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Discussion of precise voltage measurement

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current-nut question .. total waste of ones time type question

PL
Pete Lancashire
Tue, Apr 29, 2014 5:25 PM

Next spring I'm going be rewiring my house. And for 'fun' I want to drop a
couple current sensors on the input side of the main panel.

Being a beginner 'nut', I'm looking for more accuracy then needed.

Voltage, Frequency, waveform will be taken care of later, but accurate
current has be a bit flustered.

I've been reading up on CT's Iron core and Ferrite, and on Rogowski coils.
And the many new IC's on the market that take care of a lot of things.

Has someone done this before ? And if so any experiences to share ?

-pete

Next spring I'm going be rewiring my house. And for 'fun' I want to drop a couple current sensors on the input side of the main panel. Being a beginner 'nut', I'm looking for more accuracy then needed. Voltage, Frequency, waveform will be taken care of later, but accurate current has be a bit flustered. I've been reading up on CT's Iron core and Ferrite, and on Rogowski coils. And the many new IC's on the market that take care of a lot of things. Has someone done this before ? And if so any experiences to share ? -pete
B
bownes
Tue, Apr 29, 2014 6:00 PM

There was a Circuit Cellar article on this many moons ago.

Basically, it was:

Take a torroid ferrite core, wrap ~20 turns of #20 through it, pass the wire you want to sense current in through the core, and hook the output of the coil to an op amp. Look at output of op amp with a/d converter. Do some math. :)

I have a few on individual circuits in my electrical panel (sump pump, furnace, etc). I dipped the coil assembly in plasti-dip to insulate them. Have not looked at it in a long while though. The control processor croaked and I've never bothered to fix it.

Bob

On Apr 29, 2014, at 13:25, Pete Lancashire pete@petelancashire.com wrote:

Next spring I'm going be rewiring my house. And for 'fun' I want to drop a
couple current sensors on the input side of the main panel.

Being a beginner 'nut', I'm looking for more accuracy then needed.

Voltage, Frequency, waveform will be taken care of later, but accurate
current has be a bit flustered.

I've been reading up on CT's Iron core and Ferrite, and on Rogowski coils.
And the many new IC's on the market that take care of a lot of things.

Has someone done this before ? And if so any experiences to share ?

-pete


volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.

There was a Circuit Cellar article on this many moons ago. Basically, it was: Take a torroid ferrite core, wrap ~20 turns of #20 through it, pass the wire you want to sense current in through the core, and hook the output of the coil to an op amp. Look at output of op amp with a/d converter. Do some math. :) I have a few on individual circuits in my electrical panel (sump pump, furnace, etc). I dipped the coil assembly in plasti-dip to insulate them. Have not looked at it in a long while though. The control processor croaked and I've never bothered to fix it. Bob > On Apr 29, 2014, at 13:25, Pete Lancashire <pete@petelancashire.com> wrote: > > Next spring I'm going be rewiring my house. And for 'fun' I want to drop a > couple current sensors on the input side of the main panel. > > Being a beginner 'nut', I'm looking for more accuracy then needed. > > Voltage, Frequency, waveform will be taken care of later, but accurate > current has be a bit flustered. > > I've been reading up on CT's Iron core and Ferrite, and on Rogowski coils. > And the many new IC's on the market that take care of a lot of things. > > Has someone done this before ? And if so any experiences to share ? > > -pete > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.
BG
Brent Gordon
Tue, Apr 29, 2014 7:06 PM

Years ago I installed a TED-1000 (now obsolete) system from
http://www.theenergydetective.com/.  Their software is terrible but
the system works.  This system uses two current transformers and a
single voltage measurement system that all go inside your circuit
breaker box.  I don't recall the sampling rate (1 KHz maybe).  The
instantaneous voltage and current measurements are multiplied, summed,
and transmitted once per second.  The data is transmitted to a receiver
using the house wiring (similar to X-10).  People have hacked the system
to use their own receiver.

I haven't directly measured accuracy; monthly totals are usually about
5% low when compared to my electric bill.  The software compensates for
missing readings.  Resolution seems to be around 10 watts.

Brent

On 4/29/2014 11:25 AM, Pete Lancashire wrote:

Next spring I'm going be rewiring my house. And for 'fun' I want to drop a
couple current sensors on the input side of the main panel.

Being a beginner 'nut', I'm looking for more accuracy then needed.

Voltage, Frequency, waveform will be taken care of later, but accurate
current has be a bit flustered.

I've been reading up on CT's Iron core and Ferrite, and on Rogowski coils.
And the many new IC's on the market that take care of a lot of things.

Has someone done this before ? And if so any experiences to share ?

-pete

Years ago I installed a TED-1000 (now obsolete) system from <http://www.theenergydetective.com/>. Their software is terrible but the system works. This system uses two current transformers and a single voltage measurement system that all go inside your circuit breaker box. I don't recall the sampling rate (1 KHz maybe). The instantaneous voltage and current measurements are multiplied, summed, and transmitted once per second. The data is transmitted to a receiver using the house wiring (similar to X-10). People have hacked the system to use their own receiver. I haven't directly measured accuracy; monthly totals are usually about 5% low when compared to my electric bill. The software compensates for missing readings. Resolution seems to be around 10 watts. Brent On 4/29/2014 11:25 AM, Pete Lancashire wrote: > Next spring I'm going be rewiring my house. And for 'fun' I want to drop a > couple current sensors on the input side of the main panel. > > Being a beginner 'nut', I'm looking for more accuracy then needed. > > Voltage, Frequency, waveform will be taken care of later, but accurate > current has be a bit flustered. > > I've been reading up on CT's Iron core and Ferrite, and on Rogowski coils. > And the many new IC's on the market that take care of a lot of things. > > Has someone done this before ? And if so any experiences to share ? > > -pete >
PL
Pete Lancashire
Tue, Apr 29, 2014 8:48 PM

Getting 2 % is pretty easy, many commercial CT's at 0.3% at the
transformer, resistance of the wire from the CT to the load (burden in the
electrical world), and all the things that effect voltage measurements come
into play. A well designed setup can get to 0.5%.

Thanks to surplus a classic 5A CT can be found for a few $'s. More modern
instrument grade CTs are expensive unless you can grab one off the usual
auction places.

A "classic" 100A or 200A:5A is a good 4-5" square and can be as much as
2-3" thick.

Today you don't need the 5 Amps, heck 10-50 mA is good enough, so the size
can be smaller.

I've been trying to shoot for say 0.1% to 0.2%. Again for 'fun'.

Where some more fun comes in is when you get below 10%, that would be
10Amps using a 100A CT. The industry specs stop at 10%. A 0.3% transformer
is only 0.3% at full rating (and above).

Was just looking to see if anyone has come up with something new / low cost
/ etc.

On Tue, Apr 29, 2014 at 12:06 PM, Brent Gordon volt-nuts@adobe-labs.comwrote:

Years ago I installed a TED-1000 (now obsolete) system from <http://www.
theenergydetective.com/>.  Their software is terrible but the system
works.  This system uses two current transformers and a single voltage
measurement system that all go inside your circuit breaker box.  I don't
recall the sampling rate (1 KHz maybe).  The instantaneous voltage and
current measurements are multiplied, summed, and transmitted once per
second.  The data is transmitted to a receiver using the house wiring
(similar to X-10).  People have hacked the system to use their own receiver.

I haven't directly measured accuracy; monthly totals are usually about 5%
low when compared to my electric bill.  The software compensates for
missing readings.  Resolution seems to be around 10 watts.

Brent

On 4/29/2014 11:25 AM, Pete Lancashire wrote:

Next spring I'm going be rewiring my house. And for 'fun' I want to drop a
couple current sensors on the input side of the main panel.

Being a beginner 'nut', I'm looking for more accuracy then needed.

Voltage, Frequency, waveform will be taken care of later, but accurate
current has be a bit flustered.

I've been reading up on CT's Iron core and Ferrite, and on Rogowski coils.
And the many new IC's on the market that take care of a lot of things.

Has someone done this before ? And if so any experiences to share ?

-pete


volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/
mailman/listinfo/volt-nuts
and follow the instructions there.

Getting 2 % is pretty easy, many commercial CT's at 0.3% at the transformer, resistance of the wire from the CT to the load (burden in the electrical world), and all the things that effect voltage measurements come into play. A well designed setup can get to 0.5%. Thanks to surplus a classic 5A CT can be found for a few $'s. More modern instrument grade CTs are expensive unless you can grab one off the usual auction places. A "classic" 100A or 200A:5A is a good 4-5" square and can be as much as 2-3" thick. Today you don't need the 5 Amps, heck 10-50 mA is good enough, so the size can be smaller. I've been trying to shoot for say 0.1% to 0.2%. Again for 'fun'. Where some more fun comes in is when you get below 10%, that would be 10Amps using a 100A CT. The industry specs stop at 10%. A 0.3% transformer is only 0.3% at full rating (and above). Was just looking to see if anyone has come up with something new / low cost / etc. On Tue, Apr 29, 2014 at 12:06 PM, Brent Gordon <volt-nuts@adobe-labs.com>wrote: > Years ago I installed a TED-1000 (now obsolete) system from <http://www. > theenergydetective.com/>. Their software is terrible but the system > works. This system uses two current transformers and a single voltage > measurement system that all go inside your circuit breaker box. I don't > recall the sampling rate (1 KHz maybe). The instantaneous voltage and > current measurements are multiplied, summed, and transmitted once per > second. The data is transmitted to a receiver using the house wiring > (similar to X-10). People have hacked the system to use their own receiver. > > I haven't directly measured accuracy; monthly totals are usually about 5% > low when compared to my electric bill. The software compensates for > missing readings. Resolution seems to be around 10 watts. > > Brent > > > On 4/29/2014 11:25 AM, Pete Lancashire wrote: > >> Next spring I'm going be rewiring my house. And for 'fun' I want to drop a >> couple current sensors on the input side of the main panel. >> >> Being a beginner 'nut', I'm looking for more accuracy then needed. >> >> Voltage, Frequency, waveform will be taken care of later, but accurate >> current has be a bit flustered. >> >> I've been reading up on CT's Iron core and Ferrite, and on Rogowski coils. >> And the many new IC's on the market that take care of a lot of things. >> >> Has someone done this before ? And if so any experiences to share ? >> >> -pete >> >> _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/volt-nuts > and follow the instructions there. >
N
NeonJohn
Tue, Apr 29, 2014 11:16 PM

Hi Pete,

Retired utility engineer here with lots of metering experience.

If you want the right answers, don't stray from revenue metering
equipment.  FERC requires that revenue metering be within 1% of actual.
That means that even the tail of the error distribution curve has to be
better than 1%.  Most utilities I've worked with shoot for 0.25% and use
0.1% components.  CTs, PTs, revenue meters, revenue watts and VAR
transducers and so on.

The first thing you need to do is to set up your service entrance so
that you can experiment later.  That means being able to kill power to
your breaker panel.  What you want is the utility feed, a meter base, an
outdoor 200 amp service disconnect and have that feed your panel
indoors.  That way you can open the disconnect breaker and kill your
entire breaker panel and not have to try to work things hot.

The second thing I'd do is install a second meter base INSIDE between
your service disconnect and your panel.  That way you can install either
your own watt-hour meter or install jumper bars if you decide you don't
want your own meter.

You can get meter bases and meters for practically nothing here:

http://www.hialeahmeter.com/

That will be the most accurate power and energy measuring device you can
get your hands on for a reasonable amount of money.  Typically 0.1%.

Since you own the meter you can modify it.  You can install a
photo-interrupter to count disk rotations.  There is always a hole in
the disk called the anti-creep hole. (causes the wheel to stop under the
potential coil if there's no load but the wheel is still barely turning).

The Kh value printed on the meter face, normally 7.2 for 200 amp single
phase meters, is the number of WATT-hours (not KWH) that one turn of the
disk represents.  So you can total watt-hours by counting revolutions
and multiplying by Kh.  Take the rate (first derivative) and multiply by
7.2 to determine the current load in watts.

Every mechanical meter I've ever seen has 100 graduations around the
periphery of the wheel.  Some are printed and some are engraved.
There's a "zero flag" 5 divisions wide to mark the start of another
revolution.  If you rig up a retroflector sensor, you can count these
and have a 0.72 resolution.

If you want to measure voltage to revenue standards, use a voltage
transducer.  Typically the output is 0-1ma DC.  Many moons ago I settled
in on Ohio Semitronics as my supplier of transducers.

I've installed many energy audit systems in large factories where the
sum of several large load centers is compared to the input from the
utility.  The utility input is typically a pulse per X kWh.  In a large
plant such as a paper mill, the pulse would be per megawatt-hour.  The
individual measuring loops had to be quite accurate for their sum to
match the utility input to within less than a percent.  Ohio Semitronics
hardware never let me down.

The Chinese are making knockoffs that can be found on alibaba.com and
alimarketplace.com (or something like that).  I haven't used enough of
them to know their quality.

If you don't mind spending a little money, a revenue-grade 400:5 CT and
this instrument

http://www.ebay.com/itm/350423261101

Is what you need. It is a 3 phase meter but works just fine on single
phase.  I now work part-time designing induction heaters and this is my
lab standard for measuring heater power.  I matched my analog 0.1% lab
standard watt-meter exactly.  And it's true RMS.

Measuring the Edison three wire setup that we all have requires a little
setup.  You'll put the CT in your breaker panel with both hot leads
going through it.  One lead will be reversed from the other.  That way
120 volt to neutral loads are measured once while 240 volt loads are
measured twice. The meter's potential input is straight 240.

The key to making this work is to program your CT factor to HALF the
actual value.  So the real value is 400:5 or 80 but you program in 200:5
or 40.

It works like this.  A 240 volt load is measured twice so the signal is
240 X (2Xamps) * cos(theta) so the results would appear to be twice the
actual load.  But you've halved the CT factor so the indication is correct.

For a 120 volt load, the  signal 240 * amps * cos(theta).  That would
seem to be twice what the 120 volt load is pulling but again your CT
factor of half makes the reading correct.

For data processing, the meter has several digital output options.
Standard are RS-485 and RS-232.  Once a second it outputs a data
sentence similar to an NMEA signal in plain text that is easy to parse
and process further.  Optionally, the meter can have an ethernet
interface with a built-in web server.  I didn't find any value in that
so I didn't pay extra.

The revenue-grade CT and a revenue-grade meter is the only way that
you'll be able to make measurements accurate enough to compare to your
utility bill.

Especially stay away from the "solutions" that put a CT on each leg.
That creates the classical "small difference of two large values"
problem.  For example, if your heat pump is drawing 100 amps and a CF
lamp is drawing a quarter amp, the CF signal will be lost in the error
band.  Even a 0.1% 200 amp CT is +- 200 ma.  That's for each CT.  And
that's not counting the errors inherent in the circuitry that tries to
measure to that kind of resolution.

There are only two bad things that I can say about the above digital
meter.  First, the blue digits are very hard to read.  There is no
filter over the displays and the lit segments aren't very bright so it's
hard to tell which ones are lit if there is much room light.  I had to
make a hood out of black paper for mine.

The second thing is the manual.  The worst chinglish I've ever run into.
I waded through it enough to get my meter set up for my needs but it
was a chore.

Finally stay FAR away from electronic revenue meters.  Especially the
Iton brand.  I've consulted to one utility regarding electronic metering
and know the details of a couple more.  All have been unmitigated
disasters.  Failure rates are very high and accuracy is all over the place.

My rural co-op learned from these debacles and did it right.  They use
something called the Turtle system.  It involves a photo-interrupter
board that is added to the mechanical meter to count wheel turns.
Somehow it phase modulates the data at a very low baud rate the 60 hz
signal in a manner that goes back through transformers and bypasses
power factor correcting capacitors.  The data rate is very slow, hence
the name "turtle".  There's a patent describing the system but it's
probably the most obtuse document I've ever tried to read.

This system works extremely well.  I've never had a dispute between my
bill and my own meter reading.  See, even the smart utilities are
staying with mechanical meters!

Hope this helps.

John

On 04/29/2014 01:25 PM, Pete Lancashire wrote:

Next spring I'm going be rewiring my house. And for 'fun' I want to drop a
couple current sensors on the input side of the main panel.

Being a beginner 'nut', I'm looking for more accuracy then needed.

Voltage, Frequency, waveform will be taken care of later, but accurate
current has be a bit flustered.

I've been reading up on CT's Iron core and Ferrite, and on Rogowski coils.
And the many new IC's on the market that take care of a lot of things.

Has someone done this before ? And if so any experiences to share ?

-pete


volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.

--
John DeArmond
Tellico Plains, Occupied TN
http://www.fluxeon.com      <-- THE source for induction heaters
http://www.neon-john.com    <-- email from here
http://www.johndearmond.com <-- Best damned Blog on the net
PGP key: wwwkeys.pgp.net: BCB68D77

Hi Pete, Retired utility engineer here with lots of metering experience. If you want the right answers, don't stray from revenue metering equipment. FERC requires that revenue metering be within 1% of actual. That means that even the tail of the error distribution curve has to be better than 1%. Most utilities I've worked with shoot for 0.25% and use 0.1% components. CTs, PTs, revenue meters, revenue watts and VAR transducers and so on. The first thing you need to do is to set up your service entrance so that you can experiment later. That means being able to kill power to your breaker panel. What you want is the utility feed, a meter base, an outdoor 200 amp service disconnect and have that feed your panel indoors. That way you can open the disconnect breaker and kill your entire breaker panel and not have to try to work things hot. The second thing I'd do is install a second meter base INSIDE between your service disconnect and your panel. That way you can install either your own watt-hour meter or install jumper bars if you decide you don't want your own meter. You can get meter bases and meters for practically nothing here: http://www.hialeahmeter.com/ That will be the most accurate power and energy measuring device you can get your hands on for a reasonable amount of money. Typically 0.1%. Since you own the meter you can modify it. You can install a photo-interrupter to count disk rotations. There is always a hole in the disk called the anti-creep hole. (causes the wheel to stop under the potential coil if there's no load but the wheel is still barely turning). The Kh value printed on the meter face, normally 7.2 for 200 amp single phase meters, is the number of WATT-hours (not KWH) that one turn of the disk represents. So you can total watt-hours by counting revolutions and multiplying by Kh. Take the rate (first derivative) and multiply by 7.2 to determine the current load in watts. Every mechanical meter I've ever seen has 100 graduations around the periphery of the wheel. Some are printed and some are engraved. There's a "zero flag" 5 divisions wide to mark the start of another revolution. If you rig up a retroflector sensor, you can count these and have a 0.72 resolution. If you want to measure voltage to revenue standards, use a voltage transducer. Typically the output is 0-1ma DC. Many moons ago I settled in on Ohio Semitronics as my supplier of transducers. I've installed many energy audit systems in large factories where the sum of several large load centers is compared to the input from the utility. The utility input is typically a pulse per X kWh. In a large plant such as a paper mill, the pulse would be per megawatt-hour. The individual measuring loops had to be quite accurate for their sum to match the utility input to within less than a percent. Ohio Semitronics hardware never let me down. The Chinese are making knockoffs that can be found on alibaba.com and alimarketplace.com (or something like that). I haven't used enough of them to know their quality. If you don't mind spending a little money, a revenue-grade 400:5 CT and this instrument http://www.ebay.com/itm/350423261101 Is what you need. It is a 3 phase meter but works just fine on single phase. I now work part-time designing induction heaters and this is my lab standard for measuring heater power. I matched my analog 0.1% lab standard watt-meter exactly. And it's true RMS. Measuring the Edison three wire setup that we all have requires a little setup. You'll put the CT in your breaker panel with both hot leads going through it. One lead will be reversed from the other. That way 120 volt to neutral loads are measured once while 240 volt loads are measured twice. The meter's potential input is straight 240. The key to making this work is to program your CT factor to HALF the actual value. So the real value is 400:5 or 80 but you program in 200:5 or 40. It works like this. A 240 volt load is measured twice so the signal is 240 X (2Xamps) * cos(theta) so the results would appear to be twice the actual load. But you've halved the CT factor so the indication is correct. For a 120 volt load, the signal 240 * amps * cos(theta). That would seem to be twice what the 120 volt load is pulling but again your CT factor of half makes the reading correct. For data processing, the meter has several digital output options. Standard are RS-485 and RS-232. Once a second it outputs a data sentence similar to an NMEA signal in plain text that is easy to parse and process further. Optionally, the meter can have an ethernet interface with a built-in web server. I didn't find any value in that so I didn't pay extra. The revenue-grade CT and a revenue-grade meter is the only way that you'll be able to make measurements accurate enough to compare to your utility bill. Especially stay away from the "solutions" that put a CT on each leg. That creates the classical "small difference of two large values" problem. For example, if your heat pump is drawing 100 amps and a CF lamp is drawing a quarter amp, the CF signal will be lost in the error band. Even a 0.1% 200 amp CT is +- 200 ma. That's for each CT. And that's not counting the errors inherent in the circuitry that tries to measure to that kind of resolution. There are only two bad things that I can say about the above digital meter. First, the blue digits are very hard to read. There is no filter over the displays and the lit segments aren't very bright so it's hard to tell which ones are lit if there is much room light. I had to make a hood out of black paper for mine. The second thing is the manual. The worst chinglish I've ever run into. I waded through it enough to get my meter set up for my needs but it was a chore. Finally stay FAR away from electronic revenue meters. Especially the Iton brand. I've consulted to one utility regarding electronic metering and know the details of a couple more. All have been unmitigated disasters. Failure rates are very high and accuracy is all over the place. My rural co-op learned from these debacles and did it right. They use something called the Turtle system. It involves a photo-interrupter board that is added to the mechanical meter to count wheel turns. Somehow it phase modulates the data at a very low baud rate the 60 hz signal in a manner that goes back through transformers and bypasses power factor correcting capacitors. The data rate is very slow, hence the name "turtle". There's a patent describing the system but it's probably the most obtuse document I've ever tried to read. This system works extremely well. I've never had a dispute between my bill and my own meter reading. See, even the smart utilities are staying with mechanical meters! Hope this helps. John On 04/29/2014 01:25 PM, Pete Lancashire wrote: > Next spring I'm going be rewiring my house. And for 'fun' I want to drop a > couple current sensors on the input side of the main panel. > > Being a beginner 'nut', I'm looking for more accuracy then needed. > > Voltage, Frequency, waveform will be taken care of later, but accurate > current has be a bit flustered. > > I've been reading up on CT's Iron core and Ferrite, and on Rogowski coils. > And the many new IC's on the market that take care of a lot of things. > > Has someone done this before ? And if so any experiences to share ? > > -pete > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > -- John DeArmond Tellico Plains, Occupied TN http://www.fluxeon.com <-- THE source for induction heaters http://www.neon-john.com <-- email from here http://www.johndearmond.com <-- Best damned Blog on the net PGP key: wwwkeys.pgp.net: BCB68D77
BC
Brooke Clarke
Wed, Apr 30, 2014 12:08 AM

Hi Pete:

I did this may decades ago.

  1. Do not use clamp on current probes, they have very poor accuracy at low currents.

  2. Rather than using a current monitor on each circuit just use two current sensors, one on each input leg.

  3. Current transformers MUST be terminated with some load resistance, i.e. they transform an input current into an
    output current which gets changed to an output voltage by the load resistor.  I put the load resistor close to the
    current transformer so that a break in the long cable would not cause a problem.

  4. I plotted current use on an 8.5 x 11 paper in landscape mode. Each trace was offset from the prior trace by about
    1/4".  At night when not much is happening  you just have a bunch of straight lines, except for the frig which has a
    regular cycle. But if someone gets up at night you can tell.

Smart meters can provide data every  15 minutes, if they are in a network.  My smart meter gets read manually so no data.
http://www.prc68.com/I/SmartMeters.shtml

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

Pete Lancashire wrote:

Next spring I'm going be rewiring my house. And for 'fun' I want to drop a
couple current sensors on the input side of the main panel.

Being a beginner 'nut', I'm looking for more accuracy then needed.

Voltage, Frequency, waveform will be taken care of later, but accurate
current has be a bit flustered.

I've been reading up on CT's Iron core and Ferrite, and on Rogowski coils.
And the many new IC's on the market that take care of a lot of things.

Has someone done this before ? And if so any experiences to share ?

-pete


volt-nuts mailing list -- volt-nuts@febo.com
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Hi Pete: I did this may decades ago. 1) Do not use clamp on current probes, they have very poor accuracy at low currents. 2) Rather than using a current monitor on each circuit just use two current sensors, one on each input leg. 3) Current transformers MUST be terminated with some load resistance, i.e. they transform an input current into an output current which gets changed to an output voltage by the load resistor. I put the load resistor close to the current transformer so that a break in the long cable would not cause a problem. 4) I plotted current use on an 8.5 x 11 paper in landscape mode. Each trace was offset from the prior trace by about 1/4". At night when not much is happening you just have a bunch of straight lines, except for the frig which has a regular cycle. But if someone gets up at night you can tell. Smart meters can provide data every 15 minutes, if they are in a network. My smart meter gets read manually so no data. http://www.prc68.com/I/SmartMeters.shtml Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Pete Lancashire wrote: > Next spring I'm going be rewiring my house. And for 'fun' I want to drop a > couple current sensors on the input side of the main panel. > > Being a beginner 'nut', I'm looking for more accuracy then needed. > > Voltage, Frequency, waveform will be taken care of later, but accurate > current has be a bit flustered. > > I've been reading up on CT's Iron core and Ferrite, and on Rogowski coils. > And the many new IC's on the market that take care of a lot of things. > > Has someone done this before ? And if so any experiences to share ? > > -pete > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. >