Hioki BT3554 - Appendix; Appx. 4: Effects of Current Density

Appx.5
Effects of Current Density
Appx. 4 Effects of Current Density
When the Measurement target is Wide or Thick
When the measurement target is wide or thick, such as a plate or block,
SHUIRUPLQJDFFXUDWHPHDVXUHPHQWVLVGLI¿FXOWZKHQFOLSW\SHRUSLQW\SHOHDGV
are used. In such cases, a difference in the contact pressure or contact angle
could lead to variations in measurement values from a few to a few-dozen
SHUFHQW)RUH[DPSOHZKHQWKHPHDVXUHPHQWREMHFWLVDPHWDOVKHHWZLWK
dimensions of W300 × L370 × t0.4, measurement values taken from the same
location may differ markedly as shown below:
PPSLWFKSLQW\SHOHDGP
ȍ
PPSLWFKSLQW\SHOHDGP
ȍ
to 0.97 m
ȍ
&OLS7\SH/HDGP
ȍ
WRP
ȍ
This is caused by the current distribution in the measurement target, not by
the contact resistance between the probe and the measurement target.
)LJXUHVKRZVDQH[DPSOHRISORWWHGHTXLSRWHQWLDOOLQHVRQDPHWDOSODWH
Just like the relationship between wind and the barometric charts used in
ZHDWKHUIRUHFDVWVFXUUHQWGHQVLW\LVKLJKHUZKHUHWKHHTXLSRWHQWLDOOLQHVDUH
FORVHWRHDFKRWKHUDQGORZHUZKHUHWKHOLQHVDUHIDUWKHUDSDUW7KLV¿JXUH
shows that the potential gradient is greater near the sources of current. This
is because these points are in the middle from where the electric current is
spreading across the metal plate, leading to a higher current density. For this
reason, when a terminal for detecting voltage is placed near one of these
VRXUFHVRIFXUUHQWMXVWWKHVOLJKWHVWFKDQJHLQFRQWDFWSRVLWLRQFDQOHDGWR
PDMRUYDULDWLRQLQPHDVXUHPHQWYDOXHV
8VHRI+LRNLVPRGHO)RXU7HUPLQDO/HDGRUDVLPLODUOHDGWRGHWHFW
voltage on the inner side of the sources of current is necessary to avoid
these effects. In other words, the current distribution is likely to be stable
if measurement is conducted within the width (W) or thickness (t) of the
measurement target.
1
2
3
4
5
6
7
Appx. Index
Appx.
www.GlobalTestSupply.com
Find Quality Products Online at: sales@GlobalTestSupply.com