Dear Shalik Ram Joshi,

If you connect sine out (reference signal) at the input of the scope, do you see the third harmonic on the scope? It should be there. Otherwise, a square wave with the same frequency as the reference signal is much richer ii harmonics. But, the third harmonic must be in the reference signal.

Then, since you use your scope, you could look at the waveform of the excitation voltage and possibly current - these should be sinewaves with the load disconnected and connected. These waveforms should also contain the 3rd harmonic, unless the excitation signal's amplitude is too low for the scope to detect it. After you'd roughly checked for the presence of this harmonic in the excitation voltage and current, if the output signal is strong enough you will definitely see this harmonic in the input signal. Then, you can connect the input signal to the LIA. It seems that the LIA can by itself analyze the components of the input signal. You can allways try these check steps with any resistor that would not burn out in case overcurrent.

I'm suspecting that your excitation signal may be to low,that your output signal may be too low or that there is an open in your circuit. My advice would be to first make all the measurements by bringing the input signal only at the input of the scope.

Dear Shalik,

If i understood you, you connected an ac source from the lock in amplifier to the your heater. You connected the voltage on the heater to an oscilloscope. When performing fft on the acquired signal by oscilloscope you found no peak. 

The starting point for the trouble shooting is to display the signal waveform in time domain. Please show us the the acquired signal waveform! After seeing this waveform one can judge about the fft shape.

Best wishes

Dear Shalik

It's almost certain too much current to drive from the LIA output. Even if you use 10V output drive the max output current is limited to 200 mA by the internal 50 ohm resistor. By reaching the driving to the limit you are basically either distortion seriously or destroying any signal that is comig out. An external voltage to current amplifier is highly recommended. Then if you do use a driver, you need to be sure that you are measuring the 3rd harmoic of your DUT and not the distortion from the amplifier itself. I suppose that you need to have a good idea on the dynamic range you are measuring e.g. how many db between the fundamental and the 3rd harmonic that you are trying to measure. Then you probably need to look at the whether the THD of the amplifier and even the LIA are much better than what you are trying to measure.

I also noticed that you are measuring at 100 Hz which is the 2nd harmonic of the 50 Hz supply (I think that's valid in Korea). You may indeed want to look at the FFT first without any driving signal to see if you have any supply noises at 100 Hz and 300 Hz even (although unlikely at 300 Hz).

Please contact me through ZI if you need more help.

Kind Regards

Hello.

I am new to MFLI, on reading this discussion I had a doubt. The doubt is, How can we make sqaure wave as output signal from MFLI? Like if I want to check the working of an inductor, is it possible to get the I-T plot?

Please explain me how I can use the instrument in this situation.