A Consideration on Ha Value Obtained by Electrical Roughness Testers

Three types of high pass filter are used for cut-off in electrical roughness testers employed in Japan. Namely, type a and b in which the cut-off value is assessed at 70 % of maximum transmission in the system, having the straight part of the attenuation curve which the maximum slope of 6 dB per octave and 12 dB per octave, respectively, and type c in which it is assessed at 50 % of maximum transmission in the system, having the straight part of the attenuation curve with the maximum slope of 12 dB per octave. In this paper, the difference between the value of center line average Ha obtained by roughness testers with the filter of type a and c are discussed in comparison with Hrms values which are obtained from the power spectrum of three samples. The Hrms (0.75) values of the roughness curve obtained by roughness testers with the filter of type a, type b and type c, which have the same cut-off value of 0.75 mm, are 8595% of Hrms values calculated from the profile curve of the samples.