Resolving HMIRTM.EXE Error on Siemens TP900/TP1200 Comfort Panels

Problem Overview

The runtime process HMIRTM.EXE on SIMATIC HMI Comfort Panels (TP700, TP900, TP1200) running WinCC Comfort/Advanced Runtime V14 SP1 may terminate with the dialog:

"Application HMIRTM.EXE encountered a serious error and must shut down."

After the dialog is acknowledged, the HMI becomes unresponsive until power-cycled. In most field reports the runtime then operates normally for a variable period — anything from 15 minutes to two weeks — before the same dialog reappears. On the second or third occurrence within the same session, the panel may also freeze immediately on restart, requiring a full power-down. This fault is not recoverable through the panel's own restart button or via the HMI control panel "Reboot" entry.

Affected Hardware and Software Matrix

Refer to the SIMATIC HMI TP900 Comfort manual and the S7-300 CPU 315-2 PN/DP manual for hardware/firmware baselines.

Why HMIRTM.EXE Crashes — Root Cause Analysis

HMIRTM is a managed native application that handles tag polling, screen rendering, logging, alarm handling, scripts, and recipes. A fatal exception inside it is almost always one of the following five conditions:

1. STRING tag buffer overflow: The PLC supplies more characters than the configured tag length in WinCC. WinCC allocates a fixed buffer at compile time based on the configured length; if the S7 tag returns a longer string, HMIRTM writes past the buffer boundary. After a variable number of polls (depending on buffer reuse), a guard page is hit and the runtime traps with an access violation. This is the most common cause confirmed in the field — concatenation in PLC code of two STRINGs longer than the HMI tag length reliably reproduces the fault.
2. Audit Trail database overflow: When Audit Trail is enabled with a USB or SD storage target and the medium fills up, the runtime enters a retry loop on every write. After several thousand retries the write thread's stack or heap overruns and HMIRTM terminates.
3. Alarm log segment mismatch: Circular alarm logging with an HDF or RDB segment size that is smaller than a single record can produce the same heap-corruption pattern, especially when alarms carry long associated values.
4. VBS / C-script runtime fault: A scheduled script that dereferences a NULL pointer or accesses an array out-of-bounds crashes the script host, which in turn crashes the parent runtime on WinCC V14.
5. Power management / write filter: Buffered writes to internal flash on EWF (Enhanced Write Filter) configured panels can deadlock HMIRTM during graceful shutdown sequences triggered by Auto Logoff or screen-saver events.

STRING Overflow — The Dominant Field Cause

When a WinCC tag is defined as WSTRING[254] or STRING[n], the buffer on the panel side is exactly n characters. The PLC, however, can have a STRING whose actual length at runtime exceeds n — particularly after a concatenation such as:

// SCL example on CPU 315-2 PN/DP, used in field reports
#CombinedString := LEFT(IN := #StringA + #StringB, L := 254);

If #StringA and #StringB are each 100 characters, the concatenation temporarily yields a 200-character string; any path that does not properly truncate before the S7 write protocol hands the value to WinCC will overrun the panel-side buffer the next time HMIRTM polls the tag.

Diagnostic Procedure

Perform the steps below in order before applying any fix. Each step produces evidence that isolates the root cause.

1. Capture the Simatic Log: Insert a USB stick formatted FAT32. From the HMI Control Panel → "Logs", or from TIA Portal via "Online → HMI Diagnostics", pull the HMIRTM.log and the Windows CE event log. The exact faulting module and offset appear in \Flash\HMIRTM\HMIRTM.log. Compare timestamps with the dialog appearance.
2. Inspect configured tag lengths: In TIA Portal, expand HMI Tags → [your connection]. Filter on tags of type String or WString. Note the configured length column.
3. Trace live PLC strings: With the panel connected, use TIA Portal "Watch table" or STEP 7 "Monitor/Modify" to read the actual current length of the same tags. Any tag whose current PLC length exceeds the configured HMI length is a candidate.
4. Identify logging subsystems: In TIA Portal, open Historical data, Alarm logs, and Audit Trail. Note each storage path and segment size. Confirm the storage medium has free space at least 10× the segment size.
5. Disable and re-enable features (binary search): Create a stripped-down copy of the project on a separate TP900. Disable Audit Trail first — if the crash disappears, root cause is (2). Disable alarm logging — if it disappears, root cause is (3). Disable scripts — if it disappears, root cause is (4). If the crash remains with all optional features off, root cause is (1) string overflow or (5) write-filter deadlock.
6. Check firmware vs. TIA compatibility: The image version installed on the panel must match the TIA version used to compile the project. Mismatched versions are rejected at transfer but can manifest as intermittent RT faults if the panel was last updated partially. See the TP900 Comfort operating instructions for the compatible image matrix.

Solution A — Correct STRING Tag Lengths

This is the canonical fix once root cause (1) is confirmed.

1. In TIA Portal, navigate to HMI Tags → <Connection> → <Tag> and open the properties of every STRING/WSTRING tag.
2. Set Length to a value greater than or equal to the maximum possible value the PLC will ever produce, including concatenation results. For a 254-char PLC string, use 254 (default) — but verify the PLC code actually respects this limit.
3. In the S7-300 PLC code, wrap every string write that originates from concatenation with an explicit length clamp:

// Defensive SCL snippet for CPU 315-2 PN/DP
#TempLen := LEN(#StringA) + LEN(#StringB);
IF #TempLen > 253 THEN
    #TempLen := 253;          // account for STRING header length
END_IF;
#OutString := LEFT(IN := #StringA + #StringB, L := #TempLen);
#OutStringLen := #TempLen;   // update STRING length header

4. Recompile the HMI project, transfer to the panel, and restart the runtime.

Solution B — Audit Trail / Logging Subsystem

1. Open Runtime settings → Audit Trail. Confirm the storage medium (SD/USB/network share) has at least 500 MB free.
2. Reduce the Segment size to 4 MB to ensure no single record exceeds a segment.
3. Add a maintenance task on the PLC side (or a WinCC scheduled action) that rotates the log when free space drops below 100 MB.
4. If Audit Trail is not strictly required for FDA / GxP compliance, evaluate disabling it and using simple alarm logging instead.

Solution C — Alarm Logging Segment Size

1. In HMI Alarms → Alarm logs, change the segment size from any value below 32 KB to 64 KB minimum.
2. Configure Storage location to an SD card (not internal flash) to avoid EWF conflicts.
3. Verify the alarm text associated values do not exceed 64 characters; longer values should be moved to a separate tag referenced from a script.

Solution D — Scripts and Scheduled Actions

1. Audit every VBScript under Schedules and Events. Add On Error Resume Next only where appropriate, then log the error to a file:

Sub UpdateLabel
    On Error Resume Next
    Dim sVal
    sVal = SmartTags("MyTag")
    If Err.Number <> 0 Then
        Dim f, ts
        Set f = CreateObject("FileCtl.File")
        f.Open "\Storage Card SIMATIC\errlog.txt", 8  ' fmOpenWrite
        Set ts = f.CreateTextFile(False)
        ts.WriteLine "Tag read error: " & Err.Description
        ts.Close
        Exit Sub
    End If
    SmartTags("MyLabel") = sVal
End Sub

2. Ensure no script recursively calls itself or schedules a tag write that triggers another schedule.
3. Reduce cycle-triggered scripts to 1 s minimum.

Solution E — Firmware / Image Update

1. Identify the panel's current image version via Control Panel → System → About.
2. Cross-reference with the TIA Portal V14 SP1 Update 5 compatibility list in the TP900 Comfort manual entry. Download the matching image from the Siemens Industry Online Support catalog.
3. Perform a ProSave update or use an SD card with the image in \Simatic\HMI\Images\<imagefile.img> and reboot the panel. The panel will detect the image automatically.
4. After the image update, transfer the project again with "Reset to factory settings" enabled to flush any stale buffer structures.

Verification Procedure

After applying any combination of the above solutions, run the following verification before returning the line to production:

1. Stress test: Force the PLC to write maximum-length strings to every STRING/WSTRING tag for at least 24 hours continuous. Monitor HMIRTM.exe memory in Task Manager on the panel (right-click taskbar → Task Manager) — if it stabilizes below 70 % of working set, the fix is holding.
2. Log review: Pull HMIRTM.log and \Flash\System\SystemLog.txt. Confirm no new "access violation" entries.
3. Controlled restart test: Trigger the worst-case scenario (Audit Trail full, alarm log full, max-length string write) and verify the runtime does not crash.
4. Two-week soak test: Leave the panel running for at least 14 calendar days under normal production load. The reported time-to-crash in field cases ranged from 15 minutes to two weeks; the soak test must exceed the longest observed interval.

Preventive Measures and Best Practices

• Always clamp string lengths on the PLC side. Treat every HMI STRING tag as a fixed contract and enforce it in PLC code review.
• Use WSTRING only when Unicode is required; for ASCII-only labels, STRING halves memory pressure.
• Disable unused logging subsystems in TIA Portal rather than leaving them at default — defaults can include audit logging that consumes flash cycles.
• Configure the Enhanced Write Filter (EWF) to RAM mode for high-write-rate applications; persist only at controlled shutdown.
• Keep the TIA Portal version and the panel image version identical. Mixing TIA V14 SP1 Update 5 with a V13 image is a known source of intermittent RT faults.
• Maintain a 6-month firmware refresh cycle. Siemens regularly ships Comfort Panel image updates that patch internal HMIRTM memory-handling bugs.

Related Faults and Error Codes

When to Escalate

If after applying Solutions A through E and completing the verification soak test the fault recurs, open a support request at Siemens Industry Online Support. Attach:

• The exported TIA project (with password if protected).
• The complete HMIRTM.log from \Flash\HMIRTM\.
• The Windows CE SystemLog.txt.
• A screenshot of Control Panel → System → About showing the exact image version.
• The PLC STEP 7 project (or a stripped-down reproduction project) so Siemens support can replay the STRING values.

FAQ