10
10-4
FM 351 Positioning Function Module
EWA 4NEB 720 6001-02
10.3 Absolute Encoders
There are the following absolute encoders:
Single-turn encoders
Single-turn encoders form the total encoder range on one encoder revolu-
tion. You can use single-turn encoders with the following steps per revo-
lution:
– With 13 bit frame length having 2
2
to 2
13
steps.
– With 25 bit frame length having 2
2
to 2
25
steps.
Multi-turn encoders
Multi-turn encoders form the total encoder range over a number of en-
coder revolutions.
Multi-turn encoders (25 bit: tree-type):
– Steps per revolution: 2
2
to 2
13
– Number of revolutions: 2
1
to 2
12
Only absolute encoders with a serial interface are supported. The transfer of
the displacement information takes place synchronously according to the SSI
protocol (Synchronous Serial Interface). The FM 351 supports the data for-
mat from the company Stegmann.
You can only use absolute encoders (SSI) with GRAY code. Due to the ar-
rangement of the user bits within the 13 or 25 bit frame, data formats are pro-
duced which have the shape of a “tree” or “half tree”.
Single-turn encoders: “half tree” with 13 or 25 bit frame length (left justi-
fied).
Multi-turn encoders: Tree type with 25 bit frame (12 bits for number of
revolutions and 13 bits for steps per revolution).
The baud rate for the data transfer depends on the line length
(see Appendix A, Technical Data).
Single-Turn and
Multi-Turn
Encoders
Data Processing
Data Transfer
Encoders
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