Page 391 - The Mechatronics Handbook

Acceleration is an important parameter for general-purpose absolute motion measurements, vibration,
and shock sensing. For these measurements, accelerometers are commercially available in a wide range and
many different types to meet diverse application requirements, mainly in three areas: (1) Commercial
applications—automobiles, ships, appliances, sports and other hobbies; (2) Industrial applications—robotics,
machine control, vibration testing and instrumentation; and (3) High reliability applications—military,
space and aerospace, seismic monitoring, tilt, vibration and shock measurements.
Accelerometers have been in use for many years. Early accelerometers were mechanical types relying
on analog electronics. Although early accelerometers still find many applications, modern accelerometers
are essentially semiconductor devices within electronic chips integrated with the signal processing cir-
cuitry. Mechanical accelerometers detect the force imposed on a mass when acceleration occurs. A new
type of accelerometer, the thermal type, senses the position through heat transfer.

Overview of Accelerometer Types

A basic accelerometer consists of a mass that is free to move along a sensitive axis within a case. The
technology is largely based on this basic accelerometer and can be classified in a number of ways, such
as mechanical or electrical, active or passive, deflection or null-balance accelerometers, etc. The majority
of industrial accelerometers are classified as either deflection or null-balance types. Accelerometers used
in vibration and shock measurements are usually the deflection types, whereas those used for the mea-
surement of motions of vehicles, aircraft, and so on for navigation purposes may be either deflection or
null-balance type.
This article will concentrate on the direct measurements of acceleration, which can be achieved by the
accelerometers of the following types:
• Inertial and mechanical
• Electromechanical
• Piezoelectric
• Piezoresistive
• Strain gauges
• Capacitive and electrostatic force balance
• Micro- and nanoaccelerometers
Depending on the principles of operations, these accelerometers have their own subclasses.

Dynamics and Characteristics of Accelerometers
Acceleration is related to motion, a vector quantity, exhibiting a direction as well as magnitude. The
direction of motion is described in terms of some arbitrary Cartesian or orthogonal coordinate systems.
Typical rectilinear, angular, and curvilinear motions are illustrated in Figs. 19.17(a–c), respectively.

y y M
y
Pat
Pat M
−s +s θ θ
M x x
x Pat
z (a) z (b) z (c)

FIGURE 19.17 Types of motions to which accelerometers are commonly applied.

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