Magnetics Business & Technology - Spring 2015 - (Page 16)

FEATURE ARTICLE Magnet Inspection Tool with High Magnetic and Mechanic Accuracy By Sasa Spasic, CEO * SENIS AG Modern magnetic position and angle sensors consist of a combination of a permanent magnet and a magnetic field sensor. Billions of such sensors are built in automotive, industrial and consumer products each year. The characteristics of permanent magnets for such sensors must be carefully controlled. The control of the magnets often includes measurement of the magnetic field over an area or volume of interest near the magnet which is usually performed by a Magnetic Field Mapper. The magnets of interest might be as small as a few millimeters in diameter and are getting even smaller. Therefore, the magnetic fields to be measured are increasingly inhomogeneous. This trend imposes a number of difficult requirements for a good Magnetic Field Mapper, including good mechanics for accurate mutual positioning of the magnet under test and the magnetic field probe, measurement of all three components of a magnetic field at the same spot, high resolution and overall accuracy of the magnetic field measurement, and high conformity of the sensitivity vectors of the probe to the coordinate system of the mapper. SENIS has brought to the market the first Magnetic Field Mapper, type MMS-1A-RS, which meets all these requirements (Figure 1). Application Field The SENIS Magnetic Field Mapper MMS-1A-RS can be efficiently applied for: * Accurate DC and AC magnetic field measurement of all three components of magnetic field at precisely defined points around an object sized from about 1 mm to 50 cm. Magnetic field measurement range is 100 μT to 3 T. * Quality assessment tool (pass/fail analysis) in production lines for permanent magnets used for sensors in automotive industry, consumer electronics industry, energy monitoring and others * Testing tool for the development of magnet systems in research laboratories * Magnetic field mapping around small simple magnets or multi-pole magnets * Magnetic field mapping of electronic circuit PCBs (such as those of smart-phones, tablets, etc.). This application area is related to potential safety hazards caused by the stray magnetic field of magnets. * Magnetic field peak and zero value detection of magnetic encoders or code-plates as well as magnetic poles counting * Magnetic field homogeneity in magnetic angle measurement * Statistical analysis of measured data, including import/export of measured data and generating images and reports * Dimensional measurement of objects under test, much like by a simple Coordinate Measuring Machine (CMM) * Cracks and inhomogeneity detection in magnetic materials and in non-magnetized parts Fully Integrated Three-Axis Hall Probe for Magnetic Field Measurement The key component of a good magnetic field mapper is an adequate magnetic field sensor. The most suitable magnetic sensors for the purpose are sensors based on the Hall-effect. 16 Magnetics Business & Technology * Spring 2015 Figure 1. SENIS Magnetic Field Mapper consists of four main parts: (a) the mechanical part (the moving platform with three linear modules and the rotary stage); (b) the Hall Probe mounted on the Touch sensor; (c) the electronic box with digital signal processing, motor drives, encoder control, and power supply; (d) and a PC and Software for measured data acquisition, visualization, and analysis. The Mapper MMS-1A-RS incorporates a SENIS three-axis Hallprobe, which consists of a single silicon chip with monolithically integrated Hall elements for all three components of a magnetic field and signal conditioning electronics. The spatial resolution of this Hall probe is less than 100 µm. This allows simultaneous measurement of all three components of a highly non-homogeneous magnetic field in nearly single point. The Hall probe geometry allows measuring of the magnetic field vectors at a distance of 0.15 mm from a magnet surface. The probe package is adapted to the testing of small magnets: the whole probe, with the package, can enter into a hole with a diameter of 2 mm. A customized data acquisition and digital processing system triggers the magnetic field measurement at desired locations, converts the analog signals of the Hall probe into digital numbers, combines these numbers with the appropriate position coordinates, and provides the consolidated function Magnetic Field Vector of Probe Coordinates. A direct synchronization (position vs. measured magnetic field) between the Motion Control and the Data Acquisition Card (DAQ) is provided through the on-board real-time system integration bus. The acquisition of the measured data is performed with up to 50,000 samples/sec. Digital filters are applied to insure an optimal bandwidth and measured data averaging. Averaging period, number of samples, corner frequency, filter order and type are customizable. The achieved accuracy of the magnetic measurement is 0.01 percent at normal room conditions.

Table of Contents for the Digital Edition of Magnetics Business & Technology - Spring 2015

Editor's Choice
First-Order-Reversal-Curve Analysis of Multi-Phase Ferrite Magnets
Magnetics Design Tool for Power Applications
Magnet Inspection Tool with High Magnetic and Mechanic Accuracy
Research & Development
Software & Design
Industry News
Marketplace / Advertising Index
Spontaneous Thoughts: The Patent Challenge

Magnetics Business & Technology - Spring 2015