KL3312 by Beckhoff

The KL3312 is an analog input module manufactured by Beckhoff and supplied through the KL Analog Input Modules series. This terminal is intended for industrial automation systems where precise temperature readings from thermocouples must be digitized and forwarded to a controller through the K-bus backplane. Built-in cold-junction compensation allows the device to support distributed temperature acquisition without requiring external reference sensors. The module is suitable for monitoring thermal processes in machines, production equipment, and cabinet-based control systems.

The module accepts two separate thermocouple channels that use a 2-wire connection, minimizing field cabling and allowing the conductors to terminate directly at the terminal. The K-bus process image has a width of 2 × 16 bits plus two optional 8-bit values, allowing high-resolution process data and optional status information to be transferred to the PLC. Temperature values are converted at a resolution of 0.1 °C per digit, enabling the controller to detect small changes in measured temperature. The electronics receive operating power via the K-bus, so no separate supply connection is required for the terminal. Open-circuit detection identifies interrupted sensor lines, while the millivolt measurement capability allows the controller to read raw thermocouple voltages when needed.

The housing mounts on a 35 mm DIN rail compliant with EN 60715, allowing the terminal to be installed alongside other modular I/O components. Its IP20 enclosure rating makes it suitable for protected installation inside a control cabinet. Internal temperature data are formatted as 0.1 °C values in two's complement notation, allowing signed measurements to be processed directly by the controller. A watchdog interval of 100 ms monitors K-bus communication and reports an error if controller updates stop within the allotted period. Internal temperature measurement provides the cold-junction reference used to compensate for the temperature at the thermocouple connection point. This compensation improves measurement accuracy by accounting for voltage changes introduced where the thermocouple conductors connect to the terminal.