Can low precision resistors be precise? - Page 1
Forum section: electronics / beginners

author: polli
author_rank: Contributor
timestamp: August 28, 2017, 08:08:39 am
content: If I buy a roll of 5000 1% 100 ohm resistors, will I find some resistors with 0.1% precision?I'm asking this because if they first check for 0.1% resistors and then only use the resistors that failed the check for 1% resistors, I shouldn't be able to find any 0.1% resistors in my roll.

author: Circlotron
author_rank: Super Contributor
timestamp: August 28, 2017, 08:14:51 am
content: You may well find some very accurate resistors but there is no guarantee that they will remain that accurate with time or temperature.

author: hamster_nz
author_rank: Super Contributor
timestamp: August 28, 2017, 08:29:17 am
content: Are you hinting at this?http://dangerousprototypes.com/blog/2010/07/01/actual-values-of-10-tolerance-resistors/

author: wraper
author_rank: Unknown
timestamp: August 28, 2017, 08:32:55 am
content: You'll find 0.1% among them but be aware that they may be not as stable as you want. If you buy 5%, then you might have a problem because all 1% might be binned out. You may want to look at 0.1% thin film resistors with low temperature coefficient, as usual thick film types may significantly drift with temperature and time. The most stable resistor types on contrary usually have high tolerance like 5% or 10% which is then compensated by calibration.

author: Zero999
author_rank: Super Contributor
timestamp: August 28, 2017, 08:38:54 am
content: Quote from: hamster_nz on August 28, 2017, 08:29:17 amI've seen a similar thing elsewhere too. Perhaps that was the case 50 or so years ago but I doubt it with today's manufacturing methods.

author: Avacee
author_rank: Unknown
timestamp: August 28, 2017, 08:42:46 am
content: If you buy a load of 1% resistors the chances are you will some that match your requirements for those conditions at that time.However, you may get a batch that are all high, or all low, and none exactly match the value specified, but all are still within 1%.If you want quality be prepared to pay for it and how much do you cost your time at for checking a load of resistors to find ones within acceptable bounds to you.It may be cheaper to just pay for the 0.1% resistors up front.For info: Dave did 2 videos showing the resistors which he got did not have a missing gap where other resistors had been picked out.You'll see on Dave's second video (#216) the vast majority of the resistor were within spec but low and to find the ones within 0.1% would have taken ages.and

author: polli
author_rank: Contributor
timestamp: August 28, 2017, 08:45:19 am
content: Quote from: Avacee on August 28, 2017, 08:42:46 amThis should answer this question exactly. Thanks!

author: tszaboo
author_rank: Super Contributor
timestamp: August 28, 2017, 08:49:46 am
content: Yes. No. Maybe.Depends.The thing is, it is very time consuming to bin resistors. So usually we just pay the manufacturers to do it for us. If you need 1-2 precision resistors, the price is almost nothing, if you need it in high quantity, the price for each becomes nothing.

author: polli
author_rank: Contributor
timestamp: August 28, 2017, 09:00:38 am
content: Quote from: NANDBlog on August 28, 2017, 08:49:46 amThis is just curiosity, I don't plan to bin resistors myself.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: August 28, 2017, 09:26:36 am
content: You need a surplus one of these:Then you can have a cascade of spent resistors raining down from your helicopter, Matrix-style.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: August 28, 2017, 09:31:51 am
content: Some here hinted at the fact that they might not have a guarantee that they keep that accuracy over time - but those two factors don't necessarily have anything to do with each other.Also keep in mind that unlike what some people seem to think, the 1% is not a guarantee that every resistor will be within 1%, but rather an indication of what the standard deviation is (I think 2 sigma but I'm not sure). This means that most will perform (significantly) better than 1%, but some will perform worse - it's just very unlikely.This also brings me to another point about resistor tolerance: Sometimes we see people put 10 1% resistor in parallel "to make a .1% resistor" (it actually also works in series). This only works if you can assume that all the tolerances are uncorrelated. If this is not the case, and two resistors that are next to each other in the reel are not uncorrelated, then you will not get the desired tolerance - in fact it may be worse.

author: Ian.M
author_rank: Super Contributor
timestamp: August 28, 2017, 09:37:40 am
content: Here's an idea for a project for Voltnuts: An automated bandoleered component tester!It would automatically make a Kelvin connection to the component still in its bandoleer tape, to connect it to a bench DMM with logging, take the required sequence of readings, then step to the next component while ink-jet printing an ID number on the tape as it does so,

author: polli
author_rank: Contributor
timestamp: August 28, 2017, 10:25:39 am
content: Quote from: TheUnnamedNewbie on August 28, 2017, 09:31:51 amThis makes sense; in the first eevblog video linked, Dave finds that no 1% resistors (he tried 400) go above 0.5% error.

author: wraper
author_rank: Unknown
timestamp: August 28, 2017, 05:00:35 pm
content: Quote from: TheUnnamedNewbie on August 28, 2017, 09:31:51 amWrong assumption, that would indicate that manufacturer have production problems. Resistors and capacitors are 100% tested for their parameters, parts which fail specifications are discarded / binned for lower grade. Also 1% resistors usually must pass around 0.5% tolerance and 5% resistors usually must pass 2% tolerance when tested at factory. Look at 5:35 how capacitors are tested, the same applies to resistors.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: August 28, 2017, 05:03:23 pm
content: Quote from: wraper on August 28, 2017, 05:00:35 pmQuote from: wraper on August 28, 2017, 05:00:35 pmI didn't assume, rather, I was told. I guess I was misinformed.

author: Vtile
author_rank: Super Contributor
timestamp: August 28, 2017, 05:09:55 pm
content: Quote from: Ian.M on August 28, 2017, 09:37:40 amYou did forget the thermal cycling.Edit.The standard deviation bell curve might also have different peak aka mean value, which is off by some certain percentage from the nominal value. Ie. I have a few hundred 1k metal film resistors, which are all below 1k, not much but enough.

author: Ian.M
author_rank: Super Contributor
timestamp: August 28, 2017, 05:14:34 pm
content: Thermal cycling is *SLOW*. It doesn't make sense to cycle individual resistors. Put the rig and the bandoleers in an environment chamber and do a run for each temperature you want to test at. Of course that meens it either needs a bidirectional feeder or a rewind mechanism.