Deviation Percent Alarm Calculation
There are two Deviation alarm calculation types that can be implemented in CygNet: Deviation Value and Deviation Percent.
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The Deviation Value alarm calculation is included with the CygNet Standard Point Scheme. For more information on the Deviation Value alarm calculation, see Default Alarm Calculations.
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The Deviation Percent alarm calculation can only be implemented with the CygNet Enhanced Point Scheme, and is described below. See Understanding the CVS Metadata File for more information about the elements and attributes that define a CygNet Point Scheme.
For more information, see Alarm Calculation Types.
Deviation Percent
The Percent Deviation alarm uses the Deviation Percent (DEVIATION_PCT) calculation. On each update, the system calculates the percentage change from the previous value and sets the alarm bit if the percentage change exceeds the threshold. This alarm calculation uses Calculation Parameter 1 only.
The number of entries stored for this calculation is specified by the histvaluecount attribute in the CvsMetadata file for a CygNet Enhanced Point Scheme.
The following image shows the area of an Analog Alarm Settings page of a PNT Editor with an enabled Percent Deviation alarm using the Deviation Percent calculation type:
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Alarm Calculation Configuration — Deviation Percent |
Calculation Parameter
The calculation parameter for this alarm is user-provided:
- Percent Change (calcparm1) — maximum allowed percentage change before the alarm bit is set.
Equation
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Percent Change = ((Updated Value/Previous Value) -1) X 100 |
- If Percent Change ≥ maximum allowed percentage change, the alarm is set.
- If Percent Change < maximum allowed percentage change, the alarm is not set.
Example
- calcparm1 = 10
In this example, the Percent Deviation bit is set because the percentage change (79.0319%) of the updated value and the previous value is greater than the calcparm value of 10%.
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((95.322/53.243) -1) X 100 = 79.0319% |
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Alarm Calculation Results — Deviation Percent |
