Bad resistors
in [Design]
|
From: Cydrome Leader on 23 Jun 2010 12:00 DrParnassus <DrParnassus(a)hereforlongtime.org> wrote: > On Tue, 22 Jun 2010 21:58:52 +0000 (UTC), Cydrome Leader > <presence(a)panix.com> wrote: > >>what's the color code for M again? > > Wow, you really are a fresh out of or still in school know nothing > dweeb. So do people describe you as dull, humorless and quick to use childish insults like "dweeb"?
From: George Herold on 23 Jun 2010 12:10 On Jun 23, 11:50 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Wed, 23 Jun 2010 08:24:02 -0700, DrParnassus > > > > > > <DrParnas...(a)hereforlongtime.org> wrote: > >On Wed, 23 Jun 2010 19:28:15 +1000, Sylvia Else <syl...(a)not.here.invalid> > >wrote: > > >>On 23/06/2010 9:54 AM, DrParnassus 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. > > >>Still, you'd expect it to give the same wrong reading for the same > >>resistances. > > >>Sylvia. > > > That should be where their other clue comes from, because the readings > >are typically not repeatable. > > But they are, to a fraction of a per cent. In the case of the carbon > film resistor, I can hold the resistor body and see the resistor TC > effect, also repeatable. High-ohm resistors do tend to have bad TCs. > > There is nothing different between using and measuring a 10K resistor > or a 10M resistor. Or, assuming a little basic cleanliness, a 10G > resistor. > > We recently needed a 100M metal-film resistor to use in a photodiode > TIA thing. We tested a bunch of thickfilms and all had too much excess > noise; the testing itself is a nuisance. We settled on some axial RC07 Was this 1/f noise? Noise that only showed up when you drove some current through them? George H. > types, 50M 1% metal films from Dale Vishay, about $4 each. We put two > in series with a mid-air-soldered series connection, floating above > the surface-mount parts on the board so's not to waste all that board > area. > > Dale says they're expensive because hardly anybody buys them. > > Too bad about the noise. A single 0603 100M thickfilm would have been > cheap and a lot less hassle. > > John- Hide quoted text - > > - Show quoted text -
From: DrParnassus on 23 Jun 2010 12:23 On Wed, 23 Jun 2010 11:34:00 -0400, JW <none(a)dev.null> wrote: >27 cents each You pay that much for a resistor, and do not consider it other than std? You're an idiot.
From: John Larkin on 23 Jun 2010 12:26 On Wed, 23 Jun 2010 08:33:22 -0700, DrParnassus <DrParnassus(a)hereforlongtime.org> wrote: >On Wed, 23 Jun 2010 07:03:24 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > > >> >>GR had tube-based meters that would measure gigohms. >> >>John > > But not accurately. Read the Agilent and Keithley specs and then you can start weaseling about the dictionary definition of "accurately." I bet NIST measures gigohms to parts-per-million. I can do 0.1% with my home-brew rig. The old tube GR megohm meter used a mechanical meter movement, and reference resistors weren't very good back in the 1950s, so they were probably in the 10% sort of range. Look up some old manuals if you're seriously interested. You're probably not, for fear of actually learning something. John
From: DrParnassus on 23 Jun 2010 12:28
On Wed, 23 Jun 2010 08:50:37 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >Dale says they're expensive because hardly anybody buys them. If they have to do a lot run simply because one order triggered it, they lose money if it isn't a pretty big order, and SMD has expiration dates due to termination oxidation issues so they cannot simply store the over-production stock either. Though I will take old parts because they are usable for proto builds. |