Hioki DSM-8104, Instruction Manual

Page: 58 / 132

48
6.1.2 Connecting measuring terminals
Insulation resistance is measured by connecting a sample between the “INPUT” and
“OUTPUT” terminals. Insulated cable with sufficient withstand voltage to measuring
voltage can be used between the “OUTPUT” terminal and sample terminal. However,
use measuring cable with a guard (shielded-conductor cable with a densely braided
shielding braid) between the “INPUT” terminal and sample terminal. Be certain to
connect the outer conductor (shielding braid) to the “GUARD” terminal.
[Notice]
Noise that is generated by the measuring cable sometimes hampers stable
measurement of high resistance.
Use a low-noise shielded-conductor cable meeting the specification of
HIOKI as a cable connected between the “INPUT” terminal and sample for
stable measurement.
As mentioned in 6.1.1 “Functions of measuring terminals,” the “GROUND” terminal is
connected to the “OUTPUT” terminal or “GUARD” terminal by a short bar. The
difference between connection to the “OUTPUT” terminal and “GUARD” terminal is
explained below.
(1) Grounding “OUTPUT” terminal
“+” voltage must be impressed to the terminal on the grounding side when
insulation resistance (insulation resistance to the earth) of a sample (a part or
circuit), whose one wire is grounded, such as a lightning arrestor. transformer,
transmission cable and distribution cable, is measured. Connect the
“OUTPUT” terminal on the panel of the meter to the “GROUND” terminal through
the short bar, connecting the terminal on the grounding side of the sample to the
“OUTPUT” terminal through the measuring cable.
“+” voltage can be impressed to the grounding side terminal of the sample by
connecting the “OUTPUT” terminal to the grounding terminal of the sample even
if it is not connected to the “GROUND” terminal. In this case, however, noise
voltage enters the input circuit, sometimes hampering stable measurement.
Be certain to connect the “GROUND” terminal to the “OUTPUT” terminal (or to
the “GUARD” terminal).
[Warning]
Connecting the “OUTPUT” terminal and “GROUND” terminal in measurement of
a sample whose one wire is grounded, voltage of maximum 1000V is impressed
onto the “GUARD” terminal, “INPUT” terminal and outer electrode (shielding
side of the measuring cable) to the ground depending on the measuring voltage
setting.
Exercise reasonable care with an electric shock.