Hioki Super megohm SM7110 - Measurement Principle

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5
Measurement Methods Suitable
for Various Objects to Be
Measured
Insulation resistance objects to be measured vary in material, shape, electrical characteristics, and
other properties, and the suitable insulation resistance measurement method varies depending on
the object.
This chapter describes suitable insulation resistance measurement methods for di󰀨erent objects.
5.1 Measuring Components or Circuits
Measurement principle
Generally, insulation resistance is measured by measuring a current that ows from a terminal
through a measured object to another terminal, and converting the result into a resistance value.
To measure only the current that ows through the measured object, the current that does not
ow through the object (e.g., current that ows through the insulator of the object holder) must be
diverted to the GUARD terminal (on the common side of the current measurement block) so that it
does not ow into the INPUT terminal. That is, “guarding” is to make the current owing through the
outside of the measured object directly ow to the common side to prevent it from owing into the
INPUT terminal.
If you use a measurement xture, generally the component holder of the xture must be guarded.
However, measuring the insulation resistance of the xture in addition to that of the measured
object may not be problem if the insulation resistance of the xture is much, for example,
hundredfold or more, higher that of the object.
Although the structure of an actual xture may vary depending on the shape of the object to be
measured, the guard circuit must be congured in such a way that the current not owing through
the object is diverted to the GUARD terminal.
5 Measurement Methods Suitable for Various Objects to Be Measured
5
Measurement Methods Suitable for Various Objects to Be Measured