16
Figure 6: Configuration using compressed gas.
After the system zero is established, use a gas with known concentration of CO
2
to calibrate span.
Use the key to skip the “calibrate the span” setting.
Use known CO
2
Press the key to proceed.
Enter the concentration of CO
2
in ppm at the following display:
Concentration ?
__ ppm
The known concentration should flow for approximately one minute.
Press to save your selection. The system will then return to the following screen display and
reset:
ENTER to select Calibrate CO
2
H
2
O calibration follows similar procedures. Dry nitrogen gas or silicon gel (Figure 8) can be used for the
H
2
O zero, and a known partial pressure of H
2
O is used for the known H
2
O. A “DOS” program is provided
to convert relative humidity and temperature to kPa partial pressure. Run RH2KPA.EXE under DOS or in
a DOS window on a PC. Windows XP will automatically launch a DOS window if you double click on the
file name in Windows Explorer.
NOTE: H
2
O span setting should be checked once every six months. It be checked often by conducting a
photosynthesis test with the “loop back” tube in place of a leaf chamber and sampling a known
humidity of the atmosphere.
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