Thanks for all the feedback so far. You have softened some of my paranoia, but also raised some other issues I hadn't thought about -- in particular the fact that transformer response is frequency-dependent, and anything too far from the 60Hz a power transformer is meant to transmit will be attenuated -- i.e., spikes, dips, and switching noise. Right?
On Sun, May 27, 2007 at 01:31:31AM -0400, Darryl Gibson wrote: [...] > Without knowing what the application is, it's environment, signal > source, etc... it is difficult to make specific recommendations. [...] The application is a power analyzer to show me instantaneous and average true power, apparent power, power factor, RMS voltage, and line frequency, plus kWh accumulated over time. There are some great chips from Analog Devices now that integrate all this into one package with a digital output -- I just need to supply the current and voltage transducers. (I know you can get cheap devices like the "Kill-A-Watt" now to monitor plug loads, but I'm wanting to watch hard-wired appliances like HVAC, plus the actual main service for the whole house. And of course I want it to feed data straight to a PC and log it over time, which the Kill-A-Watt can't do.) The environment is a metal box in a garage, right next to the breaker panel. It will be cold in the winter and hot in the summer, but nothing that will seriously affect electronics, so long as my power supply is designed for it. Signal source will be CTs (current transformers -- donuts) put over the mains lines inside the breaker panel, plus whatever I settle on as voltage transducers. The voltage transducers will most likely sit outside the breaker panel, just plug into a regular three-prong outlet. I'm not sure how else I could do it without violating code in a big way. Well, if I use transformers, I could hard-wire them in, but I think I'd still be doing that outside the breaker panel. And yes, I will have a certified electrician to handle everything happening inside the breaker panel, like slipping the donuts over the mains lines. Of course, the "downside" of that is that he damned sure isn't going to violate code for me. So now I have to figure out if I really care about those >60Hz spikes, dips, and noise. I am thinking not, so transformers should be just fine. Then again, the reference designs for these Analog Devices chips just put a resistor divider between hot and neutral and feed it straight in without isolation. They use neutral as DC circuit ground and derive power from the hot line, so the whole circuit is tied to mains without isolation. If I did that, I would of course have to make sure that the digital interface between my measurement system and the PC that captures the data is isolated, which is pretty easy. Any thoughts on that setup? _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user