Recommendations for Mains Power Monitor / Logger
All this talk of varying mains power frequency aberrations has me
curious what is happening in my own back yard here in Tulsa in the
USA. Can some recommend a reasonable "introductory level" solution for
this? (As a fledgling Time-Nut, those two words were hard to say.😀)
At the least I would like to watch voltage and frequency, with a
configurable monitoring and logging interval. I can provide precise
timing as needed for synchronization and time-stamping. Expanded
ability to also monitor amperage, various power factors, etc is a plus
but not required at this point.
I've done some Googling and have found any number of designs. What I
can't tell is how well they work. I am pretty handy with my hands and
do not at all mind a DIY solution.
So what do the Oracles say?
Thanks!
-Pat
One possibility is to get an FNET/GridEye unit of the University of
Tennessee's monitoring stations.
Operated by the Power Information Technology Laboratory
http://powerit.utk.edu at the University of Tennessee http://www.utk.edu,
FNET/GridEye is a low-cost, quickly deployable GPS-synchronized wide-area
frequency measurement network. High dynamic accuracy Frequency Disturbance
Recorders (FDRs) are used to measure the frequency, phase angle, and
voltage of the power system at ordinary 120 V outlets. The measurement data
are continuously transmitted via the Internet to the FNET/GridEye servers
hosted at the University of Tennessee and Virginia Tech http://www.vt.edu.
I have Unit 853 of the Western Interconnection in the tabular display in
their web site (http://fnetpublic.utk.edu/tabledisplay.html). The unit,
about the size of a book, connects to the Internet via a cable to my router
and has a power line connection and a small GPS antenna. The LCD display
shows voltage and frequency; unfortunately there's no way to record this
information on site (at home or wherever).
Jeremy
N6WFO
On Sat, Mar 10, 2018 at 2:53 PM, Patrick Murphy fgdhrtey@gmail.com wrote:
All this talk of varying mains power frequency aberrations has me
curious what is happening in my own back yard here in Tulsa in the
USA. Can some recommend a reasonable "introductory level" solution for
this? (As a fledgling Time-Nut, those two words were hard to say.😀)
At the least I would like to watch voltage and frequency, with a
configurable monitoring and logging interval. I can provide precise
timing as needed for synchronization and time-stamping. Expanded
ability to also monitor amperage, various power factors, etc is a plus
but not required at this point.
I've done some Googling and have found any number of designs. What I
can't tell is how well they work. I am pretty handy with my hands and
do not at all mind a DIY solution.
So what do the Oracles say?
Thanks!
-Pat
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.
There isn't a whole lot of justification for measuring power line frequency. We are all synchronized (in the first world at least) and while there are phase instabilities, it's seldom the frequency varies enough to overcome the noise.
As for voltage, it's much more steady than several years ago. Most people have 122 Volts, give or take a couple. Again, not a whole lot of purpose in recording it.
The distortion is another story. It's never quite sinusoidal but there is also some random noise picked up between the generators and the load. Looking at the 'scope it's seldom it looks like the textbook picture of a sine wave. Chances are most distortion is odd harmonic.
Distortion probably mostly comes from loads which are not resistive, such as switching power supplies, rectifiers, fluorescent lamps, and such. These loads draw currents that are not sinusoids and so cause voltage drops that are also of that character.
Bob
On Saturday, March 10, 2018, 3:14:35 PM PST, Patrick Murphy fgdhrtey@gmail.com wrote:
All this talk of varying mains power frequency aberrations has me
curious what is happening in my own back yard here in Tulsa in the
USA. Can some recommend a reasonable "introductory level" solution for
this? (As a fledgling Time-Nut, those two words were hard to say.😀)
At the least I would like to watch voltage and frequency, with a
configurable monitoring and logging interval. I can provide precise
timing as needed for synchronization and time-stamping. Expanded
ability to also monitor amperage, various power factors, etc is a plus
but not required at this point.
I've done some Googling and have found any number of designs. What I
can't tell is how well they work. I am pretty handy with my hands and
do not at all mind a DIY solution.
So what do the Oracles say?
Thanks!
-Pat
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.
Hi
The most basic question is - what do you have already? My first adventure with
line monitoring was with a vacuum tube based counter. It was what I just happened
to have.
One basic need is something to monitor against. GPS is a pretty cheap option if you
have nothing already.
Rather than guessing from there …
Bob
On Mar 10, 2018, at 5:53 PM, Patrick Murphy fgdhrtey@gmail.com wrote:
All this talk of varying mains power frequency aberrations has me
curious what is happening in my own back yard here in Tulsa in the
USA. Can some recommend a reasonable "introductory level" solution for
this? (As a fledgling Time-Nut, those two words were hard to say.😀)
At the least I would like to watch voltage and frequency, with a
configurable monitoring and logging interval. I can provide precise
timing as needed for synchronization and time-stamping. Expanded
ability to also monitor amperage, various power factors, etc is a plus
but not required at this point.
I've done some Googling and have found any number of designs. What I
can't tell is how well they work. I am pretty handy with my hands and
do not at all mind a DIY solution.
So what do the Oracles say?
Thanks!
-Pat
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.
I've done some Googling and have found any number of designs.
Pat,
-
Safety. I usually use a low voltage step-down transformer. This gives isolation and safety. Anything from 3 VAC to 24 VAC is fine.
-
Trigger. There are dozens of schematics on the web for capturing the zero-crossing of a low-voltage sine wave. You can easily go overboard on this. Or just keep it simple and feed the signal through a resistor directly into a microprocessor input. The internal clamping diodes do their thing. A Schmitt trigger input is helpful but not necessary depending on how your software makes the measurement.
-
Timebase. Given the long-term accuracy of mains (seconds a day, seconds a year) you don't need an atomic timebase. If you collect data for a couple of days any old XO will be fine. If you plan to collect data for months you may want a OCXO. Most of us just use cheap GPS receivers.
-
Measurement. There are many ways to measure the signal. You can measure frequency directly, as with a frequency counter. You get nice data but it may not be perfect long-term due to dead time or gating effects in the counter.
So what most of us do is measure phase (time error) instead. One way is to make time interval measurements from a given mains cycle to a GPS 1PPS tick or vice versa, from each GPS/1PPS tick to the very next mains cycle. Either way you get about sample per second. If you're in search of perfection it gets a bit tricky when the two signals are in a coincidence zone.
The other approach is not to use a frequency or time interval counter at all. Instead you timestamp each cycle, or every 60th cycle. Unix-like systems have this capability. See Hal's posting. I use a picPET, a PIC microcontroller that takes snapshots of a free-running decimal counter driven by a 10 MHz timebase (OCXO or GPSDO).
The advantage of the timestamp method is that you don't ever miss samples, you can time every cycle (if you want), or throw away all but one sample per second or per 10 seconds or per minute, etc. And best of all, timestamping avoids the hassles of the coincidence zone.
-
CPU. A plain microcontroller, or Arduino, or R-Pi can be used. Or if you're on Windows and have a native or USB serial port try this simple tool as a demo:
http://leapsecond.com/tools/pctsc.exe
http://leapsecond.com/tools/pctsc.c -
An assortment of mains links:
http://leapsecond.com/pages/mains/
http://leapsecond.com/pages/mains-cv/
http://wwwhome.cs.utwente.nl/~ptdeboer/misc/mains.html
http://leapsecond.com/pages/mains/mains-adev-mdev-gnuplot-g4.png
http://leapsecond.com/pages/tec/mains-clock-ani.gif
http://leapsecond.com/pages/ac-detect/
http://leapsecond.com/pic/picpet.htm
http://leapsecond.com/pic/pp06.htm
- Final comments.
It is tempting to worry about the design, as they are so many out there on the web. Which is best? What are the pitfalls? What about noise immunity? What about precision and accuracy? My recommendation is not to over-think this. Just throw something together and see what you've got. Most of the work is with handling the data you get, doing the math, making plots, etc. If after the first day you see odd-looking 16 ms jumps in your data then you know you need to pay more attention to trigger level or noise issues.
- A sound idea.
We need someone to try out the sound card method. Send the isolated low voltage AC into the L channel and a GPS 1PPS into the R channel. "The rest is just software." Note that because you have access to the entire sine wave there's a lot you can do with this method besides making charts of time drift or frequency deviation from the zero-crossings.
For an even cheaper solution, forget the GPS receiver and the R channel -- since the PC (if running NTP) already knows the correct time. And skip the AC transformer too -- instead just hang a foot of wire off the L channel input. There's mains hum everywhere. It would be the one time in your life where the ever-present audio hum actually has a good use.
/tvb
----- Original Message -----
From: "Patrick Murphy" fgdhrtey@gmail.com
To: time-nuts@febo.com
Sent: Saturday, March 10, 2018 2:53 PM
Subject: [time-nuts] Recommendations for Mains Power Monitor / Logger
All this talk of varying mains power frequency aberrations has me
curious what is happening in my own back yard here in Tulsa in the
USA. Can some recommend a reasonable "introductory level" solution for
this? (As a fledgling Time-Nut, those two words were hard to say.😀)
At the least I would like to watch voltage and frequency, with a
configurable monitoring and logging interval. I can provide precise
timing as needed for synchronization and time-stamping. Expanded
ability to also monitor amperage, various power factors, etc is a plus
but not required at this point.
I've done some Googling and have found any number of designs. What I
can't tell is how well they work. I am pretty handy with my hands and
do not at all mind a DIY solution.
So what do the Oracles say?
Thanks!
-Pat
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.
Well, this synchronization follows the laws of physics. If the energy
generated doesn't equal the energy consumed, then the frequency may
raise or lower. This is for steam turbines. If the energy come front an
inverter from a DC tie line, as it does from the four regions in the US,
the frequency is anything it wants to be. Well not quite. Raising the
inverter frequency a hair causes the tie line to be the major source of
energy. One could track the use of energy by frequency to make
investment decisions in manufacturer's stocks.
The problem with zero crossing triggers is the amount of noise caused by
solid state power supplies and by tap changing by the power companies to
match loads to minimize transmission losses. I've considered using a
mechanical synchronous motor and slotted wheel to eliminate noise near
the zero crossing, but now that I am 80, I don't give a darn, you see.
Bill Hawkins
-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of Bob
Albert via time-nuts
Sent: Saturday, March 10, 2018 5:58 PM
There isn't a whole lot of justification for measuring power line
frequency. We are all synchronized (in the first world at least) and
while there are phase instabilities, it's seldom the frequency varies
enough to overcome the noise.
As for voltage, it's much more steady than several years ago. Most
people have 122 Volts, give or take a couple. Again, not a whole lot of
purpose in recording it.
The distortion is another story. It's never quite sinusoidal but there
is also some random noise picked up between the generators and the
load. Looking at the 'scope it's seldom it looks like the textbook
picture of a sine wave. Chances are most distortion is odd harmonic.
Distortion probably mostly comes from loads which are not resistive,
such as switching power supplies, rectifiers, fluorescent lamps, and
such. These loads draw currents that are not sinusoids and so cause
voltage drops that are also of that character.
Bob
Hi
So, how good is “good enough?”. My first attempt ran a counter with a 1 us period resolution.
(remember, it was tube based …). That turned out to be major overkill in terms of line frequency
measurement. 60.123 Hz is doing pretty well in terms of line frequency. Even to get that level, you
will be doing a bit of filtering (or you are just watching the last two digits pop around randomly).
Your typical time base in a PC is good to a few hundred ppm. That’s giving you an error in the
fourth digit of your measurement. With a bit of luck, your sound card timebase may be 5X
more accurate than your system clock. (or it may be worse …) it depends a bit on how fancy
your audio setup is.
Adding NTP to your PC will correct for any long term errors. In a rational environment it should
get you into the “few ppm” range short term and zero error long term.
A GPS gizmo will get you into the parts per billion (or better) range. It might be 100’s of ppb, but it’s
still way better than your CPU clock. The usual auction sites have lots of candidates in the sub $50
range.There are also places that are happy to sell you shields with GPS devices on them.
A fancier yet solution is a GPSDO. We are well into overkill at this point. The advantage to using
one is that it may be the time / frequency standard for your entire lab setup. You are up in the
$100 to $500 range for most of them. They will get you into 10’s or 100’s of parts per trillion.
There are indeed lots of different time sources you could use. The number of alternatives is
much larger than what’s on the list above.
Bob
On Mar 10, 2018, at 11:46 PM, Tom Van Baak tvb@leapsecond.com wrote:
I've done some Googling and have found any number of designs.
Pat,
-
Safety. I usually use a low voltage step-down transformer. This gives isolation and safety. Anything from 3 VAC to 24 VAC is fine.
-
Trigger. There are dozens of schematics on the web for capturing the zero-crossing of a low-voltage sine wave. You can easily go overboard on this. Or just keep it simple and feed the signal through a resistor directly into a microprocessor input. The internal clamping diodes do their thing. A Schmitt trigger input is helpful but not necessary depending on how your software makes the measurement.
-
Timebase. Given the long-term accuracy of mains (seconds a day, seconds a year) you don't need an atomic timebase. If you collect data for a couple of days any old XO will be fine. If you plan to collect data for months you may want a OCXO. Most of us just use cheap GPS receivers.
-
Measurement. There are many ways to measure the signal. You can measure frequency directly, as with a frequency counter. You get nice data but it may not be perfect long-term due to dead time or gating effects in the counter.
So what most of us do is measure phase (time error) instead. One way is to make time interval measurements from a given mains cycle to a GPS 1PPS tick or vice versa, from each GPS/1PPS tick to the very next mains cycle. Either way you get about sample per second. If you're in search of perfection it gets a bit tricky when the two signals are in a coincidence zone.
The other approach is not to use a frequency or time interval counter at all. Instead you timestamp each cycle, or every 60th cycle. Unix-like systems have this capability. See Hal's posting. I use a picPET, a PIC microcontroller that takes snapshots of a free-running decimal counter driven by a 10 MHz timebase (OCXO or GPSDO).
The advantage of the timestamp method is that you don't ever miss samples, you can time every cycle (if you want), or throw away all but one sample per second or per 10 seconds or per minute, etc. And best of all, timestamping avoids the hassles of the coincidence zone.
-
CPU. A plain microcontroller, or Arduino, or R-Pi can be used. Or if you're on Windows and have a native or USB serial port try this simple tool as a demo:
http://leapsecond.com/tools/pctsc.exe
http://leapsecond.com/tools/pctsc.c -
An assortment of mains links:
http://leapsecond.com/pages/mains/
http://leapsecond.com/pages/mains-cv/
http://wwwhome.cs.utwente.nl/~ptdeboer/misc/mains.html
http://leapsecond.com/pages/mains/mains-adev-mdev-gnuplot-g4.png
http://leapsecond.com/pages/tec/mains-clock-ani.gif
http://leapsecond.com/pages/ac-detect/
http://leapsecond.com/pic/picpet.htm
http://leapsecond.com/pic/pp06.htm
- Final comments.
It is tempting to worry about the design, as they are so many out there on the web. Which is best? What are the pitfalls? What about noise immunity? What about precision and accuracy? My recommendation is not to over-think this. Just throw something together and see what you've got. Most of the work is with handling the data you get, doing the math, making plots, etc. If after the first day you see odd-looking 16 ms jumps in your data then you know you need to pay more attention to trigger level or noise issues.
- A sound idea.
We need someone to try out the sound card method. Send the isolated low voltage AC into the L channel and a GPS 1PPS into the R channel. "The rest is just software." Note that because you have access to the entire sine wave there's a lot you can do with this method besides making charts of time drift or frequency deviation from the zero-crossings.
For an even cheaper solution, forget the GPS receiver and the R channel -- since the PC (if running NTP) already knows the correct time. And skip the AC transformer too -- instead just hang a foot of wire off the L channel input. There's mains hum everywhere. It would be the one time in your life where the ever-present audio hum actually has a good use.
/tvb
----- Original Message -----
From: "Patrick Murphy" fgdhrtey@gmail.com
To: time-nuts@febo.com
Sent: Saturday, March 10, 2018 2:53 PM
Subject: [time-nuts] Recommendations for Mains Power Monitor / Logger
All this talk of varying mains power frequency aberrations has me
curious what is happening in my own back yard here in Tulsa in the
USA. Can some recommend a reasonable "introductory level" solution for
this? (As a fledgling Time-Nut, those two words were hard to say.😀)
At the least I would like to watch voltage and frequency, with a
configurable monitoring and logging interval. I can provide precise
timing as needed for synchronization and time-stamping. Expanded
ability to also monitor amperage, various power factors, etc is a plus
but not required at this point.
I've done some Googling and have found any number of designs. What I
can't tell is how well they work. I am pretty handy with my hands and
do not at all mind a DIY solution.
So what do the Oracles say?
Thanks!
-Pat
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.
Bob,
Correct, measuring mains frequency to a couple of digits is not hard. What makes an interesting challenge is to monitor mains, "kitchen clock", phase drift. And to do it with cycle accuracy; no slips. Note that to measure down to 1 cycle over 1 day is 0.2 ppm. Over a month, 6 ppb, and over a year, 5e-10. So the numbers add up and you see why we use atomic standards or GPS or even NTP as a long-term reference for this.
Your measurement system needs to have short- and long-term stability ~10x better than:
http://leapsecond.com/pic/mains-adev-mdev-gnuplot-g4.png
Again, that's not asking a lot. But it makes a really fun project. Much of what you ever need to know about time & frequency metrology can be done by a student with $10 in parts and a 60 Hz outlet.
/tvb
p.s. Yes, it's very early here on the west coast, but I had to check how badly my WWVB clocks handled DST a few hours ago.
----- Original Message -----
From: "Bob kb8tq" kb8tq@n1k.org
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Sunday, March 11, 2018 4:53 AM
Subject: Re: [time-nuts] Recommendations for Mains Power Monitor / Logger
Hi
So, how good is “good enough?”. My first attempt ran a counter with a 1 us period resolution.
(remember, it was tube based …). That turned out to be major overkill in terms of line frequency
measurement. 60.123 Hz is doing pretty well in terms of line frequency. Even to get that level, you
will be doing a bit of filtering (or you are just watching the last two digits pop around randomly).
Your typical time base in a PC is good to a few hundred ppm. That’s giving you an error in the
fourth digit of your measurement. With a bit of luck, your sound card timebase may be 5X
more accurate than your system clock. (or it may be worse …) it depends a bit on how fancy
your audio setup is.
Adding NTP to your PC will correct for any long term errors. In a rational environment it should
get you into the “few ppm” range short term and zero error long term.
A GPS gizmo will get you into the parts per billion (or better) range. It might be 100’s of ppb, but it’s
still way better than your CPU clock. The usual auction sites have lots of candidates in the sub $50
range.There are also places that are happy to sell you shields with GPS devices on them.
A fancier yet solution is a GPSDO. We are well into overkill at this point. The advantage to using
one is that it may be the time / frequency standard for your entire lab setup. You are up in the
$100 to $500 range for most of them. They will get you into 10’s or 100’s of parts per trillion.
There are indeed lots of different time sources you could use. The number of alternatives is
much larger than what’s on the list above.
Bob
On Mar 10, 2018, at 11:46 PM, Tom Van Baak tvb@leapsecond.com wrote:
I've done some Googling and have found any number of designs.
Pat,
-
Safety. I usually use a low voltage step-down transformer. This gives isolation and safety. Anything from 3 VAC to 24 VAC is fine.
-
Trigger. There are dozens of schematics on the web for capturing the zero-crossing of a low-voltage sine wave. You can easily go overboard on this. Or just keep it simple and feed the signal through a resistor directly into a microprocessor input. The internal clamping diodes do their thing. A Schmitt trigger input is helpful but not necessary depending on how your software makes the measurement.
-
Timebase. Given the long-term accuracy of mains (seconds a day, seconds a year) you don't need an atomic timebase. If you collect data for a couple of days any old XO will be fine. If you plan to collect data for months you may want a OCXO. Most of us just use cheap GPS receivers.
-
Measurement. There are many ways to measure the signal. You can measure frequency directly, as with a frequency counter. You get nice data but it may not be perfect long-term due to dead time or gating effects in the counter.
So what most of us do is measure phase (time error) instead. One way is to make time interval measurements from a given mains cycle to a GPS 1PPS tick or vice versa, from each GPS/1PPS tick to the very next mains cycle. Either way you get about sample per second. If you're in search of perfection it gets a bit tricky when the two signals are in a coincidence zone.
The other approach is not to use a frequency or time interval counter at all. Instead you timestamp each cycle, or every 60th cycle. Unix-like systems have this capability. See Hal's posting. I use a picPET, a PIC microcontroller that takes snapshots of a free-running decimal counter driven by a 10 MHz timebase (OCXO or GPSDO).
The advantage of the timestamp method is that you don't ever miss samples, you can time every cycle (if you want), or throw away all but one sample per second or per 10 seconds or per minute, etc. And best of all, timestamping avoids the hassles of the coincidence zone.
-
CPU. A plain microcontroller, or Arduino, or R-Pi can be used. Or if you're on Windows and have a native or USB serial port try this simple tool as a demo:
http://leapsecond.com/tools/pctsc.exe
http://leapsecond.com/tools/pctsc.c -
An assortment of mains links:
http://leapsecond.com/pages/mains/
http://leapsecond.com/pages/mains-cv/
http://wwwhome.cs.utwente.nl/~ptdeboer/misc/mains.html
http://leapsecond.com/pages/mains/mains-adev-mdev-gnuplot-g4.png
http://leapsecond.com/pages/tec/mains-clock-ani.gif
http://leapsecond.com/pages/ac-detect/
http://leapsecond.com/pic/picpet.htm
http://leapsecond.com/pic/pp06.htm
- Final comments.
It is tempting to worry about the design, as they are so many out there on the web. Which is best? What are the pitfalls? What about noise immunity? What about precision and accuracy? My recommendation is not to over-think this. Just throw something together and see what you've got. Most of the work is with handling the data you get, doing the math, making plots, etc. If after the first day you see odd-looking 16 ms jumps in your data then you know you need to pay more attention to trigger level or noise issues.
- A sound idea.
We need someone to try out the sound card method. Send the isolated low voltage AC into the L channel and a GPS 1PPS into the R channel. "The rest is just software." Note that because you have access to the entire sine wave there's a lot you can do with this method besides making charts of time drift or frequency deviation from the zero-crossings.
For an even cheaper solution, forget the GPS receiver and the R channel -- since the PC (if running NTP) already knows the correct time. And skip the AC transformer too -- instead just hang a foot of wire off the L channel input. There's mains hum everywhere. It would be the one time in your life where the ever-present audio hum actually has a good use.
/tvb
----- Original Message -----
From: "Patrick Murphy" fgdhrtey@gmail.com
To: time-nuts@febo.com
Sent: Saturday, March 10, 2018 2:53 PM
Subject: [time-nuts] Recommendations for Mains Power Monitor / Logger
All this talk of varying mains power frequency aberrations has me
curious what is happening in my own back yard here in Tulsa in the
USA. Can some recommend a reasonable "introductory level" solution for
this? (As a fledgling Time-Nut, those two words were hard to say.😀)
At the least I would like to watch voltage and frequency, with a
configurable monitoring and logging interval. I can provide precise
timing as needed for synchronization and time-stamping. Expanded
ability to also monitor amperage, various power factors, etc is a plus
but not required at this point.
I've done some Googling and have found any number of designs. What I
can't tell is how well they work. I am pretty handy with my hands and
do not at all mind a DIY solution.
So what do the Oracles say?
Thanks!
-Pat
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.
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi
“Back in the day” we used WWV and the kitchen clock for that sort of thing……
Bob
On Mar 11, 2018, at 8:32 AM, Tom Van Baak tvb@LeapSecond.com wrote:
Bob,
Correct, measuring mains frequency to a couple of digits is not hard. What makes an interesting challenge is to monitor mains, "kitchen clock", phase drift. And to do it with cycle accuracy; no slips. Note that to measure down to 1 cycle over 1 day is 0.2 ppm. Over a month, 6 ppb, and over a year, 5e-10. So the numbers add up and you see why we use atomic standards or GPS or even NTP as a long-term reference for this.
Your measurement system needs to have short- and long-term stability ~10x better than:
http://leapsecond.com/pic/mains-adev-mdev-gnuplot-g4.png
Again, that's not asking a lot. But it makes a really fun project. Much of what you ever need to know about time & frequency metrology can be done by a student with $10 in parts and a 60 Hz outlet.
/tvb
p.s. Yes, it's very early here on the west coast, but I had to check how badly my WWVB clocks handled DST a few hours ago.
----- Original Message -----
From: "Bob kb8tq" kb8tq@n1k.org
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Sunday, March 11, 2018 4:53 AM
Subject: Re: [time-nuts] Recommendations for Mains Power Monitor / Logger
Hi
So, how good is “good enough?”. My first attempt ran a counter with a 1 us period resolution.
(remember, it was tube based …). That turned out to be major overkill in terms of line frequency
measurement. 60.123 Hz is doing pretty well in terms of line frequency. Even to get that level, you
will be doing a bit of filtering (or you are just watching the last two digits pop around randomly).
Your typical time base in a PC is good to a few hundred ppm. That’s giving you an error in the
fourth digit of your measurement. With a bit of luck, your sound card timebase may be 5X
more accurate than your system clock. (or it may be worse …) it depends a bit on how fancy
your audio setup is.
Adding NTP to your PC will correct for any long term errors. In a rational environment it should
get you into the “few ppm” range short term and zero error long term.
A GPS gizmo will get you into the parts per billion (or better) range. It might be 100’s of ppb, but it’s
still way better than your CPU clock. The usual auction sites have lots of candidates in the sub $50
range.There are also places that are happy to sell you shields with GPS devices on them.
A fancier yet solution is a GPSDO. We are well into overkill at this point. The advantage to using
one is that it may be the time / frequency standard for your entire lab setup. You are up in the
$100 to $500 range for most of them. They will get you into 10’s or 100’s of parts per trillion.
There are indeed lots of different time sources you could use. The number of alternatives is
much larger than what’s on the list above.
Bob
On Mar 10, 2018, at 11:46 PM, Tom Van Baak tvb@leapsecond.com wrote:
I've done some Googling and have found any number of designs.
Pat,
-
Safety. I usually use a low voltage step-down transformer. This gives isolation and safety. Anything from 3 VAC to 24 VAC is fine.
-
Trigger. There are dozens of schematics on the web for capturing the zero-crossing of a low-voltage sine wave. You can easily go overboard on this. Or just keep it simple and feed the signal through a resistor directly into a microprocessor input. The internal clamping diodes do their thing. A Schmitt trigger input is helpful but not necessary depending on how your software makes the measurement.
-
Timebase. Given the long-term accuracy of mains (seconds a day, seconds a year) you don't need an atomic timebase. If you collect data for a couple of days any old XO will be fine. If you plan to collect data for months you may want a OCXO. Most of us just use cheap GPS receivers.
-
Measurement. There are many ways to measure the signal. You can measure frequency directly, as with a frequency counter. You get nice data but it may not be perfect long-term due to dead time or gating effects in the counter.
So what most of us do is measure phase (time error) instead. One way is to make time interval measurements from a given mains cycle to a GPS 1PPS tick or vice versa, from each GPS/1PPS tick to the very next mains cycle. Either way you get about sample per second. If you're in search of perfection it gets a bit tricky when the two signals are in a coincidence zone.
The other approach is not to use a frequency or time interval counter at all. Instead you timestamp each cycle, or every 60th cycle. Unix-like systems have this capability. See Hal's posting. I use a picPET, a PIC microcontroller that takes snapshots of a free-running decimal counter driven by a 10 MHz timebase (OCXO or GPSDO).
The advantage of the timestamp method is that you don't ever miss samples, you can time every cycle (if you want), or throw away all but one sample per second or per 10 seconds or per minute, etc. And best of all, timestamping avoids the hassles of the coincidence zone.
- CPU. A plain microcontroller, or Arduino, or R-Pi can be used. Or if you're on Windows and have a native or USB serial port try this simple tool as a demo:
http://leapsecond.com/tools/pctsc.exe
http://leapsecond.com/tools/pctsc.c
- An assortment of mains links:
http://leapsecond.com/pages/mains/
http://leapsecond.com/pages/mains-cv/
http://wwwhome.cs.utwente.nl/~ptdeboer/misc/mains.html
http://leapsecond.com/pages/mains/mains-adev-mdev-gnuplot-g4.png
http://leapsecond.com/pages/tec/mains-clock-ani.gif
http://leapsecond.com/pages/ac-detect/
http://leapsecond.com/pic/picpet.htm
http://leapsecond.com/pic/pp06.htm
- Final comments.
It is tempting to worry about the design, as they are so many out there on the web. Which is best? What are the pitfalls? What about noise immunity? What about precision and accuracy? My recommendation is not to over-think this. Just throw something together and see what you've got. Most of the work is with handling the data you get, doing the math, making plots, etc. If after the first day you see odd-looking 16 ms jumps in your data then you know you need to pay more attention to trigger level or noise issues.
- A sound idea.
We need someone to try out the sound card method. Send the isolated low voltage AC into the L channel and a GPS 1PPS into the R channel. "The rest is just software." Note that because you have access to the entire sine wave there's a lot you can do with this method besides making charts of time drift or frequency deviation from the zero-crossings.
For an even cheaper solution, forget the GPS receiver and the R channel -- since the PC (if running NTP) already knows the correct time. And skip the AC transformer too -- instead just hang a foot of wire off the L channel input. There's mains hum everywhere. It would be the one time in your life where the ever-present audio hum actually has a good use.
/tvb
----- Original Message -----
From: "Patrick Murphy" fgdhrtey@gmail.com
To: time-nuts@febo.com
Sent: Saturday, March 10, 2018 2:53 PM
Subject: [time-nuts] Recommendations for Mains Power Monitor / Logger
All this talk of varying mains power frequency aberrations has me
curious what is happening in my own back yard here in Tulsa in the
USA. Can some recommend a reasonable "introductory level" solution for
this? (As a fledgling Time-Nut, those two words were hard to say.😀)
At the least I would like to watch voltage and frequency, with a
configurable monitoring and logging interval. I can provide precise
timing as needed for synchronization and time-stamping. Expanded
ability to also monitor amperage, various power factors, etc is a plus
but not required at this point.
I've done some Googling and have found any number of designs. What I
can't tell is how well they work. I am pretty handy with my hands and
do not at all mind a DIY solution.
So what do the Oracles say?
Thanks!
-Pat
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and follow the instructions there.<mains-adev-mdev-gnuplot-g4.png>_______________________________________________
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My 20 year old Junghans`s had no problemBert Kehren Palm City Florida
Sent from my Galaxy Tab® A
-------- Original message --------From: Tom Van Baak tvb@LeapSecond.com Date: 3/11/18 8:32 AM (GMT-05:00) To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Recommendations for Mains Power Monitor / Logger
Bob,
Correct, measuring mains frequency to a couple of digits is not hard. What makes an interesting challenge is to monitor mains, "kitchen clock", phase drift. And to do it with cycle accuracy; no slips. Note that to measure down to 1 cycle over 1 day is 0.2 ppm. Over a month, 6 ppb, and over a year, 5e-10. So the numbers add up and you see why we use atomic standards or GPS or even NTP as a long-term reference for this.
Your measurement system needs to have short- and long-term stability ~10x better than:
http://leapsecond.com/pic/mains-adev-mdev-gnuplot-g4.png
Again, that's not asking a lot. But it makes a really fun project. Much of what you ever need to know about time & frequency metrology can be done by a student with $10 in parts and a 60 Hz outlet.
/tvb
p.s. Yes, it's very early here on the west coast, but I had to check how badly my WWVB clocks handled DST a few hours ago.
----- Original Message -----
From: "Bob kb8tq" kb8tq@n1k.org
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Sunday, March 11, 2018 4:53 AM
Subject: Re: [time-nuts] Recommendations for Mains Power Monitor / Logger
Hi
So, how good is “good enough?”. My first attempt ran a counter with a 1 us period resolution.
(remember, it was tube based …). That turned out to be major overkill in terms of line frequency
measurement. 60.123 Hz is doing pretty well in terms of line frequency. Even to get that level, you
will be doing a bit of filtering (or you are just watching the last two digits pop around randomly).
Your typical time base in a PC is good to a few hundred ppm. That’s giving you an error in the
fourth digit of your measurement. With a bit of luck, your sound card timebase may be 5X
more accurate than your system clock. (or it may be worse …) it depends a bit on how fancy
your audio setup is.
Adding NTP to your PC will correct for any long term errors. In a rational environment it should
get you into the “few ppm” range short term and zero error long term.
A GPS gizmo will get you into the parts per billion (or better) range. It might be 100’s of ppb, but it’s
still way better than your CPU clock. The usual auction sites have lots of candidates in the sub $50
range.There are also places that are happy to sell you shields with GPS devices on them.
A fancier yet solution is a GPSDO. We are well into overkill at this point. The advantage to using
one is that it may be the time / frequency standard for your entire lab setup. You are up in the
$100 to $500 range for most of them. They will get you into 10’s or 100’s of parts per trillion.
There are indeed lots of different time sources you could use. The number of alternatives is
much larger than what’s on the list above.
Bob
On Mar 10, 2018, at 11:46 PM, Tom Van Baak tvb@leapsecond.com wrote:
I've done some Googling and have found any number of designs.
Pat,
-
Safety. I usually use a low voltage step-down transformer. This gives isolation and safety. Anything from 3 VAC to 24 VAC is fine.
-
Trigger. There are dozens of schematics on the web for capturing the zero-crossing of a low-voltage sine wave. You can easily go overboard on this. Or just keep it simple and feed the signal through a resistor directly into a microprocessor input. The internal clamping diodes do their thing. A Schmitt trigger input is helpful but not necessary depending on how your software makes the measurement.
-
Timebase. Given the long-term accuracy of mains (seconds a day, seconds a year) you don't need an atomic timebase. If you collect data for a couple of days any old XO will be fine. If you plan to collect data for months you may want a OCXO. Most of us just use cheap GPS receivers.
-
Measurement. There are many ways to measure the signal. You can measure frequency directly, as with a frequency counter. You get nice data but it may not be perfect long-term due to dead time or gating effects in the counter.
So what most of us do is measure phase (time error) instead. One way is to make time interval measurements from a given mains cycle to a GPS 1PPS tick or vice versa, from each GPS/1PPS tick to the very next mains cycle. Either way you get about sample per second. If you're in search of perfection it gets a bit tricky when the two signals are in a coincidence zone.
The other approach is not to use a frequency or time interval counter at all. Instead you timestamp each cycle, or every 60th cycle. Unix-like systems have this capability. See Hal's posting. I use a picPET, a PIC microcontroller that takes snapshots of a free-running decimal counter driven by a 10 MHz timebase (OCXO or GPSDO).
The advantage of the timestamp method is that you don't ever miss samples, you can time every cycle (if you want), or throw away all but one sample per second or per 10 seconds or per minute, etc. And best of all, timestamping avoids the hassles of the coincidence zone.
- CPU. A plain microcontroller, or Arduino, or R-Pi can be used. Or if you're on Windows and have a native or USB serial port try this simple tool as a demo:
http://leapsecond.com/tools/pctsc.exe
http://leapsecond.com/tools/pctsc.c
- An assortment of mains links:
http://leapsecond.com/pages/mains/
http://leapsecond.com/pages/mains-cv/
http://wwwhome.cs.utwente.nl/~ptdeboer/misc/mains.html
http://leapsecond.com/pages/mains/mains-adev-mdev-gnuplot-g4.png
http://leapsecond.com/pages/tec/mains-clock-ani.gif
http://leapsecond.com/pages/ac-detect/
http://leapsecond.com/pic/picpet.htm
http://leapsecond.com/pic/pp06.htm
- Final comments.
It is tempting to worry about the design, as they are so many out there on the web. Which is best? What are the pitfalls? What about noise immunity? What about precision and accuracy? My recommendation is not to over-think this. Just throw something together and see what you've got. Most of the work is with handling the data you get, doing the math, making plots, etc. If after the first day you see odd-looking 16 ms jumps in your data then you know you need to pay more attention to trigger level or noise issues.
- A sound idea.
We need someone to try out the sound card method. Send the isolated low voltage AC into the L channel and a GPS 1PPS into the R channel. "The rest is just software." Note that because you have access to the entire sine wave there's a lot you can do with this method besides making charts of time drift or frequency deviation from the zero-crossings.
For an even cheaper solution, forget the GPS receiver and the R channel -- since the PC (if running NTP) already knows the correct time. And skip the AC transformer too -- instead just hang a foot of wire off the L channel input. There's mains hum everywhere. It would be the one time in your life where the ever-present audio hum actually has a good use.
/tvb
----- Original Message -----
From: "Patrick Murphy" fgdhrtey@gmail.com
To: time-nuts@febo.com
Sent: Saturday, March 10, 2018 2:53 PM
Subject: [time-nuts] Recommendations for Mains Power Monitor / Logger
All this talk of varying mains power frequency aberrations has me
curious what is happening in my own back yard here in Tulsa in the
USA. Can some recommend a reasonable "introductory level" solution for
this? (As a fledgling Time-Nut, those two words were hard to say.😀)
At the least I would like to watch voltage and frequency, with a
configurable monitoring and logging interval. I can provide precise
timing as needed for synchronization and time-stamping. Expanded
ability to also monitor amperage, various power factors, etc is a plus
but not required at this point.
I've done some Googling and have found any number of designs. What I
can't tell is how well they work. I am pretty handy with my hands and
do not at all mind a DIY solution.
So what do the Oracles say?
Thanks!
-Pat
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.
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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