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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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28th Nov 2015, 9:12 pm | #21 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
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Re: Resistor
Quite possibly merely a symptom of advancing years, but I'm sure colours of resistor banding aren't as distinctive as they once were- I wonder if environmental legislation has toned down the colours. I do make sure I'm reading them under broad-spectrum illumination, preferably good ol' sunlight!
I gather that it's difficult to make gold and silver appearance tolerance band paint without resorting to fine metallic particles (or at least that's the way things were), so specific high-voltage resistors use yellow and white bands in their place to avoid tracking. This last band is further away from the others to avoid possible mis-interpretation. |
28th Nov 2015, 10:49 pm | #22 |
Nonode
Join Date: Oct 2014
Location: West Midlands, UK.
Posts: 2,181
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Re: Resistor
For the OP- THIS SITE MAY PROVE USEFUL - http://www.hobby-hour.com/electronic...calculator.php.
If the RAF mnemonic is the same as the one I was taught at college, then it's certainly not politically correct these days, but strangely enough, although I've heard others at other training places, this one sticks in my head. But ,and I don't know how common the other marking systems are now, the OP should be aware that as late as the late 60's I had a Radio & Line course book which gave a few other marking methods. lastly, one on line source, which might be worth a look, as it gives a bit of history /theory and a self teach bit., as well as another mnemonic. And I agree with last poster- I thought it was my advancing years, but once upon a time, colour 1 and two were close together and the tolerance band a lot more distant fro the last band,. These days ,it's harder to tell band 1from band 4, WRT distance. |
28th Nov 2015, 11:26 pm | #23 |
Heptode
Join Date: Oct 2009
Location: Melbourne Australia
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Re: Resistor
And when you want to replace an older resistor, but not with a 2W modern one like a PRO2, the problem is that low power 0.25W or 0.6W resistors often have 4 bands for value, and the last tolerance band is often brown or red and not really spaced away from the other four bands. Ambiguity reigns without that final ohmeter quick check for confidence.
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29th Nov 2015, 12:05 am | #24 |
Banned
Join Date: Jun 2015
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Re: Resistor colour code
Those that bother to read the rubbish that I write, might remeber I had trouble getting my latest amp working properly.
Both photographs are taken in sunlight, but the "dim" version is on my bench through a window. The "bright" is taken outside in direct sunlight. Its exactly 09:00 and the temperature is 30C ( we are expecting 38) There is not a cloud in the sky. The resistors are superb electrical devices made by Rodestein in Germany. The pics are self explanatory, I guess I designed too many circuit boards Joe I didnt mention the resistor is 274 ohms 2% NOT 270K which is what a quick glance produces Thats red, purple, yellow BLACK, red Last edited by joebog1; 29th Nov 2015 at 12:09 am. Reason: explanation |
29th Nov 2015, 10:04 am | #25 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
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Re: Resistor colour code
I think part of the problem is the coloured paint on the body. Back in time most resistors were carbon composition inside a white ceramic tube. The coloured bands showed up well, even the white one. Today manufacturers use many different body colours to identify their own make or type of resistor which makes it harder to read the colours.
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29th Nov 2015, 11:16 am | #26 |
Moderator
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Re: Resistor colour code
274 Ohms is a member of the E48 value series for 2% resistors and of course also the E96 family of 1% resistors.
Close tolerance resistors grow an extra band so Joe's resistor reads (it's photographed so the bands read right to left. It's a fifty fifty chance whenever you look at one) Red (digit 2) Purple (digit 7) Yellow (You'd normally expect multiplier 4 here, and then no more bands or a gold band or a silver band... but looking ahead it's got more 0-9 colours so this band is another digit, 4) Black (We've just had three digits so this is probably a multiplier 0, so add no more zeroes to the end) Red (huh, more bands? this is 2 for 2% tolerance. A 1% resistor would have brown here and a 5% or worse resistor wouldn't have so many bands) So that's a 5-band resistor. Some manufacturers add a sixth band but the meanings vary. For maximum confusion, the multiplier band can be gold for x0.1 for for resistors up to 100 Ohms. So having an Ohmmeter as a final arbiter to clear up ambiguty is quite important. Another clue is that close tolerance E96 resistors weren't made on the same values as ordinary E12 and E24 parts. The resistor values are on an anti-logarithmic scale so that their tolerance bounds just meet. This way a resistor manufacturer can flog every resistor he makes as one value or another. There are no gaps to fall into, and there is no overlap, so the number of values per decade is no bigger than need be. This means there is a constant ratio between adjacent values. It also means that all the values except 1, 10, 100, 1k etc aren't nice round numbers. So to express the digits in only 2 or 3 bands, the numbers have to be rounded up or down to the nearest that can be expressed. So in E12 you might have a 1.2k resistor. In E96 (1%) that value becomes more accurately written as 1.21k So once you knew the E96 values, you could recognise them on resistors and resolve the ambiguity this way. (You may have sussed that using an Ohmmeter is easier tham memorising 96 three digit numbers) This is in the past tense because some manufacturers recognised that there was a market for close tolerance resistors on good old E24 values that most people were familiar with. And this opened up ambiguities again! The only winners in this tale of chaos are the Ohmmeter manufacturers David
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29th Nov 2015, 12:35 pm | #27 | |
Nonode
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Re: Resistor colour code
Quote:
After 40 plus years of playing around with electronics, professionally as well as for "entertainment" I automatically check the value of any resistor I'm about to fit with a meter. I am not perfect and can misread a colour code. It is not unknown for resistor values to change with time - especially high value ones - and it's a problem with old-stock components. I have had brand new resistors straight from the packet which are wrongly marked (not often but manufacturers are not perfect either). If you have a meter on the bench why not use it? A few seconds to check can save hours of misplaced fault finding after the wrong part has been fitted!
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29th Nov 2015, 12:58 pm | #28 |
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Re: Resistor colour code
To what Brian's just said, I'll add that human nature is such that once you've fitted a new part, you never believe that it could be faulty. So if you do fit a wrong or bad part, you go round and round in circles looking only at everything else. The devastation to your work flow is completely out of proportion to the cause.
David
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29th Nov 2015, 1:13 pm | #29 |
Retired Dormant Member
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Location: Bristol, UK.
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Re: Resistor colour code
i must admit to doing the same and always check before fitting. The modern system with lots of fine bands often leaves me confusing some colours.
As to the colour code itself I never get help from mnemonics. It must be me because I find it as difficult to remember what the mnemonic means as to learn the whole lot by rote. This was the approach many years ago on a radar mechanics course. Eventually I simplified it a bit by recognising it was the colours of the rainbow with a couple extra on each end. Someone earlier commented on the effect of familiarity. Looking back I recognise the effect myself. When the body - tip - dot scheme was common I realise that most of the time I seemed to just know the value without thinking about it. This was particularly useful fault finding on a 'bird's nest' type of chassis. |
29th Nov 2015, 1:22 pm | #30 | |
Dekatron
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Re: Resistor colour code
Quote:
Turned out that every one of the rejected PCBs had 47-Ohm resistors where the design required 470K. The resistors were coded 470K but were 47-Ohm. The number of failed devices was pretty much identical to the number of resistors in a 'bandolier'. Given the nature of the customer - the contract specified 'no rework permitted' - the entire batch of boards was scrapped, and the supplier of the bogusly-marked resistors got to pay for the whole job to be redone from scratch, under threat that if they didn't we would do all we could to have their various quality-assurance accreditations overturned. |
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29th Nov 2015, 1:50 pm | #31 |
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Re: Resistor colour code
Odd how the digital multimeter came available at about the same time as 5 band resistors.
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29th Nov 2015, 1:59 pm | #32 |
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Re: Resistor colour code
The digital multimeter needed 5-band resistors
David
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29th Nov 2015, 4:56 pm | #33 |
Dekatron
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Re: Resistor colour code
There were many fewer values them (E12), and if you're like me your eyesight was also much better! I also never bothered with rhymes, if indeed I heard any.
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30th Nov 2015, 12:19 am | #34 |
Dekatron
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Re: Resistor colour code
When it comes to resistors under 10 ohms, gold = divide by 10, silver = divide by 100. Remember this as "gold has a higher value than silver".
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