LI-COR LI-7820, Instruction Manual

Page: 59 / 92

Section 6.
Maintenance
The LI-7820 will require little maintenance. There are no user-serviceable parts in
the instrument except for the air inlet filter, air dry-down chemical, and pump. Do
not attempt to disassemble the instrument or conduct any maintenance procedures
other than those described here.
Instrument calibration
To adjust the instrument calibration, you can set the zero and span. The span is
like a slope (the
m
in
y
=
mx
+
b
). The zero is a spectral baseline. Adjusting the zero
changes every measurement (the relationship is non-linear). Adjusting the span
changes the slope. Calibration gases should be at a pressure between ambient and
35 kPa (5 PSI) above ambient pressure. We recommend installing a >30 cm vent
before the air inlet to vent the excess pressure and prevent diffusion of ambient air
into the gas stream.
Figure 6-1. Plumbing configuration for calibration gases. Use a low pressure regulator to
reduce pressure and a 30 cm vent to avoid pressurizing the inlet.
6-1 LI-7820 N₂O/H₂O Gas Analyzer