Voltage reference??

[UberStrike88]

Hi guys,

I need to calibrate a 4000 count multimeter but i don't have any good reference
So can anyone give a a schematic to build one?
And a link to all the parts please?
I have a breadboard and a 19V Power supply
Thanks

Regards,

[Mr Eastwood]

Hi,  i've not come across a diy all-in-one calibrator circuit; but you could buy a couple of precision resistors and a voltage reference ic and use those as a simple checker. 

The only cheap thing i've seen are those pre-assembled "quick-check" ones like this..
http://www.ebay.co.uk/itm/AD584LH-4-Channel-2-5v-7-5v-5v-10v-High-Precision-Voltage-Reference-Module-/271254847241

What DMM is it?

[SeanB]

That is the problem, you will find a precise reference is hard to buy. I made one with an AD581KH, which has an accuracy of 10mV as it comes, so you can be pretty sure that a meter will read it's 10V output to within that. a 4000 count meter will likely be on a 40.00V range, so you will have a reading to within 2 digits on it.

At $21 each they are not cheap, but they were the cheapest I could get that did not need external trim, and which were 3 pin devices with little external components required other than a very stable 15v supply. Easy to make that from your laptop 19V supply using a 7815 regulator with a 100uf 35V capacitor on both input and output.. A choke filter on the input to the regulator ( small toroidal choke from a PC power supply that you will find almost anywhere, just use the one toroid that has a winding of a few turns on it) will help reduce the switching noise on it.

[UberStrike88]

It is a Uni-t UT136B
But i also want to calibrate some of those cheap 830B multimeters
Yeah i have seen those to but i want to build my own because my paypal is limited ATM :/ (being fixed called paypal they said it will be gone in 2-3 weeks)
I can get all the parts for it (I think)

[Mr Eastwood]

The UT136B spec shows that on the 4V range it's +- 0.8%, + 1 count;  so it's not that accurate.   You could do a basic check with a voltage reference like the MAX6126  3v version (cost Ģ3.53);   of course it's not a "calibration", but it would make for a quick cheap check.

[Paul Collins M0BSW]

Haven't you got a calibration centre near you,or maybe a university ,or a friendly service centre.

[UberStrike88]

Nope i don't :/ And i can't seem to find that MAX6126 on ebay where can i buy it?

[Mr Eastwood]

I normally buy from rsonline (uk);  but any supplier local to yourself.
http://uk.rs-online.com/web/p/voltage-references/7577074/

Datasheet (page 16, simple circuit)
http://docs-europe.electrocomponents.com/webdocs/1095/0900766b810958f2.pdf

Keep in mind that the "MAX6126" comes in different voltages, and different grades (see datasheet)

[Mr Eastwood]

Here's one of the 2.048v ones I was playing around with and it works well as a quick test.

[UberStrike88]

Thank you! I'm going to look for a place where i can buy it
But anyway does it really need 12.6 V Or can i just give it 12V in ?

[Mr Eastwood]

check the datasheet again - there are min / max values;  one i looked can be powered from between  2.7 - 12.6 V;  so be useful to add a regulator 7805 etc to feed it.

(edit: using the specs of your uni-t - I think i'm correct to say you would expect to measure anything between 2.030 and 2.065 volts)

[UberStrike88]

I couldn't find it
Can you show me a decent one from ebay?
http://www.ebay.com/sch/i.html?_from=R40%7CR40%7CR40&_sacat=0&LH_BIN=1&_nkw=Voltage+Reference&_sop=15

[SeanB]

Try to refine your search to precision voltage references, that way you get rid of a lot of the TL431 clones and the poorer references. Ref01 would be good enough for most 1999 count meters as is, or you can get a cheap 4.096 unit as well there quite cheap. However it will only be a single point calibration on one range.

[ProBang2]

Sorry, but:

Is it really necessary to calibrate the UT-136B ? Damaged or something else wrong with it?
Otherwise: The factory- calibration of the UTīs is quite good. Use it to check the 830īs and thatīs it.

I canīt determine any sense in the expenditure to build a voltage-reference.
You pay easily more for the V-ref as for the multimeters (UT-136B = 16€, 830 = 5€ each.)

If it really makes a difference for you, to read 5.00 instead of 4.99, then you need an other kind of DMM.
With much more counts and much better specifications. Nothing is more simple then that.

My opinion: It is more useful for you, to spent the money for parts of your project or to aquire tools.
Just my two cents.

Greetings,

Hartmut

[UberStrike88]

Well it is still within spec (i suppose) But i want to see how much it drifts over time

Try to refine your search to precision voltage references, that way you get rid of a lot of the TL431 clones and the poorer references. Ref01 would be good enough for most 1999 count meters as is, or you can get a cheap 4.096 unit as well there quite cheap. However it will only be a single point calibration on one range.

Do you mean with ref01 this ic?
http://www.ebay.com/itm/1x-REF01CZ-10V-Precision-Viltage-Reference-REF01-/121088734755?pt=LH_DefaultDomain_0&hash=item1c31737623
Or is the Ref02 good to?
http://www.ebay.com/itm/2X-REF02CP-5V-Precision-Voltage-Reference-Temperature-Trangsducer-REF02-/120921434282?pt=LH_DefaultDomain_0&hash=item1c277aa8aa