Analog dynamic range, accuracy and number of bits

Le 03/11/2012 18:03, John Larkin a écrit :

Yes correct, each ADC has it's own oscillator. No need such a 5ppm as long as i resync the internal DS modulator, one time each second.

We have specified some insulation groups and among them Currents and Voltages are two independent goups with 2KV of dieclectric strenght. That is the reason of we could not run analog signals on one and only one ADC for Current and voltage simultaneously. I admit it's an weird thing ... but guys are insisted heavily on the point ...

Remember my holidays are a non negligible part of the project ... ;-)

Le 03/11/2012 18:32, rickman a écrit :

As usual,

H.

l* =

Actually, that 'n' does not stand for "nominal" any more. Energy meter I= EC =

standards define all these terms: In - rated current / courant assign=C3=A9e (for meters connected via cur= rent =

transformers) Ib - basic current / courant de base (for directly connected meters, can= =

also be CT based!) Un - reference voltage / tension de r=C3=A9f=C3=A9rence

These are just "nominal" values used when specifying various parameters = of =

the meter, such as ranges of acceptable errors. For example, a Class 1 =

meter must have an active energy error below 1.5% at PF =3D 1 in the cur= rent =

range from 0.05*Ib to 0.1*Ib, etc.

Currently in Europe we're using the EU MID directive instead of old IEC = =

standards, but the terminology stays mostly the same.

ae

-- =

synchronized.

I sounds like they are clocked delta-sigmas with independent crystal oscillator clocks, and they need to be resynchronized once a second to correct for clock drift. If that's so, it seems like a weird architecture.

So what did the OP really mean when he wrote "I range (0,02In .. In,

Actually I think this is mixing things a bit. U may be fine for the math symbol, but when he is saying "0,8Un" shouldn't that be Un = 0,8V or something like that? But clearly he is not talking about a voltage range of of 0.8 to 1.5 volts. At this point I have no idea what he is describing here. Is he talking about a range relative to the full scale of the unit?

That makes more sense and I understand why "nominal" is used. That is just what it should mean and I didn't get that.

Rick

synchronized.

I don't see how you came to that conclusion. I doesn't really matter.

Rick

Either way, you pay for it.

Dnia 03-11-2012 o 20:26:38 rickman napisa=C5=82(a):

le =

Range relative to the "nominal" values of the unit. e.g.: Un =3D 230V, 0.8Un =3D 184V, 1.5Un =3D 345V In =3D 5A, 0.02In =3D 100mA, 10In =3D 50A

ae

Dnia 03-11-2012 o 17:10:54 John Larkin =

napisa=C5=82(a):

Mine were pretty linear, but for high accuracy meters one needs to take = =

into account the temperature-phase characteristic. Self-heating of the =

wire that goes through the CT can heat up the CT and change its phase =

shift.

ae

'U' is traditionally used by physicists to denote potential.

Using it also for electrical potential, I believe, is more of a cultural thing. E, V and U have been variously used to represent voltage.

Tim

.highlandtechnology.com  jlarkin at highlandtechnology dot com

maybe I'm thinkging 'crest factor'

Yes, I remember now using E a lot in college. I don't recall U so much, but then I did undergraduate as a chemist where we were looking at work function and chemical potentials. I mostly have forgotten more of that than I remember.

I do still remember the difference between H2O and H2SO4...

Rick

So why do they want to replace the disk meters with digital ones? You could add a VERY simple optical monitor to the disk meter to read the number of revolutions and provide all the other benefits of digital without the mess of the ADCs, etc. I suppose the old meters can be a bit more expensive than the fancy, dancy digital ones?

Rick

don't remember seeing ohm's law written other U=I*R in all my school years

current isn't written as A(mpere) or C(urrent) either but I

-Lasse

but

zed.

Cool, but how do you match the low passes? (do you measure the C's?)

George H.

ed text -

No, you're ignoring PF. It is an amazing widget but it *is* an integrating power meter, *not* a current meter.

Measure voltage and current and multiply. Why do you care about the phase angle? It's meaningless if there are any uncorrected electronic power supplies downstream.

It comes out in the wash. There is very little mass there.

Oops! Right!

Wouldn't phase angle give you power factor? Or is deviation of PF more like distortion?

range

Think harmonics (or ugly waveforms from a SMPS).

range

If you take simultaneous E and I samples at some sensible rate,

Auto-zero and then multiply the E and I samples. Lowpass filter to get power, integrate to get energy.

Compute RMS current and voltage by squaring/filtering/rooting.

Multiply RMS current by RMS voltage to get VAs.

PF = power/VAs.

The only glitch here is that we lost the leading/lagging sign of the PF. That can be fixed with some more signal processing.