GasCheck
Operating Manual V2.4
4
3.1 B
Mechanical Installation - GasCheck with linearisation Board
Four mounting holes suitable for M4 screws are provided on a 45 x 140mm
grid. If spacers are used, these should be a least 6mm high to provide
adequate clearance for the surface-mount components on the underside of the
PCB.
3.2
Aspiration
The sensors are available with two options for the aspiration of the cell:
pumped aspiration
diffusion aspiration through a permeable Vion strip (only available for
the GasCheck with self-referencing option)
3.2.1
Pumped aspiration
With pump-aspirated sensors, a separate pump is required to flow gas into the
sensor. The flow rate should be between 0.2 and 1.0 litres per minute. Lower
flow rate will lead to slow response times; higher flow rates will cause the
output to become unstable. In calculating the response time, consideration
should be given to the dead volume within the complete system comprising
both the sensor head and the pipework. The dead volumes for the various
sensor heads are:
Range
Dead volume
3000 ppm
9 cm
3
3 %
4 cm
3
10 %
4 cm
3
Connection to the sensor is via the barbed gas ports on the side of the head.
These are suitable for N3 (3 mm bore) soft flexible tubing. Neoprene and PVC
tubing is suitable, but other materials may be used provided that they are
compatible with the gas stream. Natural rubber is not recommended due to its
tendency to perish. Silicone rubber tubing is not suitable because it readily
absorbs and releases CO
2
.
Since the gas flows through the instrument, it is essential that particulate
contamination be removed from the gas stream. A filter which is capable of
removing particles above 1
m in size should be fitted upstream of the sensor.
It is good practice to use a hydrophobic filter (which prevents the passage of
liquid water) such as a porous PTFE membrane. Suitable filters are available
from Edinburgh Instruments Ltd.
