Section 4.
Maintenance
The LI-830 and LI-850 will require little maintenance. Typical maintenance pro-
cedures are described in this section.
User calibration
If the instrument is not measuring as expected, or if you have disassembled the
optical bench for any reason, you should check the zero and span settings and set
them if necessary. The zero and span are an offset and slope. The zero value ensures
that the instrument shows zero when the gas has a zero concentration. A change in
the zero will affect every measurement. The span setting ensures a correct meas-
urement at a known non-zero concentration. A change in the span affects higher
concentration measurements more than lower ones.
Setting the CO
2
zero
Always perform the zero first. To set the zero, you'll need either a tank of dry air
that is free of CO
2
or a CO
2
scrubbing chemical such as wet soda lime and a desic-
cant such as Drierite.
1
Plumb the zero-gas tank or scrubber to the air inlet.
Be sure to use an air filter to prevent contaminants from entering the optical path.
l If using tank air, the pressure of the tank is sufficient to flow the gas through
the analyzer. Allow at least 0.75 liters per minute to flow through the cell (no
more than 1.0 lpm).
l If using a scrubbing chemical, use a pump to draw air through the analyzer.
2
Install a 10 to 20 cm length of tubing to the air outlet.
This vent prevents ambient air from diffusing upstream into the optical cell.
4-1Using the LI-830 and LI-850 Gas Analyzers
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