EDM stands for "External Device Monitoring"

The role of EDM in Safety Systems

The External Device Monitoring (EDM) function is a crucial feature in modern safety relays. It monitors the feedback circuit of externally connected contactors with positively driven contacts. The signal at the EDM input is compared with the status of the safety outputs. When the safety output is active, the feedback circuit is open. When the safety output is inactive, 24V is present at the EDM input.

The normally closed contact spring of the contactors with positively driven contacts ensures that the contactors return to their safe state before being reactivated. If a safety relay with a manual reset function is used, the reset button is wired in series with the feedback loop contacts.

Figure 1: Safety sensor has shut down, Contactor are switched off, motor is off, 24 V is available at the EDM input

Figure 2: Safety sensor is switched on, Contactors are switched on, motor running, no voltage present at the EDM input

EDM Function of the RFID Safety Sensor SAFIX 3

SAFIX 3 safety sensor and the HOLDX R smart process guard locking

The SAFIX 3 safety sensor and the HOLDX R smart process guard locking not only integrate advanced RFID technology, but also include the full functionality of a safety relay with EDM function.
The SAFIX 3 / HOLDX R can be ordered with either a manual or automatic reset function. Downstream contactor devices with a current consumption of up to 500 mA can be connected to the safe OSSD outputs of the sensor. The EDM input monitors externally connected contactors with positively driven contacts.

Figure 3: EDM function with automatic reset button

Figure 4: EDM function with manual reset button

Products

Safety Sensor SAFIX

Process Guard Lock with RFID - HOLDX R