Amprobe DMIII-Multitest Power-Quality-Recorder Uživatelský manuál stáhnout pdf (Strana 92)

AMPROBE

DMIII MULTITEST

EN-90

The measuring method allows the operator to

define the specific resistance up to the depth

corresponding approximately to the distance

“a” between the rods. If you increase the

distance “a” you can reach deeper ground

layers and check the ground homogeneity.

After several  measurements, at growing

distances “a”, you can trace a profile like the

following ones, after which the most suitable

rod is chosen:

Curve1: as  decreases only in depth, it’s

possible to use only a rod in depth.

Curve2: as  decreases only until the depth

A, it’s not useful to increase the depth of the

rod beyond A.

Curve3: even at an increased depth,  does

not decrease, therefore a ring rod must be

used.

APPROXIMATE EVALUATION OF THE CONTRIBUTION OF INTENTIONAL RODS (64-

12 2.4.1)

The resistance of a rod Rd can be calculated with the following formulas ( = medium

resistivity of the ground).

a) Resistance of a vertical rod

Rd =  / L

L= length of the element touching the ground

b) Resistance of an horizontal rod

Rd = 2 / L

L= length of the element touching the ground

c) Resistance of linked elements

The resistance of a complex system with more elements in parallel is always higher

than the resistance that could result from a simple calculation of elements in parallel,

especially if those elements are close and therefore interactive. For this reason, in

case of a linked system the following formula is quicker and more effective than the

calculation of the single horizontal and vertical elements:

Rd =  / 4r

r= radius of the circle which circumscribes the link.

Earth rods distances "a" (m)

Resistivity (

m)

1 2 ... 87 88 89 90 91 92 93 94 95 96 97 ... 103 104

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Amprobe DMIII-Multitest Power-Quality-Recorder Uživatelský manuál Strana 92