AS53xx Linear Multipole Magnetic Strip

Magnet Specification

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Revision 0.1

2 - 6

Parameter

Symbol

Min

Typ

Max

Unit

Note

Cumulative error

40

20

10

µm/m

depending on accuracy grade

standard

A20

A10

Thermal Expansion

1E-4

1/K

Mechanical length expansion

Temperature Range

Tamb

-40

25

100

°C

scale mounted, no bending

Magnetization

The MS12-250 magnet strip is magnetized on the top side and bonded on a steel support with elastomer adhesive

(bottom). Note that the polarization of the magnet will change when it is rotated as the pole arrangement not

symmetric. This will influence the position of the index pulse.

An index pulse is generated when the North and South poles are placed over the Hall array as shown in Figure 2.

The incremental output count increases when the magnet is moving to the left, facing the chip with pin#1 at the

lower left corner (see Figure 2, top drawing). At the same time, the absolute position information increases.

Likewise, the position information decreases when the magnet is moved in the opposite direction. Note that there is

no hysteresis at the absolute output. In order to get a stable 12-bit absolute reading, it may be necessary to filter

the values by averaging, e.g. a moving average calculation in the external microcontroller. Averaging 4 readings

results in 6dB (=50%) noise and jitter reduction. An average of 16 readings reduces the jitter by a factor of 4.

Mounting the Magnet Strip

The magnet strip may be mounted directly on magnetic or non-magnetic surfaces. When magnetic surfaces are

used, the strip must be mounted on top of the surface, but not immersed in a cavity, as this may weaken the

magnetic field of the magnet. When mounting the magnet on a non-magnetic surface, either method is acceptable.

For more rigid demands, magnet suppliers offer customized solutions where the magnet material is directly

overmolded on the carrier, e.g. a shaft, bushing, plate, etc..

Please contact your magnet supplier for more information. A list of recommended suppliers is available for

download on the austriamicrosystems website.