calculating minimum and maximum resistor resistance

Discussion in 'Homework Help' started by axedrytouch3, May 18, 2011.

  1. axedrytouch3

    axedrytouch3 Thread Starter New Member

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    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. Jony130

    Jony130 Senior Member

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  3. Georacer

    Georacer Moderator Staff Member

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    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.
  4. t_n_k

    t_n_k Senior Member

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    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. t_n_k

    t_n_k Senior Member

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    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. axedrytouch3

    axedrytouch3 Thread Starter New Member

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    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. t_n_k

    t_n_k Senior Member

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    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.
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