D8 Series User’s Guide
Chapter 4: Operation and Setup
76
Alarm High and Alarm Low
An alarm high occurs if the process variable rises above a user-specified value. An alarm low occurs
if the process variable drops below a separate user-specified value. See Figure 4.7 below.
Enter the alarm high and low set points at the
Alarm high SP
and
Alarm low SP
parameters in the
Alarms
menu.
Set point
Alarm high SP
Alarm low SP
}
Hysteresis
Alarm high on
Alarm high off
Alarm low on
Alarm low off
High deviation
alarm off
High deviation
alarm on
Low deviation
alarm off
Low deviation
alarm on
Set point + HiDeviation value
Set point - HiDeviation value
}
Hysteresis
}
Hysteresis
}
Hysteresis
Figure 4.7
– Activation and Deactivation of Process Alarms
Deviation Alarms
A deviation alarm occurs if the process deviates from set point by more than a user-specified
amount; see Figure 4.7 above. You can set separate high and low deviation values at the
HiDeviation
value and
LoDeviation
value parameters in the
Alarms
menu.
Upon power up or when the set point changes, the behavior of the deviation alarms depends upon
the alarm function:
• If the alarm function parameter is set to
standard
, then deviation alarms do not activate until
the after the process variable has first come within the deviation alarm band. This prevents
nuisance alarms.
• If the alarm function parameter is set to
boost
, then the deviation output switches on
whenever the set point and process variable differ by more than the deviation setting,
regardless of whether the process variable has been within the deviation band. This allows
you to use boost control upon power up and set point changes.
Global Alarm
The D8 comes equipped with a global alarm output. The global output is activated if one or more of
the following conditions occurs:
• A system alarm occurs, or
• A failed sensor alarm occurs and is unacknowledged, or
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