EL1722 by Beckhoff

The EL1722 is a digital AC input terminal manufactured by Beckhoff for the EL EtherCAT Terminals series. This module captures two line-voltage signals and presents their states to an EtherCAT master, allowing plant controllers to monitor limit switches, pushbuttons, or status contacts without external level conversion. Mounted beside other terminals on a DIN rail, it adds field-sensing capability to distributed I/O stations in industrial automation.

The nominal input voltage range is 120/230 V AC, so the terminal can accept either common single-phase supply level without hardware changes. It provides 2 independent digital input channels and uses two-wire connection technology, simplifying field wiring because the neutral conductor is internally referenced. The EtherCAT backplane supplies 55 mA of E-bus current to power the internal electronics. Each input passes through a hardware filter that adds a 10 ms debounce interval, helping the terminal register mechanical contact changes accurately when the contacts bounce. The terminal has no power contacts and does not support distributed clocks, so it is intended for logic acquisition rather than time-critical synchronization. Its enclosure protection rating is IP20, which protects against contact with hazardous internal parts by fingers or similarly sized objects. The unit is intended for installation inside a suitable control cabinet.

The sensing section draws only 6 mA per channel, which reduces the load on field devices such as proximity sensors or switch loops. The maximum permissible voltage between channels is 230 V AC, helping prevent cross-coupling when different phases are present. The housing snaps onto a 35 mm mounting rail and supports operation at altitudes up to 2000 m. Its surge capability corresponds to overvoltage category II, making it suitable for building subcircuits located downstream of the main distribution board. Switching events pass through the input filter before their states are transmitted to the controller, while the channel arrangement keeps mains conductors separated from the EtherCAT backplane to minimize conducted noise.