Reintegrate PCS 7 F-I/O Safely When ACK_NEC Does Not Reintegrate a Module

Do not automatically pulse ACK_REI from PASS_OUT and ACK_REQ to force reintegration. In PCS 7 V9.1, ACK_NEC = 0 permits automatic reintegration for applicable corrected channel faults only when the process permits it; module and communication faults can still require user acknowledgment. Siemens Process Safety guidance states that ACK_REI must not be driven by an automatically generated signal for acknowledgment-required reintegration. Use the approved fail-safe user-acknowledgment path for the installed S7 F Systems and WinCC OA configuration.

What ACK_NEC and ACK_REQ control

For PCS 7 V9.1 F-channel drivers, ACK_NEC determines whether a corrected channel fault can reintegrate automatically: 0 permits automatic reintegration only when that behavior is acceptable from the safety perspective; 1 requires user acknowledgment. ACK_REQ indicates that a fault has cleared and acknowledgment is possible. A module error or communication error is not equivalent to an ordinary corrected channel fault: PCS 7 Process Safety documentation requires user acknowledgment for module errors even when ACK_NEC is not set, and states that ACK_REI must not be driven by an automatically generated signal.

Therefore, a standard-program condition such as “if PASS_OUT and ACK_REQ, then pulse ACK_REI” must not be used to force automatic reintegration. ACK_REQ is an acknowledgment request, not an authorization to reintegrate without operator action.

Use the documented reintegration path

Identify whether the event is a channel fault, module fault, or communication fault from the F-channel driver diagnostics and the ET 200SP HA / FDI / FDO diagnostics. Confirm that the underlying fault is cleared before attempting reintegration.
Check the driver configuration and the module's configured passivation and reintegration behavior. Set ACK_NEC = 0 only if the safety analysis establishes that automatic reintegration after the applicable channel fault is safe and the exact module/library behavior supports it.
For module errors or communication faults that require acknowledgment, implement a documented user-acknowledgment method. PCS 7 Process Safety documentation describes using the fail-safe F_QUITES block for operator-station acknowledgment and connecting its OUT signal to the relevant F-channel driver ACK_REI inputs; the detailed procedure and compatible acknowledgment interface must match the installed S7 F Systems/PCS 7 release.
If using a physical acknowledgment device, use a fail-safe input and a safety-program design assessed for the required safety function. The manual warns that a fault in the F-I/O group hosting an acknowledgment key can prevent reintegration through that key, so an approved alternative acknowledgment path may be necessary.
Verify the failure class, cleared diagnostic, operator acknowledgment, and restoration of valid process values before returning the affected function to service. Do not infer safety from PASS_OUT or ACK_REQ alone.

Why the proposed PASS_OUT / ACK_REQ logic is not an automatic-acknowledgment solution

PASS_OUT reports passivation state and ACK_REQ signals that acknowledgment is possible or requested, depending on the diagnosed fault and driver behavior. Combining these statuses in standard logic and automatically pulsing ACK_REI would bypass the manual acknowledgment required for module errors and communication failures. PCS 7 V9.1 documentation explicitly states that an automatically generated ACK_REI signal is not permitted for the relevant reintegration cases.

The question also describes a process where 0 is not the safety state and 1 is required for safety. That requirement needs to be included in the hazard and safety-function analysis, including what the field output does while passivated and what happens when values are restored. The forum post does not provide enough information to assess the safety of that behavior or the proposed logic.

WinCC OA considerations

The installation uses WinCC OA rather than WinCC V7.x. The PCS 7 documentation cited for F_QUITES describes an operator-station acknowledgment route in the PCS 7/S7 F Systems environment; it does not establish that the particular WinCC OA setup is configured or approved to perform that acknowledgment. Confirm the supported safety-related write/acknowledgment interface for the installed WinCC OA and S7 F Systems versions. Do not substitute an ordinary SCADA Boolean or an automatically generated command for the documented fail-safe acknowledgment mechanism.

Verification

Review the safety program and F-channel diagnostics for each relevant failure mode. In an approved test environment, confirm that a corrected channel fault follows the configured ACK_NEC behavior, that module and communication faults still require the documented user acknowledgment, and that no standard-program condition generates ACK_REI automatically. Verify that passivated and restored outputs match the safety function's specified safe state and that the interlock/permissive sequence prevents unintended actuation during reintegration. A successful acknowledgment alone does not validate the safety design.

Limitations and Operational Precautions

This is a fail-safe control-system design question. The source includes no safety requirements specification, risk assessment, SIL/PL target, F-channel block types and versions, F-parameter settings, exact diagnostic, WinCC OA integration method, or attached logic diagram. Accordingly, this article cannot approve the proposed circuit or determine whether automatic reintegration is safe for the process.

Do not change ACK_NEC, ACK_REI, PASS_ON, or safety output behavior on a live process from this discussion. Any change affects safety-program behavior and requires the site's functional-safety lifecycle, responsible safety engineer approval, change control, safety signature management, and validation appropriate to the system and jurisdiction.

Engineer FAQ

Does ACK_NEC = 0 always reintegrate an F-I/O module automatically? No. It permits automatic reintegration only for applicable corrected channel faults when allowed by the safety process. Module and communication errors can still require user acknowledgment.

What does ACK_REQ mean? It indicates an acknowledgment request or that acknowledgment is possible after the fault clears; it is not permission to generate ACK_REI automatically.

Can ACK_REI be pulsed automatically when ACK_REQ and PASS_OUT are true? PCS 7 V9.1 Process Safety guidance prohibits connecting ACK_REI to an automatically generated signal for the documented acknowledgment-required reintegration cases.

What is F_QUITES used for? It is a fail-safe block documented for implementing operator-station user acknowledgment in PCS 7/S7 F Systems. Use the procedure and interface appropriate to the installed release.

Can WinCC OA directly perform this acknowledgment? The source does not establish that. Verify the approved integration path for the specific WinCC OA and S7 F Systems versions; do not assume the WinCC-specific example transfers unchanged.

Technical References

Siemens, PCS 7 Compendium Part B – Process Safety (V9.1), Operating Manual, 10/2022, section 7.7.4–7.7.5. It distinguishes automatic reintegration on corrected channel errors from acknowledgment-required module errors and states that ACK_REI must not be driven by an automatically generated signal: PDF.
Siemens, S7 F/FH Systems – Configuring and Programming, section 5.10, “Implementation of user acknowledgment.” It describes the F_QUITES operator acknowledgment block and the acknowledgment path: PDF.
Siemens, PCS 7 Compendium Part B – Process Safety (V9.0), Operating Manual, 04/2018, section 7.7. It describes F_QUITES and warns against automatic user acknowledgment: PDF.

Reintegrate PCS 7 F-I/O Safely When ACK_NEC Does Not Reintegrate a Module