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Lasse Langwadt Christense
Guest

Wed Apr 29, 2020 2:45 am   



onsdag den 29. april 2020 kl. 02.50.46 UTC+2 skrev jla...@highlandsniptechnology.com:
Quote:
On Tue, 28 Apr 2020 17:15:36 -0700 (PDT), Lasse Langwadt Christensen
langwadt_at_fonz.dk> wrote:

onsdag den 29. april 2020 kl. 01.20.28 UTC+2 skrev Ricky C:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a écrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin_at_highlandsniptechnology.com a écrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.


https://youtu.be/xtModjpxfxM

That meter uses one voltage coil line-line, and two current coils.
That assumes that the 120-0-120 volt line is symmetric, which is
imperfect but saves money in the meter.


looks to me like it is just one line and one neutral


Guest

Wed Apr 29, 2020 2:45 am   



On Tue, 28 Apr 2020 17:15:36 -0700 (PDT), Lasse Langwadt Christensen
<langwadt_at_fonz.dk> wrote:

Quote:
onsdag den 29. april 2020 kl. 01.20.28 UTC+2 skrev Ricky C:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Le 27/04/2020 21:31, John Larkin a crit:
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Le 27/04/2020 18:30, jlarkin_at_highlandsniptechnology.com a crit:
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.


https://youtu.be/xtModjpxfxM


That meter uses one voltage coil line-line, and two current coils.
That assumes that the 120-0-120 volt line is symmetric, which is
imperfect but saves money in the meter.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

Lasse Langwadt Christense
Guest

Wed Apr 29, 2020 3:45 am   



onsdag den 29. april 2020 kl. 04.06.55 UTC+2 skrev jla...@highlandsniptechnology.com:
Quote:
On Tue, 28 Apr 2020 18:01:10 -0700 (PDT), Lasse Langwadt Christensen
langwadt_at_fonz.dk> wrote:

onsdag den 29. april 2020 kl. 02.50.46 UTC+2 skrev jla...@highlandsniptechnology.com:
On Tue, 28 Apr 2020 17:15:36 -0700 (PDT), Lasse Langwadt Christensen
langwadt_at_fonz.dk> wrote:

onsdag den 29. april 2020 kl. 01.20.28 UTC+2 skrev Ricky C:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a écrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin_at_highlandsniptechnology.com a écrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors....
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.


https://youtu.be/xtModjpxfxM

That meter uses one voltage coil line-line, and two current coils.
That assumes that the 120-0-120 volt line is symmetric, which is
imperfect but saves money in the meter.


looks to me like it is just one line and one neutral

Right. The usual US meter has one voltage coil and two current coils.
That internal element has those two current coils, but looks to be
connected in the housing to only meter one current.

That would be very rare in the USA, to meter a single 120-N service.
That's ancient.


maybe for something like stair lights ?


Guest

Wed Apr 29, 2020 3:45 am   



On Tue, 28 Apr 2020 18:01:10 -0700 (PDT), Lasse Langwadt Christensen
<langwadt_at_fonz.dk> wrote:

Quote:
onsdag den 29. april 2020 kl. 02.50.46 UTC+2 skrev jla...@highlandsniptechnology.com:
On Tue, 28 Apr 2020 17:15:36 -0700 (PDT), Lasse Langwadt Christensen
langwadt_at_fonz.dk> wrote:

onsdag den 29. april 2020 kl. 01.20.28 UTC+2 skrev Ricky C:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Le 27/04/2020 21:31, John Larkin a crit:
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Le 27/04/2020 18:30, jlarkin_at_highlandsniptechnology.com a crit:
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.


https://youtu.be/xtModjpxfxM

That meter uses one voltage coil line-line, and two current coils.
That assumes that the 120-0-120 volt line is symmetric, which is
imperfect but saves money in the meter.


looks to me like it is just one line and one neutral


Right. The usual US meter has one voltage coil and two current coils.
That internal element has those two current coils, but looks to be
connected in the housing to only meter one current.

That would be very rare in the USA, to meter a single 120-N service.
That's ancient.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

Ricky C
Guest

Wed Apr 29, 2020 4:45 am   



On Tuesday, April 28, 2020 at 10:16:55 PM UTC-4, Lasse Langwadt Christensen wrote:
Quote:
onsdag den 29. april 2020 kl. 04.06.55 UTC+2 skrev jla...@highlandsniptechnology.com:
On Tue, 28 Apr 2020 18:01:10 -0700 (PDT), Lasse Langwadt Christensen
langwadt_at_fonz.dk> wrote:

onsdag den 29. april 2020 kl. 02.50.46 UTC+2 skrev jla...@highlandsniptechnology.com:
On Tue, 28 Apr 2020 17:15:36 -0700 (PDT), Lasse Langwadt Christensen
langwadt_at_fonz.dk> wrote:

onsdag den 29. april 2020 kl. 01.20.28 UTC+2 skrev Ricky C:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a écrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin_at_highlandsniptechnology.com a écrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise..
(You'd have to have some means of getting rid of all the errors....
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.


https://youtu.be/xtModjpxfxM

That meter uses one voltage coil line-line, and two current coils.
That assumes that the 120-0-120 volt line is symmetric, which is
imperfect but saves money in the meter.


looks to me like it is just one line and one neutral

Right. The usual US meter has one voltage coil and two current coils.
That internal element has those two current coils, but looks to be
connected in the housing to only meter one current.

That would be very rare in the USA, to meter a single 120-N service.
That's ancient.


maybe for something like stair lights ?


Not likely to need a separate meter for stair lights, but we do have a lot of outdoor lights on tall poles all supplied by the power company. Typically they are billed with a fixed fee, but I believe some locations meter the electricity and bill accordingly. That could easily be 120VAC rather than 240VAC.

I noticed the unit in the video had a crack in the glass, so likely removed from service while still working.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

Michael Terrell
Guest

Wed Apr 29, 2020 6:45 am   



On Tuesday, April 28, 2020 at 10:06:55 PM UTC-4, jla...@highlandsniptechnology.com wrote:
Quote:
On Tue, 28 Apr 2020 18:01:10 -0700 (PDT), Lasse Langwadt Christensen
langwadt_at_fonz.dk> wrote:

onsdag den 29. april 2020 kl. 02.50.46 UTC+2 skrev jla...@highlandsniptechnology.com:
On Tue, 28 Apr 2020 17:15:36 -0700 (PDT), Lasse Langwadt Christensen
langwadt_at_fonz.dk> wrote:

onsdag den 29. april 2020 kl. 01.20.28 UTC+2 skrev Ricky C:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a écrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin_at_highlandsniptechnology.com a écrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet_at_free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors....
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.


https://youtu.be/xtModjpxfxM

That meter uses one voltage coil line-line, and two current coils.
That assumes that the 120-0-120 volt line is symmetric, which is
imperfect but saves money in the meter.


looks to me like it is just one line and one neutral

Right. The usual US meter has one voltage coil and two current coils.
That internal element has those two current coils, but looks to be
connected in the housing to only meter one current.

That would be very rare in the USA, to meter a single 120-N service.
That's ancient.


The last meter I saw for 120V was installed in 1945, and removed in 1966 from the garage of a house my parents bought when I was starting high school. The original owner had built a small cottage to live in while the actual house was built. After that, they cut away most of the wood floors to use it for a garage. My dad and I finished removing a center wall, and the rest of the floor because '60s cars were too wide for the missing wood. We had the separate 120V service turned off, then I ran 240 to it from the main house. My first Electronics workshop was built on the back of that building while I was in high school.

Ricky C
Guest

Wed Apr 29, 2020 6:45 am   



On Wednesday, April 29, 2020 at 12:46:36 AM UTC-4, upsid...@downunder.com wrote:
Quote:
On Tue, 28 Apr 2020 16:20:22 -0700 (PDT), Ricky C
gnuarm.deletethisbit_at_gmail.com> wrote:

But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.

Today's meter's do the same thing by measuring the instantaneous voltage and current and finding the product. It is easy to find various circuits to multiply two quantities. It's not hard to find various ways to measure voltage and current. Async voltage to PWM converters for both the voltage and the current taps, then use an XOR to find the instantaneous product. Smooth the pulses and you have an analog signal proportional to the instantaneous power.

Generate analog signals for the instantaneous voltage and current.
Generate the log of the signals and sum them giving power.

log(U) + log(I) = log(P)

If you need to sum (for averaging) individual power samples, you need
to use antilog( log(P) ) before summing different samples. The
exponential function required dynamic range is much larger than for
either log(U) or log(I).

This would require the two inputs to be biased since the input to the log can't go through zero. The bias would be subtracted out at the end potentially creating a problem of a small difference of two large signals.

Just use abs() (full wave rectification) before the log(),


There will be times of zero current and/or voltage. It's not about the sign. It's about the undefined nature of log(0) and what happens as you approach it. I can't think of a way to deal with this issue other than to add a bias. I suppose the two could be combined, abs() with a small bias added making the difference between large numbers only an issue at low values. But this is not a very practical solution anyway.

A bit of making a silk purse from a sow's ear... or gilding the lily. Pick one.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209


Guest

Wed Apr 29, 2020 6:45 am   



On Tue, 28 Apr 2020 16:20:22 -0700 (PDT), Ricky C
<gnuarm.deletethisbit_at_gmail.com> wrote:

Quote:
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.

Today's meter's do the same thing by measuring the instantaneous voltage and current and finding the product. It is easy to find various circuits to multiply two quantities. It's not hard to find various ways to measure voltage and current. Async voltage to PWM converters for both the voltage and the current taps, then use an XOR to find the instantaneous product. Smooth the pulses and you have an analog signal proportional to the instantaneous power.

Generate analog signals for the instantaneous voltage and current.
Generate the log of the signals and sum them giving power.


log(U) + log(I) = log(P)

If you need to sum (for averaging) individual power samples, you need
to use antilog( log(P) ) before summing different samples. The
exponential function required dynamic range is much larger than for
either log(U) or log(I).

>This would require the two inputs to be biased since the input to the log can't go through zero. The bias would be subtracted out at the end potentially creating a problem of a small difference of two large signals.

Just use abs() (full wave rectification) before the log(),

Jasen Betts
Guest

Wed Apr 29, 2020 9:45 am   



On 2020-04-28, Ricky C <gnuarm.deletethisbit_at_gmail.com> wrote:

Quote:
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one

for voltage. Their effect on an aluminum disk is proportional to the
product including the phase angle, in other words the complex product
of voltage and current. The meter has fixed magnets that create drag
making the rotational speed of the rotor proportional to the power
being drawn.
Quote:

So really the meter is measuring the voltage and the current

including the relative phase, then finding the product though the EM
effects on the disk.


Quote:
Today's meter's do the same thing by measuring the instantaneous
voltage and current and finding the product. It is easy to find
various circuits to multiply two quantities. It's not hard to find
various ways to measure voltage and current. Async voltage to PWM
converters for both the voltage and the current taps, then use an XOR
to find the instantaneous product. Smooth the pulses and you have an
analog signal proportional to the instantaneous power.


seems kind of dodgy, you need to keep those two clocks decorellated.

Quote:
Generate analog signals for the instantaneous voltage and current.
Generate the log of the signals and sum them giving power. This would
require the two inputs to be biased since the input to the log can't
go through zero. The bias would be subtracted out at the end
potentially creating a problem of a small difference of two large
signals.


bias precision could be a problem, you have the same issue with the
PWM scheme.

pass a current proportional to line voltage through a hall effect cell and
derive the magnetic field from the line current

output voltage will be proportional to istantaneous power.
--
Jasen.


Guest

Wed Apr 29, 2020 3:45 pm   



On Wed, 29 Apr 2020 07:46:30 +0300, upsidedown_at_downunder.com wrote:

Quote:
On Tue, 28 Apr 2020 16:20:22 -0700 (PDT), Ricky C
gnuarm.deletethisbit_at_gmail.com> wrote:

But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.

Today's meter's do the same thing by measuring the instantaneous voltage and current and finding the product. It is easy to find various circuits to multiply two quantities. It's not hard to find various ways to measure voltage and current. Async voltage to PWM converters for both the voltage and the current taps, then use an XOR to find the instantaneous product. Smooth the pulses and you have an analog signal proportional to the instantaneous power.

Generate analog signals for the instantaneous voltage and current.
Generate the log of the signals and sum them giving power.

log(U) + log(I) = log(P)

If you need to sum (for averaging) individual power samples, you need
to use antilog( log(P) ) before summing different samples. The
exponential function required dynamic range is much larger than for
either log(U) or log(I).

This would require the two inputs to be biased since the input to the log can't go through zero. The bias would be subtracted out at the end potentially creating a problem of a small difference of two large signals.

Just use abs() (full wave rectification) before the log(),


The instantaneous power product goes negative when the power factor is
<1. You've got to preserve the signs.

Just multiply! Preferably in software.

A utility-class meter might handle 30KW and needs to be accurate to a
few watts. That's borderline impossible to do with analog electronics,
borderline trivial with a mediocre ADC and a cheap uP.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard


Guest

Wed Apr 29, 2020 3:45 pm   



On Wed, 29 Apr 2020 07:57:03 -0000 (UTC), Jasen Betts
<jasen_at_xnet.co.nz> wrote:

Quote:
On 2020-04-28, Ricky C <gnuarm.deletethisbit_at_gmail.com> wrote:

and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one
for voltage. Their effect on an aluminum disk is proportional to the
product including the phase angle, in other words the complex product
of voltage and current. The meter has fixed magnets that create drag
making the rotational speed of the rotor proportional to the power
being drawn.

So really the meter is measuring the voltage and the current
including the relative phase, then finding the product though the EM
effects on the disk.


Today's meter's do the same thing by measuring the instantaneous
voltage and current and finding the product. It is easy to find
various circuits to multiply two quantities. It's not hard to find
various ways to measure voltage and current. Async voltage to PWM
converters for both the voltage and the current taps, then use an XOR
to find the instantaneous product. Smooth the pulses and you have an
analog signal proportional to the instantaneous power.

seems kind of dodgy, you need to keep those two clocks decorellated.

Generate analog signals for the instantaneous voltage and current.
Generate the log of the signals and sum them giving power. This would
require the two inputs to be biased since the input to the log can't
go through zero. The bias would be subtracted out at the end
potentially creating a problem of a small difference of two large
signals.

bias precision could be a problem, you have the same issue with the
PWM scheme.

pass a current proportional to line voltage through a hall effect cell and
derive the magnetic field from the line current

output voltage will be proportional to istantaneous power.


Halls have been used, mostly in the ancient past, in expensive and not
very accurate AC power transducers, but not, as far as I know, in
utility-worthy meters.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

Ricky C
Guest

Wed Apr 29, 2020 9:45 pm   



On Wednesday, April 29, 2020 at 10:25:04 AM UTC-4, jla...@highlandsniptechnology.com wrote:
Quote:
On Wed, 29 Apr 2020 07:46:30 +0300, upsidedown_at_downunder.com wrote:

On Tue, 28 Apr 2020 16:20:22 -0700 (PDT), Ricky C
gnuarm.deletethisbit_at_gmail.com> wrote:

But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.

Today's meter's do the same thing by measuring the instantaneous voltage and current and finding the product. It is easy to find various circuits to multiply two quantities. It's not hard to find various ways to measure voltage and current. Async voltage to PWM converters for both the voltage and the current taps, then use an XOR to find the instantaneous product. Smooth the pulses and you have an analog signal proportional to the instantaneous power.

Generate analog signals for the instantaneous voltage and current.
Generate the log of the signals and sum them giving power.

log(U) + log(I) = log(P)

If you need to sum (for averaging) individual power samples, you need
to use antilog( log(P) ) before summing different samples. The
exponential function required dynamic range is much larger than for
either log(U) or log(I).

This would require the two inputs to be biased since the input to the log can't go through zero. The bias would be subtracted out at the end potentially creating a problem of a small difference of two large signals.

Just use abs() (full wave rectification) before the log(),

The instantaneous power product goes negative when the power factor is
1. You've got to preserve the signs.


No one said to toss the sign. The point is before taking the log the absolute value can be used to make the log more tractable and the sign kept separately as in sign * exp(log(s)). Do the math by adding the log(V) to log(I) and separately multiplying the signs.

It's simple math. High school kids can do it. You should try to learn some of this stuff.


> Just multiply! Preferably in software.

I guess you missed the post about brain storming the approach. Not looking for perfect or even obviously practical. Just looking for novel.


Quote:
A utility-class meter might handle 30KW and needs to be accurate to a
few watts. That's borderline impossible to do with analog electronics,
borderline trivial with a mediocre ADC and a cheap uP.


I'm glad you understand the utility of digital electronics. Now you just need to learn to use them.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

whit3rd
Guest

Thu Apr 30, 2020 10:45 am   



On Tuesday, April 28, 2020 at 9:46:36 PM UTC-7, upsid...@downunder.com wrote:
Quote:
On Tue, 28 Apr 2020 16:20:22 -0700 (PDT), Ricky C
gnuarm.deletethisbit_at_gmail.com> wrote:

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product

log(U) + log(I) = log(P)

If you need to sum (for averaging) individual power samples, you need
to use antilog( log(P) ) before summing...


> Just use abs() (full wave rectification) before the log(),

You'll need to handle negative power, when V and I are opposite in sign. Grab
the signs before taking those absolute values!

A hybrid (keep the wheel) with some turns-counting in silicon is an elegant compromise.

Ricky C
Guest

Thu Apr 30, 2020 9:45 pm   



On Thursday, April 30, 2020 at 4:59:28 AM UTC-4, whit3rd wrote:
Quote:
On Tuesday, April 28, 2020 at 9:46:36 PM UTC-7, upsid...@downunder.com wrote:
On Tue, 28 Apr 2020 16:20:22 -0700 (PDT), Ricky C
gnuarm.deletethisbit_at_gmail.com> wrote:

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product

log(U) + log(I) = log(P)

If you need to sum (for averaging) individual power samples, you need
to use antilog( log(P) ) before summing...


Just use abs() (full wave rectification) before the log(),

You'll need to handle negative power, when V and I are opposite in sign. Grab
the signs before taking those absolute values!

A hybrid (keep the wheel) with some turns-counting in silicon is an elegant compromise.


The wheel is easy to tamper with. Just provide a magnetic field and it works like the brake slowing the meter. You can even use metered power to create the magnetic field and have the power company pay for it.

--

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

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