SM0486

LESSON 3.

ROTARY AND TORQUE MEASUREMENTS

AIPD Subcourse Number SM0486...........Mechanical

and

Electro-mechanical

Measurement Principles

Lesson Objectives......................Given learning objectives and supportive

text, you should be able to answer all

exercise questions pertaining to rotary and

torque measurements with no errors.

Credit Hours...........................One

TEXT

1.

INTRODUCTION

Sometime in your assignment as a calibration specialist you will be required to

calibrate rotary and measuring devices. Your job will be much easier if you have a

complete understanding of the terms and principles associated with rotary and

torque measurements.

You should apply what you have learned to the jobs you

perform.

Keep in mind that our goal is to help you prepare yourself for

performance when you are assigned to jobs involving rotary or torque equipment in

your laboratory.

We will begin this lesson with a discussion of rotary

measurements. After that we will take up torque measurements.

2.

Rotary Measurements.

Rotary measurements are made with several types of

instruments.

In this section we will discuss three types of rotary measurement

devices: the mechanical tachometer, the optical tachometer, and the stroboscope.

Before we begin our discussion of these instruments, look at some of the basic

principles of rotation and rotary measurement.

a. Rotation. When every part of a body, except the center, moves in a circle

and all the circles have the same center, the body is said to be in a rotary

motion. As a body rotates, it turns through an angle. There are several ways to

measure angular rotation: Among these are degrees, revolutions, or radians.

b. Angular measurement.

(1) When a radius vector rotates about a fixed point, it generates a

circle, as shown in Figure 1. The circular line formed by the head of the vector

is called the circumference of the circle. The angular displacement for a complete

revolution of the rotating radius vector is 360. Measurement of an angle which is

less than a complete revolution is frequently made in degrees.

We say a right

angle has 90 and lesser angles may have 45, 30, or some other value. This is the

degree method of indicating angular rotation.