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 Forum index » DIY Hardware and Software » Klee sequencer
0,1 % resistors
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eXisteNz



Joined: Jun 08, 2010
Posts: 45
Location: Italy

PostPosted: Thu Mar 21, 2013 6:30 pm    Post subject: 0,1 % resistors Reply with quote  Mark this post and the followings unread

Hello!
i'm approaching to build pcbs, i wonder which malfunction might arise if i put 1% in place of 0,1% resistors? and....i have not a fluke for hand match resistor, but a DMM...i read about wheatstone bridge technique for selecting 0,1 values.... anyone know well this procedure?
cheers
Nico
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Blue Hell
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PostPosted: Thu Mar 21, 2013 7:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

Your range or tuning may be off with 1% when 0.1% was specified - when nothing was specified usually 5% is assumed and 1% will be fine, or overkill - depending on pint of view. 0.1% is rare really.

Fluke is just a brand for DMMs, so that's fine prolly.

Re. Wheatstone, yes I know all the details Laughing please zoom in a bit, maybe point to a website you saw and have questions about?

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Uncle Krunkus
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PostPosted: Thu Mar 21, 2013 10:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

From what I remember,
The .1% resistors (i think only about 10 or so are specified as such) just need to be within .1% of each other. They are for gain matching the op-amp stages. They don't have to be spot on the value, just the same as each other.
So,...buy about 100 or so 1% metal film resistors of the value quoted (eg 100K), and, using your DMM, sort them into piles which are matched to .1% (ie 99.8, 99.9, 100, 100.1, 100.2, etc. When one of the piles reaches the number you need, that's the pile you use.

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eXisteNz



Joined: Jun 08, 2010
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Location: Italy

PostPosted: Fri Mar 22, 2013 4:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes i understand, but i can't match them each other because my DMM on 100k range have an accuracy of 1ohm only (i.e it can read only 99kohm 100kohm 101kohm; and not 99,1 99,2)....

As regarding W.Bridge.. if i need to match each other only, i don't need to put a potentiometer, but only 3 resistor of known 0.1 accuracy value.... is that right?

I found these resistors, and i wonder if you could identificate as precision one since i dont' know which kind are these on the photo i'm attaching, i have 7 of 10k and 8 of 100k...

Then other question is: can i use 3 resistors of the same values on the bridge? i.e. can i use my 3 100k green precision resistors (if they are) as R1, R2, R3 for match the other 1%metalfilm 100k (Rx)?

And lastly: then i measure voltage between points that aren't connected at 9v battery voltage source is that right?

Well i think that answering these questions could be a good starting point to study calculus to do next...

Sorry for my poor english and thank you sooooo much for your patience!

nico


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elmegil



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PostPosted: Fri Mar 22, 2013 5:41 am    Post subject: Reply with quote  Mark this post and the followings unread

For a Wheatstone if all you're doing is matching *to each other* don't you only need two super-accurate resistors for the top half of the bridge?

Having the third is so you can be certain that all your matches match that third one, as I understand it.... ??

I have doubt because I haven't done this....
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elmegil



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PostPosted: Fri Mar 22, 2013 7:49 am    Post subject: Reply with quote  Mark this post and the followings unread

So I did some more searching and this seems like a fairly definitive source:

http://www.muffwiggler.com/forum/topic-61933.html


one question I have though is....would it be possible for your initial go round to do something more like this to get started:

take the top two resistors, put them on either side of a high quality trimmer, put a voltage across the whole thing and then adjust the trimmer to as close to exactly 50% of the voltage as you can manage. This gives you a solid starting point, probably better than starting with two random 1% resistors.

build the rest of the bridge, put a trimmer at the bottom as well. Run your source voltage across the wipers of the two trimmers, and adjust the lower one until you get a balanced bridge (the other measurement is 0).

Then swap out one of the lower legs repeatedly, noting the difference measurement, and sorting by that measurement, with the idea that any that are at the same difference value must be high degree matches.

For future use, take three that you match this way and omit the trimmers.


I doubt that's simpler or faster than Ian's method (probably not, I don't think I would dare to compare my lack of experience with his years doing this stuff), but it had occurred to me before reading the Muff's article and I wanted to ask if I'm being logical here.
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eXisteNz



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PostPosted: Fri Mar 22, 2013 8:24 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks elmegil for your ideas and link, i'll definately try them, i really don't know if it's works because i know far less than you about this technique....
COuld you please try to identificate which type of resistor is the one i've attached above in the photo? Since i have a 7-8 100k like that, i was wondering if they're precision military grade resistors....
thank you!
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elmegil



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PostPosted: Fri Mar 22, 2013 8:45 am    Post subject: Reply with quote  Mark this post and the followings unread

Unfortunately I've never seen that kind of resistor before....
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capicoso



Joined: Nov 19, 2012
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PostPosted: Wed Mar 27, 2013 10:10 am    Post subject: Reply with quote  Mark this post and the followings unread

eXisteNz wrote:
Yes i understand, but i can't match them each other because my DMM on 100k range have an accuracy of 1ohm only (i.e it can read only 99kohm 100kohm 101kohm; and not 99,1 99,2)....



That's weird, is it an old one or something? Even my 5usd cheapest DMM can read 100,1 99,9
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eXisteNz



Joined: Jun 08, 2010
Posts: 45
Location: Italy

PostPosted: Thu Mar 28, 2013 1:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Well it's a weird cheap new Tenma DMM model 72-7925:

RANGE RESOLUTION ACCURACY
200R 0.1R +-(0.8%+3)
2K 1R +-(0.8%+1)
20K 10R "
2M 1K "
20M 10K +-(1%+2)

DISPLAY MAX: 1999

So to measure 100k i have to go in 2M range having only 1k of resolution Sad
Anyway i've hand selected them with weathstone bridge and all was ok..
After a day i've remeasure with this DMM to see if at least all 25 resistors measure the same: 21 of them measure steady 98 but there's 4 measuring 99!!! Russian Roulette dunno
At the end now i'm ordering 25 100k 0.1% resistor from my supplier!
Definately i have to buy a new DMM!
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