Principle Of Operation - LEM HEME GEO 15 Manuel D'utilisation

Principle of Operation

7 Principle of Operation
The following diagram (fig. 1) shows a simplified typical grounded distribution sys-
tem. Its equivalent circuit (fig. 2) is shown below. If R 1 , R 2 , R 3 , ... R n is combined
as R eq , then only R g and R eq are left in the circuit (see figure). If a constant volt-
age is applied to the circuit, the following equation is valid:
U
=
I
where
=
R
eq
∑
If R g and R 1 , R 2 , ... R n are about the same, and n is a large number (such as
200), then R eq will be much less than R g and maybe approach zero.
>>
R
g
Example:
If R g and R 1 , R 2 , ... R n are all 10 Ω, respectively and n = 200, then R eq by
calculation equals
1
= = , 0 05 Ω
R
1 1 1
eq
+ + +
...
10 10 10
In this example, we can see that as long as the number of multiple electrodes is
large enough, the equivalent resistance is negligible with respect to the ground
resistance to be measured.
+
R R
g eq
1
=
, i 1 2 , ,... n
1
R
i
→
( R ) 0
eq
U
= + = + =
R R 10 , 0 05 10
g eq
I
- 11 -
→
, 05 R
g