The QT4 series can cascade two or three light curtains into L- or U-shaped configurations, effectively preventing mutual light interference between multiple light curtains. It features dual independent redundant outputs that can directly drive safety relays or safety PLCs. Optional interlock and reset functions facilitate both manual and automatic resets. The QT4 series is particularly suitable for complex working conditions or applications requiring flexible protection, particularly those with frequent workpiece movement and continuous production while ensuring personnel safety.