I want to thank everyone for the great information I got in response to my question about measuring AC.
One thing I hadn't thought about with my off-the-cuff idea of simply using a voltage divider is the issue of isolating the AC return and the circuit board return. Not isolating these raises a variety of issues that I'm not prepared to deal with. So, I think they need to be isolated. The method suggested by Jonathan Malton strikes me as a really elegant and highly accurate solution to the problem. This involves the use of a voltage controlled oscillator and an optoisolator. Using op-amps for rectifying diodes is also a great idea I think. The problem of providing a separate off-line power supply for the VCO, sort of takes some of the fun out of the idea, but this problem is, nevertheless manageable. I'm also going to review IEC950 and IEC1010 as suggested by Horst Haug. The basic problem with transformers is that it's not possible to get a specification on their accuracy. In talking to Signal Transformer, they give me a verbal specification of +/-2% accuracy (no load). Advanced Components Industries, OTH, provide a verbal specification of +/-10%. The difference might be in the size of the transformers. The Signal transformer is relatively large and relatively expensive. The Advanced Transformer is of the PCB type and is very small (0.6 inches high). The lady at Advanced seems to be very knowledgeable and says that the accuracy is not simply a function of turns ratio, but also depends on the wire and core construction. She claims that they can calculate transformer accuracy simply by looking at the wire and core specifications. Max mkel...@es.com
