12-03-2013, 02:00 PM
Judging by the numbers provided, it's something in the 0.3H region, which doesn't sound very likely to me...
A couple of things:
1. The voltages are very small for a 'scope reading. Make measurements in 10s of millivolts at least, and here there's no obvious reason to not use 100s of millivolts, or indeed volts.
2. Putting the coil in series with the 'scope means that you're relying on the 1M input impedance - which is a bit on the high side. Stray capacitance could cause all sorts of problems.
I'm lucky enough to have a TF2700 for measuring inductors, but in the absence of that, I think I'd try putting 1k or 10k to ground, setting the oscillator to a low frequency and adjust the level so that the trace fills 4 divisions peak (8 peak to peak). Then wind up the frequency until it starts to roll off. Stop when it's reached 2.8 divisions peak (5.6 peak to peak). That's the -3dB of the filter. Then you can use f=2 x pi x R x L - assuming your oscillator goes high enough in frequency to roll over.
A couple of things:
1. The voltages are very small for a 'scope reading. Make measurements in 10s of millivolts at least, and here there's no obvious reason to not use 100s of millivolts, or indeed volts.
2. Putting the coil in series with the 'scope means that you're relying on the 1M input impedance - which is a bit on the high side. Stray capacitance could cause all sorts of problems.
I'm lucky enough to have a TF2700 for measuring inductors, but in the absence of that, I think I'd try putting 1k or 10k to ground, setting the oscillator to a low frequency and adjust the level so that the trace fills 4 divisions peak (8 peak to peak). Then wind up the frequency until it starts to roll off. Stop when it's reached 2.8 divisions peak (5.6 peak to peak). That's the -3dB of the filter. Then you can use f=2 x pi x R x L - assuming your oscillator goes high enough in frequency to roll over.
