13-09-2013, 04:14 PM
Transducers in real life
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Anteena
An antenna (or aerial) is an electrical device which converts electric power into radio waves, and vice
versa. It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter
supplies an oscillating radio frequency electric current to the antenna's terminals, and the antenna
radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna
intercepts some of the power of an electromagnetic wave in order to produce a tiny voltage at its
terminals, that is applied to a receiver to be amplified.
Antennas are essential components of all equipment that uses radio. They are used in systems such
as radio broadcasting, broadcast television, two-way radio,communications receivers, radar, cell phones,
and satellite communications, as well as other devices such as garage door openers, wireless
microphones,bluetooth enabled devices, wireless computer networks, baby monitors, and RFID tags on
merchandise.
Typically an antenna consists of an arrangement of metallic conductors ("elements"), electrically
connected (often through a transmission line) to the receiver or transmitter. An oscillating current
of electrons forced through the antenna by a transmitter will create an oscillating magnetic field around
the antenna elements, while the charge of the electrons also creates an oscillating electric field along the
elements. These time-varying fields, when created in the proper proportions, radiate away from the
antenna into space as a moving transverse electromagnetic field wave. Conversely, during reception, the
oscillating electric and magnetic fields of an incoming radio wave exert force on the electrons in the
antenna elements, causing them to move back and forth, creating oscillating currents in the antenna.
Hall effect sensor
A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall
effect sensors are used for proximity switching, positioning, speed detection, and current sensing
applications.
In its simplest form, the sensor operates as an analog transducer, directly returning a voltage. With a
known magnetic field, its distance from the Hall plate can be determined. Using groups of sensors, the
relative position of the magnet can be deduced.
Electricity carried through a conductor will produce a magnetic field that varies with current, and a Hall
sensor can be used to measure the current without interrupting the circuit. Typically, the sensor is
integrated with a wound core or permanent magnet that surrounds the conductor to be measured.
Galvanometer
A galvanometer is a type of sensitive ammeter: an instrument for detecting electric current. It is
an analogelectromechanical transducer that produces a rotary deflection of some type of pointer in
response to electric currentflowing through its coil in a magnetic field.
Galvanometers were the first instruments used to detect and measure electric currents. Sensitive
galvanometers were used to detect signals from long submarine cables, and were used to discover the
electrical activity of the heart and brain. Some galvanometers used a solid pointer on a scale to show
measurements, other very sensitive types used a tiny mirror and a beam of light to provide mechanical
amplification of tiny signals. Initially a laboratory instrument relying on the Earth's own magnetic field to
provide restoring force for the pointer, galvanometers were developed into compact, rugged, sensitive
portable instruments that were essential to the development of electrotechnology. A type of galvanometer
that permanently recorded measurements was the chart recorder. The term has expanded to include
uses of the same mechanism in recording, positioning, and servomechanism equipment.
Electrometer
An electrometer is an electrical instrument for measuring electric charge or electrical potential
difference. There are many different types, ranging from historical handmade mechanical
instruments to high-precision electronic devices. Modern electrometers based on vacuum
tube or solid-state technology can be used to make voltage and charge measurements with very
low leakage currents, down to 1 femtoampere. A simpler but related instrument, the electroscope,
works on similar principles but only indicates the relative magnitudes of voltages or charges.
The most modern electrometers consist of a solid state amplifier using one or more field-effect
transistors, connections for external measurement devices, and usually a display and/or data-
logging connections. The amplifier amplifies small currents so that they are more easily
measured. The external connections are usually of a co-axial or tri-axial design, and allow
attachment of diodes or ionization chambers for radiation measurement. The display or data-
logging connections allow the user to see the data or record it for later analysis. Electrometers
designed for use with ionization chambers may include a high-voltage power supply, which is
used to power the ionization chamber.