ROTARY AND TORQUE MEASUREMENTS
AIPD Subcourse Number SM0486...........Mechanical
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.
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
You should apply what you have learned to the jobs you
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
We will begin this lesson with a discussion of rotary
measurements. After that we will take up torque measurements.
Rotary measurements are made with several types of
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.