# US 2019/0170638 A1 · Wavelength modulation spectroscopy gas sensor calibration

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- Number: US 2019/0170638 A1
- Document ID: US20190170638A1
- Status: Published application
- Kind: A1
- Application number: 15/996,453
- Filed: 2018-06-02
- Published: 2019-06-06
- Earliest claimed: 2017-06-02
- Assignees: NEC Laboratories America, Inc.
- Applicants: NEC Laboratories America
- Inventors: Ming-Fang HUANG
- Web page: https://patentgrep.com/patent/US20190170638A1

## CPC

- G01N 21/274: {Calibration, base line adjustment, drift correction}
- G01N 21/39: using tunable lasers
- G01N 21/59: Transmissivity (G01N21/25 takes precedence)
- G01N 33/00: Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N 33/004: {CO or CO2}
- G01N 21/3504: for analysing gases, e.g. multi-gas analysis
- G01N 2201/1241: Multirange
- G01N 2201/12746: Calibration values determination
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

Aspects of the present disclosure describe gas sensor calibration methods and subsequent sensing methods employing same in conjunction with wavelength modulation spectroscopy (WMS). Additional aspects of the present disclosure advantageously employ WMS for highly-sensitive gas concentration measurement across a range of concentrations from ambient to a high concentration environment such as fire/smoke detection. Finally, still further aspects of the present disclosure determine and then employ two calibration factors and during measurement WMS-2f spectra to determine an inflection or “turning point” and subsequently which one of the two calibration factors to employ at a given concentration.

## Claims

### Claim 1

A wavelength modulation spectroscopy (WMS) gas sensor calibration and detection method comprising:
measuring WMS-2f amplitudes for a gas over a range of known concentrations;
identifying, from the measured amplitudes, a first calibration factor (f1) for low concentrations of the gas and a second calibration factor (f2) for high concentrations of the gas.

### Claim 2 (depends on 1)

The method of claim 1 further comprising:
generating a WMS-2f signal spectra for an unknown concentration of the gas;
determining whether the generated WMS-2f signal spectra exhibits a single peak or dual peaks; and
selecting one of the identified calibration factors f1 or f2 based on the number of peaks determined.

### Claim 3 (depends on 3)

The method of claim 3 further comprising:
determining, using the selected calibration factor, the concentration of the gas whose concentration was unknown.

### Claim 4 (depends on 3)

The method of claim 3 further comprising:
displaying and storing the determined concentration.

### Claim 5 (depends on 4)

The method of claim 4 wherein the first calibration factor (f1) and the second calibration factor (f2) are identified by their position(s) relative to an inflection point on a graph of the measured WMS-2f amplitudes.

### Claim 6 (depends on 4)

The method of claim 4 wherein the gas of unknown concentration is Carbon Dioxide gas (CO2).

### Claim 7

A wavelength modulation spectroscopy (WMS) gas sensing system comprising:
a light source;
a gas cell through which light emitted from the source is directed;
a detector that measures light that passes though the cell; and
an acquisition and control system that:
measures WMS-2f amplitudes for a gas contained in the cell over a range of known concentrations; and
identifies, from the measured amplitudes, a first calibration factor (f1) for low concentrations of the gas and a second calibration factor (f2) for high concentrations of the gas.

### Claim 8 (depends on 7)

The system of claim 7 wherein the acquisition and control system:
generates a WMS-2f signal spectra for an unknown concentration of the gas;
determines whether the generated WMS-2f signal spectra exhibit a single peak or dual peaks; and
selects one of the identified calibration factors f1 or f2 based on the number of peaks determined.

### Claim 9 (depends on 8)

The system of claim 8 wherein the acquisition and control system:
determines, using the selected calibration factor, the concentration of the gas whose concentration was unknown.

### Claim 10 (depends on 9)

The system of claim 9 wherein the acquisition and control system:
displays and stores the determined concentration.

### Claim 11 (depends on 10)

The system of claim 10 wherein the first calibration factor (f1) and the second calibration factor (f2) are identified by their position(s) relative to an inflection point on a graph of the measured WMS-2f amplitudes.

### Claim 12 (depends on 11)

The system of claim 11 wherein the gas of unknown concentration is Carbon Dioxide gas (CO2).