AS5304
Magnetic Multipole Strip MS20-150
Pole Length 2.0mm, 150 Poles
Magnet Specification
1 General
This specification defines the dimensional and magnetic properties of a multipole magnetic strip for use with the
AS5304 magnetic linear motion and off-axis rotary angle encoder.
Material: Strontium ferrite bonded
2 Dimensional Specification
Parameter
Strip Length
Strip Width
Strip Thickness
Thermal Expansion
Symbol
L
W
T
Min
Typ
300±2
10±0.2
1,3±0,
15
17
Max
Unit
mm
mm
mm
-6
Note
Active length = 300mm
Active width = 10mm
1mm rubber bonded magnet on
0.3mm stainless steel strip
x10 /K Mechanical length expansion
Density
3.5
1.43
3.65
4.64
3.8
7.85
g/cm
3
magnetic rubber
stainless steel
Delivery
Single cut pieces without adhesive, rolls of 25m, 50m (up to 100m max.)
3 Magnet Specification
Parameter
Pole Length
Pole Length Deviation
Amplitude Variation
Number of Poles
150
Symbol
L
p
Min
Typ
2.00
1
1.5
±10
Max
Unit
mm
% of 2*L
p
% of B
pk
poles
Note
Results in pole pair length of 4.0mm
(150 poles @ 1.0mm)
Measured at Bz=0,
active area
all poles within
All poles within active area
Excluding poles with L<L
P
at the ends
of the strip
AS5304 @ incremental output
Vertical component of the magnetic
field strength in the center of the strip
at 25°C
Resolution
Res
25
µm
Magnetic Field Amplitude
@
0.8mm
Distance
Magnetic Field Temperature
Drift
B
pk
mT
TkB
r
-0.2
%/K
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Revision 0.1
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AS53xx Linear Multipole Magnetic Strip
Magnet Specification
Parameter
Symbol
Min
Typ
Max
40
Unit
Note
depending on accuracy grade
standard
Cumulative error
20
10
m/m
A20
A10
Thermal Expansion
Temperature Range
Tamb
-40
25
1E-4
100
1/K
°C
Mechanical length expansion
scale mounted, no bending
Magnetization
The MS20-150 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.
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Revision 0.1
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4 Magnet Dimensions
Figure 1:
MS20-150 strip dimensions
1
2
3
4
5
6
149
150
W = 10
N
S
N
S
N
S
N
S
recommended
scanning path
T=2
L=4
L = 300
Alignment of Magnet Strip and Sensor IC
When aligning the magnet strip to the AS5304 sensor IC, the centerline of the magnet strip should be placed
exactly over the Hall array. See Figure
2
for the position of the Hall array relative to Pin #1.
Vertical Distance
The vertical distance between the magnet strip and the top of the IC package should be
≤ 0.8mm.
Note that the
vertical distance depends on the strength of the magnet. The AS5304 automatically adjusts for fluctuating magnet
strength by using an automatic gain control (AGC). There are several indicators for proper magnetic field strength
available with the AS5304. The vertical distance should be set such that
the AO voltage is between 1.0 and 4.0V.
See the AS5304 datasheet for more details.
See also
Error! Reference source not found.
for measurement data of the MS20-150 magnetic strip.
Lateral Stroke
The lateral movement range (stroke) can cover the active area of the magnetic strip (see Figure 1) as long as all
Hall sensors of the IC are covered by the magnet. The Hall array on the AS5304 has a length of 2.0mm, hence the
total stroke is
Stroke = Length of active area – length of Hal array = 300.0mm – 2.0mm = 298.0mm
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Revision 0.1
Bpk Bpk
3-7
Figure 2:
Alignment of magnet strip with AS5304 sensor IC
position value
increases
leftmost magnet position
Die C/L
S
N
S
N
S
N
S
N
S
N
3.0475±0.235
1.00
AS5304
Package
Outline
rightmost magnet position
Die C/L
position value
decreases
3.200±0.235
2.576±0.235
S
N
S
N
S
N
S
N
S
N
1.00
3.0475±0.235
vertical airgap
magnet
strip
carrier
see text
1.00 ± 0.1
Note: all dimensions are in mm
Note that the polarization of the magnet will be reversed when it is rotated or flipped (see Magnetization for more
details).
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Revision 0.1
4-7
AS53xx Linear Multipole Magnetic Strip
Magnet Specification
5 Adhesive Tape Specification
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Revision 0.1
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