Infrared trace element detection system

• US 4,785,184 A
• Filed: 05/27/1986
• Issued: 11/15/1988
• Est. Priority Date: 05/27/1986
• Status: Expired due to Fees

• Current Assignee: Spectral Sciences, Inc.
• Original Assignee: Spectral Sciences, Inc.
• Inventors: Bernstein, Lawrence S., Bien, Fritz, Matthew, Michael W.
• Primary Examiner(s): Howell, Janice A.
• Assistant Examiner(s): Hannaher, Constantine
• Application Number:
  US06/866,891
• Time in Patent Office: 903 Days
• Field of Search: 250/343, 250/345, 250/339, 356/418, 356/437, 356/440, 356/246
• US Class Current: 250/343
• CPC Class Codes: G01N 2021/3174 Filter wheel
• CPC Class Codes: G01N 2021/354 Hygrometry of gases
• CPC Class Codes: G01N 21/031 Multipass arrangements
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

An infrared trace element detection system including an optical cell into which the sample fluid to be examined is introduced and removed. Also introduced into the optical cell is a sample beam of infrared radiation in a first wavelength band which is significantly absorbed by the trace element and a second wavelength band which is not significantly absorbed by the trace element for passage through the optical cell through the sample fluid. The output intensities of the sample beam of radiation are selectively detected in the first and second wavelength bands. The intensities of a reference beam of the radiation are similarly detected in the first and second wavelength bands. The sensed output intensity of the sample beam in one of the first and second wavelength bands is normalized with respect to the other and similarly, the intensity of the reference beam of radiation in one of the first and second wavelength bands is normalized with respect to the other. The normalized sample beam intensity and normalized reference beam intensity are then compared to provide a signal from which the amount of trace element in the sample fluid can be determined.

Claims

1. An infrared trace element detection system comprising:

an optical cell;

means for introducing to and removing from said optical cell a sample fluid to be examined;

means for introducing to said optical cell a sample beam of infrared radiation including a first wavelength band which is significantly absorbed by the trace element and a second wavelength band which is not significantly absorbed by the trace element for passage through said optical cell a number of times through the sample fluid;

a detector for selectively detecting in said first and second wavelength bands the output intensities of said sample beam of radiation from said optical cell and the intensities of a reference beam of said radiation;

means, responsive to said means for selectively detecting, for normalizing the sensed output intensity of the sample beam in one of said first and second wavelength bands with respect to the other;

means, responsive to said means for selectively detecting, for normalizing the sensed intensity of the reference beam of radiation in one of said first and second wavelength bands with respect to the other;

means for comparing the normalized output intensity and the normalized reference intensity; and

means, responsive to said means for comparing, for determining the amount of trace element in the sample fluid.

2. The system of claim 1 in which said means for selectively detecting includes means for selectively transmitting in said first and second wavelength bands said sample beam and said reference beam.

3. The system of claim 2 in which said means for selectively transmitting includes chopper means having first filter means for transmitting light in said first wavelength band and second filter means for transmitting light in said second wavelength band and means for driving said chopper means to pass said first and second filter means selectively through said sample and reference beams of infrared radiation.

4. The system of claim 3 in which said first and second filter means of said chopper means are driven through the output beam from said optical cell.

5. The system of claim 3 further including sensor means for sensing the location of said chopper means.

6. The system of claim 1 in which said means for normalizing the sensed sample beam output intensity in one of said first and second wavelength bands with respect to the other includes means for dividing one of the sensed sample beam intensities by the other.

7. The system of claim 1 in which said means for normalizing the sensed reference beam intensity in one of said first and second wavelength bands with respect to the other includes means for dividing one of the detected reference beam intensities by the other.

8. The system of claim 1 in which said means for comparing the normalized sample beam intensities and the normalized reference intensities includes means for dividing one of the normalized intensities by the other.

9. The system of claim 1 in which said means for determining includes means for retrieving a stored predetermined concentration value of the trace element corresponding to the comparison parameter of the normalized sample and normalized reference beam intensities.

10. The system of claim 1 in which said means for introducing said sample includes a plurality of substantially confronting orifices arranged on opposite sides of said optical cell.

11. The system of claim 1 in which said optical cell is contained within an elongate housing having forward and rearward ends and includes forward and rearward reflector means located proximate said forward and rearward ends, respectively, of said housing.

12. The system of claim 11 in which said housing includes sealing means for withstanding high sample pressures.

13. The system of claim 12 in which said sealing means are capable of withstanding pressure of up to 850 psi.

14. The system of claim 11 in which said forward reflector means includes a single mirror.

15. The system of claim 11 in which said rearward reflector means includes a pair of mirrors with spaced-apart centers of curvature.

16. The system of claim 11 in which at least one of said reflector means is concave.

17. The system of claim 11 in which said infrared radiation in said first and second wavelength bands is introduced to and exits from said optical cell proximate the forward end of said housing.

18. The system of claim 1 further including means responsive to said means for determining for indicating the amount of trace element present in the sample fluid.

19. The system of claim 1 further including alarm means for indicating when the amount of trace element in the sample exceeds a predetermined level.

20. The system of claim 1 in which said optical cell includes a multiple reflection optical cell.

21. An infrared trace element detector for an optical cell containing a sample fluid to be examined comprising:

means for introducing to the optical cell a sample beam of infrared radiation including a first wavelength band which is significantly absorbed by the trace element and a second wavelength band which is not significantly absorbed by the trace element for passage through said optical cell through the sample fluid;

a detector means for selectively detecting in said first and second wavelength bands the output intensities of said sample beam of radiation from said optical cell and the intensities of a reference beam of said radiation;

means, responsive to said means for selectively detecting, for normalizing the sensed output intensity of the sample beam in one of said first and second wavelength bands with respect to the other;

means, responsive to said means for detecting, for normalizing the sensed intensity of the reference beam in one of said first and second wavelength bands with respect to the other;

means for comparing the normalized sample beam intensity and the normalized reference beam intensities; and

means, responsive to said means for comparing, for determining the amount of trace element in the sample fluid.

22. A fluid sample transmission system for an optical detection system comprising:

an optical cell for receiving a sample beam of radiation; and

a plurality of substantially confronting orifices arranged in opposite sides of said optical cell for introducing sample fluid to said cell.

23. An infrared trace element detection system comprising:

an optical cell;

means for introducing to and removing from said optical cell a sample fluid to be examined including a plurality of substantially confronting orifices arranged in opposite sides of said optical cell;

means for introducing to said optical cell a sample beam of infrared radiation including a first wavelength band which is significantly absorbed by the trace element and a second wavelength band which is not significantly absorbed by the trace element for passage through said optical cell through the sample fluid;

a detector for selectively detecting in said first and second wavelength bands the output intensities of said sample beam of radiation from said optical cell and the intensities of a reference beam of said infrared radiation;

means responsive to said detector for normalizing the sensed output intensity of the sample beam in one of said first and second wavelength bands with respect to the other;

means responsive to said detector for normalizing the sensed intensity of the reference beam in one of said first and second wavelength bands with respect to the other;

means for comparing the normalized sample beam intensity and the normalized reference beam intensity; and

means responsive to said means for comparing for determining the amount of trace element in the sample fluid.