Tolerances on a 0 ohm resistor... - Page 1
Forum section: electronics / general

author: Holes Flow
author_rank: Contributor
timestamp: May 31, 2020, 10:49:36 pm
content: Experts,In terms of lowest and highest value range of 5%, what should my expectations reasonably be?

author: RoGeorge
author_rank: Super Contributor
timestamp: May 31, 2020, 11:07:41 pm
content: Read the datasheet of the 0\$\Omega\$ resistors, and you'll find the resistance is not zero, but a very low value that is specified in the datasheet.In this case, that specified small value has 5% tolerance.Later edit:Quote from: Holes Flow on May 31, 2020, 10:49:36 pm- highest value is to be found in the resistor's datasheet- lowest value is not specified in the datasheet, but it is supposed that that type of zero resistors to be used as a jumper, and not as a resistor with a well specified value.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 31, 2020, 11:08:56 pm
content: And 5% of 0 is .......OMG, what's-5%of zero!!We always thought that the little black craters in boards were due to resistors burning up. Maybe they were zero ohm resistors that drifteddownin value and created mini black holes!!

author: Wolfgang
author_rank: Super Contributor
timestamp: June 01, 2020, 12:01:30 am
content: Quote from: Holes Flow on May 31, 2020, 10:49:36 pmYou could select those with a -5% tolerance out and sell them as energy sourcesSeriously: Your PCB tracks probably have a resistance in the same range, i.e., tolerances do not really matter.

author: Cerebus
author_rank: Super Contributor
timestamp: June 01, 2020, 12:31:12 am
content: Quote from: RoGeorge on May 31, 2020, 11:07:41 pmI have never seen that. Every data sheet that I've ever seen that specifies a 0 ohm resistor gives only a maximum value, not a specific, toleranced, value. e.g. The reel of Yageo 0805s I have here, the data sheet has "Zero Ohm Jumper < 0.05 Ω". Actually I measured those, out of curiosity, a while back and they came in around the 20 milliohm region, which is excellent.It would actually be quite dangerous from the manufacturers' point of view to give a specific value with a 5% tolerance because some sod who doesn't understand the difference between a "zero" ohm resistor intended for use as a jumper and a 50 milliohm resistor intended to be used as a resistor would use it as a resistor and then moan at you, or sue you, when their huge production batch doesn't work because you supplied excellent "zero" ohm resistors that were only 1 miiliohm. It would also be prohibitively expensive to test zero ohm resistors to a 5% tolerance of a specific value on a production line for sub 1 cent components. As anyone who's tried taking accurate resistance measurements below 1 ohm will tell you, it's not easy or quick.

author: bob91343
author_rank: Super Contributor
timestamp: June 01, 2020, 03:43:42 am
content: Interesting discussion but I suspect the OP had his tongue in cheek.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 01, 2020, 10:11:34 am
content: Quote from: Cerebus on June 01, 2020, 12:31:12 amMy mistake, sorry. I must have turned an assumption of mine into a rule. Doubled checked now, and couldn't find tolerance in the datasheet, just the maximum m\$\Omega\$.Thank you for pointing that out. Edited my previous explanation accordingly.I don't know where from came that 5%. Maybe it's from the ordering code. For example, this zero ohm resistorSFR01MZPJ000ordering code has the last letter J, and if the "J" were to be for some other value of a resistor and not a jumper, then a "J" in that position of the part number code would correspond to a 5% tolerance, according to the part number encoding scheme shown in thedatasheet. Just my assumption, no idea what does that 5% in the OP schematic means.

author: Holes Flow
author_rank: Contributor
timestamp: June 01, 2020, 11:15:41 am
content: RoGeorge,I was definitely posting because I was amused. However, this screenshot comes from a schematic for a MacBook, and components like this, labeled like this, are very common in these schematics from Apple.I found it quite humorous that you could compute tolerances on a zero ohm 1/20th of a watt resistor. Even as an ET in the military, we never came across these!Just trying to lighten the forums, that are typically quite serious...

author: Holes Flow
author_rank: Contributor
timestamp: June 01, 2020, 11:16:36 am
content: Right?!Quote from: Cerebus on June 01, 2020, 12:31:12 am

author: Holes Flow
author_rank: Contributor
timestamp: June 01, 2020, 11:21:17 am
content: I indeed posted this tongue in cheek, because the funniest things come from reality. It looks like everybody took it as such, considering I had a little :-) in the OP.But this is a 0201 SMD, and Apple doesn't like saying where they get things from. So I suspect, as these components are unmarked, that I would never no enough about the component to see a data sheet.Knowing it is Apple though, and all the engineering mistakes that we see with their equipment, and errors in their data sheets, something like this actually isn't that surprising.I wasn't looking for a real technical answer, because I doubt there is one. I was really surprised that there were some great answers. I just thought it was an interesting application of ohm's law, as it makes computing the maximum amount of current to generate 1/20th of a watt harder to do on the back of a napkin.Thanks for the great answers!!!

author: Cerebus
author_rank: Super Contributor
timestamp: June 01, 2020, 02:56:07 pm
content: Quote from: bob91343 on June 01, 2020, 03:43:42 amOh, I was certain of that. Often these things get taken seriously by someone, a discussion ensues and someone takes away a 'fact' from it that is about as technically reliable as the original premise and I kinda wanted to make sure that didn't happen. Normally I'd add a suitable witticism to make my comprehension of the original joke clear but on this occasion I couldn't come up with anything - toyed withi, toyed with negative resistance, superconductivity and negative heat flow and nothing came up that didn't sound so weak it would be embarrassing; Idohave a reputation to live down to, you know.

author: Cerebus
author_rank: Super Contributor
timestamp: June 01, 2020, 02:59:49 pm
content: Quote from: Holes Flow on June 01, 2020, 11:15:41 amIt's terrible the stuff they make you handle without adequate safety gear once they get you into uniform. Sorry to hear about the glowing fingertips and the other mutations.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 01, 2020, 05:13:26 pm
content: Maybe the nominal value less than the datasheet max m\$\Omega\$, whatever that nominal value happens to be for a given resistor, will not vary more than 5% over the whole range of the rest of working parameters, like temperature, humidity, load, etc.Could it be that the 5% here is a property of the resistive material itself, without bothering about the exact nominal resistance of the whole resistor?Would be interesting if somebody can ask a manufacturer. (bysomebody, I mean important enough to qualify for an engineering answer, and not just a generic PR/marketing/sales answer that all the rest of generic customers usually get)