Why an F_2oo3AI Faceplate Can Remain Abnormal After a Transmitter Recovers
A healthy transmitter or AI overview does not, by itself, prove that the F_2oo3AI safety evaluation has returned to its intended state. Check the actual channel quality, voter discrepancy state and acknowledgement requirement before treating the indication as an HMI problem. Siemens documents separate invalidity and discrepancy handling for S7 F Systems Lib V1_3 SP2; that provides a diagnostic baseline, not an unconditional HMI-only reset for an unidentified installation.
Table of Contents
- Inspect the Safety Evaluation Separately from the AI Overview
- Documented Invalidity and Discrepancy States
- Read the Actual Signal Chain
- Conditional Manufacturer Acknowledgement Procedure
- Verification
- Limitations and Operational Precautions
- Engineer FAQ
- Technical References
- Related Articles
- Related Tags
Inspect the Safety Evaluation Separately from the AI Overview
The reported application has three temperature transmitters in a 2oo3 evaluation. One signal had bad status and held its last value. After the signal was repaired, the AI overview appeared normal while the F_2oo3AI faceplate still showed that channel as bad.
That observation does not establish a stale HMI graphic. Identify the installed F-library version and compare the actual safety-channel and voter states before attempting an operator reset.
Documented Invalidity and Discrepancy States
For S7 F Systems Lib V1_3 SP2, the 2016 manufacturer manual distinguishes input invalidity through QBAD1–QBAD3 from discrepancy states such as DIS1CH and DISALL. ACK_REQ indicates a required acknowledgement.
The manual requires the QBAD input associated with each F_2oo3AI input to follow the QBAD of the corresponding F_CH_AI supplying its value. A normal display at another object does not prove that this specific quality path has recovered.
Read the Actual Signal Chain
Use this engineering diagnostic sequence with the safety-system owner:
- Confirm the installed library, block version and channel-to-voter mapping.
- Inspect the recovered transmitter's F_CH_AI value and QBAD state.
- Trace those signals to the corresponding F_2oo3AI INx and QBADx.
- Inspect DIS1CH, DISALL and ACK_REQ, together with configured tolerance and timing parameters.
- Compare the exact faceplate's connected instance and status indication with the observed block state.
This separates a continuing channel fault, a saved discrepancy condition and a possible visualization mismatch. None is diagnosed merely from the AI overview.
Conditional Manufacturer Acknowledgement Procedure
For the documented library, if the process inputs are again within the assigned tolerance, discrepancy acknowledgement depends on ACK_NEC. With ACK_NEC = 1, the manual requires a positive edge at ACK; ACK_REQ = 1 indicates that acknowledgement is required.
Apply that behavior only through the installation's existing validated operator acknowledgement route, after the responsible engineer confirms recovery and version applicability. This does not establish which HMI button is connected to ACK, nor equate alarm acknowledgement with the block's discrepancy acknowledgement.
Do not force ACK, alter ACK_NEC or relax DELTA/DIS_TIME to make the faceplate appear healthy.
Verification
Confirm recovery at the channel driver, corresponding voter inputs and relevant voter state. Then verify the faceplate against the same instance. If a documented acknowledgement was required, record the request state before and after the approved action.
Acceptance must preserve the intended voting and safety response. A changed icon or cleared alarm alone does not demonstrate that the safety evaluation is correct.
Limitations and Operational Precautions
The affected F-library version, block state and faceplate connection are unavailable. An HMI-only repair is therefore not established, and the root cause remains unresolved.
The cited procedure applies to the stated V1_3 SP2 documentation. Earlier or later library behavior must be checked separately. Do not change MODE, safety parameters or voting configuration during this display investigation. Any safety-program change requires the installation's safety change and acceptance process.
Engineer FAQ
Does a normal AI overview prove the voter input is valid?
No. Inspect the actual F-channel and QBAD path.
Is alarm acknowledgement necessarily the voter ACK signal?
No. Verify the configured operator route.
Should discrepancy limits be widened to clear the indication?
That is not a justified diagnostic remedy.
Technical References
- Siemens: S7 F/FH Systems — Configuring and Programming, June 2016, A5E37822367-AA — Appendix A.2.4.2, pages 267–271, F_2oo3AI in S7 F Systems Lib V1_3 SP2: invalidity, discrepancy acknowledgement and F_CH_AI quality interconnection.