Principle Of Operation - LEM HEME GEO 30 Manual De Instrucciones

7

Principle of Operation

The following diagram (fig. 1) shows a simplified typical grounded distribution system.
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 voltage is applied
to the circuit, the following equation is valid:
where
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.
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
=
R
1 1
eq
+ +
...
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.
HEME GEO 30
SO8130Z Rev. B
U
I
=
R
eq
∑
>>
R
g
= Ω
, 0 05
1
+
10
= +
R R
g eq
1
=
, i 1 2 , ,... n
1
R
i
→
( R ) 0
eq
U
= + =
R R
g eq
I
Principle of Operation
+ =
10 , 0 05 10 , 05
→
R
g
17