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cosFI ce ti reci koji je fazni pomak struje u odnosu na napon i za "grbave" sinuse, samo sto (u slucaju nepravilnih sinusa) tada snagu neces moci izracunati kao P=U*I*cos(fi), nego ces morati opet pristupiti rjesavanju recenog integrala.
No, matematicki je za integral beskonacno kratak, a sa "dovoljno malim" ces imati "dovoljno dobru aproksimaciju" tocne vrijednosti (npr. ako zakljucis da ti je prihvatljiva greska 1% mozes uzeti vece "dt" intervale nego ako ti je prihvaljiva greska 0.1% i sl.)
A vec sam dva puta poslao link pa ga odbijas pogledati, sto da radim vise :)
vidi "Electromechanical meters":
Po meni, mehanicki koristi upravo takav integral (u svakom beskonacno kratkom trenutku generirajuci silu proporcionalnu utrosenoj snazi).
"The electromechanical induction meter operates by counting the revolutions of a non-magnetic, but electrically conductive, metal disc which is made to rotate at a speed proportional to the power passing through the meter. The number of revolutions is thus proportional to the energy usage. The voltage coil consumes a small and relatively constant amount of power, typically around 2 watts which is not registered on the meter. The current coil similarly consumes a small amount of power in proportion to the square of the current flowing through it, typically up to a couple of watts at full load, which is registered on the meter.
The disc is acted upon by two sets of coils, which form, in effect, a two phase induction motor. One coil is connected in such a way that it produces a magnetic flux in proportion to the voltage and the other produces a magnetic flux in proportion to the current. The field of the voltage coil is delayed by 90 degrees, due to the coil's inductive nature, and calibrated using a lag coil. This produces eddy currents in the disc and the effect is such that a force is exerted on the disc in proportion to the product of the instantaneous current, voltage and phase angle (power factor) between them. A permanent magnet exerts an opposing force proportional to the speed of rotation of the disc. The equilibrium between these two opposing forces results in the disc rotating at a speed proportional to the power or rate of energy usage. The disc drives a register mechanism which counts revolutions, much like the odometer in a car, in order to render a measurement of the total energy used."
Naravno ima i svojih mogucnosti nepreciznosti takav mjerac (davno bazdarenje, "creep" itd - vidi wikipedia stranicu i IEC 62053 za detalje), no ovo sto se spominje nisu navedeni problemi istog (dakle IMHO hvata i fazne pomake i vise harmonike i ostala izoblicenja)
-- Opinions above are GNU-copylefted.
osnovni harmonik!
Sve je to OK ako se radi o osnovnim harmonicima!
da, slazem se, to sam tocno i napisao? Dakle morati ces izracunati integral dI*dV*dt kako sto sam napisao.
Kojem mekom zeljezu? U tvom uredjaju? Sve kaj se pretvori u toplinu iza brojila je utrosena energija sto se tice HEP-a. To sto mozda nije utrosena na nacin na koji si ti htio (nego na npr. spomenuto grijanje) je problem tvojih trosila koji imaju nesavrsenu iskoristivost, kaj ne? HEP ce ti uredno i to grijanje naplatiti.
Ili mislis na aluminijski disk u brojilu u kojem se stvaraju vrtlozne struje? Ili na zavojnice brojila? (Jer ni jedno nije meko zeljezo AFAICT)
U elektromehanickom brojilu tesko mozes govoriti o visim (ili nizim) harmonicima, kada ono barata iskljucivo sa trenutnom strujom i trenutnom voltazom (u spomenutom beskonacno kratkom trenutku dt). To je jednodimenzionalni prostor, ne mozes u njemu upotrebljavati dvodimenzionalne pojmove tipa "visi harmonik" (za "harmonik" - osnovni ili bili koji drugi - moras imati na x osi delta-t koji je malo duzi od beskonacno kratkog trenutka dt, kaj ne? Kak vi nacrtatao npr. trokut ako nemas x i y os, nego samo recimo y? Nikako.)
-- Opinions above are GNU-copylefted.
Jel ima u Hrvatskoj negdje za kupiti data logger kojim bi prvenstveno mjeri
alu. Nominalni napon je 3x450V, 60Hz.
Hvala!
Ima, samo mislim da ti se nece svidjati cijena. Recimo ima Fluke:
jerio napon i frekvenciju tog napona i te podatke kasnije analizirao na ra
quality.html#techspecs
Ma nije mi to zbog elektre nego za posao.
Ali da, ovaj Fluke je dosta skup.
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