EL3702 by Beckhoff

The EL3702 is an analog input terminal from Beckhoff that belongs to the EL EtherCAT Terminals series. Installed beside other I/O nodes on an EtherCAT backplane, it converts field-level voltages into digital words that the PLC can process in real time. The module is intended for instrumentation, data logging, and motion-control applications that demand deterministic signal acquisition without requiring separate, standalone measurement hardware.

Two differential input channels accept a bipolar voltage range of ±10 V and feed a converter with 16-bit resolution. The sampling hardware operates in a simultaneous sampling mode, so both channels are captured at the same moment, and the per-channel throughput reaches 100 ksamples/s. When an EtherCAT master enables Distributed Clocks, the terminal timestamps each sample for microsecond-level correlation with drives and other sensors. Power for the electronics is drawn from the E-bus, and the differential ground reference helps minimize common-mode errors. The terminal transfers data to the controller through a process image formed by n × 2 × 16-bit raw values, two 16-bit status words, and four additional bytes for diagnostic information and control flags.

The terminal mounts on a 35 mm DIN rail inside a protected control cabinet and has an enclosure rating of IP20. Integrated oversampling supports a factor of 100, allowing the device to acquire fast transient events internally and forward a block of measured values aligned with the fieldbus cycle. Time alignment between modules is further refined by a Distributed Clocks precision of < 100 ns, supporting phase-accurate measurements across distributed I/O nodes. The two differential channels acquire their signals concurrently rather than sequentially, which prevents channel-to-channel timing offsets during rapidly changing measurements. This timing behavior is useful when comparing related signals such as paired sensor outputs, synchronized motion data, or voltage waveforms captured at the same instant.