Magnetostrictive Sensor Shear Mode Crystal Mounting
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Solution Overview
Problem
Existing magnetostrictive level sensing instruments using piezoelectric crystals suffer from noisy and low-amplitude signals due to sensitive crystal positioning, require fine adjustments, and are costly due to the need for multiple specialized crystals, making them prone to false vibrations and high production costs.
Innovation Solution
A magnetostrictive position sensor employing a pair of shear mode crystals polarized in the K15 coupling direction, electrically connected by the magnetostrictive wire, and mounted on a support tray to maintain tension and clamp the wire, reducing noise and vibration sensitivity while minimizing component count and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If K33 polarized piezoelectric crystals are mounted radially from the wire to sense tensile load, then the sensor can detect torsional waves, but the signal becomes noisy and low amplitude due to sensitive crystal positioning
Solution Approach 1:
The patent changes the polarization direction of the piezoelectric crystals from K33 (longitudinal) to K15 (shear mode), which fundamentally alters how the crystals respond to mechanical stress. This parameter change allows the crystals to sense torsional waves more effectively while being less sensitive to positioning variations, thereby reducing noise and improving signal amplitude simultaneously
Solution Approach 2:
Instead of mounting crystals radially from the wire (as in conventional designs), the patent inverts the approach by mounting crystals on a support tray that clamps the wire. This inversion of the mounting configuration allows the crystals to sense torsional waves through the clamped wire rather than through direct radial contact, eliminating the noise issues associated with radial mounting sensitivity
2Reliability
If multiple wedge shaped piezoelectric crystals are arranged in a circular array to cancel spurious noise, then noise reduction is achieved, but the device becomes expensive and complex
Solution Approach 1:
The patent extracts the essential function of noise cancellation from the complex circular array of multiple crystals and achieves it with a single crystal mounted on the support tray. By using the K15 polarized crystal in a simplified configuration where the support tray clamps the wire, the patent maintains noise reduction capabilities while eliminating the need for multiple specialized crystals and complex assembly steps
Solution Approach 2:
The support tray serves multiple functions simultaneously: it mounts the piezoelectric crystal, clamps the magnetostrictive wire to maintain tension, and provides a stable mounting surface. This multi-functionality eliminates the need for separate components needed in conventional designs, thereby reducing device complexity and cost while maintaining noise reduction performance
3Measurement precision
If the sensor requires fine adjustments and tuning for optimal performance, then measurement precision is improved, but manufacturing difficulty increases
Solution Approach 1:
The support tray is designed with pre-configured mounting features and clamping mechanisms that automatically position the piezoelectric crystal and magnetostrictive wire in the correct orientation during assembly. This preliminary configuration of the mounting structure eliminates the need for fine adjustments and tuning during or after assembly, thereby simplifying manufacturing while maintaining measurement 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
The solution provides a high signal amplitude with low noise, reduced sensitivity to vibrations, and a cost-effective, easy-to-manufacture design by utilizing a differential electrical response from the crystals, which effectively senses torsional waves and maintains the magnetostrictive wire under tension without additional damping materials.
Implementation Method 1
Known magnetostrictive measurement instruments use piezoelectric crystals as a pick up sensor. Such piezoelectric crystals are generally polarized in the longitudinal direction, referred to as the K33 coupling direction in the field of electro-ceramics.
Implementation Method 2
An electrical pulse is transmitted on the magnetostrictive wire. The electrical pulse interacts with the magnetic field of the float, which creates a torque on the wire to produce a torsional force on the wire, thus initiating a torsional wave that propagates along the wire at the speed of sound.
Data Source
AI summary
A magnetostrictive level sensing instrument is used for sensing level in a process vessel and comprises an elongate tube having a near end and a distal end. A magnet is selectively positionable proximate the tube responsive to level of the processed material. A magnetostrictive wire in the tube has first and second ends. The second end is operatively secured at the tube distal end. A pair of shear mode crystals are mounted proximate the tube near end. The crystals sandwich the magnetostrictive wire proximate the first end. A sensing circuit is operatively connected to the magnetostrictive wire and the pair of crystals for generating an electrical pulse on the magnetostrictive wire whereby a magnetic field produced by the magnet interacts with the electrical pulse to produce a torsional wave on the magnetostrictive wire sensed by the pair of crystals.