Delta Over Time Alarm Calculations

There are three variations of the Delta Over Time alarm calculation. These alarm calculation types can only be implemented with the CygNet Enhanced Point Scheme. See Understanding the CVS Metadata File for more information about the elements and attributes that define a CygNet Point Scheme.

See the following subsections for details:

• Delta Value Over Time
• Delta Value Over Time Positive
• Delta Value Over Time Negative

The number of entries stored for this calculation is specified by the histvaluecount attribute in the CvsMetadata file for a CygNet Enhanced Point Scheme.

For more information, see Alarm Calculation Types.

Delta Value Over Time

The Delta Over Time alarm uses the Delta Value Over Time (DELTA_OVER_TIME) calculation. On each update, the system finds the first value that is older than the time interval specified, calculates the value and time deltas between that value and the updated value, and gets the Delta Over Time rate from those two values. If the absolute value of the Delta Over Time rate exceeds the MaxRate of calcparm1/calcparm2, the alarm is set.

Calculation Parameters

The calculation parameters for this alarm are user-provided:

• Maximum EU Difference Allowed (calcparm1) — maximum allowed change of value over the specified time interval before the alarm is set.
• Time Interval (sec) (calcparm2) — the time span used to determine the difference (delta) of the two values.

Preliminary Calculations

MaxRate = calcparm1/calcparm2   Delta Value = Updated (current) Val - Newest Val Older than Time Interval   Seconds between values = Updated time - Time of Newest Val Older than Time Interval

Equation

Delta Over Time = Delta Value / Seconds between values

• If (ABS) Delta Over Time > MaxRate, alarm is set.
• If (ABS) Delta Over Time ≤ MaxRate, alarm is not set.

Example

• calcparm1 = 10
• calcparm2 = 30

In this example, the Delta Over Time bit is set because the Delta Over Time rate (0.5384) is greater than the MaxRate (0.333).

MaxRate = 10/30 = 0.333   Delta = 36 -15 = 21   Seconds between values = 27:10 - 26:31 = 39 sec.   Delta Over Time = 21/39 = 0.5384 (exceeds MaxRate of 0.333, so bit is set)

Alarm Calculation Results — Delta Value Over Time

Delta Value Over Time Positive

The Positive Delta Over Time alarm uses the Delta Value Over Time Positive (DELTA_OVER_TIME_POS) calculation. On each update, the system finds the first value that is older than the time interval specified, calculates the value and time deltas between that value and the updated value, and gets the Delta Over Time rate from those two values. If the Delta Over Time rate exceeds the MaxRate of calcparm1/calcparm2, the alarm is set.

The following image shows the area of an Analog Alarm Settings page of a PNT Editor with an enabled Pos. Delta over Time alarm using the Delta Value Over Time Positive calculation type:

Alarm Calculation Configuration — Delta Value Over Time Positive

Calculation Parameters

The calculation parameters for this alarm are user-provided:

• Maximum EU Difference Allowed (calcparm1) — maximum allowed change of value over the specified time interval before the alarm is set.
• Time Interval (sec) (calcparm2) — the time span used to determine the difference (delta) of the two values.

Preliminary Calculations

MaxRate = calcparm1/calcparm2   Delta Value = Updated (current) Val - Newest Val Older than Time Interval   Seconds between values = Updated time - Time of Newest Val Older than Time Interval

Equation

Delta Over Time = Delta Value / Seconds between values

• If Delta Over Time > MaxRate, alarm is set.
• If Delta Over Time ≤ MaxRate, alarm is not set.

Example

• calcparm1 = 1.01
• calcparm2 = 30

In this example, the Positive Delta Over Time bit is set because the Delta Over Time rate (2.5) is greater than the MaxRate (0.0336).

MaxRate = 1.01/30 = 0.0336   Delta = 97 - 12 = 85   Seconds between values = 10:15:18 - 10:14:44 = 34 sec.   Delta Over Time = 85/34 = 2.5 (exceeds MaxRate of 0.0336, so bit is set)

Alarm Calculation Results — Delta Value Over Time Positive

Delta Value Over Time Negative

The Negative Delta Over Time alarm uses the Delta Value Over Time Negative (DELTA_OVER_TIME_NEG) calculation. On each update, the system finds the first value that is older than the time interval specified, calculates the value and time deltas between that value and the updated value, and gets the Delta Over Time rate from those two values. If the Delta Over Time rate is less than the negative MaxRate of calcparm1/calcparm2, the alarm is set.

The following image shows the area of an Analog Alarm Settings page of a PNT Editor with an enabled Neg. Delta over Time alarm using the Delta Value Over Time Negative calculation type:

Alarm Calculation Configuration — Delta Value Over Time Negative

Calculation Parameters

The calculation parameters for this alarm are user-provided:

• Maximum EU Difference Allowed (calcparm1) — maximum allowed change of value over the specified time interval before the alarm is set.
• Time Interval (sec) (calcparm2) — the time span used to determine the difference (delta) of the two values.

Preliminary Calculations

MaxRate = calcparm1/calcparm2   Delta Value = Updated (current) Val - Newest Val Older than Time Interval   Seconds between values = Updated time - Time of Newest Val Older than Time Interval

Equation

Delta Over Time = Delta Value / Seconds between values

• If Delta Over Time < - MaxRate, alarm is set.
• If Delta Over Time ≥ - MaxRate, alarm is not set.

Example

• calcparm1 = 1.01
• calcparm2 = 30

In this example, the Negative Delta Over Time bit is set because the Delta Over Time rate (-0.0571) is less than the -MaxRate (-0.0336).

MaxRate = 1.01/30 = 0.0336   Delta = 20 - 32 = -12   Seconds between values = 15:07:24 - 15:03:54 = 210 sec.   Delta Over Time = -12/210 = -0.0571 (less than - MaxRate of -0.0336, so bit is set)

Alarm Calculation Results — Delta Value Over Time Negative