Clearing the Siemens MP 377 Alarm Archive: Complete Reset Guide

Overview

The SIMATIC MP 377 (6AV6 644-...) is a 12", 15" or 19" widescreen HMI panel from the SIMATIC Multi Panel / Comfort Panel family, running WinCC flexible 2008 SP5 or, in many retrofit projects, the TIA Portal (WinCC Comfort/Advanced) runtime. Every alarm configured with logging enabled is written to an alarm archive file. Over months of production, that file grows to hundreds of megabytes and eventually fills the panel's internal flash, the CF card, or the mapped network share. Operators see "Archive full", alarms that no longer scroll correctly, or runtime warnings during startup. The fix is a controlled reset of the archive: either clear it from inside the project using the ClearLog system function, or stop the runtime, delete the archive file at the operating-system level, and let the runtime regenerate an empty archive on the next power-up.

This article covers the exact procedure for the MP 377, including how to find the archive path, how to call ClearLog from a button or scheduled task, and how to manually delete the file from Windows CE 6.0 when the source project is no longer available. It also covers the equivalent TIA Portal path, archive backup considerations, and the most common fault conditions seen on field units.

Prerequisites

• Access to the MP 377 source project (preferred), or administrative access to the panel via its CE 6.0 desktop.
• WinCC flexible 2008 SP5 / SP6 / SP7 (for SP4 / SP5 era MP 377 panels) or TIA Portal V15..V20 with WinCC Comfort/Advanced (for newer projects recompiled for the MP 377).
• Either a CF card reader, an Ethernet connection to the panel, or a USB stick to transfer a backup of the existing archive before deletion.
• Project backup (TIA Portal: Project > Archive; WinCC flexible: Project > Retrieve > Reverse Compilation is not used for runtime archives — only the project itself is needed).

How the MP 377 Stores the Alarm Archive

The MP 377 stores alarm data in a sequential file whose default path and extension depend on the runtime configuration. The three most common locations are:

The runtime writes a rolling file (e.g. AlarmLog_001.csv, AlarmLog_002.csv) when the configured segment size or time interval elapses. The active file is locked by the runtime. Deleting it while the runtime holds the handle triggers the next start-up sequence to create a fresh, empty archive. If the file is deleted while runtime is running, WinCC flexible recreates an empty file on the next archive segment boundary, but the locked segment cannot be removed until the runtime stops or rolls over.

Locating the Archive Path in the Project

The fastest way to confirm where the runtime is writing the file is to inspect the project:

1. Open the WinCC flexible or TIA Portal source project.
2. Open Project Tree > Historical Data > Alarm Log (WinCC flexible) or Project tree > HMI tags > Logs > Alarm log (TIA Portal).
3. Select the alarm log entry; the Path column or the Storage location field displays the runtime path. This is the same path the panel uses at runtime.
4. If the project is lost, see the manual method in Locating the Archive Without a Project below.

Method 1 — Clear the Archive from Inside the Project (ClearLog)

The ClearLog system function is the supported, runtime-safe way to reset the alarm archive from a button, a scheduled task, or a value-change event. The function accepts a tag parameter that identifies the log name declared in the project (e.g. AlarmLog).

Configuration in WinCC flexible 2008:

1. Place a button on the desired screen.
2. Right-click the button → Properties > Events > Press.
3. From the function list, add System Functions > Logs > ClearLog.
4. Enter the alarm log identifier (default AlarmLog). If you renamed the log in the project, enter the exact log name.

Configuration in TIA Portal (V15..V20):

1. Place a button on the screen.
2. In Properties > Events > Click, add the system function ClearLog.
3. Select the alarm log configured under HMI tags > Logs.
4. Compile and download to the panel.

When the operator presses the configured button, ClearLog deletes the active archive file and starts a new one. The operator-visible alarm list in the alarm view is also cleared if it is filtered to "not acknowledged" or "history"; the cleared entries will not reappear until new alarms occur.

Method 2 — Manual Deletion from the Windows CE Desktop

When the source project is no longer available, the archive can be deleted directly from the panel's Windows CE 6.0 desktop. This is the only practical method for legacy MP 377 units that no longer have a matching project on the engineering station.

1. Power-cycle the panel. When the WinCC flexible Runtime Loader appears, tap Exit (or the cancel button) before the runtime starts. This drops the panel to the Windows CE desktop.
2. Open My Device > My Documents and look for a subfolder with the same name as the project (e.g. \My Documents\MyHMI\Logs\).
3. If the project stores its archive on a CF card, open My Device > Storage Card MMC and look in \Logs\.
4. If the project stores its archive on a network share, the runtime will recreate the file as soon as the share is reachable. The CE 6.0 desktop does not let you browse SMB shares; use Method 3 to clear the file from the server side.
5. Select the alarm archive (e.g. AlarmLog.csv, AlarmLog_001.csv) and delete it. Do not delete the parent Logs folder; the runtime expects it to exist.
6. Close My Documents and restart the runtime from the desktop shortcut, or reboot the panel. The runtime creates a new empty archive file on the next archive cycle.

Method 3 — Server-Side Deletion for Network Archives

Many MP 377 installations map the alarm archive to a Windows SMB share on a plant historian or file server. In this case, do not attempt to delete the file from the panel.

1. Stop the runtime on the panel, or disable the alarm logging tag with a temporary project change.
2. On the file server, browse to the share (e.g. \\PLCSRV\HMI_Logs\Line3\).
3. Stop the archiving service if a third-party historian is reading the file (Siemens WinCC Archive Server, ProSave, or a custom OPC-HDA consumer).
4. Delete the active archive file (AlarmLog_xxx.csv) and any closed segments you want to clear.
5. Restart the runtime, or re-enable the alarm logging tag, and verify a new file is created.

If you cannot stop the runtime (continuous production line), the alternative is to use a scheduled task on the server to move old segments to a backup folder. Configure the Segment size and Segment time in the project to keep the rolling file small.

Method 4 — Clearing the Archive from TIA Portal (Project-Online)

When the MP 377 is online in TIA Portal, the alarm archive can be cleared without writing a button or recompiling the project.

1. Connect the engineering station to the panel via the configured route (Ethernet, PROFIBUS, USB-PPI).
2. In the project tree, expand the MP 377 → Online > Diagnostics > Alarm archive.
3. Open the alarm display that uses the same log.
4. Click the "Clear alarm archive completely" icon in the toolbar of the alarm display. This toolbar control is documented in the TIA Portal help under Editing devices and networks > Displaying alarms > Clear alarm archive completely.
5. Confirm the prompt. The active archive file is removed and a new one is started.

For the equivalent workflow in WinCC flexible, right-click the panel → Transfer > Backup / Restore can also reset the runtime data area, but that wipes all runtime data (recipe data, user administration, logs) and is not appropriate for a single-file archive reset.

Verification

After applying any of the methods above, validate that the archive is truly empty and that the runtime has started writing a new file:

1. From the panel, open the alarm view and confirm the History tab is empty.
2. Trigger a known alarm (e.g. a tag toggle) and acknowledge it. The new entry must appear in the alarm view and the archive.
3. From the engineering station, use ProSave or TIA Portal Online > Read log to download the active archive. The file should contain only the new test alarm.
4. Inspect the file system: the archive file should be a fresh CSV with only a header row (or empty DB file in SQL-backed configurations).

Troubleshooting Matrix

Configuration Parameters Reference

Backing Up Before a Reset

The ClearLog function and the manual deletion method both remove data without a Recycle Bin. Always export first:

1. From the running project, open the alarm view, switch to History, and use the export icon to save a CSV to a USB stick or network share.
2. Alternatively, use ProSave to back up the entire HMI data area. This produces a *.psb file containing recipes, user administration, and the active log segments.
3. For the TIA Portal workflow, use Online > Backup of runtime data to capture the file system as-is.

Once the backup is verified to open correctly in Excel or in a downstream historian, proceed with the reset.

Notes on the MP 377 Hardware Variants

The MP 377 family includes:

• 6AV6 644-0AB01-2AX0 — 12" touch, Windows CE 6.0
• 6AV6 644-0AC01-2AX0 — 12" key + touch
• 6AV6 644-0AD01-2AX0
• 6AV6 644-0AE01-2AX0 — 15" variants

All variants share the same Windows CE 6.0 image and the same alarm archive layout. CF card slot presence depends on the variant; for units without a CF slot, archives must be stored on internal flash or on a network share. The CF card is hot-swappable on most MP 377 units — a useful feature when a customer wants to take the archive off-site for offline analysis by simply pulling the card and reading it in a PC.

FAQ