Motrona DS230 Series, Safety Manual

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Ds230_03a_oi_e.doc / Jun-15 Page 17 / 100
5.2.2. External Encoder Supply
An external encoder supply must be done in each case via a relay which is triggered by the auxiliary
voltage of the unit. This is necessary, because the encoder supply will only be activated after the
safety unit has successfully completed its initialization and self-test.
In case of a relay failure or a failure of the external encoder voltage (switched by the relay), the
operator must ensure that the plant cannot reach a safety-critical state.
Explanation / Solution:
In case of an encoder supply failure the encoder would "rotate", but the unit is incapable to detect
speed or speed differences. In order to detect this error, the operator can use e. g. a control output
of the unit which indicates "standstill" (see Section
7.4.6 ). A master controller has to compare these
two states (plant "rotate" and control output "standstill"). If the two states differ the master
controller has to trigger an error and the plant has to go to a safe state.
Example of an external encoder supply (1 encoder is switched via 1 relay)

An external encoder supply must be done in each case via a relay which is triggered by
the auxiliary voltage of the unit.

The operator must ensure that the plant cannot reach a safety-critical state, in case of
a failure of the relay or a failure of the external encoder voltage (switched by the relay).