Gas Detector Sensor Switching and Calibration
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Solution Overview
Problem
Gas detectors used for detecting Freon gas and similar gases face a reduction in service life due to increased sensor resistance over time, and existing methods for extending this life are not reliable, especially when switching between multiple sensors.
Innovation Solution
A gas detector system utilizing multiple metal-oxide semiconductor sensors with a driving circuit that learns and stores the resistance ratio in air and gas environments, allowing for continued detection by switching sensors after a predetermined period and preheating the standby sensor to maintain accuracy and extend service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If multiple gas sensors are used sequentially to extend service life, then the service life of the gas detector is extended, but the reliability of gas detection is reduced due to increased sensor resistance over time
Solution Approach 1:
The gas detector is divided into multiple gas sensors that can be sequentially activated. When one sensor's resistance increases due to aging, the system switches to another sensor, segmenting the detection function across multiple components to extend overall service life while maintaining reliability.
Solution Approach 2:
The driving circuit continuously monitors the resistance of each gas sensor and uses this feedback to determine when to switch sensors. By detecting resistance changes and comparing them against threshold values, the system automatically transitions between sensors to maintain reliable detection throughout the extended service life.
2Duration of action of stationary object
If a new gas sensor is switched after a predetermined period, then the service life is extended, but the detection reliability is reduced during the learning period when the new sensor's air resistance must be learned
Solution Approach 1:
Before fully activating a new sensor, the system performs a learning period where the air resistance of the new sensor is measured and stored. This preliminary action ensures the sensor is properly calibrated before taking over detection tasks, preventing reliability issues during the transition period.
Solution Approach 2:
During the learning period of a new sensor, the old sensor continues to perform detection functions. This ensures continuous reliable detection while the new sensor is being calibrated, eliminating detection gaps that would occur if the old sensor was immediately deactivated.
3Use of energy by moving object
If gas sensors are used continuously without preheating, then energy consumption is reduced, but impurity accumulation on the sensor surface increases resistance and reduces detection accuracy
Solution Approach 1:
The driving circuit implements periodic preheating cycles where the sensor temperature is raised to burn off impurities, followed by normal operation at lower temperature. This periodic thermal cleaning action prevents impurity accumulation from permanently increasing resistance, maintaining detection accuracy while limiting energy consumption to only when needed.
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 system effectively extends the service life of gas detectors by maintaining reliable detection through learning the air resistance of new sensors and preheating to reduce impurity accumulation, enabling long-term use without maintenance for refrigerant leakage detection.
Implementation Method 1
gas sensors provided with a metal-oxide semiconductor whose resistance changes based upon contact with a gas
Implementation Method 2
storing values S0 corresponding to the ratio Rair0/Rgas0 between initial resistance in air Rair0 of the metal-oxide semiconductor and initial resistance of the metal-oxide semiconductor in an atmosphere Rgas0 including a predetermined concentration of gas to be detected
Implementation Method 3
preheating the standby sensor to maintain accuracy and extend service life
Data Source
AI summary
A gas detector includes metal-oxide semiconductor gas sensors and their driving circuit. The gas detector stores the ratio of initial gas sensor resistance in air and that in an atmosphere including Freon gas, for the gas sensors. The gas detector learns sensor resistance in air for a gas sensor in use and detects Freon gas by comparing the sensor resistance of the gas sensor in use with the learned resistance in air divided by the ratio. When the first gas sensor has been used for a predetermined period, both the first gas sensor and a second gas sensor are used for a learning period to continue detection of Freon by the first gas sensor and to learn the resistance in air of the second gas sensor. After completion of the learning period, Freon is detected by the second gas sensor.