What are 6.5 Digit Multimeters Good For?

:

stuff anyways.

ITER, or LIGO,

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

Jim Thompson wrote in news: snipped-for-privacy@4ax.com:

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

The sheets are 4' x 8' and the cladding is industry standard, you dopey ditz! I know because my dad made some of the very first machines that were used by the industry to make the current form factor boardstock. That would be Cincinnati Milacron, Inc., which at the time would have been named The Cincinnati Milling Machine Company. There are not very many products you could name that didn't use Cincinnati machines. Fuller brush company... Your hair brush injection molders. Ebonite... Your bowling balls, GE jet engines, FMC corp M1-A1 MBTs. All three US auto makers. The list goes on for hundreds of brands, products, industries. Now, most companies have bought Japanese machining centers. Milacron probably not doing so well... lemmie check real quick... DAMN! They have been bought out by a conglomerate with private stock! MAG Industrial Automation owns Milacron now! Oh well, they were the guys.

If you are getting it thinner, then your PCB house... isn't one. They should know how to correctly clean a PCB without losing copper. Also, your measurement accuracy can be off due to you not performing the test completely correctly.

Kind of like the vapor phase thing. It works for you, so you do not care if you are actually doing it right or not.

Sorry, but in this case, if you do not know where the error(s) get(s) introduced, you will knot know what your resultant figures mean, nor how to offset them properly to correct for the errors that get introduced in to the not quite ideal test scenario.

Not ideal? What is the bad element? YOU, Johnny boy.

All it would take is a single mistake, and the difference you refer to (600 as compared to 1000) is very likely completely due to said error.

I'd say that even though you think you are, you have failed to compensate for the lead resistance of your test. What you should do is apply a current and measure the voltage between the NUT (NodeSpan Under Test). Far better than you thinking that you can measure micro-ohms accurately, much less properly.

If you don't use copper traces on your pc boards, what do you use?

John

: :

stuff anyways.

or LIGO,

The neatest use of a 6.5 or higher DVM is for temperature measurement. It easily spots a hand at a distance of three feet.

--
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@tinaja.com

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

--
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@tinaja.com

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

Thanks for the links, but I noticed you state there that one ounce copper is

0.68 milliohms per square for 25 micrometer thickness (1 mil). I think one ounce copper is 35.6 micrometers thick (1.4 mils) and the resistivity is 0.486 milliohms per square.

or am I mistaken?

--------------------------------------- Posted through

amp

up

resistance,

them

so

your

Talk

with.

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?).

snipped-for-privacy@yahoo.com=20

from BC

:

chip,

++++expensive stuff anyways.

or ITER, or LIGO,

=20

forcing

resulting

What i was measuring was the contact resistance of some relay contacts in= =20 the closed position, also connector contacts contact resistance. And, of course, it was the best 4-terminal connections i could make.

=

offer=

on=

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

I think a lot of board houses start with 1/2 or even 1/4 oz copper. That's ideal for etching fine-pitch traces, like 5/5 rules. Then they plate up surface traces and thru-holes, the "semi-additive" process.

They tend to skimp on plating time.

John

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. Though not likely the best way to attack the problem

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

John Larkin a écrit :

Did that once. I needed a very low inductance shunt. About 0.5"x1" for a

1mR shunt above a GND plane. Two vias and you have a four wire one. Worked like a charm, but that was for a current compensating loop, so I was servoing its voltage drop to zero and its actual value didn't matter much.

--
Thanks,
Fred.

Any of our traces where we were concerned about current ended up with multiple vias tying nodes together, and used both top and bottom sides when the circuitry runs allowed for it.

Of course, I made power supplies. We had to know how to get from point A to point B. You guess as you go, and call it golden when it works, whether it is right or not.