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Guest

Sun Jan 06, 2019 8:45 pm   



My understanding is that utility meters measure instantaneous voltage and current (simultaneously) at a rate much higher than the AC period and use the sum of the products over a time period (typically a multiple of the AC period) to measure power. Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time period and calculating the product. From these two the reactive power and power factor can be calculated.

Did I leave out anything important? Or did I completely misunderstand what is going on?

Rick C.

- Get 6 months of free supercharging
- Tesla referral code - https://ts.la/richard11209

Lasse Langwadt Christense
Guest

Sun Jan 06, 2019 8:45 pm   



søndag den 6. januar 2019 kl. 20.10.39 UTC+1 skrev gnuarm.del...@gmail..com:
Quote:
My understanding is that utility meters measure instantaneous voltage and current (simultaneously) at a rate much higher than the AC period and use the sum of the products over a time period (typically a multiple of the AC period) to measure power. Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time period and calculating the product. From these two the reactive power and power factor can be calculated.

Did I leave out anything important? Or did I completely misunderstand what is going on?


https://www.analog.com/media/en/technical-documentation/data-sheets/ade9153a.pdf

Lasse Langwadt Christense
Guest

Sun Jan 06, 2019 9:45 pm   



søndag den 6. januar 2019 kl. 21.01.27 UTC+1 skrev whit3rd:
Quote:
On Sunday, January 6, 2019 at 11:10:39 AM UTC-8, gnuarm.del...@gmail.com wrote:
My understanding is that utility meters measure instantaneous voltage and current (simultaneously) at a rate much higher than the AC period ...

Yes, so far so good.
and use the sum of the products over a time period (typically a multiple of the AC period) to measure power.

Not required; those products ARE the instantaneous power, and they sum to reach the
real goal, the energy-delivered (kWh) reading. The meter just accumulates and scales
according to its time-calibration of the measurement period.

Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time period and calculating the product. From these two the reactive power and power factor can be calculated.

Most utility meters don't display such detail. Whether they calculate/record/report it, though,
is uncertain. My (new, digital) meter is less forthcoming than the old moving-dials one,
you cannot see the power (energy use rate) spinning a disk, you have to
watch, capture two digital measurement energy displays, use a stopwatch....


here I think they all have an LED that flashes once per Wh

John Larkin
Guest

Sun Jan 06, 2019 9:45 pm   



On Sun, 6 Jan 2019 12:01:22 -0800 (PST), whit3rd <whit3rd_at_gmail.com>
wrote:

Quote:
On Sunday, January 6, 2019 at 11:10:39 AM UTC-8, gnuarm.del...@gmail.com wrote:
My understanding is that utility meters measure instantaneous voltage and current (simultaneously) at a rate much higher than the AC period ...

Yes, so far so good.
and use the sum of the products over a time period (typically a multiple of the AC period) to measure power.

Not required; those products ARE the instantaneous power, and they sum to reach the
real goal, the energy-delivered (kWh) reading. The meter just accumulates and scales
according to its time-calibration of the measurement period.

Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time period and calculating the product. From these two the reactive power and power factor can be calculated.

Most utility meters don't display such detail. Whether they calculate/record/report it, though,
is uncertain. My (new, digital) meter is less forthcoming than the old moving-dials one,
you cannot see the power (energy use rate) spinning a disk, you have to
watch, capture two digital measurement energy displays, use a stopwatch...


Time-of-use billing measures average power over some intervals, like 5
minutes maybe.

Online connected meters can report everything: power, voltage, power
factor.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

John Larkin
Guest

Sun Jan 06, 2019 9:45 pm   



On Sun, 6 Jan 2019 11:30:16 -0800 (PST), Lasse Langwadt Christensen
<langwadt_at_fonz.dk> wrote:

Quote:
sndag den 6. januar 2019 kl. 20.10.39 UTC+1 skrev gnuarm.del...@gmail.com:
My understanding is that utility meters measure instantaneous voltage and current (simultaneously) at a rate much higher than the AC period and use the sum of the products over a time period (typically a multiple of the AC period) to measure power. Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time period and calculating the product. From these two the reactive power and power factor can be calculated.

Did I leave out anything important? Or did I completely misunderstand what is going on?


https://www.analog.com/media/en/technical-documentation/data-sheets/ade9153a.pdf


The ADCs used in power metering need not have high sample rates nor
low noise; a few LSBs of noise are actually good. We are trying to
gather statistics on millions of samples of the E*I product, not
reproduce the waveforms. The Sampling Theorem doesn't apply here.

I sold hundreds of thousands of channels of AC power metering that
used single-slope ADCs sampling at around 27 Hz.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

whit3rd
Guest

Sun Jan 06, 2019 9:45 pm   



On Sunday, January 6, 2019 at 11:10:39 AM UTC-8, gnuarm.del...@gmail.com wrote:
> My understanding is that utility meters measure instantaneous voltage and current (simultaneously) at a rate much higher than the AC period ...

Yes, so far so good.
>and use the sum of the products over a time period (typically a multiple of the AC period) to measure power.

Not required; those products ARE the instantaneous power, and they sum to reach the
real goal, the energy-delivered (kWh) reading. The meter just accumulates and scales
according to its time-calibration of the measurement period.

Quote:
Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time period and calculating the product. From these two the reactive power and power factor can be calculated.

Most utility meters don't display such detail. Whether they calculate/record/report it, though,
is uncertain. My (new, digital) meter is less forthcoming than the old moving-dials one,
you cannot see the power (energy use rate) spinning a disk, you have to
watch, capture two digital measurement energy displays, use a stopwatch...


Guest

Sun Jan 06, 2019 10:45 pm   



On Sunday, 6 January 2019 19:10:39 UTC, gnuarm.del...@gmail.com wrote:

Quote:
My understanding is that utility meters measure instantaneous voltage and current (simultaneously) at a rate much higher than the AC period and use the sum of the products over a time period (typically a multiple of the AC period) to measure power. Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time period and calculating the product. From these two the reactive power and power factor can be calculated.

Did I leave out anything important? Or did I completely misunderstand what is going on?

Rick C.

- Get 6 months of free supercharging
- Tesla referral code - https://ts.la/richard11209


Most are electromagnetic followed by a mechanical gear train adder. They are insensitive to imaginary power.


NT

Mike
Guest

Sun Jan 06, 2019 11:45 pm   



On 1/6/2019 12:19 PM, Lasse Langwadt Christensen wrote:
Quote:
søndag den 6. januar 2019 kl. 21.01.27 UTC+1 skrev whit3rd:
On Sunday, January 6, 2019 at 11:10:39 AM UTC-8, gnuarm.del...@gmail.com wrote:
My understanding is that utility meters measure instantaneous voltage and current (simultaneously) at a rate much higher than the AC period ...

Yes, so far so good.
and use the sum of the products over a time period (typically a multiple of the AC period) to measure power.

Not required; those products ARE the instantaneous power, and they sum to reach the
real goal, the energy-delivered (kWh) reading. The meter just accumulates and scales
according to its time-calibration of the measurement period.

Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time period and calculating the product. From these two the reactive power and power factor can be calculated.

Most utility meters don't display such detail. Whether they calculate/record/report it, though,
is uncertain. My (new, digital) meter is less forthcoming than the old moving-dials one,
you cannot see the power (energy use rate) spinning a disk, you have to
watch, capture two digital measurement energy displays, use a stopwatch...

here I think they all have an LED that flashes once per Wh

If you have an old PDA, like a Palm Pilot, with an IR sensor, it's
relatively
easy to read/log those flashes to track usage.

Lasse Langwadt Christense
Guest

Sun Jan 06, 2019 11:45 pm   



søndag den 6. januar 2019 kl. 22.48.13 UTC+1 skrev Mike:
Quote:
On 1/6/2019 12:19 PM, Lasse Langwadt Christensen wrote:
søndag den 6. januar 2019 kl. 21.01.27 UTC+1 skrev whit3rd:
On Sunday, January 6, 2019 at 11:10:39 AM UTC-8, gnuarm.del...@gmail.com wrote:
My understanding is that utility meters measure instantaneous voltage and current (simultaneously) at a rate much higher than the AC period ...

Yes, so far so good.
and use the sum of the products over a time period (typically a multiple of the AC period) to measure power.

Not required; those products ARE the instantaneous power, and they sum to reach the
real goal, the energy-delivered (kWh) reading. The meter just accumulates and scales
according to its time-calibration of the measurement period.

Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time period and calculating the product. From these two the reactive power and power factor can be calculated.

Most utility meters don't display such detail. Whether they calculate/record/report it, though,
is uncertain. My (new, digital) meter is less forthcoming than the old moving-dials one,
you cannot see the power (energy use rate) spinning a disk, you have to
watch, capture two digital measurement energy displays, use a stopwatch...

here I think they all have an LED that flashes once per Wh

If you have an old PDA, like a Palm Pilot, with an IR sensor, it's
relatively
easy to read/log those flashes to track usage.


afaiu quite a few of those used have also have an IR serial port and with a reasonable easy to guess code you can read out all the instantaneous and accumulated values

Rob
Guest

Sun Jan 06, 2019 11:45 pm   



John Larkin <jjlarkin_at_highlandtechnology.com> wrote:
Quote:
On Sun, 6 Jan 2019 11:30:16 -0800 (PST), Lasse Langwadt Christensen
langwadt_at_fonz.dk> wrote:

søndag den 6. januar 2019 kl. 20.10.39 UTC+1 skrev gnuarm.del...@gmail.com:
My understanding is that utility meters measure instantaneous voltage and current (simultaneously) at a rate much higher than the AC period and use the sum of the products over a time period (typically a multiple of the AC period) to measure power. Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time period and calculating the product. From these two the reactive power and power factor can be calculated.

Did I leave out anything important? Or did I completely misunderstand what is going on?


https://www.analog.com/media/en/technical-documentation/data-sheets/ade9153a.pdf

The ADCs used in power metering need not have high sample rates nor
low noise; a few LSBs of noise are actually good. We are trying to
gather statistics on millions of samples of the E*I product, not
reproduce the waveforms. The Sampling Theorem doesn't apply here.

I sold hundreds of thousands of channels of AC power metering that
used single-slope ADCs sampling at around 27 Hz.


It may matter. When the current is far from sinusoidal, the computed
power may be much more when the calculation is not done carefully, or
when there are problems with the filtering.

A while ago there was some local coverage here in the Netherlands on a
consumer tv programme about the fact that so many customers observe an
increased energy consumption when they have a "smart meter" installed.
Usually before that, they had an electromechanical meter of the
"Ferraris" type, and now it is replaced with an electronic meter with
remote readout capabilties (called "smart meter" here).

Of course the difference is not related to the remote readout but to
the electronic measurement technology.

I studied the relevant regulations for an electricity meter and also
mailed with the responsible person at the authority. It turns out that
nowhere in the regulations the non-sinusoidal current problem is
discussed. The only thing appearing in the standards is the handling
of Cos-Phi. The meter should indicate kWh, not kVAh.

However, in today's households there tends to be a non-sinusoidal
current due to small switchmode powersupplies (that are not mandatory
to have powerfactor correction), LED lamps, etc.
The result is that the electronic meter registers more than the Ferraris
meter. How much more, that depends on the exact make and model of meter.

But that is all within spec, because THERE IS NO SPEC.
When you claim the meter is wrong, it is being checked with a resistive
load and of course that is metered correctly...

The difficult problem of course is: what is reasonable. One could also
argue that the Ferraris meter displayed a too-low value, as the
electricity companies have to deal with the non-sinusoidal current
which causes them all kinds of problems. The customer should pay for
that or stop doing it.

The last word has not been said about it, but for now I have deferred
the change to a smart meter, and so have many others.

Mike
Guest

Mon Jan 07, 2019 10:20 am   



In article <2b479eeb-d642-42b6-88b3-32b821830455_at_googlegroups.com>,
Lasse Langwadt Christensen <langwadt_at_fonz.dk> wrote:

>> > here I think they all have an LED that flashes once per Wh

Here (UK) even my Siemens, non-smart-but-digital, meter has a blink-per-wH
LED (orange) which you could monitor externally with a sensor without
tampering.

Quote:
If you have an old PDA, like a Palm Pilot, with an IR sensor, it's=20
relatively
easy to read/log those flashes to track usage.

afaiu quite a few of those used have also have an IR serial port and with a=
reasonable easy to guess code you can read out all the instantaneous and a=
ccumulated values


It has the split-IR port too (TX, RX halves) for setup/reading (never used
since install).

Elektor ran a project for this, with details of the coding/electronics for the
IR port. Some features are behind an encrypted/password wall, presumably
stuff like "reset counter" and "change tarriff settings" :)

Found it: Elektor (UK) 2002 March, "IEC 1107 Electricity Meter Interface"
(although Wikipedia refers to it as IEC *6*1107, later renamed to IEC
62056-21)

https://en.wikipedia.org/wiki/IEC_62056

--
--------------------------------------+------------------------------------
Mike Brown: mjb[-at-]signal11.org.uk | http://www.signal11.org.uk

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elektroda.net NewsGroups Forum Index - Electronics Design - Utility Power Meters

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