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.
