Beckhoff EL1918 Safety Input Terminal EtherCAT
The Beckhoff EL1918 is a TwinSAFE digital input terminal for the EtherCAT system. It provides 8 fail‑safe input channels that can be used to connect emergency stop buttons, safety gates, light curtains, and two‑hand controls. The terminal achieves SIL 3 (IEC 61508) and PL e (ISO 13849-1) safety integrity. It is part of the Beckhoff EL series and communicates via the TwinSAFE protocol (FSoE).
Input Specifications
Number of channels: 8 (fail‑safe).
Input voltage: 24V DC (20.4–28.8V).
Input current: 3 mA typical.
Input type: Type 3 (IEC 61131-2), sink/source.
Response time: < 10 ms (configurable filter).
Each channel has two internal redundant signal paths with cross‑circuit detection. Inputs support dual‑channel (redundant) connection with discrepancy time monitoring (0–500 ms).
Safety Features
Cross‑circuit detection between channels.
Open‑circuit detection (wire break).
Short‑circuit to 24V or 0V detection.
External test pulse tolerance up to 1 ms.
Configurable input filter (0.2–20 ms).
EtherCAT and TwinSAFE
The EL1918 communicates via the EtherCAT bus (E‑bus) at 100 Mbit/s. It uses the TwinSAFE protocol (FSoE) for failsafe data exchange. The terminal supports distributed clocks (DC) for synchronized input sampling. Up to 128 TwinSAFE devices can be connected in a network.
Diagnostics and LEDs
LEDs: RUN (green, EtherCAT state), ERR (red, communication error), SAFE (green, safety logic OK), and per‑channel input LED (green). The terminal stores diagnostic events (1000 entries) with time stamps. Diagnostic messages include wire break, cross‑circuit, and discrepancy errors.
Power and Isolation
The terminal draws 100 mA from the E‑bus (5V) and requires an external 24V DC for the inputs (via power contacts). Isolation: 1500 Vrms between input side and E‑bus. Protection against reverse polarity and transients.
Environmental and Mechanical
Dimensions: 100 mm height x 24 mm width x 68 mm depth (typical Beckhoff terminal housing). Weight: 80 g. Mounting: DIN rail (35 mm). Operating temperature: -25°C to +60°C; storage: -40°C to +85°C. Humidity: 5% to 95% non-condensing. Protection class: IP20. Vibration: 5 g (10–150 Hz).
Configuration and Software
Configuration is done with TwinCAT 3 (Build 4024 or later) and the TwinSAFE Editor. The terminal’s safety parameters (filter time, discrepancy time) are set in the F‑CPU project. The EL1918 does not contain a logic engine; it sends input data to a TwinSAFE logic terminal (e.g., EL6910) for processing.
Certifications
SIL 3 (IEC 61508), PL e (ISO 13849-1), TÜV certified. Also meets EN 62061 and EN 61800-5-2.
Typical Applications
Connecting multiple emergency stops, guard door switches, and light curtains to a safety PLC. The 8‑channel density saves space in safety networks for packaging machines, robots, and conveyor systems.
Ordering and Documentation
Beckhoff order number: EL1918. The terminal is supplied with a label sheet and an end cap (EL9011). Manual: TwinSAFE EL1918 Documentation (TB8200).
