Surface Acoustic Wave Scale with Hall-Based Environmental Compensation
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Solution Overview
Problem
Existing electronic weighing devices face challenges in achieving high accuracy and stability under varying environmental conditions, particularly due to temperature and humidity, which affect the phase linearity and frequency response of surface acoustic wave (SAW) delay line oscillators, leading to potential errors in weight determination.
Innovation Solution
The use of a Hall effect sensor and magnet combination to measure magnetic field strength, coupled with a processor to determine the mode of the SAW delay line oscillator, and a push oscillator to maintain optimal operating conditions, along with temperature and humidity compensation, ensures accurate weight measurement by correlating magnetic field measurements to the frequency response modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic force restoration technology is used to achieve high accuracy weighing, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the magnetic force restoration system with a surface acoustic wave-based measurement system. Instead of using electromagnets and mechanical restoration mechanisms, the invention uses piezoelectric transducers to generate and detect surface acoustic waves on an elastic member, converting the weighing function into an acoustic wave frequency measurement system that is simpler and more reliable.
Solution Approach 2:
The patent changes the measurement parameter from magnetic force balance to surface acoustic wave frequency. By measuring the frequency of surface acoustic waves that propagate along the elastic member under load, the system achieves high precision weighing through frequency measurement rather than mechanical balance, simplifying the overall system architecture.
2Device complexity
If load cell technology is used for weighing, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent replaces strain gauge-based load cell technology with surface acoustic wave technology. Instead of measuring resistance changes in strained wires, the invention uses piezoelectric transducers to generate and detect surface acoustic waves, whose frequency changes with applied load. This substitution maintains mechanical simplicity while achieving superior measurement precision through frequency-based detection.
Solution Approach 2:
The patent utilizes surface acoustic waves—mechanical vibrations that propagate along the surface of the elastic member. By exciting these vibrations with piezoelectric transducers and measuring their frequency characteristics under different loads, the system achieves high precision weighing while maintaining a simple mechanical structure without complex electronic compensation circuits.
3Measurement precision
If surface acoustic wave transducers are used for weighing, then measurement precision is improved, but reliability deteriorates due to environmental sensitivity
Solution Approach 1:
The patent implements a feedback mechanism using a push oscillator that continuously monitors the surface acoustic wave frequency and adjusts the transducer operating conditions accordingly. This feedback loop compensates for environmental variations by maintaining the transducer at its optimal operating point, ensuring stable and reliable measurements across different temperature and humidity conditions.
Solution Approach 2:
The patent dynamically adjusts the operating parameters of the piezoelectric transducers based on environmental conditions. By changing the excitation frequency and other operational parameters in response to temperature and humidity variations, the system maintains measurement precision and reliability across different environmental conditions, preventing drift and instability.
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 provides enhanced accuracy and stability in weight measurement by accounting for environmental factors, reducing errors and ensuring precise determination of the SAW oscillator mode, thereby improving the overall performance of SAW-based weighing devices.
Implementation Method 1
The piezoelectric transducers each include a pair of interdigitated electrodes formed on a corresponding piezoelectric substrate. An amplifier is operably coupled between the first and second piezoelectric transducers. The output of the amplifier is supplied to the interdigitated electrodes of the first piezoelectric transducer, which causes the first piezoelectric transducer to function as a transmitter and emit a SAW
Implementation Method 2
This propagating SAW is transmitted over the gap between the first and second piezoelectric transducers and induces a similar propagating SAW along the surface of the second piezoelectric transducer. The second piezoelectric transducer functions as a receiver transducer that generates an oscillating voltage signal
Implementation Method 3
A magnet is spaced from a Hall effect sensor. The magnet is configured to produce a magnetic field, and the Hall effect sensor is configured to measure strength of the magnetic field which is related to displacement of the elastic member and the weight of the load
Data Source
AI summary
Surface acoustic wave (SAW) weighing apparatus and related methods are provided for measuring weight of a load employing a displaceable elastic member that is displaced by the load. A piezoelectric SAW transducer is coupled to the elastic member. The piezoelectric transducer along with an amplifier electrically coupled thereto form a delay line oscillator circuit that is configured to generate an oscillating signal in response to displacement of the elastic member by the weight of the load. A magnet is spaced from a Hall effect sensor. The magnet produces a magnetic field, and the Hall effect sensor is configured to measure strength of the magnetic field which is related to displacement of the elastic member and the weight of the load. Circuitry generates frequency data that characterizes frequency of the oscillating signal. The frequency data is related to displacement of the elastic member and the weight of the load.