Change the sample rate of a data log

Change the sample rate of a data log to change how often the data log collects tag values, in milliseconds, on the HMI device. For example, to collect data every 30 seconds, specify 30,000 milliseconds as the sample rate. The default sample rate is 1,000 milliseconds or every second. Valid sample rates range from 500 milliseconds to 60,000 milliseconds.
To change the sample rate of a data log
  1. In the
    Project Explorer
    , expand the
    Data Logs
    folder and double-click the data log. The data log opens in the
    Data Log
     tab.
    TIP:
    Right-clicking the data log in the
    Data Logs
     folder and clicking
    Open
     opens the data log.
  2. In the box after
    Sample Rate
    at the top of the data log, select how often the data log collects data. For example, select
    500
    ms to have the data log collect data every half second.
    TIP:
    Tips:
    • Changing the sample rate causes previously collected data to no longer appear in the data log when the project downloads again.
    • If there is no change to the sample rate, log duration, or number of tags in the data log, previously collected data in the data log remains unchanged when re-downloading the project to the HMI device.
    • The
      Sample Rate
      box has a red outline if it does not contain a valid entry.
    • The data log contains tag values with the specified sample rate from all controllers.

Trend Chart Timespan

The Trend Chart component supports displaying both live and historical process data. To provide greater visibility into long-term process behavior, the maximum trend timespan has been extended from 1 hour to 24 hours.
When configured with a long timespan, the chart can display data collected over an entire day while continuing to update in real time.

Configuring the Timespan

The Timespan property defines the period of historical data displayed in the chart window.
The maximum supported value is:
  • 86,400 seconds (24 hours)
When a 24-hour timespan is configured, the chart continuously displays the most recent 24 hours of available data.
For example, if the current time is 14:00, the chart displays data collected between 14:00 on the previous day and 14:00 today.

Historical Data Integration

Trend Charts can retrieve historical samples from a Data Log.
When a trace is connected to a tag that is also logged by a Data Log object, historical values can be displayed in the chart when the user views older data or configures a long timespan.
The amount of available historical data depends on the Data Log configuration, including:
  • Sample Rate
  • Log Duration
  • Retention settings
For example, if a Data Log stores one week of data, the Trend Chart can display historical samples from that period.

Performance Recommendations

The Trend Chart supports timespan values from few seconds up to 24 hours. When a timespan is greater than 1 hour is configured, larger amounts of historical data may need to be processed and rendered. To maintain optimal performance, the following recommendations apply

Recommended Configuration for 24-Hour Timespan

For optimal performance, use:
  • sample Rate: 5000 ms or greater
  • maximum: 4 visible traces per screen on 5510 panels
The four traces can be displayed:
  • in a single Trend Chart object, or
  • across multiple Trend Chart objects
The recommendation applies to the total number of visible traces displayed on the screen.

High-Frequency Sampling

If the timespan is longer than 1 hour and if the Sample Rate is configured to:
  • 1000 ms or less
The following recommendations apply:
5510 Panels
  • Maximum recommended traces:
    2 visible traces per scree
    n
5310 Panels
  • Maximum recommended traces:
    1 visible trace per screen
These recommendations help maintain responsive chart updates and smooth navigation when large amounts of historical data are available.

Data Reduction and Rendering Optimization

When the number of samples exceeds the available horizontal screen resolution, the Trend Chart automatically optimizes the data before rendering.
This situation can occur when:
  • displaying a 24-hour timespan,
  • viewing historical data,
  • opening previously logged data,
  • resuming a chart after it has been paused.
The optimization process divides the visible timespan into pixel-sized intervals. For each interval, up to two values are preserved:
  • the minimum value,
  • the maximum value.
This technique preserves:
  • spikes,
  • peaks,
  • valleys,
  • overall signal shape,
While significantly reducing the number of points that must be rendered.
Only samples that would otherwise be drawn to the same screen pixel are removed.
As a result, the visual appearance of the chart remains unchanged while rendering performance is improved.

Live Data Operation

During normal live operation, incoming samples are rendered directly.
No data reduction is applied unless the number of samples exceeds the available rendering resolution.
Live trend data is cached only for the currently displayed screen. When the user switches to another screen, the cache associated with the previous screen is cleared.
As a result, when the screen is opened again, the trend data must be recalculated and optimized as described above.

Best Practices

When using long timespans:
  • Configure the same Sample Rate in both the Trend Chart and the associated Data Log whenever possible.
  • Use a Sample Rate of 5000 ms or greater for 24-hour trends.
  • Limit the number of simultaneously visible traces according to panel capabilities.
  • Be aware that longer Data Log retention periods increase the amount of historical data available for processing.
Following these recommendations helps ensure smooth chart rendering and responsive operator interaction, even when displaying large amounts of historical process data.
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