7.1.38 LVOC - Low Voltage Open Circuit
Measurement
Range |
Test
Voltage |
Test
Frequency |
Basic
Accuracy |
100μV to 650V |
1mV to 5V |
20Hz to 3MHz |
0.1% |
Where used
The low voltage open circuit test is used to confirm that windings have the correct ratio of turns between them, and that the phasing of the windings is correct. This test is used for 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 region. On the AT3600 only, a high voltage open circuit test is available for testing line frequency transformers at their operating point (up to 270V, 1kHz and 2A). See also the test TR – turns ratio.
Measurement conditions
To measure low voltage open circuit, the test signal is applied to one winding called the energized winding. The voltages across another winding (or the same, energized winding) is measured. The low voltage open circuit measurement is the rms value of the voltage measured and can be an ac or a dc voltage.
It is recommended that you choose the winding with the highest number of turns as the one to be energised.
Choosing test conditions
The recommended test conditions depend on the inductance of the energised winding; they are given in the table below assuming that the energised winding is the one with the highest number of turns:
Inductance of the
Energised Winding |
Preferred test signal |
Frequency |
Voltage |
100nH → 1μH
1uH → 10μH
10uH → 100μH
100uH → 1mH
1mH → 10mH
10mH → 100mH
100mH → 1H
1H → 10H
10H → 100H
100H → 1kH
1kH → 10kH |
300kHz
100kHz
30kHz
10kHz
1kHz
100Hz
100Hz
50Hz
50Hz
50Hz
20Hz |
10mV
30mV
50mV
100mV
100mV
100mV
300mV
1V
5V
5V
5V |
The test conditions can also be determined automatically by the AT3600 according to this table:
Voltage |
Specified |
Auto |
Auto |
Frequency |
Specified |
Specified |
Auto |
Note that a ‘fixed’ voltage signal cannot be used with an ‘Auto’ frequency.