Hello,

CASP is using a single frequency whereas EFM uses two frequencies.

CASP is using the amplitude of the harmonics, where as EFM also uses amplitudes of signals at non-harmonic frequencies. EFM is more complicated than CASP in that regard.

An application note on CASP is available online:

http://www.bio-logic.net/wp-content/uploads/20111020-Application-note-37.pdf

I also attach it here.

I also attached the paper related to EFM.

I hope this helps.

Nicolas

Aside from the 1 vs. 2 frequency difference, EFM also includes causality factors in the results that serve as a check on the quality of the data.  

Both techniques are based on the same underlying electrochemical response, and so give the same data (icorr, beta anodic and beta cathodic).  Both are "non-desctructive" though they do both use higher amplitude signals than other non-destructive tests and so in cases where the Tafel constants are known--or are largely irrelevant as with inhibitor studies--many researchers prefer the smaller signals and easier understanding from LPR or EIS.  

Thank you very much, Nicolas Maurer and Jacob ketter