Electronics > Beginners

Multimeters and Resistors

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Kohlrak:

--- Quote from: Vtile on November 24, 2017, 12:55:44 pm ---
--- Quote from: Kohlrak on November 24, 2017, 12:41:27 pm ---
--- Quote from: Vtile on November 24, 2017, 12:23:54 pm ---
--- Quote from: IanB on November 24, 2017, 11:32:07 am ---
--- Quote from: Kohlrak on November 24, 2017, 11:25:44 am ---So it's not scientific notation, but a direct "see 2 color numbers, with this many zeros after it decided by third band." That makes it easier. So black brown black for 1 ohm.
--- End quote ---

The third band is a multiplier: x0.1, x1, x10, x100, etc.

Therefore 1 ohm is brown black gold (10 x 0.1 = 1).

--- End quote ---
The easiest method to sort this color coding in someones head (my own opinion) is that you learn that black = 0, brown = 1, Red = 2, Orange = 3 and then learn (...to read from the cheat sheet like pros do) the data represented in each band. ie. Brown-Black-Red-Gold is in plain human language. One - Zero - Two zeros - tolerance +-10% from nominal value, which makes a 1000 ohms nominal and 1k in engineering lingo. Letter k comes from the word kilo, which means thousand (https://en.wikipedia.org/wiki/Metric_prefix).

The trap here, is that when you get first resistor in your hands that do have 5 or 6 bands you are totally lost a moment since it does have three value bands and multiplier band, again do like pros do, look from the fact/cheat sheet.

In moment of panic and self-doubt use the meter to make a sanity check. If that doesn't help take a hammer.

--- End quote ---

The correlation to colors and 0s was already sinking in just before reading this. So i assume that, too, 5 and 6 band ones work exactly the same way, instead of the 3rd being a decimal or some other unnecessarily convoluted system?

--- End quote ---
The resistors that do have more than 4 bands are a bit unclear as what each do mean. In resistors 5 to 7 bands the three first bands represent a value and fourth is multiplier. Yes you are in correct path with your thoughts. The next band (5th) is pretty safe to assume to be always the tolerance, but the rest of the bands can generally be pretty wildly anything, however the 6th band is typically a multiplier for the temperature dependency of the resistance (in parts per million = ppm). The inconsistencies of the system comes from the fact that the coding system have its roots somewhere in 1920s or 1930s with only 3 color bands and fixed +-25% tolerance (or something huge from todays perspective).

Edit. PS. Also the body / background color do have its own meaning coded to it, but it is chosen freely by manufacturer as far as I know. Although everyone tries to copy each other and keep the system somewhat logical.

Edit2. Hopefully I didn't wrote a total gibberish as sometimes happens when thinking with two languages simultaneously.

--- End quote ---

So if i see 4 bands, interpret as normal. 5 bands, i basically handle it the same way, just moving what i consider the 4th band to the 5th band position. 6 and 7 bands, I treat as 5 bands with extra info that I probably don't need, because that is extra information that i wouldn't get with other bands. Unless, of course, i needed that information in the first place, where i'll probably get a proper key for the meaning of those bands with the resistors themselves. Except in special cases where i'm dealing with something someone else made instead, where i essentially have to track down the manufacturer and hope play nice and tell me what they really mean. But basically, 6 and 7 are company standards, as opposed to universal standards like the first 5 bands.


--- Quote ---From all of the posts, I have determined that you have a situation where you are "caught between a rock and a hard spot", since you are having troubles reading color bands and also having trouble reading your resistances on your meter. I truly have the color band reading problem as well, so I use my meter.

--- End quote ---

Pretty much. But now that I have reliably tested my meter and know it is accurate, i managed to build a 2 resistor cheatsheet (2 resistors sacrificed to paper with their proper values written on them to calibrate against other multimeters if mine somehow goes bad).


--- Quote ---With that said, IMHO, I would would op to simply learn how to use the meter and check each resistor for resistance. I have setup a place on my breadboard for checking resistors quickly by touching a couple of bare wires, which I have set apart a nominal distance and I have my meter leads connected via quick grab clips. I don't even bother looking at color codes unless I am stuck some place without my meter, at which time I always seem to figure out the resistance from the color codes if they are 4 band after looking at different angles and varying light (takes forever).

--- End quote ---

And it's not helping that the reflection half blinds me.


--- Quote ---I also recommend that you study a book on basic electronics before you hurt yourself. There are plenty of good books and online tutorials available. Your comment about checking the resistance with your meter and being concerned about your heart has given away that you are not learned at all about electricity and electronics. The resistance of your body was causing the different readings while touching the leads. The meter output is such high resistance and low voltage that you would not be harmed by the current.
--- End quote ---

I exaggerated a little for humor. Though, when my results varied considerably i found it strange. especially when the leads were directly touching the leads of the resistor. By touching the leads of the multimeter the resistance went down which confused me. I would say it was the result of oil from my skin, but when i pinched 1 end together and touched the other lead of the multimeter without touching the resistor, it still went down which does actually confuse me.

That said, I only played this dangerously because the multimeter is powered by a 9volt, and i'm pretty sure the capacitor wouldn't be able to hold enough to fry me. Believe me, i have done some stupid things in life before, so i learned my lesson a long time ago. For fun, the worst one i've done was when i was in single digits (or just into double digits, while i'm 28 now), I wasn't thinking and when a cord got stuck in the power strip, and my wise self felt it was necessary to use my middle finger for leverage... between the prongs... Fortunately, i was on the 3rd floor of a cement building, so it found my finger to be the path of least resistance, as opposed to my leg or something which would've taken my heart. On the flip side, both places i've worked (a chicken factory, and a nursing home) i've gotten shocked by the equipment (a conveyor belt and air sucker at the chicken factory, while a convection stove and a steam table at the nursing home) not being properly grounded. I'm pretty sure there was enough current both times that it would've got us (as in, i wasn't an electrician, but a regular worker, and other people were getting shocked) killed if it was more than just a single arm making the connections. What's worse is, the chicken plant was a fairly wet environment.

I do appreciate your concern, though. You have to be careful when working with stuff like this, which is precisely why i want to avoid AC, since it's way more dangerous than anything i'll be working with, because I know sometimes i forget something's connected after i get brain fatigue.

kalel:
There are at least two factors that will affect the resistance measurements that I consider as a newbie. I know there will be many others that I don't even know about.

1 - Touching any of the exposed probe contact of the resistor can affect the readings
2 - Pressure is important, the probe should have solid contact with the resistor leads, that's why the clamp probe can be easier to use (plus makes it easier not to touch the component or probe while measuring)

Of course if the resistor lead or the probe is more oxidized than usual for whatever reason, that oxide layer might affect the readings, but I haven't had such an issue yet.

daybyter:
I just got me a pack of envelopes (just regular letter envelopes). You can buy a pack of 50 or 100 for cheap.
Then measured my resistors and put those with the same value in the same envelope and wrote the value on the envelope.
Then put the envelopes in a paper box, where I keep them sorted.
That is a very cheap and compact solution.

kalel:

--- Quote from: daybyter on November 24, 2017, 02:09:14 pm ---I just got me a pack of envelopes (just regular letter envelopes). You can buy a pack of 50 or 100 for cheap.
Then measured my resistors and put those with the same value in the same envelope and wrote the value on the envelope.
Then put the envelopes in a paper box, where I keep them sorted.
That is a very cheap and compact solution.

--- End quote ---

This is a good idea for some other components as well.

Kohlrak:

--- Quote from: kalel on November 24, 2017, 02:05:28 pm ---There are at least two factors that will affect the resistance measurements that I consider as a newbie. I know there will be many others that I don't even know about.

1 - Touching any of the exposed probe contact of the resistor can affect the readings
2 - Pressure is important, the probe should have solid contact with the resistor leads, that's why the clamp probe can be easier to use (plus makes it easier not to touch the component or probe while measuring)

Of course if the resistor lead or the probe is more oxidized than usual for whatever reason, that oxide layer might affect the readings, but I haven't had such an issue yet.

--- End quote ---

At this point I want to avoid much more spending until i can get a decent job. But, in between (calming my mind), I want to work with this stuff after i finished making my universal assembler (programming assembler) project.


--- Quote from: daybyter on November 24, 2017, 02:09:14 pm ---I just got me a pack of envelopes (just regular letter envelopes). You can buy a pack of 50 or 100 for cheap.
Then measured my resistors and put those with the same value in the same envelope and wrote the value on the envelope.
Then put the envelopes in a paper box, where I keep them sorted.
That is a very cheap and compact solution.

--- End quote ---

You, sir, are brilliant.

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