How AMR Sensors (Magnetic Switches) Works ?

Outline

AMR sensor is a sensor using a magnetic resistance value changing according to the strength of the magnetic field.
It uses together with a magnet.

AMR: Anisotropic Magneto Resistance

Because the lineup of sensitivity and the size is wide, you can choose the optimal product according to the usage.

  • There is a product of two types depending on the direction of the magnetic field detection.
    Horizontal direction type: AS-M series
    Vertical direction type: AS-V series
  • There are large variations, such as a package, high accuracy type and a sampling period.
    (low consumption current, high – speed sampling, always drive)

AMR sensor is independent of magnetic pole. (One output for S or N pole)

The horizontal detection type has the following features.

  • Compared to Hall IC, our sensor has wide detection area.
    It is more flexible for design. (mount location)
  • AMR sensor is not mechanical components like the lead switch.
    So it holds small size and high reliability.
Compared to Hall IC, our sensor has wide detection area. It is more flexible for design. (mount location)

As for vertical detection type, the replacement from Hall IC is possible.

Applications

AMR sensor is the best for the usage such as the mobile devices for the noncontact switch.

Open/Close detection

  • For Mobile phones, Note – size PCs, Digital cameras and more…
  • For Refrigerators, Washing machines and other Home appliances
  • For Security equipments
Open/Close detection

Flow meter for boiler (Detection of vane’s rotation)

Flow meter for boiler (Detection of vane's rotation)

Pulse encoder (Detection of Ring type Magnet)

Pulse encoderPulse encoder

2pieces of Magnetic switches and Ring type Magnet

Land 2 sensors on the board, one slant 45 deg.
When the magnet rotates, it can detect rotation and direction depend on 2 sensors detect phase difference.

 

 

Principle

Basic characteristic

  • AMR element is made of a perm alloy (Fe, Ni) thin film resistor.
  • It can be same motion, if it reverse N and S of the magnet, because plus side and minus side have symmetry characteristics.
Operation image in the horizontal detection typeOperation image in the horizontal detection type

Block diagram

  • AMR sensors incorporate 1 package both AMR element and CMOS IC piggyback type.
  • It designs 3 terminals; VDD, VSS and VOUT.
  • It include sampling circuit to prevent current draw.
Block diagram

Chattering prevention

  • Magnetic field has hysteresis to prevent chattering.
    (Chattering is a phenomenon in which an electric signal repeats intermittence by detailed and very quick mechanical vibration, when the point of contact of a relay or a switch changes.)
  • When the magnet approach to the sensor and the magnetic flux density exceeds MOP, VOUT changes from H to L.
  • When the magnet leaves and the magnetic flux density decreases below MRP, VOUT changes from L to H.
Chattering prevention

 

Horizontal direction type: Features of AS-M series

Difference from Hall IC

Difference from Hall IC
AMR sensor
(Horizontal direction type)
Hall IC
Detection direction Magnetic
resistance effect
Hall effect
Sensor Material Ni and Fe Si type
InSb type
Detection Magnet Field Horizontal Vertical
Detection area Wide Narrow
  • AMR sensor has wide detection area because AMR sensor can use wide magnetic field.
    More flexible for design (Mount location)
  • It can make up for error of soldering. It can design magnet smaller and flatter than Hall IC.
Relation between sensor and magnetic fieldRelation between sensor and magnetic field

Difference from a reed switch

AS-M series (Horizontal direction type) has the following features compared with a reed switch.

  • Small size and low price
  • Available for low supply voltage
  • It is high reliability against the impact and the fall
Usage exampleUsage example

 

Vertical direction type: Features of AS-V series

  • Available at same type magnet as a Hall IC by our original process.
  • Two kinds of packages.
    AS-V20TA-R ⇒ Land compatibility as SOT23 package
    AS-V20NA-R ⇒ Land compatibility as SON4 package

Vertical direction type: Features of AS-V series