Sensing Systems and Methods for the Estimation of Analyte Concentration

Abstract

A method of gas sensing performed by a processor electrically coupled to a gas sensor includes obtaining, by the gas sensor, a first electrical signal indicating a response of the gas sensor to a concentration of a target gas at the gas sensor, generating one or more second electrical signals according to the first electrical signal, determining a first condition in which the concentration at the gas sensor is increasing using the first electrical signal and the one or more electrical second signals, determining a second condition occurring after the first condition in which the concentration at the gas sensor is substantially constant using the first electrical signal and the one or more second electrical signals, and calculating a concentration value of the target gas according to the first electrical signal and the one or more second electrical signals. The calculating is performed while the concentration is substantially constant.

What is claimed is: 
     
         1 . A method of gas sensing performed by a processor electrically coupled to a gas sensor, the method comprising:
 obtaining, by the gas sensor, a first electrical signal indicating a response of the gas sensor to a concentration of a target gas at the gas sensor;   generating one or more second electrical signals according to the first electrical signal;   determining a first condition in which the concentration of the target gas is increasing at the gas sensor using the first electrical signal and the one or more electrical second signals;   determining a second condition in which the concentration at the gas sensor is substantially constant using the first electrical signal and the one or more second electrical signals, the second condition occurring after the first condition; and   calculating a concentration value of the target gas according to the first electrical signal and the one or more second electrical signals, the calculating performed while the concentration is substantially constant.   
     
     
         2 . The method of  claim 1 , wherein the first electrical signal comprises a resistance of the gas sensor. 
     
     
         3 . The method of  claim 1 , wherein the one or more second electrical signals comprise a derivative of the first electrical signal. 
     
     
         4 . The method of  claim 1 , wherein the one or more second electrical signals comprise an integral of the first electrical signal. 
     
     
         5 . The method of  claim 1 , further comprising:
 determining a third condition in which the concentration at the gas sensor is substantially constant and approximately zero using the first electrical signal and the one or more second electrical signals; and   calibrating the gas sensor while the concentration is substantially constant and approximately zero.   
     
     
         6 . The method of  claim 1 , further comprising:
 determining a third condition in which the concentration at the gas sensor is decreasing using the first electrical signal and the one or more second electrical signals, the third condition occurring after the second condition.   
     
     
         7 . The method of  claim 6 , further comprising:
 determining a fourth condition in which the concentration at the gas sensor is substantially constant and approximately zero using the first electrical signal and the one or more second electrical signals; and   calibrating the gas sensor while the concentration is substantially constant and approximately zero.   
     
     
         8 . The method of  claim 1 , further comprising:
 determining a first subcondition of the first condition in which the concentration of the target gas is below a threshold concentration according to the first electrical signal and the one or more second electrical signals;   setting a stored calibration coefficient to a first coefficient in response to determining the first subcondition;   determining a second subcondition of the first condition in which the concentration of the target gas is not below the threshold concentration according to the first electrical signal and the one or more second electrical signals;   setting the stored calibration coefficient to a second coefficient in response to determining the second subcondition; and   wherein calculating the concentration value of the target gas further comprises calculating the concentration value of the target gas according to the stored calibration coefficient, the first electrical signal, and the one or more second electrical signals.   
     
     
         9 . A gas sensing system comprising:
 a gas sensor disposed on a first substrate, the gas sensor being configured to detect a target gas and generate a first electrical signal indicating a response of the gas sensor to a concentration of the target gas at the gas sensor,   a processor operatively coupled to the gas sensor, and   a memory storing a program to be executed by the processor, the program comprising instructions for
 obtaining, by the gas sensor, the first electrical signal indicating a response of the gas sensor to the concentration of the target gas at the gas sensor, 
 generating one or more second electrical signals according to the first electrical signal, 
 determining a first condition in which the concentration of the target gas is increasing at the gas sensor using the first electrical signal and the one or more electrical second signals, 
 determining a second condition in which the concentration at the gas sensor is substantially constant using the first electrical signal and the one or more second electrical signals, the second condition occurring after the first condition, and 
 calculating a concentration value of the target gas according to the first electrical signal and the one or more second electrical signals, the calculating performed while the concentration is substantially constant. 
   
     
     
         10 . The gas sensing system of  claim 9 , wherein the first electrical signal comprises a resistance of the gas sensor. 
     
     
         11 . The gas sensing system of  claim 9 , wherein the one or more second electrical signals comprise a derivative of the first electrical signal. 
     
     
         12 . The gas sensing system of  claim 9 , wherein the one or more second electrical signals comprise an integral of the first electrical signal. 
     
     
         13 . The gas sensing system of  claim 9 , wherein the program further comprises instructions for:
 determining a third condition in which the concentration at the gas sensor is substantially constant and approximately zero using the first electrical signal and the one or more second electrical signals; and   calibrating the gas sensor while the concentration is substantially constant and approximately zero.   
     
     
         14 . The gas sensing system of  claim 9 , wherein the program further comprises instructions for:
 determining a third condition in which the concentration at the gas sensor is decreasing using the first electrical signal and the one or more second electrical signals, the third condition occurring after the second condition.   
     
     
         15 . The gas sensing system of  claim 14 , wherein the program further comprises instructions for:
 determining a fourth condition in which the concentration at the gas sensor is substantially constant and approximately zero using the first electrical signal and the one or more second electrical signals; and   calibrating the gas sensor while the concentration is substantially constant and approximately zero.   
     
     
         16 . The gas sensing system of  claim 9 , wherein the program further comprises instructions for:
 determining a first subcondition of the first condition in which the concentration of the target gas is below a threshold concentration according to the first electrical signal and the one or more second electrical signals;   setting a stored calibration coefficient to a first coefficient in response to determining the first subcondition;   determining a second subcondition of the first condition in which the concentration of the target gas is not below the threshold concentration according to the first electrical signal and the one or more second electrical signals;   setting the stored calibration coefficient to a second coefficient in response to determining the second subcondition; and   wherein calculating the concentration value of the target gas further comprises calculating the concentration value of the target gas according to the stored calibration coefficient, the first electrical signal, and the one or more second electrical signals.   
     
     
         17 . A method of gas sensing performed by a gas sensing system comprising a processor electrically coupled to a gas sensor, the method comprising:
 (1) obtaining, by the gas sensor, a first electrical signal indicating a resistance of the gas sensor to a concentration of a target gas at the gas sensor;   (2) generating a second electrical signal indicating a derivative of the first electrical signal according to the first electrical signal;   (3) comparing the derivative to zero;   (4) checking a current status of the gas sensing system in response to determining in step (3) that the derivative is substantially equal to zero;   (5) comparing the resistance to a threshold resistance in response to determining in step (4) that the current status is not a processing state;   (6a) in response to determining in step (5) that the resistance is less than the threshold resistance, setting a stored calibration coefficient to a first calibration coefficient value;   (6b) in response to determining in step (5) that the resistance is not less than the threshold resistance, setting the stored calibration coefficient to a second calibration coefficient value;   (7) repeating steps (1) through (4) in response to setting the stored calibration coefficient in step (5a) or step (5b); and   (8) setting the current status to the processing state and calculating a concentration value of the target gas using the stored calibration coefficient.   
     
     
         18 . The method of  claim 17 , further comprising:
 (9) comparing the derivative to a first threshold derivative in response to determining in step (3) that the derivative is not substantially equal to zero;   (10) setting the current status to a preparation state and repeating steps (1) through (4) in response to determining in step (9) that the derivative is greater than the first threshold derivative; and   wherein step (5) is performed in response to also determining that the current status is not the preparation state.   
     
     
         19 . The method of  claim 18 , further comprising:
 (11) comparing the derivative to a second threshold derivative in response to determining in step (9) that the derivative is not greater than the first threshold derivative, the second threshold derivative being less than zero;   (12) checking the current status of the gas sensing system in response to determining in step (11) that the derivative is less than the second threshold derivative; and   (13) setting the current status to a recovery state and repeating steps (1) through (4) in response to determining that the current status is the processing state or the recovery state.   
     
     
         20 . The method of  claim 17 , wherein:
 the first calibration coefficient value corresponds with a first regime in which the gas sensing system is approaching equilibrium with an ambient environment; and   the second calibration coefficient value corresponds with a second regime in which the gas sensing system has reached substantial equilibrium dominated by specific adsorption of the target gas.