Sensor - The Electronic Nose Artificial Olfaction Technology - page 50

sensor, specific applications and equipment. Despite the advances made in
vibration monitoring and analysis equipment, the selection of sensors and the way
they are mounted on a machine remain critical factors in determining the success
of any monitoring list.
The three parameters detected in place of motion, by vibration monitors are:
1. Displacement
2. Velocity
3. Acceleration
These parameters can be measured by a variety of motion sensors and are
mathematically related. Selection of a sensor proportional to displacement,
velocity, or acceleration depends on the frequencies of interest and the signal
levels concerned.
Transducers involved in vibration measurement:
• LVDT
• Eddy current
• Capacitive
• Hall
Velocity Sensors
Velocity sensors are used for low to medium frequency measurements. They are
useful for vibration monitoring and balancing operations on rotating machinery.
As compared to accelerometers, velocity sensors have lower sensitivity to high
frequency vibrations. The mechanical design of the velocity sensor; an iron core
moving within a coil in a limited magnetic field, no clipping of the generated
signal occurs, but smooth saturation. Velocity sensor is used for medium to low
frequency (1-1,000 Hz) measurements. It acts as a low-pass filter (reduce high
frequency signals). Traditional velocity sensors employ an electromagnetic sensor
to pick up the velocity signal.
Accelerometers
Accelerometers are widely used to measure tilt, inertial forces, shock, and
vibration. They find wide usage in automotive, medical, industrial control, and
other applications. Acceleration integrated to velocity can be used for low fre-
quency measurements.
The basic acceleration sensor has a good signal to noise ratio over a wide
dynamic range. They are useful for measuring low to very high frequencies and
available in a wide variety of general purpose and application-specific designs.
Acceleration sensors come in a variety of sorts both regarding their performance as
well as the underlying principles used for sensing. On the rough end of the
spectrum one finds the sensors meant to be used, e.g., in car as airbag deployment
sensors whereas on the other end the very sensitive (micro-g) sensors are found
which are intended for use, e.g., for seismic applications. Accelerometers are
extremely versatile and widely used for industrial machinery monitoring. Mainly