What are 6.5 Digit Multimeters Good For?

On a sunny day (Fri, 12 Mar 2010 15:03:42 -0600) it happened John Fields
jfields_at_austininstruments.com> wrote in
8talp59g6d4lma3q6p93ttnnsn4cnm6m71_at_4ax.com>:

On Fri, 12 Mar 2010 20:15:16 GMT, Jan Panteltje
pNaonStpealmtje_at_yahoo.com> wrote:

On a sunny day (Fri, 12 Mar 2010 09:33:25 -0800) it happened D from BC
myrealaddress_at_comic.com> wrote in <MPG.26041ac522f727379896f0_at_209.197.12.12>:

In article <hndc5b$37k$1_at_news.albasani.net>, pNaonStpealmtje_at_yahoo.com
says...
On a sunny day (Thu, 11 Mar 2010 17:56:35 -0800) it happened D from BC
myrealaddress_at_comic.com> wrote in <MPG.26033f321480b139896e5_at_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.
I have a controlled current souce.
Stuff 1 A through the .1 resistor and measure the voltage drop?
---
And you've determined the accuracy of the current source and the
resistor, how???

JF

The question was not about accuracy, but how to measure .1 Ohm.

On Tue, 16 Mar 2010 06:58:50 -0700, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 16 Mar 2010 00:06:53 -0500, "Randomly"
fburfell2000_at_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


The sheets are 4' x 8' and the cladding is industry standard

http://www.tinaja.com/whtnu09.asp#d02-19-09

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: don_at_tinaja.com

Please visit my GURU's LAIR web site at http://www.tinaja.com

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

On Tue, 16 Mar 2010 05:02:11 -0700,
"JosephKK"<quiettechblue_at_yahoo.com> wrote:

On Sun, 14 Mar 2010 17:54:07 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:

On Sun, 14 Mar 2010 18:46:36 -0700,
"JosephKK"<quiettechblue_at_yahoo.com> wrote:

On Fri, 12 Mar 2010 10:44:39 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:

On Fri, 12 Mar 2010 09:33:25 -0800, D from BC
myrealaddress_at_comic.com> wrote:

In article <hndc5b$37k$1_at_news.albasani.net>, pNaonStpealmtje_at_yahoo.com
says...

On a sunny day (Thu, 11 Mar 2010 17:56:35 -0800) it happened D from BC
myrealaddress_at_comic.com> wrote in <MPG.26033f321480b139896e5_at_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

On Tue, 16 Mar 2010 09:40:50 -0500, "Randomly" =
fburfell2000_at_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 trac
=
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 the
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? =20
=09
--------------------------------------- =09
Posted through http://www.Electronics-Related.com

Damn you do not read very well do you? JL stated that he orders boards =
by=20
sheet resistivity (al least when he thinks it matters, did you pick u
on=
=20
the test trace?).

On Tue, 16 Mar 2010 09:40:50 -0500, "Randomly" =
fburfell2000_at_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? =20
=09
--------------------------------------- =09
Posted through http://www.Electronics-Related.com

Damn you do not read very well do you? JL stated that he orders boards =
by=20
sheet resistivity (al least when he thinks it matters, did you pick up
on=
=20
the test trace?).

You've lost me. What did I say that was not valid? Perhaps my past
experiences with cheap chinese pcb manufacturers has tainted my outlook but
I am missing what point you are trying to make.

---------------------------------------
Posted through http://www.Electronics-Related.com

On Tue, 16 Mar 2010 09:40:50 -0500, "Randomly" =
fburfell2000_at_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? =20
=09
--------------------------------------- =09
Posted through http://www.Electronics-Related.com

Damn you do not read very well do you? JL stated that he orders boards =
by=20
sheet resistivity (al least when he thinks it matters, did you pick up
on=
=20
the test trace?).

You've lost me. What did I say that was not valid? Perhaps my past
experiences with cheap chinese pcb manufacturers has tainted my outlook but
I am missing what point you are trying to make.

---------------------------------------
Posted through http://www.Electronics-Related.com

On Wed, 17 Mar 2010 08:36:49 -0500, "Randomly"
fburfell2000_at_n_o_s_p_a_m.n_o_s_p_a_m.yahoo.com> wrote:

On Tue, 16 Mar 2010 09:40:50 -0500, "Randomly" =
fburfell2000_at_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? =20
=09
--------------------------------------- =09
Posted through http://www.Electronics-Related.com

Damn you do not read very well do you? JL stated that he orders boards =
by=20
sheet resistivity (al least when he thinks it matters, did you pick up
on=
=20
the test trace?).

You've lost me. What did I say that was not valid? Perhaps my past
experiences with cheap chinese pcb manufacturers has tainted my outlook but
I am missing what point you are trying to make.

---------------------------------------
Posted through http://www.Electronics-Related.com


He cries because some of his "engineering" involves relying directly on
a specific length of trace to provide a specific micro-ohm resistance to
make his circuit function in a repeatable manner, which is important.

On Wed, 17 Mar 2010 20:12:16 -0700, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:

On Wed, 17 Mar 2010 08:36:49 -0500, "Randomly"
fburfell2000_at_n_o_s_p_a_m.n_o_s_p_a_m.yahoo.com> wrote:

On Tue, 16 Mar 2010 09:40:50 -0500, "Randomly" =
fburfell2000_at_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? =20
=09
--------------------------------------- =09
Posted through http://www.Electronics-Related.com
Damn you do not read very well do you? JL stated that he orders boards =
by=20
sheet resistivity (al least when he thinks it matters, did you pick up
on=
=20
the test trace?).
You've lost me. What did I say that was not valid? Perhaps my past
experiences with cheap chinese pcb manufacturers has tainted my outlook but
I am missing what point you are trying to make.

---------------------------------------
Posted through http://www.Electronics-Related.com

He cries because some of his "engineering" involves relying directly on
a specific length of trace to provide a specific micro-ohm resistance to
make his circuit function in a repeatable manner, which is important.


Not so. I have toyed with the idea of using pcb traces as current
shunts and such, but I've never done it.

On Wed, 17 Mar 2010 20:12:16 -0700, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:

On Wed, 17 Mar 2010 08:36:49 -0500, "Randomly"
fburfell2000_at_n_o_s_p_a_m.n_o_s_p_a_m.yahoo.com> wrote:

On Tue, 16 Mar 2010 09:40:50 -0500, "Randomly" =
fburfell2000_at_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? =20
=09
--------------------------------------- =09
Posted through http://www.Electronics-Related.com

Damn you do not read very well do you? JL stated that he orders boards =
by=20
sheet resistivity (al least when he thinks it matters, did you pick up
on=
=20
the test trace?).

You've lost me. What did I say that was not valid? Perhaps my past
experiences with cheap chinese pcb manufacturers has tainted my outlook but
I am missing what point you are trying to make.

---------------------------------------
Posted through http://www.Electronics-Related.com


He cries because some of his "engineering" involves relying directly on
a specific length of trace to provide a specific micro-ohm resistance to
make his circuit function in a repeatable manner, which is important.


Not so. I have toyed with the idea of using pcb traces as current
shunts and such, but I've never done it. The only time trace
resistance really matters to me is when I do high-current stuff, where
lower is always better.

John