Basic Knowledge of AMR Sensors (Magnetic Switches)
- Basic Characteristics -
- AMR sensor is a product which utilized the magnetic thin films such as nickel and iron.
- MR element made of Ni-Fe called perm alloy is formatted on wiring layer of the semiconductor IC.
- When the external magnetic field is applied to MR element, the resistant rate of MR element will change.
Then voltage difference occurs.
- AMR sensor consists of bridge circuits (which consists of 4 MR resistances) .
- 4 MR resistances are divided into 2 groups, and it is arranged so that each may become perpendicular.
- MR element has unique characteristics that the resistance rate drops when the external magnetic field is applied perpendicularly to the current. When the resistance rate drops, the neutral voltage point of the bridge circuit will change. This change is input as analog voltage signal into the IC.
- IC built-in amplification circuit inside judges automatically whether the input analog is higher or lower than the threshold voltage. Then ON/OFF digital output is performed.
- 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.