ruffrecords
Well-known member
As part of the work on the Mastering EQ project I have been testing a board that contains a number of separate inductors wired in series.
You would therefore anticipate that the inductance between any two point would be equal to the sum of the individual inductors between them. The string starts at the top left with a 6.8mH inductor. I measured the inductor before I put it in and it was close to 7mH (i.e within 5%). I calculated the capacitor for the required frequency (8KHz) fitted it and tested. I found the frequency was lower than it should be. So, I measured the value of the 6.8mH inductor in circuit and the reading I got was 7.8mH which is about 15% out. I recalculated the capacitor for this value, fitted it and the measured frequency was very close to 8KHz.
This was unexpected and my suspicion is that it is caused by coupling (mutual inductance) between the 6.8mH inductor and its neighbours. They are fairly close to each other but I would have expected the coupling between them to be so small as to make no measurable difference. What do you think?
Cheers
Ian
You would therefore anticipate that the inductance between any two point would be equal to the sum of the individual inductors between them. The string starts at the top left with a 6.8mH inductor. I measured the inductor before I put it in and it was close to 7mH (i.e within 5%). I calculated the capacitor for the required frequency (8KHz) fitted it and tested. I found the frequency was lower than it should be. So, I measured the value of the 6.8mH inductor in circuit and the reading I got was 7.8mH which is about 15% out. I recalculated the capacitor for this value, fitted it and the measured frequency was very close to 8KHz.
This was unexpected and my suspicion is that it is caused by coupling (mutual inductance) between the 6.8mH inductor and its neighbours. They are fairly close to each other but I would have expected the coupling between them to be so small as to make no measurable difference. What do you think?
Cheers
Ian