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MEASUREMENT TOOLS

May 26, 2019 - Engine Mechanic Development
MEASUREMENT TOOLS

1. Vernier Caliper

Jangka Sorong (Vernier Caliper).

A vernier caliper consists of a high quality metal ruler with a special vernier scale attached which allows the ruler to be read with greater precision than would otherwise be possible. The vernier scale provides a means of making measurements of distance (or length) to an accuracy of a tenth of a millimeter or better. Although this section will be devoted to the use of the vernier caliper, it should be noted that vernier scales can be used to make accurate measurements of many different quantities. In the future, you will also use an instrument with a vernier scale to make precise readings of angular displacements.

Looking at the vernier caliper in Fig. 1, notice that while the units on the rule portion are similar to those on an ordinary metric ruler, the gradations on the vernier scale are slightly different. The number of vernier gradations is always one more than the number on rule for the same distance. The line on the vernier which is aligned with one on the rule tells us the fraction of the units on the rule. For example, in Fig. 1 the vernier reads 1.440 cm or 0.567 in.

To use the vernier caliper:

  1. Roll the thumb wheel until the jaws are completely closed (touching each other). Now check whether the caliper is reading exactly zero. If not, record the caliper reading, and subtract this number from each measurement you make with the caliper.
  2. Use either the inside edges of the jaws, or the outside edges of the two Lookings at the top of the caliper to make your measurement. Do not use the tips of the prongs. Roll the thumb wheel until these surfaces line up with the end points of the distance you are measuring.
  3. To read the caliper: Record the numbers which correspond to the last line on the rule which falls before the index line on the vernier scale. On the following page, this would be 32 since the index line falls just after the 32 cm line.
  4. Count to the right on the vernier scale until you reach a vernier line which lines up with a line on the rule and record the number of this vernier line as your last digit. on the following page it is the ninth vernier line which is aligned with one on the rule, so the whole distance is 32.9 cm.

The following pages show six vernier scales, similar to that on the vernier caliper, which will allow you to test your ability to read a vernier caliper.

2. MICROMETER

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