Re: [time-nuts] DeLorme Tripmate GPS receiver
I peeled open the shield can without too much deformation, so it can be restored. I found that it's a single board, with the DSP on one side, and the RF section on the other. It is a Rockwell chipset, with 11577-11 DSP, and 6732-13 RF. On searching I found that this seems to be called their Jupiter GPS from circa late 1990s - I found quite a lot of info at the module level, but not for the actual ICs, like pinout data. The set includes all the usual GPS stuff including 1 PPS, and is capable of several levels of on-ness. So, if the uP that makes it a DeLorme merely sets some control lines to activate it, then I should be able to override them to force it always on - if I can figure them out. If instead the uP programs something internal to the DSP to control power states, then fuggetabout it - it will be junk. So, does anyone know of the Jupiter chipset, and where to find chip-level info for these parts? Ed ___ 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] LNA and Alias
Hi all, My phase noise measurements system give erroneous results in close in phase noise measurements, I got humps in the 1Hz-1000Hz area as high à 20 dB more than expected. The setup is using a mixer to compare reference and DUT witch drive an LNA http://www.ko4bb.com/~bruce/LowNoiseMixerPreamp.html , the output is driving an AD7760 ADC and an op amp circuity is connected to the VFC reference to achieve quadrature. The results are analyzed with an homebrew FFT charting software After struggling with different configurations, switched different LNA, ADC , sound card. A scope connected to the LNA output indicate steady 20MHz residuals just before the ADC ( around 10 mv peak-peak). In fact , it seems that the mixer 20Mhz residuals ( DUT + REF ) are entering the ADC and so theses alias give erroneous results in the 1Hz-100Hz area, displaying unexpected artifacts. In order to fix the problem I will probably include an analog filter just before the ADC input (same as LNA input 1nF 80µH), but I want to know if some more sophisticated measures should be undertaken as an 5th Order Lowpass Filter. I have not found many clue about alias problems in phase noise measurements literature so I may have missed something ? Any advice Loïc ___ 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.
Re: [time-nuts] Simple AC mains zero-cross detector
Chuck wrote: Transformers, such as are in wall warts, etc..., are wound in a way that is pretty good for 50Hz/60Hz operation, but have had nothing intentionally done to normalize operation at any other frequency. Nor have they had anything done to improve the fidelity of the signal they pass. I frequently recommend small 120:12v or 120:6.3v power transformers as 600 ohm line to voice coil transformers for audio applications. I have tested scores of them, and have yet to find one that is not flat from at least 20Hz to 15kHz -- often significantly better -- if operated at no more than 1/2 its rated 60Hz power. The distortion is typically < 1% at that power level. [I have not measured transformers from wall warts, but I expect that many if not most of them conform to the same general specs.] Typically, they are running very near the edge where the core is entering saturation, That depends on the current you are drawing. The ZCD circuit doesn't draw anywhere close to the transformer's rated current, so core saturation is no worry at all. Because of the nature of transformers, a transformer isolated ZCD will propagate every of the various frequencies it passes, with a different delay. The transformer's group delay is not an issue at the 1uS level. However, the input filter I specified has non-constant group delay, which varies about 40uS from 10Hz to 600Hz (the range of frequencies where I observed significant components of grid transients). So, there is a tradeoff. If accurate timing of transients is more important than some spurious noise responses, the ZCD should be built without the filter capacitors (C1 and C5 on the schematic), as noted in the description. In that case, the group delay is within 1uS for all frequencies above ~10Hz. Note that this also applies to any other detector, including those using optoisolators -- any input filtering will create non-constant group delay. 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.
Re: [time-nuts] Simple AC mains zero-cross detector
Ed wrote: It seems to me that a low voltage secondary should be OK by using a fast comparator IC rather than a transistor to decide - the gain of the IC allows for much smaller detection levels, so the equivalent zero-crossing velocity could be the same. An IC tripping in a 10 mV band should provide the same effective ZC velocity at 12 V input as a transistor working around 100 mV with 120 V input. Or am I missing something? When the switching band gets that small, device noise, input offset voltage drift, and other errors have a proportionally greater effect. I actually built a similar circuit with a 12v transformer and an LT1720 comparator, and it had worse jitter than the two-transistor circuit with a 120v feed. In this case, there is no substitute for starting with a higher-slew-rate signal. (Yes, the LT1720 did marginally better than the two-transistor circuit when both were fed from 120v -- but the fussiness of working with a fast comparator and the small gain over the two-transistor circuit made the latter the better choice, particularly in a design being put "out there" for others to build.) 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.
Re: [time-nuts] Did a member of time-nuts buy this?
Mike, That was a nice set of homework reading you provided for us. People might have missed it. Cheers, Magnus I have a few Rubidiums and OCXOs I'd like to get running for a month or so to stabilize. During this time, I'd like to monitor the performance to discover any bad units and see which are the best ones. For example, TVB shows a 100:1 variation in ADEV in FE-405B Rubidiums. The section is titled "Variation in FE-405B" in http://leapsecond.com/pages/fe405/ Clearly, it would be futile to try to use a bad unit in setting up a gpsdo. I need some means of measuring the performance of these units while they are running. A dozen HP5370's would be out of the question. I did some research to find the different methods available and decide which has the lowest per-channel cost and best performance. Here are some of the references I found. I discarded most of the poor ones and tried to keep only the ones that talk about measurements in the picosecond or femtosecond range. I did not include DMTD since the concept is so simple. The Reviews help to get oriented, but sometimes it takes reading the papers and the patents to see the timing diagrams and understand what the author is trying to do. There are many different variations on the FPGA approach. I would be concerned about the development time, the large DNL, and the problems with crosstalk on multi-channel units. The TI THS788 looks good on paper, but it is single-source, not well stocked, and there is lttle information on crosstalk between channels. It is also quite expensive per channel. There are no application notes and little or no information on usage on the web. The Thesis generally have excellent reviews worth reading. Articles Simple PICTIC 250ps time interval counter http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:pictic Griffiths Time to Digital converters http://www.ko4bb.com/~bruce/TDC.html [time-nuts] Experience with THS788 from TI?- Attila Kinali's post on TDC methods https://www.febo.com/pipermail/time-nuts/2012-March/065337.html Reviews Review of methods for time interval measurements with picosecond resolution http://ztc.wel.wat.edu.pl/met4_1_004.pdf Low resource FPGA-based 32 Channel Time to Digital Converter - Excellent review of TDC techniques and measurement verification http://arxiv.org/vc/arxiv/papers/1206/1206.0679v3.pdf Design, construction and tests of a high resolution, high dynamic range Time to Digital Converter - Excellent review of TDC methods and test techniques http://inspirehep.net/record/1313667/files/getfile.pdf Review Of Sub-Nanosecond Time-Interval Measurements http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-pub-1331.pdf Chapter 1 Time Interval Measurement Literature Review http://www.rrsg.ee.uct.ac.za/members/jon/activities/timcs.pdf Time intervals measurements and generation methods review http://www.ohwr.org/attachments/128/Time_Interval_Measurements_Techniques.pdf Papers A Cyclic CMOS Time-to-Digital Converter With Deep Sub-nanosecond Resolution http://ntur.lib.ntu.edu.tw/bitstream/246246/2007041910021548/1/00777354.pdf A 96-Channel FPGA-based Time-to-Digital Converter http://arxiv.org/pdf/physics/0502062.pdf Complete and Compact 32-Channel System for Time-Correlated Single-Photon Counting Measurements http://ieeexplore.ieee.org/ielx7/4563994/6588410/06617673.pdf?arnumber=6617673 Design and Development of GPS Receiver for PNSS-1 http://www.suparco.gov.pk/pages/presentations-pdf/day-1/session-2/12C-II/1.pdf A Novel Ultra-fast High Resolution Time-domain EMI Measurement System based on Field Programmable Gate Arrays https://mediatum.ub.tum.de/doc/1163324/1163324.pdf High Precision Frequency Measurement System Based on Different Frequency Phase Processing (in Chinese) http://xbzrb.tjujournals.com/oa/pdfdow.aspx?Type=pdf&FileName=11acd53a-876d-4ab0-8906-572aa3836215.pdf A 51-dB SNDR DCO-Based TDC Using Two-Stage Second-Order Noise Shaping http://www28.cs.kobe-u.ac.jp/pdf/1205_konishi_iscas.pdf Integrated High-Resolution Multi-Channel Time-to-Digital Converters (TDCs) for PET Imaging - Discusses 100 fs Gated-ring-oscillator (GRO) http://cdn.intechopen.com/pdfs-wm/12913.pdf A 26 ps RMS time-to-digital converter core for Spartan-6 FPGAs http://arxiv.org/pdf/1303.6840v1.pdf A High-Resolution Flash Time-to-Digital Converter Taking Into Account Process Variability http://conferences.computer.org/async2007/PRS/15-minas-async07.pdf Principles and Instrumentation in Time-of-flight Mass Spectrometry http://www.wiley.com/legacy/wileychi/ms/articles/1519_a.pdf TEMPERATURE SENSING CRYSTAL HTS-206 - maybe more stable than thermistor http://www.abcelectronique.fr/composants/telechargement_datasheet.php?id=385911&part-number=HTS-206 A novel method of measurement of time and amplitude of analog signals based solely on FPGA units http://koza.if.uj.edu.pl/pet-symposium-2013/talks/17.pdf A 16 channel high resolution (<11 ps RMS) Time-to-Digital Converter in a Field Programmable Gate Arra
[time-nuts] New NTP client software (preview) released
I have just put the first preview release of my new NTP client software up on github. https://github.com/bsdphk/Ntimed You can read more about it here: http://phk.freebsd.dk/time/ We'll see where it goes from there... -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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.
Re: [time-nuts] Simple AC mains zero-cross detector
Didier wrote: 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. The transformer I used is a dual C core "pseudo-toroid" -- it has one primary and one secondary winding on one bobbin and the other primary and secondary winding on the other bobbin (on the opposite side of the core). The primary-to-primary isolation of any transformer wound this way should actually be better than its primary-to-secondary isolation. Of course, not all small power transformers are built this way. However, the primary-to-primary isolation of any small commercial power transformer should be sufficient not to cause any safety problems in the ZCD application. Hipot ratings are regulated by standards and are generally greater than 1500v from any winding to any other winding, and even if there were an effective interwinding capacitance of 200pF between primary windings, the 60Hz current in the ZCD ground would be no more than single-digit uA at a maximum. (By comparison, ground-fault interruptors trip at 4-6mA -- 1000 times greater than this.) The actual effective primary-to-primary capacitance is likely to be very much less than 200pF, and the capacitive leakage current from the 120v to 120v isolation windings should be comparable to the capacitive leakage from the Vcc supply. All that said, there is certainly nothing wrong with using two transformers "back to back," as you suggest, to improve isolation. It is also how anyone in a 200 or 240v country would generate isolated 120v: 240:12 ==> 24:240. 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.
Re: [time-nuts] Simple AC mains zero-cross detector
It seems to me that a low voltage secondary should be OK by using a fast comparator IC rather than a transistor to decide - the gain of the IC allows for much smaller detection levels, so the equivalent zero-crossing velocity could be the same. An IC tripping in a 10 mV band should provide the same effective ZC velocity at 12 V input as a transistor working around 100 mV with 120 V input. Or am I missing something? Ed ___ 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.
Re: [time-nuts] Simple AC mains zero-cross detector
Hi Charles, I have a question about the accuracy of your scheme, given transient effects. Transformers, such as are in wall warts, etc..., are wound in a way that is pretty good for 50Hz/60Hz operation, but have had nothing intentionally done to normalize operation at any other frequency. Nor have they had anything done to improve the fidelity of the signal they pass. Typically, they are running very near the edge where the core is entering saturation, not because it is a good thing, but rather because it minimizes the amount of copper and iron, and the physical size necessary, for a given amount of power output The trade off being efficiency... a little more heat is generated, and that is the customer's problem to deal with, not the manufacturer's... but I digress. In the 99 and 44/100 th's percent of the usage of a transformer coupled ZCD, the positive and negative zero crossings are going to come chugging along predictably about every 8.3 milliseconds. And, the degree which their arrival is unpredictably 8.... milliseconds, is what I believe to be the the realm of the grid-nut. One facet of that unpredictability is what I am interested in, for the purposes of this post: Suppose, that one of the grid-nut persuasion is interested in the timing of the occasional crash transient where somewhere during the course of a cycle, an unintentional zero crossing occurs due to a transient that drags the grid voltage through ground. With an opto isolator protected ZCD, the transient will be propagated to the logic side by way of the usual speed of light, and will remain true to the fixed delay introduced by the optoisolator ZCD... The optoisolated ZCD has no ability to affect where the crossings occur, or for the most part, how often the crossings occur; it will faithfully register and send the glitch along to the logic side for measurement. A transformer isolated ZCD, is different in this regard, however. Because of the nature of transformers, a transformer isolated ZCD will propagate every of the various frequencies it passes, with a different delay. What this means, is that as long as the zero crossings keep chugging along at a nominally 60Hz rate, you will have your touted sub-microsecond timing accuracy; but, introduce one crash transient that causes a significantly early zero crossing, and you will be introducing frequency components other than 60Hz, and will cause the crash transient's time-of-occurrence to be misrepresented, and will also cause the subsequent zero crossing's time-of-occurrence to be misrepresented... all due to the transformer's inability to induce all frequencies with the same speed. This same uncertainty will occur even if the so called crash transient does not pull the sine wave all the way to zero, but only wounds it a little. Thoughts? -Chuck Harris ___ 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.
Re: [time-nuts] DeLorme Tripmate GPS receiver
I opened it up and found a 4 by AA cell battery holder for power, and a single module that looks pretty proprietary. One side of the module has a patch antenna, and the other has the brain. I assume there's an RF board in between, but cannot open it further without possible damage - the shielding can is soldered at the edges of the brain board. Ed ___ 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.
Re: [time-nuts] Simple AC mains zero-cross detector
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 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.
Re: [time-nuts] Homebrew frequency counter, new board test result
Li ang, Bob, On 12/20/2014 06:22 PM, Bob Camp wrote: Hi On Dec 20, 2014, at 10:28 AM, Li Ang wrote: 4) add 74ALV2G14 since FPGA does not support schmitt input I would suggest trying it with a non-schmitt trigger part as well. It should be a simple swap out since it’s a leaded part. In some cases the trigger level hysteresis is not helpful. The better over voltage immunity of the leaded parts compared to the FPGA inputs *is* a good idea. They also are a lot easier to swap out if you blow one out accidentally. I have been able to get much lower noise by using a sine to square shaper. I have modified my TADD-2 to output the shaped clock. For better counters, the difference is noticeable. You want such an amplifyinng stage prior to the schmitt-trigger to gain yourself out of the slew-rate limit. test instruments 1) HP6622A as power supply 2) FE5650 rb as reference 3) PRS10 rb as DUT I would toss an OCXO or two into the mix eventually. I concur. ——— It looks like the three “4 layer FPGA” plots all cluster tightly at just under 2x10^-10 at 1 second as long as linear regression is turned off. That’s pretty good performance. I *think* I’m seeing that correctly on the plots. If I’m not, let me know. The two plots with linear regression are still a bit “interesting”: The plot with ref and DUT the same ( green) still is showing data that is in the “to good to be true” range. The averaging process of the linear regression is probably still causing this. If the filtering of the regression spans a significant part of the tau (or beyond it) I don't trust the numbers for that part of the slope without the pre-filter bandwidth is noted. I would like to see the MDEV variants of these plots. The plot with ref and DUT not the same (RED) shows some sort of spur. That could indeed be a spur from one or the other of the Rb’s. It also could be something in your lab. Turning out the light is a good thing to check. Because of the low frequency, I would suspect a spur on the Rb. Put another way, the counter is not making a mistake in this case. It’s reporting what is actually going on with the inputs. Another test source (or pair of sources) would help sort this out. There can a reason to see if there is something modulating into the trigger point, which is the danger with schmitt-trigger inputs. Something else to look at: Check your results vs input level. In other words, attenuate one of the input signals and see what happens. I would start with 3 or 6 db and go from there. The attenuation does not have to be precise. The frequencies involved are not high enough to require fancy parts. The idea is to check if the input noise level of the gates is a problem for you. If the data quickly get worse as you attenuate, they need some help. If damping the signal causes a sizeable increase in amplitude, you most likely have a slew-rate problem on the input. If you damp your signal by 6 dB and get 6 dB higher noise, then you definitively have slew-rate/amplitude problems. Cheers, Magnus ___ 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] Lucent KS-24361; resolution TI 10 ns only?
i noticed that the resolution of the PPS TI relative to GPS is 10 ns. is there a scpi command to get a better resolution? a few trivial observations: my boxes have been up and running for a few days only, but they seem to behave pretty well. however, a few things kept me busy for a while: i plugged the data cable into the diagnostic port of unit 0 because it is the one that is on, while unit 1 is in stand-by mode. new values for the cable delay, the elevation mask and the position were accepted and could be queried, but they were not visible on the status screen and had no effect (e.g. sats below the new angle were still used). only when i plugged the cable into the diagnostic port of unit 1 (in stand-by) the new values were accepted, displayed, and used. i find this behaviour rather strange... communication can be speeded up a bit by selecting 19200 baud instead of the default 9600 baud. i prefer UTC time displayed over GPS time. while it was possible to switch to UTC time, it was not displayed in the status window. it was necessary to power cycle (!) the units to see UTC time. the units work nicely with GPSCon, even on my mac with CrossOver. without all the information available on this list (and in the 58503 manual) i would never have been able to bring these boxes to life. many thanks to the list! hans ___ 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.
Re: [time-nuts] Simple AC mains zero-cross detector
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.
