Vaisala GMP343 - Manual (Page 48)

User’s Guide ______________________________________________________________________
46 ___________________________________________________________________M210514EN-E
(T, P, RH, and O
2
). The temperature, pressure, relative humidity, and
oxygen compensations are enabled as a factory default (default
environmental parameters: pressure 1013 hPa, relative humidity 50 % RH,
oxygen 20.95 % O
2
). The compensation settings are specific to the selected
measurement range, so selecting a suitable measurement range also
optimizes the compensation performance.
The compensation algorithm of GMP343 eliminates the dependences of
the CO
2
measurement, whether they are related to the physics of the
measurement or the instrument itself. The temperature compensation of
GMP343 is based on built-in temperature sensor while the values of the
other environmental parameters should be changed by the user, if they vary
from the default.
Note, that from the measurement accuracy point of view, the effect of
humidity and oxygen is less significant compared to the effect of
temperature and pressure.
Without compensation, the effect of oxygen on the CO
2
reading is
approximately - 0.09 % of reading / % O
2
. In most circumstances, the
oxygen concentration does not vary from the default, so normally there is
no need to change the oxygen concentration settings.
Without compensation, the effect of humidity on the CO
2
reading is
approximately 0.05 % of reading / g/m
3
H
2
O. Since relative humidity is
strongly dependent on temperature, the humidity dependence is in terms of
absolute humidity, g/m
3
H
2
O.
Compensation of each environmental parameter can be disabled/enabled
individually by setting the corresponding software parameter 'OFF' or
'ON', or by choosing CO2RAWUC for the measurement quantity (see
FORM command).
The internal compensation of GMP343 is the most accurate way to
compensate for changing environmental parameters. However, if more
information is needed on different compensations, please contact your
Vaisala representative.