HALL EFFECT

GEAR-TOOTH SENSORS

–ZERO SPEED

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Figure 5

DIFFERENTIAL FLUX DENSITY

Pole Piece Design. A pole piece may be used at the face of the

magnet to smooth out the magnet-face offsets. A 0.020” (0.51 mm)

thick, soft-iron pole piece will bring the field non-uniformity down to

the

±1%-to-±3% range. Note that pole pieces will minimize but not

eliminate the non-uniformity in the magnet face field. Front pole pieces

will almost always result in a reduced maximum air gap.

Ferrous Targets. The best ferrous targets are made of cold-rolled

low-carbon steel. Sintered-metal targets are also usable, but care

must be taken to ensure uniform material composition and density.

The teeth or slots of the target should be cut with a slight angle

so as to minimize the abruptness of transition from metal to air as the

target passes by the sensor. Sharp transitions will result in magnetic

overshoots that can result in false triggering.

Gear teeth larger than 0.10” (2.54 mm) wide and at least 0.10”

(2.54 mm) deep provide reasonable working air gaps and adequate

change in magnetic field for reliable switching. Generally, larger teeth

and slots allow a larger air gap. A gear tooth width approximating the

spacing between sensors (0.088” or 2.24 mm) requires special care in

the system design and assembly techniques.

ASSEMBLY TECHNIQUES

Due to magnet face non-uniformities and device variations, it is

recommended that applications requiring precision switching utilize a

mechanical optimization procedure during assembly. Without a pole

piece, the inherent magnet face offsets can be used to pre-bias the

magnetic circuit to obtain any desired operating mode. This is

achieved by physically changing the relative position of the magnet

behind the sensor to achieve the desired system performance objec-

tive. For example, with a rotating ABS gear, the objective might be a

50% duty cycle at maximum air gap. Similar objectives can be set for

ignition (crank and cam position) sensing systems.

Non-precision speed sensing applications do not require optimiza-

tion. For applications where mechanical optimization is not feasible,

non-zero speed devices such as the UGN/UGS3059KA ac-coupled

gear-tooth sensor are available.

A

1

3

Dwg. MH-002-8D

0.075"

1.89 mm

BRANDED

SURFACE

ACTIVE AREA DEPTH

2

0.088"

2.23 mm

0.015"

0.38 mm

NOM

E1

E2

0

-2000

AIRGAP FROM PACKAGE FACE IN INCHES

Dwg. GH-035

2000

1000

0

-1000

-1500

0.025

0.050

0.100

0.125

1500

0.075

-500

500

0.070

-200

AIRGAP FROM PACKAGE FACE IN INCHES

Dwg. GH-036

200

100

0

-100

-150

0.080

0.090

0.110

0.120

150

0.100

-50

50

SENSOR LOCATIONS

(

±0.005” [0.13 mm] die placement)