EL3121 BECKHOFF 1-Channel Analog Input 4-20mA EtherCAT Terminal

Product Overview

The EL3121 (EL 3121) is a high-precision 1-channel analog input terminal designed for the acquisition of 4 to 20 mA signals via a differential input architecture. With an exceptional 16-bit resolution and support for Distributed Clocks (DC), this EtherCAT Terminal provides synchronized, high-speed data sampling with a conversion time of approximately 40 microseconds. In demanding industrial sectors such as precision chemical dosing, oil and gas processing, and high-speed motion feedback, the EL3121 is a critical component for monitoring process variables. Its differential technology and 500 V electrical isolation ensure superior common-mode rejection and signal integrity, shielding sensitive control logic from the electrical noise typical of long-distance sensor runs in factory environments.

Technical Configuration

The EL3121 is engineered for rapid signal processing and advanced diagnostics. The differential input design allows for the measurement of current signals with a common-mode voltage of up to 10 V, while the internal resistance is kept low at typically 85 Ohms (plus diode voltage). The hardware features an input filter limit frequency of 5 kHz, which can be further refined through activatable FIR (Finite Impulse Response) or IIR (Infinite Impulse Response) digital filters. It supports both standard and compact process images and includes integrated limit value monitoring to trigger alarms within the EtherCAT cycle. The module is fully compatible with the 100 Mbit/s EtherCAT E-bus and is housed in a compact 12 mm polycarbonate terminal casing, requiring no manual hardware address configuration.

Technical Specifications

Technical FAQs

How does the "Distributed Clocks" feature benefit the EL3121?

Distributed Clocks allow the EL3121 to sample the analog signal at a precise, synchronized moment across the entire EtherCAT network. This is vital for applications requiring time-stamped data or precise coordination between multiple input channels and motion axes.

Can the EL3121 handle signal spikes from the field?

Yes, the module is designed with a surge voltage resistance of up to 35 V. Furthermore, the high-speed conversion and internal limit value monitoring allow the controller to react almost instantaneously to over-current or surge conditions reported in the process data.

What is the advantage of a differential input over a single-ended input for 4-20 mA?

The differential input of the EL3121 measures the voltage drop across an internal shunt between two signal leads, rather than against a common ground. This effectively cancels out common-mode noise and ground potential differences that can otherwise distort current measurements over long cable lengths.

Engineering & Installation Guide

Wiring and Shielding for 16-bit Precision:

To maintain the integrity of 16-bit data, use shielded twisted-pair (STP) cables. The shield should be connected to the functional earth (FE) at the cabinet entry using a low-impedance terminal. For the EL3121, the positive and negative signal leads must be connected to the differential input terminals. Ensure a stripping length of 8–9 mm to ensure the spring-actuated contact is secure.

Digital Filter Configuration:

For high-frequency applications, use the default 5 kHz filter. However, if your signal is prone to low-frequency electrical noise, activate the FIR or IIR filters via the CoE (CanOverEtherCAT) settings in TwinCAT. The FIR filter is particularly effective for suppressing 50/60 Hz mains interference, though it may slightly increase the effective response time compared to the 40-microsecond raw conversion.

ATEX Compliance in Hazardous Zones:

The EL3121 is certified for Zone 2 hazardous areas. For such installations, ensure the terminal is mounted in an enclosure that provides at least IP54 protection. Do not disconnect the terminal or field wiring while the E-bus is powered, as arcing could pose an ignition risk in explosive atmospheres. Regularly check the double slot and key connection between side-by-side modules to ensure a vibration-resistant mechanical bond.