Siemens SIMATIC FM 351 - System of Units

Machine Data and Incremental Dimensions
8-5
FM 351 Positioning Module
C79000-G7076-C351-02
8.2 System of Units
Selecting a Unit
In the configuration software of the FM 351, you can select one of the following
systems of units for entering and outputting data:
• mm (default)
• inches
• degrees
Note
If you change the unit in the parameter dialogs, the values are calculated in the
new system. This can lead to rounding errors.
If you change the system of units by programming with the jobs “write machine
data” and “activate machine data”, the values are not automatically recalculated.
System of Units in the Parameter DB
Address Name Data
Type
Initial Value Description
8.0 UNITS DINT L#1 Units
1 = 10
-3
mm
2 = 10
-4
inches
3 = 10
-4
degrees
4 = 10
-2
degrees
6 = 10
-3
degrees
Standard System of Units
In this manual, the limit values are always specified in the system of units mm.
To define the limits in other systems of units, please make the following
conversion:
To convert.... Calculate
mm  inches Limit value (inches) = limit value (mm)  0.1
mm deg 10
-4
(4 decimal places)
10
-3
(3 decimal places)
10
-2
(2 decimal places)
Limit value (degrees) = limit value (mm)  0.1
Limit value (degrees) = limit value (mm)  1
Limit value (degrees) = limit value (mm)  10
Relationship between Increments and System of Units
The encoder signals of a connected encoder are evaluated by the FM 351 and
converted to the current system of units. For the conversion, the resolution is used
(see Section 8.7, page 8-22).
If the FM 351
• has counted 10 increments and
• a resolution of 100 m per increment is set by the encoder parameters,
this means that the axis was moved by a distance of 1 mm.