Hioki BT3554-50, Инструкция по эксплуатации, Страница: 171 / 188

157
Effects of Current Density
11.4 Effects of Current Density
When an object under measurement is wide or
thick
When an object under measurement is wide or thick, such as a
plate or block, performing accurate measurements is difficult when a
Clip Type Lead or Pin Type Lead is used. In such cases, variations
in the contact pressure and contact angle could lead to variations
in measurement values from a few to a few-dozen percent. For
example, when the instrument measures resistance of a metal sheet
370 mm long, 300 mm wide, and 0.4 mm thick, measured values
will significantly vary even the probes are placed into contact at the
same locations on the sheet.
• Pin Type Lead
with a pin-to-pin distance of 0.2 mm: 1.1 m
Ω
• Pin Type Lead
with a pin-to-pin distance of 0.5 mm: 0.92 m
Ω
to 0.97 m
Ω
• Model 9287-10 Clip Type Lead: 0.85 m
Ω
to 0.95 m
Ω
(Model 9287-10 has been discontinued)
This is not due to the contact resistance between probes and the
object under measurement but the current distribution in the object.
Figure 1 illustrates an example of plotted equipotential lines
on a metal plate. Just like the relationship between winds and
atmospheric pressure patterns, used in weather forecasts, current
density is higher where the equipotential lines are close to each
other; and lower farther apart. This figure shows that the vicinity of
the current injecting points has steeper potential gradients. This is
because the electric current, just now spreading across the metal
plate, has a higher current density. Thus, when voltage detecting
terminals are placed near the current injecting points, just the
slightest change in contact positions can lead to major variation in
measured values.
HIOKI BT3554F961-00 HIOKI BT3554F961-00