L2 - Inductance Match - Voltech AT5600 User Manual

C H A P T E R 7 – T E S T S
7.17. L2 – Inductance Match
Where Used
The inductance match test calculates the ratio between two inductances on two
windings. An equivalent series inductance measurement is performed on each
winding by measuring the complex impedance.
This test is suitable for switched mode power supply transformers, and audio &
telecommunication transformers. It checks matching between windings.
Measurement Conditions
When calculating, inductance match the tester performs two inductance
measurements. Firstly, the unit applies an AC voltage across the first winding; it
then measures the voltage across and the current through the winding using
harmonic analysis. The measured voltage is divided by the current to obtain a
complex impedance and the inductance is calculated. This is then repeated for
the second winding. The inductance match is the ratio of first to second winding
inductance.
The test signal can have a frequency in the range 20Hz to 3MHz, and an
amplitude from 1mV to 5V.
Generally, it is not necessary to measure the inductance at the normal operating
conditions of the transformer, which could involve, for example, voltage levels of
hundreds of volts. This is because the B-H curve can normally be assumed to be
linear in the operating region, and the inductance measured at a low level
represents the inductance that will appear in use.
Also, it can usually be assumed that the inductance value does not vary
significantly with frequency. Therefore, although high frequencies are available
with the tester, measurement frequencies above a few hundred kilohertz should
be used with caution. This is because the errors caused by the stray inductance
and capacitance of your fixture may become much more significant at these
frequencies. Compensation can be used to eliminate these errors.
The following table suggests suitable test conditions for different values of
expected average inductance:
AT5600 User Manual 98-119 issue 14
A N D T E S T C O N D I T I O N S
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