AG001-01 NVE, AG001-01 Datasheet - Page 128

• Manufacturer Part Number: AG001-01
• Description: KIT ENGINEERING EVALUATION
• Manufacturer: NVE

Specifications of AG001-01

• Rohs Status: RoHS non-compliant
• Sensor Type: Magnetic. GMR (Giant Magnetoresistive)
• Interface: Analog
• Embedded: No
• Utilized Ic / Part: AA & AB Series Analog Sensors
• Voltage - Supply: -
• Sensitivity: -
• Sensing Range: -
• Other names: 391-1003

The magnetic particles in the ink of most currencies, and also any magnetic stripes on the currency,
can be magnetized and demagnetized by an external field. With only the earth’s field present, the bill’s
magnetic properties can be seen. However, the signal increases when using an external field.
This external magnetic field can be set up in a few different orientations, either in a front/back biasing
configuration or positioned “upstream” of the sensor. The back biasing configuration typically consists
of an electro/permanent magnet glued to the under side of the sensor or to the under side of the PCB.
The magnet should be aligned to produce the minimum output from the sensor. The ferromagnetic
particles in the bill will magnetize and thus distort the field to produce a field in the sensitive direction
at the sensor. Front biasing works in much the same manner except in this case the source of external
field is coming from the other side of the bill.
Positioning the magnet “upstream” from the sensor consists of magnetizing the bill before it reaches
the sensor—this terminology comes from an application where the bills are moving past the sensor on
a conveyer belt or rollers. With a magnet placed near the moving bill, the bill is magnetized before
passing the sensor. The application’s geometrical requirements, strength of magnet, as well as sensor-
bill distance will determine which configuration works the best in each application. The following are
some graphs that show the characteristics of back-biasing an AA002 sensor.
To determine the sensitivity of back biasing positioning, the magnet was moved along the sensors
sensitive axis. The goal was to position the magnet so that there is minimum field in the sensitive
direction. To obtain this, one pole of the magnet must be directly under the sensing resistors of the
bridge. Note the steep slope around the zero output, which makes exact positioning difficult.
Ma g net
Magnet
www.nve.com
Bill
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AA002-02
- 128 -
Back biasing
Flux
Front biasing
4 leads, V+,V-
Out+, Out-
Passive
mounting
Application Notes