ASME B46.1-2019 pdf download

ASME B46.1-2019 pdf download.Surface Texture (Surface Roughness, Waviness, and Lay).
Static Measuring Force Variation. This is the change instaticmeasuringforce inthe zdirectionoverthe entire z measuring range of the pickup. 3-3.5.4 Dynamic Measuring Force. The dynamic measuring force is the instantaneous normal force asso- ciated with the motion ofthe stylus as it is traversed rela- tive to the surface. This force may be difficult to quantify and varies with amplitude and spatial wavelength of the surface irregularities, stylus location on the surface, and the instrument traversing speed. 3-3.5.5 Total Stylus Force. In all cases, a minimum total stylus force (static and dynamic) should be applied to maintain contact with the surface during measurement to avoid situations in which the stylus leaves the surface during traverse. 1 3-3.5.6 Pickup Transmission Characteristic. This function indicates the percentage of the amplitude of a sinusoidal surface profile transmitted by the pickup as a function of surface spatial wavelength (see Section 9). 3-3.5.7 Pickup Measuring Range. The pickup measuring range is the z-axis range over which the surface profile heights can be properly assessed by the pickup. 3-3.5.8 Pickup Measuring Resolution. The pickup measuringresolutionis the smallestzprofile heightincre- ment detectable by the pickup. Often, this is a function of the magnification selection and should be reported for each available magnification. 3-3.5.9 Pickup Range-to-Resolution Ratio. The pickup range-to-resolution ratio is the ratio of total z- axis measuring range to the pickup measuring resolution at a given magnification.
Analog-to-Digital Converter. The analog-to- digital converter (ADC) converts the analog z signal to discrete, digital values. These values, together with the sampling rate and stylus traverse speed, or x-axis encoder reading, make up the digital representation of the traversed profile. 3-3.8.2 Nyquist Wavelength. The Nyquist wavelength is the shortestdetectable wavelength fora given sampling rate. This wavelength is computed as twice the x-axis spacing of the digital values (the sampling interval). It should be noted that in practical terms, the measured amplitude of a sinusoidal profile at this wavelength may be smaller than its actual amplitude because of the phase difference between the sampled data points and the profile peaks and valleys. Refer to Section 9 for further information pertaining to sampling interval. 3-3.8.3 Aliasing. When analog data containing wave- lengths shorterthan the Nyquistwavelength are sampled, these wavelengths will be falsely represented as wave- lengthslongerthantheNyquistwavelength.Thisphenom- enon is referred to as aliasing and is depicted in Figure 3-3.8.3-1. 3-3.8.4 Antialiasing Filter. The antialiasing filter removes wavelengths shorter than the Nyquist wave- length prior to digitization. This eliminates the potential for aliasing. This filtering can be the result ofmechanical filtering due to the finite stylus tip or the resultofan elec- tronic filter typically incorporated in the analog-to-digital converter. 3-3.9 Primary Measured Profile Theprimarymeasuredprofileisthecompleterepresen- tationofthemeasuredworkpiecesurfaceafterapplication of a short-wavelength filter to eliminate high frequency noise or artifacts (see Section 9). 3-3.10 Instrument Sinusoidal Transmission Function The instrument sinusoidal transmission function describes the percentage of transmitted amplitude for sine waves of various wavelengths at given tracing speeds as represented in the analog or digital signal prior to filtering. This transmission function describeProfile Filter Evaluation Length. Typically the evaluation length is chosen to include at least five roughness long-wavelength cutoff lengths, λc. However, depending on the size of the measurement area, it may be necessary to limit the evaluation length to include fewer than five roughness cutoff lengths, λc. In this case, the evaluation length used should be noted on the appropriate documentation. Some instruments may automatically change the roughness long-wavelength cutoffto maintain five cutofflengths within the evaluation length. Therefore, care must be taken to ensure that the proper roughness cutoff length, λc, is used. 3-3.21 Profile Recording and Display After filtering, the measured profile is typically plotted on a graph for visual interpretation. Digital instruments can also store the discrete data points for further numer- ical analysis and graphical display. 3-3.21.1 z-Axis Magnification. The z-axis magnifica- tion is the ratio of the displayed profile heights to the actual heights of the corresponding surface features on the workpiece. This magnification may also be repre- sented as a surface z displacement (in units of length) per scale division on a graph. 3-3.21.2 x-Axis Magnification. The x-axis magnifica- tion is the ratio of the length of the displayed profile to the actual length traversed by the stylus. This magni- fication can also be represented as surface displacement (in units of length) per scale division on a graph. 3-3.21.3 Magnification Ratio (Aspect Ratio). The magnification ratio or aspect ratio is the ratio of the z- axis magnification to the x-axis magnification.