AG920-07E NVE, AG920-07E Datasheet - Page 9

• 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

Gradiometers
NVE’s gradiometers, or differential sensors, rely on the field gradient across the IC to generate an
output. In fact, if one of these sensors is placed in a uniform magnetic field, its output voltage will be
zero. This is because all four of the bridge resistors are exposed to the same magnetic field, so they all
change resistance together. There is no shielding or flux concentration on a gradiometer. A simple
representation of a gradiometer is shown in the diagram below:
Because all four bridge resistors contribute to the sensor’s output, at maximum differential field NVE’s
gradiometers can provide double the output signal of our magnetometer parts—approximately 700 mV
with a 5V supply. In practice, the gradient fields are typically not high enough to give this maximum
signal, but signal levels of 50 mV to 200 mV are common.
NVE’s GMR differential sensors are typically designed with two of the bridge resistors at one end of
the IC, and two at the other end. The spacing between the two sets of resistors, combined with the
magnetic field gradient on the IC, will determine the output signal from the sensor element. NVE
offers three standard spacings for differential sensors: 0.3 mm, 0.5 mm, and 1.0 mm. If a different
spacing is desired, contact NVE for development cost and schedule for a custom product.
The most popular application for differential sensors is in gear tooth or magnetic encoder detection. As
these structures move or spin the magnetic field near their surface is constantly varying, generating a
field gradient. A differential sensor, properly placed, can detect this movement by sensing the
changing field gradient and provide an output for each gear tooth or each magnetic pole (see the GT
Sensor section of this catalog for a more detailed explanation). Applications for these devices include
detecting the speed and position of electric motor shafts or bearings, automotive transmission gear
speeds, axle shaft speed in Anti-lock Braking Systems (ABS), or linear gear-tooth position.
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Gradiometer
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Introduction
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