Transducers

C

H

Transducer Characteristics

A

P

T

E

R

6

6

P

revious chapters have discussed the fundamental motion characteristics of machinery, including the inter-relationship

between displacement, velocity, acceleration, and frequency. Rotor mode shapes

and the role of mass distribution, support characteristics, stiffness, and damping

have also been reviewed. These physical characteristics have been expanded to

examine some of the analytical computations available. It is understandable that

mathematical modeling techniques provide some powerful tools for predicting

the behavior of rotating equipment. However, it must be recognized that the real

world is always more complicated than the models that are developed to explain

physical phenomena. At best, the mathematical models are approximations of

the actual physical system, and improvement or refinement of the model is often

dependent upon correlations with field observations, and direct machinery measurements.

Over the years, many knowledgeable individuals have stated and restated

that one good measurement is worth a thousand expert opinions. Hence, it is not

only desirable, it is mandatory that machinery measurements be considered as a

major problem solving tool. This topic will be explored from the standpoint of

static measurements, such as position measurements versus machine clearances. In addition, the complex dynamic measurements associated with machinery vibratory behavior will be addressed throughout this text. Within this

chapter, specific consideration will be given to the dynamic measurement transducers, and their associated signal characteristics.

In most cases, mechanical motion cannot be adequately quantified with

human senses. Although the human eye can observe objects vibrating at amplitudes of 10 Mils,p-p, and the ear can detect frequencies of 10,000 Hz, and differential acceleration levels of 0.1 G’s,o-p are normally considered to be unpleasant,

there are...