feedback path are separate signals. The project or a physical device must provide the returned state.

Which signals should I inspect on VlvL? Trace FbkOpen and FbkClose, along with the command and the Pcs7DiIn or simulation signals feeding them.

Why can every valve show the same error in a course project? A common simulation mode or shared feedback configuration may be missing, but inspect each instance and its channel mapping before concluding that is the cause.

Can I use the Siemens SIMV example in any PCS 7 project? It is documented for PCS 7 SMART V9.0. Adapt it only after checking that the project uses compatible blocks and a matching simulation structure.

Does PLCSIM automatically return a limit-switch state? The source case reports that the input must be supplied in its simulation. Check the configured PLCSIM inputs and confirm the state arrives at the block.

What does MonTiDynamic control? In the APL V9.0 function documentation, it is the period for the expected dynamic feedback response after a control signal.

Should I set Monitor to zero to clear the alarms? Not as a substitute for the missing feedback. Siemens documents this as disabling monitoring, which changes error reporting and resets monitoring errors.

How do I know whether feedback polarity is reversed? Compare the physical or modeled switch state with the documented normal state and observe the resulting value at FbkOpen and FbkClose during open and close commands.

What proves the issue is resolved? The expected feedback values reach the correct APL inputs after each command, and the monitoring error remains cleared through the configured response interval.

Technical References

Siemens, Advanced Process Library (V9.0) Function Manual, 03/2017, A5E39147331-AA, section 2.1.3.4 “Feedbacks” (feedback monitoring and MonTiDynamic). Open the Siemens manual.
Siemens, PCS 7 SMART Getting Started - Part 2 (V9.0 with APL), 12/2017, A5E42181452-AA, section 7.3 “Simulation charts and chart-in-chart technique,” especially pp. 59–65 (CFC valve-state simulation and feedback chart I/Os). Open the Siemens guide.
Siemens, PCS 7 SMART Getting Started - Part 1 (V9.0 with APL), 12/2017, A5E42181435-AA, section 6.3.6 (process roles of Pcs7DiIn, VlvL and Pcs7DiOu). Open the Siemens guide.

Why PCS 7 APL VlvL Shows a Feedback Error in Simulation