KL1808 by Beckhoff

The KL1808 is a digital input terminal produced by Beckhoff within the KL Digital Input Terminals series. It collects field-level signals and places them in the control system's process image, allowing PLC programs to monitor device states without routing individual signal wires back to the CPU. Eight input channels are available, so one terminal can receive signals from several sensors while communicating through the internal Bus Coupler backplane. The unit supports spring-actuated direct plug-in connections, which simplify wiring and maintain secure contact under the vibration commonly found in industrial control cabinets.

Each channel is designed for a nominal sensing voltage of 24 VDC, and the module draws an input current of only 3 mA per channel. This low current requirement allows proximity sensors and limit switches to operate without placing a heavy load on the upstream power supply. Signal chatter is suppressed by a 3.0 ms input filter that blocks brief transients while preserving normal machine response times. Compliance with EN 61131-2 Type 1/3 ensures that the on-state and off-state thresholds align with standard control voltages. Field wiring uses a two-wire connection scheme, allowing each sensor's signal and common conductors to connect directly to the terminal.

Panel space is conserved because the terminal has a housing width of only 12 mm, supporting high channel density on a DIN rail. Its overall dimensions are 15 × 100 × 70 mm, which provide a compact enclosure for the input electronics and connection points. The internal K-bus draws 15 mA, allowing multiple terminals to share a Bus Coupler without quickly reaching its available power limit. An IP20 protection rating makes the KL1808 suitable for installation inside a protected control enclosure. Sixteen push-in connection points accommodate solid, stranded, or ferruled conductors while providing vibration-resistant terminations for field wiring.