my first PCB has a trace measuring 0.1 Ohm resistance - Page 1
Forum section: electronics / beginners

author: donbright
author_rank: Newbie
timestamp: October 12, 2020, 05:24:08 pm
content: (edited.too late to remove this.. so ill retype it so the replies dont look weird.)i got a PCB made and thought a trace should have 0 ohms but it had 0.1 ohms,i thought jumper wires and traces should be 0 ohms, after i wrote this i went back and measured everything... turns out my meter fluctuates between 0 and 0.1 ohms, on jumper wires, traces, everything. so basically i was going under wrong assumptions and too quick measurement.thanks

author: voltsandjolts
author_rank: Unknown
timestamp: October 12, 2020, 05:27:56 pm
content: 0.1 Ohms is fine, don't worry about it.

author: wraper
author_rank: Unknown
timestamp: October 12, 2020, 05:32:02 pm
content: First of all how precise is your measurement? If it's only the last digit on your multimeter then this measurement is not precise. It could be a 0.01 Ohm of difference that makes such difference in reading. Also you need a 4 wire measurement to really trust such readings since contact resistance with probes could be dominating in such measurement. Secondly all depends on trace length, width and copper thickness. You can calculate expected trace resistance.https://www.allaboutcircuits.com/tools/trace-resistance-calculator/

author: donbright
author_rank: Newbie
timestamp: October 12, 2020, 05:38:43 pm
content: thanks @wraperi went back and measured as soon as i clicked 'post' and u are right, my old multi-meter fluctuates between 0 and 0.1, especially if i leave it on a few seconds, and i was just assuming things are 0 ohms when they arent.

author: mag_therm
author_rank: Frequent Contributor
timestamp: October 12, 2020, 05:55:14 pm
content: Some multimeters have a feature that can null your probe resistance, so the next measurements are more accurate.On Extech meter here, short the probe tips and press "Rel" button.Then the display will read 0.00 and the next resistance readings will be more accurate.Works for L and C too, I think.

author: wraper
author_rank: Unknown
timestamp: October 12, 2020, 06:06:04 pm
content: Quote from: mag_therm on October 12, 2020, 05:55:14 pmIt does not make readings any more accurate. It simply does subtraction job automatically, so you don't need to do subtraction yourself.

author: pwlps
author_rank: Frequent Contributor
timestamp: October 12, 2020, 07:04:17 pm
content: For such low resistances you would need a 4-point measurement, but I don't know if your multimeter has a 4-point resistance probing capability.https://en.wikipedia.org/wiki/Four-terminal_sensingYou might arrange it yourself though, using a current source and a voltmeter.

author: WattsThat
author_rank: Frequent Contributor
timestamp: October 12, 2020, 07:41:35 pm
content: QuoteWell, you thought wrong. Practically speaking, nothing has a resistance of zero ohms. If we could make conductors with zero resistance, we wouldn’t need fuses.With zero resistance, you could push a million amps through it and have no heat generated. The world would be a very different place if we could do that.

author: Zero999
author_rank: Super Contributor
timestamp: October 12, 2020, 09:16:18 pm
content: Zero Ohm conductors do exist. They're known as superconductors, but only work at low temperatures and up to a certain current density.Of course, for practical purposes, everything has a resistance. An ordinary multimeter, with a resolution of 0.1Ohm, is no good for measuring resistances this low.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: October 15, 2020, 01:23:07 am
content: An LM317 can be used as a very simple and reasonably accurate current sink or source.You feed in current at the input, pin, and put a resistor between the output and the adjust pins and use the asjust pin as your second terminal.The reference voltage is around 1.25V, so with a 12.5Ohm resistor, you get a 100mA current source or sink, and by tweaking the resistor you can calibrate the current.Then, with any simple Power supply (between 5 and 30V) which can deliver those 100mA you have a simple measurement adapter to do 4-wire measurements with your DMM by measuring the voltage over your PCB track.