Apparatus and methods for predicting gas sensor sensitivity changes

1. A method for monitoring gas sensor sensitivity, comprising:

repeatedly determining a gas sensor response from a gas sensor by exposing the gas sensor to a gas; and

transmitting each gas sensor response, information identifying a gas detector, and calibration time values to a remote computer; and

using the remote computer to:

calculate a trend of sensitivity values for the gas detector over time based on the received gas sensor responses and corresponding calibration time values;

determine a renewal time of the gas sensor when the calculated trend intersects a predetermined value; and report the renewal time.

2. The method according to claim 1 , wherein at least one of the sensitivity values is determined by a bump test, wherein the sensitivity values are determined based on a dynamic response of the gas sensor to the gas.

3. The method according to claim 2 , wherein the bump test has a duration of less than 45 seconds.

4. The method according to claim 3 , wherein the bump test is configured to end before a gas sensor response has stabilized.

5. The method according to claim 4 , wherein at least one of the sensitivity values is determined during a calibration, wherein the sensitivity value is determined based on a stable response of the gas sensor to the gas.

6. The method according to claim 5 , wherein the gas detector is configured to measure a flow rate of the gas past the gas sensor.

7. The method according to claim 1 , wherein the method comprises:

determining a bump-test sensitivity value by a bump test;

determining a calibration sensitivity value by a calibration; and

adjusting, based on the calibration, at least one of: the bump-test sensitivity value and a confidence interval associated with the bump-test sensitivity value.

8. The method according to claim 1 , wherein the method comprises:

determining a bump-test sensitivity value by a bump test;

determining a calibration sensitivity value by a calibration;

assigning confidence intervals to the bump-test sensitivity value and the calibration sensitivity value, wherein the bump-test confidence interval is larger than the calibration confidence interval.

9. The method according to claim 8 , wherein the method comprises using the remote computer to detect anomalous results by identifying determined sensitivity values which are outside the calculated sensitivity trend.

10. The method according to claim 9 , wherein the method comprises using the remote computer to calculate a fit coefficient, the fit coefficient being a measure of a variance of sensitivity data over time with respect to the calculated trend; and to adjust the determined renewal time based on the calculated fit coefficient.

11. The method according to claim 10 , wherein the renewal time is re-calculated after each calibration.

12. The method according to claim 11 , wherein the gas detector is configured to measure environmental conditions at a time of the calibration, and transmit the measured environmental conditions to the remote computer; and wherein the remote computer is configured to calculate the trend of sensitivity based on most recent determined sensitivities which are within a predetermined environmental condition range.

13. The method of claim 12 , wherein the environmental conditions comprise one or more of: humidity, pressure and temperature.

14. The method according to claim 13 , further comprising measuring a location of the gas detector at the time of the calibration, and transmit the measured location to the remote computer; and wherein the remote computer is configured to calculate the trend of sensitivity based on the most recent determined sensitivities which are within a predetermined location range.

15. The method according to claim 14 , wherein the remote computer is configured to determine a mathematical form of the trend based on sensitivity data received from other gas sensors of a same type.

16. The method according to claim 15 , wherein the remote computer is configured to identify a gas sensor replacement by detecting a jump in sensitivity followed by a decline in sensitivity following a new trend.

17. The method according to claim 16 , wherein the trend is monitored over at least 3 months and comprises at least 10 received sensitivity values from the gas detector.

18. The method according to claim 17 , wherein the gas sensor has a unique identification number which is transmitted with the sensitivity values.

19. A system for monitoring gas sensor sensitivity comprising:

a gas sensor configured to repeatedly determine a gas sensor response by exposing the gas sensor to a gas; and

a remote computer configured to receive each gas sensor response, information identifying a gas detector, and calibration time values;

wherein the remote computer is further configured to:

calculate a trend of sensitivity values for the gas detector over time based on the received gas sensor responses and corresponding calibration time values;

determine a renewal time of the gas sensor when the calculated trend intersects a predetermined value; and

report the renewal time.

20. A method for determining gas sensor sensitivity comprising:

repeatedly performing a bump test by exposing a gas sensor to a gas and measuring dynamic gas sensor responses;

transmitting the dynamic gas sensor responses, information identifying a gas detector, and calibration time values to a remote computer; and

using the remote computer to:

compare the dynamic gas sensor responses to one or more calibration curves;

calculate a trend of sensitivity values for the gas detector over time based on the received dynamic gas sensor responses and corresponding calibration time values; and

determine a sensitivity value of the gas sensor when the calculated trend intersects a predetermined value; and

report the sensitivity value.