Gas sensors and method of using same

• US 5,741,413 A
• Filed: 06/26/1996
• Issued: 04/21/1998
• Est. Priority Date: 12/18/1993
• Status: Expired due to Fees

• Current Assignee: SEM Company Limited
• Original Assignee: SEM Company Limited
• Inventors: Capetanopoulos, Constantine Dean
• Primary Examiner(s): Tung, T.
• Application Number:
  US08/670,425
• Time in Patent Office: 664 Days
• Field of Search: 204/415, 205/782, 205/782.5, 205/783
• US Class Current: 205/783
• CPC Class Codes: G01N 33/0062 concerning the measuring method or the display, e.g. intermittent measurement or digital display

Abstract

A method of calibrating and using a device for the determination of the concentration of an active gas in a mixture of gases wherein the device incorporates a gas sensor (4) and has gas diffusion barrier means (A) and (B), one of which may be closed by a valve (12). The signal from the sensor is recorded at first and second times after closing the valve, and a value for the concentration of an active gas is calculated from the signals and the time difference.

Claims

1. A method of calibrating a device for determining the concentration of an active gas in a gas mixture the device comprising a gas sensor which consumes active gas by reaction at a sensing element and which produces an output signal proportional to the rate of reaction of active gas, the sensor having a gas diffusion barrier means between the gas mixture and the sensing element, valve means actuable to close or restrict said gas diffusion means, means for recording output signals from the sensor and means for processing said output signals, wherein the method of calibrating the gas sensor includes the steps of passing a gas of known concentration at constant temperature and pressure over the sensor to provide a constant output from the sensor, actuating the valve means to close or restrict the gas diffusion barrier means, recording a first output signal at a first time subsequent to the closing or restricting of said gas diffusion barrier means, recording a second output signal at a second time subsequent to the first time, recording the time interval therebetween, and processing the output signals and the time interval to calculate a constant for the device at constant temperature and pressure for the active gas.

2. A method for determining the concentration of an active gas in a gas mixture using a device comprising a gas sensor which consumes active gas by reaction at a sensing element and which produces an output signal proportional to the rate of reaction of active gas, the sensor having a gas diffusion barrier means between the gas mixture and the sensing element, valve means actuable to close or restrict said gas diffusion means, means for recording output signals from the sensor and means for processing said output signals, wherein the method includes the steps of passing the active gas over the gas sensor, actuating the valve means to close or restrict the gas diffusion barrier means, recording a first output signal at a first time subsequent to the closing or restricting of said gas diffusion barrier means, recording a second output signal at a second time subsequent to the first time, recording the time interval therebetween, and processing the output signals and the time interval utilizing a constant for the device calculated according to the method of claim 1 thereby to calculate a value for the concentration of active gas.

3. A method for determining the concentration of an active gas in a gas mixture using a device comprising a galvanic electrochemical gas sensor which consumes active gas by reaction at a sensing element and which produces an output signal proportional to the rate of reaction of active gas, the sensor having a gas diffusion barrier means between the gas mixture and the sensing element, valve means actuable to close or restrict said gas diffusion means, means for recording output signals from the sensor and means for processing said output signals, wherein the method including the steps of passing the active gas over the gas sensor, actuating the valve means to close or restrict the gas diffusion barrier means, recording a first output signal at a first time subsequent to the closing or restricting of said gas diffusion barrier means, recording a second output signal at a second time subsequent to the first time, recording the time interval therebetween, and processing the output signals and the time interval utilizing a constant for the device calculated according to the method of claim 1 thereby to calculate a value for the concentration of active gas.

4. A method according to claim 1 in which the constant is calculated using the equation:

##EQU2## in which C₀ is the concentration of active gas in parts per million S_t is the sensor output signal at the first time, in uA,

S_2t is the sensor output signal at a second time, in uA

t is the time difference between the first and second times, in second, and

A is a constant of the device at constant temperature and pressure, for a given gas.

5. A method for determining the concentration of an active gas in a gas mixture using a device comprising a gas sensor which consumes active gas by reaction at a sensing element and which produces an output signal proportional to the rate of reaction of active gas, the sensor having a gas diffusion barrier means between the gas mixture and the sensing element valve means actuable to close or restrict said gas diffusion means, means for recording output signals from the sensor and means for processing said output signals, wherein the method includes the steps of calibrating the device according to the method of claim 1, passing the active gas over the gas sensor, actuating the valve means to close or restrict the gas diffusion barrier means, recording a first output signal at a first time subsequent to the closing or restricting of said gas diffusion barrier means, recording a second output signal at a second time subsequent to the first time, recording the time interval therebetween, and processing the output signals and the time interval utilizing a constant for the device calculated according to the method of claim 1 thereby to calculate a value for the concentration of active gas.

6. A method according to claim 5, wherein the gas sensor is a galvanic electrochemical sensor.

7. The device of claim 5, wherein the gas diffusion barrier means comprises a plurality of capillaries, the valve means comprises a plunger actuated by a piston rod arrangement operated by a solenoid to seal all or less than all of the capillaries while calibrating the device.

8. The method of claim 1, wherein the gas diffusion barrier means comprises a plurality of capillaries, the valve means comprises a plunger actuated by a piston rod arrangement operated by a solenoid to seal all or less than all of the capillaries while calibrating the device.

9. A device for determining the concentration of an active gas in a gas mixture comprising a gas sensor having a sensing element and capable of producing an output signal proportional to the rate of reaction of the active gas at the sensing element, which sensor incorporates at least first gas diffusion barrier means, valve means for closing or restricting said at least first gas diffusion barrier means, means for recording a first output signal from the sensor at a first time subsequent to the closing of the valve means, and for recording a second output at a second time subsequent to said first time, and means for processing the said first and second output signals with the time interval between said first and second times to calculate a value for active gas concentration.

10. A device according to claim 9 in which a second gas diffusion barrier means is provided having a higher resistance to flow of gas than said first gas diffusion barrier means.

11. A device according to claim 9 in which the gas sensor is a galvanic electrochemical sensor.

12. A device according to claim 9 in which the gas diffusion barrier means comprises at least one capillary.

13. A device according to claim 12 in which the gas diffusion barrier means is a single capillary.

14. A device according to claim 12 in which the gas diffusion barrier means comprises a plurality of capillaries.

15. A device according to claim 9 in which the valve means comprises a plunger actuated by a piston rod arrangement operated by a solenoid.

16. A device according to claim 9 in which the gas sensor is an electrochemical CO sensor.