TEL AFA4000/2, Installation And Operating Manual

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AFA4000/2 Airflow Monitor / p.45
airflow through the sensor. This will lead to too much sensitivity being required to
calibrate the unit which can lead to instability of the readings or incorrect readings at
low velocities.
3. For fume cupboards with a single-skin side-wall, or double-skin, with a small gap
between them, it may not be possible to achieve the ideal sensing position using a
flexible tube.
With a single-skin side-wall it is possible to fix the sensor on the outside of the fume
cupboard and connect directly to the inner chamber in the ideal position. This
method can only be used for up to two fume cupboards when they are positioned
side by side, using the two outer walls.
An alternative method is to mount the sensor on the front of the fume cupboard and
connect it using a short flexible tube to a rigid wall tube attached to the inner side-
wall. Position the open end of this rigid wall tube in the ‘ideal position’ for example,
100 mm back from the sash, and 100 mm higher than the normal sash opening.
Fume cupboards with a large internal height can present a difficulty because the tube
length to reach the ideal position may be longer than 1m. Where possible, use a tube
of 1 metre or less, which may result in a sensing position higher than the ideal.
When fitting a sensor to a ’narrow wall’ fume cupboard for the first time, it may be
necessary to try various combinations of rigid and flexible tube to find the best
combination and position.
4. The sensor should not be mounted in a position where it is subject to draughts from
the laboratory air input or ventilation system.
5.2 Installation
5.2.1 AFA4000/2
1. Use the cut-out details provided with the unit (Figure 17) to cut-out and drill the
holes in the fume cupboard for the AFA4000/2 mounting bracket.
Make sure that the AFA4000 fits into the cut-out before proceeding.