Voltech AT5600, Руководство пользователя

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C H A P T E R 7 – T E S T S A N D T E S T C O N D I T I O N S
AT5600 User Manual 98-119 issue 14
Page 101
7.7. LS or LP - Inductance (Series or Parallel Circuit)
Where Used
The AT5600 offers two basic alternative ways to confirm that the transformer has
been assembled properly, with the appropriate number of primary and secondary
turns, the right grade of magnetic material for the core, and the correct air gap if
required.
When testing signal, pulse and switched mode power transformers, where the
normal operating conditions require only small excursions of the B-H curve, never
extending beyond the linear regions, a measurement of primary inductance,
together with a turns ratio test is used.
(For line frequency transformers, designed to operate over the full extent of the B-
H curve, including the non-linear regions, the preferred method is to use a
magnetizing current test applied to a primary winding, followed by an open-circuit
voltage test for every other winding.)
Measurement Conditions
To measure inductance, the tester applies an AC voltage across the selected
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
the complex impedance and the inductance is calculated.
The test signal can have a frequency in the range 20Hz to 3MHz, and 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 primary inductance: