Measuring LC-resonance frequency - Stupid problem

[nickagian]

I would like to measure experimentally the resonance frequency of an LC network. The L is 1mH with 0.3Ω losses and the C is 10μF, having resonance at around 1.5-1.6 kHz.

What I have done so far is the following:

(1) I provide a sinus from a function generator to the LC network
(2) Keeping constant the amplitude, I vary the frequency of the input sinus
(3) I then measure the voltage drop across the L (or the C) with an oscilloscope

or

(4) Alternatively I measure the current through the L (or the C) by using a multimeter.

However I cannot see neither the voltage nor the current increasing too much. Actually the voltage doesn't seem to have any difference (probably due to insufficient resolution of the oscilloscope??). The current is increased but by a really really small amount (some micro-amps).

Do I make some silly mistake that I cannot think of right now? I was thinking that maybe the function generator's output resistance (50Ω) is not proper for my experiment. Should I intervene some buffer between the generator and the circuit?

 

[crutschow]

The problem is that the series impedance of your components at the resonant frequency is only 10 ohms, thus the 50 ohm generator impedance is affecting your measurement.

You might try connecting the components in parallel rather than series. Since a parallel resonant circuit has a high impedance, it may be easier to see the resonant peak.

 

[Mr RB]

Maybe you could dump a decent current pulse into the LC network, and look on the 'scope for signs of ringing?

Or use a comparator oscillator that will oscillate at the natural freq of the LC, rather than injecting a fixed frequency.

 

[user_88]

... Along the lines of Mr RB's suggestion: devise a circuit to input a repetitive train of impulses ....
For practical implementation, the input signal would be a rectified square wave, positive only, with an extremely short duty cycle.
This type of excitation would hopefully generate a ringing signal response that would be visible on your oscilloscope.
,,, haven't actually tried this ... so there could be complications of some sort.