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 =[
     
    #1
  2. Jony130

    Jony130 Senior Member

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    #2
  3. Georacer

    Georacer Moderator

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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.
     
    #3
  4. t_n_k

    t_n_k AAC Fanatic!

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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)
     
    #4
  5. t_n_k

    t_n_k AAC Fanatic!

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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?
     
    #5
  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%
     
    #6
  7. t_n_k

    t_n_k AAC Fanatic!

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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.
     
    #7
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