Self-Powered Wheatstone Bridge Flow Sensor Using NTC and PTC Resistors
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Solution Overview
Problem
Traditional Wheatstone bridge flow sensors face thermal instability issues due to heater resistors with positive temperature coefficients, leading to increased resistance and potential damage, and require additional circuitry for power supply, affecting accuracy and reliability.
Innovation Solution
A Wheatstone bridge flow sensor is fabricated on a semiconductor substrate with a flow channel, using a configuration of positive and negative temperature coefficient resistors arranged across the flow channel and in thermal cavities, eliminating the need for external heaters and achieving self-powered operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a heater resistor with positive temperature coefficient is driven by constant current source, then heating effect is achieved, but resistance increases with temperature causing thermal instability and potential damage
Solution Approach 1:
The patent changes the temperature coefficient parameter from positive to negative by using NTC thermistors instead of conventional PTC heater resistors. This parameter change fundamentally alters the thermal behavior: NTC resistors decrease their resistance when heated, creating a self-regulating effect that prevents thermal runaway and improves reliability while maintaining heating capability.
Solution Approach 2:
The patent converts the harmful thermal runaway effect into a beneficial self-regulating mechanism. The resistance increase in conventional heaters that causes thermal instability is replaced by resistance decrease in NTC thermistors, which automatically reduces power consumption when temperature rises, turning potential damage into protective feedback.
2Adaptability or versatility
If a separate heater is added to the sensor, then heating function is achieved, but device complexity increases due to additional circuitry
Solution Approach 1:
The patent merges the heater and temperature sensor functions into a single component by using NTC thermistors that perform both heating (when current flows) and temperature sensing simultaneously. This eliminates the need for separate heater circuitry and reduces overall device complexity while maintaining full heating functionality.
Solution Approach 2:
The NTC thermistor serves multiple functions: it acts as a heater when current is applied, a temperature sensor when measuring resistance changes, and a self-regulating element that protects against overheating. This multi-functionality reduces the number of components needed and simplifies the overall device architecture.
3Measurement precision
If temperature sensor is positioned to avoid thermal influence from flow sensor, then measurement accuracy is improved, but thermal communication with fluid is reduced
Solution Approach 1:
The patent eliminates the need for a separate reference temperature sensor by using the NTC thermistor's own resistance characteristics. The sensor serves itself by comparing its resistance at different temperatures, removing the requirement for additional sensing elements that would need thermal isolation, thereby maintaining both accuracy and thermal coupling.
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 configuration enhances sensor sensitivity, reduces power requirements, and maintains high dynamic range with low thermal mass properties, improving accuracy and reliability while eliminating the need for separate heaters.
Implementation Method 1
the two resistors mounted across the flow channel or in thermal proximity to the flow channel comprise at least one negative temperature coefficient of resistance (NTC) resistor and at least one positive temperature coefficient of resistance (PTC) resistor
Implementation Method 2
the two resistors mounted across the flow channel or in thermal proximity to the flow channel comprise at least one negative temperature coefficient of resistance (NTC) resistor and at least one positive temperature coefficient of resistance (PTC) resistor
Implementation Method 3
Fluid flowing through the fluid passageway establishes thermal communication with said at least two of said at least four resistors mounted on the base substrate across the flow channel or in thermal proximity to the flow channel, thereby changing the output sensing voltages across the Wheatstone bridge according to fluid flow through the flow channel
Data Source
AI summary
A Wheatstone bridge flowmeter is provided with a flow channel on a top surface of the base substrate, with two resistors of the Wheatstone bridge in thermal communication with the flow channel. One resistor in the flow channel, on one side of the Wheatstone bridge, has a negative coefficient of resistance (NTC) and the other resistor in the flow channel, on the other side of the Wheatstone bridge, has a positive coefficient of resistance (PTC). At least two of the resistors in the Wheatstone bridge are mounted in at least one cavity space, so that one resistor on each side of the Wheatstone bridge is in thermal isolation from the flow channel, thereby allowing sensing of voltages across the Wheatstone bridge according to fluid flow through the flow channel.