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
105
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