Nivetec UNICONT PMM-500, User And Programming Manual

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pmm5111a0600p_01
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PARAMETER
SV-
DISPLAY
PV-
DISPLAY
ADJUSTMENT RANGE
DEFAULT
VALUE
Deviation
Alarm 2 Value
Only visible when

=

set
Parameter is repeated
in Set-up Mode

±span from setpoint 5
Band Alarm 2 Value
Only visible when

=

set
Parameter is repeated
in Set-up Mode

1 LSD to full span from setpoint 5
Alarm 2
Hysteresis
Parameter is repeated
in Set-up Mode

1 LSD to
100% of
span (in
display
units) on
“safe” side
of alarm
point As for Alarm 1. 1
Disabled:

Loop Alarm Enable

Enabled:

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
 -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.
