Section 2
Model 601/601P/602/602P/603 NDIR Analyzer
California Analytical Model 600_NDIR_Series_v10.0 CE
Operators Manual
Page 18 of 86
2.4.
Infrared Gas Analyzers
The infrared gas analyzer measures gas concentration based on the principle that each type of
gas component shows a unique absorption line spectrum in the infrared region.
The instrument consists of an infrared light source, a chopper, a measuring cell, and a detector
filled with a gas mixture containing the gas component to be measured. The operating
principle of the instrument is described with reference to Figure 2-1. The infrared light source
emits infrared light in all directions. The light emitted forward is transmitted and reflected into
the detectors.
The infrared light emitted backward is reflected by a reflecting surface and is added to the
infrared light emitted forward. Arranged between the infrared light source and measuring cell
is a chopper blade which rotates to modulate the infrared light beam at regular frequency. The
modulated infrared light beam thus formed passes through the measuring cell filled with a
sample gas where the light energy is partially absorbed or attenuated before it reaches the
front chamber of the detector. Both the front and rear chambers of the detector are filled with
the gas component to be measured.
The infrared light energy is partially absorbed in the front chamber and residual light is
absorbed in the rear chamber, thereby increasing pressure in both chambers. Since the
detector is designed to produce a pressure difference between the front and rear chambers, a
slight gas flow is produced through a path connecting these chambers with each other.
This slight flow is converted into an AC electrical signal by a microflow sensor arranged in the
path connecting the chambers with each other. The AC signal is amplified and rectified to a
DC voltage supplied to the output terminals and indicator (Figure 2-4). Figure 2-2 shows the
detector output signal with the greatest amplitude when zero gas is flowing in the measuring
cell. Amplitude is reduced as the concentration of measured gas component increases (Figure
2-3)
Chopper Motor
Sample Cell
Micro — Flow Sensor
Front Chamber
Exhaust
Sample In
Infrared Source Unit
Infrared Source
Rear Chamber
Detector
Chopper Blade
Figure 2-1 Single NDIR Analyzer
Summary of Contents for 600-NDIR
Page 1: ......
