temperature coefficient of resistance

Discussion in 'General Electronics Chat' started by murari, Feb 6, 2008.

  1. murari

    Thread Starter New Member

    Feb 6, 2008
    3
    0
    hi

    i managed to thoroughly confuse myself working on a project on the temp coeff. i hope someone can help......

    if Resistance has a linear variation with temperature over a temperature range, alpha should be a constant over this range....

    if we are to find R of Platinum wire (say) at 50°C in terms of R at 0°C,
    alpha = 0.004

    R = R(0°C) * (1+ 0.004 * 50)
    = 1.2 * R(0°C)

    but if we calculate R at 0°C in terms of R at 50°C,

    R(0°C) = R *(1+0.004 * (-50))
    = 0.8 * R

    This gives me R(0°C) = 0.96* R(0°C) :confused:

    can anyone tell me where i went wrong??
     
  2. recca02

    Senior Member

    Apr 2, 2007
    1,211
    0
    R(0°C) = R *(1+0.004 * (-50))
    there should be zero instead of -50.

    where u put -50 is the place where temp difference between ref and the desired value with sign is substituted. it is (Temp(at which R is to be calculated)-Temp(taken as reference))

    A (-50) simply means resistance at -50°C....Chill out!:cool:
     
  3. murari

    Thread Starter New Member

    Feb 6, 2008
    3
    0
    Sorry... i guess i wasn't as clear as i could have been....
    R throughout stands for R at 50°C while R(0°C) is... well... R at 0°C

    In the second case, the diff in temp is -50 if i use 50°C as ref temp...

    That is, if alpha is independent of the ref temp...
     
  4. recca02

    Senior Member

    Apr 2, 2007
    1,211
    0
    i think the problem here is u're keeping the R constant when changing the reference.

    u see at 50°C the ref will change to that value.

    in above case u'r ref is seemingly R at 0°C ....say R(0)
    in the second case it must be R(50).
    and needless to say, they are different.
     
  5. murari

    Thread Starter New Member

    Feb 6, 2008
    3
    0
    oh...k
    thanks
    lucky i got that cleared before my viva :D
     
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