Siemens SINAMICS S120 Getting Started page 140

Performing basic parameterization
6.3 Drive axes
Preparing actual values
To transfer the encoder position from the drive to an open-loop control / position control, the
"Cyclical actual value" = Gn_XIST1 and "Absolute actual value" = Gn_XIST2 (n = 1 or 2,
number of the encoder) data is used in a telegram. The values can be set only for absolute
encoders.
● The incremental position change of the encoder is transferred to the controller in the
"Cyclical actual value" Gn_XIST_1. The drive evaluates only the counting pulses of the
encoder, which it then uses to form the "Cyclical actual value".
● The cyclical values of the encoder requested by the controller prior to the transfer are not
transferred in the "Absolute actual value" = Gn_XIST2.
Gn_XIST_1 and Gn_XIST_2 contain the following information:
● Encoder pulse count (Gn_XIST_1)
● Fine resolution (Gn_XIST_1)
● Multiturn information (Gn_XIST_2)
Fine resolution p0419 (XIST_1)
Encoders with their sampling mechanism provide significantly more precise information than
that determined with the pulse counts. They can be evaluated by the drive unit and
transferred as fine resolution to the controller. Change the fine resolution, for example, when
increased precision is required for machining a workpiece.
Fine resolution for incremental encoders
For incremental encoders, the analog signals of the C and D tracks are evaluated. A position
value is determined uniquely via the two analog voltage values in all four quadrants of a
revolution. The analog voltage values allow a high fine resolution, e.g. 11 bits = 2048.
Together with a resolution of 11-bit (= 2048) encoder pulses per revolution this gives a 22-bit
resolution.
Figure 6-6
138
Incremental encoders
Getting Started, 12/2018, 6SL3097-5AG30-0BP0