3-Axis Hall Effect

Known since the late 19th century, the Hall effect is the most common method for measuring medium to high fields, across a wide range of applications.

In fact, sensor applications – proximity sensors, rotation sensors, current sensors, etc. – are economically much more significant than measurement applications and have propelled the Hall element into mass production.

A Simple Integration System

A modern Hall element consists of a thin plate of semiconductor material. When a current is injected parallel to the plate, a perpendicular magnetic field causes the conductors to move left or right, resulting in a voltage difference between the left and right edges.

Almost Instantaneous Measurement

Sensitivity can be adjusted by varying the current; it’s possible to measure both positive and negative field components; and it’s straightforward to integrate such a sensor into a fully electronic measurement system.

Delicate Measurement

• A Hall element typically generates a voltage deviation at zero field
• The sensor’s response is only approximately linear
• As temperature increases, more conductors become available, and the device’s sensitivity changes
• Hall plates also age, causing long-term sensitivity drift
• Planar Hall effect, where a field in the plane of the Hall plate creates a response, leads to interference among vector field components
• As wires form current loops, moving a Hall probe in a strong field induces a voltage and biases the measurement
• At cryogenic temperatures and with strong fields, Hall conductivity becomes quantized

Calibration, a Key Element of Success

To compensate for these physical effects, a Hall device must be carefully calibrated and periodically recalibrated.

Assuming linearity of response, calibration is usually performed at zero and at the positive and negative limits of the measurement range.

For zero field calibration, a zero Gauss chamber can be used. For high-end calibration, a high-field reference magnet is needed. For the ultimate reference, the magnet is controlled, or even regulated, by NMR.

3-Axis Sensors to Enhance Measurement

To compensate for planar Hall effect or other sources of interference, highly complex 3D calibration and deconvolution are required. That’s why Metrolab advocates the use of triaxial sensors that minimize information loss.

If the response is significantly non-linear, calibration at one or more intermediate field values is necessary. To compensate for temperature effects, the entire calibration must be repeated at least at two temperatures.