In WinCC Tag Logging, create timers, then a process value archive, then add tags with an acquisition cycle and an archiving cycle. Acquisition decides how often the value is read, archiving decides how often it is stored. Configure a compressed archive for long-term data and a backup path so closed segments are kept, then display everything through the WinCC Online Trend Control.
- Acquisition cycle and archiving cycle are different settings; confusing them is why archives either miss transients or fill up.
- Archive sizing is arithmetic, not guesswork: tags multiplied by rate multiplied by retention.
- Without a backup path, closed archive segments are overwritten and the history you were relying on is gone.
How Tag Logging Is Structured
Open Tag Logging from WinCC Explorer. Three objects have to exist before a single value is stored.
- Timers: the cycles available to the whole project, from 500 ms upwards. Add the ones your process needs before creating archives.
- Process value archive: the container that holds logged tags. Most projects use several, grouped by plant area or by retention requirement.
- Archive tags: the individual tags inside an archive, each with its own acquisition and archiving settings.
A compressed archive is a separate object that condenses an existing archive into longer-interval values, keeping a minimum, maximum or average per interval. It is how you keep a year of trend data without keeping a year of one-second samples.
Values must already be scaled into engineering units by the PLC before they are archived. Storing raw analog counts leaves you with an archive nobody can interpret three months later; see PLC analog input scaling in TIA Portal.
Acquisition Cycle, Archiving Cycle and Sizing
Each archive tag has two independent settings, and understanding the difference is the single most useful thing in Tag Logging.
| Setting | What it controls | Effect |
|---|---|---|
| Acquisition cycle | How often WinCC reads the value from the PLC | Communication load |
| Archiving cycle | How often a value is written to the archive | Archive size |
| Archiving on change | A value is stored only when it changes | Small archives for slow signals |
| Hysteresis | Change must exceed a band before storing | Filters measurement noise |
| Processing | Store actual, minimum, maximum, average or sum per cycle | Keeps transients visible at slow archiving rates |
Reading every second and archiving every ten gives you responsive screen values without a ten-times larger archive. Setting the processing to maximum on that same tag means a one-second spike still appears in the ten-second record instead of being missed between samples.
Sizing the archive
Multiply the number of tags by the number of values per hour by the retention period. Fifty tags archived every ten seconds is 18,000 values an hour, 432,000 a day. Decide the retention before configuring, set the archive size accordingly, and leave headroom.
Compression, Backup and Long-Term Archives
A process value archive is a rolling store. When it fills, the oldest segment is overwritten. Two mechanisms keep history beyond that point.
Compressed archives
Create a compressed archive that reads an existing archive and stores one value per longer interval, using minimum, maximum, average or the actual value. A common pattern keeps one second detail for a week and hourly averages for two years, in two separate archives.
Archive backup
Enable backup in the archive configuration and give it a destination path, preferably on a server share rather than the SCADA PC. Each segment is copied as it closes, and segments can be linked back in later for an investigation.
- Verify the backup path is reachable and has space; a failed backup is silent unless you check.
- Include the backup share in the plant IT backup routine.
- Document the retention: how long online, how long in backup, and who can restore it.
- For long-term reporting, export to CSV or push to SQL Server rather than querying the live archive.
Where production reporting is the goal rather than process investigation, feeding a database is usually the better route than growing the archive indefinitely.
Build WinCC archives and reports in class
Sessions cover Tag Logging, compressed archives, backup and SQL Server reporting on real projects.
Trend Control and Table Control Configuration
Add the WinCC Online Trend Control in Graphics Designer and configure it properly rather than accepting defaults.
- Trends: add one per tag, choosing the archive tag for history or the process tag for a purely online curve.
- Value axes: give each measurement type its own axis with a fixed range. Automatic scaling makes every curve look identical and hides the deviation you were looking for.
- Time axis: set a default window that matches the investigation, typically one shift, and allow the operator to change it.
- Ruler and statistics: enable the ruler window so exact values, minimum, maximum and average can be read for a selected period.
- Toolbar: enable scroll, zoom, and the button that jumps to a specific date and time.
Always plot the setpoint alongside the process value. A curve at 178 degrees means nothing on its own; the same curve two degrees under its setpoint for an hour is a finding.
Add the WinCC Online Table Control beside the trend for the same archive. Engineers reading exact numbers, and anyone exporting data to Excel, will use the table far more than the graph.
The panel-level version of the same job is covered in HMI trends and data logs.
Hands-On Lab: Build a WinCC Archive and Trend Screen
Hands-on- WinCC Explorer with a connected PLC or simulated tags
- One analog process value and its setpoint as WinCC tags
- A writable path for archive backup
- Estimated time: 45 minutes
Create timers and the archive
Add the cycles you need in Tag Logging, then create a process value archive with a defined size.
Add archive tags
Add the process value and setpoint with a one second acquisition cycle and a ten second archiving cycle.
Set processing and hysteresis
Set the process value to store the maximum per archiving cycle and add a small hysteresis.
Configure backup
Enable archive backup with a destination path and confirm a segment is copied when it closes.
Build the trend screen
Add an online trend control with both tags on one fixed axis, enable the ruler, and add a table control below it.
Acquisition and archiving cycles are set independently, spikes survive the archiving cycle, backups are landing at the destination, and the trend shows process value against setpoint on a fixed axis.
Frequently asked questions
What is the difference between acquisition cycle and archiving cycle in WinCC?
The acquisition cycle is how often WinCC reads the tag from the PLC. The archiving cycle is how often a value is written to the archive. Reading faster than you archive keeps screens responsive without inflating the archive.
How do I keep short spikes visible at a slow archiving cycle?
Set the archive tag processing to maximum or minimum instead of actual value, so the extreme within each archiving cycle is stored rather than whatever the value happened to be at the sample instant.
What is a compressed archive used for?
Condensing an existing archive into longer intervals with minimum, maximum or average values, so long-term history can be kept without storing every original sample.
Where should archive backups be stored?
On a server share included in the plant IT backup routine, not on the SCADA PC itself. Confirm the path is reachable, because a failing backup gives no obvious warning on screen.