Vaisala GMW90 - Manual (Page 67)

Chapter 5 _______________________________________________________________ Maintenance
VAISALA ________________________________________________________________________ 65
Effect of Pressure on CO
2
Measurement
Ambient pressure affects the CO
2
reading of GMW90. If the ambient
pressure differs from the normal pressure 1013 hPa, the transmitter can
correct the reading if you enter the correct pressure value to the
transmitter using an MI70 indicator or a computer (ENV command).
When adjusting the transmitter, you can also correct your reference
concentration (for example, the value on the gas cylinder label) according
to the graph below.
1402-025
Figure 25 Effect of Pressure on CO2 Reading
Notes for T Adjustment
Temperature adjustment is always a simple 1-point offset correction.
Notes for RH Adjustment
1-point humidity adjustment affects both offset and gain, depending on
the adjustment condition. In a dry condition (for example, 11 %RH),
offset is adjusted more than gain.
The 1-point humidity adjustment requires that the target condition is at
least 50% of the currently measured value. This prevents the user from
making excessive corrections that are very unlikely to be needed.