West Control Solutions MRC 9000 - Manual (Page 119)

Edition 3
Rev G
Section 4 4-37
11. Press the to advance to the next parameter, ALARM 1 TYPE.
* When CONTROL LOOP OPEN is selected for ALARM TYPE and NON PID is selected for CONTROL TYPE (CONTROLLERS section of
CONFIGURATION), prompt LOOP ALARM TYPE will be displayed
The CONTROL 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 facility repeatedly checks the control output(s) for saturation. For PID, saturation is either or both
outputs being at the maximum or minimum. For On/Off control, saturation is the control output being ON. If an
output is found to be in saturation, a timer is started; thereafter, if the saturated output has not caused the process
variable to be corrected by a pre-determined amount (V) after a time (Loop Alarm Time) 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 the value in the correct sense, or when the output comes
out of saturation, the Loop Alarm is de-activated.
For PID contron, the internal Loop Alarm Time is always set to twice the inverse of the reset value (Integral Time
Constant) parameter. For ON/OFF control, the value of the LOOP ALARM TIME parameter is used..
The value of V is dependant upon the input type:
Temperature: 2 o C or 2 o F
Linear Ranges: 10 least significant display units
For a single output controller, the saturation condition is simply 0% and OUT 1 MAX %. For dual output control-
lers, the saturation condition considers the combination of the two output types, reverse or direct, and responds
accordingly.
NOTES: Correct operation of the Loop Alarm depends upon reasonably accurate PID tunings and the Loop
Alarm is automatically disabled during manual control. Upon exit from manual control, the Loop Alarm is auto-
matically re-enabled (if selected).
Note: Process Values
must have been defined
previously in order for
ALARM prompts to
appear.
Ax1 ALARM TYPE
OFF
Selections for recorder only
OFF
PROCESS - HIGH
PROCESS - LOW
RATE - RISING
RATE - FALLING
Additional selections for use
with controller option
BAND - WITHIN
BAND - OUTSIDE
DEVIATION - ABOVE
DEVIATION - BELOW
CONTROL LOOP OPEN*
Press the to change, then to
desired value, then press the .
P
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