Re: integrating true RMS wattmeter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: dest <dest@xxxxxxxxxxxxx>

Hallo Jim.

> Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

>>"Variation in Yokogawa from calculated due to integration times, manual
>>data entry, and TCR (temp coeff. of resistance) effects of heater
>>element(s)."
>>
>>what? nippon meter was so SLOW??? what does it mean - "manual data
>>entry"?


> I think you're misunderstanding what was written.  I think he was
> using a heater as a load, and almost all resistance heaters change
> their resistance as the temperature changes.


i understand this, but i don`t fully understand what does "integration
times" mean - are you trying to say, that it is the load who`s
integrating? % ) integrating what - applied voltage, to change it`s
temperature, to affect it`s current and affect at the end readings?
imo that`s overcomplicated % )

>>e) "The experimental design was basically use the controller to power
>>a 120VAC,1.56kW floor heater.  Inductance is trival (shaded pole
>>blower) and 1500W heater."
>>
>>so you have tested the thing only at 60Hz? and at LINEAR load???
>>what`s the point in that


> I think that a wise person might do the easy test first: resistive
> loads at low frequency sine wave to verify performance, before moving
> on to reactive loads and non-sinusoidal.


Jim - i`m not against Dave or his ckt here - quite the contrary,
"coilers" do need ckts as simple as possible. my question was - what
is the point in _publishing on tcml_ results of this basic, trivial
tests, which can verify that thing is working somehow ONLY? you see -
text file for ckt was created in feb '97, i`ve read archives till sep
'97 currently, but still haven`t seen results of testings on real load
up to here.
i didn`t have fancy nippon stuff at home or work (as most listies i
think), so i just can`t know how this thing would act in real life.
for example - maybe i`m wrong, but imo the thing can`t cope with loads
with high crest factor, even if crest factor is about 2, and you
measure at more than half scale level (roughly speaking).
i would never build any form of "best man friend" or other sstc`s so i
just don`t care, but i like to know limitations of things which i`m
working with (if they really exist of course).

>>  - anybody can go and buy $5 ferrodynamic
>>wattmeter for example - it would be more accurate and linear in such
>>case : ))) my $3 50Hz _mechanical_ meter accuracy rating is 1.5!

> But your mechanical meter is exceedingly inconvenient to do things
> like feeding the data in real time to a data logger.


you know what? : ) when i bough this $3 meter here, my more lucky
fellow in Moscow bough $5 1KHz (iirc) blown up electrodynamic one,
opened him up and found small a&d circuit on discrete elements in there,
so he can use this s#it in conjunction with his (blown up too for now
: DDD) pc : )

>>f) "The differential voltages (Vshunt) and (Vload) are in fact
>>MULTIPLIED to the form:
>>39 X Rshunt/Rmultipler * Vload * Iload"
>>
>>then why do you advice to reduce Rshunt (to 250 uOhm!) instead of
>>changing oa gain for example? is it limitation of optocoupler, oa,
>>something other? there are many other oa & optos here.

> To reduce the power dissipated in the shunt perhaps?


at 11KW there would be only 2.5W here - imo not much for ''4.6" of #14
AWG THHN copper wire (1.00 milli-ohm)'', or you concerned with TCR of
shunt?

>>10) "The only concern I have with this design is there is minimal circuit
>>board clearance through the optocoupler (0.1 and 0.3 inches)."
>>
>>are you speaking about hv spikes in the mains? so strong, that they can
>>cause breakdown of 2.5mm of air? don`t you think that in that case you
>>better shut your coil down immediatelly instead of trying to measure
>>it`s power consumption? % )

> If you want to build something that would meet regulatory
> requirements for isolation


NO - "coilers" don`t need this, and it is even written in that word
document - "Adapted for Tesla HV Resonant Circuit Use"! : )

>>11) this circuit is darned simple - maybe we can use a couple of
>>additional elements to get real _electronic_ accuracy? : )

> Certainly. That design is 10 years old, at least.


can you (as much more educated electronic hobbyist than i was many
years ago :D) suggest something in that direction? or maybe totally
different (but still simply enough) approach (probably using modern
circuit technology)?

-----
I don't doubt that my logic is flawed, could somebody tell me where?
08-08-97 (c) Gary Lau