HT instruments T2100 - Manual (Page 15)

T2000-T2100
EN – 14
Fig. 13: Three-point method: third test R3
Under these conditions, assuming that the resistance of the cables connecting the rods is
negligible, the following relationships are valid:
R1 = RA + RB
(3)
R2 = RB + RC
(4)
R3 = RC + RA
(5)
where the values R1, R2 e R3 are measured by the instrument.
CAUTION
The relationships (3), (4) and (5) are to be considered valid only provided that
it is possible to neglect the effect of “mutual influence” among the rods
connected in series, i.e. with rods
placed at a sufficient distance between
them (equal to at least 5 times the length of a single rod or 5 times the
maximum system diagonal) so that they do not influence each other.
The result of the relationships (3), (4) and (5) is:
RA = (R1 + R3 – R2) / 2
 Resistance of rod A
and consequently:
RB = R1 – RA
 Resistance of rod B
RC = R3 – RA
 Resistance of rod C