LI-COR LI-6400, Manual

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LPL Topics
Analog Measurements
Using the LI-6400 23-71
Zero and Span
Figure 23-34 is concerned with measuring just two channels, but notice that
4 channels are actually defined. In addition to channels 15 and 16, channels 0
and 1 also got defined. WhatÕs going on here?
The A/D converter in the LI-6400 needs some reference measurements for ac-
curacy. It must look at a true 0V signal now and again, and also a true 5.0 volt
signal. Channel 0 provides the former, and channel 1 provides the latter.
LI-6400 Analog Channels
A standard LI-6400 has 24 analog channels (Table 23-28), and 8 reference
channels (Table 23-29). Note that the library file
“/Sys/Lib/StdAnalogIn”
provides
variable names for these channels, which should be used rather than the num-
bers.
Table 23-28. LI-6400 Analog Input Channels
Channel Channel Descriptions Variable Name
0 Zero reference channel aZeroChan
1 Span reference channel aSpanChan
2 Battery aBattChan
3 CO2 Reference aCO2AChan
4 CO2 Sample aCO2BChan
5 H2O Reference aH2OAChan
6 H2O Sample aH2OBChan
7 IRGA background temp aTirgaChan
8 CO2 Reference AGC aAgcCAChan
9 H2O Reference AGC aAgcHAChan
10 CO2 Sample AGC aAgcCBChan
11 H2O Sample AGC aAgcHBChan
12 Cooler block temp aTblkChan
13 Leaf temp sensor aTleafChan
14 Flow meter aFlowChan