Browse Prior Art Database

Spectrophotometer With Linear Output

IP.com Disclosure Number: IPCOM000089768D
Original Publication Date: 1977-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Rudberg, BL: AUTHOR

Abstract

Spectrophotometers are instruments that are useful in analyzing the properties of materials by measuring the reflectance or transmittance of the materials at different wavelengths. While some spectrophotometers use photomultiplier tubes as detectors, such tubes are relatively expensive. Solid-state photovoltaic devices, such as silicon detectors, are cheaper than the photomultiplier tubes, but present some difficulties because of their variable response at different wavelengths. In addition, in spectrophotometers employing dual light paths, the light paths themselves exhibit some different characteristics that provide for a variable response across the different wavelengths.

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Spectrophotometer With Linear Output

Spectrophotometers are instruments that are useful in analyzing the properties of materials by measuring the reflectance or transmittance of the materials at different wavelengths. While some spectrophotometers use photomultiplier tubes as detectors, such tubes are relatively expensive. Solid- state photovoltaic devices, such as silicon detectors, are cheaper than the photomultiplier tubes, but present some difficulties because of their variable response at different wavelengths. In addition, in spectrophotometers employing dual light paths, the light paths themselves exhibit some different characteristics that provide for a variable response across the different wavelengths. Shown in the drawing is a spectrophotometer using solid-state detectors for their low-cost and using a dual-beam system, which spectrophotometer is provided with means for compensating for different variables at different wavelengths so as to achieve a relatively constant compensated output for the same intensity of light at each wavelength.

Referring to the drawing, light from sample 1 passes through a fiber-optic bundle 2 and is directed toward a rotary opaque wheel 3 having a CVF (circular variable filter) 4 therein. CVF 4 extends for 180 Degrees around wheel 3 so that light from bundle 2 passes through the filter and into a fiber-optic bundle 5 only during one half of a revolution of wheel 3. CVF 4 acts as a monochromator for analyzing the light from sample 1. Bundle 5 is connected to a silicon detector 6. In a similar manner, light from a reference 7 traverses a fiber-optic bundle 8 that is located diametrically opposite bundle 2 so as to transmit light through a fiber- optic bundle 9 to a silicon detector 10 during the other half of the revolution of wheel 3. While two detectors have been shown, it should be apparent that a single detector may also be used. The output from detectors 6 and 10 are fed to an analog switch 12 that is controlled by latch 13 so as to pass the output of detector 6 to a variable gain amplifier 14 during one half of a revolution of wheel 3 and to pass the output from detector 10 to amplifier 14 during the other half.

A shaft encoder 16 is integrated with or coupled to wheel 3 so as to provide a home pulse for each revolution of wheel 3 and to provide degree pulses for each ...