The detectors respond to thermal energy, so it is necessary to precisely regulate the detectors’ tem-
perature. This allows for differentiation of thermal gradient noise from the received signals from
the optical path. The detection system is shown in Figure 4-1 below.
Ribbon Cable
Connector
Gold Plated
Optical Path
Gold Plated
Parabolic Reflector
Source
Detector
Broad Band IR Source
CO
2
Filters
3.95 & 4.26 µm
H
2
O Filters
2.35 & 2.59 µm
Pressure Transducer
Heating Element Heating Element
Gas Inlet
Gas Outlet
Thermistor Thermistor
Figure 4-1. Schematic diagram of the LI-840A optical bench.
4-3Section 4. Theory of Operation
Section 4
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