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Appendix 3 Unstable Measurement Values
A
5
Appendix
(4) Wider/Thicker DUTs
If the DUT has a certain width or thickness like boards or
blocks, it will be difficult to measure accurately using Pin Type
Leads or Clip Type Leads. By using such measurement
probes, there may be considerable fluctuation of the measured
value due to contact pressure or contact angle. For example,
when measuring a W300 x L370 x t0.4 mm metal board, the
measured values are fairly different, even if measuring the
same points, as shown below:
•
0.2mm pitch Pin type lead: 1.1m

•
0.5mm pitch Pin type lead: 0.92m to 0.97m

•
Model 9287-10 Clip Type Lead: 0.85m to 0.95m

This does not depend on the contact resistance between
probes and the DUT, but on the current distribution on the DUT.
Fig. 7 is an example of plotting equivalent electric potential
lines of a metal board. Similar to the relation between atmo-
spheric pressure distribution and wind on a weather forecast
diagram, current density is higher in locations where the equiv-
alent electric potential lines are narrowly spaced, and lower in
locations where they are widely spaced. Through this example,
it is shown that the electric potential slope is larger around cur-
rent applying points. This phenomenon is caused by high cur-
rent density while current expands on the metal board. Due to
this phenomenon, measured values should be rather different,
even if the connected position difference is quite slight, in case
connecting voltage detection terminals (of measurement
probes) near current applying points.
It is known that such effects can be minimized by detecting the
voltage within the space between the current contact points.
Generally, if the distance between the voltage detection points
and their corresponding current application points (CUR, POT
terminals) is greater than the width (W) or thickness (t) of the
DUT, current distribution may be considered uniform.
As shown in Fig. 8, POT leads should be 3W or 3t mm or more
inside from the CUR leads.
(5) Unstable Temperature of the DUT
Copper wire resistance has a temperature coefficient of about 0.4%/

C. Just holding a copper wire in the hand
raises its temperature, causing its resistance to be increased as well. When the hand is removed from the
wire, temperature and resistance decrease.
Varnished windings are more susceptible to temperature increase, so the resistance tends to be relatively
high.
Use an instrument with a temperature-compensation function such as the Hioki RM3544, RM3545, and
RM3548 to minimize copper-like temperature dependence.
Current
Applying
Figure 7. Equipotential lines on a metal
board (W300 x L370 x t0.4 mm)

Applying 1 A current on points on edges and
plotting equivalent electric potential lines at
each 50

V level
0.1m

0.2m

0.3m

0.4m

3W, 3t
or more
3W, 3t
or more
Figure 8. Probe Positions on
Wider/Thicker DUT
H
CUR
H
POT
L
POT
L
CUR