Magnetoresistive sensor
The magnetoresistive sensors are based on the magnetoresistive effect. The magnetoresistive effect is the change of the resistivity of a current carrying ferromagnetic material due to a magnetic field. MGR sensor can be called as magnetically controllable resistors
The below figure shows the Magnetoresistive effect.
When the current is passed through the ferromagnetic material the internal magnetisation vector(M) of the ferromagnetic material is parallel to the current flow. When an external magnetic field is applied in applied opposite to the direction of the current flow as shown in the figure the internal magnetisation vector changes its position(M1) by an angle depending on the strength of the magnetic field. The resistance depends on the angle formed by the internal magnetisation vector(M) of the ferromagnetic material and the direction of the current(I) flow. Resistance is largest if the current flow and the internal magnetisation vector are parallel. The resistance in ferromagnetic material is smallest if the angle is 90° between the current flow and the internal magnetisation vector.
Normally 4 sensors are connected in a Wheatstone bridge configuration to form a complete MGR sensor with each resistor arranged to maximize sensitivity and minimize temperature influences. In the presence of a magnetic field, the values of the resistors change, causing a bridge imbalance and generating an output voltage proportional to the magnetic field strength. The Wheatstone bridge configuration provides reduction of temperature drift and doubles the signal output
The advantages of MGR sensor are
Non contact operation so there is no wear and friction. Hence unlimited number of operating cycles
high reliability due to their rugged construction
Low and stable offset
Due to its high sensitivity it can be used to measure weak magnetic fields
Low sensitivity to mechanical stress
Much more Insensitive to vibrations than inductive sensors
high operating temperature
wide operating frequency range (0 Hz to 1 MHz)
can be used in harsh environments
Reasonable cost
can measure zero speed
small size
fast response
The disadvantages of MGR sensor are
Some of the applications of MGR sensor are
wheel speed sensors
angle measurement
linear displacement measurement
current measurement
Earth magnetic field detection for compass and navigation applications
Metal detection
Magnetic field measurement
