where V is the measured voltage, X
F
is the full scale value for cell pressure output (entered in the
Settings Window as the 2.5 or 5V value, up to 115 kPa), X
Z
is the zero value entered, and Vmax
is the full scale DAC output voltage selected (5V or 2.5V).
Converting Current Output to ppm CO
2
or mmol/mol H
2
O
Current output can be measured by connecting the positive input of the data logging device to
positions 11 or 13 (4-20 mA 2 or 4-20 mA 1), and the negative input to position 12 or 14
(GND). The current output at positions 11 and 13 is non-isolated, and is rated to drive a 250
ohm load.
Note: These channels mirror their respective voltage output channels; current output channel
1 uses the variable chosen for voltage output 1, and current output channel 2 uses the vari-
able chosen for voltage output 2. Similarly, a voltage output of 0 volts corresponds to a cur-
rent output of 4 mA, and when the voltage outputs are at full scale (2.5 or 5 V), the current
output will be 20 mA.
To convert current output (I) to CO
2
or H
2
O concentration in your computer or other output
device, the following equation can be used:
3-9
Section 3
3-12 Section 3. Operation
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