This general equation can be converted into simple multipliers, based on the two available
voltage output ranges and the CO
2
(maximum 20,000 ppm) or H
2
O (maximum 100% RH)
range. These can be any value, depending on what is chose for the 0V and the full scale 2.5V
and 5V DAC output values. Each multiplier can then be entered in the data logging device to
convert raw voltage to CO
2
or H
2
O values. Table 3-1 below lists some examples of values for this
multiplier; simply choose your DAC output range in the second row, and then select the LI-
840A CO
2
range in the first column (the full scale value minus the zero value); follow across to
find the appropriate multiplier. Note that this table assumes that the zero value (X
Z
) is zero; if it
is not zero, the offset will need to be added onto the final result.
DAC Output Range
0-5V 0-2.5V
X
F
- X
Z
Multiplier (ppm/Volts)
1000 ppm 200 400
2000 ppm 400 800
5000 ppm 1000 2000
20000 ppm 4000 8000
Table 3-1. Multipliers for converting voltage output to CO
2
readings (no offset).
3-33Section 3. Operation
Section 3
To Next Page
