EL3311 by Beckhoff

The EL3311 is a single-channel thermocouple input module produced by Beckhoff within the EL EtherCAT Terminals series. It inserts into an EtherCAT I/O strand and forwards temperature data to a controller in real time. Inside automated systems, the terminal conditions microvolt signals from industrial thermocouples so the PLC can supervise heating, cooling, or safety interlocks.

It provides bus-side isolation of 500 V, shielding the control network from field-level transients and minimizing ground-loop currents in mixed-signal systems. The internal cold-junction sensor maintains an accuracy of ±2.0 °C and has a temperature coefficient below 40 mK/K, so compensation error stays low even when cabinet temperature drifts. The default thermocouple type is K, and input voltages are captured over a ±75 mV range, providing coverage for Types J, T, and other low-level sensors as well. Conversion is handled by a 16-bit sigma-delta converter that oversamples and filters noise before data are reported to the EtherCAT master at a granularity of 4 µV/digit. One input is connected through two-wire terminals, and differential voltage to ground must remain within ±2 V to preserve measurement integrity.

Open-circuit recognition is active, so broken sensor lines are flagged to the PLC without extra wiring and can trigger immediate fault routines. Temperature values are reported with a resolution of 0.1 °C/digit, enabling precise oven or chiller regulation from a supervisory HMI. Field wiring may extend up to 30 m, providing flexibility for distributed probes inside machinery while staying within the supported analog bandwidth. The housing carries an IP20 rating, indicating finger-safe protection for cabinet installation and requiring installation in a suitable enclosure when moisture or dust is present.