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I N S T R U C T I O N
M A N U A L
R E V
4 . 2
SECTION 1 SYSTEM DES CRIPTION
TRANSMISSOMETER /RETRO REFLECTOR
The OPM4001 is a precision, double-pass, dual beam Transmissometer that consists of a transceiver (transmitter/receiver) mounted
on one side of a stack or duct and a passive reflector mounted on the opposite side. The light source, photo detectors, and all
measurement/reference optics used in opacity measurement are housed in the transceiver.
NORMAL MODE OF OPERATION
The Dual beam measurement system has a stack mounted Transmissometer sensor system consists of an optical transceiver
mounted on one side of the stack and a retro reflector mounted on the other. To avoid errors due to ambient light, the wide band
lamp (See Drawing) is electronically modulated and projects a collimated beam of light, which is split into a reference beam, and a
measurement beam by an optical Beam splitter. The reference beam is directed to the reference detector, RD. The measurement
beam is projected across the stack to a Retro
reflector that returns the beam back across the
stack to a beam splitter and directs the
measurement beam to the measurement
detector, MD. A portion of the returning light is
also sent to the TTL (Thru the Lens) bulls-eye
target viewed through a window provided at the
rear of the Transmissometer. The bulls-eye is
used to correct changes in alignment and is
unique in that no moving parts are used!
The ratio of the measurement and reference
detectors is used to provide Transmittance 2 (T
2 ) signal. Because the same light source is used
for both detectors, and a Measurement /
Reference ratio is used throughout for the
calculations, the monitor is insensitive to
variations
in
light
intensity.
Since
all
measurements are made on a ratio basis, all
resulting computations are independent of the absolute intensity of the light source or contamination of the optics associated with
the collection and focusing of the energy from the lamp. The (T 2 ) signal is converted to a current format and sent to the control unit
for processing. At the control unit the signal is processed to read 0-100% Opacity, provide alarms and outputs.
5
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Troubleshooting
