Development Of Portable Roughness Tester Based On DSP System

On the surface of the tiny fluctuations between peaks and troughs is defined as thesurface roughness of the object, which is a major part of the indexes of the surfacequality.For two or more spare parts, friction of their contact surface, workpiece abrasion,sealing degree and fatigue degree of spare parts will be influenced by roughness valueof spare parts’ surface.This paper developed a suitable production site and mobilemeasurement of small instruments-handheld surface roughness measuring instrument. Ithas extensive application range, high measurement accuracy, more calculatingparameters and convenient operation and is in accordance with requirement of ISOInternational Standard for surface roughness tester.This device is a contact-type measuring instrument by adopting inductive sensor ascontact. To improve detection sensitivity and system SNR of inductive sensor, the paperdesigned weak signal processing by taking low distortion Wien bridge sinusoidaloscillating circuit as exciting signal source and precision phase-sensitive rectifyingcircuit as signal processing core based on weak signal detection principle. By applyingtransformer to block carrier signal, it improved detection sensitivity of system and givenstructure diagram and analysis of specific parameters for subsequent signal processingcircuit and other hardware circuits.In the digital signal processing part, first introduced the roughness of the maintechnical parameters and calculations of these parameters, and according to thecorresponding national standards, determined using a Gaussian filter to the digital signalfiltering. Then shows the design principle of the Gaussian filter,and through researchmulti-level Butterworth analog filter approximate Gaussian filter,design the IIR typedigital filter. Finally, show the instrument measurement error testing and error analysis.This approach solves the Gaussian filter design complexity and achieve difficultproblem.The experiment demonstrated that this handheld surface roughness tester hasachieved expected standard. It has simple measurement operation, comprehensive function, quick measurement, stable accuracy, convenient to carry and is able tomeasure major parameters of the latest international standard.