What Is Gaussmeter?

In 1896, Edwin Herbert Hall discovered in the process of working on his doctoral thesis that if electrical current was passed through a thin strip of gold while it was exposed to a magnetic field, a small but measurable voltage was developed across this strip at right angles to both the direction of current and field, proportional to both.

This effect results from the Lorentz force on moving electrons in a magnetic field, which forces them to one side of the strip. They build up a charge there until the charge is just sufficient to counter the effect of the magnetic field.

These devices are known today as Hall-effect sensors. They are made of semiconductor material, not for the amplifying effects used in transistors, but merely because such materials have a high electrical resistance.

The higher resistance forces the electrons in the current stream to move at a higher speed, which increases the resulting voltage. A Hall sensor measures magnetic field strength in a very small region, nearly at a point (a typical sensor might have an active site on the order of 0.030 in across).

Only the part of the magnetic vector which is normal (that is, at right angles) to the Hall element is measured, so the sensor must be oriented in that direction. Most gaussmeters on the market today use Hall sensors.

A few, however, use some other principle, such as magnetoresistors, which change their resistance in a magnetic field; magnetoresonance, a method used in medical MRI scanners; and, for less accurate devices, mechanical gaussmeters, which use the attraction of two permeable materials for each other, against a spring, in the presence of a magnetic field.

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