West Control Solutions N8100 - Manual (Page 22)

if the saturated output has not caused the process variable to be corrected by a
pre-determined amount V after a time T has elapsed, the Loop Alarm goes active.
Subsequently, the Loop Alarm facility 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 saturated output comes out of saturation, the Loop
Alarm is de-activated.
For PID control, the Loop Alarm Time T is always set to twice the value of the Reset
(Integral Time Constant) parameter. For On/Off control, the user-defined value of
the Loop Alarm Time Set Up parameter (see Subsection 2.2.28) is used.
The value of V is dependent upon the input type:
° C ranges: 2 ° C or 2.0 ° C
° F ranges: 3 ° F or 3.0 ° F
Linear ranges: 10 least significant display units
For single output Controllers, the saturation limits are 0% and Out1Max%. For dual
output Controllers, the saturation limits are –100% and Out1Max%.
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 facility. Upon exit from Manual
Control Mode or after completion of the Pre-Tune routine, the Loop Alarm is
automatically re-enabled.
2.2.28 Loop Alarm Time
When full ON/OFF control is selected (i.e. Proportional Band 1 is set to 0) and Loop
Alarm is enabled, this parameter determines the duration of the saturation
condition after which the Loop Alarm will be activated. This parameter is omitted
from the Set Up display sequence if ON/OFF control is not selected or Loop Alarm
is disabled.
2.2.29 Scale Range Decimal
Point
This parameter, applicable only if a linear
input is fitted, defines the position of the
decimal point in values of the process
variable, setpoint, alarm levels and
recorder outputs as shown on the right.
2-11 O054-2
59125
Value Decimal Point Position
0 xxxx
1 xxx.x
2 xx.xx
3 x.xxx