Automatic calibration mode for carbon dioxide sensor

• US 20020157447A1
• Filed: 04/27/2001
• Published: 10/31/2002
• Est. Priority Date: 04/27/2001
• Status: Active Grant

• Current Assignee: Amphenol Thermometrics, Inc. (Amphenol Corporation)
• Original Assignee: GSBS Development Corp. (SPX Corporation)
• Inventors: Schell, Michael B.
• Granted Patent: US 6,588,250 B2
• Time in Patent Office: Days
• 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. An automatic calibration mode for a carbon dioxide sensor, said mode comprising:

(a) determining a baseline carbon dioxide concentration value for sensor operation;

(b) injecting a zero gas into said sensor;

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

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

2. The calibration mode according to claim 1, further comprising:

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

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

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

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

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

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

10. The calibration mode 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 calibration mode according to claim 1, further comprising:

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

12. The calibration mode 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 calibration mode 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 calibration mode 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 subsequent to said drop, said stable reading indicating a constant flow of a calibration gas to said sensor.

15. The calibration mode 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 calibration mode according to claim 1, wherein said zero gas is nitrogen.