Voltage amplifier (15mV signal on 120VAC offset) for shunt resistor/current sensing

[J_Sieg]

Hi,
I'm looking to create a simple circuit to convert current on a nominal 120VAC line into a voltage. I have a few designs but am having some difficulty keeping parts count low and maintaining accuracy.

What I have is as follows:
- I am using a shunt resistor, outputting 1mV per ampere of current (0-15mV total).
- I take the output from the shunt resistor (120VAC +/- 15mV) and use it as an input for two op-amps (running single supply [+3V] differential amplification).
- From the op-amps, I take the output and make it positive only via some diodes, then through a filtering capacitor.
- This gives me a voltage proportional to the current, or should..

The problems I am having have to deal with two things...
First is parts count. That is a hugely inefficient way to do things, having two entire amplification circuits, even with a dual op amp. I am wondering if there is a way to do this with a single amp.
Second, pin voltage is exceeded, as even though the voltage differential is 15mV max, it is on a 120V offset.

Do any of you have ideas on how to simplify this circuit? Op amps that might handle 120V on a pin, preferably at a low cost? That also take monopolar power? I tried a voltage divider, but if I divide the offset, I also divide the signal and lower my read resolution.

Thanks!

[Averagesupernova]

Two words: Current Transformer.

[J_Sieg]

That would be nice, and non-contact, too...
But how could I get 3V for 15A? What is the inductance of the primary wire? Orientation of the other coil? How do I calibrate it?

edit: forgot to specify, it would be ideal if this was non-disruptive (ie, could be installed as either a pass-through device or purely inductive, with no need for circuit disconnection/disassembly to install the unit).

[berkeman]

You can just use a current clamp meter or probe on one of the AC mains wires (hot or neutral):

http://us.fluke.com/usen/products/Fluke+330.htm

Or you can make your own current transformer with a core secondary windings, and an amplifier. See the links at the bottom of this wikipedia page:

http://en.wikipedia.org/wiki/Current_transformer

[MATLABdude]

Depending on how much current you're trying to measure, maybe a Hall Effect sensor? CUI makes some (sold at DigiKey), but it starts around 3A:
http://www.cui.com/srchresults.asp?catky=560054&subcatky=731029&subcatky2=825892

But if you only want to take one or two-off measurements (and you're not, say, designing instrumentation or making a long-term current monitor / logger), buy yourself a current clamp as berkeman suggests. Aside from Fluke, Extech and Meterman make more affordable (yet high-quality) clamps. If you want to splurge, get the ones that do AC AND DC current measurement (the cheaper ones only do AC--which might be all you need).