# Quick Guide to Precision Measuring Instruments 70/76

PG68Figure 2 Target points for determining the Maximum Permissible Probing ErrorFigure 3 Target measurement planes for the maximum permissible scanning probing error and its evaluation conceptThis measurement was included in the dimensional measurement in ISO 10360-2:2009. However, it is specied as "CMMs using single and multiple stylus contacting probing systems" in ISO 10360-5:2010.The measurement procedure has not been changed, and the following should be performed.Measure the dened target points on a standard sphere (25 points, as in Figure 6) and use all the results to calcu-late the center position of the sphere by a least squares method.Then, calculate the distance R from the center position of the sphere by a least squares method for each of the 25 measurement points, and obtain the radius difference Rmax - Rmin. If the radius difference, to which a compound uncertainty of forms of the stylus tip and the standard test sphere are added, is equal to or less than the specied value, it can be judged that the probe has passed the test.Maximum Permissible Single Stylus Form ErrorPFTU, MPE [ISO 10360-5:2010]This is the accuracy standard for a CMM if equipped with a scanning probe. Scanning probing error was standardized in ISO 10360-2:2009 for the rst time. The test procedure under this standard is to perform a scanning measurement of 4 planes on the standard sphere and then, for the least squares sphere center calculated using all the measurement points, calculate the range (dimension ‘A’ in Figure 3) in which all measurement points exist. Based on the least squares sphere center calculated above, calculate the distance between the calibrated standard sphere radius and the maximum measurement point or minimum measurement point, and take the larger distance (dimension ’B’ in Figure 3). Add an extended uncertainty that combines the uncertainty of the stylus tip shape and the uncertainty of the standard test sphere shape to each A and B dimension. If both calculated values are less than the specied values, this scanning probe test is passed.Maximum Permissible Scanning Probing Error MPETHP [ISO 10360-4:2000]22.5゜22.5゜a22.5゜22.5゜22.5゜StylusScan plane 2Scan plane 1Scan plane 4Scan plane 345ºCalibrated value ofstandard sphere radiusLeast square sphereLeast square sphere centerABMeasurement pointCoordinate Measuring Machines