Thermal Flow Sensor Zero Point Adjustment via Heating Power Control
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Solution Overview
Problem
Calorimetric flow sensors face challenges in achieving accurate and temperature-stable zero point adjustments due to manufacturing tolerances and inhomogeneities, leading to significant deviations in microfluidic applications with small measuring ranges.
Innovation Solution
The solution involves using two adjacent or partially overlapping heating elements to adjust the zero point by shifting the temperature profile, ensuring thermal balance and precise offset compensation, which is more stable and independent of temperature changes compared to electronic adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser trimming is used to adjust the zero point, then the zero point can be adjusted, but it cannot be used on all substrates or layers and manufacturing complexity increases
Solution Approach 1:
The patent replaces the mechanical/laser-based trimming process with an electronic control approach. Instead of physically trimming the temperature sensors or heating elements, the system uses electronic feedback control to adjust the heating power supplied to the heating elements, thereby compensating for manufacturing variations and achieving zero point adjustment without physical modification of the substrate or layers.
Solution Approach 2:
The patent changes the control parameter from physical geometry (laser trimming of sensor dimensions) to electrical parameters (heating power supply). By adjusting the electrical parameters of the heating elements through feedback control, the system achieves zero point adjustment without altering the physical structure, making it compatible with all substrate and layer configurations.
2Measurement precision
If electronic offset correction is used in the signal path, then the zero point can be adjusted electronically, but temperature stability at the zero point is only achieved to a limited extent
Solution Approach 1:
The patent implements a feedback control system that continuously monitors the temperature at the temperature sensors and adjusts the heating power accordingly. This closed-loop feedback mechanism ensures that the temperature profile is dynamically maintained, providing both accurate zero point adjustment and long-term temperature stability. The feedback control compensates for drift and environmental variations, achieving superior temperature stability compared to static electronic offset correction.
Solution Approach 2:
The patent performs preliminary heating power adjustment during calibration to establish the correct zero point before actual measurements. By determining the appropriate heating power values in advance through calibration procedures, the system ensures that the temperature profile is optimized for accurate measurements from the start, avoiding the need for continuous post-measurement adjustments and improving overall temperature stability.
3Measurement precision
If heating power is increased to compensate for zero point offset, then the zero point can be adjusted, but the measuring range and precision are compromised
Solution Approach 1:
The patent applies different heating power levels to different regions or elements based on their specific requirements. Instead of uniformly increasing heating power across the entire sensor, the system locally adjusts the heating power to each temperature sensor or heating element according to its position and function. This localized control allows precise zero point adjustment at specific locations while maintaining appropriate heating levels elsewhere, preserving the overall measuring range and precision.
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 method achieves high precision (at least 10ppm) and adjustable ranges (10% - 1000% of the measuring range), surpassing the limitations of existing methods like laser trimming, with excellent temperature stability and independence at zero flow.
Implementation Method 1
thermal measuring devices are known which make use of the fact that a (flowing) medium transports heat
Implementation Method 2
a (flowing) medium transports heat
Implementation Method 3
at least one heating element and at least one temperature sensor in order to determine the flow of the medium
Data Source
Figure 1~4
AI summary
Thermal flow sensor (1) for determining the flow rate of a medium (2), having: a substrate (3); a first and second temperature sensor (4a, 4b) which are arranged on the substrate (3), wherein the first and second temperature sensors (4a, 4b) are in the form of heatable temperature sensors (5a, 5b) or in the form of a first non-heatable temperature sensor (6a, 6b) which has an associated first heating element (7a), and in the form of a second non-heatable temperature sensor (6b) which has an associated second heating element (7b); a feed unit (8) which supplies a first heating power, which is predetermined during a comparison operation, to the first heatable temperature sensor (5a) or to the first heating element (7a) by means of a first signal (9a), and supplies a second heating power, which is predetermined during the comparison operation, to the second heatable temperature sensor (5b) or to the second heating element (7b) by means of a second signal (9b); an evaluation unit (10) which determines a temperature difference (ΔT) between the first temperature sensor (4a) and the second temperature sensor (4b) during a measurement operation in order to determine the flow rate of the medium (2), and determines a measurement value, which represents the flow rate of the medium (2), on the basis of the temperature difference (ΔT).