Figure 4-2 Two-channel sensor connection
* = positively-driven auxiliary contacts/mirror contacts
4.3.2 Cross-circuit detection
Cross-circuit detection is a diagnostic function of a safety relay that detects short-circuits and
cross-circuits between the input channels (sensor circuits) during two-channel sensing or
reading. A cross-circuit can be caused, for example, by a cable casing being squashed. In devices
without cross-circuit detection, this can mean that a two-channel EMERGENCY STOP circuit does
not trip even though only one NC contact is faulty (secondary error).
With 3SK1 devices, a cross-circuit is detected in the sensor circuits by means of signals with
dierent clock pulses. If the clocked signals overlap, the device detects a cross-circuit. With 3SK1
basic units, cross-circuit detection can be deactivated to allow electronic sensors to be evaluated
(that monitor themselves as well as the cable to the evaluation unit).
4.3.3 Enabling circuit (safety-related output)
An enabling circuit provides a safety-related output signal. From an external viewpoint, enabling
circuits usually act as NO contacts (however, in terms of functionality, safety-oriented opening
is always the most important aspect).
An individual enabling circuit that is redundantly congured internally in the safety relay can be
used for SIL 3 / PL e.
Note: Enabling current paths can also be used for signaling purposes.
3SK1 safety relays are only equipped with enabling circuits with NO functionality. This means
that when the safety function is triggered, or a fault is detected, the enabling circuits will always
transfer to the safe state (NO contact open).
4.3.4 Signaling circuit
A current signaling path provides a safety-related output signal.
With 3SK1 relays, the signaling circuits are always implemented as NC circuits. This means that
when the safety function is triggered, or a fault is detected, the signaling circuits will close.
Safety systems - General information
4.3 Basic terminology
SIRIUS 3SK1 Safety Relays and 3RQ1 Positively-Driven Coupling Relays
44 Equipment Manual, 05/2021, A5E02526190021A/RS-AE/005
To Next Page
Loading...
Need help?
General