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Lock in amplifier

  1. Jul 9, 2009 #1
    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 dont 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.
  2. jcsd
  3. Jul 10, 2009 #2


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    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?
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