SM0486

LESSON 4.

VIBRATION MEASUREMENTS AND EQUIPMENT

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

and

Electro-Mechanical

Measurement Principles

Lesson Objective.......................Given learning objectives and supportive

text, you should be able to answer all

exercise questions pertaining to vibration

theory, Velocity Pickup 4-102A, Vibration

Meter

1-117,

and

vibration

pickup

calibrators with no errors.

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

TEXT

1.

INTRODUCTION

Unwanted vibrations exist whether we like them or not.

Many of the inflight

operating characteristics of jet aircraft, rockets, and missiles are affected by

mechanical vibrations can be reduced it their location and magnitude are known.

This chapter includes information on pickups, vibration meters, and vibration

pickup calibrators.

2.

VIBRATION THEORY.

You must increase your understanding of vibration

terminology as you learn more about the nature of different types of vibration and

vibration measurement techniques and principles.

a. Vibration Terminology.

You have used many of the terms associated with

the vibration testing. It is important that you understand the meanings of these

terms and new terms as they relate to the vibration measurement process. Most of

the terms are defined as they are used.

However, there are some terms which you

should understand before you begin a study of vibration measurements. These terms

are as follows:

FREQUENCY---Cycles per second, each cycle representing the motion-of a device

or mass from its mean position to one extreme of travel, to the other extreme, and

its return to the mean position.

DEFLECTION OR AMPLITUDE---The distance a device or mass travels from the mean

position to either extreme.

DISPLACEMENT---Represents the travel from one extreme to the other.

ACCELERATION---The maximum rate of change of velocity during

a

cycle.

Acceleration is expressed technically in centimeters or feet per second.

b. When you examine the first term listed, you may question the definition

provided for frequency.

Since a vibrating body moves a maximum distance from a

reference point and then moves a maximum distance in the

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