Page 119 - Instrumentation Reference Book 3E

104 Vibration

6.4 Literature
There exist many general books on the kinds of
transducers that are in use. An IMEKO biblio-
graphy, Sydenham (1983), is a useful entry point
to the literature of measurement technology.
Of the many general instrument texts that are
available, very few actually address the subject
of vibration as a distinct chapter. Where included,
relevant material will be found under such headings
IC I
I as velocity and acceleration measurement, accelero-
q=sq d meters, position sensing, and piezoelectric systems.
where S is ~ccelerome~er charge renririvity Texts containing a chapter-length introductory
aq IS accrleranon
system 1ran91er ~ e, ~ S, discussion include Herceg (1972). Norton (1969),
c,
cosfllcienr -; and Oliver (1971).
~
Figure 6.20 Equivalent circuit for piezoelectric sensot There are, as would be expected, some (but
when interrogated, as a charge-generating device, by an only a few) works entirely devoted to vibration
operational amplifier technique.
and related measurands. The following will be of
value to readers who require more than the
restricted introduction that a chapter such as this
This shows that the user need only define the provides: Bruel and Kjaer (1975, 1982), Endevco
sensor charge sensitivity S, and the feedback (1980), Harris and Crede (1961), Trampe-Broch
capacitance Cf in order to be able to relate output (1980), and Wallace (1970).
voltage from the preamplifier to the acceleration The various trade houses that manufacture
of the sensor. vibration-measuring and -testing equipment also
often provide extensive literature and other forms
6.3.5 Measurement of shock of training aids to assist the uncertain user.
Shock is a sudden short impulse of applied force
that generates very large acceleration (100,000 g 6.5 References
can arise) and is not recurrent. It can be regarded
as a once-only occurrence of a vibration wave- Bently Nevada, Bently Book One (application notes on
form, although sometimes it is used to describe a vibration and machines), Bently Nevada, Minden,
short burst of oscillation. Nev. (1982)
Understanding the behavior of a given vibra- Bruel & Kjaer, Vibration Testing Systems, Bruel &
tion sensor requires Fourier analysis of its Kjaer, Naerum, Denmark (1975)
response to a truncated wave shape. The mathe- Bruel & Kjaer, Piezoelectric Accelerometer and Vibra-
matics becomes more complex. Theoretical study tion PreampliJer Handbook, Bruel & Kjaer, Naerum,
Denmark (1976)
does lead to the generalization that as the wave- Bruel & Kjaer, Acoustics, Vibration & Shock, Luminance
form becomes more like a single pulse of high and Contrast, National and International Standards and
magnitude and very short duration, the frequency Recommendations, Bruel & Kjaer, Naerum, Denmark
band of the sensor must be widened if the (1981)
delivered output is to be a satisfactory replica of Bruel & Kjaer, Measuring Vibration-an Elementary
the actual input vibration parameter. Fidelity Introduction, Bruel & Kjaer, Naerum, Denmark (1982)
increases as the period of the natural frequency Crandall, S. H. Random Vibration, Wiley, New York
of the sensor becomes shorter than the pulse (1959)
length. An idea of the variation of responses with Endevco, Shock and Vibration Measurement Techno-
logy, Endevco Dynamic Instrument Division, San
natural frequency and damping is available in Juan Capistrano, Calif. (1980)
graphs given in Harris and Crede (1961). An Harris, C. M. and C. E. Crede, Shock and Vibration
example is that is Figure 6.18. Handbook Val. I, Basic Theory and Measurements,
The very large forces exerted on the transducer McGraw-Hill, New York (1961, reprinted in 1976)
require a design that recognizes the need to with- Herceg, E. E. Handbook of Measurement and Control,
stand large transient forces without altering HB-72, Schaevitz Engineering, Pennsauken, N.J.
mechanical strains in the sensor system. (1972, revised 1976)
Well designed shock sensors can accurately Jones, B. E. “Feedback in instruments and its applications”
measure single half-sine-wave pulses as short as in Instrument Science and Technology, B. E. Jones, (ed.),
Adam Hilger, Biistol, U.K. (1982)
5ps. Some amount of ringing in the output is Klaasen, K. B. ”Piezoelectric accelerometers” in Modern
usually tolerated in order to provide measure- Electronic Measuring Systems, Regtien, P. P. L. (ed.),
ment of very short duration shocks. Delft University Press, Delft (1978)