Hioki IM3533 - Appendix3 Measurement of In-Circuit Compo- Nents

Appendix3 Measurement of In-circuit Components
A4
Measure an in-circuit component after providing guarding.
Referring to the following figure, when measuring a resistance value
for the resistor
R
2
, even if the tips of the two probes are contacted
against the ends of the resistor
R
2
, considering the sum of the cur-
rent flowing through the resistor
R
2
and the current flowing through
the resistors
R
3
and R
4
, what is obtained is the resistance value for
the parallel combination:
If as shown in the next figure a guard terminal is used, the current
flowing through the resistors
R
3
(not flowing through R
4
) is absorbed
by this guard terminal, so that the resistance value for the resistor
R
2
is accurately measured.
Appendix3 Measurement of In-circuit Compo-
nents
RR
2
R
3
R
4
+
R
2
R
3
R
4
++
----------------------------------
=
R
4
R
3
R
2
R
1
HL
Guard terminal
R
4
R
3
R
2
R
1
HL
• The accuracy of measurement will not be improved in cases where for example R
2
>> R
3
and R
3
is close to zero.
• As shown in the figure below, it is not possible to use this type of separation process for
testing of the impedance values of two resistors or other elements of identical types which
are connected in parallel, or for testing of the impedance values of a coil and a capacitor
which are connected in parallel.
Two resistors in parallel
Coil and capacitor in parallel