BECKHOFF EL3208 8-Channel RTD Input Terminal 16-Bit Pt100/Ni1000

Product Overview

The EL3208 (EL3208) is a high-density (HD) 8-channel analog input terminal designed for precise temperature measurement within the EtherCAT I/O system. Engineered for multi-zone thermal monitoring in industrial furnaces, plastic injection molding machines, and HVAC plant engineering, the EL3208 supports a wide range of Resistance Temperature Detectors (RTD), including Pt100, Pt1000, and Ni1000 sensors. By integrating 8 measurement channels into a single 12 mm housing, it provides an exceptionally high I/O density, significantly reducing the required space on the DIN rail. The 16-bit resolution ensures a temperature granularity of 0.1 Celsius per digit, allowing for the stable and accurate thermal control necessary for sensitive chemical or manufacturing processes.

Technical Configuration

The hardware architecture of the EL3208 utilizes 2-wire connection technology for all 8 channels, optimized for space-saving installations where sensor leads are relatively short or lead-wire resistance can be compensated via software. The terminal features an integrated digital filter that can be configured through the TwinCAT System Manager to adjust conversion times between 3 ms and 1600 ms, allowing engineers to balance between high-speed response and superior noise suppression. For added system safety, the EL3208 includes limit value monitoring and sensor breakdown/short-circuit detection. The module is powered entirely via the E-bus, drawing a typical 140 mA, and provides 500 V electrical isolation to protect the internal EtherCAT communication from field-side interference.

Technical Specifications

Technical FAQs

How do I compensate for lead-wire resistance with a 2-wire connection?

Since the EL3208 uses a 2-wire method, the resistance of the connection cable adds to the sensor's value. You can compensate for this in the TwinCAT software by measuring the cable resistance and entering an offset value in the terminal's CoE (CanOpen over EtherCAT) settings to maintain accuracy.

Can the EL3208 measure standard resistors or potentiometers?

Yes. In addition to temperature sensors, the terminal can be configured for pure resistance measurement within the range of 10 Ohm to 4 kOhm. This makes it versatile for monitoring potentiometer positions or other resistive transducers.

What happens if a sensor wire breaks?

The EL3208 detects open circuits. When a wire break is detected, the status bit for the affected channel is set in the process image, and the value typically moves to the maximum limit (e.g., 0x7FFF), allowing the PLC logic to trigger a safety shutdown or alarm.

Engineering & Installation Guide

• Wiring for High Density: The EL3208 uses a High-Density (HD) housing. Due to the tight terminal spacing, it is mandatory to use ferrules for stranded wires (0.14 to 0.75 mm²) to ensure individual strands do not bridge across adjacent channels. Use a calibrated stripping tool to maintain a precise 8–9 mm stripping length.

• EMI and Signal Integrity: Even with 16-bit filtering, RTD signals are millivolt-level and susceptible to noise. Always use shielded cabling for sensor leads, and ground the shield at the entry to the control cabinet. Avoid routing sensor cables in the same duct as high-power AC motor leads or VFD output cables.

• Filter Configuration: For applications with slow temperature shifts (like large vats or ambient air), increase the conversion time to 1600 ms. This enhances the 50/60 Hz noise rejection and provides a much smoother signal for your PID control loops.

• Thermal Considerations: When mounting multiple EL3208 terminals side-by-side, ensure the cabinet ambient temperature does not exceed 60 Celsius. While the module is low-power, the density of 8 channels means adequate vertical airflow is required for long-term drift stability.