Sensor - The Electronic Nose Artificial Olfaction Technology - page 49

Capacitive sensors:
Capacitive sensor is one of the modern developments in sensor transducer tech-
nology [ 10 ]. Capacitive sensors directly sense a variety of things—motion,
chemical composition, electric field and, indirectly, sense many other variables
which can be converted into motion or dielectric constant, such as pressure,
acceleration, fluid level, and fluid composition. They are built with conductive
sensing electrodes in a dielectric, with excitation voltages and detection circuits
which turn a capacitance variation into a voltage, frequency, or pulse width var-
iation. The range of application of capacitive sensors is amazing [ 10 ].
Capacitive displacement sensors ''are non-contact devices capable of high-
resolution measurement of the position or change in position of the target''. They
are also able to measure the thickness or density of non-conductive materials.
Capacitive displacement sensors are used in a wide variety of applications
including semiconductor processing, assembly of precision equipment such as disk
drives, precision thickness measurements, machine tool metrology, and assembly
line testing [ 10 ].
Application:

• Capacitive technology is displacing Piezo resistance in silicon implementations
of accelerometers and pressure sensors, and innovative applications like fin-
gerprint detectors and infrared detectors are appearing on silicon with sensor
dimensions in the microns and electrode capacitance of 10 fF, with resolution to
5 9 10 -18 F.
• Capacitive sensors in oil refineries measure the percent of water in oil, and
sensors in grain storage facilities measure the moisture content of wheat.
• In the home, cost-effective capacitive sensors operate soft-touch dimmer
switches and help the home craftsman with wall stud sensors and digital con-
struction levels.
• Laptop computers use capacitive sensors for two-dimensional cursor control and
transparent capacitive sensors on computer monitors are found in retail kiosks.
• Many applications like flow (convert flow to displacement), pressure, liquid
level, thickness measurement, and many more are there where capacitor sensor
is used.

2.4.6 Vibration Sensor

Vibrations created by an industrial machine are a direct indication of the
machine's health monitoring programs and recording of the machine's vibration
history allows prediction of problems and shut downs a machine before serious
damage. Vibration monitoring is also widely used as a diagnostic tool to determine
the cause and location of a problem, and how to fix it.
The vibration sensor detects shock intensity caused by sudden knocks or hits
and continuous vibration due to faulty ball-bearings on fans and other equipment.
The

shock levels and monitoring durations can be set for each individual