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Contents 1 Introduction 2 Specifications 3 Build your probe 4 Calibrating the Probe

Introduction

Joe Sundermier introduced me to this very cheap Hall probe that can be used to measure magnetic field. The probe is made by Allegro MicroSystems Inc.. It is a small integrated circuit that will return the reading of a magnetic field when 4.5 to 5.5 V is applied to it's input. The original paper where the idea appeared is: Hands-on magnetic field measurements with a GMR sensor, by Joseph Priest in Phys. Teach. 37, 345 (1999). We use a newer generation probe with 4.5 V.

Specifications

The sensor we have is A1321EUA-T. To find out how to wire the sensor to go this web site http://www.allegromicro.com/sf/1321/

Build your probe

Bill Leacock put together a gauss probe.

	Materials required Sensor Telefone wire 3 AA batteries and holde Nuts and bolts Piece of Mahogany (cheap wood also works)
	Solder three wires to the sensor legs as shown in this picture. The middle pin is acommon ground. One is for the 4.5V (three batteries), and the last one is for thereading of the magnetic field. The reading is in Volts that need to be converted into the proper magnetic field value - more on this below.
	Drill two holes and fix the bolts.
	Connect the telephone wire, red to +V, black to ground and Yellow to Signal.
	Detail of sensor mounted at the end of a wand.
	The entire assembly
	Another shot of the entire assembly. Now properly labeled. To read magnetic field you need to read the DC voltage between ground and Vout.

Calibrating the Probe

The sensor we used is rated to a sensitivity of 5 mV/Gauss. We calibrated this probe against a Professional grade gaussmeter -LakeShore 410.

To perform calibration we used a strong magnet and positioned the two probes, the Magic Wand and LakeShore 410, nearly on top of each other. Negative values are for the South pole of the magnet. Note that for zero field, the sensor reads 2.25V. The resulting measurements are show in the plot and the measured sensitivy is approximately 5.0 mV/Gauss and confirms the manufacturer's claimed probe sensitivity.