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3.2.2
Span gas composition
All channels of the analyser can be span calibrated by using a single gas mixture. The default gas
composition has been specified as follows :-
However these can be changed by the operator to match exactly with the certified calibration gas
supplied. From the calibration menu press key '4-Check/Set gases". This screen shows the existing
calibration gas target values for each of the four calibration gases. Use keys '1-4' to select the require gas
and follow the on-screen instructions. Leading zeros should be entered where necessary i.e. 0999ppm.
3.2.3
Span
The span calibration procedure is as follows.
1
Turn on the gas cylinder and adjust the flow.
2
If required, connect the exhaust port of the analyser to a suitable discharge point.
3
Connect the gas cylinder and flow adapter to the inlet port of the analyser.
4
Allow the gas to flow for 3 minutes.
5
While in the read screen check that the readings have stabilised.
6
From the calibration screen press key '2-Span Channels'. A brief warning screen is
displayed advising caution. Press key '1' to acknowledge the caution and continue the
calibration.
7
The message "Please wait..." is displayed while the instrument completes the
calculations. When complete a summary screen will be shown that displays the status for
each channel either okay or FAILED! There are a number of reasons for a particular
channel to fail to span calibration (see troubleshooting).
8
Turn off the gas and disconnect the hoses
9
Switch the pump on and purge the analyser with ambient air for 5 minutes.
3.2.4
Trouble Shooting
Zero calibration failed - A possible reason for this is because the instrument is trying to zero to a level
which is outside the pre-determined range set when the unit was first calibrated at the factory. To rectify
this, first ensure the unit contains absolutely none of the gas which is being zeroed. Repeat the zeroing
process but extend the time that Nitrogen is flowing. If it will not zero, then refer to the instructions given
in the 'Factory Settings' section. If the Gas Analyser continues to fail in zeroing then the unit must be
returned to Geotechnical Instruments (UK) Ltd for investigation.
Span calibration failed - Firstly, check the span gas targets are set to the correct values and match those
of the certified calibration gas. If not, correct and retry. Repeat the entire procedure, including zeroing the
channel and then calibrate the span. Ensure the reading is stable before spanning the channel. This
message may also appear if attempting to span when not using a gas containing concentrations of all four
calibration gases
.
3.2.5
Return to factory settings
The calibration factors for each channel can be returned to the initial factory settings via the calibration
menu. This can be used if an incorrect calibration has been performed. This default calibration will not be
as accurate as a good user calibration.
Page 7
O2
21%
CO2
1000 ppm
CO
20 ppm
Isobutylene
10 ppm
Balance
N2
Geotechnical Instruments
CODAOM002 Iss.06
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