This document describes the features and measurement techniques of an instrument used to measure earth electrode resistance and soil resistivity. It can measure resistance from 0.01 to 200 KΩ. The instrument is IP54 rated and allows for 2, 3, and 4-point testing using attached rods or stakeless measurement. It has user-selectable test frequencies and output voltages. The document explains the principles and procedures for two-terminal, three-terminal, attached rod, stakeless, and four-terminal resistance and resistivity measurements. Potential and current probe resistances and ground noise voltages are also discussed.

1. 1
DET4TC2
Measurement of Earth electrode resistance and soil
resistivity……….

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Introduction
 Unique solution to the measurement of earth or
ground electrode resistance and soil resistivity
 Range of resistance 0.01 to 200 KΩ

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Features
IP54 rated
2,3 and 4 point testing
Attached rod technique
Stake less measurement
User selectable test frequency (94,105,111 and128
Hz)
Dry cell or non-rechargeable battery
User selectable output voltage

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i)Potential probe resistance
 Resistance between the potential stakes and it should be within
range for accurate measurement
 Rp limit: 100 KΩ (50 V output voltage) and 50 KΩ (25 V output
voltage)
ii)Current probe resistance
 Resistance between the current stakes and it should be within range
for accurate measurement
 Rc limit: 100 KΩ (50 V output voltage) and 5 KΩ (25 V output
voltage)
iii)Ground noise voltage
 The disturbance or interference caused by the formation of
unwanted ground loop due to external device and system
 Can be rejected upto 40 v peak to peak
 Calculated by following procedure
a) Connect the circuit as shown in fig
b) set the rotary switch to the V position

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FIG: Instrument connection for measuring ground
noise voltage
c) Then, ground noise voltage will be displayed by
pressing TEST button

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Principle of operation
i)Two terminal resistance measurement
 Required two earth points i.e. one earth electrode and
another is good ground connection
 DET injects an a.c. current into the system under test and
measures the voltage develop
When two terminal test is selected , DET instrument automatically connected
C1-P1 and C2-P2

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 Procedure
i) connect circuit as shown in fig
ii) Set the rotary switch to 2P position
iii) Set the required frequency
iv) Click Test button
v) Resistance will be displayed

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ii) Three terminal resistance measurement
 Fall of potential test
 Accurately measures the resistance of an earth electrode
 Uses auxiliary stake along with two terminal method
 DET injects an ac current of known magnitude and
measure voltage
Here, C1 and P1 terminals are connected together at the
electrode under test

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 In this case, the potential stake is moved by fixed
increment in a straight line between electrode under test
and current stake
 In each location, the resistance is calculated by R= V/I
then, a graph is plotted of resistance vs potential stake
position
 The resistance of the electrode under test is taken to be
the point at which the curve is flattest
 The earth electrode is consider to be surrounded by
concentric shells of earth shown in fig. The current probe
is also surrounded by earth shell but of smaller influence

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 It is necessary to locate current probe to the far way so
that influential shell do not overlap

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iii) Three terminal resistance measurement using ART
(Attached Rod technique)
 Classic three terminal test has the disadvantage that
electrode under test must be disconnected from the
system it is supposed to protect at the event of fault
 But here that system is connected
 Current I splits into two paths i.e. I = I1 +I2

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 The current I2 is calculated using Iclamp
 Then, Resistance is calculated by R= V/I2 or V/(I-I1)
 Like previous away, graph is plotted to obtain exact electrode
resistance

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iv) Two clamp stake less resistance measurement
 If electrode under test is connected to a network of other
electrodes as shown in figure and unsafe to disconnect
 Requires both Iclamp and Vclamp
 Using Vclamp defined test voltage is injected into the
system inducing current I which is measured by Iclamp

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v) Four terminal resistivity measurement
 Used for measuring resistivity of the soil
 Stakes are kept as shown in figure with equal distance
 As usual, resistance R is calculated
 Then, soil resistivity is calculated as 2*π*A*R

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THE END
Any
Queries??
Prepared By:
Er. Niroj Bahadur Bhujel