OMGEMN1.41
GEM2000 Range Gas Analysers
Page 60
Copyright 2009 Geotechnical Instruments (UK) Limited
Instructions for Use - Mixture 2:
When using the gas mixture 2 to perform a full user calibration of the gas analyser it is
advisable to follow this sequence of operations.
It is probably easiest at this point to set the span values of the different gases that will be
used to calibrate the instrument. The span value is the concentration of the calibration
gas.
Step 1
From the ‘Main Gas Read Screen’ select ‘Menu’.
Select ‘Key 1’ from the menu and use ‘Key 8 - Scroll Down’ and select
‘Field Calibration’.
From the ‘CHECK CALIBRATION’ screen select ‘Key 3’ to edit target
concentrations.
Scroll and press the ‘Enter’ key to select required gas channel.
Enter the appropriate value for the highlighted channel then press the
‘Enter’ key.
Step 2
When using gas mixture 2 set CH
4
at 5%, CO
2
at 10% and O
2
at 20.8%
(air).
Press the ‘Enter’ key.
Step 3
Go on to Zero All Channels Process
In addition to the calibration process the gas analyser should have the
methane and any auxiliary channel zeroed prior to taking readings at
the start of the monitoring session. For this zeroing operation none of
the calibration equipment is required. Remove gas source if attached.
Ensure this operation is performed in clean fresh air.
Step 4
Press
and allow the pump to run for approximately two minutes or
until reading stabilises; this purges the unit of gas.
Step 5
Press
to switch off the pump.
Step 6
Zero All Channels
From the ‘Check Calibration’ screen:
Press
to select ‘Calibration Menu’.
Press
to select ‘Zero Channels’.
Press
to select ‘Zero ALL’.
‘USER ZERO COMPLETE’ should be displayed.
Alternatively, the option ‘ZERO CH4’ is available from the ‘ZERO
CHANNELS’ menu. Selecting this option will zero all of the channels
except CO
2
and
O
2.
Repeat for other channels if required (except O
2
)
Step 7
Go on to Zero O
2
Channel Process with Mixture 2
Unlike zeroing the methane or auxiliary channels, the oxygen channel
