AMR Sensors (Magnetic Sensors)Fundamentals of magnetic sensors: principles of operation for AMR sensors (magnetic switches)

Principles of operation for AMR sensors

Principles of Operation for AMR Sensors (Magnetic Switches) Explanatory Video

This video explains the resistance value fluctuations when the magnetoresistive element is subjected to a magnetic field.

Magnetoresistive element

In a magnetoresistive element, the resistance changes when a magnetic field is applied perpendicular to the electrical current direction. AMR sensors have a wide range of placement patterns as shown in the figure, and they consist of a combination of elements that change the resistance (R1, R4) and elements that do not change the resistance (R2, R3).

AMR sensor operation

When a magnetic field is applied, the resistance values drop for the magnetoresistive elements R1 and R4, and a potential difference occurs between midpoint A and midpoint B.
When the potential difference exceeds the specified setting value (threshold value), the sensor ON/OFF output is switched.

Sensor block diagram

3-terminal Configuration

A magnetic block is a single package of an AMR element and an IC that converts the output signals to digital signals.
This is a three-terminal configuration consisting of an input terminal (VCC), GND terminal (GND), and output terminal (OUT). The configuration has a sampling circuit for reducing the current consumption.

Chattering prevention

Chattering is a condition where electrical signals repeat intermittently due to subtle, but extremely fast mechanical vibrations when the relay and switch contacts are switched. This is one cause of malfunctions in electronic circuits.
To prevent chattering, hysteresis is implemented in the active magnetic field.
When a magnet approaches the sensor and the magnetic field exceeds the MOP, OUT changes from H to L.
When a magnet moves away from the sensor and the magnetic field drops below the MRP, OUT changes from L to H.