With Metrolab’s PM1055 permanent magnet range, scientists now have access to an ultra-compact solution for calibrating Hall probes with a high level of precision. With a side opening wide enough to insert an NMR probe, each PM1055 can even be turned into a real secondary field reference… that fits into the palm of your hand!
Question: what is the main drawback with using Hall probes? If you have one, you should find the answer straight away: calibration. Although they are quick and easy to use, and fairly precise (up to 100 ppm), Hall teslameters must be scrupulously calibrated in order to correct factors such as offset, non-linearity and temperature sensitivity. Because these parameters vary over time, in practice this means recalibrating the probe before each set of measurements… And because the laboratories where you conduct your experiments are not always next to the national Weights and Measures office, you use a conventional reference magnet which, in addition to being rather heavy, is half the size of your desk!
Good news: Metrolab – which modestly produces the world’s only handheld three-axis Hall teslameter – also offers handheld reference magnets! The PM1055 range comprises cylindrical permanent magnets generating a highly uniform 0.01 to 0.5 T field in their gap. Their compactness is unrivalled on the market: 80 mm in diameter, 39 mm high (55 mm for the 0.5 T) and about 1 kg in weight. In spite of these ultra-small dimensions, PM1055 magnets have two wide side openings enabling Hall and NMR probes to be inserted. Another feature of Metrolab’s magnets is their very low fringe fields – thus minimizing interference due to ferrous objects around the magnet: you no longer need to calibrate your Hall probe in the middle of the Sahara Desert!
Metrolab duly calibrates each PM1055 using an NMR probe, and its individual characteristics (exact field in the middle of the pole and at several points of the periphery, measurement temperature) are marked on the label.
With a temperature coefficient of 0.2%/°C or less – primarily due to the temperature coefficient of the permanent magnet material – PM1055 magnets can be used as-is for calibration to 1%.
For applications requiring more precise calibration, a built-in auxiliary coil can reduce field variations to the order of a few ppm. Combining the permanent magnet with one of their NMR teslameter systems, Metrolab proposes a complete secondary field reference as used by Weights and Measures… but that fits into the palm of your hand.
This unrivalled performance-to-size ratio is the fruit of Metrolab’s (long) experience, having specialised in high-precision magnetic measurement since 1985. The magnetic "cap" on each end of the magnet comprises an iron yoke, a permanent magnet – pre-magnetised for the highest fields, or magnetised in-house by Metrolab for low fields – and a pole to channel the field. To obtain a magnetic field uniform enough to be able to measure with NMR, the geometry of the two poles is obviously critical. Once the PM1055 has been assembled, Metrolab shims it, using a proprietary mechanism and an NMR probe.
Please refer to the web page for more detailed information. Note that the conceptual simplicity of the magnet also allows for easy customization, for example custom field strengths. Simply contact us to discuss your requirements.
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