System and method for sensing and analyzing gases

• US 20070202012A1
• Filed: 11/01/2004
• Published: 08/30/2007
• Est. Priority Date: 11/12/2003
• Status: Active Grant

• Current Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Original Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Inventors: Steichen, John, Betsill, Harry
• Granted Patent: US 7,763,208 B2
• Time in Patent Office: Days
• US Class Current: 422/98
• CPC Class Codes: G01N 33/0031 comprising two or more sensors, e.g. a sensor array electrochemical electrode arrays G01N27/27

Abstract

Disclosed herein is a device and method for converting the resistances of an array of metal oxide sensors into digital signals, wherein the sensors respond to the concentration of gases surrounding the sensor array. The device includes an electronic excitation device that provides an excitation voltage to the sensors; analog-to-digital signal conversion devices that convert the resistances of the sensors to digital signals; and means for calculating gas concentrations from the digital signals.

Claims

1. A device for converting the resistances of an array of metal oxide sensors into digital signals, wherein the sensors respond to the concentration of gases surrounding the sensor array, and wherein the device comprises:

an electronic excitation device that provides an excitation voltage to the sensors;

analog-to-digital signal conversion devices that convert the sensor resistances to digital signals; and

means for calculating gas concentrations from the digital signals.

2. The device of claim 1, wherein the electronic excitation device provides an excitation voltage to the sensors that periodically reverses polarity.

3. The device of claim 1, wherein the electronic excitation device provides an excitation voltage comprising a short pulse to each sensor, the pulse being applied for less than 10% of the measurement time for each sensor.

4. The device of claim 1, wherein the electronic excitation device provides an excitation voltage comprising a constant direct current voltage.

5. The device of claim 1, wherein each analog-to-digital signal conversion device converts the resistance of each sensor to a digital number representing the ratio of the sensor resistance to a standard resistance.

6. The device of claim 1, wherein each analog-to-digital signal conversion device converts the resistance of each sensor to a digital number representing the log of the ratio of the sensor resistance to a standard resistance.

7. The device of claim 1, wherein each analog-to-digital signal conversion device converts the resistance of each sensor to a digital number representing the numerical log of the sensor resistance.

8. The device of claim 1, wherein each analog-to-digital signal conversion device converts the resistance of each sensor to a digital number representing the reciprocal of the sensor resistance.

9. The device of claim 1, wherein a multiplexer reduces a number of electrical connections between each sensor of the sensor array and the corresponding analog-to-digital conversion device by multiplexing the sensor resistances.

10. The device of claim 1, wherein the sensor array is contained in a housing that includes a cable for connecting the array to the device and an information storage device so that information about the calibration of the sensor array is included in one of the housing or the cable.

11. The device of claim 1, wherein the sensors are arrayed on one surface of a strip of electrically insulating material and a heater is aligned with the array on the other side of the electrically insulating strip, and wherein the temperature of the heater is controlled with a temperature control circuit.

12. The device of claim 11, wherein the heater is comprised of two dissimilar metals forming a thermocouple near the array, the heater being a source of heat and simultaneously a temperature measurement point for the temperature control circuit.

13. The device of claim 11, wherein two sensing conductors are attached to opposite ends of a heat-generating section of the heater to form heat sensing leads of a four-wire resistance measuring circuit.

14. The device of claim 11, wherein one of the sensors is a thermistor that is a control point for the temperature control circuit and a variable in the determination of gas concentrations.

15. The device of claim 11, wherein the control point temperature is calculated from the sensor resistances.

16. A method for converting the resistances of an array of metal oxide sensors into digital signals, wherein the sensors respond to the concentration of gases surrounding the sensor array, and wherein the method comprises:

performing an electronic excitation voltage to the sensors with an electronic excitation device;

converting the sensor resistances to digital signals with analog-to-digital signal conversion devices; and

calculating gas concentrations from the digital signals.

17. The method of claim 16, wherein the electronic excitation step comprises providing an excitation voltage to the sensors that periodically reverses polarity.

18. The method of claim 16, wherein the electronic excitation step comprises providing an excitation voltage comprising a short pulse to each sensor, the pulse being applied for less than 10% of the measurement time for each sensor.

19. The method of claim 16, wherein the electronic excitation step comprises providing an excitation voltage comprising a constant direct current voltage.

20. The method of claim 16, wherein each analog-to-digital signal conversion device converts the resistance of each sensor to a digital number representing the ratio of the sensor resistance to a standard resistance.

21. The method of claim 16, wherein the converting step comprises converting the resistance of each sensor to a digital number representing the log of the ratio of the sensor resistance to a standard resistance.

22. The method of claim 16, wherein the converting step comprises converting the resistance of each sensor to a digital number representing the numerical log of the sensor resistance.

23. The method of claim 16, wherein the converting step comprises converting the resistance of each sensor to a digital number representing the reciprocal of the sensor resistance.

24. The method of claim 16, further comprising reducing a number of electrical connections between each sensor of the sensor array and the corresponding analog-to-digital conversion device by multiplexing the sensor resistances.

25. The method of claim 16, further comprising providing a housing that contains the sensor array and includes a cable for connecting the array to the device and an information storage device so that information about the calibration of the sensor array is included in one of the housing or the cable.

26. The method of claim 16, further comprising:

arraying the sensors on one surface of a strip of electrically insulating material;

aligning a heater with the array on the other side of the electrically insulating strip; and

controlling the temperature of the heater with a temperature control circuit.

27. The method of claim 26, wherein the heater is comprised of two dissimilar metals forming a thermocouple near the array, the heater being a source of heat and simultaneously a temperature measurement point for the temperature control circuit.

28. The method of claim 26, further comprising:

attaching two sensing conductors to opposite ends of a heat-generating section of the heater to form heat sensing leads of a four-wire resistance measuring circuit.

29. The method of claim 26, wherein one of the sensors is a thermistor that is a control point for the temperature control circuit and a variable in the determination of gas concentrations.

30. The method of claim 16, further comprising:

arraying a first plurality of sensors on a surface of an electrically insulating material;

arraying a second plurality of sensors on another surface of the electrically insulating material;

aligning a heater within the electrically insulating material, between the sensor arrays; and

controlling the temperature of the heater with a temperature control circuit.