How to Show the MonAnL Alarm Limit in a PCS 7 Message

For the ticket's PCS 7 V8.1 SP1 project with APL V8.1, MonAnL message instance MsgEvId1 maps associated value 4 to input ExtVa104; it does not map PV_AH_Lim directly to that value. Supply the same high-limit signal to both PV_AH_Lim and ExtVa104, then format value 4 in the message text as @4R%.0f@ for a REAL shown with zero fractional digits. Validate the exact display in the project's target runtime.

How MonAnL message associated values are mapped

For PCS 7 APL V8.1, the MonAnL manual lists the message-associated values for MsgEvId1: associated values 4 through 8 map to ExtVa104 through ExtVa108. For MsgEvId2, associated values 4 through 8 map to ExtVa204 through ExtVa208. These are the user-available message values; the token @4...@ refers to associated value 4, so for the first message instance it reads ExtVa104.

PV_AH_Lim is not itself listed as the associated value 4 input. The same manual lists PV_AH_Out as the output for the high alarm limit and says the output parameters mirror their corresponding limit inputs. This gives the chart an output carrying the configured high limit, but it does not document a direct self-connection from that output back to another input on the same MonAnL instance.

Route the high limit to associated value 4

A CFC block input cannot be wired directly to another input. Make the alarm limit available from a common source output, then connect that output to both destinations:

Identify the signal or project parameter that supplies the high alarm limit. If the value currently exists only as a constant assigned to PV_AH_Lim, use the project's established way of exposing that value as a CFC output; do not create a second independently maintained limit.
Connect the common source output to MonAnL.PV_AH_Lim and to MonAnL.ExtVa104 for MsgEvId1.
In the MsgEvId1 high-alarm message text, use associated value 4 with a REAL format, for example @4R%.0f@ when the displayed value should have zero digits after the decimal point.
Keep the existing PV placeholder if the operator also needs the measured process value, or label the replacement text clearly as the configured high alarm limit.
Compile and deploy the relevant project changes using the site's PCS 7 V8.1 SP1 change-control and OS update procedure.

This uses the documented ExtVa104 message input and the general PCS 7 associated-value text syntax. The exact source object and project compile/deploy steps depend on how the existing CFC chart and message texts are configured.

Choosing the displayed precision

The associated-value syntax has three relevant parts: 4 selects associated value 4, R identifies a REAL, and %...f specifies a fixed-point display format. Siemens' STEP 7 V5.5 manual defines the optional .y field as the number of digits after the decimal point. Thus @4R%.0f@ requests zero displayed fractional digits.

The available documentation does not specify whether this message formatting rounds or truncates a REAL at zero fractional digits, and the discussion's numerical examples were not independently confirmed. If the display's rounding behavior affects an operator decision, check it in a test project with representative values before deployment. Keep the source value at full precision in the control logic.

Alternative using an exposed limit output

APL V8.1 documents PV_AH_Out as the high alarm limit output corresponding to PV_AH_Lim. If the project already routes that output through a separate chart source or connector, that value can be used to supply the associated-value input. Do not assume a self-connection from PV_AH_Out to ExtVa104 on the same MonAnL instance is permitted or has the intended scan behavior; the cited APL manual does not specify such wiring.

A single common upstream source feeding both PV_AH_Lim and ExtVa104 avoids input-to-input wiring and avoids maintaining two separate numerical settings.

Applicability to MsgEvId1 and MsgEvId2

The high alarm limit message described in the question belongs to MsgEvId1; for this message instance, associated value 4 is ExtVa104. The APL manual separately maps associated value 4 for MsgEvId2 to ExtVa204. Confirm which message instance the edited alarm uses before changing the token or wiring. A text field referring to value 4 will not select ExtVa104 if the event comes from the second message instance.

Verification

In a project copy or other approved test environment, use a known high alarm limit and a different process value so the two displayed quantities can be distinguished. Trigger the applicable high alarm through the project's approved test method and confirm that the message reports the limit supplied to ExtVa104, while the process value remains available in the appropriate message/faceplate field.

Also confirm that the message uses MsgEvId1, that the CFC source fans out to both PV_AH_Lim and ExtVa104, and that the OS displays the updated text after the approved compile and deployment procedure. Test representative fractional values if zero-decimal formatting is used. This procedure has not been lab-tested.

Limitations and Operational Precautions

This guidance is scoped to the ticket's stated PCS 7 V8.1 SP1 project and Siemens APL V8.1 documentation. The documented mapping supports ExtVa104 for associated value 4 on MsgEvId1; exact wiring depends on the project's existing limit source and chart structure.

PV_AH_Lim is an input. Do not attempt to connect it directly to the input ExtVa104. The APL manual exposes PV_AH_Out as an output reflecting the configured limit, but it does not establish that feeding that output back into an input on the same block instance is supported. Prefer one project-defined source that feeds both inputs, or verify any alternative chart arrangement in the exact PCS 7/CFC version.

The format @4R%.0f@ requests zero digits after the decimal point; do not treat this as a numeric conversion in the PLC or as proof of a particular rounding rule. Changing message text or CFC wiring requires the project's normal review, backup, compile, deployment and operator verification process.

Engineer FAQ

What does @4R%.0f@ reference?

It selects associated value 4, declares the value as REAL and requests a fixed-point format with zero digits after the decimal point. In MonAnL MsgEvId1, associated value 4 maps to ExtVa104.

Is PV_AH_Lim automatically associated value 4?

The APL V8.1 manual does not list it that way. It lists ExtVa104 as associated value 4 and PV_AH_Out as the output corresponding to PV_AH_Lim. Provide the limit to the associated-value input through a suitable CFC signal source.

Can two MonAnL inputs be connected directly to each other?

No. Use an output signal as the common source for PV_AH_Lim and ExtVa104, rather than attempting an input-to-input connection.

Does %.0f truncate 1.5423 to 1?

The cited STEP 7 format documentation defines the number of fractional digits but does not state the rounding-versus-truncation rule for this message display. Verify the exact behavior in the target PCS 7 runtime if it matters.

What changes if the message comes from MsgEvId2?

Associated value 4 for MsgEvId2 maps to ExtVa204, not ExtVa104. Check the event's message instance and route the limit to the matching input.

Technical References

Siemens, Process Control System PCS 7 – Advanced Process Library (V8.1), Function Manual, 07/2014, A5E33257529-AA, §3.3.5 “MonAnL messaging” and §3.3.6 “MonAnL I/Os,” pp. 410–418. It maps MsgEvId1 associated value 4 to ExtVa104, MsgEvId2 associated value 4 to ExtVa204, lists PV_AH_Lim, and documents PV_AH_Out as the high-limit output. https://cache.industry.siemens.com/dl/files/917/90682917/att_106487/v1/s7jal81b_en-US.pdf
Siemens, Programming with STEP 7, Manual, 05/2010, A5E02789666-01, §16.4.1 “Adding Associated Values to Messages,” pp. 362–364. It describes the message token structure, R as REAL, and the fixed-point formatting field. https://cache.industry.siemens.com/dl/files/107/45531107/att_91661/v1/S7pr___b.pdf
Siemens, Process Control System PCS 7 – Engineering System, A5E00164234-02, §5.10.3 “Important Features of Message Configuration.” It explains that an associated-value field in the message text displays the linked process value. https://cache.industry.siemens.com/dl/files/448/15229448/att_77191/v1/PHB_PCS7_e.pdf