What are 6.5 Digit Multimeters Good For?
in [Design]
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From: Archimedes' Lever on 16 Mar 2010 07:36 On Tue, 16 Mar 2010 00:06:53 -0500, "Randomly" <fburfell2000(a)n_o_s_p_a_m.n_o_s_p_a_m.yahoo.com> wrote: >>It's interesting to calculate the resistance of traces and actually >>measure them. Most pcb houses skimp on plating, so when you specify "1 >>oz" copper, you seldom get it. > >The only place copper is plated is in the holes. The 1 oz copper layer for >traces is a copper sheet that is laminated to the board. It's rolled out to >the proper 1.4 mil thickness when it's manufactured. It's not plated on by >the PCB manufacturer. > >You may be making measurement errors when you measure the traces, 1 amp can >be a lot of current on small traces and you may be heating that trace up >quite a bit. Copper has a substantial thermal coefficient of resistance, >heat it up by 25C and the resistance goes up 10%. Try dropping your current >to 0.1A and see how your measurements change. > Oh no! Don't ruin his bent belief that he has been getting ripped off all these years! His bent perceptions of reality must be kept in place or he'll explode, taking half the city with him!
From: JosephKK on 16 Mar 2010 07:54 On Sun, 14 Mar 2010 18:53:21 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Sun, 14 Mar 2010 18:32:13 -0700, >"JosephKK"<quiettechblue(a)yahoo.com> wrote: > >>On Sun, 14 Mar 2010 00:36:08 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >> >>>On a sunny day (Sat, 13 Mar 2010 08:13:20 -0600) it happened John Fields >>><jfields(a)austininstruments.com> wrote in >>><l37np519aum4a3r6n9aetaona9ij7hesm7(a)4ax.com>: >>> >>>>On Sat, 13 Mar 2010 13:27:35 GMT, Jan Panteltje >>>><pNaonStpealmtje(a)yahoo.com> wrote: >>>> >>>>>On a sunny day (Fri, 12 Mar 2010 13:00:04 -0800) it happened D from BC >>>>><myrealaddress(a)comic.com> wrote in <MPG.26044b27299d843e9896f7(a)209.197.12.12>: >>>>> >>>>>>In article <hne8fg$uqm$1(a)news.albasani.net>, pNaonStpealmtje(a)yahoo.com >>>>>>says... >>>>>>> >>>>>>> On a sunny day (Fri, 12 Mar 2010 10:50:48 -0600) it happened John Fields >>>>>>> <jfields(a)austininstruments.com> wrote in >>>>>>> <ekrkp5lg8obtcmftn2tmq8adsnlte9u59e(a)4ax.com>: >>>>>>> >>>>>>> >On Fri, 12 Mar 2010 12:30:31 GMT, Jan Panteltje >>>>>>> ><pNaonStpealmtje(a)yahoo.com> wrote: >>>>>>> > >>>>>>> >>On a sunny day (Thu, 11 Mar 2010 17:56:35 -0800) it happened D from BC >>>>>>> >><myrealaddress(a)comic.com> wrote in <MPG.26033f321480b139896e5(a)209.197.12.12>: >>>>>>> >> >>>>>>> >>>6.5 digit multimeters sell around $1000.00. >>>>>>> >>>For electronics development, are these $1000 multimeters really >>>>>>> >>>necessary? >>>>>>> >>>What are they good for? >>>>>>> >> >>>>>>> >>They are not needed, all you need is a 5 Euro multimeter, >>>>>>> >>and in extreme cases a precise reference. >>>>>>> >>That means if you use one of those reference chips, you borrow >>>>>>> >>the very accurate multimeter for a day, measure your reference chip, >>>>>>> >>write it down, and use that to calibrate your cheap multimeter, >>>>>>> >>or o compute it's real value, >>>>>>> >>Saved: 1000$ >>>>>>> > >>>>>>> >--- >>>>>>> >If you don't _need_ the accurate multimeter, then how do you get around >>>>>>> >the fact that unless you use _it_ to measure the reference, your cheap >>>>>>> >multimeter is pretty much a boat anchor? >>>>>>> > >>>>>>> > >>>>>>> >JF >>>>>>> >>>>>>> Sorry can you explain that again in electronics English? >>>>>> >>>>>>He means you still need an accurate tool to make use of a less accurate >>>>>>tool. Which raises the question, why have the less accurate tool? >>>>>> >>>>>>btw... Boat anchor is a term I sometimes use for large heavy antiqued >>>>>>test equipment. >>>>>>Pre LCD scopes are boat anchors. >>>>> >>>>>Yes, OK, but Fields did not read very well, >>>>>you only need the accurate one ONCE. >>>>>And that means you can go to a place and have yor reference measured. >>>> >>>>--- >>>>You seem to be the one having trouble with the language since even if >>>>it's used only once, you still _need_ the higher accuracy instrument in >>>>order to determine the error in the lower accuracy one. >>>> >>>>JF >>> >>>No you do not, how do you think those instruments came about? >>>In your theory nothing could ever be made. >>>:-) >> >>You are missing some concepts here. >>There are things called reference cells, the voltage across the >>terminals is dependant on the chemistry/physics. Similar to and >>far lower tech to make than bandgap references. The terminal >>voltage can be determined to 6 places before putting the meter >>leads to them and are repeatable and reliable. >>Ratiometric methods can maintain resolution and accuracy in a large >>variety of situations, see R/2R DAC systems. >>With these concepts in hand you would not have bothered to make your >>comment. >>Or maybe you do not credit anyone else with these few bits of >>typical electrical engineering knowledge. > > >Do people still use standard cells? > >John As far as i know they were relegated to primary standards labs some 30+ years ago. I would bet on not finding them in anyplace else (any more), maybe only at NIST class calibration reference services now.
From: JosephKK on 16 Mar 2010 08:02 On Sun, 14 Mar 2010 17:54:07 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Sun, 14 Mar 2010 18:46:36 -0700, >"JosephKK"<quiettechblue(a)yahoo.com> wrote: > >>On Fri, 12 Mar 2010 10:44:39 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >> >>>On Fri, 12 Mar 2010 09:33:25 -0800, D from BC >>><myrealaddress(a)comic.com> wrote: >>> >>>>In article <hndc5b$37k$1(a)news.albasani.net>, pNaonStpealmtje(a)yahoo.com >>>>says... >>>>> >>>>> On a sunny day (Thu, 11 Mar 2010 17:56:35 -0800) it happened D from BC >>>>> <myrealaddress(a)comic.com> wrote in <MPG.26033f321480b139896e5(a)209.197.12.12>: >>>>> >>>>> >6.5 digit multimeters sell around $1000.00. >>>>> >For electronics development, are these $1000 multimeters really >>>>> >necessary? >>>>> >What are they good for? >>>>> >>>>> They are not needed, all you need is a 5 Euro multimeter, >>>>> and in extreme cases a precise reference. >>>>> That means if you use one of those reference chips, you borrow >>>>> the very accurate multimeter for a day, measure your reference chip, >>>>> write it down, and use that to calibrate your cheap multimeter, >>>>> or o compute it's real value, >>>>> Saved: 1000$ >>>>> >>>>> Of course there are exceptions, >>>>> but in places where that counts they usually have a lot of ++++expensive stuff anyways. >>>>> Usually places where nothing really useful is done, like in CERN, or ITER, or LIGO, >>>>> etc. >>>> >>>>How about mohm measurements? Maybe that's handy. >>>>My DMM only goes to 0.1 ohm. >>>>I thought of measuring DCR of coils or pcb trace resistance for sim >>>>accuracy. >>>> >>>> >>> >>>Measuring milli-Ohms is tricky. Ideally you'd like 4-point-probe >>>measuring... voltage "viewing" pins are separate from current forcing >>>pins. >>> >>>I'd do it with an AC current source, so you can gain-up the resulting >>>voltage. >>> >>> ...Jim Thompson >> >>So, you know some interesting tricks to make an AC current source >>accurate to 0.01%? A lot of people would interested, especially if >>it was a clean sine source. With a good clean DC current source i >>have seen measurements all the way to 0.00002%. There be tradeoffs >>here. > >Why do need "accuracy" to 0.01%? What are you trying to measure to >that kind of accuracy? > > ...Jim Thompson Perhaps i wanted to get credible results on contact resistance repeatability. Or maybe i need to verify a current measuring shunt.
From: John Larkin on 16 Mar 2010 09:52 On Tue, 16 Mar 2010 04:24:59 -0700, Archimedes' Lever <OneBigLever(a)InfiniteSeries.Org> wrote: >On Mon, 15 Mar 2010 22:26:58 -0500, "krw(a)att.bizzzzzzzzzzzz" ><krw(a)att.bizzzzzzzzzzzz> wrote: > >>On Mon, 15 Mar 2010 20:17:05 -0700, Archimedes' Lever >><OneBigLever(a)InfiniteSeries.Org> wrote: >> >>>On Mon, 15 Mar 2010 19:53:04 -0700, John Larkin >>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>On Mon, 15 Mar 2010 19:47:01 -0700, Archimedes' Lever >>>><OneBigLever(a)InfiniteSeries.Org> wrote: >>>> >>>>>On Mon, 15 Mar 2010 12:11:23 -0700, John Larkin >>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>> >>>>>>On Fri, 12 Mar 2010 18:56:02 -0800, Archimedes' Lever >>>>>><OneBigLever(a)InfiniteSeries.Org> wrote: >>>>>> >>>>>>>On Fri, 12 Mar 2010 15:23:12 -0800, John Larkin >>>>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>>> >>>>>>>> >>>>>>>>Except that you never get too much copper... always too little. >>>>>>>> >>>>>>>>John >>>>>>> >>>>>>> >>>>>>> Maybe from your board house, dipshit. >>>>>> >>>>>>Measure the sheet resistivity of traces on a few of your boards and >>>>>>tell us what you see. >>>>>> >>>>>>John >>>>> >>>>> >>>>> You do know that we do not use copper boards any more, right? >>>> >>>>I didn't know that. What do you use? >>>> >>>>John >>> >>> It is an RoHS world, John. What do you think we use? >> >>What does RoHS have to do with Copper, AlwaysWrong? > > The field is called "intermetallics". I wouldn't expect a ditz like >you to get it, always-fucked-in-the-head. >> >>> It ain't HASL over Copper or SMOBC, I'll tell ya. >> >>IOW, you don't know. > > You wouldn't know what I know. You never will. You are pathetic, >Williams. So if your PCB conductors aren't copper, what are they? John
From: John Larkin on 16 Mar 2010 09:58
On Tue, 16 Mar 2010 00:06:53 -0500, "Randomly" <fburfell2000(a)n_o_s_p_a_m.n_o_s_p_a_m.yahoo.com> wrote: >>It's interesting to calculate the resistance of traces and actually >>measure them. Most pcb houses skimp on plating, so when you specify "1 >>oz" copper, you seldom get it. > >The only place copper is plated is in the holes. The 1 oz copper layer for >traces is a copper sheet that is laminated to the board. It's rolled out to >the proper 1.4 mil thickness when it's manufactured. It's not plated on by >the PCB manufacturer. > >You may be making measurement errors when you measure the traces, 1 amp can >be a lot of current on small traces and you may be heating that trace up >quite a bit. Copper has a substantial thermal coefficient of resistance, >heat it up by 25C and the resistance goes up 10%. Try dropping your current >to 0.1A and see how your measurements change. I think my measurements are accurate, and I often include a test trace whose geometry is suitable for accurate sheet resistance measurement. If I include a fab note demanding a minimum sheet resistance, or say "START WITH 1 OZ COPPER" I usually get below 600 uohms/square. If I just say "COPPERCLAD 1 OZ" I usually don't. John |