Default Alarm Calculations

There are several default calculation types that are associated with point types and are included in the CygNet Standard Point Scheme.

For more information, see Alarm Calculation Types.

See the following subsections for details:

• Deviation Value
• Digital Value Equal
• Maximum Value
• Minimum Value
• String Filter
• Value Range

Deviation Value

The Deviation alarm uses the Deviation Value (DEVIATION_VAL) calculation. On each update, the system calculates the change in engineering units from the previous value and sets the alarm bit if the change equals or exceeds the threshold. This alarm calculation uses Calculation Parameter 1 only.

The following image shows the area of an Analog Alarm Settings page of a PNT Editor with an enabled High Deviation calculation.

Calculation Parameter

• Deviation Value (calcparm1) – maximum allowed threshold change before the alarm bit is set

Equation

• If deviation value ≥ maximum allowed change, alarm is set.
• If deviation value < maximum allowed change, alarm is not set.

Example

• calcparm1 = 25

In this example, the High Deviation bit is set because the absolute change in value (-79.052) is greater than the calcparm value of 25.

Digital Value Equal

The Digital alarm uses the Digital Value Equal (DIGITAL_EQUAL) calculation. On each update, if the value matches the state selected by the user, then the alarm bit is set, otherwise it is cleared. This alarm calculation uses Calculation Parameter 1 only.

The following image shows the area of a Digital Alarm Settings page of a PNT Editor with an enabled Digital Alarm calculation.

Calculation Parameter

• Applies when Off? (Y/N) (calcparm1) – Digital State/Value

• On update, if current value = digital state/value, alarm is set.
• On update, if current value ≠ digital state/value, alarm is not set.

Example

• calcparm1 = N

In this example, the Digital Alarm bit is set because the updated state matches the calcparm state (N).

Maximum Value

The High Alarm and High Warning alarms use the Maximum Value (MAX_VALUE) calculation. On each update, the system will check the value and set the alarm bit if it is equal to or more than the threshold. This alarm calculation uses Calculation Parameter 1 only.

The following image shows the area of an Analog Alarm Settings page of a PNT Editor with an enabled High Alarm calculation.

Calculation Parameter

• Setpoint Value (calcparm1) — threshold value at which the alarm is set when the updated value equals or exceeds the setpoint

• On update, if current value ≥ setpoint value, alarm is set.
• On update, if current value < setpoint value, alarm is not set.

Example

• calcparm1 = 150

In this example, the High Alarm bit is set because the updated value (165.1762) exceeds the calcparm1 value (150).

Minimum Value

The Low Alarm and Low Warning alarms use the Minimum Value (MIN_VALUE) calculation. On each update, the system will check the value and set the alarm bit if it is less than or equal to the setpoint value. This alarm calculation uses Calculation Parameter 1 only.

The following image shows the area of an Analog Alarm Settings page of a PNT Editor with an enabled Low Warning calculation.

Calculation Parameter

• Setpoint Value (calcparm1) — threshold value at which alarm is set when the updated value is at or below this value

• On update, if current value ≤ setpoint value, alarm is set.
• On update, if current value > setpoint value, alarm is not set.

Example

• calcparm1 = 12

In this example, the Low Warning bit is set because the updated value (11.84) is less than the calcparm1 value (12).

String Filter

The String Alarm has two calculation options: String Filter case-insensitive (STRING_VAL_CI) and String Filter case-sensitive (STRING_VAL_CS). On each update, if the new value matches the calcparm1 comparison string (without regards to case for case-insensitive, and with regards to case for case-sensitive) the alarm bit is set, otherwise it is cleared. This calculation supports wildcards. This alarm calculation uses Calculation Parameter 1 only.

The following image shows the area of a String Alarm Settings page of a PNT Editor with an enabled String Filter (case-insensitive) calculation.

Calculation Parameter

• Setpoint Value (calcparm1) — user-provided comparison string.

• On update, if current value = setpoint value, alarm is set.
• On update, if current value ≠ setpoint value, alarm is not set.

Example

• calcparm1 = EXCEPTION

In this example for a STRING_VAL_CI calculation, the String Alarm bit is set because the updated value (Exception) matches the calcparm1 value (regardless of case).

Value Range

The various Out-of-Range alarms use the Value Range (VALUE_RANGE) calculation. On each update, the system will check the value and set the alarm bit if it is outside the allowed range.

The following image shows the area of an Analog Alarm Settings page of a PNT Editor with an enabled Out-of-Range calculation.

Calculation Parameter

• High OOR Value (calcparm1) — maximum engineering units threshold
• Low OOR Value (calcparm2) — minimum engineering units threshold

• On update, if current value ≥ maximum threshold or ≤ minimum threshold, alarm is set.
• On update, if current value is within the range between maximum and minimum thresholds, alarm is not set.

Example

• calcparm1 = 25
• calcparm1 = 3

In this example, the Out-of-Range bit is set because the updated value (2) is outside the range defined by calparm1 and calcparm2.