Process Alarms
Process alarms alert you when the module has exceeded configured high or low limits for
each channel. You can configure the following alarm trigger points in Engineering
Units:
- High High
- High
- Low
- Low Low
To use the Process Alarms, you must complete the following tasks:
- Enable the alarms
- Configure the trigger points
Enable Process Alarms
When the module tags are created, the Process Alarm tags are disabled by default.
To enable, uncheck Disable All Alarms, and then enable individual process alarms in
output tags (example,
O.Chxx.LAlarmEn
= 1).Configure Alarm Trigger Points
You must configure the Process Alarm with a trigger point. That is, set values in
Engineering Units that, once the signal reaches the value, the alarm is
triggered.
Process Alarm trigger points are related to the Scaling parameters that you configure
for the channel. The Engineering Units that are established in Scaling determine the
Process Alarm trigger points. That is, the available trigger point values are in
engineering units.
For example, consider a channel that uses the Current (mA) input type, the 4…20 mA
input range, and scales the High and Low Engineering values of 100% and 0%,
respectively. The available Process Alarm values range from 0…100.
In this case, if the High Limit alarm is set to 50%, when the input signal reaches 12
mA, the High Limit alarm is set. The alarm is set because Scaling was configured for
Percentage of Full Scale and a signal value of 12 mA is 50% of the full scale of
engineering units.
IMPORTANT:
Process Alarm values are in engineering units and must be recalculated when
the scaling parameters are changed. Recalculate Units in the Module
Properties dialog helps to recalculate the Process Alarm values and all
other configurations with engineering units. Failure to update the Process
Alarm values can cause the alarm alert not to take effect that could be
misinterpreted as a hardware problem.
For example, an analog input module channel that uses Current (mA) input type
with Process Alarms enabled has the following configuration parameters:
- Scaling values:
- High Engineering = 100.0000%
- Low Engineering = 0.0000%
- Process Alarming:
- High High Limit = 100.0000%
- High Limit = 100.0000%
- Low Limit = 0.0000%
- Low Low Limit = 0.0000%
If you change the scaling High/Low Engineering values to 5 Kg/0 Kg,
Recalculate Units suggest changing the Process Alarm values to 5/0 to make
sure that the application continues to operate as expected.
Alarm Deadband
You can configure an alarm deadband to work with these alarms. The deadband lets the
process alarm status bit remain set, despite the alarm condition disappearing, as
long as the input data remains within the deadband of the process alarm.
The following graphic shows input data that sets each of the four alarms at some
point during module operation. In this example, latching is disabled; therefore,
each alarm turns Off when the condition that caused it to set ceases to exist.
Alarm Deadband Alarm Settings
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