# Help function generator...

#### JonnyP

Joined Mar 6, 2013
4
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:

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.

[]´s
João Rocha – UFRJ - Brazil

#### Ron H

Joined Apr 14, 2005
7,014
What is the inductance?

#### JonnyP

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

#### MrChips

Joined Oct 2, 2009
23,560
You need a power amplifier, something like an LM675.