Optical fluid analyzer

• US 4,306,152 A
• Filed: 07/23/1979
• Issued: 12/15/1981
• Est. Priority Date: 07/23/1979
• Status: Expired due to Term

• Current Assignee: Forney Corporation (Graham Holdings Company)
• Original Assignee: Anarad, Inc. (Leonardo S.p.A.)
• Inventors: Ross, Thaddeus C., Burrows, Donald E.
• Primary Examiner(s): Smith, Alfred E.
• Assistant Examiner(s): Howell, Janice A.
• Application Number:
  US06/059,798
• Time in Patent Office: 876 Days
• Field of Search: 250/252, 250/341, 250/343, 250/344, 250/345, 250/565
• US Class Current: 250/343
• 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

Abstract

An optical fluid analyzer uses the extent of optical, preferably infrared absorption of a fluid to be analyzed to determine the concentration of a selected constituant of the fluid. A first detector detects light after absorption by the fluid at a wavelength at which the selected constituant has a characteristic absorption for conversion into an electrical signal indicating the concentration of the selected constituant and a background from absorption of other constituants of the fluid for a measurement processing channel. A second detector correspondingly converts light after absorption by the fluid, but at a different wavelength at which the absorption at least approximates the background absorption alone for a neutral processing channel. The signals from the measurement and neutral processing channels are then subtracted to reduce the level of the background signal so that the level of the signal from the characteristic absorption can be more accurately processed to indicate the concentration of the selected constituant. The analyzer further has a first adjusting arrangement requiring ony a readily available, staple fluid to compensate for variations in the analyzer operation and a separate, second adjusting arrangement for presetting the analyzer with a standard fluid. Both the background subtraction and separate adjusting features of the analyzer particularly adapt it for analyzing liquid fluids.

Claims

1. An optical fluid analyzer, comprising:

a sample chamber for receiving a fluid sample;

optical means for providing an optical signal of the concentration in the fluid of a selected constituant of the fluid in the sample chamber on a background from the other constituants of the fluid;

neutral channel processing means for converting the optical signal into an electrical signal at least approximating the background portion of the optical signal;

measurement channel processing means for converting the optical signal into an electrical signal of the concentration of the selected constituant and the background; and

output means combining the electrical signals for subtracting the neutral channel signal at least approximating the background from the measurement channel signal of concentration and background, whereby at least much of the background portion of the signal is removed from the combined signal for more accurately extracting the concentration-indicating signal from the combined signal is further electrical signal processing.

2. An optical fluid analyzer as in claim 1 wherein the optical means comprises a light source from which light is absorbed by the selected constituant of the fluid in the sample chamber at a characteristic wavelength proportionally to the concentration of the selected constituant in the fluid and by the other constituants of the fluid, wherein the neutral channel processing means comprises first filter and detector means for response to the light absorption at a wavelength other than the characteristic wavelength of the selected constituant, and wherein the measurement channel processing means comprises second filter and detector means for response to the light absorption at the characteristic wavelength of the selected constituant.

5. An optical fluid analyzer as in claim 1, 3 or 4 wherein the optical means further comprises:

a reference chamber for receiving a reference fluid of known optical absorption;

a light source from which light is absorbed by the selected constituant of the fluid in the sample chamber at a characteristic wavelength proportionally to the concentration of the selected constituant in the fluid and by the other constituants of the fluid;

means for defining a first optical path from the light source into the sample chamber and a second optical path from the light source into the reference chamber;

means for alternately passing light from the source along the first and second optical paths;

first filter and detector means for response to the light absorption at a wavelength other than the characteristic wavelength of the selected constituant of light from both the sample and reference chambers; and

second filter and detector means for response to light absorption at the characteristic wavelength of the selected constituant of light from both the sample and reference chambers.

3. An optical fluid analyzer, comprising:

a sample chamber for receiving a fluid sample;

optical means for providing an optical signal indicating the extent of optical absorption of a fluid in the sample chamber at a wavelength at which a selected constituant of the fluid to be analyzed has a characteristic optical absorption, whereby to indicate from the extent of absorption the concentration of the selected constituant of the fluid to be analyzed;

processing means for converting the optical signal into an electrical signal;

first adjusting means in the processing means for setting the electrical signal to zero when a staple fluid which does not optically absorb significantly in relation to the fluid to be analyzed is in the sample chamber, whereby to compensate for variations in the analyzer operation with only the staple fluid as often as desired;

separate, second adjusting means in the processing means for setting the electrical signal to zero when a standard fluid known to optically absorb correspondingly to the fluid to be analyzed except for the absorption of the selected constituant is in the sample chamber, whereby to preset the analyzer to provide a zero electrical signal from the processing means when there is no optical absorption at the wavelength of the optical means; and

means for introducing the staple fluid, standard fluid, and fluid to be analyzed into the sample chamber.

4. An optical fluid analyzer as in claim 3 wherein the optical signal has a background level from the other constituants of the fluid to be analyzed when the fluid to be analyzed is in the sample chamber, and wherein the processing means comprises:

neutral channel processing means for converting the optical signal into an electrical signal at least approximating the background portion of the optical signal;

measurement channel processing means for converting the optical signal into an electrical signal of the concentration of the selected constituant and the background; and

output means combining the electrical signals for subtracting the neutral channel signal at least approximating the background from the measurement channel signal of concentration and background, whereby at least much of the background portion of the signal is removed from the combined signal for more accurately extracting the concentration-indicating signal from the combined signal in further electrical signal processing.