LC tank circuit for measuring inductance with LM319

[snake0]

Another problem is when I lower the values of the caps/inductor to get a higher frequency it doesn't oscillate, even after reducing the resistors in the circuit. Perhaps this design isn't suitable for FM frequencies?

 

[CDRIVE]

Ah! OK mates I understand now.

What is the input Z of your scope? If it's an Arduino/PC based scope I would think that negative signals to the input would be verboten. I would also guess (I have no experience with Arduinos) that it would employ protection diodes to prevent this. If that's the case the answer to your question lies there.

Chris

 

[CDRIVE]

Another problem is when I lower the values of the caps/inductor to get a higher frequency it doesn't oscillate, even after reducing the resistors in the circuit. Perhaps this design isn't suitable for FM frequencies?

The Colpitts Osc. lends itself well to Crystal Osc. design as stated in the link I posted. That doesn't translate to a being the best design for VFO or broadband oscillator design. Are you under the impression that your going to be able to measure uH to mH or even Henries without providing a range switch to change the values of C1, C5 & C6? I don't think that any LC osc. of any known design is going to do that.

Chris

 

[Arouse1973]

The shorted turn sucks power out of changes in the magnetic field. Since this results in loss of energy it lowers the Q.

Yes Steve I think your right, the shorted turn will have a high circulating current (Eddy) whose energy must come from somewhere and this is the coil. Its the same as adding series resistance.
Adam