The HI SASH POS ALARM item is used to set the position of
the high sash alarm. INPUT SEL 1, must be set to SASH POS
VERT before setting this item.
NOTE: The Sash Position Potentiometer must be calibrated
before using this menu item.
The DAMPER ALARM item sets the damper opening alarm
setpoint for both Normal and Setback modes. If the Model
FHC50 controller opens the damper more than the DAMPER
ALARM setpoint, it will activate Relay B.
NOTE: Relay B must be configured to DAMPER OPEN for the
DAMPER ALARM to be active.
DAMPER ALARM activates Relay B. DAMPER
ALARM does not activate audible or visual alarms.
SETPOINT/ALARM CONSTRAINTS
There are a number of constraints that prohibit you from incorrectly adjusting the set points. These are as follows:
1. The control SETPOINT and SETBACK set point have a lower limit of 60 ft/min. This is because generally accepted lab practices
indicate that fume hood containment is lost below this face velocity.
2. The controller has been designed so that the LOW ALARM set point must be set at least 20 ft/min below the control SETPOINT when
the FHC50 is set for face velocity control and 50 cfm when the FHC50 is set for flow control. For example, if the control SETPOINT is
100 ft/min, the LOW ALARM set point cannot be greater than 80 ft/min. This prevents nuisance alarms from occurring during natural
system fluctuations.
3. The controller has been designed so that the HIGH ALARM set point must be set at least 20 ft/min above the control SETPOINT
when the FHC50 is set for face velocity control and 50 cfm when the FHC50 is set for flow control. For example, if the control
SETPOINT is 100 ft/min, the HIGH ALARM set point cannot be less than 120 ft/min. This prevents nuisance alarms from occurring
during natural system fluctuations.
4. The monitor has been designed so that the LOW ALARM set point must be at least 40 fpm below the HIGH ALARM set point when
the FHM10 is set for face velocity control and 100 cfm below the HIGH ALARM set point when the FHM10 is set for flow control.
5. The ALARM RESET item selects how the alarms will terminate when controller returns to the safe range. The face velocity alarms all
terminate the same; they are either LATCHED or UNLATCHED. If UNLATCHED is selected, the low alarm automatically turns off
when the face velocity exceeds the low face velocity alarm value by 20 ft/min or the low flow alarm value by 50 cfm. Conversely, the
high alarm automatically turns off when the face velocity drops 20 ft/min below the high face velocity alarm set point or 50 cfm below
the high flow alarm set point. If LATCHED is selected, the alarms will not terminate until the RESET key is pressed.
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