Hioki FT3151 - Appx. 2 Measurement Principle

Appx.3
Measurement Principle
Appx. 2 Measurement Principle
(1) 3-pole method (precise measurement)
The gure below shows the basic circuit principle for earth
resistance measurement.
The measurement current I, driven by the oscillating voltage of the
oscillator, ows through the loop formed in the following order: the
oscillator, Rc, Rx, and C.T.
Where the voltage between the measurement terminals E and S(P)
is given by Ex; the resistance between the measurement terminal E
and the slider S of the variable resistor, by Rs; and the voltage drop
at the variable resistor, by Es, if the galvanometer is balanced, the
following equations then apply:
Ex = IRx
Es = IRs/n (n: C.T. winding ratio)
Ex = Es
Hence
Rx = Rs/n
Then, if the dial connected directly to the sliding resistor has a scale
of 1/n for Rs, the dial reading corresponds to the earth resistance
Rx.
Galvanometer
Synchronous
rectier
Oscillator
S(P)
1:n
H(C)
Rp
RcRx
E
S
Rs
Measurement principle diagram (3-pole measurement)
Ind.Appx.
7
6
5
4
3
2
1