MD-5060
10
The unknown resistance (
Rx
) is connected between
Vt
and
R
terminals. Its value
determines the current passing through the circuit, which in turn is indicated by the
microammeter. The value of
Rx
can be determined as follows:
V
Rx
=
-
Ri
I
In many cases the resistance to be measured is in parallel with other stray resistances which influence
on Rx should be minimum and if possible, zero.
A typical example of this situation is when the insulation resistance between primary and secondary
windings of a transformer mounted inside a metal housing is to be measured.
Rx
: Insulation resistance between primary and secondary winding.
R1
: Insulation resistance between primary winding and housing.
R2
: Insulation resistance between secondary winding and housing.
If megohmmeter (terminals
Vt
and
R
) is connected to transformer terminals
A
and
B
, and
considering that the resistance of the turns on each side of the transformer may be
disregarded as compared with the insulation resistance between primary and secondary
windings measured by megohmmeter,
Rx
appears to be in parallel with (
R1 + R2
).
The situation is changed if we connect the transformer housing to
GUARD
terminal.
