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hoods this low point is on the bottom row in the centre and is a convenient position to
measure and for future reference when checking the alarm during annual maintenance.
4.
Take time when measuring the face velocities for the calibration procedure to allow for
the velocities across the open sash to stabilise. If the velocities are changing or are
turbulent during the sampling period the alarm will detect this and ask you to repeat the
sample.
5.
When using a Fume Hood with Horizontal Sliding sashes open the sashes to the normal
max safe working opening for the Low Air sample.
6.
When calibrating or re-calibrating the alarm it is important to ensure that the Adapter and
hose is connected to the SM6 sensor on the fume hood as per figure 2. If the Adapter and
hose is not connected the sensor will not ‘see’ a change in the airflow during the
calibration procedure and when switched to the Run condition the display will show a
fixed reading that will not change when the fume cupboard velocity changes. This only
applies during the calibration mode. If in normal running after successful calibration the
vent kit becomes disconnected the air flow across the sensor will fall and the alarm will
go into the AIR FAIL condition.
2.4 Calibration Guidelines :-
1.
Calibrate the airflow monitor according to the instructions in set 2.1. To successfully
calibrate the monitor, it will be necessary to change the face velocity by moving the sash
position. Typical calibration conditions are set to face velocity air sample differences of
at least 20 feet per minute. The airflow monitor is factory set to be calibrated with a
difference of at least 50 fpm and can be changed by changing the “lower/higher air
sample difference”. The following suggested in flow face velocity speeds are
recommended to successfully calibrate. Typical low air alarms are set 10-20 fpm below
operation speeds. Follow step 2 below
.
Low Air
Alarm Set
Point
Hood
Operating in
Flow Speed
Low
Calibration
Set Point
High
Calibration
Set Point
40 – 50 fpm
60 fpm
40 – 60 fpm
100 – 120 fpm
60 – 70 fpm
80 fpm
50 – 90 fpm
100 – 150 fpm
80 – 90 fpm
100 fpm
50 - 110 fpm
100 – 170 fpm
