LI-COR LI7200RS, Инструкция по эксплуатации

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Section 4.
User Calibration
The LI-7200RS’s measurement accuracy depends upon its calibration. There are
two major components to the calibration: 1) determining the values of calibration
coefficients, and 2) setting zero and span. During a factory calibration, both of these
steps are performed. The values of the coefficients that are determined should be
valid for several years. The zero and span adjustments are used to bring the
LI-7200RS's actual response into line with its previously determined factory
response, at least at two points.
Important: Check the zero and span at regular intervals; monthly at first, and
then adjust the frequency according to the stability of the instrument; see How
Stable are Zero and Span? below.
How Stable are Zero and Span?
The analyzer's zero is primarily affected by temperature, and the state of the
internal chemicals. The internal chemicals should be changed annually (see
Repla-
cing the Internal Chemicals on page 5-4). The zero's response to temperature is rel-
atively small (typically 0.1 or 0.2 ppm per °C for CO
2
, or 0.01 mmol/mol/°C for
H
2
O). Also, this drift is measured at the factory, and subsequently compensated for
in software (equation 8-3), so the effective zero drift should be quite small. There-
fore, the zero should be quite stable over a several month period, but you might
want to check it after an extreme temperature change (>30 °C).
The analyzer's span is affected by temperature, pressure, and the state of the internal
chemicals.
4-1 LI-7200RS Enclosed CO₂/H₂O Analyzer