Almlimit Row Edit: General Limits tab

HiHi Alarm Check

Select to configure the HighHigh alarm limits. For further information, refer to RealTime tables.

Hi Alarm Check

Select to configure the High alarm limits. For further information, refer to RealTime tables.

Lo Alarm Check

Select to configure the Low alarm limits. For further information, refer to RealTime tables.

LoLo Alarm Check

Select to configure the LowLow alarm limits. For further information, refer to RealTime tables.

HiHi Alarm Limit

Enter the HighHigh alarm limit.

Hi Alarm Limit

Enter the High alarm limit.

Lo Alarm Limit

Enter the Low alarm limit.

LoLo Alarm Limit

Enter the LowLow alarm limit.

Enable ROC Alarm

Select to enable the Rate Of Change (ROC) alarm. If the rate of change exceeds the configured rate of change limits, the system generates an alarm.

For further information, refer to RealTime tables.

ROC Type

Select the method to use in calculating the ROC.

Options:

• baseline method - use the baseline method

• custom method - use the baseline method with the additional fields below:

  • Negative Rate of change limit

  • Time Interval for ROC

    In the baseline method, the system calculates the ROC as the difference between the current and previous poll, divided by the difference in time between these consecutive polls. This yields a rate in Engineering Units (EGUs) per second, which the system then compares against the ROC limit. The system generates an alarm if either positive or negative ROC occurs.

    The custom method works to reduce nuisance alarms by allowing you to specify the delta time between values, as opposed to the system calculating the ROC between consecutive polls. In addition, the custom method allows for different ROC limits for positive and negative ROC.

    The system calculates custom ROC by recording multiple poll cycles (up to 30) and calculating the ROC between values that are separated in time by at least the delta time value that you specify (Time Interval for ROC):

    ROC = (Current Value - Value at Delta Time ago) / Delta Time

    Where:

    "Delta Time" = Time Interval for ROC.

    It is best to set the Delta Time to a multiple of the poll cycle time. For example, if poll cycles are 10 seconds, set the Delta Time to a value divisible by 10.

    Note: Baseline alarms are not persistent. However, Custom ROC alarms are persistent. Subsequent to a Custom ROC alarm, the system continues to calculate the ROC each poll using the above method, and maintains the alarm state so long as the ROC over the Delta Time exceeds limits. For custom ROC alarms, once the limit is no longer exceeded, a return-to-normal alarm will be generated.

Rate Of Change limit (Units/ Sec)

Enter the maximum, positive allowable ROC (Engineering Units (EGUs) per second).

Negative Rate of change limit (Units/Sec)

Enter the maximum, negative allowable ROC (EGUs per second).

Time Interval for ROC (Units/ Sec)

Enter the time interval over which the system should calculate the ROC.

Creep Detection Enabled

Select to enable the Creep Detection alarm. If the almlimit value creeps out of its calibrated state by a value that exceeds the Creep Deviation Alarm Limit, the system generates an alarm.

For further information, refer to RealTime tables.

Creep Deviation Limit

Enter the maximum deviation value (EGUs) that is acceptable before calibration deteriorates.

Flatline Detection Enabled

Select the checkbox to enable Flatline Alarming. If an analog, a rate, or a flowTotalConfig value does not change within the Timeout value (min), the system generates an alarm.

Timeout value (min)

Enter the maximum amount of time (in minutes) that can pass without an analog, a rate, or a flowTotalConfig value changing.