What are 6.5 Digit Multimeters Good For?
in [Design]
|
From: Randomly on 16 Mar 2010 10:40 >>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. Well if you are sure you are not heating your traces up when you measure them it sounds like you need to talk to your fab about the issue. Get them to explain their fabrication process and what the variables are that can affect the sheet resistance. 1 oz copper is just an arbitrary standard, what's important is to know what sheet resistance you can expect out of them and how variable it can be. It's good to know what the sheet resistances and dielectric constants of all the board options they offer so you can get what you need out of them. If it's an important aspect of your board design you have to specify it, you can't leave it to chance since they may change suppliers, or processing, or subcontract it out etc. Talk to them, find out what the options are and what they are comfortable with. If you are not satisfied find another fab. What fab are you using? --------------------------------------- Posted through http://www.Electronics-Related.com
From: John Larkin on 16 Mar 2010 11:15 On Tue, 16 Mar 2010 09:40:50 -0500, "Randomly" <fburfell2000(a)n_o_s_p_a_m.n_o_s_p_a_m.yahoo.com> wrote: > >>>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. > >Well if you are sure you are not heating your traces up when you measure >them it sounds like you need to talk to your fab about the issue. Get them >to explain their fabrication process and what the variables are that can >affect the sheet resistance. 1 oz copper is just an arbitrary standard, >what's important is to know what sheet resistance you can expect out of >them and how variable it can be. It's good to know what the sheet >resistances and dielectric constants of all the board options they offer so >you can get what you need out of them. If it's an important aspect of your >board design you have to specify it, you can't leave it to chance since >they may change suppliers, or processing, or subcontract it out etc. Talk >to them, find out what the options are and what they are comfortable with. >If you are not satisfied find another fab. > >What fab are you using? > >--------------------------------------- >Posted through http://www.Electronics-Related.com We use several board houses. I am used to the concept that a "1 Oz" board may have 750 uohms per square, and on most boards it doesn't matter. If it does matter, as when high currents are involved, I make sure the fab notes clearly demand true 1 Oz, and include a test trace. When I do include such a note, I usually get a phone call about it. John
From: Jim Thompson on 16 Mar 2010 11:41 On Tue, 16 Mar 2010 05:02:11 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >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. If you do some kind of 4-point measuring arrangement, contact resistance doesn't matter. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: John Larkin on 16 Mar 2010 12:05 On Tue, 16 Mar 2010 05:02:11 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >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. I sometimes measure the tempco curves of milliohm manganin current shunts, before and after annealing. You need a ppm-stable current source and a really good DVM to do that. A good, properly annealed shunt will have a tempco of a few PPM/K around its designed turning point, the flat part of the tempco parabola. ftp://jjlarkin.lmi.net/Manganin.zip This sort of thing is impressively tedious. John
From: Jim Yanik on 16 Mar 2010 14:40
Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in news:2k9vp55rdm7a7rifvqqnqud93vr7cd1be4(a)4ax.com: > On Tue, 16 Mar 2010 05:02:11 -0700, > "JosephKK"<quiettechblue(a)yahoo.com> wrote: > >>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. > > If you do some kind of 4-point measuring arrangement, contact > resistance doesn't matter. > > ...Jim Thompson consider the low value resistors used to current sense in high current power supplies. If you want to measure a 0.1 or 0.05ohm R,a 4-wire ohms measurement is the way to do it. Plus,such DMMs are used in remote data collection systems;your DMM is far away from the DUT,out of a hostile environment,yet you still can get an accurate measurement. -- Jim Yanik jyanik at localnet dot com |