HMI trend logging stops when short file names run out

Symptoms and what each points to

Match your symptom before you touch anything:

• Logging stops exactly at the 23:59 to 00:00 boundary, after days of good files, with free space left on the stick. That is the short-name limit. Run the directory check below.
• The panel reports the drive full, or files stop while space remains and no long number series appears in the folder. That points at storage and rollover settings, not at names.
• The panel copies one day of logs and then stops copying. That is the copy action's duration setting, not a name collision. The one-day USB log copy fix covers it: set the copy button to hold.

Where the 999 name limit comes from

The stick in your panel is formatted FAT, and FAT keeps a short 8.3 name for every file: up to eight characters, a period, and up to three characters of extension, ASCII characters only. The 8.3 file name format goes back to DOS, and its character rules are written into the published file-server protocol specifications these systems follow. For a long name, FAT stores an alias in the LONGFI~1.TXT pattern, with a tilde and a number.

The trend loggers that produce this symptom go one step further: they build the short name from the first three letters of the long file name and a three-digit counter. Screen 1_LineTrendGraph1.txt, Screen 2_LineTrendGraph1.txt and Screen 3_LineTrendGraph1.txt become Scr~001.txt, Scr~002.txt and Scr~003.txt. Three digits cap the series at 999 unique names per prefix in one folder, and the logger does not overwrite an old file to free a name. Six trends on three screens named Screen 1, Screen 2 and Screen 3 are therefore six names a day against a single counter.

Read the trend folder before you change anything

1. Take the stick off the panel safely and copy every trend file to a computer. These files are the only copy of the trend history, and every step after this one is easier with a backup in hand.
2. List the trend folder with short names shown. In a Windows command prompt, the dir command with the /x switch prints the short alias in its own column beside each long name. Look for the pattern: one prefix, a tilde, a rising three-digit number.
3. Write down the highest number in the series and the number of trend files the panel writes per day. Days of logging left = (999 minus the highest number) ÷ files per day.
4. Compare the first three letters of the long names of all your logged trends. Shared letters mean a shared series. Screens named Screen 1 and Screen 2 look different to you and identical to the counter.

Example: two production days from a nearly full series

A press line logs six trends across three screens named Screen 1, Screen 2 and Screen 3. Every long name starts with Scr, so all six daily files draw on one series. Commissioning trials before launch already wrote 987 files into the folder, which now holds Scr~001.txt through Scr~987.txt.

Day 1 of production adds six names at the midnight rollover: 987 + 6 = 993. Day 2 adds six more: 993 + 6 = 999. At the day 3 boundary the logger needs a 1000th unique short name in that folder. A three-digit series has no 1000th name, so logging stops at 23:59 with 28 GB still free on the stick.

The burn rate sets the calendar everywhere else. The same six trends starting from an empty folder run 999 ÷ 6 = 166.5, so the series dies during day 167. One trend a day on its own prefix runs 999 days, close to three years. Rename the screens and the folder starts three independent series instead of one.

The fix: distinct three-letter prefixes

1. Back up the trend files from the stick to a computer before you edit the project or the folder.
2. List every screen that holds a logged trend and write down the first three letters of each screen name. Group the ones that share letters; each group is one series heading for the same 999.
3. Rename the screens so every logged screen starts with three different letters. Pump Room, Mezzanine and Basement give Pum~, Mez~ and Bas~: three independent series. Pick names your operators recognize, because the screen name is what the logger builds the file name from.
4. Run the project software's validation and repair anything that pointed at the old names: navigation links, popup calls, objects referenced by screen.
5. Download the revised project to the panel the way you normally do.
6. Once the old logs are copied off, put the stick back or start with a freshly formatted one, and let the panel run through two consecutive midnights. Six trends should produce six new files each day under the new prefixes.

Keep the old folder on the computer, not on the stick the panel writes to, so the history stays retrievable. A rename changes file names only; if your series was never near 999, the rename changes nothing and the checks in the next section are your path.

If the series is far from 999

A highest number under about 100 with free space left means the name limit is not what stopped you. Two checks cover most of the rest: what the logger does when the stick fills, which the oldest-file rollover check walks through, and whether a new file starts at midnight at all, which the midnight rollover walkthrough explains. Once logging runs again and daily files pile up at six a day, combining the daily log files into one CSV keeps the analysis from becoming a filing chore.

Recommendation

Recommendation: When daily trend logging stops at the day boundary with free space left, read the highest number in the short-name series before anything else. If 999 minus that number, divided by the files you log per day, leaves less than a week of midnights, back up the logs, rename every logged screen with a distinct three-letter prefix, and watch two consecutive rollovers before you call it fixed. Keep stick swaps and logger settings for the case where the series sits far from 999. More fixes of this kind are collected in the shop-floor screens section.

Questions