AEMC 4620 User Manual

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AEMC 4620 User Manual Manual pdf 36 page image

34 Digital Ground Resistance Tester Model 4620 and 46305.5 Soil Resistivity Measurement Procedure(4-Point)Given a sizeable tract of land in which to determine the optimum soil resis-tivity, some intuition is in order. Assuming that the objective is low resis-tivity, preference should be given to an area containing moist loam asopposed to a dry sandy area. Consideration must also be given to thedepth at which resistivity is required.• Disconnect the shorting link from the X and Xv terminals.• Arrange the electrodes in a straight line. Be sure that distancesbetween electrodes are identical.Example: 10 ft between each electrode for auxiliary ground elec-trodes that will be driven 10 ft deep (See Figure 18).• The distance between poles is proportional to the average depthof the soil sample you wish to make.• The electrodes should be placed at a depth of approximately 6"(0.15m), so that the depth is approximately 1/20th of the distancebetween electrodes.• Use leads to connect the X, Xv, Y, and Z electrodes to the respec-tive terminals on the Digital Ground Resistance Tester.• Press the “Test” button.• Read the resistance level (R) indicated on the display.• In the event of difficulties in performing measurements,consult the previous instructions concerning ground resistancemeasurements.• Apply the following formula in order to determine resistivity (ρ):ρ = 2π x R x AA = distance between electrodes in cmρ = resistivity in ΩcmR = ohms reading obtained on Model 4620/4630Example 1: For measurement performed in soil with a high limestone content, thereading is R = 225Ω, with A = 300cm (3m).ρ = 2π x 225Ω x 300cmρ = 423,900Ωcm