I am using PicoScope 6 to measure the output from a thermopile sensor. The output is expected to be a pure sine wave but it isn't due to external thermal noise. I would like to calculate the Signal to Noise Ratio (SNR) based on the measured values. This can be done in Pico software using a spectrum mode. In order to understand the theory behind the calculation, I would like to write a MATLAB code and compare the two results.
As far as I know, SNR can be written as 20*log10(Vrms_signal/Vrms_noise). When I checked the equation in the PicoScope6 User's Guide, the equation is
I don't quite understand this equation as from my understanding, if we treat the datum and its harmonics as the signal, other data as the noise, the equation should be (RMS value of datum)/(RMS value of all values excluding datum and its harmonics).
I am not sure if my understanding is correct. Could anyone help me? Many thanks in advance.