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MapacheRaper
Joined: Feb 15, 2018 Posts: 166 Location: Spain
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Posted: Sun Jun 24, 2018 2:55 am Post subject:
Recomend me a nice and cheap DMV to Vbe match transistors... |
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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)
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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??
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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?
Thaaanks! |
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blue hell
Site Admin
Joined: Apr 03, 2004 Posts: 24079 Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320
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Posted: Sun Jun 24, 2018 3:45 am Post subject:
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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. _________________ Jan
also .. could someone please turn down the thermostat a bit.
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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Posted: Sun Jun 24, 2018 5:18 am Post subject:
Re: Recomend me a nice and cheap DMV to Vbe match transistors... |
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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. _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube |
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gabbagabi
Joined: Nov 29, 2008 Posts: 651 Location: Berlin by n8
Audio files: 23
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Posted: Sun Jun 24, 2018 5:32 am Post subject:
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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 |
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MapacheRaper
Joined: Feb 15, 2018 Posts: 166 Location: Spain
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Posted: Sun Jun 24, 2018 3:16 pm Post subject:
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@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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gabbagabi
Joined: Nov 29, 2008 Posts: 651 Location: Berlin by n8
Audio files: 23
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Posted: Mon Jun 25, 2018 1:31 am Post subject:
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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: 38 Location: Ayrshire Scotland
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MapacheRaper
Joined: Feb 15, 2018 Posts: 166 Location: Spain
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Posted: Mon Jul 09, 2018 4:10 pm Post subject:
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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!! |
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