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 Forum index » DIY Hardware and Software
Recomend me a nice and cheap DMV to Vbe match transistors...
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MapacheRaper



Joined: Feb 15, 2018
Posts: 101
Location: Spain

PostPosted: Sun Jun 24, 2018 2:55 am    Post subject: Recomend me a nice and cheap DMV to Vbe match transistors... Reply with quote  Mark this post and the followings unread

1/
So Im in the stage of matching trannies. The theory and the circuit I´ll be using is more or less clear (the Ian Fritz way), but Im finding less than common that a multi reads until .001V.

I have one 4 digits 1999 counts multi coming home. Can it reach the 1 mV range?. (the counts/precision concept is a bit blurry yet)

2/
ANother question is... if in 2018 precision voltimeters cost a kidney, how did they do it in the Moog times with totally unreliable analog devices??


3/
And finally I have seen that kind of minialligators that seems superhandy to test things:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

I would like to buy some. Whats the name of this thingies?

Thaaanks!
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Blue Hell
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PostPosted: Sun Jun 24, 2018 3:45 am    Post subject: Reply with quote  Mark this post and the followings unread

Four digits means just that 'four digits' .. 1999 counts means that the leftmost digit can not be a 2 .. so internally the value range is limited from -1999 to +1999.

It does say nothing about accuracy or sensitivity, only about how many digits it can show. Of course for a high precision device you'd need more digits than for a low precision one (but extra digits do not automatically mean higher precision, it is a suggestion only).

The count does say something about resolution though, when you'd have a full scale of 1.999 V the smallest change in voltage you can see would be 0.001 V (or 1 mV). Again, this needs not be accurate, the accuracy will have to come from an accuracy spec.

Accuracy usually is given as a "percentage of full scale". When, for example, for that same 1.999 V Range the accuracy would be given as 1% this would mean 1% of 1.999V .. or about 0.020 (20 mV).

Then there is a thing called measurement range. In the examples above I've used a range of 1.999 V - other ranges could be 19.99 V, 199.9V on the upper side, or 0.1999 V etc. on the lower side. These ranges would be mentioned tho as 200V, 20V, 2V, 200mV .. even when that 2 can not even be displayed (but it is close enough).

When the full scale error would be 1%, and the range would be 200mV the accuracy would be 2mV.

Then another thing, the last digit in a digital measurement device is always rounded, so when you see a 3 there for instance, it might also actually be a 2 or a 4.

Then in the old days .. you now are looking into a device with high absolute precision .. but measurements can often in a cheaper way be done with high relative precision. This however usually needs a better (physical) understanding of the measurement device the thing being measured and how they interact.

A 100 µA analog meter (full scale) is (and was) relatively cheap, and when it has a good calibrated scale you can easily get a reading with a 1 or 2 µA precision.

When you'd make a 'difference measurement' (like a balancing weight scale) with this it would mean that you could tell the difference between two voltages or currents with a very high precision. Now if one of the voltages or currents would be a reference (like on the scale you would have a reference weight of say 1 kg) you'd know the thing to be measured with a very high precision.

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PHOBoS



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PostPosted: Sun Jun 24, 2018 5:18 am    Post subject: Re: Recomend me a nice and cheap DMV to Vbe match transistors... Reply with quote  Mark this post and the followings unread

MapacheRaper wrote:
3/
And finally I have seen that kind of minialligators that seems superhandy to test things:
I would like to buy some. Whats the name of this thingies?

I don't know if there is an official name but you should be able to find something if you look for IC test hooks.

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g.gabba



Joined: Nov 29, 2008
Posts: 449
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PostPosted: Sun Jun 24, 2018 5:32 am    Post subject: Reply with quote  Mark this post and the followings unread

elektrouwe has posted something very neat on the other side of the iron cuirtain
https://www.muffwiggler.com/forum/topic-153845.html&highlight=

with this u dont need a dvm to match very closely

iam planing to try this with a 4024/4067 combi on breadboard using an oscilator from the rack to make it even simpler. May a 4017 to make it simplerer?

happy matching Smile
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MapacheRaper



Joined: Feb 15, 2018
Posts: 101
Location: Spain

PostPosted: Sun Jun 24, 2018 3:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

@BlueHell, I have had to read it 4 times but I get it. It seems you have some good chunk of solid electronics knowledge. Thanks for the detailed explanation.

@PHOBoS Yeah, that´s it: test hooks and ebay shows a lot of them. Cool.

G.Gabba. I have to reread slowly the post to understand what´s happening in this circuit. In fact in one of the things that keep me hooked. Some months ago a minimaly complex circuit was like an egyptian hieroglyph. Now I look at them and there´s an eureka moment where it clicks and makes sense. With some designs I get even a deep sense of beauty in the concetp/diagram. Kind of stendhal sindrome. It´s like growing a new sense or learning a new language. It´s fascinanting.

Thank you guys
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g.gabba



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PostPosted: Mon Jun 25, 2018 1:31 am    Post subject: Reply with quote  Mark this post and the followings unread

well, the circuit is very much like a sequenzer,
it is a circuit with a multiple output.
each output gets set "ON" one after the other, only one at a time.

To each output a transistor or a diode is connectet, they are called there "DUT-Device-Under-Test"

All the duts share also a common point, where ur oszilloskope is connected too (after an amplification)

So the duts get measured one after the other, but rather then measuring the absolute values u are measuring "delta" - the difference between them. and because the signal is amplified by 1000 u get for 1mV difference on the dut 1V difference on the oszilloscope.

in the end u just keep changing the duts until the Line on the oszi is quite flat between two of them, cos then u have a matched pair.
without writing down one number!
that quite clever!
well done elektrouwe!
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electrotech



Joined: Apr 24, 2013
Posts: 35
Location: Ayrshire Scotland

PostPosted: Tue Jun 26, 2018 12:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm about to match some transistors using the Ian Fritz 'bridge' method and I'll be using my newest meter, an ANENG AN8008.
https://www.banggood.com/ANENG-AN8008-True-RMS-Digital-Multimeter-AC-DC-Current-Voltage-Resistance-Frequency-Capacitance-Test-p-1157985.html?rmmds=search&stayold=1&cur_warehouse=CN

This is a 9.999 count meter which not only has a 999.9mV range but also two other mV ranges - 99.99mV and 9.999 mV..... that's a resolution of 1uV !
It does have a small 'dead-band' of +-5uV on it's 9.999mV range but that doesn't really matter here.
Lastly, it doesn't cost that much Very Happy
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MapacheRaper



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Posts: 101
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PostPosted: Mon Jul 09, 2018 4:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

MapacheRaper wrote:
electrotech wrote:
I'm about to match some transistors using the Ian Fritz 'bridge' method and I'll be using my newest meter, an ANENG AN8008.
https://www.banggood.com/ANENG-AN8008-True-RMS-Digital-Multimeter-AC-DC-Current-Voltage-Resistance-Frequency-Capacitance-Test-p-1157985.html?rmmds=search&stayold=1&cur_warehouse=CN

This is a 9.999 count meter which not only has a 999.9mV range but also two other mV ranges - 99.99mV and 9.999 mV..... that's a resolution of 1uV !
It does have a small 'dead-band' of +-5uV on it's 9.999mV range but that doesn't really matter here.
Lastly, it doesn't cost that much Very Happy


I have followed your counseil and I have bought the ANENG AN8008. It works wonders. Incredible bang for the buck.

Let´s match these transistors!
Thanks!! Razz
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