AG920-07E NVE, AG920-07E Datasheet - Page 109

• Manufacturer Part Number: AG920-07E
• Description: KIT EVALUATION GT SENSOR
• Manufacturer: NVE

Specifications of AG920-07E

• Sensor Type: Magnetic. GMR (Giant Magnetoresistive)
• Interface: Analog
• Embedded: No
• Utilized Ic / Part: ABL & AKL Series GT Sensors
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Supply: -
• Sensitivity: -
• Sensing Range: -
• Other names: 391-1063

Application Notes for GT Sensors
General Theory of Operation of Differential Sensors (Gradiometers)
Differential sensors, or gradiometers, provide an output signal by sensing the gradient of the magnetic
field across the sensor IC. For example, a typical GMR sensor of this type will have four resistive
sensor elements on the IC, two on the left side of the IC, and two on the right. These resistive sensor
elements will be wired together in a Wheatstone bridge configuration. When a magnetic field
approaches the sensor IC from the right, the right two resistive sensor elements will decrease in
resistance before the elements on the left. This leads to an imbalance condition in the bridge, providing
a signal output from the bridge terminals.
Note that if a uniform magnetic field is applied to the sensor IC, all the resistive sensor elements will
change at the same time and the same amount, thus leading to no signal output from the bridge
terminals. Therefore, a differential sensor cannot be used as a magnetometer or an absolute field
detector; it must be used to detect the presence of a magnetic gradient field.
Gradient fields are present at the edge of magnetic encoders and magnetically biased gear teeth. As a
result, differential sensor elements are ideally suited for speed and position detection in these
applications.
GT Sensor Operation with Permanent Magnet Bias
Magnetic encoders generate their own magnetic field, but a gear tooth wheel does not, so if a
differential sensor is to be used to detect gear teeth, a permanent magnet is required to generate a
magnetic bias field. The differential magnetic sensor will then be used to detect variations in the field
of the permanent magnet as the gear tooth passes by in close proximity.
R3
R4
Field Decreases as Distance from Source Increases
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R1 and R2 see a Larger Field than R3 and R4
GT Sensor
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R1
R2
Application Notes
Out-
Magnetic
R4
R2
Source
Point
Field
of
R1
R3
Out+