Land 4500 MKII Premier, Operation And Maintenance Manual

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Model 4500 Premier Dust and Opacity Monitor
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C3-2 Principle of Operation
The Land Model 4500 Premier is the most sensitive opacity monitor available. It can accurately measure
stack opacity below 1%. The Model 4500 Premier has been developed from the highly successful Land
Model MkII
+
, which already has a well-deserved reputation for reliability and accuracy. Unlike normal
opacity monitors, each Model 4500 Premier is individually tested over its full operating temperature
range to ensure that it meets its own extremely low drift specification. 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 3 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.
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1 2 8 9
3 6 7 4
10
5
Transmissometer
Key
1. LED light source 7. Reference Detector
2. Flood LED 8. Concave Mirror
3. 50/50 Beam Splitter 9. Span Filter
4. Collimating Lens 10. Zero Point Reflector
5. Collimated Beam 11. Automatic Fail Safe Shutter (Optional)
6. Measurement Detector 12. Diffuser
The Transceiver is illustrated above. Light from source LED1 (1) passes through the diffuser
(12) 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 is focused by the lens (4) onto measurement detector
(6). The portion of
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