Siemens SIMATIC S5 Manual page 57

Installation Guidelines
3.4 Replacing the Position Encoder
The steps you must take to remove the encoder for repair or replacement are
listed below, and must be carefully observed.
Proceed as follows to remove the encoder:
Switch off the 24 V power supply for the module.
Disconnect the encoder cable from the module.
Repair the encoder or insert a new one.
Connect the encoder and switch on the module's 24 V power supply.
The position control monitor is activated when an automatic mode that outputs
an analog setpoint greater than 5 V is invoked.
The encoder pulses are compared to the setpoint over a period of ten IP cycles.
Once the IP 266 has ascertained that the counting direction for setpoint and
actual value are in conformance, the monitor is deactivated.
C A U T I O N :
The module's 24 V power supply must always be switched off before removing
the encoder for repair or replacement, as only then can the monitor detect
position control errors.
Once an encoder has been replaced or repaired and reinstalled, the new
position of the zero mark makes reproduction of an old reference point, if any,
impossible.
3-6
IP 266
EWA 4NEB 812 6057-02