Method and apparatus for determining mirror position in a fourier-transform infrared spectrometer
AssigneeNicolet Instrument Corporation
InventorRobert R. Badeau
Life of this patent
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Abstract
The position of the moving mirror (20) in a Fourier-transform infrared spectrometer is monitored with a circuit which has an incremental counter formed of a plurality of cascaded up/down counters (82, 84, and 86) that count the pulses received by a laser detector (42) to yield a relative position count. A microprocessor (100) maintains an absolute position count by reading the counters (82, 84, and 86) and updating its absolute position count at regular intervals. A portion of the circuit is dedicated to discriminating the direction of the moving mirror (20) by gating circuitry connected to the digitized output of the laser detectors (42, 44).
Claims20
Apparatus for use in determining the position of the moving mirror in a Fourier-transform infrared spectrometer of the type which includes an interferometer with a moving mirror, a laser which directs its beam into the interferometer, a laser detector for detecting the intensity of the laser light exiting from the interferometer, and a microcomputer system adapted to utilize information on the postion of the moving mirror to control the motion of the moving mirror and to correlate the position of the moving mirror with the signal obtained from an infrared detector in the spectrometer, comprising:
- (a) incremental counter means, connected to the laser detector and to the microcomputer, for counting pulses from the laser detector up or down in response to an up or down control signal and having a maximum bit capacity, with the count kept by the counter means returning to zero when the maximum bit capacity of the counter means is exceeded or returning to the maximum bit capacity number when the count in the counter means is decremented below zero, the output of the counter means being connected to the microcomputer system for access by the microcomputer system;
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- (b) means connected to the laser light detector for discriminating the direction of motion of the moving mirror in the FTIR spectrometer and providing an up control signal to the incremental counter means when the moving mirror is moving in one direction and a down control signal to the incremental counter means when the moving mirror is moving in the other direction.
An infrared spectrometer comprising:
- (a) a Michelson interferometer with a moving mirror;
- (b) a positioning laser having a light beam directed into the interferometer;
- (c) a laser detector for detecting the intensity of laser light exiting from the interferometer;
- (d) an infrared detector for detecting the intensity of infrared exiting from the spectrometer;
- (e) a microcomputer system having an absolute positive register in its memory for storing the position of the moving mirror and adapted to utilize information on the position of the moving mirror to control the motion of the moving mirror and to correlate the position of the moving mirror with the signal obtained from the infrared detector in the spectrometer;
- (f) incremental counter means connected to the laser detector and to the microcomputer for counting pulses from the laser detector and having a maximum bit capacity, the output of the counter means being connected to the microcomputer system for access by the microcomputer system;
- (g) means, connected to the laser light detector for discriminating the direction of motion of the moving mirror in the FTIR spectrometer and providing an up control signal when the moving mirror is moving in one direction and a down control signal when the moving mirror is moving in the other direction;
- and
- (h) means, receiving the up and down control signals from the means for discriminating the direction of motion, for coordinating the count of the incremental counter means with the up and down control signals to properly increment or decrement the absolute position count maintained in the absolute position register of the microcomputer system.
A method of tracking the position of a moving mirror in a Fourier-transform infrared spectrometer interferometer comprising the steps of:
- (a) directing the light beam of a laser into the interferometer;
- (b) detecting the pulses of the laser light exiting from the interferometer with a laser detector;
- (c) discriminating the direction of motion of the moving mirror from the detected laser light pulses and producing an up control signal when the moving mirror is moving in one direction and a down control signal when the moving mirror is moving in the other direction;
- (d) counting the pulses detected from the laser detector up or down in response to the up or down control signal with an incremental counter connected to the laser detector, the incremental counter having a maximum bit capacity, with the count kept by the incremental counter returning to zero when the maximum bit capacity of the counter is exceeded or returning to the maximum bit capacity number when the count in the counter is decremented below zero, the counter producing an output;
- (e) accessing the output of the counter with a microcomputer system at a rate such that the period of time between accessing the microcomputer system is less than the period of time required for the incremental counter to advance one half of its maximum number of counts.
Dependencies are inferred from the claim text.