STB8827
Series Operation Manual Chapter 5 Execute LCR Operation and Some Examples
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Hc Hp Lp Lc
Shielding ground
Shielding plate
Test terminal
Cx
Metal conductor
Figure 5-2 Eliminate the influence of stray capacitance
When the DUT has high impedance(such as small capacitance), the influence
of stray capacitance cannot be ignored. Figure 5-1 is an example of the use of 4
terminal pair measurement. In this figure, Cd is connected with Cx in a parallel
way and when a conductance plate is positioned under DUT, capacitance Ch will
connect with Cx in parallel after connecting with Cl in series and by this way the
measurement result will have errors. If a ground conductor is installed between
high and low terminals, Cd can be reduced to Min. Meanwhile if the ground
terminal is connected to the conductance plate, the influence of Ch and Cl will be
eliminated.
When the DUT is low impedance (such as small inductance, large
capacitance), a large current will flow through test leads Hc and Lc. In this case,
electromagnetic coupling between test leads becomes the main source
of test errors
except the influence of the contact resistance on test terminals. If
this coupling cannot be eliminated, it will bring unexpected influence on test
results. Generally, contact resistance affects the resistance of impedance and
electromagnetic affects the reactance of impedance. Test terminals can adopt
4TP connection method. For 4TP connection, the currents flow though Hc and Lc
are equal in value and opposite in direction with those flowing through each
shielding terminals. By this way, the magnetic fields produced by these currents
can be mutually offset and further eliminate the influence of mutual inductance
coupling on test results.
5.4 Operation example for testing inductance with
STB8827
A
Test Condition
Function: Ls-Q
Frequency: 5.5kHz
Level: 1.5Vrms
Internal impedance: 100
Ω
