linearity of an electronic system

[harrysmith]

Hello everyone.
how to know in electronics that a system is linear or non-linear. for example how to know if a sensor whatever is linear or non-linear ?
 

[TimFox]

All analog systems are non-linear:  the correct question is how to quantify the non-linearity.  Non-linearity will depend on signal level.  Possible answers, depending on what type of system and available equipment:
1.  For an amplifier, if you have two variable attenuators of known accuracy.  Connect generator through first attenuator to amplifier input, and connect appropriate meter through second attenuator to output.  Start with second attenuator at reasonably high attenuation and adjust generator and input attenuator to achieve “reasonable” level at meter.  Proceed to increase input attenuator (decreasing amplifier input), noting output attenuation required to obtain same meter reading.  This old-fashioned method does not rely on wide dynamic range accuracy of generator level or meter accuracy.
2.  Use an distortion meter (or spectrum analyzer) to measure distortion products as a function of signal level.  Either harmonic distortion or two-tone modulation products.
Linearity is not exactly synonymous with proportionality, when there is a constant offset with zero input for DC systems.
What kind of systems are of interest to you?

[David Hess]

In either case, a known linear excitation is applied to the transducer or electronic system and the result is measured.  For systems which can process AC, excitation can be a sine wave and distortion or distribution measured, a triangle wave or ramp and distribution measured, or DC levels.

[harrysmith]

precisely on a datasheet of a BPW41N photodiode sensor. or I can know its linearity. do we observe these graph characteristic of the datasheet. if so how ?
https://pdf1.alldatasheet.com/datasheet-pdf/view/26252/VISHAY/BPW41N.html

[Cerebus]

Much more fundamentally, if you apply signal A to a system and record the response A_out, then do the same with signal B, result B_out, then apply the sum A+B as input and the output (A+B)_out is the same as the sum of the previously recorded outputs A_out + B_out then the system is linear, by definition.

[harrysmith]

can we confirm the linearity from the graph of the BPW41N datasheet if yes which graph is conserne ?

[T3sl4co1l]

Fig.3 shows a linear response.

Just how many posts are you going to write on this subject?  Have you read the definition of "linearity"?  Do you know how to prove a system is linear?

Tim