Siemens SIMATIC FM 452, Manual

Page: 82 / 210

Machine Data and Cam Data
8-14
FM 452 Electronic Cam Controller
C79000-G7076-C452-04
Result After Setting the Reference Point
After setting the reference point, the relationship between the encoder and
coordinate system is as follows:
The reference point coordinate on the axis (-125) is assigned to the encoder value
(1798) calculated from the absolute encoder adjustment.
SLE SLS
Axis
–1000 1000 0
V
alue of absolute encoder
0
2047
REF
–125
1798
Value from absolute
encoder adjustment
875
Encoder range covered by this encoder
1024 –1023
0
The encoder supplies 2048 defined values. The working range is defined by the
software limit switches. Due to the selected resolution of 1 mm per pulse, the
encoder can, however, cover a larger working area than intended with the software
limit switches.
With the set resolution the working range is already covered with 2001 values.
Therefore, in the example there are 47 pulses “left over” which lie symmetrically
about the working range.
Alternative: Mechanical Adjustment of an Encoder
You can obtain a correct relationship between the coordinate system and the
encoder as follows:
1. Move the axis to a reproducible position (for example the start software limit
switch).
2. Enter this coordinate value in the machine data as the reference point
coordinate.
3. Read the encoder value displayed at this position in the service dialog of the
user interface.
4. Enter this value as the absolute encoder adjustment in the machine data.
A correct actual value is then always displayed after parameter assignment.
Instead of steps 3. and 4., you can also set the encoder to zero with “Reset” (if this
exists) and enter the value “0” as the absolute encoder adjustment in the machine
data.