Data Logger
Data can be logged and saved in the iX Developer database.
Any number of tags can be connected to a data logger, and data values irrespective of type can be logged. A project can have multiple data loggers with different sampling alternatives.
If you want to open a database file to inspect logged data, then you need to install an appropriate third party database viewer tool.
Logged data can also be viewed in the trend viewer object by selecting a LogItem for a curve in the Edit Curves dialog.
If iX Runtime is restarted at some point during the data logging, an additional empty row is added in the Data Logger table in order to clearly visualize the interruption in the Trend Viewer.
Note
Logging of data consumes system resources and memory. To save memory, it is preferable that all LogItems that should be logged with the same sampling intervals are placed in the same data logger.
Any individual data logger database can be exported in csv format using the Database Export action. It is recommended to use the database export method rather than the backup method.
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Data Logging Strategies
Logging of data can be made at time intervals or based on changed tag values.
Logging of data can be made either by collecting all samples at every log event, or by collecting only changed values. Collecting only changed values saves memory and improves performance.
If the log items are displayed in a trend viewer, note that there is a limit on log period when showing real time values in the trend. For panels this limit is once per second, and for PC projects 100 milliseconds. This means that if a trend is used to display values from a data logger that logs more often than the limit, curves will look different depending on if in history mode or real time. This is because history will display values from the data logger, and this has no limit in intervals.
Logging Based on Time Interval
To collect data that changes frequently, logging data based on time interval is recommended.
Logging Based on Changed Tag Value
To control sampling of data by other means than regular time interval, you have to set up a separate tag to be used as a trigger. When the value of the trigger tag changes the log item is logged.
The HMI panel uses a Flash SSD (Solid State Drive) for storage. Flash SSDs have no moving parts, providing high reliability and fast performance. However, the lifespan of the drive is determined by the number of read and write operations, which the manufacturer tracks using proprietary algorithms. As the algorithm is confidential, the exact lifetime cannot be calculated, but only the number of reads and writes are published.
To maximize the lifespan of the Flash SSD, minimize the number of write operations. Follow these best practices to reduce the risk of premature wear:
Store the database on an SD Card – To reduce Flash SSD wear, store the database on an SD card, see Use SD Card to Reduce Flash Wear.
Limit logging accuracy – Avoid logging data with higher accuracy than required, such as floating point values.
Use hysteresis for fluctuating values – Reduce high fluctuations by using the hysteresis feature in the connected controller.
Separate fast and slow changing values – Log fluctuating values in one logger and stable values in another.
Minimize logging frequency – Only log at the necessary refresh rate.
Disable logging when not needed – Turn off logging when the machine is idle or not in use.
Use default logger setting – Enable the Log Changes Only option in the Data Logger Properties to log only when a value changes.
Keep log size small – Log only the necessary data with the fewest rows possible.
Avoid extensive file writing in scripts – Limit file writing when controlling storage through scripts.
Adding a Data Logger
A data logger can be added to the project from the Insert ribbon tab. The data logger configuration pages are used to set up which values to log.
Parameter | Description |
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Name | Symbolic name for the logged tag |
Tag | Tag to log |
Expression | See section Expressions |
Clicking the Settings button accesses the Data Logger settings.
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Note
Data Logger items cannot be called "Time" or "Id" because these names are reserved.
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General Settings
Parameter | Description |
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Log with interval | To collect data that changes frequently, use the Log with interval of option, and define time interval in seconds. Minimum interval is 1 second. |
Log on tag event | To control sampling of data by other means than regular time interval, select the Log on tag event option, and select the tag to use as trigger. Data will be sampled when the tag value changes. |
Log changes only | By logging changes only saves memory. The option Log changes only can be combined with either the “Log with interval of” or the “Log on object event” option. Data will only be logged if the value differs from the last logged value. |
Max number of logged rows | The maximum number of tag values to save in the database. When the number of collected items becomes larger than the set value, the oldest item will be overwritten. The value must be within the size of the available amount of memory in the HMI panel in runtime. |
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Actions
Event | Description |
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Log item Value changed | When a value of an particular log item has changed |
Log values updated | When any log value is updated |