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Chapter 6: Maintaining Your Filtered Enclosure
• External Alarm allows an external signal to sound the alarm,
such as a sash open switch, or a “fail” signal from the building
airflow system.
• Alarm Disable allows an external signal to prevent a “low”
airflow alarm from occurring.
• Night Setback allows an external signal to prevent a “low”
airflow alarm from occurring (not any different from Alarm
Disable above other than the terminology.)
Contact Labconco for ordering information on this special PCB.
Calibration
1. Ensure the flow switch and alarm circuit board are installed
and operational.
2. Allow the enclosure to operate for at least two minutes.
3. If factory installed, the monitor will alarm at 60±10 fpm
with the inflow velocity set at 90±10 fpm.
4. To change the factory setting, set the inflow velocity
required by your Safety Officer to the desired alarm
condition using the speed control adjustment procedure
outlined in Chapter 6.
5. Once the alarm condition is set, use a small screwdriver to
turn the adjustment screw on the airflow switch
counterclockwise (facing the screw) until the “low” airflow
red LED lights and the audible flow alarm sounds.
6. Adjust the inflow velocity to the nominal operating point
required by your Safety Officer.
7. Over time the HEPA filter will load and eventually slow
the inflow velocity. Once the alarm condition is met,
simply increase the speed control outlined in Chapter 6 or
replace the HEPA filter if the speed control is maximized.
8. The table below lists typical alarm conditions based on
normal operating conditions. Typical alarm conditions are
set at face velocities of 10 to 30 feet per minute below the
normal operating conditions due to supply air and exhaust
air fluctuations, as well as room air cross drafts. Consult
your Safety Officer for proper operating speeds.
Enclosure Operating In-Flow
Speed
Alarm Condition Set Point
Speed
100 ± 10 fpm 70-90 fpm
90 ± 10 fpm 60-80 fpm
80 ± 10 fpm 50-70 fpm
70 ± 10 fpm 50-60 fpm
60 ± 10 fpm 50 fpm