Why did resistors have such tighter tolerances in the old days - Page 1
Forum section: electronics / general

author: BobbyK
author_rank: Regular Contributor
timestamp: February 21, 2016, 06:04:12 pm
content: Comparing apples to apples, (e.g. 5% resistors) from a new Yageo batch from Mouser, and some really old 5% ones I had from over 10 years ago, I noticed that the old ones are all very close to the actual value (e.g. 9 out of 10 10K resistors were within 0.2% resistance value) while with the new ones, the measured values were all over the place (though still within 5% tolerance).This was a bit weird, so I measured my old 1K and 47K resistors too, and those too were amazingly close to the marked value. New ones were not.Has the quality of resistor manufacturing gone down, or is something else happening here (e.g. different tmepco's, binning of good vs bad tolerances, etc.?)

author: dreamwatcher
author_rank: Newbie
timestamp: February 21, 2016, 06:17:13 pm
content: Interesting question in a academic sense.However, metal film 1% resistors are so cheap these days is there really a need to buy carbon 5% resistors?Perhaps only low quality manufacturers bother to make carbon resistors anymore while the normal+ quality manufacturers just produce metal film these days.Maybe hardly anybody makes carbon based resistors anymore, and companies are selling out their old stock that consisted of resistors that were just in tolerance.Of course, these are just guesses off the top of my head and I could be completely off base.

author: BobbyK
author_rank: Regular Contributor
timestamp: February 21, 2016, 06:28:22 pm
content: But that's the weird thing, even with 1% metal film resistors, they seem to manufacture them to be just barely within that acceptable 1% nowadays, while it seems in the old days, they tried to achieve maximum accuracy. Is it just that the attitudes in designers have changed?These days if you are designing something that needs absolutely accurate values, e.g. a filter, or measurement instrument, you just go and buy those expensive .1% parts, and for everything else, you just get whatever is cheapest. It seems back in the days, customers would have expected to get 10K resistors when they asked for 10K resistors, and maybe there was some marketing value is saying "our 10K resistors measure very close to 10.000 Ohms)? I am just thinking out loud here, would be nice to hear from someone actually in manufacturing or sales of components if that is true...

author: dannyf
author_rank: Super Contributor
timestamp: February 21, 2016, 07:01:47 pm
content: QuoteNot sure if it is true. I randomly checked 5 1k resistors (those 1000 pieces for 1 dollar kind), and they come in 4 - 8 ohms apart.

author: timb
author_rank: Super Contributor
timestamp: February 21, 2016, 07:11:45 pm
content: Quote from: BobbyK on February 21, 2016, 06:28:22 pmIt would interesting to see what the spread on modern 0.1% resistors would be. I've got a ton of 0.5% and 0.1% precision wirewound units from old gear and they're actually a lot closer to 0.05-0.01% than they are stated tolerance. (Now, this could simply be because they were binned by Power Designs, Tek, Fluke, HP, etc. before assembly.)That said, most of the old 5% carbon comp resistors I've pulled (the brown ones with painted color coding on them) were very much all over the place in a 5% range. Same with 1% metal film units. The exception is some that I've pulled from precision power supplies and meters, they seem much, much tighter. (But again, I suspect they were individually binned by the instrument manufacturers.)

author: wraper
author_rank: Unknown
timestamp: February 21, 2016, 07:12:01 pm
content: Are new resistors metal film? Or do you compare metal film vs carbon film resistors by the chance?

author: Aodhan145
author_rank: Frequent Contributor
timestamp: February 21, 2016, 07:24:46 pm
content: Quote from: BobbyK on February 21, 2016, 06:28:22 pmI wouldn't buy those resistors.

author: Zero999
author_rank: Super Contributor
timestamp: February 21, 2016, 07:29:09 pm
content: Quote from: Aodhan145 on February 21, 2016, 07:24:46 pmHe meant 10×103Ohms, not 10 Ohms. Many European countries use a full stop '.' as a separator, rather than a comma ',' and the comma for the decimal place, rather than the full stop. There was some talk about standardising it to do it the European way but many people here wouldn't like it. I prefer to use the space as a separator to avoid confusion.

author: SeanB
author_rank: Super Contributor
timestamp: February 21, 2016, 07:42:52 pm
content: Very simple, they are the sort bands out of the manufacturer. The 5% ones are all those that were less than 5% tolerance, but which did not pass the closer binning for 2%, 1% and 0.5% tolerance devices, so were dropped in the bin of 5% devices. The better ones were sold off at a premium while these lower ones were the ones that are not junk, but rather than scrapping them they are still usable as low cost, and can be sold to cover material cost and plant time. You will find there are very little 10% resistors, as the basic setting will not make many, only on initial startup as they fine tune for the batch, and those are trimmable to 5% in any case during manufacturing laser or grinding up to value.In the old days you would find the manufacturer was out to fit a tolerance, and thus made a resistor that was trimmed to the nominal value so it would never drift out of the band, and they simply remarked the tolerance if there was an order for looser tolerance. Now they go for the faster production cycle time and sort out the lower ones from higher grade for the price premium. Before they trimmed slower so the final value from trim was closer to setpoint, but as you speed up the trim rate then mechanical tolerances and delays to move stuff make the per unit variance higher, but the final test ( which is very fast using modern equipment) can still read the result accurately and then deposit the part in the appropriate value bin.0.5% parts are the most expensive, and for the price of 1 you can get the same profit as 20 5% parts, so worthwhile to get them out of the distribution as separate parts, leaving the hole where they, along with the 1% and 2% parts, were in the nominal spread of values.The older manufacturers used to do incoming QC and resort resistors for a particular band of tolerance ( or for a certain TC if they knew they needed it) as it was cheaper to buy say 100k of resistors with a spread and sort out the ones that were suitable from the bulk, then use them in that critical application, then use the rest ( still in the spec as well) for non critical applications. Cheaper than ordering a special value resistor or a special TC, and they also benefited from bulk discount along with having a spare part that was then OEM only.

author: BurnedResistor
author_rank: Regular Contributor
timestamp: February 21, 2016, 10:58:46 pm
content: Quote from: BobbyK on February 21, 2016, 06:04:12 pmIts quite a small sample... Could it just be that the one sepecific batch you own happen to be much better? If you got them for cheap there is also a chance that they are lower tolerance rebatched along the way (Unlikely though...)Maybe it is a manufacturing effecinty thing. Granted I know little to nothing about resistor production, but I suspect the smaller the tolerances of a resitor, the more expensive they are to produce. Companies could have dialed in their processes in such a way that they make use of the whole 5%, they might as well. Where as in earlier times they would produce at a lower tolerance than they sell for as the processes where less precise, meaning they had a buffer to still meet the spec.. Just a theory though

author: BobbyK
author_rank: Regular Contributor
timestamp: February 22, 2016, 06:49:21 am
content: Quote from: SeanB on February 21, 2016, 07:42:52 pmThat makes a lot of sense. So maybe, I got lucky with the old resistors, and they just happened to be really good production units, but they didn't get binned out, so they ended up in my batch, and with the newer ones, all the really tightly-toleranced one just got binned out, and I am left with the cheapie 2cent/piece resistors. As a hobbyist though, I wished they had stayed with the old system - that way everyone would have been able to sort out really tight tolerances for e.g. filters or critical stuff, and use the rest for everything else without paying the exorbitant prices. Would large companies who used a lot of e.g. resistors (HP, TEK,...) do their own binning back in the days?

author: Aodhan145
author_rank: Frequent Contributor
timestamp: February 22, 2016, 07:00:36 pm
content: Quote from: wilfred on February 22, 2016, 01:33:47 amI know it was just a joke.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 22, 2016, 07:11:43 pm
content: Ten isn't enough of a sample size to even verify if they are within 10%. You need about ten thousand to make this statement.

author: dannyf
author_rank: Super Contributor
timestamp: February 22, 2016, 09:51:07 pm
content: "Ten isn't enough of a sample size to even verify if they are within 10%"Depending on the variance, even one observation can be sufficient to within an arbitrary level of precision.

author: BobbyK
author_rank: Regular Contributor
timestamp: February 23, 2016, 12:46:27 pm
content: Quote from: T3sl4co1l on February 22, 2016, 07:11:43 pmObviously, but I tried the same experiment with three batches of different resistance. And I checked way more than ten on each resistance. when I say "9 out of 10" that was just one measurement set - overall, the resistances were all really close to printed value. Now it is possible that all the batches of old resistor I own are just from really good manufacturers, or that I am really really lucky, but the explanation with the binning, and quicker selection rates during production does make sense to me.

author: SteveyG
author_rank: Unknown
timestamp: February 23, 2016, 03:15:11 pm
content: Quote from: dreamwatcher on February 21, 2016, 06:17:13 pmDefinitely - many applications NEED carbon based resistors. Metal film resistors are not necessarily drop-in replacements.

author: Maxlor
author_rank: Frequent Contributor
timestamp: February 23, 2016, 03:30:57 pm
content: The binning hypothesis seems plausible and should be easy to verify: In a given batch of 5% resistors, you should find very few that are actually close to the nominal value, instead most of them should be in the 2%-5% or maybe 1%-5% range, since the ones closer to nominal would have been sorted into a different bin. I'll test some next time I have nothing better to do

author: Maxlor
author_rank: Frequent Contributor
timestamp: February 23, 2016, 04:25:13 pm
content: I tested 94 resistors. They're Multicomp 5% 6.8k 1/8W through-hole resistors (single batch), and surprisingly they are a lot closer together than I would have thought. None is off by more than 0.7% from their average value (I used average, not nominal, since I don't have a suitable reference to compare my meter against. The average value is 6.776k, and the meter is specced at 0.3%+3.)I don't the manufacturing date, I think they were bought from Farnell about 6 years ago, so I'm guessing they're younger than 10 years.The result indicates that at least Multicomp doesn't seem to bother with binning these. Maybe other manufacturers do.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 23, 2016, 08:10:39 pm
content: Now that's starting to look goodYou need to do ahttps://en.wikipedia.org/wiki/Student%27s_t-testto get a better idea of it (I don't have the data, you have the data; and I'm not going to attempt a reconstruction from the graph), but I think the confidence level will be quite good that they are better than 5%, and may be reasonably (p > 0.95) in the 1 or 2% range.FWIW, resistors are usually something like 3\$\sigma\$ with a cutoff, so a 5% resistor is \$\sigma = 1.7\$%. Sigma in that sample looks to be in the 0.3% range, so there will be a function relating confidence level to actual precision.Tim

author: Zero999
author_rank: Super Contributor
timestamp: February 23, 2016, 08:44:46 pm
content: Quote from: Aodhan145 on February 22, 2016, 07:00:36 pmThe problem is on the Internet no one can see your body language or facial expressions. This is why we have smilies.

author: Seekonk
author_rank: Super Contributor
timestamp: February 23, 2016, 10:16:01 pm
content: Quote from: Aodhan145 on February 21, 2016, 07:24:46 pmI had a water plant come to our company asking us to build some boards for them. These were LED indicators for valve position. The factory rep had just submitted a $35,000 bid to upgrade the system to solve the problem of the boards burning up, they had replaced a half dozen boards already. A forensic analysis indicated a 12 ohm resistor had been substituted for a 12,000 ohm resistor on all original and replacement boards. Someone in the chain got the convention wrong. The manufacturer was in Italy. There had to be at least a thousand units out there with the same problem. I managed to salvage half the boards that didn't get burnt through and used caps instead of the resistor which was poorly rated for the application.

author: Maxlor
author_rank: Frequent Contributor
timestamp: February 23, 2016, 10:57:04 pm
content: Quote from: Seekonk on February 23, 2016, 10:16:01 pmSeems like something that could happen to an Excel user. When writing CSV files, Excel uses the localized number format. And more, it tries to be "smart" about it: when a German Excel finds the number "10.000", it assumes the period is a thousands separator, so it reads 10k. If Excel finds "10.00", it assumes it's a decimal point and reads 10. Do a load-modify-write with a different language Excel than the one that created the CSV file, you get many of your numbers corrupted. Not fun. Especially if noone notices the cause of the problems and fingers start being pointed at equipment you builtIt doesn't help of course that when exporting an CSV, english excel uses "," as the field separator by default