About delta storage mode

AVEVA Historian supports four storage modes:

• No storage - No data values are stored.

• Forced storage - All collected data values are stored.

• Cyclic storage - Only data values that occur at a specified time interval are stored.

• Delta storage - Only changed data values are stored.

Using delta storage mode, the Historian stores data based on a change in a value. Delta storage writes a historical record only if the current value changes from the previous value. Delta storage is also called "storage by exception." Delta storage is typically used to store discrete values, string values, and analog values that remain constant for long periods of time. For example, you don’t want to store the value of the discrete tag "PUMPON" every ten seconds if the pump usually stays on for months at a time. The value is stored along with a timestamp of when the change occurred, to an accuracy of 1 ms.

The following types of deadbands can be applied for delta storage:

• Time deadband

• Value deadband

• Rate of change (swinging door) deadband