Hioki FT3151 - Page 126

Appx.4
Measurement Principle
(2) 2-pole method (simplied measurement)
The gure below shows the basic circuit principle for a simplied
earth resistance measurement using an existing earthing body.
Where the earth resistance of the existing earthing body is given by
Ro; and the earth resistance of the measurement object, by Rx, the
same equation as for the 3-pole method applies:
Rx + Ro = Rs/n
Thus, the earth resistance can be found by adding the earth
resistance of the existing earthing body (Ro) to the earth resistance
of the measurement object (Rx).
In addition, the FT3151 uses a signicantly low measurement
current, in order that the leakage current circuit breaker of a
commercial power supply does not be tripped when the grounded
side of an AC outlet is used as existing earthing body.
Synchronous
rectier
Oscillator
S(P)
1:n
H(C)
Galvanometer
Rs
E
Rx
S
Ro
Measurement principle diagram (2-pole measurement)