Voltmeter input resistors and strange color bands - Page 1
Forum section: electronics / projects

author: Yansi
author_rank: Super Contributor
timestamp: December 26, 2016, 01:07:48 pm
content: Hello again!In my last thread we have discussed a bit about multimeter chipset MAX134, and it has just reminded me of something: I have a box of a pound or so of these resistors. They are 1Mohm, but having a strange yellow color band. Please see the photo (sorry for the not greatest WB).There are four bands: Brown, black, green ( = 1Mohm, confirmed by measurement) and a separate thicker yellow band. But yellow is not used for tolerance marking (never seen that), but yellow seems to mark 25ppm tempco, according to for example this:https://cdn.instructables.com/FGG/TBC9/H4VQNQFG/FGGTBC9H4VQNQFG.MEDIUM.gifAlso the base color of the resistor is light blue, like some metalized resistors use. Also the resistors are not small at all, they are I think 0617 size (6mm dia, 16mm length), like 3 or 4W resistor.Is this some kind of precision resistors? Do you have any ideas where these could be used?That brings in the other question: Possibly input resistor for a voltmeter? Low tempco being the obvious, the size (wattage) of the resistor more likely being a high voltage rating, to withstand for example 1000V or more.is it possible these could be used as voltmeter input resistors? Or what kind of resistors are suitable on voltmeter inputs, to withstand the 1000V range including line transients?Thanks,Yansi

author: KhronX
author_rank: Frequent Contributor
timestamp: December 26, 2016, 01:12:00 pm
content: Using several resistors in series is a common practice, to extend the voltage rating (and in some cases, the power dissipation, where needed).Most often seen in switchmode power supplies, either as the discharge resistor(s) for the X2 caps, or as the trickle-charge / start-up resistor for current-mode PWM or all-in-one flyback controller chips.

author: bktemp
author_rank: Super Contributor
timestamp: December 26, 2016, 01:30:59 pm
content: Maybe the last band is gold? It looks a bit more orange than the usual yellow. So probably 1M 5%.I doubt it is the tempo marking because the temco band is always the band after the tolerance band and typically only used for 1% or better. I have never seen a resistor with a tempco band but no tolerance band.The resistors look similar to VR68 series high voltage resistors, also the last band has a similar colour:http://media.digikey.com/photos/Vishay%20BC%20Photos/VR68%20Series.jpg

author: Yansi
author_rank: Super Contributor
timestamp: December 26, 2016, 01:40:51 pm
content: Putting a few in series is the most obvious way doing with cheap common resistors. My chinese autorange multimeter also uses 4 MELF packaged ones in series on the voltage input.But are there some resistors, exactly for that purpose, without the need to put a few in series? (except those special ceramic hybrids, that are purposely custom made for high tech insrtrumentation)bktemp: I have warned yout about the WB (white balance) on the photo. The yellow is really bright yellow, not orange. There is no other band. But I think you have nailed it, these most likely are the Vishay VR68 series.From the datasheet itself:Yellow and gray are used instead of gold and silver because metal particles in the lacquer could affect high-voltage properties.So most likely 1M 5% high voltage rated resistor, 1000V / 1W. Thanks for helping to identify them!

author: Brutte
author_rank: Frequent Contributor
timestamp: December 26, 2016, 03:40:14 pm
content: Quote from: bktemp on December 26, 2016, 01:30:59 pm+1That is from E24 series. Three bands for value and one for tolerance. 1M, 5%.

author: Yansi
author_rank: Super Contributor
timestamp: December 26, 2016, 04:09:42 pm
content: As I have clearly stated, it is not gold, it is YELLOW. Read above for explanation, before posting such.

author: TheAmmoniacal
author_rank: Unknown
timestamp: December 26, 2016, 04:57:10 pm
content: Quote from: Yansi on December 26, 2016, 04:09:42 pmNo, that is gold.

author: Yansi
author_rank: Super Contributor
timestamp: December 26, 2016, 05:20:13 pm
content: Yellow. And do not force me to pick you some new great name

author: TheAmmoniacal
author_rank: Unknown
timestamp: December 26, 2016, 05:21:10 pm
content: Quote from: Yansi on December 26, 2016, 05:20:13 pmAurum, then.

author: Yansi
author_rank: Super Contributor
timestamp: December 26, 2016, 06:32:01 pm
content: Okay, but consider next time please, that someone might don't like spam. And I don't mean the meat, I would likely eat it right now. Our govt recently had a great idea to make a law, that all shops have to be closed on holidays like these. One can't even go and buy anything to eat here and the fridge is close tu NULL. Stupid govt morons...