12. Sensors
If temperature compensation is static, this is indicated in the menu ´Measuring
channel´ by symbol .
If the temperature is measured externally, this is indicated by the symbol .
Automatic temperature compensation can be disabled by program-
ming the reference channel for the measuring channel to itself.
12.2.6 Atmospheric pressure compensation
Some measured variables depend on the ambient atmospheric pressure (see
13.2.13, measuring range list ´with PC´) - with the effect that large deviations
from normal pressure (1013 mbar) may lead to measuring errors.
e.g. Error per 100 mbar Compensation range
Rel. humidity, psychrometric approx. 2% 500 to 1500 mbar
Mixture ratio, capacitive approx. 10 % Vapor pressure VP up to bar
Dynamic pressure approx. 5% 800 to 1250 mbar (error < 2%)
O
2
saturation approx. 10% 500 to 1500 mbar
It is important therefore, especially when working at significant altitudes above
sea level, to take due account of atmospheric pressure (approx. -11 mbar /
100 meters above mean sea level, MSL). This device now incorporates - for
the first time - a dedicated atmospheric pressure sensor, which is used auto-
matically for all functions requiring pressure compensation. This atmospheric
pressure value is also made available in a function channel. (see 13.2.13.1)
Alternatively, atmospheric pressure can be measured using an external sen-
sor. If the channel designation has ´*P´ (s. 13.2.1), the measured value con-
cerned will be used for atmospheric pressure compensation for the following
channels. However, ´Atmospheric pressure´ can still also be programmed in
´Device settings´ ´Device compensation´. s. 13.6.4 To resume internal
measuring operations this value must be deleted. The atmospheric pressure
used for a channel is shown in ´Settings´ ´Channel functions´ ´Channel
compensation´. (see 13.2.14)
If atmospheric pressure compensation is static, this is indicated in the menu
´Measuring channel´ by symbol . If the atmospheric pressure is measured
externally, this is indicated by the symbol .
12.2.7 Cold junction compensation (CJC)
Cold junction compensation (CJC) for thermocouples is normally performed
completely automatically. In order to ensure the highest possible level of accu-
racy on this device with its 10 sockets - even in difficult thermal conditions (e.g.
thermal irradiation) - the socket temperatures are acquired by means of two
precision NTC sensors in measuring sockets M0 and M9 and then calculated
by linear interpolation separately for each socket. The exact cold junction tem-
perature of each channel is shown in ´Settings´ ´Channel functions´
´Channel compensation´. (see 13.2.14)
44 ALMEMO
®
710
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