MIC 1400 Manual
Edition 1
45
Loop Alarm Enable
This parameter is the means by which the user can enable or disable the
Loop Alarm. The Loop Alarm is a special alarm which detects faults in the
control feedback loop by continuously monitoring process variable re-
sponse to the control output(s).
The Loop Alarm, when enabled, repeatedly checks the control output(s) for
being at the maximum or minimum limit. If an output is found to be at the
limit, the Loop Alarm mode starts a timer; thereafter, if the high output has
not caused the process variable to be corrected by a predetermined
amount V after a time T has elapsed, the Loop Alarm goes active. Subse-
quently, the Loop Alarm mode repeatedly checks the process variable and
the control output(s). When the process variable starts to change value in
the correct sense or when the output comes below the limit, the Loop Alarm
is deactivated.
For PID control, the Loop Alarm Time T is always set to twice the value of
the Auto Reset parameter. For ON/OFF control, the user defined value of
the Loop Alarm Time Set Up parameter is used.
The value of V is dependent upon the input type:
Deg C:
2
°
C or 2.0
°
C
Deg F:
3
°
F or 3.0
°
F
Linear Range:
10 least significant display units
For single output instruments, the limits are 0% and Out 1 Max %. For dual
output instruments, the limits are -100% and Out 1 Max %.
Notes:
1. Correct operation of the Loop Alarm depends upon reasonably accurate
PID tuning.
2. The Loop Alarm is automatically disabled during Manual Control mode
and during execution of the Pre-Tune mode. Upon exit from Manual mode
or after completion of the Pre-Tune routine, the Loop Alarm is automatically
re-enabled.
