Quick Guide to Precision Measuring Instruments

PG24Height Gages01020304050607080900.01mmmmmm8070604030201050900817282122.11Scribing stylusReference surface01020304050607080900.01mmmmmm0807060403020105090182755125.11ScribingstylusReference surface Measuring upwards from a reference surfaceVernier Height gageMechanical Digit Height gage(1) Main scale 79 mm(2) Vernier 0.36 mm Reading 79.36 mmGraduation 0.02mmMeasuring downwards from a reference surfaceCounter 122 mmDial 0.11 mmReading 122.11 mmCounter 125 mmDial 0.11 mmReading 125.11 mm79101101234567Main scaleVernier scale7910110123456(1)1. Potential causes of errorLike the caliper, the error factors involved include parallax effects, error caused by excessive measuring force due to the fact that a height gage does not conform to Abbe's Principle, and differential thermal expansion due to a temperature difference between the height gage and workpiece. There are also other error factors caused by the structure of the height gage. In particular, the error factors related to a warped reference edge and scriber installation described below should be studied before use.2. Reference edge (column) warping and scriber installationLike the caliper, and as shown in the following gure, measurement errors result when using the height gage if the reference column, which guides the slider, becomes warped. This error can be represented by the same calculation formula for errors caused by nonconformance to Abbe's Principle.Installing the scriber (or a lever-type dial indicator) requires careful consideration because it affects the size of any error due to a warped reference column by increasing dimension h in the above formula. In other words, if an optional long scriber or lever-type dial indicator is used, the measurement error becomes larger.How to readGeneral notes on use of Height Gageslfhahhf = h = h alfhalfhahhExample: Effect of measuring point positionWhen h is 150 mm, the error is 1.5 times larger than when h is 100 mm.

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