Quick Guide to Precision Measuring Instruments
PG31Quick Guide to MeasurementNo.ItemCalibration methodDiagram of calibration setupTools for calibration1Wide-range accuracy(1) For an indicator of 0.01 mm graduation: Displace the contact point so as to move the pointer clockwise in increments of 0.1 mm with reference to the graduations from the zero point to the end point of the measuring range while taking readings of the calibration tool at each point and determine this accuracy from the error curve drawn by plotting the differences of each "indicator reading - calibration tool reading".(2) For an indicator of 0.002 mm graduation: Displace the contact point so as to move the pointer clockwise in increment of 0.02 mm with reference to the graduations from the zero point to the end point of the measuring range while taking readings of the calibration tool at each point and determine this accuracy from the error curve drawn by plotting the differences of each "indicator reading - calibration tool reading". The instrumental error of the calibration tool shall be compensated prior to this measurement.Supporting standDial test indicatorMicrometer head orlength measuring unit Micrometer head or measuring unit (graduation: 1µm or less, instrumental error: within ±1µm), supporting stand2Adjacent error3Retrace errorAfter the completion of the wide-range accuracy measurement, reverse the contact point from the last point of measurement while taking readings at the same scale graduations as for the wide-range accuracy measurement and determine the retrace error from the error curve plotted.4RepeatabilityaHolding the dial test indicator with its stylus parallel with the top face of the measuring stage, displace the contact point quickly and slowly ve times at a desired position within the measuring range and determine the maximum difference in indication.Supporting standDial test indicatorMeasuring stageMeasuring stage, Supporting stand, and Gauge block of grade 1 as stipulated by JIS B7506 (Gauge block)bHolding the stylus parallel to a gauge block placed on the measuring stage, move the gauge block to and fro and left to right under the contact point within the measuring range and determine the maximum difference in indication.Gauge blockMeasuring stage5Measuring forceHolding an indicator by the case or stem, displace the contact point gradually and continuously in the forward and backward directions respectively and take a reading of measuring force at the zero, middle and end points of the measuring range in each direction.• PerformanceThe maximum measuring force in the forward direction shall not exceed 0.5N. The difference between the maximum and minimum measuring forces in one direction shall not exceed 0.2N (20gf). Note that the smallest possible measuring force is desirable for indicators.Dial test indicatorTop pan type spring scale Top pan type spring scale (graduation: 2gf or less) or force gage (sensitivity: 0.02N or less)Notes: There are no JIS standards applicable to models with a graduation of 0.001 mm. Therefore, referring to JIS B 7533-1990 for inspecting the wide-range accuracy and adjacent error, the accuracy is measured by moving the contact point 0.01 mm clockwise from the start point of the measuring range to the end point with reference to the graduations. Dial Test Indicator Standard B7533-1990 (Extract from JIS/Japanese Industrial Standards)Accuracy of indicationPermissible indication errors of dial test indicators are as per the table below.Graduation (mm)Measuring range (mm)Wide range accuracyAdjacent errorRepeatabilityRetrace error 0.010.555330.881.0104*10.0020.232120.28*1: Applies to indicators with a stylus over 35 mm long.Remarks: Values in the table above apply at 20°C.