Help function generator...

Discussion in 'The Projects Forum' started by JonnyP, Mar 7, 2013.

  1. JonnyP

    Thread Starter New Member

    Mar 6, 2013
    4
    0
    I need some function generator help in AC bridge circuit.

    First of all sorry for any English mistake, as it is not my native language.

    First post here and I expect not to be the last. Just found this forum in google.

    Just some background… I work as a researcher in a laboratory at my University. My main focus application in eddy current testing (http://en.wikipedia.org/wiki/Eddy-current_testing).

    So let´s go. The main focus of eddy current testing is using coils interacting with conductive materials to measure a variation of characteristics of those materials. I am using an AC bridge circuit to measure difference of two identical coils as can be seen below:

    [​IMG]

    Everything is going well except that when I connect the AC generator to the bridge circuit (the coils have ~50ohm and I used another 50ohm resistor and a trimpot to balance the bridge) I see that the voltage amplitude of the sine wave drops. So I am supposing that the circuit is draining more current than the AC generator can supply, which can damage the equipment (I´ll post all my assumption, to show all my steps, please correct If I am wrong at any part!).

    So I made a non-inverting buffer using a LM324, which works well while disconnect from the bridge, but when I use the output of the buffer to feed the bridge the sine wave become all fuzzy. And now I am stuck at this point… I need a circuit that feeds the bridge without damaging the AC generator. Can you help me?

    Just some more data:
    - Frequency of the sine wave: 5-30 kHz
    - Amplitude of the sine wave: 4 volts peak-to-peak.

    Thanks in advance!

    []´s
    João Rocha – UFRJ - Brazil
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    What is the inductance?
     
  3. JonnyP

    Thread Starter New Member

    Mar 6, 2013
    4
    0
    It is about 6mH each coil.
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,447
    3,362
    You need a power amplifier, something like an LM675.
     
  5. JonnyP

    Thread Starter New Member

    Mar 6, 2013
    4
    0
    Thank you! With this chip the only modification that I must do is not to use as buffer, but decrease the amplitude of the input signal and have a gain of 10 or more in the op amp, right?
     
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