Magnetics Business & Technology - Fall 2012 - (Page 9)

By PHiliP Keller, MarKeting & Product ManageMent • MetrolaB tecHnology sa FEATURE ARTICLE Three-Axis Magnetic Field Measurement: From Nanoteslas to 14 Tesla A new generation of handheld 3-axis magnetometers, introduced a few years ago, is capable of measuring magnetic field strengths in the range from milliteslas to 3 tesla. [1] Recent developments have extended this measurement range upward, to 14 T, as well as downward, into the nanoteslas, all within the same family of ultra-compact, USB-powered instruments. The keys are innovative sensor technologies and calibration. Three-Axis Hall Magnetometer on a Chip: mT to 3 T The key technological breakthrough underlying the introduction of Metrolab’s High-Field Three-Axis Hall Magnetometer THM1176-HF was an integrated circuit called MAG3D. On a single CMOS IC, it combines three orthogonal Hall sensors, current sources, amplifiers, range switching and spinning-current error correction. In fact, it is a complete 3-axis Hall magnetometer on a chip (see Figure 1 on page 10). The commercial version of this IC supports four measurement ranges: 0.1, 0.5, 3 and 20 T, with a resolution of 0.3 mT on the lowest scale. Roughly speaking, this one chip can measure field strengths from milliteslas to 20 tesla. However, the specified nonlinearity on the 20 T range is 2 T; clearly, such measurements are worthless without correcting for nonlinearity and other “secondary” effects such as temperature drift. The THM1176-HF does all of this; the limitation is simply the availability of calibration magnets up to 20 T. Calibration magnets are special. To ensure that the Hall probe and the reference instrument [3] “see” the same field, the field must be very uniform and stable. The gap must be large enough to allow the 3-axis Hall assembly to be turned in all directions. Finally, the temperature of the Hall probe must be controllable , in other words, well insulated from water-cooled pole faces or superconducting coils. Metrolab’s primary calibration magnet is a 2-ton electromagnet that, with the required gap, goes to about 1.7 T. In addition, we use a superconducting whole-body MRI magnet [4] to obtain additional calibration points at ±3 T, and a zero-gauss chamber for a point at 0 T. The usable range of a THM1176-HF with the MAG3D sensor is thereby limited to ±3 T. 3 T to 14 T: High-Field Calibration Magnets 3 T is currently the highest field strength allowed for standard medical imaging, so calibrating to higher field strengths requires a different type of magnet. Possible choices include the superconducting, small-bore magnets used for NMR spectroscopes, now standard equipment in chemistry labs. Some of these magnets can go to very high field strengths, 20 T and more, and feature a warm Magnetic measurement Go where no one has gone before! Choose the world’s most compact 3-axis Hall magnetometer and get highaccuracy measurements of previously inaccessible magnetic fields! The latest addition to the family, the THM1176 High Field Compact model, has a probe thinner than a climber’s fingernail. The THM1176 Low Field model, on the other hand, is ideal for measuring disturbances involving weak magnetic fields. All models include a USB interface, standard communication protocols, a full-featured instrument command set, turnkey operation on PC or Mac, and easy programmability Pantone 286 Pantone 032LabVIEW. via The 3-axis Hall Magnetometer TMH1176 family High Field model Low Field model High Field Compact model www.metrolab.com Magnetic precision has a name annonce187x121.indd 2 26/07/10 15:11 www.MagneticsMagazine.com Fall 2012 • Magnetics Business & Technology 9 http://www.metrolab.com http://www.MagneticsMagazine.com

Table of Contents for the Digital Edition of Magnetics Business & Technology - Fall 2012

Magnetics Business & Technology - Fall 2012
Contents
Editor's Choice
Permanent Magnet Motors in Application
Three-Axis Magnetic Field Measurement: From Nanoteslas to 14 Tesla
Characterizing Permanent Magnet Materials with a Vibrating Sample Magnetometer
Research & Development
Magnets • Materials • Measurement
Application • Component Developments
Industry News
Marketplace
Advertising Index
Spontaneous Thoughts: And the Wisdom to Know the Difference

Magnetics Business & Technology - Fall 2012