Thermal Flow Sensor Using Pulsed Heating and Differential Integration
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Solution Overview
Problem
Existing thermal sensors for measuring fluid flow velocity face challenges in achieving high accuracy due to small temperature fluctuations and high energy consumption, making them costly and unsuitable for battery-operated devices.
Innovation Solution
A method using a thermal sensor with a heating resistor and a sensor resistor, where the heating resistor is pulsed to heat the sensor resistor, and both resistors' currents are integrated over time to form a differential signal, which is then amplified and converted to indicate fluid flow velocity accurately, with low power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sensor element is heated in a pulsed manner to measure flow rate from temperature increases, then the flow rate can be measured, but very small temperature fluctuations must be precisely recorded which leads to high demands on measuring devices and high operating and manufacturing costs
Solution Approach 1:
The measurement process is segmented into distinct phases: heating phase where the heating element raises sensor temperature, and measurement phase where temperature recovery is monitored. This segmentation allows separate optimization of heating efficiency and measurement precision, reducing overall device complexity while maintaining accuracy.
Solution Approach 2:
The patent changes the measurement parameter from direct temperature fluctuation measurement to measurement of temperature recovery rate after pulsed heating. By monitoring how quickly the sensor returns to ambient temperature, the system achieves high flow rate measurement accuracy without requiring detection of extremely small temperature variations, thereby simplifying the measuring device.
2Measurement precision
If large heating currents are used to heat the sensor element, then the temperature increases are sufficient for measurement, but the energy consumption is too high for battery operation over several years
Solution Approach 1:
The heating element operates in periodic pulsed manner rather than continuously. During each pulse, the heating element rapidly heats the sensor, then remains inactive while the sensor cools. This periodic action provides sufficient temperature variation for accurate measurement while dramatically reducing average power consumption to enable multi-year battery operation.
Solution Approach 2:
The measurement process continuously monitors the sensor's temperature recovery phase, which contains the flow rate information. By making the measurement during the cooling phase rather than requiring continuous heating, the system maintains measurement capability while minimizing energy consumption during the heating intervals.
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 approach enables precise measurement of fluid flow velocity with reduced power consumption, making it suitable for battery-operated devices and cost-effective, while maintaining high accuracy across varying flow rates.
Implementation Method 1
the heating resistor heating the sensor resistor
Implementation Method 2
the sensor resistance has a temperature coefficient α and a base resistance R0
Data Source
Figure 1
AI summary
The method involves warming a heating resistor (14) during the duration of a filament current pulse. The current flowing in an integrator (20) for a predetermined time period is detected by a sensing resistor (16), where the current flowing in another integrator (22) during a predetermined time period is detected by a reference resistor (34). An average sensing resistor value and an average reference resistor value are determined and amplified. A difference signal of the average sensing resistor value and average reference resistor value is formed in an instrumentation amplifier (24). An independent claim is included for a measuring device for measuring the flow rate of fluids, particularly for implementing the flow rate measuring method, with a measurement circuit.