AMR Sensors (Magnetic Sensors）Fundamentals of magnetic sensors: what is an AMR (magnetic) sensor?

AMR is an abbreviation for Anisotropic Magneto Resistance. These are elements that have a function where the resistance decreases when a magnetic field is applied, and this function is dependent on the direction of the magnetic force lines applied to the element (anisotropic).

The material of the AMR element is a ferromagnetic metal that is an alloy of nickel, iron, and other metals.
Because the positive and negative sides have symmetric characteristics, the same operation is performed even if the north and south poles of the magnet are reversed. This characteristic is used to enable the gathering of high-accuracy, high-reliability data without making contact. Also, the capability of detecting without contact can be used in a wide range of applications such as open/close detection, rotation detection, and position detection.

Murata's sensors are built on the same PCB as the ICs and AMR elements. An IC is used to perform digital processing of the analog signals from the AMR element, and the output is converted to Hi and Lo level digital output so that no signal processing is required by the customer.

The sensitivity of the AMR sensor is the strength of the magnetic force that turns on (or off) the AMR sensor. The ON sensitivity (Hon) is the magnetic force that turns on the AMR sensor which was off with no or weak magnetic field, and the OFF sensitivity (Hoff) is the magnetic force that turns off the AMR sensor which was on with a strong magnetic field. The sensitivity of the AMR sensor varies by AMR sensor, and the Hon and Hoff in the datasheet indicate the specific range for that product.

For example, the sensitivity standards for the MRMS501A-001 are "Hoff: 0.5mT to Hon: 2.5mT".

Magnetic force lines are invisible. Magnetic force lines are not absorbed by plastic and other non-magnetic bodies and pass through to the opposite side. Magnetic sensors use these features to enable detection.
For example, the advantages can be easily utilized in the following usage situations.