Hioki DSM-8104, Instruction Manual

Page: 64 / 132

54
6.2.3 When measuring jig is not used
When making measurement without using a jig or other means, use a measuring lead
with a test rod or a measuring lead with an alligator clip as an option and connect it to
the part to be measured.
Both of the measuring leads that are connected to the “OUTPUT” terminal have no guard,
while the measuring lead connected to the “INPUT” terminal has a guard. The
measuring lead with a test rod has a guard including a test rod so that measurement can
be performed by holding the test rod by hand. The alligator clip of the measuring lead
with an alligator clip is not guarded. Connect it to a terminal of the sample and measure
the sample with a hand off.
Connect the terminals on the panels and handle the meter by the same method as that
when a jig is used.
[Tip] Resistance values of insulation resistance naturally vary depending on the
insulating material. Impacts by measuring voltage, temperature and measuring
time are not small.
Typically, insulating materials are complex circuits with resistances and
electrostatic capacities that are connected serially and in parallel. Therefore,
impressing voltage to an insulating material, a dielectric absorption current and
leakage current corresponding to a charging current flow.
Insulation resistance is calculated by measuring this leakage current and
converting it into a resistance value. Generally, a dielectric absorption current is
substantially large compared with a leakage current and time constant of it is very
large depending on the type of insulating material so that a long time is needed till
a dielectric absorption current becomes smaller than a leakage current. When
insulation resistance is measured using such insulating material as a sample,
insulation resistance is low in measurement for a short time, becoming high longer
the measuring time is. The time constant and insulation resistance of a dielectric
absorption current vary significantly depending on the voltage impressed to the
insulating material. In general, insulation resistance lowers higher the measuring
voltage is.
Temperature also affects greatly. The type of insulating material also makes a
difference, but insulation resistance generally lowers higher the temperature is.
Correct measurement of insulation resistance is time consuming and is also
difficult.
Depending on the withstand voltage of a sample, measuring voltage sometimes
cannot be decided freely. Values obtained in one minute as measuring time are
used as measuring time and one-mute values of insulation resistance are used by
adding measuring voltage such as “DC 500V 1000M
Ω .
When comparing insulation resistances, measurement must be made after
deciding measuring voltage and measuring time. It is sometimes important to
shorten measuring time (or inspection time) of parts and other samples. In this
case, it is important to measure after deciding a time within a range in which
correlation can be taken with a one-minute value.