Gas Flow Sensor Circuit Multiplexing Current Sources
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Solution Overview
Problem
Existing gas flow sensors face limitations in measuring a wide range of flows due to sensitivity issues at zero flow and large flows, with thermoelectric sensors being unable to determine absolute temperature and thermoresistive sensors requiring multiple resistances at different temperatures, leading to inaccuracies.
Innovation Solution
A gas flow measuring circuit using a current loop arrangement with multiple current sources and multiplexing to alternately connect these sources with reference and variable resistors, allowing for precise measurement of resistance changes and minimizing self-heating, combined with a controller that adapts to different measurement methods like calorimetric, anemometric, and time of flight principles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermoelectric sensors are used for flow measurement, then the sensor can detect temperature differences, but it cannot determine absolute temperature
Solution Approach 1:
The sensor system is divided into separate functional components: thermoelectric sensors for detecting temperature differences and thermoresistive sensors for measuring absolute temperature. This segmentation allows each sensor type to perform its optimal function while collectively providing comprehensive temperature measurement capabilities.
Solution Approach 2:
The patent combines thermoelectric sensors (for temperature difference detection) with thermoresistive sensors (for absolute temperature measurement) within the same sensor system. This merging enables the system to achieve both differential temperature detection and absolute temperature determination, resolving the limitation of thermoelectric sensors alone.
2Measurement precision
If thermoresistive sensors are used with multiple resistances at different temperatures, then temperature detection is possible, but manufacturing tolerances and temperature sensitivity cause inaccuracies
Solution Approach 1:
Different regions of the sensor system use different sensor types optimized for their specific functions. Thermoresistive sensors are placed in locations where absolute temperature measurement is needed, while thermoelectric sensors are positioned for temperature difference detection. This local optimization reduces the impact of manufacturing tolerances by using appropriate sensor types in appropriate locations.
Solution Approach 2:
The system changes the measurement parameter from relying solely on resistance values (which are sensitive to manufacturing tolerances) to using voltage measurements from thermoelectric sensors for temperature difference detection. This parameter change reduces sensitivity to resistance value variations caused by manufacturing tolerances.
3Device complexity
If a single current source is used for multiple resistors, then circuit complexity is reduced, but measurement accuracy decreases due to current variations
Solution Approach 1:
The current source system is segmented into multiple independent current sources, each dedicated to specific resistors. This segmentation ensures that each measurement channel receives a stable, dedicated current, improving measurement accuracy while maintaining manageable circuit complexity through systematic organization.
Solution Approach 2:
The patent introduces current source multiplexing means as an intermediary component that manages the connection between current sources and resistors. This intermediary enables precise control of current distribution and allows for accurate measurement by ensuring stable current supply to each resistor during its measurement phase.
4Measurement precision
If heating current is increased to improve signal strength, then measurement sensitivity increases, but self-heating of resistors causes measurement errors
Solution Approach 1:
The system uses periodic switching between different measurement modes and time-multiplexed measurement sequences. By alternating between applying heating current and measuring resistance/voltage, the system achieves adequate signal strength during heating phases while allowing cooling periods that prevent excessive self-heating and measurement errors.
Solution Approach 2:
The heating current is dynamically controlled and adjusted based on measurement requirements and thermal conditions. The system optimizes the heating current level to provide sufficient signal strength while maintaining temperatures that avoid self-heating errors, adapting the current level to operational conditions.
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
This solution provides a high dynamic range flow sensor capable of measuring larger flows with improved accuracy and stability, allowing for absolute measurements and reducing the impact of manufacturing tolerances and temperature sensitivity, enabling reliable gas flow detection across various conditions.
Implementation Method 1
one or more heating element(s) that can be heated by an electric current
Implementation Method 2
The sensor electrodes can be realized as resistors, which change their resistance in dependence of the temperature
Implementation Method 3
The thermal time of flight is determined from the transport of heat from the heating element to the downstream sensor in the gas flow
Data Source
AI summary
A gas flow measuring circuit includes at least one reference resistor and at least one variable resistor that varies in accordance with the characteristics of the flow of a gas and means for determination of the difference between the reference resistor and variable resistor, with at least one current loop arrangement including first current source means coupled in series with said reference resistor and second current source means coupled in series with said variable resistor wherein both resistors are connected to ground for providing an ideally constant current through the respective resistor to produce first voltages across the reference resistor and second voltages across the variable resistor, and voltage measuring means for measuring the voltage difference between said reference resistor and said variable resistor to produce a characteristic voltage difference representative of the characteristics of the gas.