Charles, A commend regarding your ZCD. You propose to use a dual 120V primary transformer to generate the isolated 120V AC needed by your circuit. Unless specifically designed for that purpose, the isolation between the two 120V primaries of a common transformer is probably not as good as the isolation between primary and secondary, which could be a safety hazard. Since small transformers with a 120V primary and a true 120V secondary are hard to find, a better way would be to use two "regular step-down" transformers back to back, like two door bell transformers: 120-24-120. You would then get double isolation.
Didier KO4BB On Sun, Dec 21, 2014 at 2:52 AM, Charles Steinmetz <csteinm...@yandex.com> wrote: > > Mike wrote: > > From a Time-Nut perspective, isn't phase/frequency of the (nominal) 60 Hz >> all we'd be interested in? Phase is best measured at a zero crossing as >> this is the (only) phase measurement point which is independent of >> amplitude. >> > > That is the primary interest (as I understand it -- I am not, myself, a > grid-nut), and the reason the "simple ZCD" circuit uses this approach. But > grid-nuts are also interested in perturbations of the grid voltage caused > by grid sections going offline and coming back, lightning strikes, etc., > etc. (After all, simply monitoring the ebb and flow of the line frequency > is about as interesting as watching the tide come in and go out, so they > naturally want some occasional excitement.) These anomalies can be > detected by their effect on the zero crossings of the mains voltage, so one > data collection serves both purposes at the time-nuts level. > > While the ZCD approach is ideal for monitoring the grid phase/frequency, > and as a bonus provides timing information about grid anomalies, it does > not capture all of the information about anomalies. If you are a utility > concerned about grid security or making sure that "new energy" sources play > nicely with the grid, you probably want more information about anomalies > than time-stamped zero crossings provide. Magnus described a system used > by utilities to track grid anomalies in greater detail. My reply agreed > that zero cross detection is not the tool of choice for utilities with such > concerns, and noted the different needs of grid-nuts and utilities. > > Grid-nuts are well established, and the vast majority of them use > time-stamped zero crossings as their data sets. I was concerned that many > grid-nuts seem to use non-isolated feeds from the mains that, while "safe > enough" under normal conditions, are not preferred practice. I also > thought that the timing relationship between the ZCD and the actual zero > cross could be improved and stabilized with a new ZCD. So, I designed the > "simple ZCD" circuit to provide an isolated source of very predictably > timed pulses with fast edges. I tested it and it proved to be reliable and > to have very stable timing with respect to the line zero crossings, so I > published it and announced it on-list with the first message in this thread. > > Since then, the thread has taken on a life of its own and ranged very far > from the initial, simple proposition of improved zero cross detection. > There has been a flurry of comments mostly aimed not at whether the "simple > ZCD" is a good AC mains zero cross detector, but more toward whether zero > crossings are what grid-nuts should be interested in in the first place. > Since I am not, myself, a grid-nut, I cannot really speak to what grid-nuts > "should" be interested in. I do think that time-stamped zero crossings > have many significant advantages when one is interested in comparing notes > with others, and it is comparatively easy data to collect with good > accuracy -- so, IMO, the choice of grid-nuts to settle on time-stamped zero > crossings was eminently rational. The "simple ZCD" has proven to be an > excellent front end for such a data collection, and is a project within the > skills of anyone who knows which end of a soldering iron to grip. I am > happy to answer any questions that potential builders may have. > > Personally, I think the thread has more than run its course and should be > laid to rest. But if it is to continue, please accept as a given that > grid-nuts decided long ago that time-stamped zero crossings are the > appropriate data to collect, and focus on the narrow topic of the "simple > ZCD" as a means for accurately detecting zero crossings of the AC mains. > > > Best regards, > > Charles > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.