Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: Redcap on March 08, 2011, 04:57:00 AM
-
Hey all,
I've found some resistors laying around, but the value has rubbed off the container I had them in.
Because I'm colorblind, I find it very difficult to (correctly) tell what color the bands are in order to find out the values.
Is there any way I can find the value without having to rely on the color bands..? :(
Thanks in advance,
Redcap
-
I know I can use a multimeter to find out how much resistance it has, but how do I know if this is within the 10% tolerance or if the resistor is damaged?
-
You are probably aware of the fact that resistors come in different preffered number ranges (e.g. E6 series, E12, E24, etc.). Commonly, the E6 series is used for 20% tolerances, E12 for 10%, and E24 for 5%. Most color blind people can still typically see the differences on the tolerance bands (None, Gold, or Silver). If they are 10% tolerance resistors that would limit the values to the E12 range: 10 12 15 18 22 27 33 39 47 56 68 82. With only 12 possible combinations per decade, your best guess on the color values (even if color blind) combined with a multimeter reading is likely to give you a pretty good idea of the correct value, particularly if you have several of the same value resistors.
For example, you have a resistor with no tolerance band making it a 20% tolerance resistor and placing it in the E6 series (10 15 22 33 47 68).
The first two bands could be red or orange, but you can't tell. RED-RED would be 22 which is part of the E6 series, RED-ORANGE or ORANGE-RED would be 23 or 32 respectively, which aren't part of the E6 series so we can discount those possibilities. ORANGE-ORANGE would be 33 which is also part of the E6 series.
So given 22 or 33 as the possible resistor value. With a 20% tolerance that would give us a range of 17.6 to 26.4 for RED-RED or 26.4 to 39.6 for ORANGE-ORANGE.
Lastly we look at our multiplier band and compare with a multimeter reading. For example if its yellow, you would have a multiplier of 10^4.
Your multimeter reading is 36.2Kohms, which places it solidly in the ORANGE-ORANGE range. After measuring a couple more resistors they all fall within the ORANGE-ORANGE range so you can be confident that they are all ORANGE-ORANGE-YELLOW resistors and are all within the 20% tolerance.
-
I know I can use a multimeter to find out how much resistance it has, but how do I know if this is within the 10% tolerance or if the resistor is damaged?
You only need to know tolerances for manufacturing purposes, meaning you can be sure that the batch will fit within a certain range.
The multimeter will give you an exact value, making the tolerance a useless value for a small project.
That said, if you measure a few thousand resistors and write down the value of each, you'll find them within X% off from a specific value, giving you the tolerance.
-
Thank you both very much for your replies :)
knossos, thanks for taking the time to write that reply. You've made a lot of things "click" and have given me a very solid starting point for future reference.
-Re-reading what I wrote in my question, I've worded it badly, but both have given answers I was needing, cheers :)