LC oscillator with a resistance

[meereck]

Hello,
my aim is to measure JUST a change in an inductive loop. Thus, I dont need to get an accurate measurement. The problem is that the loop I want to measure has about 100-200Ohms, which causes troubles with oscillator.

I tried the following schematic but it works well if the inductance has got zero resistance:
**broken link removed**
If I connect a resistor in series with the inductance (simulation of a long inductive wire), the oscillator frequency becomes much lower and change in inductive loop cannot be recognized, since it almost does not react to it.

Can anyone suggest me what to change in the schematic or tell me what a better oscillator which copes with an inductance with resistance would be?

To conclude my approach, I have a long inductive wire and I want to measure the change in its inductance. I dont care if it oscillates at 50kHz or 100kHz, I just need to know if the frequency changes from the normal osc frequency.

I hope it is understandable.
Thanks in advance, regards meereck

 

[FvM]

I would suggest an oscillator like this or a colpitts-circuit with a transistor

 

[meereck]

Thank you for a reply. I will give a try tomorrow. I assume I can connect pin 4 to ground instead of a negative voltage.
What is the purpose of R4?
Have a nice weekend,
Mirek

 

[carrier]

hi
are your load is a still inductance?
if yes you can use colpits oscilator and reply to guidance you.

 

[FvM]

Hello,

the circuit can't be used with single supply (Pin 4 at ground). It would need a virtual ground then. I thought, it could be meaningful, to have one loop inductor terminal grounded,

R4 is essential to achieve stable oscillator operation, setting the gain somewhat above the minimum value.