EL3312 by Beckhoff

The EL3312 is a temperature-measurement input terminal from Beckhoff that belongs to the EL EtherCAT Terminals series. It accepts thermocouple signals and digitizes them so that an EtherCAT controller can monitor process temperatures without separate wiring hubs or analog cards. By occupying a single slice on a DIN rail, the unit streamlines distributed data acquisition in industrial automation cells where compact signal conditioning and networked I/O are required.

This terminal provides 2 channels, allowing two thermocouples to be connected through 2-wire connection technology that simplifies field cabling. Conversion is performed with an internal resolution of 16-bit, providing sufficient granularity for precise control loops. A 500 V bus isolation barrier separates the sensor side from the system backplane, protecting the controller from ground shifts. The EtherCAT backplane has a current draw of only 200 mA, an important figure when planning total station current. Installation follows the 35 mm mounting rail standard, and plug-in wiring can be routed up to 30 m without repeaters. A built-in mechanism detects broken leads so that the controller can recognize open circuits immediately. The housing has an IP20 rating, making it suitable for enclosed control cabinets.

The integrated cold-junction sensor has an accuracy of ±2.0 °C, and its 40 mK/K temperature coefficient keeps reference error low across ambient temperature changes. An analog input filter with a 1 kHz cutoff attenuates high-frequency noise before conversion. Once the data are processed, the EtherCAT process image delivers 16 bytes of input to the PLC while sending 8 bytes in the other direction for configuration and diagnostics. Temperature values are reported with a display increment of 0.1 °C/digit, allowing small changes to be represented clearly. The combination of cold-junction compensation, input filtering, and broken-wire detection supports stable thermocouple monitoring under changing operating conditions.