Siemens SIMATIC S7-300 Manual page 195

When crossing the RPS, a signal length of ∆t
sured!
Using a reversing
If it is possible for the axis to be "behind" the reference point switch when
switch
you start reference point approach, a reversing switch can be installed at the
end of the axis in the approach direction, in order to reverse the axis in the
direction of the reference point switch.
On axis movements with referencing feed, a signal length of ∆t
cycle must be assured for the reversing switch!
Example
The value for the reference-point shift (MD27) is traveled after the synchro-
nization point is reached.
Without reference-
The following table describes how a reference can be recorded without a ref-
point switch (RPS) erence-point switch.
R+, R–
or Start
Note
Please see also Section 9.1.3!
FM 354 Servo Drive Positioning Module
Axis position Approach direction from MD18
RPS
Reference point
Recording of syn-
chronization
1. Instantaneous position is defined as reference point (refer-
ence-point coordinate).
2. Value for reference-point shift is traveled.
Description of Functions
2 FM cycle must be as-
Reversing Emergency
switch limit switch
Sequence of movements
2 FM
9-19