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The tment of the plate should then be checked to ensure a gas tight seal has been achieved. The
bulb should be depressed whilst blocking the adjacent port with a nger; the T4 may at this point
indicate an alarm on the O
2
sensor this is due to the pressure effect on the oxygen sensor. The hand
aspirator bulb should not return to the rounded shape if a gas tight seal has been achieved. If the
bulb does return to is normal shape, reposition the aspirator plate and repeat this test.
Allow the O
2
sensor to stabilise before continuing.
The sample hose must then be attached to the aspirator plate on the left hand side (as viewed from
the front) adjacent to the base of the arrow on the aspirator plate.
Place the sample tube into the area to be sampled and depress the aspirator bulb. Allow the bulb to
return to its rounded shape and then depress the bulb again. Repeat this process to get a constant
sample ow to the sensors.
Every depression of the aspirator bulb should pull the sample approximately 25cm up the tube.
Therefore to sample from a 5 meter hose – at least 20 aspirations will be required, however a
minimum of 1 minute is recommended to ensure a stable sample is read.
The maximum length of the sample hose allowable is 30m.
It should be noted that for sample hose lengths greater than 5m the oxygen sensor may initially go
into a falling alarm state for approximately 1 minute, due to pressure effects, before settling back
down to read accurately.
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