Emerson Rosemount CCO 5500, Справочное руководство

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Appendix A
Theory of operation
A.1 Infrared source unit
At the heart of this unit is a small heater assembly designed to give a high intensity
uniform source of infrared energy. The heater assembly can provide in excess of two years
of continuous operation with a power consumption of only 26 watts. The heater has a
stainless steel cylindrical core, plasma coated with refractory, and around which is a
Kanthal heating element. This is then enclosed within refractory fibers and encapsulated in
an aluminum cartridge. In the infrequent event of failure, you can easily replace the
complete heater assembly on site.
A motor-drive disc then chops the radiation emitted by the heater, and a lens focuses the
radiation across the duct. A small DC motor drives the chopper disc. A radiation detector
monitors the phase and frequency of the chopper disc to provide a reference signal that
the control unit uses.
A stepper motor and gear box assembly swing a small calibration cell containing pure
reference gas (CO) into the sight path to enable continuous calibration updates. The
chopper motor and stepper motor represent the only moving components in the entire
system.
A printed circuit board mounted at the front of the unit provides control circuitry for the
heater, the motors, and the reference ware detector.
Figure A-1 illustrates the operation of the source and receiver units.
Theory of operation
Reference Manual 103