Spectrophotometer

Details Spectrophotometer Spectrophotometer

1974-12-05

1976-01-27

Lawrence, James W.

Radiant energy

Invisible radiant energy responsive electric signalling

Ultraviolet light responsive means

250365, 250238, 350 61, 356 51, 356207, G01J 300, G01J 346, G01J 556, G01N 2126

Patent

active

039354636

ABSTRACT:
An improved spectrophotometer of the non-dispersive absorption type useful for detecting the presence of SO.sub.2 in a gaseous sample, despite the simultaneous presence of NO.sub.2. Ultraviolet light from a commercially-available source impinges upon a fixed phosphor screen which fluoresces to produce ultraviolet radiation at a first wavelength, at which both SO.sub.2 and NO.sub.2 absorb radiation; and at a second wavelength at which absorption by SO.sub.2 is minimal but NO.sub.2 absorption is approximately the same as at the first wavelength. The radiation is directed through a sample chamber having windows which are transversely slidable to effect cleaning without destroying the integrity of the chamber seal, then introduced into an envelope enclosing filters and a pair of photosensors. One photosensor receives light at the second wavelength and produces a signal which reflects the attenuation by NO.sub.2 at that wavelength. The other sensor has disposed in front thereof a filter for blocking the second wavelength, and passing the first; and a phosphor for converting the passed (first) wavelength radiation into radiation at the second wavelength, which is then detected to produce a measure of the combined effect of NO.sub.2 and SO.sub.2. A comparison circuit then detects the differential between the first and second photosensors to determine the concentration of SO.sub.2. Means are provided to maintain the lamp, sample chamber and envelope at predetermined temperatures. A source of mercury vapor within the envelope saturates the interior of the envelope with the vapor for selectively attenuating undesired radiation at the 254 wavelength.

REFERENCES:
patent: 2411672 (1946-11-01), VanDenAkker
patent: 3731091 (1973-05-01), Rosso et al.
patent: 3778162 (1973-12-01), Gant et al.
patent: 3819945 (1974-06-01), Egan et al.
patent: 3861802 (1975-01-01), Belmear, Jr.

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