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#1
05-18-2011, 10:30 PM
 axedrytouch3 New Member Join Date: May 2011 Posts: 2
calculating minimum and maximum resistor resistance

hi, i'm new to DC circuits, i'm currently taking DC circuit class in college. i know nothing about DC circuits, as of now i'm having trouble solving these stuff on my homework

on my homework they gave an example

22 | Red Red Black Gold | 2 2 0 5%

and it says (5%)(22) = (0.05)(22) = 1.1

max value = 22 +1.1 = 23.1
min value = 22 - 1.1 = 20.9

but it doesn't tell alot since there's not steps or info on what to do first...

so what do i do with these then?
6.8 | blue gray red gold | 6 8 2 5%
100 | red black red gold | 2 0 2 5%
220 | red red brown gold | 2 2 1 5%

if anyone can tell me step by step on what to do i can try to figure out what to do and solve the rest of the problems by myself. thanks in advance =[
#2
05-18-2011, 10:49 PM
 Jony130 Senior Member Join Date: Feb 2009 Location: Poland/Wroclaw Posts: 2,492

What you don't understand.
If you have 4 band resistor code, then the last band will be golden or silver.
And the third band is a multiplier
http://en.wikipedia.org/wiki/Electronic_color_code
http://samengstrom.com/24614782/en/r...or_Color_Codes

For example
blue gray red gold = 6 8*100 = 6.8KΩ 5%
red black red gold = 2 0*100 = 2KΩ 5%
#3
05-18-2011, 11:53 PM
 Georacer Super Moderator Join Date: Nov 2009 Location: Athens, Greece (GMT +2) Posts: 4,875

The last band tells you about the tolerance of the resistor value. A 5% resistor will have a value that is within a 5% limit of its nominal value.
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#4
05-19-2011, 12:03 AM
 t_n_k Senior Member Join Date: Mar 2009 Posts: 4,950

I think axedrytouch3 wants to know how to work out the range of values a resistor might have given its nominal value and tolerance.

The reasoning used is as follows

1. Say you have a nominal 22Ω resistor with 5% tolerance.
2. The actual resistor value could be as low as 22Ω - 5% of 22Ω
3. Or the actual resistor value could be as high as 22Ω + 5% of 22Ω
4. Do the calculation to find that 5% of 22Ω is 1.1Ω
5. The actual resistor value could be as low as 22Ω - 1.1Ω = 20.9Ω
6. The actual resistor value could be as high as 22Ω + 1.1Ω = 23.1Ω

A slightly different way to calculate the range is to state that the possible range is from 95% of 22Ω (or 20.9Ω) to 105% of 22Ω (or 23.1Ω)
#5
05-19-2011, 12:41 AM
 t_n_k Senior Member Join Date: Mar 2009 Posts: 4,950

This question reminded me of a few subtleties associated with the notion of tolerance.

I've never worked in the component manufacturing area but I presume resistors a made in a process whereby every resistor isn't actually checked to make sure it falls within a certain range of values. I guess samples are taken from any particular batch run and routinely tested for compliance.

I assume also that the manufacturing process makes nominal resistor values which are "Normally" distributed. The Normal distribution is assigned a standard deviation σ. In a truly Normally distributed population, 99.7% of all samples would fall within 3 standard deviations of the population mean μ.

Suppose a manufacturer produces 100Ω ±5% resistors. Suppose also that the 100Ω production process is Normally distributed with a currently known σ of 2 ohms. What proportion of manufactured 100Ω resistors produced would fall outside of the stated tolerance? So ±5% is therefore ±2.5σ and 98.76% of produced items would fall within the tolerance range. So the manufacturer knows that 1.24% of all produced 100Ω resistors will likely fall outside of the stated tolerance. Would the manufacturer be satisfied with that situation? If not what could be done?
#6
05-19-2011, 12:43 AM
 axedrytouch3 New Member Join Date: May 2011 Posts: 2

yes i need to find out the min and max for each of the following

resistor(nominal value)| color | 1 2 3 4
6.8 | blue gray red gold | 6 8 2 5%

100 | red black red gold | 2 0 2 5%

220 | red red brown gold | 2 2 1 5%
#7
05-19-2011, 01:01 AM
 t_n_k Senior Member Join Date: Mar 2009 Posts: 4,950

Well I outlined the method in post #4. You should now make an attempt. Don't just expect to get the answers. Post your working and see how things progress from there.

 Tags calculating, maximum, minimum, resistance, resistor

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