ExcDev, ExcDevPercent, ExcMax, and ExcMin

Exception Deviation

ExcDev

Specifies (in the point's engineering units) how much a point value may differ from the previous value before the interface reports the new value to Data Archive. Typically, you set ExcDev to a slightly smaller value than the precision of the instrument system.

ExcDevPercent

Specifies the exception deviation in percent of Span rather than in engineering units. A typical value is 1% of Span. However, if the Span attribute is set incorrectly, your exception reporting will also be incorrect.

When you change ExcDev or ExcDevPercent, the other is automatically updated to be compatible. If you change both attributes at once, ExcDevPercent overrides ExcDev.

For digital, string, and Blob tags, ExcDev and ExcDevPercent are set to zero and ignored.

Exception Maximum

ExcMax

Specifies the maximum time (in seconds) between events that the interface reports to Data Archive. After the specified ExcMax time elapses, the interface sends the new value to Data Archive, regardless of whether the new value is different from the last reported value. For example, it is possible for the incoming data to be a single value for many days. If ExcMax is set to 600 seconds (10 minutes) then a value is not discarded due to exception if the previous event time stamp was more than 10 minutes before that.

Exception Minimum

ExcMin

Specifies the minimum time (in seconds) between events that the interface reports to Data Archive. For example, if ExcMin is 5, the interface discards any values collected within five seconds of the last reported value. Typically, you set ExcMin to zero.