Swinging door deadband: rate, value, and deadband override period

The following graphic illustrates the effect of a rate deadband combined with a value deadband and a deadband override period.

Assume point 1 is stored to disk. Point 3 makes it through the value deadband check, allowing points 2 and 3 to be evaluated for rate change. Assuming the point exceeds the rate change requirement, then point 2 is stored.

Adding a value deadband alone could result in distortion of the stored data.

For example, suppose that the rate deadband is specified such that point 12 does not get stored. That is, the change in slope between points 2 through 3 and points 12 through 13 is not greater than the rate deadband. In that case, the data representation (points 1, 2, and 15) is grossly distorted because the value deadband is discarding key points.

To allow for better representation, a deadband override period may optionally be specified. If the elapsed time between the last stored point and the currently received point is more than the specified deadband, then the point immediately prior to the currently received point is stored. In this example, the elapsed time between point 2 and point 10 is more than the deadband, so point 9 is stored. The data actually stored to disk (points 1, 2, 9, and 15) is a better approximation of the original data.

It is important to note that after point 9 is stored, subsequent rate calculations use the slope between points 2 and 3 as the baseline for subsequent storage decisions because point 2 was last point that was stored normally by storage.

The deadband override period can have any value and is not related to the real-time window value.