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Fig. 5-1 schematic diagram of the influence of stray capacitance
Fig. 5-2 schematic diagram of eliminating the influence of stray capacitance
The effect of stray capacitance can not be ignored when the measured part is of high impedance
(such as small capacitance). Fig. 5-1 shows an example of measuring the measured part with four
terminals.In the picture, Cd is parallel to Cx, when the conductor plate is under the tested part.The
capacitor Ch is connected with Cl in series and is parallel to Cx.This will result in errors in the
measurement results.Placing a grounding conductor between the high and low ends of the test, Cd
can be minimized.At the same time, if the grounding terminal is connected to the lower conductor
plate, the influence of Ch and Cl will be eliminated.
When the measured part is low impedance (such as small inductance, large capacitance), Due to
the large current flowing through the measuring line Hc and Lc, besides the influence of the
contact resistance at the testing end, the electromagnetic coupling between the measuring lines
becomes the main source of the measurement error. Without eliminating the coupling, the
unexpected influence on the test results will be produced.Generally speaking, the contact
resistance affects the resistance part of the test impedance, while the electromagnetic coupling
affects the reactance part of the test impedance.The test end can adopt four-terminal-pair
connection method to make the current flowing through Hc and Lc and the current flowing
through each shielding end equal in magnitude but opposite in direction, so that the magnetic field
produced by Hc and Lc can cancel each other and eliminate the influence of mutual inductance
Содержание JK2817N
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