EL2904 BECKHOFF TwinSAFE 4-Channel Safety Digital Output Terminal

Product Overview

The EL2904 (EL 2904) is a high-integrity safety digital output terminal designed for the TwinSAFE system, enabling the secure execution of safety functions within an EtherCAT network. This 4-channel module provides 24 VDC at 0.5 A per channel and is engineered to meet the most stringent global safety standards, including SIL 3 and PL e. In high-risk industrial environments such as robotic work cells, heavy-duty pressing, and automated logistics, the EL2904 is the primary component for switching off safety-relevant actuators like contactors, signal lamps, or motor starters. By utilizing the Safety over EtherCAT (FSoE) protocol, it ensures reliable communication and rapid fault response, directly protecting personnel and machinery from operational hazards.

Technical Configuration

The EL2904 architecture is built on the TwinSAFE protocol, which allows for the integration of safety-related signals into a standard EtherCAT terminal segment. It supports both 1-wire and 2-wire connection technologies, offering flexibility in wiring actuators. The module features integrated active current measurement, requiring a minimum load of 20 mA to ensure precise monitoring of the output state. One of its core technical advantages is the parameterizable watchdog time, which dictates the fault response time in the event of a communication interruption. The hardware is housed in a 24 mm polycarbonate casing and includes ATEX marking (II 3 G Ex nA IIC T4 Gc), permitting installation in Zone 2 hazardous areas when properly enclosed.

Technical Specifications

Technical FAQs

Can the EL2904 be used without a TwinSAFE Logic terminal?

No, the EL2904 is a safety slave device. It must be paired with a TwinSAFE Logic terminal (such as the EL6900, EL6910, or a TwinSAFE-capable controller) which executes the safety logic and manages the FSoE communication cycle.

What happens if the load on a channel is less than 20 mA?

The EL2904 performs active current measurement for diagnostic purposes. If the connected load is below 20 mA, the module may report a "Broken Wire" or load error because the current is too low for the internal sensors to verify the output state accurately.

How does the "Watchdog Time" parameter affect machine safety?

The watchdog time defines the maximum period the terminal will wait for a valid safety telegram before entering a "Safe State" (outputs deactivated). This must be calculated based on your total system reaction time requirements to ensure the machine reaches a stop before a hazard occurs.

Engineering & Installation Guide

TwinSAFE Address Configuration:

Every EL2904 must have a unique TwinSAFE address assigned via the DIP switches located on the side of the terminal or through TwinCAT software (depending on the hardware revision). Ensure this address matches the configuration in your TwinCAT Safety project. Failure to match these addresses will prevent the FSoE connection from establishing, resulting in a safety "Com Error."

Wiring for Safety Integrity:

For applications requiring SIL 3 or PL e, ensure that the wiring is protected against external cross-circuits. When using 2-wire technology, both the output and the corresponding 0V return should be managed to ensure the diagnostic tests (light tests) can accurately detect short circuits to the 24V supply or ground. Use the recommended stripping length of 8–9 mm for all connections to ensure a gas-tight fit in the spring-loaded terminals.

Mounting and Heat Dissipation:

The EL2904 is designed for horizontal installation on a 35 mm DIN rail. Given its higher current consumption (221 mA from the E-bus), ensure the power supply terminal (e.g., EK1100 or EK1200) can provide sufficient current for the entire segment. If the total E-bus current exceeds 2A, a power feed terminal must be inserted to prevent communication drops or overheating of the bus contacts.