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low-end Lp) and shielding terminal corresponding to each test terminal.The purpose of shielding
ends is to reduce the influence of stray capacitance on the ground and reduce electromagnetic
interference.Hc, Hp, Lc and Lp should be connected on the lead of the component under test to
form a complete four-terminal measurement to reduce the influence of the lead and connection
point on the test results (especially loss measurement).Especially when the low impedance
component is tested, the voltage sampling terminal Hp and Lp should be connected to the lead end
of the component to prevent the lead resistance from being added to the measured impedance. The
connecting principle is Hp, and the voltage detected by Lp should be the actual voltage on the
tested component.In other words, it is better not to connect Hc, Hp and Lp, Lc with the tested
component lead after connecting, otherwise it will increase the test error.
If the contact point and lead resistance Rlead are much smaller than the measured impedance (for
example: Rlead<Zx/1000, The requirement error is less than 0.1%.),Hc, Hp and Lp, Lc can be
connected together and then connected to the two ends of the tested element (measured at both
ends).It is much better to use a measuring fixture than to use a measuring wire (Kelvin fixture
attached to the instrument) for some high precision measurements.When Kelvin test line is tested
at 10 kHz frequency, good results can be obtained, but when the frequency exceeds 10 kHz,
Kelvin test line is difficult to meet the test requirements.Because at high frequencies, the change
of the gap between the wires directly changes the stray capacitance and inductance of the test
terminal, and the test wire is always difficult to fix.Therefore, the test fixture should be used as
much as possible when measuring at higher frequencies. If the test fixture can not be used because
of the limited conditions, the state of the test line should be as consistent as possible when the
instrument is cleared.Whether you use a test fixture provided by the instrument or a Kelvin test
cable or a user-made fixture, you should meet the following requirements.
1. The distribution impedance must be minimized, especially when measuring high impedance
components.
2. Contact resistance must be minimized.
3. The contact points must be short circuited and open circuited.Short circuit and open circuit "0"
can easily reduce the influence of test fixture distribution impedance on measurement.for open
circuit "0"
，
The test terminal should be the same as the tested part
，
separated at the same
distance.For short circuit clear "0"
，
Low impedance short circuit board should be connected
between the test end, or make Hc, Lc direct connection, Hp, Lp direct connection, and then
connect the two together.
Note: When the device under test is polar, attention should be paid to "high potential terminal"
before testing, please connect to the front panel "or Hc, Hp terminal, and"low potential
terminal"to the front panel marked"-"or Lc, LP terminal.
Warning: please discharge when measuring polar components, so as to avoid damaging the
instrument.
5.3 Eliminating the influence of stray impedance
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