On the LI-840/A, there are four spacers between the shield
and detector. Collect the four spacers.
3
Separate the detector from the optical path.
Be sure that the inside of the optical path is clean. It
should be free of dust and other contaminants. Clean it if
needed, as described in the instruction manual.
4
Install the new O-ring that is included with the
detector.
5
Install the replacement optical detector.
On the LI-840/A, place the four spacers on the screws so
they fit between the shield and detector circuit board.
Tighten the screws firmly.
6
Press the tube over the hosebarb—be sure it covers
both barbs on the hosebarb.
7
Work the optical bench into the foam.
8
Connect the wiring harnesses to the detector and
source.
9
Reassemble the instrument.
Make sure that the foam insulation on the inside top
cover is positioned over the optical bench; it is required
for thermal stability. Reconnect the top cover ribbon
cable and then install the top cover.
Important:
LI-840's that are running older software must
be updated to the latest LI-840A embedded software,
which is available for free from
10
Zero and span the analyzer as described in the instruc-
tion manual.
A simple zero and span will be adequate if the span gas is
close to the concentrations you will measure. A dual span,
however, will bring the instrument performance within
specifications across the full measurement range. If you
do not have zero and span gases, send the instrument
back to LI-COR for a factory recalibration.
LI-8100/A Source and Detector
Replacement
The LI-8100A Soil Gas Flux System the source and detector
on this optical bench can be replaced if they fail. These
instructions describe how to change the source, detector
and/or optical bench. A Phillips head screwdriver and a 1/2”
open end wrench are the only tools needed to replace the
source and/or detector in all instruments. To replace the
source or detector:
Component
Part Number
Source
8100-902
Detector
800-906
Optical Bench
800-904
Note:
Be sure that you are properly grounded to avoid elec-
trostatic discharge that can damage the electronics. Use an
anti-static wrist strap, electrostatic discharge grounding
mat, or occasionally touch bare metal that has a clear path
to ground, such as an unpainted computer case.
1
Power the instrument off and remove the battery or
other external power source.
Allow the instrument optical bench to cool for about 10
minutes.
2
Open the Analyzer Control Unit and remove the
access panel by loosening the 4 thumbscrews.
3
Remove both air filters by pressing the orange part of
the quick-connect fittings toward the white part of
the connector and pulling the filter out.
Discard the filters. There are replacement filters included
that can be used during reassembly.
3
