Gas Sensor Thermistor Heating Reversal for Accurate Measurement
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Solution Overview
Problem
Existing gas sensors face issues with thermal history differences between thermistors, leading to inaccuracies in gas concentration measurements.
Innovation Solution
A gas sensor design that alternates the connection and heating temperatures of thermistors, adjusting current flow to equalize self-heating amounts and minimize thermal history differences, using a control circuit to manage the thermistor connection and heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the first and second thermistors are heated to different temperatures (150°C and 300°C) to acquire detection signals, then gas concentration can be measured, but a difference in thermal history occurs between the two thermistors leading to measurement inaccuracies
Solution Approach 1:
The patent implements periodic action by alternating the heating temperatures of the first and second thermistors between two periods. In the first period, the first thermistor is heated to 150°C and the second to 300°C. In the second period, the heating temperatures are reversed. This periodic temperature reversal ensures that both thermistors experience the same thermal history sequence, eliminating thermal history differences while maintaining the ability to measure gas concentration at different temperatures.
Solution Approach 2:
The patent applies preliminary action by performing a preliminary heating process before measurement. Both thermistors are heated to high temperatures (300°C) in advance to eliminate any previous thermal history differences. This preliminary thermal equilibrium ensures that when measurement begins, both thermistors start from the same thermal state, allowing for accurate comparative measurement while maintaining their respective operating temperatures during actual measurement.
2Ease of operation
If the first and second thermistors are connected in series with different heating temperatures to enable gas detection, then detection signal can be obtained, but self-heating amounts differ between thermistors causing thermal history differences
Solution Approach 1:
The patent applies dynamics by making the heating temperatures and connection configuration changeable rather than fixed. The control circuit dynamically adjusts the heating temperatures of the first and second thermistors based on the measurement period. In the first period, the first thermistor is heated to 150°C and the second to 300°C. In the second period, these temperatures are reversed. This dynamic adjustment allows the system to maintain different operating temperatures for gas detection while equalizing thermal history through periodic reversal.
Solution Approach 2:
The patent changes the temperature parameters of the thermistors periodically. The control circuit sets the heating temperature of the first thermistor to 150°C and the second thermistor to 300°C in the first period, then reverses these parameters in the second period. This parameter change strategy allows the system to operate with different temperatures for optimal gas detection while ensuring both thermistors experience identical thermal history sequences, eliminating measurement errors caused by thermal history differences.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design effectively reduces thermal history differences, ensuring accurate and consistent gas concentration measurements by equalizing self-heating amounts across thermistors.
Implementation Method 1
a first heater configured to heat the first thermistor; a second heater configured to heat the second thermistor
Implementation Method 2
heating the first and second heaters such that the heating temperature of the second heater is higher than the heating temperature of the first heater
Implementation Method 3
a detection circuit including a first thermistor and a second thermistor; generate an output signal indicating a concentration of a gas to be measured based on a detection signal appearing at a connection point between the first thermistor and the second thermistor
Implementation Method 4
the level of a detection signal appearing at the connection point of two series-connected thermistors
Data Source
AI summary
Disclosed herein is a gas sensor that includes: first and second thermistors; first and second heaters configured to heat the first and second thermistors, respectively; and a control circuit. The control circuit is configured to, in a first period, generate an output signal based on a detection signal appearing at a connection point between the first and second thermistors by making the heating temperature of the second heater higher than the heating temperature of the first heater. The control circuit is configured to, in a second period, make the heating temperature of the first heater higher than the heating temperature of the second heater and switch the connection relation so as to make an amount of a current flowing through the first thermistor and an amount of a current flowing through the second thermistor different from each other.