Siemens Sinamics S120 Function Manual page 297

In order to determine the position at the motor/load, in addition to the position actual value of
the absolute encoder, it is also necessary to have the number of overflows of the absolute
encoder.
If the power supply of the control module must be powered-down, then the number of
overflows must be saved in a non-volatile memory so that after powering-up the position of
the load can be uniquely and clearly determined.
Example: Gear ratio 1:3 (motor revolutions p0433 to encoder revolutions p0432), absolute
encoder can count 8 encoder revolutions (p0421 = 8).
Figure 6-15 Drive with odd-numbered gearboxes without position tracking
In this case, for each encoder overflow, there is a load-side offset of 1/3 of a load revolution,
after 3 encoder overflows, the motor and load zero position coincide again. The position of
the load can no longer be clearly reproduced after one encoder overflow.
If position tracking is activated via p0411.0 = 1, the gear ratio (p0433/p0432) is calculated
with the encoder position actual value (r0483).
Figure 6-16
Drive functions
Function Manual, (FH1), 01/2012, 6SL3097-4AB00-0BP2
Odd-numbered gears with position tracking (p0412 = 8)
Basic functions
6.20 Position tracking
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