Technical data

Basic functions

4.1 Encoder settings

Connection of the SINAMICS S120 to the Technology CPU

Product Information, 09/2011, A5E00480378-04

Fine resolution (parameter 418 / Parameter 419 in the drive)

Encoders can provide much more precise information via their internal sampling mechanism

(sine / cosine oscillations, sub-sampling on a etched pane of glass). These can be evaluated

by the drive unit, and transferred to the PLC as a fine resolution.

The encoder actual values that can be transferred from the drive to the PLC are limited to

32-bit, however. If, for example, a standard multiturn encoder with a 12-bit (4096) multiturn

resolution and an 11-bit (2048) encoder resolution is used, there will be just

32-12-11 = 9 bits (512) remaining in the encoder actual value for transferring the

fine resolution.

If a greater fine resolution is to be transferred in the encoder actual value, the multiturn

resolution of the encoder actual value is reduced; although this increases the precision of the

encoder, it does reduce the encoder's absolute measuring range.

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With the technology CPU, the fine resolution for the cyclical actual value (Gn_XIST_1) is to

be set as a multiplication factor of the cyclical actual value. The factory setting of 11 bits is

correct for all standard Siemens motor encoders. It does not normally have to be changed.

The multiplication factor of the absolute actual value (Gn_XIST_2) is the fine resolution of the

absolute actual value. The factory setting of 9 bits is correct for all standard Siemens motor

encoders and does not have to be changed.

The multiplication factor of the absolute actual value is usually smaller than the multiplication

factor of the cyclical actual value, as there is more multiturn information to be transferred in

the absolute actual value (Gn_XIST_2).

If an incremental encoder is used, the absolute actual value (Gn_XIST_2) is structured

exactly as the cyclical actual value (Gn_XIST_1). The multiplication factor of the absolute

actual value (Gn_XIST_2) is then irrelevant.