Vaisala GMP231 - Manual (Page 19)

Chapter 2 ___________________________________________________________ Product Overview
VAISALA ________________________________________________________________________ 17
Environmental Compensation
GMP231 improves the CO
2
measurement accuracy by applying various
environmental compensations. GMP231 compensates for the effects of:
- Pressure
- Temperature
- Background gas oxygen (O
2
) content
- Background gas relative humidity (%RH)
Compensation parameters are configured on the order form when
ordering the probe, and can later be updated using serial commands,
MI70 Indicator, or I
2
C protocol. If the probe is integrated in a system that
measures one or more of the compensation parameters, they can be
updated to the probe continuously.
You can also turn off any of the compensations. In that case, GMP231
uses the default compensation value that is mathematically neutral for the
probe’s internal compensation model.
For the effect of the compensations on measurement accuracy, refer to
Table 42 on page 85.
Pressure Compensation
There is a pressure sensor on the component board of the GMP231 that
provides a live measurement of ambient pressure. GMP231 can
compensate the CO
2
measurement based on this pressure reading, or it
can use a fixed setpoint. Using the GMP231’s own sensor is
recommended for most applications.
If pressure compensation is turned off, GMP231 uses the default
compensation value of 1013.2 hPa.
Temperature Compensation
GMP231 can measure the approximate temperature of the CARBOCAP
®
sensor for compensation, or use a fixed setpoint. The temperature
measurement is accurate enough to be useful for compensation, and is
recommended for use unless a dedicated temperature measurement is
available and can be regularly updated to the GMP231.
If temperature compensation is turned off, GMP231 uses the default
value of +37 °C (+98.6 °F).