Ametek Land 4500 MKIII, User Manual

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Opacity and Dust Monitor
User Guide
Model 4500 MkIII
C - 8
C6.2 Principle of Operation
The Land Model 4500 MkIII has been developed from the highly successful
Land Model 4500 MkII+, which already has a well-deserved reputation for
reliability and accuracy. The main light source uses three green LEDs in a
special configuration (patent pending) to ensure homogeneity over the entire
transmitted light beam. The light source is modulated at a frequency of 1
kHz, to reduce electrical noise and eliminate errors due to ambient light. A
second light source, the (patented) “Flood LED” is used to reduce the effect
of temperature drift in the detectors to an almost immeasurable low level.
Electronic modulation eliminates the need for a mechanical chopper and so
the only moving parts are the motors used in the calibration system. These
motors have a very low duty cycle and are very reliable.
Transmissometer
Key
1. LED light source 7. Reference Detector
2. Flood LED 8. Concave Mirror
3. 50/50 Beam Splitter 9. Upscale Filter
4. Collimating Lens 10. Zero Reflector
5. Collimated Beam 11. Diffuser
6. Measurement Detector
The Transceiver is illustrated above. Light from source LED1 (1) passes
through the diffuser (11) and on to the 50/50 beamsplitter (3). The
transmitted portion passes on to the lens (4) which projects a well-defined,
collimated beam (5) across the measuring path to the distant Retro-
Reflector. Light returned from the retro-reflector is focused by the lens (4)
onto measurement detector (6). The portion of light originally reflected by
the beamsplitter (3) falls on the concave mirror (8) which focuses it on to
reference detector (7). The opacity value can be calculated from the ratio of
the signals from the two detectors.
5
1 2 8
4
9
10
6
7
3
11