Home made DMM accuracy check - calibration ..

[Kiriakos-GR]

I have to point out one amazing for my taste link ..

Tips about basic test and calibration tools .

http://lategahn.2log.de/index.php?calibration-standards-introduction

I got very excited , and ordered all ready the parts for the DC calibrator .
Found the major chip in Germany , and I have just buy it ..

Now I am looking for resistors ... 

[DJPhil]

Good find!

I bookmarked that one for future reference. Thanks for the heads up.

[Kiriakos-GR]

You are welcome ...    

Now I am looking for Military Film metal resistors ..
And I do have locate my ebay source ...

But I do have one question .. is at the film metal resistors .. quality issues ?

I find easily  offers of  30 or 50 resistors of your choice for few dollars.
And I am ready to trust more the  VISHAY brand , than  no-name ones.

Are any better brands than this ?

[saturation]

Be careful about buying parts off eBay or unknown distributors especially based in China, there are a lot of counterfeit electronic parts.

You are welcome ...   

Now I am looking for Military Film metal resistors ..
And I do have locate my ebay source ...

But I do have one question .. is at the film metal resistors .. quality issues ?

I find easily  offers of  30 or 50 resistors of your choice for few dollars.
And I am ready to trust more the  VISHAY brand , than  no-name ones.

Are any better brands than this ?

[rf-loop]

Are any better brands than this ?

Vishay is good but can not forget Caddock for precision resistors
http://www.caddock.com/

But Vishay VHP100 series reistors are good (low TC and low ageing)
http://www.datasheetcatalog.org/datasheet/vishay/vhp100.pdf

maybe using with cheap 0,02 - 0,05% Voltage reference these are littlebit overkill, but not if try make true lab grade references. (but it is totally different case)  


-----------------------------------

Maybe Vishay have not yet move manufacturing to China... (but many many highly trusted brands are... maybe also we can soon wait Chinese most high brands.

Counterfeits... some times (some special) counterfeits are also better than originals.. sometimes value is as waste.

btw many chinese ebay etc sellers get components and equipments also from western countries factories production lines... (u want one surplus/waste container or do you want 100. Opening these waste containers may be very "eyes opening surprice")

[Kiriakos-GR]

Well I got the decision to start my own  High precision decade resistors box.  

I had on my boxes one nice  10 way selector .

And found in China , 0.1 Ohm resistors Vishay Dale..

So, soon I will be ready to build the first step of my decade box.
The cost of the resistors was an overkill like 15$  

http://www.vishay.com/docs/30206/lvr.pdf

My plan are the scale  0.1 - 20K

About the overkill in the tolerance of the resistors , the meters that I would like to check,
has an error of  2-3% at the Ohm scales ,  so I think that anything as resistor at 1% tolerance ,
it will do fine.

[363616]

One place to get nice components is from surplus high quality measurement equipment.  Sometimes the shipping cost can be prohibitive unless you can find the stuff locally.  About 8-10 years ago I found a local guy who was selling surplus government equipment out of his garage.  One of the things I got from him was an old HP differential voltmeter for $10.  It didn't work, but it had lots of good components and hardware when I scrapped it.  HP analog meters from their instruments are quite good -- I built a microgram scale from one that worked like a charm.  The differential voltmeter had some high quality resistors inside (many of them were matched pairs to 0.01% or better) and stamped with their value, tolerance, and date of manufacture (around 1967 if I remember).  One of those resistors is my primary resistance standard, around 1.1 kohms.

I also bought from that guy a Fluke 893A differential voltmeter, an instrument I used in the 70's when doing R&D at Varian.  This meter probably dates from about the same time and it is dead-nuts accurate and reads exactly the same as my beloved HP3456, another legendary instrument. 

I also got an Ithaco lock in amp for scrap parts.  It was US government surplus and was a gold mine for parts (I think it had 4 or 5 10-turn pots with counter dials in it).

[northernlight]

Hi everyone,

I'm currently building a voltage reference too. My thought was to be able to test the 2V or 4V and 20V or 40V DC range. So I found the AD REF195 with 5V +- 2 mV for the higher range. For the lower range I'm between the LM4140 with 1,024 V @0,1%, 10ppm/°C and the ones with 3 or 6ppm/°C. The tolerance of the reference voltage is influenced by the tolerance of the supply voltage. A 7812 has got usually 5%. So I'm using a LP2951ACN @ about 6,5V for the AD REF195 and a LP 2950 CZ3,0 (behind the 2951) for the LM4140 (Uin max 5,6V). They have a tolerance of 0,5%. Voltage regulators work better with a little load, so I'm putting a LED @10mA behind the 2951 and a 3k resistor behind the 2950. A diode in +Uin and a Transil at Uin and both Uref complete the design.

For resistors I'm going with 0,1% from Yageo. I simply use 4mm sockets and solder the resistors (10/100/1k/10k/100k/1M) connected between them. Since many of my DMM are rated 1% in ohms and my best DMM at 0,15%, that is good enough.

[Kiriakos-GR]

One place to get nice components is from surplus high quality measurement equipment.  

Found another source ...  

How about aircraft switches for military use ..    

I am Crazy I know that ..
Just got  6 of those ...  (payed and they will be shipped tomorrow from US )
Got a better price as lot of 6 , but I can not publish it ..  

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=140206409746

About Janco ... http://www.esterline.com/controlsystems/JANCO/JANCOHome/tabid/2474/Default.aspx

I am going to do an ultimate quality Decade resistors Box , even looking for only 15ppm 0.1% resistors.

Its very hard to locate the components , but I am trying , at list I found the selectors,
and the 0.1 Ohm resistors .

Now I have on target   the Electronic Project Box  ..  and some of the needed values of resistors.

[alm]

If you're going for best accuracy, make sure to provide Kelvin connections, which is especially important for the low resistors (eg. 0.1 ohm), otherwise you might as well not go through all that trouble. You would need double pole rotary switches for that. This only helps for meters that can do four-wire resistance measurements, but (almost) any high-precision meter supports that.

[Kiriakos-GR]

Well the ones that I got as minimum are  0.1  = 0.10 mOhms
Found the the same resistors as  0.01  so those must be the absolute 1mOhm 

So , sorry for the misinformation.

Before seconds I got all the rest ,  minus the 1R , that looks that the seller does not have an listing or stock.

In few hours I will know more .. as I am waiting for his message, and to combine shipping.

 

[Kiriakos-GR]

By the way I need some help ... how do you call in English this type of box .

Give me as many descriptions as possible .. Thanks.

[EEVblog]

By the way I need some help ... how do you call in English this type of box .
Give me as many descriptions as possible .. Thanks.

Typically that would be a "sloping desktop console"
They are 3 key words I'd use, but there are almost certainly others.

Dave.

[Zad]

Definitely a Desk Console case. http://www.maplin.co.uk/Module.aspx?ModuleNo=1693

Don't forget, so long as component ageing isn't a huge issue, and you have access to something that is calibrated, you can use standard components and calibrate many of the errors out with trimmers.

[DJPhil]

"sloping desktop console"

Exactly.

Here's a few links to some examples from Hammond.

The main enclosure page has pdf catalog links at the bottom for various worldwide distribution chains.

1456 Series - SECM Series - 500/515/519 Series

Hope that helps.

[Kiriakos-GR]

Thanks for the Help people ..

The market are full of truly nice products ...  

The one at the right , the woody one took my hart .. and gave me ideas..




At the place that I work , they had an German Decade ,
the box was made only for hard plastic ..

Something that bothers me , are if the box should be isolated "full plastic" ,
or with aluminum front mask ..

I need to stay away of any issues , caused by the contact of the Rotary Switch's axle .
Because everything will be connected in series.

( By the way all above resistors are  Vishay ones )    
And the seller has run out of 1R  ones ...
 

.

[Rhythmtech]

Woody was definitely the way to go!

[jimmc]

I'm a bit worried about those switches, with a contact rating of 5 Amps @ 28vdc, the contacts are likely to be a silver alloy of some form.
This may give problems when used in a 'dry' circuit i.e. little or no voltage / current; for switching such circuits gold contacts are more reliable but will have a maximum current rating measured in mA.

see http://www.allaboutcircuits.com/vol_4/chpt_4/2.html for details

Extract:
With all this discussion concerning the reduction of switch contact arcing, one might be led to think that less current is always better for a mechanical switch. This, however, is not necessarily so. It has been found that a small amount of periodic arcing can actually be good for the switch contacts, because it keeps the contact faces free from small amounts of dirt and corrosion. If a mechanical switch contact is operated with too little current, the contacts will tend to accumulate excessive resistance and may fail prematurely! This minimum amount of electric current necessary to keep a mechanical switch contact in good health is called the wetting current.

Normally, a switch's wetting current rating is far below its maximum current rating, and well below its normal operating current load in a properly designed system. However, there are applications where a mechanical switch contact may be required to routinely handle currents below normal wetting current limits (for instance, if a mechanical selector switch needs to open or close a digital logic or analog electronic circuit where the current value is extremely small). In these applications, is it highly recommended that gold-plated switch contacts be specified. Gold is a "noble" metal and does not corrode as other metals will. Such contacts have extremely low wetting current requirements as a result. Normal silver or copper alloy contacts will not provide reliable operation if used in such low-current service!


Using 0.1 Ohm resistors is problematic there is no way that you will be able to get better than around 10% accuracy without using a 4 terminal technique.
see http://www.allaboutcircuits.com/vol_1/chpt_8/9.html

With 6 switches in series the total contact resistance will be well over 100 mOhm!
To get an idea of a commercial decade box see http://www.allaboutcircuits.com/vol_1/chpt_8/9.html
note the residual resistance is specified as less than 0.25 Ohm


I would certainly use a metal case, connecting the case to earth will reduce interference pick-up significantly. With a maximum resistance of 1.1111 MOhm the insulation resistance of the switch contacts to the mounting bush should not be a problem (>>1000 MOhm)

Jim

[Kiriakos-GR]

Jim I truly appreciate all the effort that you did , for all those details .

My friend  @alm did wrote about ...

Kelvin (4-wire) resistance

Few messages above ,
and by searching I did found the same sources .  

About the switches  they have an contact resistor as  0.002  / end of life max 0.020 Ohm .

I am going nuts because I can not find any 1R 0.1% tolerance on Ebay .  
I will have to use 1R 1% ...

About the box, I have on my scope one very large one,
so to add  7 switches   +  6 stand alone  standard values of resistors +  10V DC calibration module.
So , other than Decade box , it would be an DMM tester in " large scale "  

More info soon ,  as soon I will have lock my targets , as Box and  pointing knobs .  

There is no room now to step back , this is a costly project , and I have pay the 60% of the total cost.
 

[Kiriakos-GR]

Got my knobs today ... about 10 of them .. 

The best that I could find ...  ( Taiwan )

[Kiriakos-GR]

Ok my shopping basket become full , got it all .. 

One last detail stands in the way ,
Zero Ohm resistors ( connection link  0.010 Ohm  ) or   or silver plated copper wire !! 


If some one has a preference , just say it , and justify it ..

Thanks .

[Kiriakos-GR]

Hmm ok , solve that too.

Just ordered  silver plated copper 1mm  1M long ,
and ANTEX  special solder with silver ..

This 0.8mm (approx 21SWG) solder wire is fast melting, easy to use and ideal for use on micro electronics, fine wires, and most general soldering operations. With silver content which provides the added benefit of a lower melting point and a low resistance solder joint. Melting point 207° to 217°C   Tin content  97.0%   Silver content   2.5%    Copper content 0.5%  With a flux core.

Thats it ..   now I will start planning , the position of the parts at the face plate ..

link from the box ...     http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=390216247453

As about the 1R resistors, I found only 1R 1% 1/4W ,  well got them too. ( 50 of those , price per pack )

[Kiriakos-GR]

Just did another weird  "buy "  ..  

If the resistor box , its just the beginning in the principal of testing multimeters ,
this one that I got, its the next step ..

• 10mV, 100mV, 1V ranges
• 10mA, 100mA ranges
• 0.1% accuracy
• 0 - 8V available
• Precision 10-turn dial
• Battery Powered 9V PP3
• Battery level indicator

Description:

The 1030 is a compact, low cost, portable voltage and current calibrator for general purpose signal injection. It is suitable for voltage and current loop signal simulation as well as thermocouple simulation. The precision 10-turn dial provides a conventional feel to setting the output with a setting resolution of 1 part in a 1000 (0.1%)

PDF http://www.timeelectronics.com/download/1030v1c.pdf

Pricing in the US http://easthillsinstruments.com/electrical/electrical-source/time-electronics-1030-microcal-voltage-current-source.html

My ebay Price http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=280535080797
My price  31 EUR shipped ..  

Home page  http://www.timeelectronics.com/1030-Voltage-and-Current-Source.html

Pricing in UK as 320 pounds.


.
The left one  


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[Kiriakos-GR]

DALE 0.1 Ohm .... arrival ..  Spot on   



.

[Kiriakos-GR]

I will probably start an new thread, about my new project " Home made PRO Decade box " .

But I can not hide my excitement , from the arrival of the special switches.

They came today , and it's one little box, hides one very seriously packaging ...
Box + soft paper towel + air sealed bag + mini bag .

The main contact looks Gold plated .

Looks really luxurious and high quality ..