1. A method of testing at least one of an industrial process and at least a first and second sensor for determining fault conditions therein, comprising the steps of: operating the at least first and second sensor to redundantly detect at least one physical variable of the industrial process to provide a first signal from said first sensor and a second signal from said second sensor, each said signal being characteristic of the one physical variable; obtaining a difference function characteristic of the arithmetic difference pairwise between said first signal and said second signal at each of a plurality of different times of sensing the one physical variable; obtaining a frequency domain transformation of said first difference function to procure Fourier coefficients corresponding to Fourier frequencies; generating a composite function over time domain using the Fourier coefficients; obtaining a residual function over time by determining the arithmetic difference between the difference function and the composite function, the residual function having reduced serially correlated noise; operating on the residual function using computer means for performing a statistical analysis technique to determine whether an alarm condition is present in at least one of the industrial process and the at least first and second sensor, the residual function including white noise characteristics of an uncorrelated function of reduced skewness relative to the difference function and being input to the statistical analysis technique; and said at least first and second sensor providing alarm information to an operator of the industrial process allowing modification of at least one of the industrial process and said at least first and second sensor when an alarm condition is detected.