44 www.megger.comThe other challenges faced in testing large ground systems relate to the capabilities of the test instrument. Improved technology has made it possible for instruments to be designed that address problems created by the characteristics and conditions found in and around large ground systems.For the Slope Method to provide meaningful results, accurate measurement of the variations at different points is critical. Since large ground systems typically have resistance values of less than 0.5 Ω, the differences can be quite small. An instrument with 1 mΩ measurement resolution can indicate the small differences between low readings. Noise is a major problem in testing large ground systems, and must be addressed to ensure accurate results. To be effective, the test instrument must be designed to overcome the effects of significant noise in the test environment. Among the technical capabilities that can help offset the noise problem are:n A variable test frequency (rather than a single, fixed test frequency) which can help remove any stray noise that could affect the reading.n A high peak-to-peak interference suppression level.n A sophisticated filter system to reject more noise.n Various current settings to improve the signal-to-noise ratio when necessary.
