Patent ID: 6985344

Claim:
A Short and Overload Isolator (SOI) device, having an input and an output, for detecting and isolating shorted or overloaded sections of a two wire polling loop, comprising: a. a bi-directional switch connecting the SOI device input to the SOI device output, wherein as polling loop power is initially applied to the SOI device input, the switch is maintained OFF for a time while the SOI device output is electronically tested for a possible complete or resistive short, and if a short is detected, the switch is maintained OFF, establishing a disconnected polling loop branch until the short is removed; b. a uni-directional drive circuit which, if a short is not detected, is applied to the SOI device output to test for possible overloads or device powered-on shorts, wherein the uni-directional drive circuit avoids possible powered-on shorts on the SOI device output from temporarily appearing on the SOI device input, and if an overload or powered-on short is detected, operation of the drive circuit is terminated and the switch is maintained OFF, establishing a disconnected polling loop branch until the short is removed, and if an overload or powered-on short is not detected, the switch is turned ON, establishing bi-directional connection from the SOI device input to the SOI device output and normal polling loop signaling operation.