1. SENSORS AND TRANSDUCERS

2. 1
SENSORS AND
TRANSDUCERS
TRANSDUCERS:
1- Antenna
2- Hall effect
3- Cathode ray tube
4- Hydrophone
SENSORS:
1- Ionizing radiation, subatomic particles
2- Electric current, electric potential, magnetic, radio
3- Optical, light, imaging, photon
4- Proximity, presence
5- Sensor technology
6- Acoustics and vibration
9- Temperature sensors
10- Pressure sensors
11- Automotive sensors
DONE BY:
Andrew Achraf William
Toka Mohamed Rashad
Ahmed Hatem el Sharkawy
Anas Jalal Sulaiman
Mariam Emad
Abdelrahman Amr El-Adawy

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A transducer is a device that converts one form of energy to another form
of energy. Energy types include electrical, mechanical, electromagnetic chemical,
acoustic, and thermal energy. Usually a transducer converts a signal in one form
of energy to a signal in another (for example, a loudspeaker converts an electric
signal to sound), but any variable attenuation of energy may serve as input; for
example, the light reflecting off the landscape, although it is not a signal, conveys
information that a transducer can convert (which is what image sensors, one
form of transducer, do). A sensor is a transducer whose purpose is to sense (that
is, to detect) some characteristic of its environs. A sensor is used to detect a
parameter in one form and report it in another form of energy, often an electrical
signal. For example, a pressure sensor might detect pressure (a mechanical form
of energy) and convert it to electrical signal for display at a remote gauge.
Transducers are widely used in measuring instruments.
Antenna:
Introduction:
Antennas are basic components of any electric
system and are connecting links between the
transmitter and free space or free space and the
receiver. Thus antennas play very important role
in finding the characteristics of the system in
which antennas are employed. Antennas are
employed in different systems in different forms.
That is,
in some systems the operational characteristic of the system are designed
around the directional properties of the antennas or in some others systems, the
antennas are used simply to radiate electromagnetic energy in an omnidirectional
or finally in some systems for point-to-point communication purpose in which
increased gain and reduced wave interference are required.

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Definition:
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.
Applications:
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.
How does it work in general?
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 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.
Antennas can be designed to transmit and receive radio waves in all
horizontal directions equally (omnidirectional antennas), or preferentially in a
particular direction (directional or high gain antennas). In the latter case, an
antenna may also include additional elements or surfaces with no electrical
connection to the transmitter or receiver, such as parasitic elements, parabolic

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reflectors or horns, which serve to direct the radio waves into a beam or other
desired radiation pattern.
Antenna Characteristics:
An antenna is a device that is made to efficiently radiate and receive
radiated electromagnetic waves. There are several important antenna
characteristics that should be considered when choosing an antenna for your
application as follows:
• Antenna radiation patterns
• Power Gain
• Directivity
• Polarization
Antennas Types:
There are many different types of antennas. Antennas most relevant to designs
at 2.4GHz that are further detailed are as follows:
• Dipole Antennas
• Multiple Element Dipole Antennas
• Yagi Antennas
• Flat Panel antennas
• Parabolic Dish antennas
• Slotted Antennas
• Micro strip Antennas
Hall Effect sensor:
Introduction:
There is a simple way to measure
magnetism with a device called a Hall-effect
sensor or probe, which uses a clever bit of
science discovered in 1879 by American
physicist Edwin H. Hall (1855–1938). Hall's work
was ingenious and years ahead of its time: no-one really knew what to do with it
until decades later when semiconducting materials such as silicon became better
understood. These days, Edwin Hall would be delighted to find sensors named
for him are being used in all kinds of interesting ways.

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Definition:
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.
How does the Hall Effect work?
1. When an electric current flows through a
material, electrons move through it in pretty
much a straight line.
2. Put the material in a magnetic field and the
electrons inside it are in the field too. A force
acts on them (the Lorentz force) and makes
them deviate from their straight-line path.
3. Now looking from above, the electrons in this example would bend as
shown. With more electrons on the right side of the material than on the
left, there would be a difference in potential (a voltage) between the two
sides, as shown by the green arrowed line. The size of this voltage is
directly proportional to the size of the electric current and the strength of
the magnetic field.
Using the Hall effect:
You can detect and measure all kinds of things with the Hall-effect using what's known
as a Hall-effect sensor or probe. Typically made from semiconductors (materials such as
silicon and germanium), Hall-effect sensors work by measuring the Hall voltage across two of
their faces when you place them in a magnetic field. Some Hall sensors are packaged into
convenient chips with control circuitry and can be plugged directly into bigger electronic
circuits. The simplest way of using one of these devices is to detect something's position. For
example, you could place a Hall sensor on a door frame and a magnet on the door, so the
sensor detects whether the door is open or closed from the presence of the magnetic field. A
device like this is called a proximity sensor. Hall-effect sensors used in a brushless DC motor
(used in such things as floppy-disk drives), you need to be able to sense exactly where the
motor is positioned at any time. A Hall-effect sensor stationed near the rotor (rotating part of
the motor) will be able to detect its orientation very precisely by measuring variations in the

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magnetic field. Sensors like this can also be used to measure speed (for example, to count
how fast a wheel or car engine cam or crankshaft is rotating).
Cathode ray tube:
Definition:
A cathode ray tube (CRT)
is a specialized vacuum tube in
which images are produced
when an electron beam strikes
a phosphorescent surface.
(CRT) is a vacuum tube
containing one or more electron
guns, and a fluorescent screen used to view images. It has a means to
accelerate and deflect the electron beam(s) onto the screen to create the
images. The images may represent electrical waveforms (oscilloscope), pictures
(television, computer monitor), radar targets or others. CRTs have also been
used as memory devices.
>> A CRT is an electronic tube designed to display electrical data.
The basic CRT consists of four major components.
1. Electron Gun
2. Focusing & Accelerating Anodes
3. Horizontal & Vertical Deflection Plates
4. Evacuated Glass Envelope
Working of CRT:
Heater element is energized by alternating current to obtain high emission
of electron from cathode. Control
grid is biased negative with respect
to cathode it controls the density of
electron beam to focus the electron
beam on the screen focusing anode
is used. the focusing anode operate

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at a potential of twelve hundred (1200 V) and accelerating anode at 2000 V to
accelerate the electron beam. Two pairs of deflection plates provided in the CRT
these deflection plates are mounted at right angle to each other to provide
electron beam deflection along vertical and horizontal axis of the screen. The
screen consists of a glass which is coated by some florescent material lie zinc
silicate, which is semitransparent phosphor substance. When high velocity
electron beam structs the phosphorescent screen the light emits from it. The
property of phosphor to emit light when its atoms are excited is called
fluorescence.
Applications of CRT:
 In cathode ray oscilloscope
 As a display device in radar
 In televisions
 In computer Monitors
Ionizing radiation, subatomic particles
The most common type of instrument is a
gas filled radiation detector. This instrument
works on the principle that as radiation passes
through air or a specific gas, ionization of the
molecules in the air occurs. When a high
voltage is placed between two areas of the gas
filled space, the positive ions will be attracted
to the negative side of the detector (the
cathode) and the free electrons will travel to the
positive side (the anode). These charges are collected by the anode and cathode
which then form a very small current in the wires going to the detector. By placing
a very sensitive current measuring device between the wires from the cathode
and anode, the small current measured and displayed as a signal. The more
radiation which enters the chamber, the more current displayed by the
instrument.
Bubble chamber:

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A bubble chamber is a vessel filled with a superheated transparent liquid (most
often liquid hydrogen) used to detect electrically charged particles moving
through it.
Function and use:
It is normally made by filling a large cylinder with a liquid heated to just below its
boiling point. As particles enter the chamber, a piston suddenly decreases its
pressure, and the liquid enters into a superheated, metastable phase. Charged
particles create an ionization track, around which the liquid vaporizes, forming
microscopic bubbles. Bubble density around a track is proportional to a particle's
energy loss.
Bubbles grow in size as the chamber expands, until they are large enough to be
seen or photographed. Several cameras are mounted around it, allowing a three-
dimensional image of an event to be captured.
The entire chamber is subject to a constant magnetic field, which causes
charged particles to travel in helical paths whose
radius is determined by their ratios and their
velocities. Since the magnitude of the charge of all
known charged, long-lived subatomic particles is
the same as that of an electron, their radius of
curvature must be proportional to their momentum.
Thus, by measuring their radius of curvature, their
momentum can be determined.
The bubble chamber proved very useful in the
study of high-energy nuclear physics and
subatomic particles, particularly during the 1960s.

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Electric current, electric potential, magnetic and radio
 CURRENT SENSOR:
“A current sensor is a device that detects
electric current (AC or DC) in a wire, and
generates a signal proportional to it. The
generated signal could be analog voltage or
current or even digital output. It can be then
utilized to display the measured current in an
ammeter or can be stored for further analysis in a data acquisition system or can
be utilized for control purpose”
The sensed current and the output signal can be:
1--Alternating current input:
The output is either:
1- Analog output, which duplicates the wave shape of the sensed current
2-bipolar output, which duplicates the wave shape of the sensed current
sensed currentthe average or RMS value of thewhich is proportional tounipolar output,-3
2--Direct current input:
1- Unipolar: with a unipolar output, which duplicates the wave shape of the sensed current
2-digital output: which switches when the sensed current exceeds a certain threshold
The figure above shows the current sensor …

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Applications:
This application illustrates how
current sensing can cost effectively sense
the failure of a critical lamp load in a piece
of process equipment. A lithograph dryer
is used in the production of expensive
reproduction prints. The inks used for this
medium are cured by ultraviolet lamps. The inks are laid down in stages to
achieve the four color reproduction process. The inks are cured by the ultraviolet
lamps between stages. A lamp failure or a decrease in lamp intensity can ruin
this process. The undercurrent monitor is utilized to detect when the operating
current falls below a predetermined level for the number of lamps in use. Any
change in current below the preset level is viewed as a fault and the output
contacts are used to shut down the process for repair.
(Lithographic dryer) …
 ELECTROSCOPE:
“An electroscope is an early scientific
instrument that is used to detect the presence and
magnitude of electric charge on a body. It was the
first electrical measuring instrument.”
There are 2 types of electroscopes:
1- pith-ball electroscope
“A pith-ball electroscope was invented by British schoolmaster and physicist
John Canton in 1754,[2] consists of a small ball of some lightweight
nonconductive substance, originally a spongy plant material called pith, although
modern electroscopes use plastic balls. The ball is suspended by a silk thread
from the hook of an insulated stand. In order to test the presence of a charge on
an object, the object is brought near to the uncharged pith ball.[3] If the object is
charged, the ball will be attracted to it and move toward it.”

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2- Gold-leaf electroscope
“The gold-leaf electroscope was developed
in 1787 by British clergyman and physicist
Abraham Benet, as a more sensitive
instrument than pith ball or straw blade
electroscopes then in use. It consists of a
vertical metal rod, usually brass, from the
end of which hang two parallel strips of thin
flexible gold leaf. A disk or ball terminal is
attached to the top of the rod, where the
charge to be tested is applied. To protect the gold leaves from drafts of air
they are enclosed in a glass bottle, usually open at the bottom and mounted
over a conductive base. Often there are grounded metal plates or foil strips in
the bottle flanking the gold leaves on either side.”
Applications:
1) It can be used to detect high Voltage. When charged, the leaves separate
because like charges repel.
2) It can be used to detect radioactivity. When subjected to strong ionizing
radiation, it will discharge the device, so the leaves will fold together since the
charge bleeds off. It is assumed that the insulation is perfect. Also, humidity in
the air will tend to bleed off the charge over time. - it is not a very sensitive
radioactivity detector - do NOT count on it to warn you of dangerous levels of
radiation!
3) For determining the polarity of a high Voltage. (Charge it with the unknown,
then bring it close to another high Voltage of known polarity and see if the
leaves stay apart or if they collapse….

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 DOPPLER RADAR:
Doppler radar is specialized radar that makes use of the Doppler effect to
produce velocity data about objects at a distance. It does this by beaming a
microwave signal towards a desired target and listening for its reflection, then
analyzing how the frequency of the returned signal has been altered by the
object's motion. This variation gives direct and highly accurate measurements
of the radial component of a target's velocity relative to the radar. Doppler
radars are used in aviation, sounding satellites, meteorology, police speed
guns, radiology and healthcare fall detection and risk assessment, nursing or
clinic purpose and bistatic radar
APPLICATIONS:

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 PROXIMITY SENSOR:
A proximity sensor often emits an
electromagnetic field or a beam of
electromagnetic radiation (infrared, for
instance), and looks for changes in the
field or return signal. The object being
sensed is often referred to as the proximity
sensor's target. Different proximity sensor
targets demand different sensors. For
example, a capacitive or photoelectric sensor might be suitable for a plastic
target; an inductive proximity sensor always requires a metal target.
Applications :
1- Detects Aluminum Components
2-Detects Lead Frames (Aluminum/Copper)
3-Inspects High-speed Table Movement
4-Detects Bottle Caps
5- Positioning at the Welding Site
OPERATING PRINCIPLES
How do proximity sensors work?
Inductive & Capacitive
Their operating principle is based on a high
frequency oscillator that creates a field in
the close surroundings of the sensing surface. The presence of a metallic object (inductive)
or any material (capacitive) in the operating area causes a change of the oscillation
amplitude. The rise or fall of such oscillation is identified by a threshold circuit that changes
the output state of the sensor. The operating distance of the sensor depends on the
actuator's shape and size and is strictly linked to the nature of the material (Table 1 & Table
2.). A screw placed on the back of the capacitive sensor allows regulation of the operating
distance. This sensitivity regulation is useful in applications, such as detection of full
containers and non-detection of empty containers.

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Metal detector :
Metal detector is an electronic instrument which detects the presence of
metal nearby. Metal detectors are useful for finding metal inclusions hidden
within objects, or metal objects buried underground. They often consist of a
handheld unit with a sensor probe which can be swept over the ground or
other objects. If the sensor comes near a piece of metal this is indicated by a
changing tone in earphones, or a needle moving on an indicator. Usually the
device gives some indication of distance; the closer the metal is, the higher
the tone in the earphone or the higher the needle goes. Another common type
are stationary "walk through" metal detectors used for security screening at
access points in prisons, courthouses, and airports to detect concealed metal
weapons on a person's body.
HOW DOEAS A METAL DETECTOR WORK?
Metal detectors work by transmitting an electromagnetic field from the search
coil into the ground. Any metal objects (targets) within the electromagnetic
field will become energized and retransmit an electromagnetic field of their
own. The detector’s search coil receives the retransmitted field and alerts the
user by producing a target response. Minelab metal detectors are capable of
discriminating between different target types and can be set to ignore
unwanted targets.
WHAT ARE THE CONTENTS OF THE SYSTEM?
1- Battery
The battery provides power to the detector.
2- Control Box
The control box contains the detector’s electronics. This is where the transmit
signal is generated and the receive signal is processed and converted into a
target response.

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3- Search Coil
The detector’s search coil transmits the
electromagnetic field into the ground and
receives the return electromagnetic field
from a target.
Transmit Electromagnetic Field (visual
representation only - blue)
4- The transmit electromagnetic field
Energizes targets to enable them to be
detected.
5- Target
A target is any metal object that can be
detected by a metal detector. In this
example, the detected target is treasure, which is a good (accepted) target.
A target is any metal object that can be detected by a metal detector. In this
example, the detected target is treasure, which is a good (accepted) target.
6- Unwanted Target
Unwanted targets are generally ferrous (attracted to a magnet), such as nails,
but can also be non-ferrous, such as bottle tops. If the metal detector is set to
reject unwanted targets then a target response will not be produced for those
targets.
7- Receive Electromagnetic Field
The receive electromagnetic field is generated from energized targets and is
received by the search coil.
8- Target Response (visual representation only - green)
When a good (accepted) target is detected the metal detector will produce an
audible response, such as a beep or change in tone. Many Minelab detectors
also provide a visual display of target information.

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APPLICATIONS:
1- Security screening
The development of these systems continued in a spin-off company and
systems branded as Metor Metal Detectors evolved in the form of the rectangular
gantry now standard in airports. In common with the developments in other uses
of metal detectors both alternating current and pulse systems are used, and the
design of the coils and the electronics has moved forward to improve the
discrimination of these systems. In 1995 systems such as the Metor 200
appeared with the ability to indicate the approximate height of the metal object
above the ground, enabling security personnel to more rapidly locate the source
of the signal. Smaller hand held metal detectors are also used to locate a metal
object on a person more precisely.
2- Industrial metal detectors
The basic principle of operation for the common industrial metal detector is
based on a 3 coil design. This design utilizes an AM (amplitude modulated)
transmitting coil and two receiving coils one on either side of the transmitter. The
design and physical configuration of the receiving coils are instrumental in the
ability to detect very small metal contaminates of 1mm or smaller. Today modern
metal detectors continue to utilize this configuration for the detection of tramp
metal.
The coil configuration is such that it creates an opening whereby the product
(food, plastics, pharmaceuticals, etc.) passes through the coils. This opening or
aperture allows the product to enter and exit through the three coil system
producing an equal but mirrored signal on the two receiving coils. The resulting
signals are summed together effectively nullifying each other.
3- Civil engineering
In civil engineering, special metal detectors (cover meters) are used to
locate reinforcement bars inside walls.

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Geophone
What is a geophone?
A geophone is a device that converts ground movement (displacement) into
voltage; the deviation of this measured voltage from the base line is called the
seismic response and is analyzed for structure of the earth.
Construction:
In the past geophones were these passive analog devices and typically comprise
a spring-mounted magnetic mass moving within a wire coil to generate an
electrical signal. Recent designs have been based on microelectromechanical
systems (MEMS) technology which generates an electrical response to ground
motion through an active feedback circuit to maintain the position of a small piece
of silicon.
The response of a coil/magnet geophone is proportional to ground velocity, while
MEMS devices usually respond proportional to acceleration. MEMS have a much
higher noise level (50 dB velocity higher) than geophones and can only be used
in strong motion or active seismic applications.

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Microphone
What is a microphone?
A microphone is an acoustic-to-electric transducer or sensor that converts
sound in air into an electrical signal.
Construction:
Most microphones today use electromagnetic induction (dynamic
microphones), capacitance change (condenser microphones) or piezoelectricity
(piezoelectric microphones) to produce an electrical signal from air pressure
variations. Microphones typically need to be connected to a preamplifier before
the signal can be amplified with an audio power amplifier or recorded.
Uses:
Microphones are used in many applications such as telephones, hearing
aids, public address systems for concert halls and public events, motion picture
production, live and recorded audio engineering, two-way radios, megaphones,
radio and television broadcasting, and in computers for recording voice, speech
recognition, VoIP, and for non-acoustic purposes such as ultrasonic checking or
knock sensors.
Varieties:
Condenser microphone, Dynamic microphone, Ribbon microphone, Carbon
microphone, piezoelectric microphone, Fiber optic microphone, Laser
microphone, Liquid microphone, MEMS microphone

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Nanosensors
Nanosensors are any biological, chemical, or surgical sensory points used
to convey information about nanoparticles to the macroscopic world. Their use
mainly includes various medicinal purposes and as gateways to building other
nanoproducts, such as computer chips that work at the nanoscale and
nanorobots. Presently, there are several ways proposed to make nanosensors,
including top-down lithography, bottom-up assembly, and molecular self-
assembly.
Predicted applications
Medicinal uses of nanosensors mainly revolve around the potential of
nanosensors to accurately identify particular cells or places in the body in need.
By measuring changes in volume, concentration, displacement and velocity,
gravitational, electrical, and magnetic forces, pressure, or temperature of cells in
a body, nanosensors may be able to distinguish between and recognize certain
cells, most notably those of cancer, at the molecular level in order to deliver
medicine or monitor development to specific places in the body. In addition, they
may be able to detect macroscopic variations from outside the body and
communicate these changes to other nanoproducts working within the body.
One example of nanosensors involves using the fluorescence properties of
cadmium selenide quantum dots as sensors to uncover tumors within the body.
By injecting a body with these quantum dots, a doctor could see where a tumor
or cancer cell was by finding the injected quantum dots, an easy process
because of their fluorescence. Developed nanosensor quantum dots would be
specifically constructed to find only the particular cell for which the body was at
risk. A downside to the cadmium selenide dots, however, is that they are highly
toxic to the body. As a result, researchers are working on developing alternate
dots made out of a different, less toxic material while still retaining some of the
fluorescence properties. In particular, they have been investigating the particular
benefits of zinc sulfide quantum dots which, though they are not quite as
fluorescent as cadmium selenide, can be augmented with other metals including

21. 20
manganese and various lanthanide elements. In addition, these newer quantum
dots become more fluorescent when they bond to their target cells. (Quantum)
Potential predicted functions may also include sensors used to detect specific
DNA in order to recognize explicit genetic defects, especially for individuals at
high-risk and implanted sensors that can automatically detect glucose levels for
diabetic subjects more simply than current detectors. DNA can also serve as
sacrificial layer for manufacturing CMOS IC, integrating a nanodevice with
sensing capabilities. Therefore, using proteomic patterns and new hybrid
materials, nanobiosensors can also be used to enable components configured
into a hybrid semiconductor substrate as part of the circuit assembly. The
development and miniaturization of nanobiosensors should provide interesting
new opportunities.
Other projected products most commonly involve using nanosensors to
build smaller integrated circuits, as well as incorporating them into various other
commodities made using other forms of nanotechnology for use in a variety of
situations including transportation, communication, improvements in structural
integrity, and robotics. Nanosensors may also eventually be valuable as more
accurate monitors of material states for use in systems where size and weight
are constrained, such as in satellites and other aeronautic machines.

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Thermal sensors
1-Thermometer:
A thermometer is a device that measures. A thermometer has two
important elements: the temperature sensor (e.g. the bulb on a mercury-in-glass
thermometer) in which some physical change occurs with temperature, plus
some means of converting this physical change into a numerical value (e.g. the
visible scale that is marked on a mercury-in-glass thermometer).
Electronic thermometers:
You simply touch the
thermometer probe onto the object
whose temperature you want to
measure and the digital display gives
you an instant temperature reading.
Electronic thermometers work in an
entirely different way to mechanical
ones that use lines of mercury or
spinning pointers. They're based on the
idea that the resistance of a piece of metal changes as the temperature changes.
As metals get hotter, atoms vibrate more inside them; it's harder for electricity to
flow, and the resistance increases. Similarly, as metals cool down, the electrons
move more freely and the resistance goes down. An electronic thermometer
works by putting a voltage across its metal probe and measuring how much
current flow through it.
The main advantage of thermometers like this is that they can give an
instant reading in any temperature scale you like Celsius, Fahrenheit, or
whatever it happens to be. But one of their disadvantages is that they measure
the temperature from moment to moment, so the numbers they show can
fluctuate quite dramatically, sometimes making it difficult to take an accurate
reading.

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2-Pyrometer:
Hot objects it gives off heat radiation in all directions, the radiation it
produces is related to its temperature in a very predictable way. So if you can
measure the radiation, you can precisely measure the temperature even if you're
standing some way off. That's the theory behind a pyrometer: a very accurate
kind of thermometer that measures something's temperature from the heat
radiation it gives out.
There are two basic kinds of pyrometers: optical pyrometers, where you
look at a heat source through a mini-telescope and make a manual
measurement, and electronic, digital pyrometers that measure completely
automatically
a- optical pyrometers:
It’s a type of pyrometer where you look
at a heat source through a mini-telescope and
make a manual measurement. It measures
the temperature, at a safe distance, by
comparing the radiation the hot object
produced with the radiation produced by a hot
filament
You look through a telescope eyepiece, through a red filter (1 in the figure), at
the object you're measuring. What you see is a dull red glow from the hot object
with a line of brighter light from the filament (3 in the figure) running right through
it and. You turn a knob on the side of the pyrometer (2 in the figure) to adjust the
electric current passing through the filament. This makes the filament a bit hotter
or colder and alters the light it gives off. When the filament is exactly the same
temperature as the hot object you're measuring, it effectively disappears because
the radiation it's producing is the same color. At that point, you stop looking
through the eyepiece and read the temperature off a meter (4 in the figure). The
meter is actually measuring the electric current through the filament, but it's
calibrated so that it effectively converts current measurements into temperature.

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b- Digital pyrometers:
They measure heat radiation from hot
objects using semiconductor-based, light-
sensitive photocells (similar to tiny solar cells,
but designed to respond to both visible and
infrared radiation). Pyrometers like this are
often shaped like guns, with built-in detectors,
signal amplifiers, power sources, and
temperature meters. You point them at the
object you want to measure and press the
trigger. At the same time, a heat source (such
as a hot filament) built into the pyrometer fires
up and starts shooting infrared radiation toward
the detector chip. Meanwhile, incoming radiation passes through a lens on the
front of the detector. An optical chopper (a rotating disc with holes in it driven by
an electric motor) interrupts the beam dozens of times each second so the
detector is alternately receiving radiations from the internal heat source and the
external hot object. The detector chip can't measure absolute amounts of
radiation, only differences, so it works by comparing the radiation from the two
sources. By subtracting the measurements it makes of its own, known heat
source from the alternating measurements it makes of the unknown heat source,
it can very accurately figure out the temperature of the object you're trying to
measure.

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Pressure sensors
Barometer
A barometer is a scientific instrument used to measure atmospheric
pressure. Pressure tendency can forecast short term changes in the weather the
two traditional kinds of barometer are called Torricellian and dial barometers.
Aneroid (dial) barometers:
It consists of a sealed, air-tight
metal box inside. As the air pressure
rises or falls, the box either squashes
inward a tiny bit or flexes outward. A
spring is cunningly attached to the box
and, as the box moves in and out in
response to the changes in air pressure,
the spring expands or contracts and
moves the pointer on the dial. The dial is
calibrated so you can read the air
pressure instantly.
These small, flexible metal boxes are called an aneroid cell, which is made
from an alloy of beryllium and copper. This capsule is prevented from collapsing
by a strong spring. Small changes in external air pressure cause the cell to
expand or contract. This expansion and contraction drives mechanical levers
such that the tiny movements of the capsule are amplified and displayed on the
face of the aneroid barometer.