8
8-14
FM 351 Positioning Function Module
EWA 4NEB 720 6001-02
Table 8-4 Machine Data for the Encoder, continued
Machine Data and
Assignment
Description
Increments per encoder
revolution
1 to 2
25
The machine data Increments per encoder revolution gives the number of increments
which the encoder produces per revolution. The FM 351 determines the resolution
from this value and the machine data Displacement per encoder revolution.
Incremental encoder
Any value from the input range shown opposite can be entered.
The FM 351 counts each edge of the 90° displaced signals from the incremental en-
coder, that is, four increments per signal period are counted and processed by the
FM 351 (see also Chapter 10.1).
Absolute encoder
The upper limit is limited by the total number of encoder steps. It is defined by the
product of the Number of revolutions and the Increments per encoder revolution.
Only values in steps of a power of two are allowed as input.
For the limits there is a difference between the various encoder models:
Single-turn encoders (no. of revs = 1) with 13 bit frame length:
– Minimum value = 4
– Maximum value = 8192
Multiturn encoders (no. of revs. > 1) with 25 bit frame length:
– Minimum value = 4
– Maximum value = 8192
Single-turn encoders with 25 bit frame length, no. of revs. = 1 and no. of incre-
ments per encoder revolution > 8192:
– Minimum value = 4
– Maximum value = 2
25
Baud rate
0.125 MHz
0.250 MHz
0.500 MHz
1.000 MHz
With the baud rate you define the speed of the data transfer from SSI encoders to the
FM 351.
This entry has no significance for incremental encoders.
The maximum line length is dependent on the following four stages:
0.125 MHz ³ 320 m
0.250 MHz ³ 160 m
0.500 MHz ³ 63 m
1.000 MHz ³ 20 m
Take note that with increasing line length the transfer rate must be set lower.
Counting direction
Normal
Inverted
With the machine data Encoder counting direction you match the direction of the
displacement measurement to the direction of axis movement.
Machine Data and Increments
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