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)

can anyone tell me where i went wrong??