Power Meter accuracy
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From: Tim Williams on 11 May 2010 12:39 "Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message news:hsbn1p$k1a$1(a)news.albasani.net... >>> If they use a 10 bits ADC, then for a max of 2 kW the miniumum is >>> already 2 W. >> >>2mW* > > A 10 bit ADC has 1024 steps > 2000 / 1024 is just about 2 > ??????????????? > > Hello? Presumably, they're converting voltage and current seperately. 1/1024 = -60dB, or 2kW/1e6 = 2mW. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Tim Williams on 11 May 2010 12:41 "Grant" <omg(a)grrr.id.au> wrote in message news:3mthu5l2ecooh7cvqe0lkr0ei1fatiilai(a)4ax.com... >>"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >>message >> >>>>> If they use a 10 bits ADC, then for a max of 2 kW the miniumum is >>>>> already 2 W. >>>> >>>>2mW* >>> >>> 2 W >> >>So they have an analog multiplier first? > > Did you not hear the whoosh as it flew over their heads? :) Gee, I think I just embarassed John into not replying. I must be getting *good*. ;-) Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: D Yuniskis on 11 May 2010 13:35 Hi Joe, Joe G (Home) wrote: > "Joe G (Home)" <joe.g(a)optusnet.com.au> wrote in message > news:4be68200$0$12142$afc38c87(a)news.optusnet.com.au... >> Hi All, >> >> What can the home power meter in the meter box read down to 1watt or >> less? > > Sorry, I was talking about power meters that measure power for the > utilities companies. "Classic" meters are nominally ~1% devices. Doesn't sound very impressive until you think about the wide operating range (environmental as well as electrical) that they have to operate in as well as their long term reliability *and* low cost. Modern "solid state" devices usually start at 1% and get better. E.g., there are 0.5% class devices, 0.2% class, etc. Of course, the SS devices place some "burden" (a few W) on the line this has to be accounted for (either in the design or in the billing). KWH meters are amusing devices. More effort is expended on all sorts of insane details (register ratio, watthour constant, etc.) that belong in a lexicon specific to just KWH meters. And, lots of "rule of thumb" stuff that often seems arbitrary to an "outsider" :-/ Keep in mind the types of folks who use/install these things. They aren't typically concerned with the same sorts of metrics that engineers would... > I know TI AD and others have power meter reference designs.
From: John Larkin on 11 May 2010 14:28 On Tue, 11 May 2010 11:41:13 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"Grant" <omg(a)grrr.id.au> wrote in message >news:3mthu5l2ecooh7cvqe0lkr0ei1fatiilai(a)4ax.com... >>>"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >>>message >> >>>>>> If they use a 10 bits ADC, then for a max of 2 kW the miniumum is >>>>>> already 2 W. >>>>> >>>>>2mW* >>>> >>>> 2 W >>> >>>So they have an analog multiplier first? >> >> Did you not hear the whoosh as it flew over their heads? :) > >Gee, I think I just embarassed John into not replying. I must be getting >*good*. ;-) > >Tim I have no idea what either of you are talking about. Is the 2mW* thing some sort of joke? Please explain it. John
From: John Larkin on 11 May 2010 14:29 On Tue, 11 May 2010 11:39:55 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message >news:hsbn1p$k1a$1(a)news.albasani.net... >>>> If they use a 10 bits ADC, then for a max of 2 kW the miniumum is >>>> already 2 W. >>> >>>2mW* >> >> A 10 bit ADC has 1024 steps >> 2000 / 1024 is just about 2 >> ??????????????? >> >> Hello? > >Presumably, they're converting voltage and current seperately. >1/1024 = -60dB, or 2kW/1e6 = 2mW. > >Tim How much does the line voltage change where you live? John
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