Value deadband (wwValueDeadband)

A value deadband for retrieval controls the value resolution of data returned in delta mode. Any data values that change less than the specified deadband are not returned. The deadband is a percentage of a tag’s full scale in engineering units.

The deadband "base value" is reset each time that a value is returned, so that the last value returned acts as the basis for the deadband.

Changes in quality will force a value to be returned even if the value deadband has not been met.

The following illustration shows an example of applying a value deadband:

Data is retrieved for the time period starting with TS and ending with TE. All points in the graphic represent data values stored on the historian. The gray areas represent the value deadband, which starts anew with every returned value. Only the green points (P2, P5, P6, P7, P9, P10, P11) are returned. The other points are not returned because they fall within a deadband.