Oscillator with an inductance with nonzero resistance

[meereck]

Hello,
I need to measure ONLY a change in inductance of a loop (long wire) which has got resistance about 30-200 ohms.
I have tried to build the oscillator according to this schematic : http://ironbark.bendigo.latrobe.edu.au/~rice/lc/
but the problem is it works well with an inductance with almost zero resistance only.
If I connect my loop, it behave wrongly. I guess because of the energy disappation?

Therefore, I need to modify that circuit, or use another another one. Unfortunately, I haven't found anything about how to make an oscillator with an resistive inductor.

I read about using a negative resistance circuit but I have no clue how to employ that.
I have also heard about using a transformer (perhaps it is called tapped inductors?).

To summarize my approach:
I only need to detect a change in inductance of a wire loop.
I prefer to have an oscillator with TTL output and to measure therefore the frequency (in a microcontroller)

May I ask you for some hints on that?
Thanks in advance,
Best regards Meereck

 

[berkeman]

What is the range of inductance that you are trying to measure, in addition to the 30-200 Ohms of real resistance?

I would probably approach it by driving a signal from a known source impedance, and measuring the in-phase and quadrature components of the divided AC voltage waveform. That will give you values for both the real resistance and the reactive inductive impedance.

 

[meereck]

What is the range of inductance that you are trying to measure, in addition to the 30-200 Ohms of real resistance?

I would probably approach it by driving a signal from a known source impedance, and measuring the in-phase and quadrature components of the divided AC voltage waveform. That will give you values for both the real resistance and the reactive inductive impedance.

thanks for a reply.
The inductance will be about 100-300 microH, its pure resistance will be 30-200Ohm.
>>measuring the in-phase and quadrature components of the divided AC voltage waveform.
Right, but this will probably be quite difficult to measure by a common microcontroller such as a PIC. Would you have any supporting circuit for that?

cheers M.