Despatch P1400+ Temperature Controller - Manual (Page 84)

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Logical Combination of Alarms Type: General Definition
Two alarms may be combined logically to create an AND/OR situation. Any suitable output may be
assigned as a Logical Alarm Output, configured for Reverse-acting or Direct action.
Also refer to
Alarm Operation
Table 27. Logical Alarm Outputs
Logical OR: Alarm 1 OR Alarm 2
Direct Acting Reverse-Acting
OFF OFF OFF OFF OFF ON
ON OFF ON ON OFF OFF
OFF ON ON OFF ON OFF
A
L
A
R
M
1
ON
A
L
A
R
M
2
ON
O
U
T
P
U
T
ON
A
L
A
R
M
1
ON
A
L
A
R
M
2
ON
O
U
T
P
U
T
OFF
Logical AND: Alarm 1 AND Alarm 2
Direct Acting Reverse-Acting
OFF OFF OFF OFF OFF ON
ON OFF OFF ON OFF ON
OFF ON OFF OFF ON ON
A
L
A
R
M
1
ON
A
L
A
R
M
2
ON
O
U
T
P
U
T
ON
A
L
A
R
M
1
ON
A
L
A
R
M
2
ON
O
U
T
P
U
T
OFF
Loop Alarm Enable Type: Controller Parameter
Enables or disables a loop alarm. A loop alarm is a special alarm, which detects faults in the control
feedback loop, by continuously monitoring process variable response to the control output(s). The
loop alarm can be tied to any suitable output. When enabled, the loop alarm repeatedly checks if the
control output(s) are at the maximum or minimum limit. If an output is at the limit, an internal timer is
started: thereafter, if the high output has not caused the process variable to be corrected by a
predetermined amount 'V' after time 'T' has elapsed, the loop alarm becomes active. Subsequently,
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 is no longer at the
limit, the loop alarm is deactivated.
For PID control, the loop alarm time 'T' is always twice the Automatic Reset parameter value. For
On-Off control, a user defined value for the Loop Alarm Time parameter is used.
The value of 'V' is dependent upon the input type. For Temperature inputs, V = 2°C or 3°F. For
Linear inputs, V = 10 least significant display units
Control output limits are 0% for Single output (Primary only) controllers and -100% for Dual output
(Primary and Secondary) controllers.
Correct operation of the loop alarm depends upon reasonably accurate PID tuning. 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.
Display code =
LAEn ,default value = diSA ,
Also refer to Loop Alarm Time , Manual Mode , On-Off Control , Pre-Tune , and Process Variable .