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Magnetoresistive Sensors - Magnetic Sensor Technology

Magnetic Speed Sensor MR P1600

A magnetoresistive (MR) sensor comprising a layered structure formed on a substrate includes a first and a second thin film layer of magnetic material separated by a thin film layer of non-magnetic metallic material such as Cu, Au, or Ag, with at least one of the layers of ferromagnetic material formed of either cobalt or a cobalt alloy. The magnetization direction of the first ferromagnetic layer, at zero applied field, is set substantially perpendicular to the magnetization direction of the second ferromagnetic layer which is fixed in position. A current flow is produced through the sensor, and the variations in voltage across the MR sensor are sensed due to the changes in resistance produced by rotation of the magnetization in the front layer of ferromagnetic material as a function of the magnetic field being sensed.

Giant Magnetoresistance Effect (GMR)

Electron scattering at the magnet/non-magnet interface in a magnetic layered structure depends on whether electron spin is parallel or antiparallel to the layer magnetic moment. It is observed that the resistance of the structure is much higher when the magnetic moments of the adjacent magnetic layers are aligned antiparallel than when they are parallel. Switching from the antiparallel to the parallel configuration can be achieved by an applied magnetic field. The effect is called giant magnetoresistance (GMR) and is illustrated in the enclosed figure. 

The GMR Switch integrates GMR sensor elements with digital onboard signal processing electronics. The GMR Switch offers unmatched precision and flexibility for magnetic field sensing. The GMR Switch accurately and reliably senses magnetic fields with less error than any other magnetic sensor available. There is little shift in the magnetic field operate point of the GMR switch over voltage and temperature extremes. This enables high precision, tight tolerance magnetic sensing assemblies.

The GMR Switch can operate over a wide range of magnetic fields, and is the most precise magnetic sensor on the market. It is the clear choice for a digital output magnetic sensor.

The AMR sensor chip works as a "strong field" sensor; sensor magnetization follows the cogwheel's stronger magnetic field. Since sensor signals are dependent only on the resulting angle between the direction of magnetic field and current, the amount of magnetization is not critical. The sensor chip, therefore, measures a mere 0.5 × 1.8 mm². The strong field principle also produces a signal that is widely independent of mechanical tolerances.

To create a fixed 90-degree phase relationship between channels A and B, the AMR sensor chip comprises two sets of four ferromagnetic metal strips. A Wheatstone's Bridge arrangement shifts one against the other by a quarter of the cogwheel's pole pitch. Each magnetic pole, consequently, gives a complete and practically harmonic-free sinusoidal signal that is suitable for multiplying signals using interpolation. The index signal is produced digitally, prompted by the signal of an additional AMR sensor in the magnetic disc's index pole.

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