Re: [time-nuts] Simple AC mains zero-cross detector
On Thu, 18 Dec 2014 01:26:06 -0500 Charles Steinmetz csteinm...@yandex.com wrote: There has been some lively debate about how much filtering (if any) is acceptable here. On the one hand, the AC line is a very noisy source at frequencies above the fundamental, while the fundamental frequency is determined mainly by massive rotating machinery that cannot change frequency very quickly. On the other hand, if you pass the signal through a narrow filter you could miss the glitches that interest the folks who collect such data (grid switching transients, lightning strikes, etc.), or they could be delayed and smeared out in time so determining when they occurred would be problematic. The filtering in the circuit I posted (two-pole RC lowpass with a -3dB frequency of ~475 Hz) is a good compromise. It filters out the worst of the locally-generated hash without masking grid events. For those who want their data raw, the filter can be omitted as noted in the description sheet that accompanies the schematic. (You did download and read the material before posting about it, right?) Of course I looked at the schematic. It is a very basic cascade of single pole RC filters with components separated by a factor of 10 to prevent component interaction. Not much of a filter and the corner is probably a bit soft considering the load impedance is not infinite, but rather a switch. Why not use a lower voltage transformer, preferably not at a lethal voltage. You only need a couple of volts to drive the rest of the circuit. If you are going to look at glitches, that should be done by sampling the AC (transformer coupled obviously). Basically the circuit to detect period is dedicated to that function. Since the frequency won't vary significantly, a high order filter wouldn't be an issue, as long as you don't care about delay. ___ 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
Gary n...@lazygranch.com wrote: Zero crossing and frequency measurement are not the same thing. Generally you zero cross detect to switch a load with the minimum glitch. For frequency measurement, I'd filter the signal before counting it. Grid-nuts are interested in *both* the instantaneous frequency of the grid and also the transients indicative of grid events (grid switching transients, lightning strikes, etc.). So, a data collection system for grid-nuts must capture data sufficient to determine both the instantaneous grid frequency and the time-of-occurrence of grid events. If you time stamp the zero crossings, you have all of the information you need to compute frequency with any desired windowing, filtering, or averaging function you desire (and much more). So, yes, they are the same thing when the thing is frequency measurement, but ZCD gives you the freedom to set the filtering parameters in post-processing rather than at hardware design time. Of course, in addition to whatever windowing/filtering/averaging algorithm you may apply in post-processing, you can also filter the signal at the data collection stage. This can improve the accuracy of frequency determinations where little post-processing averaging is done (what a time-nut would think of as low-tau measurements). There has been some lively debate about how much filtering (if any) is acceptable here. On the one hand, the AC line is a very noisy source at frequencies above the fundamental, while the fundamental frequency is determined mainly by massive rotating machinery that cannot change frequency very quickly. On the other hand, if you pass the signal through a narrow filter you could miss the glitches that interest the folks who collect such data (grid switching transients, lightning strikes, etc.), or they could be delayed and smeared out in time so determining when they occurred would be problematic. The filtering in the circuit I posted (two-pole RC lowpass with a -3dB frequency of ~475 Hz) is a good compromise. It filters out the worst of the locally-generated hash without masking grid events. For those who want their data raw, the filter can be omitted as noted in the description sheet that accompanies the schematic. (You did download and read the material before posting about it, right?) 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] STEL-1173/CM Source
Hello! On 18/12/2014 5:37, Magnus Danielson wrote: Ed, On 11/15/2014 04:38 PM, Ed Palmer wrote: Yes, I'm sure. I did check the cabling. :) If I was somehow measuring the Tbolt or 4065A against itself, there wouldn't be any frequency offset. The Oscilloquartz 3210 (which appears to be an OEM'd 4065A) is spec'ed at 3E-13 @ 100K seconds. The 4065C is even better at 8.5E-14 with a noise floor of 5E-14. My OSA 3210 is not the same core as 4065A. The Oscilloquartz that has the same core as the 4065A is the 3120 (EUDICS 3120 they call...), not 3210. I'm now doing a comparison of a Lucent KS-24361 against it, and have not yet enough data for 100K seconds although it is showing an ADEV there around 3e-13. Regards, Javier ___ 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] STEL-1173/CM Source
On 12/18/2014 11:00 AM, Magnus Danielson wrote: Ed, On 11/15/2014 04:38 PM, Ed Palmer wrote: Yes, I'm sure. I did check the cabling. If I was somehow measuring the Tbolt or 4065A against itself, there wouldn't be any frequency offset. The Oscilloquartz 3210 (which appears to be an OEM'd 4065A) is spec'ed at 3E-13 @ 100K seconds. The 4065C is even better at 8.5E-14 with a noise floor of 5E-14. My OSA 3210 is not the same core as 4065A. Looks like I had a dyslexic moment! It turns out that Oscilloquartz produced both 3120 and 3210 Cesium standards. No confusion there! The 3120 appears to be an OEM'd 4065A or, to be specific, the core module is. The core is then wrapped with an Oscilloquartz power supply, buffers, communications and monitoring system. The 4065A appears to be the same core with a Datum/FTS wrapper. My data run is continuing. The end of the graph is flopping around as usual, but it's now showing Total Deviation of about 1.4E-13 @ 100K seconds with a total of 226 800 readings at 1 second intervals. Frequency offset error is still 6E-13. Autocorrelation of the results shows diurnal spikes at approximately 86 160 and 172 310 seconds (i.e. one and two sidereal days). Most likely thermal sensitivity. Got myself some STEL 1173 in PLCC 44 from that source. Thanks for sharing link! You're welcome. Glad I could help. 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] The future of atomic clock - short video from the NPL (UK)
This short video may be of interest: https://www.youtube.com/watch?feature=player_detailpagev=r8Y53QOm_3s ET reporter Tereza Pultarova has visited the ‘guardians of time’ at the National Physical Laboratory to learn how to make future atomic clocks more precise and fit them into hand held devices. Talking to Professor Patrick Gill at the exact same place which redefined the conception of precise time six decades ago, we’ve learned the world may be close to another giant leap in precise time keeping. And let’s not forget to mention the newly launched Quantum Metrology Institute that will help push quantum tech from lab to market. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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
Gary n...@lazygranch.com wrote: Why not use a lower voltage transformer, preferably not at a lethal voltage. You only need a couple of volts to drive the rest of the circuit. As you can see from the schematic, the voltage is diode-clamped almost immediately to ~ +/- 1.5v. The reason for using a 120v winding is to take advantage of the free slope enhancement provided by the higher voltage. The 120v winding provides a signal with a zero-cross slew rate of ~65mV/uS. A 12v winding would slew only ~6.5mV/uS. The faster the slew rate, the more accurately one can locate the zero crossings. If you are going to look at glitches, that should be done by sampling the AC (transformer coupled obviously). Basically the circuit to detect period is dedicated to that function. Since the frequency won't vary significantly, a high order filter wouldn't be an issue, as long as you don't care about delay. You are suggesting two separate data collections, one geared toward grid frequency and one geared toward glitch detection. That's fine, and might be preferable if it provided better results than using just one data collection. But using a higher-order hardware filter does not provide better frequency determination than post-processing the ZCD data. The circuit presented allows one data collection to do both functions well. It has enough filtering to prevent local interference from corrupting the data, it can locate 60Hz zero crossings to within 1uS (i.e., frequency resolution significantly better than 0.01 Hz, single-shot, which can be filtered/averaged to get whatever resolution you want in post-processing), and it can locate transient events to within 1uS. Win-win. 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
I actually needed to do real ZCD for thyristor switching off incredibly noisy bad AC suppplies used down mines in third world countries. I used a digital PLL to lock to the AC line volts waveform with a simple detector with a threshold of 50V set by a zener driving an opto. I think the loop time constant was set very slow, several seconds as the AC came from a gererator so very slow to change as you have the inertia of the massive armature in the generator. Logging this over several days on the mains network showed it slowing slightly during the day and then speeding up at night to give the right number of cycles per day. It was insensitive to voltage. We did find that isolating the zener opto via a transformer gave a temperature dependant phase shift, exactly what you don't want for switching thyristors. Tom Harris celephi...@gmail.com On 19 December 2014 at 08:16, Charles Steinmetz csteinm...@yandex.com wrote: Gary n...@lazygranch.com wrote: Why not use a lower voltage transformer, preferably not at a lethal voltage. You only need a couple of volts to drive the rest of the circuit. As you can see from the schematic, the voltage is diode-clamped almost immediately to ~ +/- 1.5v. The reason for using a 120v winding is to take advantage of the free slope enhancement provided by the higher voltage. The 120v winding provides a signal with a zero-cross slew rate of ~65mV/uS. A 12v winding would slew only ~6.5mV/uS. The faster the slew rate, the more accurately one can locate the zero crossings. If you are going to look at glitches, that should be done by sampling the AC (transformer coupled obviously). Basically the circuit to detect period is dedicated to that function. Since the frequency won't vary significantly, a high order filter wouldn't be an issue, as long as you don't care about delay. You are suggesting two separate data collections, one geared toward grid frequency and one geared toward glitch detection. That's fine, and might be preferable if it provided better results than using just one data collection. But using a higher-order hardware filter does not provide better frequency determination than post-processing the ZCD data. The circuit presented allows one data collection to do both functions well. It has enough filtering to prevent local interference from corrupting the data, it can locate 60Hz zero crossings to within 1uS (i.e., frequency resolution significantly better than 0.01 Hz, single-shot, which can be filtered/averaged to get whatever resolution you want in post-processing), and it can locate transient events to within 1uS. Win-win. 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] Simple AC mains zero-cross detector
Gary n...@lazygranch.com wrote: Why not use a lower voltage transformer, preferably not at a lethal voltage. You only need a couple of volts to drive the rest of the circuit. As you can see from the schematic, the voltage is diode-clamped almost immediately to ~ +/- 1.5v. The reason for using a 120v winding is to take advantage of the free slope enhancement provided by the higher voltage. The 120v winding provides a signal with a zero-cross slew rate of ~65mV/uS. A 12v winding would slew only ~6.5mV/uS. The faster the slew rate, the more accurately one can locate the zero crossings. If you are going to look at glitches, that should be done by sampling the AC (transformer coupled obviously). Basically the circuit to detect period is dedicated to that function. Since the frequency won't vary significantly, a high order filter wouldn't be an issue, as long as you don't care about delay. You are suggesting two separate data collections, one geared toward grid frequency and one geared toward glitch detection. That's fine, and might be preferable if it provided better results than using just one data collection. But using a higher-order hardware filter does not provide better frequency determination than post-processing the ZCD data. The circuit presented allows one data collection to do both functions well. It has enough filtering to prevent local interference from corrupting the data, it can locate 60Hz zero crossings to within 1uS (i.e., frequency resolution significantly better than 0.01 Hz, single-shot, which can be filtered/averaged to get whatever resolution you want in post-processing), and it can locate transient events to within 1uS. Win-win. 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
csteinm...@yandex.com said: The circuit presented allows one data collection to do both functions well. It has enough filtering to prevent local interference from corrupting the data, it can locate 60Hz zero crossings to within 1uS (i.e., frequency resolution significantly better than 0.01 Hz, single-shot, which can be filtered/averaged to get whatever resolution you want in post-processing), and it can locate transient events to within 1uS. Win-win. What sort of interference do you see? What does an interesting transient event look like? If you are going to post-process the data anyway, why not collect raw data and let the post-processing take care of the local interference? That lets you defer decisions about the appropriate filtering. Is there any database of events that I can check when I see something interesting? Or turn things around and pick an event and see what it looks like when it gets here? I've been collecting frequency data for my local power line. I grab the PPS style time stamps and counts from a modem control pin every 10 seconds. No filtering, just a transformer. I occasionally get an extra count. It's pretty obvious when you look at the graphs. They happen ballpark of once a month. A while ago, I was trying to capture the audio too, so I could look at the area around the extra counts. I never got anything clean. I think that setup had grounding problems. Maybe it's time to try again. -- These are my opinions. I hate spam. ___ 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] Choke Rings and Points North
Hi Here is some actual RF data on a number of antennas: http://www.ngs.noaa.gov/ANTCAL/ There also is a pretty good document on how the calibration is performed. It appears that if you are after ps or mm then a calibration file on the antenna type being used is needed. Pointing north to be able to use that file would be a requirement. If we ever get into the sub ns world for Time Nuts time transfer, calibrated antennas may be needed. *IF* an uncalibrated antenna is much worse than the survey antennas, then you might get into the couple of ns level as the sat’s moved around. Still not a real big deal for a GPSDO. Un-corrrected ionosphere issues versus angle will be a larger issue. Bob hOn Dec 17, 2014, at 8:49 AM, Jim Lux jim...@earthlink.net wrote: On 12/17/14, 4:36 AM, Bob Camp wrote: HI On Dec 17, 2014, at 1:07 AM, Chuck Harris cfhar...@erols.com wrote: I would venture that the extent of the magic was to note the physical center of the array, and call that the phase center. As long as you always orient the antenna in the same direction, any errors that might exist in the real phase center will be consistent, and could be corrected for by noting the offset from a benchmark. I’m afraid that’s what they do as well. Just spin it and see what a dial indicator reads sort of thing. I think that I’d want something that actually did some microwave tests …. B The UNAVCO data is an actual RF test. And from a manufacturing standpoint, I would imagine that typical tolerances are better than 0.001 (25.4 microns). Changes much bigger than that would show up as VSWR changes, which *is* something that they check in manufacturing. The Leica artichoke multiband choke ziggurats (they're not flat, so I have a hard time calling it a ring) are cast and then machined. Casting isn't what I would think is a precision operation, but it probably is real consistent from unit to unit. ___ 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] Simple AC mains zero-cross detector
There is an interesting article in the Nov/Dec issue of Inside GNSS describing the robust measurement of ...voltage and current phasors at widely dispersed locations in a power grid. A Phase Measurement Unit measures and time stamps the voltage and current phasors ...thousands of times per second... to an accuracy of 1 us using GPS. The authors discuss several strategies for dealing with jamming and spoofing of the civil GPS signals. It's a good read. See http://www.insidegnss.com/node/4281 Mike -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Hal Murray Sent: Wednesday, December 17, 2014 3:28 AM To: Discussion of precise time and frequency measurement Cc: hmur...@megapathdsl.net Subject: Re: [time-nuts] Simple AC mains zero-cross detector csteinm...@yandex.com said: That one is not ideal for this task, because (i) its output pulse is symmetrical about the mains zero cross, and (ii) the hysteresis zone is not well characterized and will drift with temperature and input voltage. So, there is no edge that is well characterized in relation to the AC mains zero cross. What are you going to do with data from the line accurate to 1 microsecond? -- These are my opinions. I hate spam. ___ 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] Simple AC mains zero-cross detector
Hi Using GPS timing for power network analysis and control dates back into the 1980’s. The guys at Quebec Hydro set up the first system I’m aware of. They had tried it with Loran-C before, but the noise in the vicinity of a major power station made that impossible. GPS being microwave helped them a lot with that part of it. They did a paper at FCS(?) on the results. Back then being able to actually get very accurate phase data over a 100’s of mile range was a pretty novel thing. Using GPS timing for this actually pre-dates the whole CDMA / GPSDO thing. Bob On Dec 18, 2014, at 5:59 PM, Mike Garvey r3m...@verizon.net wrote: There is an interesting article in the Nov/Dec issue of Inside GNSS describing the robust measurement of ...voltage and current phasors at widely dispersed locations in a power grid. A Phase Measurement Unit measures and time stamps the voltage and current phasors ...thousands of times per second... to an accuracy of 1 us using GPS. The authors discuss several strategies for dealing with jamming and spoofing of the civil GPS signals. It's a good read. See http://www.insidegnss.com/node/4281 Mike -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Hal Murray Sent: Wednesday, December 17, 2014 3:28 AM To: Discussion of precise time and frequency measurement Cc: hmur...@megapathdsl.net Subject: Re: [time-nuts] Simple AC mains zero-cross detector csteinm...@yandex.com said: That one is not ideal for this task, because (i) its output pulse is symmetrical about the mains zero cross, and (ii) the hysteresis zone is not well characterized and will drift with temperature and input voltage. So, there is no edge that is well characterized in relation to the AC mains zero cross. What are you going to do with data from the line accurate to 1 microsecond? -- These are my opinions. I hate spam. ___ 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. ___ 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
Hal wrote: What sort of interference do you see? There is a general grass on the entire waveform. At our location, the tops of the sine wave are clipped off (as the power is delivered). See attached image (the orange trace is the AC we receive from the grid; cyan is the distortion residual from a distortion analyzer -- there are rich harmonics out to the 20th or so within -50dB of the fundamental). The image is not properly scaled to show the high-frequency grass. What does an interesting transient event look like? It all depends. They are not all that fast (unless your house feed gets struck by lightning, in which case what does it look like in the data collection is the least of your worries), and usually comparable in amplitude to the power signal +/- 10dB (again, unless there is a very close lightning strike), so they generate extra zero crossings spaced anywhere from low mS to tens of mS. If you are going to post-process the data anyway, why not collect raw data and let the post-processing take care of the local interference? That lets you defer decisions about the appropriate filtering. There is enough high-frequency grass to reduce the precision of your zero crossing determinations. Since there is no useful information on grid behavior at these frequencies, it is better to remove it to improve your zero-cross precision. You can do a lot with post-processing, but you can't fix EVERYTHING in the mix. You have to start with the best data collection you can get, which in this case means filtering out the low-amplitude stuff above 1kHz or so. Is there any database of events that I can check when I see something interesting? Or turn things around and pick an event and see what it looks like when it gets here? Not that I'm aware of. (But as I noted previously, I'm not personally a grid-nut). 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] Cheap 5370A on eBay
#151518774079 Currently at $49.95 plus shipping. It's showing a ROM error (7.7) on startup. I asked what the error was this morning and they posted pictures this afternoon. It could be a candidate for one of John Seamons' 5370 processor replacement boards assuming nothing else is wrong. I have the minimum bid in, but if anyone else wants it, go for it; I already have one. Orin. ___ 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] HP 5370A to B conversion
List, I won a 5370A from ebay. Though it seems to be missing the A channel level knob, the unit was shown powered up with the correct 0.0 on the display, although the unit was sold as non-working for parts or repair. But the price was right with a best offer accepted. So assuming (gulp) that the unit works after fixing the A channel problem. is it practical or desirable to convert this to a B unit? I have one of the new processor boards with the BBone option that I can use in the unit. Advice requested. Regards, Perrier ___ 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.
