| Additional information |
SIR Model S-5001 is a Non-Pulsed U.V. Fluorescence Sulfur Dioxide Analyzer.
In the analyzer, optically filtered pure monochromatic U.V. light from a Zinc lamp is focused onto the SO2 reaction chamber. This beam is of invisible U.V.light and is termed the excitation beam or sometimes the "primary beam". The intensity of the beam is directly viewed by the primary beam intensity measuring detector (control detector). The same beam is viewed at right angles by a
wavelength selective photomultiplier (PM) detector which is tuned by an optical discrimination filter to reject the primary beam radiation, but to be sensitive to radiation in a discrete portion of the visible spectrum. SO2 molecules intercepting the primary beam are U.V. energized through primary beam light absorption. These excited molecules "de-energize" themselves by re-emitting light at a higher wavelength (lower energy). The re-emitted light is given off in all
directions, and a portion of it, the secondary beam, is viewed through the
primary beam "blocking" filter by the photomultiplier detector.
Model S-5001 uses non-pulsed U.V. radiation, which effectively doubles the
detected signal as compared to a chopped light instrument, thereby significantly increasing the signal-to-noise ratio. The usual task of correcting for PM and control detector dark current normally performed by light pulsing is achieved by a microprocessor controlled shutter system which periodically and momentarily
blocks the primary beam. This blocking is done over a short time interval relative to the non-blocked time. |