Data collection methods

The OPC-UA collector has 3 methods to collect measurement data, which are referred to as the collection type of a measurement.


Polled measurements are read every x milliseconds (minimum of 1000ms), which is the collection interval. This data collection method should be used for measurements for which the value changes regularly over time. Configure the interval depending on how frequent you want to collect data points for this measurement.


Monitored measurements collect data on every change of the measurements value. This data collection method uses a subscription on the OPC-UA server that notifies the collector whenever a change occurs (Note that this depends on the scanning frequency of the OPC-UA device). Typically, monitored measurements are configured for boolean or string data types that indicate an equipments state, f.e. for a valve that opens and/or closes only a few times per hour.

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Event measurements collect all OPC-UA Alarms & Conditions events from the OPC-UA server. This data collection method uses a subscription on the OPC-UA server that notifies the collector of all events that occur under the configured node. Measurements of this collection method need to set their datatype to raw.

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In case of polled measurements, the source of the timestamp is taken from the system where the collector is running on. In case of monitored and event measurements, the timestamp is taken from the update message received from the OPC-UA server, in which case that is used. We cannot take the timestamp of insertion, as in the case of buffering that can be days later than the actual sampling.

Collector health

OPC-UA Specific collector health messages. See here for all generic collector health messages.

You can find the collector health and the collector history in the detail view on the right, when selecting a collector in the historian admin webpage.

Collector health history

Error initializing collector

An error occurred when initializing the OPC-UA collector. This indicates a collector setting hasn’t been configured correctly or the OPC-UA server isn’t reachable during initialization.

Error connecting to OPC-UA server

The OPC-UA server isn’t reachable for an initialized collector on a connection attempt.

Disconnected: timeout heartbeat

The collector lost connection to the OPC-UA server.