Basic Knowledge of AMR Sensors (Magnetic Switches)
AMR sensor is a sensing device utilizing the magnetic resistance rate change being affected by the strength of the external magnetic field. It is used together with a magnet.
AMR: Anisotropic Magneto Resistance
Thanks to the wide variety of sensitivity range and its size, you can choose the best product which satisfies your requirement.
AMR sensor is independent of magnetic polarity, meaning that it detects the strong positive magnetic field and the strong negative magnetic field in the same manner.
AMR sensor has wider detection area compared to Hall IC, therefore it has much more design flexibility in terms of mounting location.
- Unlike Reed Switch, AMR sensor is not a mechanical component.
- Therefore, it can be kept small in its size and maintain high reliability.
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AMR sensor is one of the best fit for its usage such as non-contact switches for mobile devices.
- For Mobile phones, Notebook PCs, Digital cameras and more…
- For Refrigerators, Washing machines and other Home appliances
- For Security equipments for doors/windows
- Smart gas meter
- Smart water meter etc.
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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.
- 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.
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AMR Sensor: Features of MRMS series
Difference from Hall IC
||Ni and Fe
|Detection Magnet Field
- AMR sensor detects a horizontal magnetic field which gives you Design Flexibility allowing a single magnet to support multiple sensing positions in terms of mounting locations.
- By this feature, AMR sensor has a merit to be used even for the space conscious applications.
Relation between sensor and magnetic field
Difference from a reed switch
AMR Sensor has the following features compared with a reed switch.
- Small in size and relatively inexpensive in price.
- Strong shock-tolerant and vibration-tolerant; which leads to high reliability.
- Longer life expectancy thanks to its Contact-less feature.
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