hey guys i have a safety relay f121 and in the datasheet under the subtitle "characteristics" It said that it has the feature of "Crossfault monitoring", what this phrase means, exactly?
A 'Safety Relay' (sometimes called an Emergency Stop module) is an assembly of 'Positively Guided Relays'.
These have the moving contacts locked together in a rigid frame, so if one contact welds or jams and cannot move, none of the other contacts can change over.
The typical arrangement has one or two latching relay circuits which are in line with the chain (or twin parallel chains) of emergency stop switch contacts.
The 'turn on' circuit for these is also fed through a separate 'reset enable' relay in the module. The coil of this extra relay is in turn fed via normally closed contacts on the latching relay(s).
The overall function is that the latching relays must be in the off state before the power-on circuit is enabled.
If any relay jams, the power-on circuit is not enabled. This is the fault monitoring function.
The outputs from the overall 'safety relay' module are a series chain of normally open contacts on the latching relay plus normally closed on the reset enable relay.
This ensures the reset relay cannot stick in and override the safe turn-on feature.
