Page 16 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Introduction to Vibrations

F = MA (1.1)

Where:
M= Mass in pounds (1 pound Mass = 32.1739 Pounds)
A= Acceleration (feet per second per second)
F = Pounds of Force

Note that the force of an object at rest is WG [its weight W
times the acceleration of gravity G]. Since the standard accelera-
tion of gravity is 32.1739 feet per second per second, mass is sim-
ply an object’s weight times the acceleration of gravity.
Thus by measuring vibration in terms of acceleration, the
force imparted by the vibration is also considered. It is this force
that is important in determining the potential hazard to the ma-
chine and its components while undergoing vibration.

PHASE

Phase is the position of a vibrating object with respect to
another object at a given point in time. In the simple example
shown in Figure 1-4, two weights are vibrating 180 degrees out of
phase with each other.

180°
A A

B B
1 Cycle
(360°)

Figure 1-4. Phase Relationship 180° Out of Phase