These device combinations led to the development of the first safety relay from the German automation manufacturer Pilz, the PNOZ.
Time Delay Safety Relays[6] allow for a controlled sequence of operations before activating or deactivating outputs.
[8] A normal relay uses a wire coil and the mechanical movement of the metal contacts to switch the load on and off.
For this reason, many European, American, national and international norms and safety standards prohibit the use of simple relays or contactors on hazardous machines.
[9] The typical design of a first-generation safety relay is based on the classic three-contactor combination.
The redundant design ensures that wiring errors do not lead to the loss of the safety function.