Patent ID: 6407539
Filing Date: 2002-06-18
Classification: G01R

Abstract:
An apparatus for the determination of the degree of lightning protection of a structure having metallic structural elements by determining an electromagnetic field transfer function for each test location selected from among metallic conductors, such as lightning rods, located in the proximity of the top of said structure, which apparatus comprises:a) a signal generation instrumentation subsystem which is operatively connected to each said test location in succession and the earth surrounding said structure, which signal generation instrumentation subsystem is capable of injecting a low-level test current at a plurality of specific test frequencies into a selected test location; b) a receiver instrumentation subsystem comprising: i) an internal component intended to be disposed within said structure to measure the electric field created by the injection of said low-level test current into said selected test location and comprising: A) an electric field antenna which is disposed within said structure to measure the electromagnetic field at the position where said antenna is disposed; B) a fiber optic transmitter operatively connected to said antenna and capable of converting the electromagnetic field measurement of said antenna into an optical signal; and, C) an optical fiber cable operatively connected to said fiber optic transmitter and capable of conducting said optical signal; ii) an external component intended to be disposed outside said structure to analyze the electric field created by the injection of said low-level test current into said test location and comprising: A) an fiber optic receiver operatively connected to said optical fiber cable and capable of converting said optical signal to an electrical signal; B) a frequency spectrum analyzer operatively connected to said fiber optic receiver and capable of converting said electrical signal to an electric field value in volts RMS (root-mean-square) per meter; and, c) a computing device operatively connected to said signal generation instrumentation subsystem and said receiver instrumentation subsystem and capable of matching the data received from said receiver instrumentation subsystem with the low-level test current injected at each test location by said signal generation instrumentation subsystem, and analyzing such data to provide an overall assessment of the ability of said structure to adequately dissipate the energy of a lightning strike in order to determine a safe stand-off distance for critical assets or personnel within the structure.