AEMC 4620 User Manual

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AEMC 4620 User Manual Manual pdf 35 page image

Digital Ground Resistance Tester Model 4620 and 4630 333. Soil resistivity directly affects the design of a grounding system, andit is to that task that this discussion is directed. When designing anextensive grounding system, it is advisable to locate the area of lowestsoil resistivity in order to achieve the most economical groundinginstallation.5.4.2 Types of Resistivity MeasurementsThere are two types of resistivity measurements:• 2-Point methodThe 2-Point method is simply the resistance measured betweentwo points.• 4-Point methodFor most applications, the most accurate method is the 4-Pointmethod, which is used by the AEMC® Instruments Model 4620and 4630 Ground Testers. The 4-Point method, as the nameimplies, requires the insertion of four equally spaced, in-line elec-trodes into the test area. A known current from a constant currentgenerator is passed between the outermost electrodes (X and Z).The potential drop (a function of the resistance) is then measuredacross the two innermost electrodes (Xv and Y). The Models 4620and 4630 are calibrated to read directly in ohms.b< A20 A A AZ electrodeY electrodeXv electrodeX electrodeΩFigure 18