Normalizing The Encoder Signal; Define The Resolution - Siemens SINAMICS G120D Operating Instructions Manual

7.6.3

Normalizing the encoder signal

7.6.3.1

Define the resolution

Distance unit (LU): the resolution of the position actual value in the inverter
The inverter calculates the position actual value of the axis using the neutral position unit LU
(Length Unit). The distance unit LU is independent of whether the inverter controls e.g. the
position of an elevating platform or the angle of rotary table.
Firstly, for your application define the required resolution. In other words: Which distance or
angle corresponds to the length unit (LU)?
The following rules apply when selecting the distance unit LU:
1. The higher the resolution of the distance unit LU, the higher the accuracy of the position
control.
2. If you select a resolution that is too high, then the inverter cannot represent the position
actual value over the complete axis traversing range. The inverter responds with a fault in
the case of an overflow when representing the number.
3. The resolution of the distance unit LU should be less than the maximum resolution that is
obtained from the resolution of the distance-encoder.
Normalize the encoder signal
Preconditions
● You are online with the STARTER .
● You have selected the "Mechanical system" screen.
● You have defined the required resolution for your particular application (e.g. 1 LU ≙ 1 µm
or 1 LU ≙ 1/1,000° (1 millidegree).
Procedure
To normalize the encoder signal, proceed as follows:
1. Enable the settings so they can be edited.
2. Enter the gear ratio of the axis. Load revolutions.
3. Motor revolutions
Unknown gear ratio
If you do not know the gear ratio, then you must measure the ratio, for example by
manually rotating the motor and counting the load revolutions.
Example: After 5 motor revolutions, the load has turned through 37 °. The ratio is
therefore 37 ° / (5 × 360 °). You must then enter the following values into STARTER:
–
–
Converter with control units CU250D-2
Operating Instructions, 04/2015, FW V4.7.3, A5E34261542B AB
②
37 [load revolution]
③
1800 [motor revolution]
Advanced commissioning
7.6 Basic positioner and position control
165