20
Part Two
ALARM CONSTRAINTS
There are a number of constraints built into the software that prevent users from programming conflicting alarm information. These are as follows:
1. The AOC does not allow the pressure alarms to be programmed within 20 ft/min (0.00028 in. H
2
O at 0.001 in. H
2
O) of the control set point.
Example: The control
SET POINT
is set at -0.001 in. H
2
O. The
LOW ALARM
set point cannot be set higher than -0.00072 in. H
2
O. Conversely, the
HIGH ALARM
set point cannot be set lower than -0.00128 in. H
2
O.
2. The minimum flow alarm:
MIN SUP ALM
must be programmed to be at least 50 CFM less than the minimum flow set point.
3. The pressure alarms:
LOW ALARM, HIGH ALARM
can be programmed for positive or negative pressure. However, both the low and high alarm must be
set either positive or negative. The AOC does not allow one positive alarm and one negative alarm.
4. Alarms do not terminate until the pressure or flow slightly exceeds alarm set point.
5. The
ALARM RESET
item selects how the alarms will terminate when controller returns to the safe range. The pressure and flow alarms all terminate the
same; they are either latched or unlatched. If unlatched is selected, the alarms automatically turn off when the value slightly exceeds set point. If latched is
selected, the alarms will not terminate until the controller returns to set point
and
the
RESET
key is pressed.
6. There is a programmable
ALARM DELAY
that determines how long to delay before activating the alarms. This delay affects all pressure, remote and flow
alarms.
7. The
MUTE TIMEOUT
item sets the length of time the audible alarm is off for all pressure and flow alarms.
8. The display can only show one alarm message. Therefore, the controller has an alarm priority system, with the highest priority alarm being displayed. If
multiple alarms exist, the lower priority alarms will not display until after the highest priority alarm has been eliminated. The alarm priority is as follows:
Pressure sensor - low alarm
Pressure sensor - high alarm
Low supply flow alarm
Low exhaust flow alarm
Data
error
9. The low and high pressure alarms are absolute values. The chart below shows how the values must be programmed in order to operate correctly.
-0.2 inches H
2
O
0
+0.2 inches H
2
O
(maximum negative)
(maximum positive)
High Negative
Low Zero
Low
Positive High
Negative
Set point
Negative
Positive
Set point
Positive
Alarm Alarm
Alarm Alarm
The value of each set point or alarm is unimportant (except for small dead band) in graph above. It is important to understand that the negative (positive) low
alarm must be between zero (0) pressure and the negative (positive) set point, and that the high alarm is a greater negative (positive) value than set point.
