Effect of noise on surface roughness measurements

The actual noise signals affecting roughness measuring instruments were measured when a computerized system using a stylus of 2.5 /spl mu/m was traversing an ultrahigh finished optical flat surface. These measurement showed that the noise level may vary over a wide range according to the rigidity of the set-up or the amount of vibration in the instrument and its environment. The effect of the signal to noise ratios on the assessed average roughness value of a measured surface are studied. A sinusoidal roughness signal was mathematically generated, and the noise signals as actually obtained using the computerized system were added together. Charts representing the effect of the signal/noise were constructed to evaluate the noise effect on the assessed values of roughness. The effect of the roughness amplitude band width that could be measured accurately at different amplifier magnifications are represented by charts. These charts show that the useful range is considerably reduced at higher magnifications due to the effect of noise. It was concluded that noise has an influence on the surface roughness results of a stylus instrument specially when finely produced surfaces are measured.