A safety relay improves machine safety in a cost-effective manner. Safety relays are simple devices, essentially a relay with positively driven contacts, designed to be used in safety-critical applications. The force-guided contacts in safety relays ensure that when a fault occurs within a safety device, the relay will de-energize and halt the machine operation. http://www.pilz.com
A safety relay has terminals for connection to both the control circuit and to the broken contacts of the safety devices it monitors. When the safety device is enabled, typically by an operator, the relay coil is energized and the NO contacts close, sending a signal to the machine control system that it is safe to start the next operation.
At this point, the safety relay output is in a safe state and can only change when the safety device is turned off or when a fault is detected within the safety circuit. Once the safety relay has detected that a fault has occurred, it will return the system to a safe state by de-energizing the control circuit, and all safety relay contacts will revert to their open state. http://www.pilz.com
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