Emerson Rosemount OPM3000, Instruction Manual

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Instruction Manual Rev B
6
Section 1 - System Description and Specifications
The OPM3000 Opacity Monitor provides continuous, low maintenance, precision measurement of opacity in industrial
applications. It is a cost-effective instrument that serves as an aid in operating pollution and/or process control
equipment.
Principal of operation
The Dual beam measurement system has a stack mounted Transmissometer sensor system consisting 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 lamp 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 RCU for processing. At the control unit the signal is
processed to read 0-100% Opacity, provide alarms and outputs.