IoT difference filter
Navigation: Configuration > IoT > Data > IoT difference filter
The IoT difference filter page controls which metric values are forwarded to IoT destinations by suppressing redundant data. When a metric is added to this page, the device compares each newly polled value against the last transmitted value. If the change falls within the configured tolerance (value range), the value is discarded. Only when the deviation exceeds the threshold, or the configured time interval elapses without any change, is a new value transmitted. This mechanism significantly reduces network traffic and storage requirements in IoT applications where data sources report measurements at high frequency but actual process values change infrequently. Metrics must first be defined on the Metrics page before they can be selected here. Changes take effect after clicking Apply settings, but must be saved persistently via the Save page to survive a reboot.
Prerequisites
- At least one metric must be configured on the Metrics page. If no metrics exist, the Metrics dropdown on this page will be empty.
- At least one IoT data source must be configured (e.g., under Configuration > IoT > Sources) and mapped to the metric for the filter to have practical effect.
Settings
The page displays a table of filter rules. Each row defines a difference filter for one metric. Use the + button to add a new filter entry.
- Metrics
- Selects the metric to which this filter rule applies. The dropdown lists all metrics defined on the Metrics page. If the list is empty, navigate to the Metrics page first and create a metric definition.
- Value range
- Defines the relative tolerance threshold for filtering. Values that lie within this relative tolerance compared to the last transmitted value are filtered out and not forwarded to the destination. When a new value exceeds the threshold, it is transmitted and becomes the new reference for subsequent comparisons. Set this value according to the acceptable measurement deviation for the process variable — for example, a value of 5 filters out changes of less than 5%.
- Filter interval
- Specifies the maximum time interval between transmitted values. If the measured value does not change beyond the tolerance within this interval, it is filtered out. After the interval expires, the current value is transmitted regardless of whether it has changed. This ensures that destinations receive periodic updates even for stable process values, confirming that the data source is still active.
Recommendation
Configure the value range and filter interval according to the characteristics of each process variable. For slowly changing measurements such as ambient temperature, a larger tolerance and longer interval reduce unnecessary traffic. For rapidly fluctuating values where timely updates are critical, use a smaller tolerance and shorter interval. Review the data volume at the configured IoT destinations to verify that the filter settings achieve the desired reduction without discarding operationally relevant changes.