2
SECTION 3 • UNDERSTANDING YOUR ACCELEROMETER
WHAT IS AN ACCELEROMETER?
An accelerometer is a device for measuring shock and vibration. An
accelerometer transduces the acceleration of an object into a proportional
analog signal. The analog signal indicates the real-time, Instantaneous
acceleration of the object on which the accelerometer
IS
mounted.
HOW DOES
IT
WORK?
Piezoelectric Accelerometers
Mounted within the accelerometer housing is a piezoelectric crystal affixed to a
small mass. This mass is coupled to the supporting accelerometer base
through the piezoelectric crystal. When the accelerometer is subjected to an
acceleration, the mass exerts a force on the crystal. This force results in a
charge output of the crystal that is directly proportional to the input
acceleration.
There are many piezoelectric crystal materials that are useful in
accelerometer construction
.
The most common materials used are ceramic
Lead Metaniobate, Lead Zirconate, Lead Titanate and natural quartz crystal.
There are also many different mechanical configurations of the masses and
crystals within the accelerometer case.
The materials and physical construction used iIn an accelerometer design
are selected to furnish the particular performance characteristics desired.
For more information about the construction of your accelerometer refer to
the appropriate sales bulletin or contact OMEGA Engineering, Inc
.
HIGH IMPEDANCE OR LOW IMPEDANCE?
There are two distinctly different types of accelerometers that are
manufactured. These are high impedance and low impedance" types.
Essentially, if the output sensitivity is specified in mV/g (millivolts per g) such
as 10mV/g or 100mV/g, then you are working with a low impedance sensor. If
the output sensitivity is specified in units of pC/g
(picocoulombs charge per g)
then you are working with a high impedance sensor.
OMEGA
'
s accelerometers are the low impedance type of accelerometer
(see Figure 3-1). A low impedance accelerometer is one in which the
electronics required to detect the charge generated by the piezoelectric crystal
are built right into the case of the sensor. In this way, "high" to "low" impedance
transformation is done at the point of measurement and only low impedance
signals are transmitted from the sensor
.
The low impedance output is
desirable for driving long cables and it provides a proper Impedance match to
virtually all conventional data acquisition systems.
