LI-COR LI7200RS, Instruction Manual

Page: 137 / 226

Are the diagnostic flags (PLL, etc.) OK? Under
Diagnostics
, check the diagnostics.
See Diagnostic Messages on page 7-27 for more information.
Zero and Span OK? Go to the
Calibration
page and make sure the current values of
zero and span are near 1.
Absorptances Make Sense, Densities Don't
If the absorptance value seems correct (rough rule of thumb: absorptance = 0 when
density = 0, CO
2
absorptance is about 0.1 with a mole fraction of about 400 ppm,
and H
2
O absorptance is about 0.1 with a mole fraction of about 20 mmol/mol), but
the displayed values of density or mole fraction are obviously bad, then the problem
is in one of the following: calibration coefficients, span parameter, pressure value,
and the band broadening value (CO
2
only).
Readings Very Noisy
Put the calibration tube in place to dampen the natural fluctuations. You don't
need a gas flowing through the tube. The variability in absorptance values should
be low, with only the 4th decimal place changing once in a while. If density or
mole fraction is still noisy, watch the temperature and pressure values to see if they
are the source of the noise (or change to a hand entered, constant value to try this).
Check the calibration coefficients and band broadening value (if the problem is
with CO
2
) to make sure they are correct.
Section 6. Troubleshooting
6-7 Bad CO2 or H2O Readings