An Optical Time Domain Reflectometer (OTDR) sends light pulses through a fibre optic cable. These pulses travel down the fibre and reflect when they encounter inconsistencies, like breaks, splices, or bends. Here's a guide to identifying the location of a break in a fiber optic cable, including the tools and techniques needed for accurate diagnosis. For some. These length testers use a “round-robin” method of measuring fiber length. The round trip time that the light takes to travel through both fibers is converted to length in kilometers, then divided by two. Measure up to 4,921 feet (1,500 metres) of fiber in seconds Quick set-up. No lengthy set-up necessary Find problems quickly. Six-second test time—no more blind troubleshooting that can waste hours Visible in dark areas.