AG920-07E NVE, AG920-07E Datasheet - Page 112

• 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

As a solution to these potential problems, NVE’s AKL-Series GT Sensors offer internal signal
processing which compensates for temperature variation, sensor output variation, and magnet/target
variation. This results in a stable digital output signal with wide tolerance for magnet placement and
quality. For analog applications, NVE offers the following guidelines for biasing GT Sensors with
permanent magnets:
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NVE recommends about 1.5 mm distance from the back of the sensor to the face of the
magnet, in order to keep the flux lines at the sensor element “flexible” and able to follow the
gear teeth with relative freedom. This distance can be achieved by putting the sensor on one
side of a circuit board, and the magnet on the other.
To fix the position of the magnet on the circuit board more precisely, the board can be made
thicker, and a pocket can be machined into it to hold the magnet. This service is readily
available from most circuit board manufacturers.
Various high temperature epoxies can be used to glue the magnet in position; NVE
recommends 3M products for this purpose.
If zero speed operation is not required, AC coupling the sensor to any amplifier circuitry will
remove the offset induced in the sensor by the magnet.
If zero speed operation is required, some method of zeroing the magnet-induced offset voltage
from the sensor will be required for maximum airgap performance. NVE’s AKL-Series
sensors have this feature built in, and NVE’s DD001-12 signal conditioning IC also includes
this feature.
GT Sensor ICs are centered in the plastic package, so placement of the permanent magnet
should be symmetrical with the package.
Ceramic 8 magnets are a popular choice in this application, and provide good field
characteristics and low cost. However, C8 magnets lose substantial magnetic strength at
higher temperatures. For analog output applications where a consistent signal size over
temperature is desirable, use of an Alnico 8 magnet (the most temperature stable magnet) is
recommended. Samarium-Cobalt magnets and Neodymium-Iron-Boron magnets are not
recommended because they are so strong that they tend to saturate the GMR sensor element.
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Application Notes