Figure 1. Location of adjustment button
1 Adjustment button (covered by a detachable screw).
Adjustment with reference gases
For the adjustment procedure with gases, you need the probe that is going be adjusted, accurate reference gas(es), a
pressure regulator, a flow meter, a field check adapter (can be ordered from Vaisala) and flexible tubing with 3 mm
(1/8 in) inner diameter. For information on available accessories and ordering, see Spare parts and accessories.
Reference gases
To achieve reliable results, reference gases must be traceable to appropriate standards (for example NIST).
If adjustment is done by using 1 reference gas (1-point adjustment), the concentration of the gas must be near to
the concentration values in which the device is used.
When adjustment is done only in 1 point, this results in high accuracy only near to the adjustment
point, not necessarily over the whole measurement range.
When using 2 reference gases (2-point adjustment), the reference gas concentrations should represent the low-
end and the high-end of the measuring range. The low-end concentration should be less than 20 % of the
measuring range of the probe. The 0 gas can be N
2
gas with a purity of N5.0 (or better). The high-end gas can
be mixture of CO
2
and N
2
with concentration near to the upper limit of the measuring range, being 110 % of the
range at maximum. Accuracy of the concentrations should be 1 % (or better). Difference between the reference
gas concentrations should be more than 20 % of the measuring range.
Making a 2-point adjustment
CAUTION! Make sure to check the following when carrying out the adjustment:
Give the correct reference concentrations in the correct units
Wait until the reading has fully stabilized before accepting the reading.
CAUTION! Reverting to factory settings is not possible after the adjustment.
The difference between the 2 references must be at least 20 % of the measuring range of the probe.
See also Field Check Adapter 26150GM Quick Reference Guide (M210450EN), available at
www.vaisala.com/gm70.
1. Insert the probe into the field check adapter until the perforated filter is covered ((1) in Figure 1).
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