LI-COR LI-8100A - The Measurement Flow Path; The Bellows Flow Path

6-4
Using the 10 and 20 cm Survey Chambers
The Measurement Flow Path
Air flow generated by a diaphragm pump inside the Analyzer Control Unit provides
a steady flow of air to the Survey Chamber, with minimal pulsations. Air flow to
the chamber provides mixing without using fans that can cause pressure gradients.
Air returning from the chamber passes through a filter before it enters the optical
bench of the infrared gas analyzer in the Analyzer Control Unit. The analyzer
optical bench measures CO
2
and H
2
O concentrations simultaneously; these
concentrations are then used to calculate flux rate.
O
N
/O
FF
Automated Soil
CO
2
Flux System
O
N
/O
FF
P
O
W
E
R
IR
G
A
R
E
A
D
Y
A
C
T
IV
E
L
O
W
B
A
T
T
E
R
Y
R
E
A
D
Y
O
N
/O
FF
O
N
/O
FF
Diaphragm
Pump
To Chamber
From Chamber
Filter
Analyzer
Bench
Analyzer Control Unit
20 cm Survey
Chamber
Figure 6-3. The measurement flow path to the Survey Chambers.
The Bellows Flow Path
A separate pressure/vacuum air flow system is used to drive the bellows to raise
and lower the chamber. A diaphragm pump provides air flow to a series of valves
controlled by a pressure transducer. Pressurized air fills the bellows and drives the
chamber closed; a vacuum raises the chamber and vents excess air out of the
Analyzer Control Unit.