RMS value & noise measurements

[CassiopeiaA]

I am confused about very fundamental question.

Why does the rms value of number of electrons collected from a signal(like in photoconductor) gives you the noise in that signal.

 

[mfb]

That is the definition of noise.

More electrons without signal -> more noise. rms is chosen because it is a nice quantity to look at.

 

[Babadag]

See:
http://en.wikipedia.org/wiki/Root_mean_square

 

[sophiecentaur]

I am confused about very fundamental question.

Why does the rms value of number of electrons collected from a signal(like in photoconductor) gives you the noise in that signal.

To get a good idea of the 'amount' of Noise entering a system, you can't look at the 'peak' value because, in the short term, it could vary a lot. Doing an RMS calculation is effectively looking at the power arriving (V²/R) at every instant and adding it up over a relatively short period of time. RMS is an attempt to replace the randomly varying noise with one equivalent (average) voltage. It's the most basic measure of noise and assumes that the noise is of a Gaussian nature.
The actual effect of random variations in a signal (noise) is different from application to application and a simple RMS measurement may not be representative. It is common to use a 'weighted' noise measurement, where the noise signal is passed through a filter before the RMS value is calculated so that, for instance, the frequency sensitivity curve of the ear is included in audio noise measurement.
In the case of a photo detector, you can get a very 'grainy' sort of noise with very high peaks. RMS will iron these out and may give a far too optimistic assessment.

 

[alphy]

The root mean square (RMS) value is a measure of the average magnitude of a signal. In the case of noise, it represents the average amplitude of the fluctuations in the signal. When measuring noise in a signal, the RMS value is used because it takes into account both the positive and negative fluctuations, providing a more accurate representation of the overall noise level.

In the case of a photoconductor, the number of electrons collected is directly related to the intensity of the light hitting the sensor. As the light intensity varies, the number of electrons collected will also vary, resulting in fluctuations in the signal. These fluctuations can be seen as noise in the signal.

By calculating the RMS value of the number of electrons collected, we are essentially measuring the average amplitude of these fluctuations, giving us an indication of the level of noise present in the signal. This is a common method for measuring noise in electronic systems and can provide valuable information for further analysis and improvement of the system.

I hope this helps to clarify the relationship between RMS value and noise measurements. Please let me know if you have any further questions.