Gas analyzer

• US 3,932,754 A
• Filed: 03/27/1974
• Issued: 01/13/1976
• Est. Priority Date: 01/22/1973
• Status: Expired due to Term

• Current Assignee: OFC Corp. (New Hampshire) (Corning Incorporated)
• Original Assignee: Infrared Industries, Inc.
• Inventors: Ross, Thaddeus C., Riedl, Max J.
• Primary Examiner(s): Church, Craig E.
• Application Number:
  US05/455,345
• Time in Patent Office: 657 Days
• Field of Search: 250/343, 250/344, 250/345, 250/346
• US Class Current: 250/343
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A multiple gas analyzer is disclosed utilizing the infrared absorption principle for determining the quantity of two or more gases with a sample tube and a reference tube in parallel orientation with an infrared source between one end of the two tubes, and an infrared detector assembly between the other end of the tubes. Immediately opposed to each end of the tubes are a pair of mirrors, one being a transmitting mirror remote from the infrared source and directing the infrared beam in parallel paths through the reference tube and sample tube, and a receiving mirror opposite the infrared detector assembly to focus the infrared beam after passing through the tubes on to the infrared detectors. A chopper disc is interposed between the infrared source and the transmitting mirror to provide intermittently direct pulses to the infrared beam through the reference tube and sample tube to the infrared detectors, and a circuit is provided to compare the differential of signal strength from the two signals generated by each of the detectors and to calibrate the same with regard to the gas content being read. Filters are provided in the infrared detector assembly for that particular wave length in which the gas finds its signature for photon absorption. In the circuit, provision is made to first calibrate the unit for ambient variables, and thereafter to calibrate the unit against a factory determined span gas sample by means of vignetting the sample chamber to simulate a convenient up-scale reading of the particular gas being calibrated. Further adjustment is provided for comparing the high scale with the low scale in the course of sampling to thereby fully calibrate the unit and check the same during its operation.

Claims

1. A gas analyzer of the infrared absorption character comprising, in combination,

a frame,

a sample tube,

a reference tube,

said sample and reference tubes both being supported by the frame,

an infrared source positioned at one end of the tubes,

a detector means comprising a plurality of detectors and a filter over each of said detectors appropriate to a component to be analyzed positioned at a spot remote from the infrared source,

a transmitting mirror remote from the infrared source and said tubes proportioned optically to receive, to split, and to image the split parts of the infrared beam back through each the sample tube and the reference tube in substantially equal intensity,

a receiving mirror remotely opposed to said transmitting mirror and opposite the detector means optically proportioned to direct the respective imaged split parts of the infrared beam from said tubes toward the respective ones of said plurality of detectors,

the path lengths of said infrared beam from said infrared source to said sample tube and to said reference tube and from said sample tube and said reference tube to said detector means being identical and the length of said sample and reference tubes being identical, and wherein all elements of the optical system are identical, whereby the optical system of said gas analyzer is completely balanced,

chopper means interposed in said pathway between the infrared source and detector means to alternatively direct the path of the imaged parts of the infrared beam through the sample tube and reference tube so apertured that energy never passes through both tubes simultaneously but rather passes through each tube for less than one half the time for one rotation of the chopper means thereby alternately gating energy through the reference tube and the sample tube with a time gap therebetween,

and readout means in circuit relationship to each of said detectors to compare the signal attenuation through the sample chamber with the reference chamber and calibrate the same to read the concentration of gas specific to the wave length of the detector'"'"'s associated filter proportional to the signal differential between the reference tube and the sample tube, thereby enabling the gas analyzer to read out two or more components simultaneously without time sharing, said readout means in circuit relationship to each of said detectors comprising,

amplifier means for amplfying the output signal from said detector,

gain control means directly coupled to said amplifier means,

a reference clamp for clamping to ground the output signal during the time the infrared beam passes through the reference tube,

an automatic gain control amplifier for providing a peak-to-peak signal of a pre-established value, the clamped and amplitude stabilized signal from said gain control means and said reference clamp being coupled to said automatic gain control amplifier,

means for sampling the signal amplitude as said infrared beam passes through said sample tube,

means for storing said sampled output, and

means for coupling said stored sampled output to meter means for indicating the variation in signals between said reference tube and said sample tube from the same detector as the copper alternately directs signals through each of said tubes.

2. In the gas analyzer of claim 1,

said chopper means being positioned between the infrared source and the transmitting mirror.

3. In the gas analyzer of claim 1 said detectors are aligned in close proximity one to another, and the related filters are positioned in close proximate relationship to each detector.

4. In the gas analyzer of claim 1,

vignetting means positionable to a stationary position to interrupt the path of radiation from said source through the sample chamber,

said vignetting means being proportioned to a desired full meter reading equivalent to the concentration of the particular gas involved thereby simulating the photon absorption of that particular gas as the same passes through the sample tube, whereby said gas analyzer is provided with means for calibrating the same to full meter strength, based upon a simulation of a known standard span gas.

5. In the gas analyzer of claim 1, each of said meter means comprising,

means providing for a high range scale reading and a low range scale reading,

switch means for presetting the meter for the high range or low range scale reading,

an adjustment means on the low range scale reading whereby, when a particular reading is observed on the high range scale reading, the low range scale reading may be switched into operation, and calibrated to read the same reading as noted on the high range scale reading.

6. In the gas analyzer of claim 5,

the ratio between the high range and low range scale readings being two to one.

7. In the gas analyzer of claim 1, further including trimmer resistance means for calibrating said readout means to compensate for variations in the readings thereof for span gases and exhaust gases, whereby the presence in the exhaust gases of several constituents which differ slightly from the spectral signatures of the pure span gases but whose contributions are conventionally included in the total measurement can be compensated for when actual exhaust gases are analyzed.

8. In the gas analyzer of claim 7, wherein said trimmer resistance means are arranged to be disconnected from circuit relationship with said readout means during calibration of the gas analyzer using span gases.

9. In the gas analyzer of claim 7, pump means for positively directing the exhaust gas through the sample tube, said pump means arranged to be rendered inoperative during calibration of the gas analyzer using span gases, said trimmer resistance means being arranged to be automatically disconnected from circuit relationship with said readout means when said pump means is rendered inoperative.