Bad resistors
in [Design]
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From: Spehro Pefhany on 23 Jun 2010 07:54 On Wed, 23 Jun 2010 19:30:39 +1000, the renowned Sylvia Else <sylvia(a)not.here.invalid> wrote: >On 23/06/2010 3:00 PM, Phil Allison wrote: >> "Jan Panteltje" >>> Got 10 resistors on tape marked 2M7. >>> Used one, circuit did not work right. >>> Took some testing ... before I measured the resistors. >>> Of the 10 several are 620 k and not 2M7. >>> Bought from www.voti.nl, so beware. >>> All are marked with the right color code for 2M7. >>> >>> New to me :-) >> >> >> ** Though pretty rare, I have come across wrongly marked resistors in a >> piece of commercial equipment !! >> >> Dozens of resistors colour coded as 3.3kohms were in fact 4.7 kohms. >> >> The correct value WAS 4.7 kohms - so the equipment maker knew about the >> wrong coding !! > >Or just fed strips out of the 4.7K box into the machine that loads >components onto the board, and never noticed that they were marked as 3.3K. > >Sylvia. That was my first thought. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff(a)interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
From: Sylvia Else on 23 Jun 2010 08:33 On 23/06/2010 8:18 PM, Jan Panteltje wrote: > On a sunny day (Wed, 23 Jun 2010 19:28:15 +1000) it happened Sylvia Else > <sylvia(a)not.here.invalid> wrote in<88e2dfF7mgU3(a)mid.individual.net>: > >> On 23/06/2010 9:54 AM, DrParnassus wrote: >>> On Tue, 22 Jun 2010 21:51:47 GMT, Jan Panteltje >>> <pNaonStpealmtje(a)yahoo.com> wrote: >>> >>>> Got 10 resistors on tape marked 2M7. >>>> Used one, circuit did not work right. >>>> Took some testing ... before I measured the resistors. >>>> Of the 10 several are 620 k and not 2M7. >>>> Bought from www.voti.nl, so beware. >>>> All are marked with the right color code for 2M7. >>>> >>>> New to me :-) >>> >>> A normal handheld DVM barely measures 1MOhm correctly so anything up >>> there and over will not likely be easily measured with cheap handhelds. >> >> Still, you'd expect it to give the same wrong reading for the same >> resistances. >> >> Sylvia. > > Exactly, and teh righ treading for correct ones. > And 620 k is not even in that E series, it is 560k 680k. > > Maybe I can sell these on Ebay for a minimum of 1000$ to somebody, > just like rare stamps? > Any takers at 1000$? > Aaagh! Don't do it. If you succeeded, we'd see the electronics market flooded with deliberately incorrectly marked resistors from China. ;) Sylvia.
From: George Herold on 23 Jun 2010 09:28 On Jun 22, 11:23 pm, DrParnassus <DrParnas...(a)hereforlongtime.org> wrote: > On Tue, 22 Jun 2010 18:50:38 -0700, John Larkin > > > > > > <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >On Tue, 22 Jun 2010 17:59:40 -0700, John Larkin > ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > > >>On Tue, 22 Jun 2010 16:54:15 -0700, DrParnassus > >><DrParnas...(a)hereforlongtime.org> wrote: > > >>>On Tue, 22 Jun 2010 21:51:47 GMT, Jan Panteltje > >>><pNaonStpealm...(a)yahoo.com> wrote: > > >>>>Got 10 resistors on tape marked 2M7. > >>>>Used one, circuit did not work right. > >>>>Took some testing ... before I measured the resistors. > >>>>Of the 10 several are 620 k and not 2M7. > >>>>Bought fromwww.voti.nl, so beware. > >>>>All are marked with the right color code for 2M7. > > >>>>New to me :-) > > >>> A normal handheld DVM barely measures 1MOhm correctly so anything up > >>>there and over will not likely be easily measured with cheap handhelds.. > > >>AlwaysWrong! > >>AlwaysWrong! > >>AlwaysWrong! > > >>1.1 meg and 4.7 meg, 5% resistors read... > > >>Fluke 8845A benchtop 1.08220 M 4.6390 M > > >>Fluke 87 handheld 1.083 M 4.64 M > > >>Fluke 75 handheld 1.084 M 4.66 M > > >>The last two haven't been calibrated in years. > > >>The biggest problem is the terrible TC of the carbon film resistors. > > >>I'll try a cheap Extech when I get home. > > >>AlwaysWrong! > >>AlwaysWrong! > >>AlwaysWrong! > > >>John > > >Extech model 26: 1.088, 4.68. It's pretty cold, been soaking in the > >garage for a year or so. It's a pretty nice meter, for a cheapie: it > >does t/c temperature, capacitance, frequency, duty cycle. > > >Oh, did I mention that you're AlwaysWrong? > > 7.5Mohm/V? Hahahahaha what a cheap meter! My old analog meter was > 20MOhm per volt input impedance. > > And you actually think that the CLAIMED 1.2% accuracy claim of > resistance readings applies at the fringes of the scale? Sure, bub. At > 40M Ohm, 'coffee breath' changes the reading. > > A 40M Ohm scale? > > Hahahahahahaha... Sure, bub. You would not even be able to zero the > meter and the basic Ohms test circuitry is too low in voltage to test > values that high. > > Even then accurate readings can only be counted on if the meter is > permanently mounted in a 'breeze free', humidity controlled box and the > reading be taken from within with all those values logged for each > reading. > > Outside the box, one could acquire a reading that can be between 7 and > 12 percent off the mark on the bottom of range values and even worse than > that as resistance goes up toward the top of the range..- Hide quoted text - > > - Show quoted text - What an idiot. My fluke 189, with 1% 100 Meg resistors... answer 100.2 Meg. Input impedance is only 10Meg. No problems. Why do you bother posting here? George H.
From: John Larkin on 23 Jun 2010 10:05 On Tue, 22 Jun 2010 21:50:58 -0700, Robert Baer <robertbaer(a)localnet.com> wrote: >John Larkin wrote: >> On Tue, 22 Jun 2010 16:54:15 -0700, DrParnassus >> <DrParnassus(a)hereforlongtime.org> wrote: >> >>> On Tue, 22 Jun 2010 21:51:47 GMT, Jan Panteltje >>> <pNaonStpealmtje(a)yahoo.com> wrote: >>> >>>> Got 10 resistors on tape marked 2M7. >>>> Used one, circuit did not work right. >>>> Took some testing ... before I measured the resistors. >>>> Of the 10 several are 620 k and not 2M7. >>>> Bought from www.voti.nl, so beware. >>>> All are marked with the right color code for 2M7. >>>> >>>> New to me :-) >>> A normal handheld DVM barely measures 1MOhm correctly so anything up >>> there and over will not likely be easily measured with cheap handhelds. >> >> >> AlwaysWrong! >> AlwaysWrong! >> AlwaysWrong! >> >> 1.1 meg and 4.7 meg, 5% resistors read... >> >> Fluke 8845A benchtop 1.08220 M 4.6390 M >> >> Fluke 87 handheld 1.083 M 4.64 M >> >> Fluke 75 handheld 1.084 M 4.66 M >> >> >> The last two haven't been calibrated in years. >> >> The biggest problem is the terrible TC of the carbon film resistors. >> >> I'll try a cheap Extech when I get home. >> >> AlwaysWrong! >> AlwaysWrong! >> AlwaysWrong! >> >> >> John >> >> > I bet the Extech will correlate rather well with the Flukes; i have >one and it reads within 0.2% worst case for all (valid) values except >when the value is less than a few hundred ohms where contact resistance >becomes part of the reading. Extech makes nice stuff. I think FLIR bought them to keep them from introducing a competitive IR imager. John
From: DrParnassus on 23 Jun 2010 11:15
On Wed, 23 Jun 2010 00:49:51 -0700 (PDT), crasic <trueurssian(a)gmail.com> wrote: > >The bands can change color, especially with age or heat. You're an idiot. It ids baked enamel. If the color has changed, the part has been subjected to too much heat. > >Or it could have been a batch of mismarked resistors that the >equipment maker got for cheap You ain't real bright. |