as5311 austriamicrosystems, as5311 Datasheet - Page 18

• Manufacturer Part Number: as5311
• Description: High Resolution Magnetic Linear Encoder
• Manufacturer: austriamicrosystems

AS5311
Data Sheet
11 AS5311 Off-axis Rotary Applications
The AS5311 can also be used as an off-axis rotary encoder, as shown in Figure 3. In such applications, the
multi-pole magnetic strip is replaced by a multi-pole magnetic ring. The ring can have radial or axial
magnetization.
Figure 16: Angular resolution and maximum speed versus ring diameter
The number of incremental steps per revolution can be calculated as:
Note that the circumference (d*π) must be a multiple of one polepair = 2mm, hence the diameter of the magnet
The maximum rotational speed can be calculated as:
where
Note:
www.austriamicrosystems.com
160000
140000
120000
100000
80000
60000
40000
20000
ring may need to be adjusted accordingly:
nbr_polepairs
d
max_rot_speed = maximum rotational speed in revolutions per minute rpm :
max_lin_speed = maximum linear speed in mm/sec (=650 mm/s for AS5311)
further examples are shown in the “Magnet Selection Guide”, available for download from the
austriamicrosystems website
http://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Linear-Encoders
0
AS5311 off-axis rotary resolution & speed
20
40
= the number of pole pairs at the magnet ring
= diameter of the ring in mm; the diameter is taken at the locus of the Hall elements
max_
underneath the magnet
ring diameter [mm]
incrementa
resolution
speed rpm
rot
60
incrementa
_
speed
d
=
l
_
nbr
80
steps
=
l
max_
_
_
polepairs
steps
=
Revision 1.00
1024
100
lin
π
=
d
700
600
500
400
300
200
100
0
_
*
1024
*
speed
π
nbr
*
2
mm
*
2
_
In off-axis rotary applications, very high
angular resolutions are possible with the
AS5311.
The number of steps per revolution
increases linearly with ring diameter.
Due to the increasing number of pulses per
revolution, the maximum speed decreases
with increasing ring diameter.
Example:
a magnetic ring with 41.7mm diameter has
a resolution of 65536 steps per revolution
(16-bit) and a maximum speed of 305 rpm
d
*
polepairs
60
*
Res
[bit]
15
16
17
π
=
39000
d
131072
Steps /
32768
65536
Rev.
*
π
Diameter
[mm]
Ring
20.9
41.7
83.4
Speed
[rpm]
Max
609
305
152
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