Siemens SIMATIC S5 Manual page 103

Description of the Individual Operating Modes
For "reference point synchronized" the excitation pattern counter on the module must be
synchronized with the counter in the power unit.
Synchronization
"Reference point synchronized" has been selected with "yes" in the machine data.
The power unit is capable of being monitored. When the power unit is switched off, afloat-
ing contact is closed.
If the IP247 recognizes that this contact has closed (See digital inputs/outputs), it sets
its excitation pattern counter to "O", The counter in the power unit is set to "O" when it is
switched on.
The power unit can be reset.
Before starting the "reference point approach" mode, the I P247 outputs a reset signal
for 100 ms (see digital inputs/outputs). This signal resets the excitation pattern counter
of the power unit. The counter on the IP247 is also set to "O".
The power unit cannot be reset and cannot be monitored.
In this case, the IP247 and the power unit must always be switched on and off together.
Sequence of the reference point approach
A reference point approach goes through the following steps: (see Fig. 4/7 "Reference point ap-
proach" with reversal at the limit switch.)
BA 5 (reference point); run; start
Select "reference point" (mode 5) with the parameter "run".
2)
Send the start command.
The drive traverses in the opposite direction from the reference direction at the refer-
ence speed.
4)
The direction is reversed at the hardware limit switch, the axis traverses at reference
speed until after the precontact.
5)
After leaving the precontact, the axis brakes and traverses in a direction opposite ref-
erence direction to the precontact. This movement is at the speed corresponding to
the start-stop frequency.
6) Once the precontact is recognized, the axis stops and then leaves the precontact in
single steps in the reference direction.
7) Depending on whether or not you have selected synchronization, the reference point
approach is completed at different positions:
Synchronization: no
Once the module recognizes that the precontact has been left, the reference point
approach is completed, the coordinate of the reference point is entered as the
actual value and the reference point is marked as existing (axis attribute).
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