The safety relays in the KFD2-RSH series from Pepperl+Fuchs combine a diagnostic function, line fault transparency and double redundancy in a 1oo3 architecture (one out of three). The function of the switching contacts is automatically checked during each switching operation. Monitoring of the entire signal circuit for line faults without additional wiring is ensured by the line fault transparency. The relays are immune to test pulses and are therefore compatible with digital output cards of all commercially available control systems. The core of the modules is the 1oo3 architecture with the double redundant design of the switching contacts. Three contacts are arranged in series for DTS (de-energized-to-safe) applications and two groups of three parallel contacts each for ETS (energized-to-safe) signal circuits. Even if up to two contacts in a group fail, the safety function is still guaranteed. The modules' integrated diagnostic function moves the three contacts one after the other with a time delay for each switching operation. In ETS applications, all three relays of the two contact groups are closed once first in the event of three consecutive switching events. During the delay time, the device checks whether this contact closes the circuit. Faulty contacts are detected. The diagnosis of the DTS device takes place during the reclosing process: First, two relay contacts are closed simultaneously, then the third contact is also closed with a time delay. No current must flow before the third contact closes, otherwise this relay is defective as it no longer disconnects the circuit. A different relay is tested with each switching cycle. After switching three times, the relay module is fully tested once without any additional effort.