Automated FTIR gas analyzer

• US 20080179529A1
• Filed: 01/30/2007
• Published: 07/31/2008
• Est. Priority Date: 01/30/2007
• Status: Active Grant

• Current Assignee: Airgas Incorporated (Air Liquide SA)
• Original Assignee: Airgas Incorporated (Air Liquide SA)
• Inventors: DesPlaines, Edward Russell, Weiss, Steve, Shock, Robert, Cotteleer, Mike, Paradis, Terry, Gruenbacher, James, Bertuleit, William, Jacaruso, Richard, Perdion, Cliff, Camardo, Joe
• Granted Patent: US 7,598,494 B2
• Time in Patent Office: Days
• US Class Current: 250/343
• CPC Class Codes: G01N 2021/3595 using FTIR
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A system for certifying a concentration of gas in a cylinder includes a gas cell configured to receive a sample gas from a cylinder, and an FTIR module coupled to the gas cell for scanning the sample gas and forming a beam spectrum. A processor is coupled to the FTIR module for calculating an intensity response of the sample gas based on the beam spectrum. A storage device is included for storing data points of a plot of intensity response of a known gas versus concentration levels. The processor is configured to interpolate between the stored data points of the plot to determine an interpolated data point corresponding to the intensity response of the sample gas. The processor provides to the user a concentration level of the sample gas, based on the interpolated data point.

Claims

1. A system for certifying to a user a concentration of gas in a cylinder comprising:

a gas cell configured to receive a sample gas from a cylinder,

an FTIR coupled to the gas cell for scanning the sample gas and forming a beam spectrum,

a processor coupled to the FTIR for calculating an intensity response of the sample gas based on the beam spectrum,

a storage device for storing data points of a plot of intensity response of a known gas versus concentration levels,

wherein the processor is configured to interpolate between the stored data points of the plot to determine an interpolated data point corresponding to the intensity response of the sample gas, and

provide to the user a concentration level of the sample gas based on the interpolated data point.

2. The system of claim 1 wherein

the processor is configured to execute an integration algorithm for determining an area of at least one region of the beam spectrum, and provide the determined area as the intensity response of the sample gas.

3. The system of claim 2 wherein

the storage device includes data points of a plot of area versus concentration levels of the known gas.

4. The system of claim 3 wherein

the processor includes a curve fitting algorithm for finding data points of the intensity response of the known gas versus concentration levels, based on a plurality of scans performed by the FTIR on a corresponding plurality of cylinders each containing the known gas, and

the processor is configured to store the data points in the storage device as the plot of intensity response of the known gas versus concentration levels.

5. The system of claim 4 wherein

the curve fitting algorithm depends on at least ten scans performed by the FTIR on a corresponding ten cylinders containing the known gas.

6. The system of claim 4 wherein

the curve fitting algorithm uses at least one of a linear, quadratic, cubic or quartic orders of a polynomial equation.

7. The system of claim 1 including

the gas cell configured to receive a standard gas from a cylinder and a zero gas from another cylinder,

the FTIR configured to scan the standard gas and the zero gas, and

the processor is configured to calculate an intensity response of the standard gas and an intensity response of the zero gas,

wherein the intensity response of the sample gas is Xn, the intensity response of the standard gas is Yn, and the intensity response of the zero gas is Zn, and

a resultant intensity response of the sample gas is based on the following equation:

$\mathrm{Rn}=\left(\frac{\mathrm{Ya}}{\mathrm{Yn}-\mathrm{Zn}}\right)<br><br>\mathrm{Xn}-\left(\frac{\mathrm{Ya}}{\mathrm{Yn}-\mathrm{Zn}}\right)<br><br>\mathrm{Zn}$

where;

Xn is the sample results,

Yn is the standard results,

Ya is the actual results of the standard gas provided by the user,

Zn is the zero results,

n is the number of the triad (3 per analysis), and

Rn is the resultant intensity response of the sample gas.

8. The system of claim 1 including

the gas cell configured to receive a standard gas from a cylinder and a zero gas from another cylinder,

the FTIR configured to scan the standard gas and the zero gas, and

the processor is configured to calculate an intensity response of the standard gas and an intensity response of the zero gas,

wherein a resultant intensity response of the sample gas is calculated based on a sequence of first, second and third triads,

the first triad includes a scan order of scanning first the zero gas, second the standard gas, and third the sample gas, and then computing a first correction,

the second triad includes a scan order of scanning first the standard gas, second the zero gas, and third the sample gas, and then computing a second correction,

the third triad includes a scan order of scanning first the standard gas, second the sample gas, and third the zero gas, and then computing a third correction, and

the resultant intensity response is based on the first, second and third corrections.

9. The system of claim 1 including

a gas divider disposed between the gas cell and the cylinder for diluting the concentration of the sample gas in the cylinder,

wherein when the sample gas in the cylinder has a concentration level greater than the concentration levels of the known gas stored in the storage device, then the gas divider is configured to dilute the sample gas before scanning.

10. The system of claim 1 including

a valve disposed at an output port of the gas cell,

the valve adaptively tunable to vent the gas from the output port,

wherein the processor includes a PID algorithm to tune the valve to vent the gas at a predetermined pressure level, and

the FTIR begins scanning the sample gas after the PID algorithm tunes the valve to vent at the predetermined pressure level.

11. A system for certifying a concentration of gas in a cylinder comprising:

a gas cell configured to receive a gas and provide an optical path for an interference measurement on the gas,

a first valve disposed at an output port of the gas cell,

the first valve adaptively tunable to vent the gas from the output port,

a processor for adaptively tuning the first valve to vent the gas at a first pressure level,

an interferometer coupled to the gas cell for forming an interferogram of the gas, and

a storage device for storing the interferogram,

wherein the interferogram is formed after the first valve is tuned to vent the gas at the first pressure level, and

the interferogram is compared with at least another interferogram previously stored in the storage device to certify the concentration of the gas.

12. The system of claim 11 including

a second valve disposed at an input port of the gas cell,

wherein the second valve is configured to throttle the gas into the input port at a second pressure level, and

the processor is configured to adjust the throttle of the second valve at the second pressure level.

13. The system of claim 12 wherein

the processor is configured to adaptively tune the first pressure level to a pressure level higher than the second pressure level.

14. The system of claim 11 wherein

the processor includes an algorithm to adaptively tune the first valve using at least one of proportional action, integral action and derivative action.