ELX5151 by Beckhoff

The ELX5151 is a single-channel digital input terminal produced by Beckhoff within the EL EtherCAT Terminals series. Installed on a DIN rail alongside other I/O modules, it forwards the state of one field sensor to the EtherCAT process image, allowing PLCs to react to fast edges or count pulses from proximity switches or rotary encoders. The terminal provides an intrinsically safe, bus-coupled interface that eliminates the need for separate barrier modules while maintaining precise timing through its compact and standard PDO mappings.

The module handles signal bursts up to 50 kHz, so high-speed transducers can be connected without missing events. A rising edge is recognized once the loop current reaches at least 2.1 mA, and the signal is considered low when the current falls to 1.2 mA or less. The fixed 0.2 mA switching hysteresis suppresses contact bounce. Internal timestamping lets the controller poll the captured value with 100 ns accuracy, supporting deterministic motion or counting tasks. The terminal transfers data in two formats: a 10-byte compact PDO that minimizes bus load and a 16-byte standard PDO that exposes extended diagnostic flags. One logical channel is present, and the interpolation engine offers 8-bit resolution when finer time-domain reconstruction is required.

Wire integrity is supervised, and a cable-break alarm is generated when the current drops to 200 µA or less. A short circuit is detected when the line current exceeds 6.0 mA, while the intrinsically safe short-circuit current is limited to 12.4 mA. For sensor excitation, the terminal delivers an intrinsically safe 8.2 VDC supply. Under open-circuit conditions, the voltage rises to 10.72 V, but the output power is limited to 33 mW to meet Ex ia requirements. The intrinsically safe circuit limits thermal and spark energy so the channel can connect to suitable field devices in hazardous areas.