System for remote chemical analysis

• US 4,663,961 A
• Filed: 09/17/1985
• Issued: 05/12/1987
• Est. Priority Date: 09/17/1985
• Status: Expired due to Term

• Current Assignee: Rosemount Analytical, Inc. (Emerson Electric Company)
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Nelson, Robert L., Ryan, Frederick M.
• Primary Examiner(s): Kreitman, Stephen A.
• Application Number:
  US06/777,108
• Time in Patent Office: 602 Days
• Field of Search: 73/590, 73/643, 73/24, 73/61.1 R, 250/343, 250/353
• US Class Current: 73/24.02
• CPC Class Codes: G01J 2003/2866 Markers; Calibrating of scan
• CPC Class Codes: G01J 3/1256 using acousto-optic tunable filter; acousto-optic elements or systems G02F1/11, G02F1/33
• CPC Class Codes: G01J 3/2803 using photoelectric array detector
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 21/35 using infrared light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/3577 for analysing liquids, e.g. polluted water
• CPC Class Codes: G01N 2201/08 Optical fibres; light guides

Abstract

The improved system for remote chemical analysis of this invention includes a quartz halogen bulb as a source of infrared light, quartz fibers leading to and from a sample cell, a non-collinear thallium arsenic selenide, AOTF to perform spectral analysis and a lead selenide detector, Both the AOTF and the detector are interfaced with a microcomputer. Under the control of the microcomputer, this equipment gathers and interprets transmission spectra obtained through the passage of infrared light through the sample cell. Microcomputer interface provides rapid random-access to the RF frequency driving the AOTF, which selects the wavelength of light to be examined and also provides routines for sample averaging and the comparison of various reference spectra. An acousto-optic device mounted in an enclosure which includes input and output crystal fiber connectors is also provided.

Claims

1. An improved system for remote chemical analysis wherein a sample species is disposed in a location remote from the means whereby the analysis is effected comprising:

a sample cell means adapted to receive therein or convey therethrough a species of interest to be analyzed which species has predetermined infrared absorption characteristics, said sample cell means having window means on opposed sides thereof for the passage of light therethrough;

an infrared light source;

an acousto-optic tunable filter analyzer system, which system comprises an acousto-optic tunable filter having an optically aligned acousto-optic crystal through which the infrared radiation is passed at a predetermined angle relative to the crystal optic axis, an acoustic transducer means coupled to a variable frequency rf energy source and to the acousto-optic crystal to launch acoustic waves into the crystal to interact with a selected narrow bandwidth portion of the infrared radiation to make it distinguishable from the remaining infrared radiation, which selected narrow bandwidth portion is a function of the frequency of the rf energy and acoustic waves;

means for focusing light from said infrared light sorce onto said acousto-optic tunable filter at the predetermined angle;

at least a first optical fiber which transmits the selected narrow bandwidth portion from the acousto-optic crystal to said sample cell;

a second optical fiber disposed between said sample cell means and an infrared radiation detection means;

said infrared radiation detection means generating an output signal as a function of the output filter infrared radiation having passed through said sample cell means;

computing means to which the detection means output signal is applied for determining the species present in said sample cell means and including means for the pulsed operation of the rf energy source to determine timing and frequency of rf energy applied to the acoustic transducer made into the acousto-optic crystal to determine the infrared wavelength selectivity for tuning of the acousto-optic tunable filter.

2. The improved system for remote chemical analysis according to claim 1 wherein the acousto-optic tunable filter is a thallium arsenic selenide crystal.

3. The improved system for remote chemical analysis according to claim 1 wherein the acousto-optic tunable filter includes polarizers disposed on the input and output sides of the crystal.

4. An improved system for remote chemical analysis wherein a sample species is disposed in a location remote from the means whereby the analysis is effected comprising:

a sample cell means adapted to receive therein or convey therethrough a species of interest to be analyzed which species has predetermined infrared absorption characteristics, said sample cell means having window means on opposed sides thereof for the passage of light therethrough;

an infrared light source;

a first optical fiber;

means for focusing light from said infrared light source into said first optical fiber which is in communication with said sample cell means;

a second optical fiber disposed between said sample cell means and an acousto-optic dispersive light filter (AODLF) analyzer system;

means for focusing the infrared radiation after modification by the absorption characteristic of the sample species onto said second optical fiber for the transmission of the so-modified infrared radiation to said AODLF analyzer system; and

said AODLF analyzer system including an optically birefrigent crystal having an optical input face, and optical output face said optical input face being disposed a predetermined angle which is normal to the incident light, means acoustically coupled with one of said sides for launching acoustic waves into said crystal at a predetermined fixed frequency wherein each wavelength resolution element which emerges from the optical output face is at a different diffracted angle, and wherein the predetermined angle of the optical input face is selected such that for the fixed acoustic frequency, there is a minimum in the Bragg angle with frequency, while the diffracted Bragg angle increases linearly with frequency, an acoustic transducer means coupled to a variable frequency rf energy source and to the crystal to launch acoustic waves into the crystal;

an infrared radiation detector array which detects the output infrared radiation from the acousto-optic dispersive light filter and generates an output signal as a function of the output filtered infrared radiation; and

computing means to which the detection means output signal is applied for determining the species present in the sample cell and including means for the pulse operation of the rf energy source to determine timing and frequency of rf energy applied to the acoustic transducer mated to the acousto-optic crystal to determine the infrared wavelength selectivity for tuning of the acousto-optic tunable filter.

5. The improved system for remote chemical analysis according to claim 4 wherein the acousto-optic tunable filter is a thallium arsenic selenide crystal.

6. The improved system for remote chemical analysis according to claim 4 wherein the acousto-optic tunable filter includes polarizers disposed on the input and output sides of the crystal.

7. An acousto-optic device for spectral analysis use in a fiber optic system comprising:

a housing defining an enclosure in which is mounted an acousto-optic device having an optically aligned acousto-optic crystal through which radiation is passed at a predetermined angle relative to the crystal optic axis, an acoustic transducer means coupled to the acousto-optic crystal to launch acoustic waves into the crystal to interact with a selected narrow bandwidth portion of the radiation to make it distinguishable from the remaining radiation, which selected narrow bandwidth portion is a function of the frequency of an RF energy drive in communication with said transducer means;

optical fiber input connector means disposed on a side of said housing proximate the input face of the acousto-optic crystal and adapted to removably receive thereon an optic fiber;

optical fiber connector output means disposed in said housing approximate the output face of said crystal and adapted for interconnection with an optical fiber; and

RF connector means disposed on said housing and in electrical communication with said acoustic transducer means of said acousto-optic crystal and adapted to be coupled to an RF energy source.

8. The acousto-optic device according to claim 7 including lens means disposed in said housing between the input connector and the input face of the acousto-optic crystal.

9. The acousto-optic device according to claim 8 including lens means disposed in said housing between the output face of the crystal and the output optical connector means.

10. The acousto-optic device according to claim 7 including lens means disposed in said housing between the output face of the crystal and the output optical connector means.