Electrical noise of carbon film resistors

Hi,

I've been told that carbon film resistors are electrically noisy. I'd like some clarification of what that means.

1. Does it mean that the resistance of the resistor changes over time when a current is applied to it?

2. Does the resistance of the resistor nevertheless stay within the rated tolerance?

3. Do metal film resistors have the same issue?

Richard

U = R.i + noise(i,v,t)

Resistor composition determines what is in "noise".

A perfect resistor will have only thermal noise (which you cannot eliminate), real resistors will have more noise due to materials used, etc.

1. The resistance is not affected. It's just the random noise that can be higher than the theoretical thermal (Johnson) noise for the resistance value.

2. It stays within the rated tolerance.

3. Metal film resistors generally have a noise value close to the theoretical thermal value.