Siemens SIMATIC FM 351 - Machine Data for the Encoder

Machine Data and Incremental Dimensions
8-15
FM 351 Positioning Module
C79000-G7076-C351-02
8.5 Machine Data for the Encoder
Definition
The encoder supplies position information (see Chapter 10, page 10-1) to the
module that evaluates the information and calculates an actual value based on the
resolution.
You can only be sure that the calculated actual value of the axis position matches
the actual axis position when the information in the machine data of the encoder is
correct.
Data in the Parameter DB
Address Name Type Initial Value Comment
20.0 ENC_TYPE DINT L#1 Encoder type and frame length:
Range of values:
1 = 5 V incremental
2 = 24 V incremental
3 = SSI 13-bit frame length
4 = SSI 25-bit frame length
With the “frame length”, you specify the clock frame output by the FM 351.
Address Name Type Initial Value Comment
24.0 DISP_REV DINT L#80000 Distance per encoder revolution:
Range of values:
1 m to 1 000 000 000 m
With the machine data “distance per encoder revolution” you inform the FM 351 of the distance
covered by the drive system per encoder revolution.
The value “distance per encoder revolution” depends on how the axis is set up and how the encoder is
installed. You must take into account all transmission components such as couplings or gearing.
Section 8.7 (page 8-22) describes the relationship between the machine data “distance per encoder
revolution” and “increments per encoder revolution”.
Moto
r
Encoder
Gear unit
Moto
r
Encoder
Gear unit