DMM Volts/Ohm Calibration Club - anyone interested?

[Alex Nikitin]

I would prefer a very small and light box - about 4'' x 3'' x 1''  which should survive any postal abuse. I've found a nice 10K 3ppm/C 0.1% 0.001% W/W resistor to use in it, by the way  .

Cheers

Alex

[Nuno_pt]

Alex, that is looking good, only.

[BradC]

OK, there seems to be interest from the EU, some from the USA but nil from Australia.

Count me interested. I'm in Perth and have a 3457A which is out of cal. I'm not a volt nut but I did build a 10V reference from an AD587KNZ to check my handheld meters. I use the 3457A for relative measurements, so I'm not in need of absolute accuracy. It'd be nice to know if it was close though (either it and/or my AD587 are within tolerance, but in which direction and how close is a mystery).

[guenthert]

I'm not a volt nut but I did build a 10V reference from an AD587KNZ to check my handheld meters.

That's the denial phase. 

[enut11]

Hi all. There are some wonderful suggestions in this thread and lots of expertise from long standind members. Inevitably there are different expectations and requirements depending on how high on the metrology ladder you are.

There is no reason that everyone could not be satisfied, but it is unlikely to happen with a single design. Also, unless something happens soon, this will end up being discussed forever.

May I suggest a staged approach:
1) We start with a simple but accurate and stable 10v (7v) and 10k roving standard to start the ball rolling.
2) If this works, and members are gathering useful information, we move to a more complex/versatile roving standard.
3) Finally, implementing an automated system loved by some of the more experienced members to save calibration time.

In the long term, I see a place for all three of the above as there will always be different levels of experience and different requirements.

If you accept this approach, please suggest a design and BOM for stage (1).
enut11

[retrolefty]

I'm not a volt nut but I did build a 10V reference from an AD587KNZ to check my handheld meters.

That's the denial phase. 

 Good one.  In my day we were satisfied with a fresh D cell as our reference. 

[VK5RC]

Hi All
Some Aussie guys are interested and emailing about voltage references, I am awaiting a good 10MOhm resistor.
In the meantime I downloaded RF Scientific's Data Logger program, I had a Prologix GPIB to USB interface, after a bit of problem with Win 7 making the logs file Read only, finally got it to work, imported into excel. I am not good at this stuff
Below is my first graph of data, no temp yet, It shows the early drift immediately after switch on of a 3458A (quite old - bought with dying NVRAM and transplanted old Cal data into new NVRAM) and KKMoon's old multi-voltage reference (eBay one).

[VK5RC]

Hi All,
A bit of a story, about a year ago I bought an old 3458A with the flat NVRAM battery problem, how I fixed it up (with a lot of help from TiN and other sources on the net) see  https://www.eevblog.com/forum/repair/minor-repair-hp3458a/
The problem is how good was the rest of the unit, it now passes self test and in comparison to an out of calibration 34461 it seemed reasonably accurate in terms of DCV, ACV, ohms.
I bought about 4 months ago a 03458-66509, the voltage reference unit out of 3458A, It only needs a single positive supply but it didn't come with the little (special) plastic cover for the LTZ1000ACH. Some of these surplus units on eBay are also of questionable heritage.

For a voltage reference unit I decided to use a metal box with polystyrene lining, I used a small cube of builders foam ( I heated it in the oven to 130C without adverse effect) and it isn't conductive - for the LTZ1000 cover.
For power I sought a low noise linear regulator, the TPS7A4901, seemed to fit the bill, certainly could cover the 30-40mA needed at 15V. An adapter board was used to get it onto my favourite one off project material , veroboard. The was fitted inside the box and was supplied from a lab PSU at 18V. The voltage supply is floating.
A Fluke temp probe was left inside the box so its temperature could be monitored during the experiments.
Photos of the inside of the box looking at the linear reg board. the top of the 03458-66509, the brown wire is the temp probe (K type)

[VK5RC]

The wire used to conduct the voltage reference is twisted pair silver coated copper, PTFE insulation and shielded. Like this http://www.ebay.com.au/itm/381447862950?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
The lugs I used came from JW Solutions. the 2758-fork from http://jswilley.com/Accessories.html - they are not cheap but are beautifully made.
Below is a photo of connecting them, I used Deoxit to clean the binding posts and the lugs before hand tightening the posts. The lugs are crimped then a light heat shrink applied.
The reference (metal) box is used inside another plastic box to try and reduce the effect of air currents and the terminals covered with a cloth

[VK5RC]

I tried to get a Rasp Pi talking to the 3458A to record the results but it was beyond my programming skills so I tried the RF Scientific freeware as I also had a Prologix GPIB USB adapter. I found it pretty easy. Below are my first results. DrFrank's comments re EMC effects were quite significant , about 10-50uV or so even with shielded cable bonded to the metal box of the reference and the guard post of the 3458A. Similarly door opening and closing in my small 'shack' ( I am an amateur radio op - total floor area ~12m>2).
Below are my results, the upper graph show my data over 8hours or so, the shack temperature slowly rose during the day from 17.5 C at the beginning to 18.2 at the end. The temperature inside the reference box was between 29.7 and 30.1C.
The two/3 dips in the raw data coincide when the 3458A was sampling just after I opened the door.

Settings 10V manual range, 4hr warm up then DC ACAL. NPLC 100, sampling every 120secs
The internal temp rose a little (31.5 to 32.1C) during the day and I recall its Internal last cal temp was in the mid 30s . I can't recall the Basic command to get it out of it again!

I am pretty happy with the results in terms of stability . I will repeat the whole setup soon to see if I get the same!
I wonder if the age of my unit (15+yrs or so) may have allowed the DMMs reference  to stabilise. My unit was obviously used pretty seriously before as it has been calibrated 16 times before, the last was by Agilent in 2009.
Any comments , suggestions or questions appreciated.
Thanks to dave, TiN, DrFrank, pelule, VintageNut, mimmus78, quarks and plesa and other EEV metrology contributors.

[plesa]

I tried to get a Rasp Pi talking to the 3458A to record the results but it was beyond my programming skills so I tried the RF Scientific freeware as I also had a Prologix GPIB USB adapter.

If you want I can post script for logging 3458A to file and website running on RPi2/3 which on webpage display the graphs.
Similar like TiN did on his website. 10MB csv take a few tens of second to redraw, but it is much faster that Excel
The tutorial on xDevs is slightly out of date.
Or if more members here will be interested I can make the RPi image ( Raspbian+GPIB+webpage) or send update to TiN to publish it.
After that you will needs to only make minor changes in scripts.
RPi should be better from EMI perspective than PC with monitor or laptop.

[TiN]

VK5RC

Good job on documenting, thanks for report. You don't really need to care on digits after 1uV, as they down in the noise anyway.
Also your reference output seem to be one of highest voltage I saw posted. I tend to think it's a good thing actually.

plesa

The tutorial on xDevs is slightly out of date.

But it woooorks!    

I know, could be better.

If you have image, I'd love to host it as well for 3458A newcomers.

[enut11]

@plesa
Yes please. I want to use RP3 to record data so any help welcome. Currently waiting for delivery of GPIB to USB converter.
enut11

[plesa]

The tutorial on xDevs is slightly out of date.
But it woooorks!    
I know, could be better.
If you have image, I'd love to host it as well for 3458A newcomers.

Started new thread and image will be ready soon with actual Raspbian.
https://www.eevblog.com/forum/metrology/raspberry-pi23-logging-platform-for-voltnuts/

[enut11]

@VK5RC
WRT the gold coated copper fork lugs, I could not see a price on the website without requesting a quote. Could you give an indicative price? These appear to be the best alternative to copper banana plugs.
enut11

[VK5RC]

@enut11, I can't recall the price, I have a vague+++ recollection it ended up being about AUD 5 each. I think quarks in his post https://www.eevblog.com/forum/metrology/diy-low-emf-cable-and-connectors/ reply no 16 in 2013 had them at just under USD$3 each.

[enut11]

Thanks VK5RC. At the other end, for boxed references, I was wondering if these copper terminals are suitable?
enut11
Look at this on eBay http://www.ebay.com/itm/201566753958

[TiN]

Look at this on eBay http://www.ebay.com/itm/201566753958

If one to pay 26$ for connector, I'd rather go to real deal for same money instead of shoddy ebay seller for audiophools.

[lukier]

If one to pay 26$ for connector

$26 for 4, which changes the game. But I'd be worried that these eBay audiofoolery ones are just copper plated or similar hoax. Maybe some forum member got a set and can confirm this is copper all the way through.

[plesa]

If one to pay 26$ for connector

$26 for 4, which changes the game. But I'd be worried that these eBay audiofoolery ones are just copper plated or similar hoax. Maybe some forum member got a set and can confirm this is copper all the way through.

It is 26 foe each Why not Pomona 3770 for $10?

[lukier]

It is 26 foe each Why not Pomona 3770 for $10?

I'm pretty sure the auction title says 4pcs, so $25.99 is for four, and the lowthermal one is similar price for qty 1.

[plesa]

It is 26 foe each Why not Pomona 3770 for $10?

I'm pretty sure the auction title says 4pcs, so $25.99 is for four, and the lowthermal one is similar price for qty 1.

I mean LowThermal. They are nice...

[VK5RC]

Thanks VK5RC. At the other end, for boxed references, I was wondering if these copper terminals are suitable?
enut11
Look at this on eBay http://www.ebay.com/itm/201566753958

At the  reference end , I have soldered the PTFE wire straight onto the circuit, means a slightly bulkier unit when not in use, but my thinking is that it avoids a set of metal to metal contacts out in the open  to potentially muck stuff up. While soldering has some issues, you will have to solder a jumper wire not only to the reference but also to the back end of the terminal.
I must admit to being a bit sceptical about those being pure copper, a comment of robrenz (in the quarks diy-low-emf leads post) is that pure copper is very difficult to work and those posts have a lot of detail, makes me think copper coated ?brass.

[plesa]

At the  reference end , I have soldered the PTFE wire straight onto the circuit, means a slightly bulkier unit when not in use, but my thinking is that it avoids a set of metal to metal contacts out in the open  to potentially muck stuff up. While soldering has some issues, you will have to solder a jumper wire not only to the reference but also to the back end of the terminal.

Majority of PCB with gold layer has copper-nickel-gold inter metalic structure instead of copper-gold. So EMF is still there.

[ez24]

Can someone give a summary of what is going on, ie a status report?  Is there something or is this just chit chat?
thanks