Reliable Detection of Single Wire Breaks in a Balanced Transmission Line System
Original Publication Date: 1981-Oct-01
Included in the Prior Art Database: 2005-Feb-12
When only one wire in a long, shielded, twisted pair cable breaks, the capacitive coupling between the broken wire and the shield may permit enough signal strength to pass to permit receiving of a signal at the receiver albeit unreliably. In order to reliably detect the broken wire, the center taps of the coupling transformers T1 and T2 at the ends of the twisted pair cable are connected to signal ground. At the receiver end, a transformer T3 is interposed in the ground connection. Under normal operations, the currents I1 and I2 in the wires of the twisted pair are equal and no center tap current flows. If one of the wires breaks, center tap current will flow from the shield to the center tap. This unbalanced current is detected by a band-pass amplifier 11 tuned to the data rate.