8.5 digit DMMs

[quarks]

opened because it was OT in another thread
https://www.eevblog.com/forum/testgear/new-agilent-34461a-6-5-digit-bench-multimeter/msg258268/#msg258268

Here is a collection with more details about the kings of the DMMs:

Advantest R6581 / ADCMT 6581
http://translate.google.de/translate?hl=de&sl=ja&tl=en&u=http%3A%2F%2Fwww.adcmt.com%2Ftechinfo%2Fproduct%2Fend_of_sale%2FR6581D%2Fco_R6581D.html&sandbox=1

Datron/Wavetek 1271 and 1281
http://www.fluke.com/fluke/uses/Multimetros-Digitales/Fluke-1281.htm?PID=56003
http://datronconnection.com/749/Datron_1281.php

Fluke 8508A (Option 01 for rear input Ratio meassurement)
http://us.flukecal.com/products/standard-laboratory-meters/8508a-reference-multimeter

HP/Agilent 3458A (Option 02 or HFL for best DC accurracy)
http://www.home.agilent.com/en/pd-1000001297%3Aepsg%3Apro-pn-3458A/digital-multimeter-8-digit?cc=US&lc=eng
http://www.fluke.com/fluke/r0en/digital-multimeters/HP-3458-HFL.htm?PID=56270

Keithley 2002
http://www.keithley.com/products/dcac/dmm/highper

PREMA 6048
http://translate.google.de/translate?hl=de&sl=auto&tl=en&u=http%3A%2F%2Fohh.de%2F6048.htm&sandbox=1

Solartron 7081
http://www.perdrix.co.uk/Solartron7081/index.htm
Our member Mickle T. had some great posts on modifying a 7081 on bbs.38hot.net but they seem to be deleted
but here is his great work saved
http://www.ko4bb.com/manuals/index.php?dir=09)_Misc_Test_Equipment/Solartron/Solartron_7081)

Transmille 8080, 8081 and 8881
http://www.transmille.co.uk/8080.htm
http://www.transmille.co.uk/8081.htm
http://www.transmille.co.uk/8881.htm

ZIP Nauchpribor KM300
http://translate.google.de/translate?hl=de&sl=ru&tl=en&u=http%3A%2F%2Fwww.znp.ru%2Fprod%2Fkm300.htm&sandbox=1

edit: cleanup links and added ZIP Nauchpribor KM300 (listed in Mickle T. DMMs8.5.doc)
edit: revised DCV Chart (with input from Dr.Frank about 3458A 1kV range)

[casper.bang]

Heh, so while Agilent uses Fluke equipment for calibrating, Fluke uses Datron? I wonder what Datron is measured up against then?!

[eevblogfan]

Umm have A look at JJ (Josephson junction )  google it up 

[Shas-O]

Just bought a 3458 and sent it back, see new post.

The current posts are loose because they are fused !!

affects readings when leads are moved


Derek 

[saturation]

This was posted on the forum some years ago but I can't find the original thread, so here's a relink:

http://translate.googleusercontent.com/translate_c?depth=1&hl=en&rurl=translate.google.com&sl=zh-CN&tl=en&twu=1&u=http://tm.eefocus.com/stupid/blog/08-06/150647_4b553.html&usg=ALkJrhg-IqXNS7q9DW7EUk8ncQywK4IDbQ

[quantumvolt]

No, I don't think you want too much. I would like to have it too.

But I wonder - what do you people who have 8 1/2 digit meters do with set-up, cables and measurement calculation (adding a loop to zero potential or ratio scaling or ...).

I have (after a discussion elsewhere in the forum) checked that the 6 1/2 digit Agilent 34401A quite clearly indirectly measures a 10 Ohm series resistor between a voltage source and the meter (5 Ohm is also detected, but 1 Ohm disappears in noise). With 10 MOhm input impedance 10 Ohm is 1ppm. So this effectively renders the DMM as a 7 1/2 digit (19.999 999) resolution (not accuracy) instrument in RS232 mode for 10 V DC.

Today I got a board from Geller that came in at 10.00009 Volt (very happy - means my meter is well within 10 V DC spec - last calib 2003). The reference is stable to 5 decimal points (1ppm for 10 Volt) when averaging the last 10 readings. It suddenly hit me I wanted to check with shorter and better cables. Result: 10.00012 Volt. We are talking about 30 microVolt or 3ppm change as a result of lower cable resistance and better contact/connection (fleabay banana to crocodile). I would have guessed around 1 microVolt [10V in 10 MOhm is 1 microAmpere in max 1 Ohm cable resistance is some 1 or less  microVolt]. But I have checked and rechecked, so it might be bad connection, thermocouple effect and .... (I don't know). On another pair of cables the effect was less than 10 microVolt.

So I guess measuring at 1ppm and below level is not just like start the meter and read ...? I would like to hear a tale of measuring and verifying with a control calculation on sub ppm level ...

[alm]

Today I got a board from Geller that came in at 10.00009 Volt (very happy - means my meter is well within 10 V DC spec - last calib 2003). The reference is stable to 5 decimal points (1ppm for 10 Volt) when averaging the last 10 readings. It suddenly hit me I wanted to check with shorter and better cables. Result: 10.00012 Volt. We are talking about 30 microVolt or 3ppm change as a result of lower cable resistance and better contact/connection (fleabay banana to crocodile). I would have guessed around 1 microVolt [10V in 10 MOhm is 1 microAmpere in max 1 Ohm cable resistance is some 1 or less  microVolt]. But I have checked and rechecked, so it might be bad connection, thermocouple effect and .... (I don't know). On another pair of cables the effect was less than 10 microVolt.

My guess is indeed offset voltages due to thermal EMF. It would be quite terrible for cable resistance. And why would you measure voltage references with a 10 Mohm input impedance? Set it to > 10 Gohm and cable resistance should be irrelevant.

[quantumvolt]

Why I would use 10 MOhm to measure a voltage reference? Because it is the default setting for the meter. Changing it o 10 GOhm+ stores the setting in volatile memory only, so next time you power the box the 10 MOhm is back. And I am too lazy to set it. And if I set it, I have to turn it off again because of too much noise in general hands-on sloppy everyday measurements ... Hard life.

My lesson from the experiment is that when I am checking my "references" for drift, the total cable/connector set up can be as important or more than the input impedance effect. I knew that just my body's influence on noise/field/whatever changes the readings and so do powered units surrounding the set-up, but now I understand why you might have to leave your meter, reference and cables untouched for a week in order not to introduce shifts in stability measurements. And if you are interested in accuracy (I expect nothing more than "realistically" +-0.01% -  the 34401A is only +-0.0035% per year DC 10V), I now understand why you look for gold-plated or other fine plugs/posts/connectors ...

[Mickle T.]

8,5-digit DMMs summary table and RMS noise chart.

[PedroDaGr8]

robrenz has mentioned previously the tellurium is not important for Thermal EMF properties. It is added to make the copper easier to machine (he's a machinist with years of experience).

[BravoV]

robrenz has mentioned previously the tellurium is not important for Thermal EMF properties. It is added to make the copper easier to machine (he's a machinist with years of experience).

+1, this, is well written in my personal note, he posted this somewhere in this forum. 

Btw, just fyi he is a pro machinist and also a volt ... I mean microvolt nut, and I guess just few trivial thermal emf difference will not make him sleep well at night. 

[robrenz]

Must have trend plot with statistics and histogram. like the 8846A and 34461A

[Fsck]

- way more affordable so a hobbyist afford it relatively easily (this is a delusion)
- decent memory, some kind of volatile memory as primary which can be backed up to say NVM every x readings, #M's of points or more
- 1U or 2U, not really sure on preference. Thinking 2U if touch screen just to make life easier.
- all sides of case must end at right angles.
- a 4 year, 4 sigma or greater confidence interval (>99.9937%) *effective* measurement error to be +/- 1 least significant digit of the resolution for all measurable values. (this value is the combination of [% error + x of range])    <a geek can dream right?>
-

[Fsck]

a weird idea: a log of calibration history and adjustments stored in some NVM, maybe in some form of table

[Fsck]

the ability to take shrouded banana plugs would be nice though hardly a deal breaker.

[free_electron]

the ability to take shrouded banana plugs would be nice though hardly a deal breaker.

WE DONT WANT NO EFFING SHROUDED BANANA PLUGS !!!! Whoever invented those should be tarred, feathered, drawn, quartered, shot, drowned and fed to the rats !

Them bloody shoruded blugs are compatible with almost nothing.

[Hypernova]

Hey, how about an optional "Low Jack" and WiFi-- so if it gets stolen, it can report it's location whenever it finds a WiFi (or LAN) connection that is open to the Internet...

Might as well add a GPS beacon if you're going down that route.

[Fsck]

the ability to take shrouded banana plugs would be nice though hardly a deal breaker.

WE DONT WANT NO EFFING SHROUDED BANANA PLUGS !!!! Whoever invented those should be tarred, feathered, drawn, quartered, shot, drowned and fed to the rats !

Them bloody shoruded blugs are compatible with almost nothing.

it's why I made unshrouded to shrouded "adapters" so I can use my probes (not on an 8.5d dmm)

[alm]

I like the shrouded banana plugs for measuring higher voltages, even in lower energy circuits. My compromise is that I use shrouded cables for most multimeters (I think the 3458a is one of the few currently available multimeters without shrouded jacks) and unshrouded for other stuff like power supplies.

I wouldn't be holding my breath for a replacement. This is probably a low volume, high R&D cost item, so it'll take a long time for it to start making profit, especially since militarily spending is down compared to when the 3458a was designed.

[Bored@Work]

it DOES make sense for a hand-held meter that you might be probing around inside of an AC distribution panel, but NOT a friggin' bench meter!

Why do you think people don't use bench meters for higher voltages?

By the way, you can get binding posts that take shrouded plugs. However, the safety versions of them, well, meh. Multi contact SPK4

http://uk.farnell.com/mc-multi-contact/23-0410-21/connector-panel-mount-black/dp/1116219?Ntt=1116219

[alm]

By the way, you can get binding posts that take shrouded plugs. However, the safety versions of them, well, meh. Multi contact SPK4

http://uk.farnell.com/mc-multi-contact/23-0410-21/connector-panel-mount-black/dp/1116219?Ntt=1116219

Are these as clumsy and inconvenient to use as they look?

[Bored@Work]

By the way, you can get binding posts that take shrouded plugs. However, the safety versions of them, well, meh. Multi contact SPK4

http://uk.farnell.com/mc-multi-contact/23-0410-21/connector-panel-mount-black/dp/1116219?Ntt=1116219

Are these as clumsy and inconvenient to use as they look?

Yes, they are.

[Fsck]

I wonder if a screen with an abnormally high refresh rate would be beneficial for live graphing functions (trendplot, etc. etc)

[alm]

How would this display look after being turned on 24/7 for 10 years? Because that's the kind of usage a typical 8.5 digit meter might see.

[Fsck]

How would this display look after being turned on 24/7 for 10 years? Because that's the kind of usage a typical 8.5 digit meter might see.

I think you're a little bit under on your timeframe. the 3458a was introduced in somewhere around 1988.. probably like the 20+ years. they'll probably be in service for a while yet
you'd probably need to plan for a 30-40+ year 24/7 lifetime.
but, then again, VFDs tend to dim over that kind of online time and yet many pieces of equipment with vfd screens are still popularly sold on the used market and in some cases, still produced.