SENSORS AND TRANSDUCERS

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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 the which is proportional to unipolar 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

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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.