Help Me With Lock-in Amplifier for Third Harmonic Voltage Measurement

[appsci]

I need a help with lock in amplifier. I want to measure third-harmonic voltage from lock in amplifier. I have metal liner on a film on the substrate and I pass ac current through this metal liner which acts both as a heater and a thermometer. I want to calculate the third harmonic voltage from this. I have differential amplifier circuit where I eliminate the primary voltage component with the help of lock-in amp. I just don't know where to connect what.

Should I connect the BNC connector to the input of lock in amp, that subtracts the two voltage. Should I have to connect the cable in osc out or ref in.

 

[Redbelly98]

If I understand this circuit correctly, then:

"V1-V2" would be connected to the lock-in input. It's probably labeled "signal" or "input" or "signal in" or "V in"

You'll need to connect something to "ref in" on the lock-in, so that it has a reference frequency. Perhaps directly from the voltage generator, or you might use V2 for this. Be careful that voltages are not too high or too low for the lock-in -- do you have the manual? It would be good to check what voltage level is required for the reference, as well as how much voltage would damage the lock-in.

That being said, I have some questions to help me understand better what is going on:

What is the make and model of the lock-in?

Do you have the manual?

Does the lock-in have a "3rd harmonic" or "3f" mode?

In the circuit diagram, are a, b, c and d actual devices or circuit elements, or are they just labels for nodes in the circuit?

Are the BNC jacks on the differential amp grounded to the case?

Are either of the voltage supply outputs (+ or -) grounded?

 

[oswaler]

I would suggest seeking guidance from a knowledgeable colleague or consulting a detailed manual for your specific lock-in amplifier model. However, based on the information provided, here are some recommendations:

1. Connect the BNC connector from your differential amplifier circuit to the input of the lock-in amplifier. This will allow the lock-in amplifier to receive the signal from your experiment.

2. Connect the cable from the lock-in amplifier's output (osc out) to your data acquisition system or oscilloscope. This will allow you to view and record the third harmonic voltage measurement.

3. The reference input (ref in) of the lock-in amplifier can be used to improve the signal-to-noise ratio of your measurement. You can connect a signal generator or a reference signal from your experiment to this input.

4. Make sure to properly configure the settings on your lock-in amplifier, such as the frequency range and filter settings, to accurately measure the third harmonic voltage.

Overall, it is important to carefully read the lock-in amplifier's manual and understand its functions and settings to ensure accurate measurements. If you are still unsure, it is always best to consult with an expert or the manufacturer for further assistance.