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ppm

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Simon:
so a resitor has a temperature coefficient of 50 ppm/C what does this mean ? a rise in resistance of 0.005 % for every C ?

Kiriakos-GR:
Do you plan to build an decade ?   :)

alm:
Correct. ppm is parts per million, so 1 ppm = .0001%. The correct term would be ppm/?C = ppm/K, since ppm/C would be ppm per Coulomb.

Simon:

--- Quote from: Kiriakos-GR on August 15, 2010, 03:41:41 pm ---Do you plan to build an decade ?   :)

--- End quote ---

no, I was just trying to understand the thermal specs of resistors as I plan putting considerable current through a few

Kiriakos-GR:
Well I have another question puzzling me , I think its a stupid one ,
but I will say it any way ...

Does the 1/4W  film metal , can take more abuse than the carbon ones 1/4W .

In some resistor decade boxes , I found predefined  Max amperes ratting for its selector = team of resistor values.

1) I do not know how they predefine those ratings ..
2) At 12 volts  at about the 680 Ohm and under ,  the resistor specs  1/4W , comes at the none critical conditions ( low amperes that makes some sense with the ohms law )      

I like also to know the max non - dangerous current for my own decade box .
but only the 0.10 ohms are at 5W ,  all the rest are at 1/4W ( 1 - 10 - 100 ohm  1K 10K 100K )

But as I said and above , If I was aware of the standard (reference)  voltage , I would be able to calculate it,
but with out an predefined voltage , there is  no standard value for Amperes ...

So, how they do it ?    

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