MAN0585.P65
Issue 01 - 11/99
2987M5023
74
the concentration of the gas at the end of the tubing. This effect
is known as adsorption and is more noticeable with certain
gases, particularly hydrogen sulphide, sulphur dioxide and
chlorine.
For example, when using 75ppm hydrogen sulphide in 5mm
diameter neoprene tubing the reduction in gas concentration is
approximately 1ppm/metre. That is, the concentration would
be reduced to 70ppm at the end of a 5 metre length of tubing.
If the inside of the tubing is wet, the adsorption effect on
hydrogen sulphide is aggravated and the resulting reduction in
concentration could be as high as 5 or 6ppm/metre.
WARNING
PTFE tubing MUST be used for chlorine or sulphur dioxide
test gas - rubber is NOT suitable.
If it is suspected that the tubing is wet, it should be dried by
hanging vertically (with both ends pointing downwards) for at
least 24 hours. DO NOT attempt to dry it with a compressed air
supply as this may leave traces of silicone oil which can damage
or affect the response of the Minigas Mk5 sensors.
6. CALIBRATING THE MINIGAS MK5
Figure 4 Gas Calibration Kit
Flow Regulator
Pressure
Gauge
On/Off Valve
Gas Tube
Calibration
Hood
Minigas
Gas
Cylinder
Carrying
Case