KL3312 Beckhoff 2-Channel Thermocouple Input Terminal

Product Overview

The KL3312 (KL3312) is a high-precision 2-channel analog input terminal specifically designed for the direct connection of thermocouples in a Beckhoff Bus Terminal system. It utilizes 2-wire technology to process signals from various thermocouple types, including J, K, L, B, E, N, R, S, T, and U. The module features an integrated microprocessor that performs linearization across the entire temperature range and provides internal cold junction compensation, eliminating the need for external compensation hardware. With its "fine granularity" design and built-in open-circuit (wire break) recognition, the KL3312 is an essential component for temperature monitoring in industrial furnaces, plastic injection molding, and thermal processing plants.

Advanced Diagnostics & Flexibility

The Beckhoff KL3312 is engineered for high operational safety. Each channel is equipped with an Error LED that instantly signals a broken wire or open circuit, allowing maintenance teams to identify sensor failures without complex software troubleshooting. Beyond temperature measurement, the module can be configured for low-voltage mV measurement (±30 mV or ±120 mV), making it a versatile tool for various bridge-based sensors. The temperature range and sensor type can be selected freely via the Bus Coupler or controller software, ensuring the terminal can adapt to changing process requirements without hardware swaps.

Technical Specifications

Technical FAQs

How does "Open-Circuit Recognition" improve system reliability?

Thermocouples are prone to mechanical wear and vibration-induced breaks. The KL3312 continuously monitors the circuit's continuity; if a wire snaps, the Error LED lights up and a status bit is sent to the PLC. This prevents the control system from interpreting a failed sensor as a "low temperature" and erroneously increasing heater power.

Can I use the KL3312 for non-thermocouple voltage signals?

Yes. The terminal can be configured for mV measurement mode. This is particularly useful for small signal outputs from specialized laboratory equipment or sensors that output within the ±120 mV range, providing a high-resolution 16-bit data format in the process image.

What cabling is required for the KL3312?

To maintain accuracy, you must use compensation cables or thermocouple extension wires made of the same materials as the thermocouple itself up to the terminal connection. Using standard copper wire will create unintended "parasitic" thermocouples at the connection points, leading to significant temperature measurement errors.

Field Engineering & Installation Guide

• Grounding for Earthed Thermocouples: If using earthed (grounded) thermocouples, ensure the shield is connected to the functional earth. For differential inputs, the common-mode voltage should not exceed ±2 V relative to ground to maintain 12-bit accuracy.

• Cold Junction Accuracy: For the most accurate internal cold junction compensation, avoid placing the KL3312 next to high-heat-generating modules (like power supply terminals or motor starters). A stable ambient temperature at the terminal block is critical for the internal NTC sensor's precision.

• Shielding: Always use the shield terminals provided on the KL3312. Proper shielding is essential to protect the low-microvolt thermocouple signals from the electromagnetic noise typically generated by nearby VFDs or heavy switching gear.

Engineering Advantages

The KL3312 stands out for its integrated intelligence. By handling the complex linearization and compensation algorithms on-board the microprocessor, it frees up the main PLC's CPU cycles for other control tasks. Its compact 12 mm housing allows for high-density temperature monitoring in space-constrained panels. Whether configured for standard Type K monitoring or high-temperature Type S applications, the KL3312 provides a robust, industrial-grade interface that ensures long-term stability and precise thermal control.