Automatic calibration mode for carbon dioxide sensor

• US 6,588,250 B2
• Filed: 04/27/2001
• Issued: 07/08/2003
• Est. Priority Date: 04/27/2001
• Status: Expired due to Term

• Current Assignee: Amphenol Thermometrics, Inc. (Amphenol Corporation)
• Original Assignee: Edwards Systems Technology, Inc.
• Inventors: Schell, Michael B.
• Primary Examiner(s): RAEVIS, ROBERT R
• Application Number:
  US09/842,622
• Publication Number:
  US 20020157447A1
• Time in Patent Office: 802 Days
• Field of Search: 73/10.6, 73/10.7, 340/632, 340/526
• US Class Current: 73/1.06
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 33/0006 Calibrating gas analysers
• CPC Class Codes: G01N 33/004 for CO, CO2
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

An automatic calibration mode for a carbon dioxide sensor is based on using a zero gas. The sensor is designed to recognize a distinctive rate of change pattern of carbon dioxide concentrations that would be indicative of a zero calibration routine. This approach can be used for other infrared sensors.

Claims

1. A method for automatic calibration of a carbon dioxide sensor, comprising the steps of:

determining a baseline carbon dioxide concentration value for sensor operation;

injecting a zero gas into said sensor;

determining whether at least one drop in carbon dioxide concentration value occurs below the baseline value over a predetermined time period; and

activating recalibration of said sensor when said drop in carbon dioxide concentration occurs.

2. The method according to claim 1, further comprising:

recognizing a predetermined rate of change pattern of carbon dioxide concentrations.

3. The method according to claim 2, further comprising:

resetting the sensor'"'"'s calibration, once said predetermined rate of change pattern is identified, based on the carbon dioxide concentration measured.

4. The method according to claim 1, wherein the step of determining the baseline carbon dioxide concentration value for sensor operation is user-definable.

5. The method according to claim 1, wherein the step of determining the drop in carbon dioxide concentration over said predetermined time period is user-definable.

6. The method according to claim 1, wherein said drop is 200 parts per million over a five-minute period.

7. The method according to claim 1, wherein said drop includes a range from 200 to 300 ppm over 15 to 30 seconds.

8. The method according to claim 1, wherein said drop in sensor reading over a five-minute time period is indicative of a zero gas, causing the sensor to recalibrate said reading to be a zero point.

9. The method according to claim 1, wherein the step of activating recalibration includes resetting the sensor'"'"'s calibration with a microprocessor-driven switch.

10. The method according to claim 1, further comprising:

performing a diagnostic routine to determine stability of one or more sensor readings over another predetermined period of time.

11. The method according to claim 1, further comprising:

activating an alarm strategy when the step of activating recalibration occurs.

12. The method according to claim 11, wherein said step of activating an alarm strategy includes activating at least one of a visible and audible alarm.

13. The method according to claim 11, wherein said step of activating an alarm strategy includes activating at least one of a visible and audible alarm upon a single occurrence of resetting of the sensor'"'"'s calibration.

14. The method according to claim 11, wherein said step of activating an alarm strategy includes activating at least one of a visible and audible alarm upon a stable reading for a 30-second period, said stable reading indicating a constant flow of a calibration gas to said sensor.

15. The method according to claim 1, wherein a variation in sensor reading of said carbon dioxide concentration being measured does not exceed a background noise of said sensor.

16. The method according to claim 1, wherein said zero gas is nitrogen.

21. The method according to claim 1, further comprising:

means for recognizing a predetermined rate of change pattern of carbon dioxide concentrations.

17. A system for automatically calibrating a carbon dioxide sensor, said system comprising:

means for determining a baseline carbon dioxide concentration value for sensor operation;

means for injecting a zero gas into the sensor;

means for determining whether at least one drop in carbon dioxide concentration value occurs below the baseline value over a predetermined time period; and

means for activating recalibration of the sensor when said drop in carbon dioxide concentration occurs.

18. The system according to claim 17, wherein the means for determining the baseline carbon dioxide concentration value for sensor operation allows a user to define said baseline carbon dioxide concentration value.

19. The system according to claim 17, wherein the means for determining the drop in carbon dioxide concentration over said predetermined time period allows a user to define said drop in carbon dioxide concentration over said predetermined time period.

20. The system according to claim 17, further comprising:

means for activating an alarm strategy when said means for activating recalibration are used.

22. An apparatus for automatic calibration of a carbon dioxide sensor, comprising:

a detector for determining a baseline carbon dioxide concentration value for sensor operation;

an injector for injecting a zero gas into the sensor, said injector in communication with the sensor;

a microprocessor, wherein said microprocessor determines whether at least one drop in carbon dioxide concentration value occurs below the baseline value over a predetermined time period, said microprocessor in communication with said detector; and

a switch wherein, said switch switches on to activate recalibration of the sensor when said drop in carbon dioxide concentration occurs, said switch being in communication with said microprocessor and the sensor.

23. The apparatus according to claim 22, wherein said detector for determining a baseline carbon dioxide concentration value for sensor operation, accepts user-defined input.

24. The apparatus according to claim 22, wherein the said microprocessor accepts user-defined input.