IP21 addlastvalue
Depending on the compression settings in IP21 historians it can happen that when TrendMiner fetches values for digital and string tags the historian does not return the latest registered value. As digital and string tags typically change value less than analog tags this can be a performance optimization on historian side.
However, the TrendMiner appliance expects values at the start and end timestamp of each requested interval. During forward indexing this implies that TrendMiner is requesting the most recent data (the ‘now’ moment). If the historian at that point does not return a value, the TrendMiner connector assumes the value has not changed and adds the last known value as the value for the end timestamp to comply with the request it receives from the appliance.
As a result, it can happen that this value change is not stored in the TrendMiner index and the search results and visualization are wrong. This behaviour only applies to IP21 historians due to its compression settings and only for digital and string tags due to the nature of their behavior (fewer state changes), e.g. pumps changing state.
For IP21 the connector can be configured to not add the last value. As a result, the appliance will not receive the requested end value to store in its index and will try to index the same time period again during its next forward index cycle. Typically, by then the historian does return the value changes and the index is built up correctly.
This behavior can be configured on the connector.
Parameters:
<add key="ip21.addlastvalue" value="true"/>
The default value: true
To fix issues with IP21 digital and string tags, change this value to false.
Supported as of connector version: <v.3.5.2923-5f4a8fb>
Supported for the following data source providers:
Aspentech IP21