OMG100N1.21
G100 Range
Page
32
Copyright Geotechnical Instruments (UK) Limited
7.5.1 Zero CO
2
Channel:
For maximum accuracy it is recommended that the CO
2
Channel is zeroed using bottled
gas (certified 100% N
2
). However, if nitrogen
gas is not available the optional soda lime
filter kit can be fitted to the gas inlet. This allows the user to perform a zero using normal
air as the soda lime filter will absorb virtually all CO
2
from the sample air. For both these
options select 'Key 1-Zero with N
2
' from the user calibration menu.
If neither of the recommended methods is available the user can select the option to
perform an air calibration. This option assumes that the user has access to fresh air at
around 390ppm. Generally, this can be found outside or in a well ventilated corridor
(typically, an office or lab would have a higher CO
2
concentration).
1)
From the ‘Calibration’ Menu, press ‘Key 2 - CO
2
channel’.
User Calibration
2)
Press either ‘Key 1 - Zero with
N
2
’ (
recommended) or ‘Key 2 - Zero with Air’
from
the menu. Then, either attach the 100% N
2
or sample pipe to allow access to fresh
air.
3)
Ensure the zero gas has flowed and is stable.
4)
Press the ‘Start’ key. The instrument will now wait (approximately 60 seconds) for
the gas reading to stabilise at the correct level. If zeroing with air press the ‘Pump’
key to draw in fresh air.
5)
The instrument will then indicate a successful zero has been completed. Press the
soft-key ‘Accept’ to confirm the calibration and ‘Store’ the new user offset.
Alternatively,
soft-key
‘Reject’ to exit without change.
Note: If the calibration failed then purge and try again or select a different air
source.
If using G110 – very high concentrations of CO
2
may take up to
30
minutes
to purge completely.
7.5.2 Span CO
2
Channel:
It is recommended that the instrument is spanned to target the desired reading range
(e.g. 5%); ideally this should not be a low level close to zero.
1)
If not already preset, enter the
span target
, i.e. certified concentration of your
calibration gas. Press ‘Key 1’ and enter the new value. Then attach the gas and
open regulator valve to allow the gas to flow.
2)
Press the ‘Start’ key and wait for the reading to stabilise. This can take a couple of
minutes.