Pulsed Self-Heating Bridge Flow Sensor for Low-Power Sensing
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Solution Overview
Problem
Existing flow sensors are bulky, costly, and complex due to the need for a dedicated heater resistor and control circuit, which increases size, cost, and power consumption, limiting their operational lifetime and efficiency.
Innovation Solution
A flow sensor design utilizing two upstream and two downstream self-heating resistive elements arranged in a bridge circuit, eliminating the need for a dedicated heater resistor, where the resistive elements are pulsed to heat above ambient temperature, detecting temperature imbalances caused by fluid flow to measure flow rate, and powered off between measurement cycles to conserve energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dedicated heater resistor and control circuit are used in the flow sensor, then the sensor can maintain stable heating for accurate measurements, but the size, cost, and complexity of the sensor increase
Solution Approach 1:
The patent combines the heater resistor function with the existing resistive sensing elements in the bridge circuit. The same resistive elements that detect flow changes also serve as heating elements when current is applied, eliminating the need for a separate dedicated heater resistor and reducing overall sensor complexity while maintaining measurement capability
Solution Approach 2:
The resistive elements in the bridge circuit are designed to perform multiple functions: they serve as both sensing elements for detecting flow-induced resistance changes and as heating elements for maintaining temperature differential across the flow path. This multi-functionality reduces the number of components needed in the sensor design
2Measurement precision
If a dedicated heater resistor and control circuit are used in the flow sensor, then the sensor can maintain stable heating for accurate measurements, but the power consumption increases
Solution Approach 1:
The patent implements periodic pulsed heating cycles where current is applied to the resistive elements only during measurement phases rather than continuously. The sensor alternates between heating phases (when current flows through resistive elements to create temperature differential) and measurement phases (when current is reduced or stopped), reducing overall power consumption while maintaining measurement accuracy during active sensing periods
Solution Approach 2:
The sensor employs dynamic control of current flow through the resistive elements, adjusting the timing and duration of heating pulses based on measurement requirements. This dynamic operation allows the sensor to consume power only when needed for heating and measurement, rather than maintaining constant power consumption, thereby reducing average power usage while preserving measurement capability
3Measurement precision
If continuous current is supplied to the flow sensor, then accurate measurements can be taken, but the operational lifetime is limited due to power consumption
Solution Approach 1:
The sensor operates in periodic cycles alternating between heating phases (with current flow) and measurement/rest phases (with reduced or no current flow). During measurement phases, current is supplied to heat the resistive elements and take readings; during rest phases, current is minimized or stopped entirely. This periodic operation significantly extends battery life and operational lifetime while maintaining measurement accuracy during active sensing windows
Solution Approach 2:
The sensor discards continuous power consumption in favor of intermittent power usage patterns. By allowing the system to enter low-power states between measurements and only activating power consumption when measurement data needs to be collected, the sensor recovers operational lifetime without sacrificing the ability to take accurate measurements 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
This design reduces the size, cost, and complexity of flow sensors while enabling accurate, intermittent measurements, allowing for extended operational periods using various power sources, such as batteries, with reduced power consumption.
Implementation Method 1
resistively heating at least one upstream resistive element of the two upstream resistive elements and at least one downstream resistive element of the two downstream resistive elements to a temperature above an ambient temperature in response to supplying the current to the sensor
Implementation Method 2
detecting an imbalance in the bridge resulting from a temperature difference between the least one upstream resistive element and the at least one downstream resistive element in response to the flow of a fluid past the flow sensor
Data Source
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AI summary
In an embodiment, a method of sensing a flow comprises performing a measurement cycle for a first period of time, powering off the at least one upstream resistive element and the at least one downstream resistive element for a second period of time, and performing another measurement cycle for a third period of time. Performing the measurement cycle comprises supplying a current to the upstream resistive element and the downstream resistive element arranged in a bridge, resistively heating the upstream resistive element and the downstream resistive element to a temperature above an ambient temperature, and detecting an imbalance in the bridge resulting from a temperature difference between the at least one upstream resistive element and the at least one downstream resistive element in response to the flow of a fluid past the flow sensor.