KL3311 by Beckhoff

The KL3311 is a thermocouple input terminal produced by Beckhoff for the KL Analog Input Modules series. It serves as a temperature acquisition point within decentralized control systems, delivering digitized measurement data to a PLC through the internal K-bus of a terminal stack. By translating sensor voltages into engineering units, the module supports precise thermal regulation tasks in process equipment, packaging lines, and building automation panels.

This terminal accepts a single sensor channel, and the field wiring uses a 2-wire connection that minimizes the terminal count while maintaining adequate lead compensation for most installations. Converted values are transferred to the controller across a data field of 1 × 16 bits, providing adequate numerical range for high-resolution temperature calculations. The basic conversion step is 0.1 °C per digit, so the smallest incremental change recorded by the module equals one-tenth of a degree Celsius. Under calibrated conditions, total system uncertainty remains within ±0.5% FS, allowing integration into applications that require limited error margins. Electrical and mechanical attachment is achieved with a 35 mm DIN rail, allowing the terminal to be mounted next to power supplies, bus couplers, and other I/O modules without additional brackets. The design includes open-circuit detection, so disconnected thermocouples are identified immediately. An optional 1 × 8-bit status byte can be inserted into the process image for diagnostic information.

Protection against incidental contact is rated at IP20, making the terminal suitable for installation inside standard control cabinets. Cold-junction compensation is handled by an onboard sensor through internal temperature measurement, which provides the reference needed for accurate thermocouple readings. Watchdog supervision defaults to 100 ms; if the bus cycle exceeds this period, the module places its process data into a safe state. The installation position is variable, providing flexibility when arranging terminal stacks in compact enclosures. The electronics receive their power via the K-bus, eliminating the need for a separate power feed. The single input channel and optional status information conserve terminal-stack space when an application requires only one thermocouple measurement point.