Nirsystems Incorporated

Philip A McGee

Kenneth P VonBargen

In an optical instrument for infrared spectral analysis of powder, an improved fiber optic probe is provided. Fiber optics carry light to and from the probe and the fiber optics terminate in the probe in a fiber optic endface. A sapphire rod is positioned to abut the fiber optic endface. The sapphire rod has a distal endface arranged at slightly less than one-half the maximum acceptance angle of the optic fibers in the probe.

Powder fiber optic probe having angled end in NIR optical analyzing

In a spectrophotometer having an oscillating grating, an entrance slit and an exit slit and a light source to irradiate said grating through said entrance slit, the grating and the light source are mounted on a heat sink plate and a fan is provided to blow air over both sides of said heat sink plate. A temperature sensing transducer is mounted in the heat sink plate to sense the temperature of the heat sink plate and the output of the temperature sensor is amplified by an amplifier to energize the electric motor of the fan to control the speed of the fan in accordance with the temperature sensed by the temperature sensor to thereby maintain the temperature of the heat sink plate at a constant value upon the system reaching equilibrium. In this manner, the wavelength drift of the system is reduced to a very low value.

Spectrophotometer with fan speed control for temperature regulation

An optical grating is oscillated at a high rate to scan a narrow wavelength band of light through the spectrum dispersed by the grating. The grating is connected integrally with the rotor of a motor, which is energized to oscillate its rotor between selected limits. The direction of rotation of the motor is controlled by an H drive circuit connected to a coil of the motor. The speed of the motor is controlled by a pulse train applied to the motor coil through the H drive. The pulse train has a duty cycle varying inversely with the motor speed. The duty cycle of the pulse train is controlled by a counter which is connected to count high frequency pulses and which is reset each time the grating rotates through an angular increment. The limits of the oscillation of the grating and the rate of rotation of the grating between the limits are selectively variable. Output readings from the spectrophotometer are taken at equal angular increments of the grating and these readings are converted to values occurring at equal wavelength increments by a computer.

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Beltsville, MD, United States of America

Philip A McGee