Voltech AT5600 User Manual page 122

C H A P T E R 7 – T E S T S
Average Inductance
(Geometric Mean)
100nH →
1uH →
10uH
→
100uH
→
1mH
→
10mH
→
100mH
→
1H
→
10H
→
100H
→
1kH
→
Wherever possible, this table should be used for all inductance tests. The
inductance range should be chosen based on minimum value of inductance
expected.
When choosing the test conditions, the following potential problems should be
considered:
Current levels
The upper voltage limits should be chosen to give a maximum current level of
about 100mArms for the lowest inductance expected. In some cases, this current
may cause core saturation, and a lower voltage should be used. The minimum
voltage level must be chosen so that the test current does not become so low that
it cannot be sensibly measured. The lower voltage limits in the table above
always give test currents higher than 3µA RMS.
Self-Resonant Frequency
At lower frequencies, the capacitance of the windings can normally be ignored
because its impedance is much higher than that of the inductance. However, at
very high frequencies, this is not so, the capacitance dominates, and inductance
cannot be measured. The self-resonant frequency of the transformer is the
change-over point between these two regions.
Normally to get a good measurement of inductance, the test frequency should be
less than 20% of the resonant frequency of the transformer.
In general, high values of inductance will have a high inter-turn capacitance and
hence a low resonant frequency. Where there is a choice of test frequencies
always use the lower value, to minimize any problems due to self-resonance.
Please also see
14.6.13 for specific advice on programming the test, and
10.2.18 for test accuracy specification
AT5600 User Manual 98-119 issue 14
A N D T E S T C O N D I T I O N S
Table 6
1uH
10uH
100uH
1mH
10mH
100mH
1H
10H
100H
1KH
10KH
Test Conditions for Inductance Match Measurement
Preferred test signal
Frequency
300KHz 10mV
100KHz 30mV
30KHz 50mV
10KHz 100mV
1KHz 100mV
100Hz 100mV
100Hz 300mV
50Hz 1V
50Hz 5V
50Hz 5V
20Hz 5V
Voltage
Page 122