Question:
What must be observed when using the 'Modulo' traversing range and safety functions of SM301 that require an evaluation of an additional position encoder via the FDB_dnActPosIn_p input of the LS_Feedback system block?
Answer:
When SSI encoders or fieldbus encoders are connected to the 9400, the FDB_dnActPosIn_p interface of the LS_Feedback system block is used to transfer the actual position to the position control. The safety module also receives the encoder position via this interface if the position encoder must be monitored in parallel to the motor encoder (two-encoder concept). For this, the position is internally differentiated because the speed signal is monitored.
In the case of a Modulo traversing range, the position cyclically overflows after reaching the end of the cycle, e.g. from 360° to 0°. If the differentiation is effected at the overflow point, the resulting speed signal may become so high that the speed discrepancy monitoring responds.
I.e. if the application requires an actual position representation in a Modulo measuring system, the safety module cannot monitor an encoder on the LS_Feedback interface. In this case, only the motor encoder can be used for the encoder-relevant safety functions:
'Single-encoder concept'. This must be considered when configuring the motor because encoder type and encoder mounting must be suitable for this.
