sensors and tranducers

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ME 4326 ANALOG AND DIGITAL ELECTRONICS

ASSIGNMENT NO 01

NAME : KULATHUNGA H.G.G.

REG NO : RU/E/2009/095

DATE : 11/11/2011


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CONTENT


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1. LIGHT DEPENDENT RESISTER

Light dependent resistor is such type of sensor whose resistance varies with the light

intensity. Generally light dependent resister also known as LDR, photo resister and cadmium

sulfide cell. LDR are made of a high resistance semiconductor. When due to the falling oflight with high enough frequency, photons absorb by the bound electrons of the

semiconductor and jumps in to the conduction band. Therefore it creates free electrons in the

conduction band and cause to reduce the resistance and resulting is conduct electricity

through the conduction band. Wide spectral response, Low cost and wide ambient

temperature range are the most common features of the LDRs. The typical circuit symbol

and the actual image of a LDR is as shown in the below.

Fig no 01: Symbol for LDR Fig no 02: Light dependent resister

1.1APPLICATIONS

Camera light meters.

Street lights. Clock radios.

Alarm devices.

Outdoor clocks.

Light interruption detectors.
http://en.wikipedia.org/wiki/File:LDR.jpghttp://en.wikipedia.org/wiki/File:Photoresistor.svg


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2.PHOTOTRANSISTOR

Phototransistor is a type of photo sensitive device. Ordinary transistors exhibit photosensitive

effect when they are exposing to the light. In phototransistors also used that concept. The

structure of phototransistor is specifically optimized for photo application. Normally base

areas and collector areas of phototransistors are larger than that of normal transistors and alsothey are made using diffusion and iron implantation. In early phototransistors used

germanium and silicon and also that structure is known as homo-junction structure. In

modern photo transistors used type three-five materials such as gallium arsenide, also this

structure is known as heterojunction mesa-structure.

Fig no 03: homo-junction structure Fig no 04: heterojunction mesa-structure

The actual operation of a transistor depends on the biasing arrangement and light frequency.

For instance consider if a PN junction is forward biased, the increase in current due to thelight incident is considerably insignificant. But for the reversed biased PN junction that is

considerable. So the operation mode of phototransistor must be reversed biased. In a

phototransistor the base current is replaced with current induce due to the light intensity.

Also in this case the physical base can be kept as open terminal or it can be used to bias up to

the steady state level. The typical phototransistor and its circuit symbol are as shown below.

Fig no 05: Phototransistor Fig no 06: symbol of phototransistor


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The typical electro-optical characteristics curves are shown as bellow,

Fig no 07: Collector power dissipation vs

ambient temperature.

Fig no 08: Spectral sensitivity

Fig no 09: Relative collector current vs

ambient temperature

Fig no 10: Collector current vs Irradiance


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Fig no 11: Collector dark current vs ambient

temperature

Fig no 12: Collector current vs collector-

emitter voltage

Mostly phototransistors are low cost visible and near IR photo detection, available with gains

from 100to 1500, moderately fast response times and available in wide range.

APPLICATIONS

Write protect control in floppy drive

Margin controllers in printers

Monitor paper position in copiers

Monitor paper stack height in

copiers

LED light source

Security systems

Safety shields

Encoders

Photoelectric controllers

Remote residential electric meterreading

Coin counters

Lottery card readers

Position sensors in joysticks

Remote controllers

Camera shutter control


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3.0 CMOS SENSORS

CMOS sensor is active pixel sensor. An active pixel sensor is an image sensor and consisting

of an integrated circuit containing an array of pixel sensors, each pixel containing a photo

detector and an active amplifier. In CMOS sensors that integrating circuit construct with the

technology of complementary metal oxide semiconductor.

The fig no 13 shows a typical CMOS sensor. In CMOS sensors consists with pixilated metal

oxide semiconductors and they converts light in to electric charge and process into electronicsignals. The charge to voltage conversion takes place in each pixel of the sensor. The sensor

consist amplifiers, noise corrections and digitization. Therefore the output of the sensor would be

a digital.

APPLICATIONS

Security cameras

PC videoconferencing

Bar code scanners

Fax machine

Consumer scanners

Toys

Bio metric

Automotive uses

Fig no 13: CMOS sensor


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4.0 CCD SENSORS

Charge Couple Device (CCD) is a major technology for digital imaging. In a CCD sensor there

are photosensitive diodes on the surface of the sensor and it absorbs photon from light and

produce charges representing sensed pixels and CCD is used to read out these charges. Also the

pixel measurements are processed by the circuitry surrounding the sensor. Thereby mostfunctions of system takes place outside the sensor itself. When considering the structure of the

sensor it consists out of three layers, the bottom layer consists of photosites, the intermediate

layer consist layer of color filters that determines which color each site records and the top layer

consists with layer of micro lenses and it gathered the light. The typical CCD sensor is as shown

below.

Fig no 14: CCD image sensor

Generally CCD sensors are expensive, consume more power, produce high quality and low noise

images also more pixels and high fill factor than compared to the CMOS image sensors.

APPLICATIONS

Photographic applications

Scientific applications

Industrial applications


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5.0 THERMISTOR

Thermistor is a semiconductor device which is used for sense the temperature. Thermistors have

property of varies the resistance proportional to their temperature. There are two types of

thermistors, such Negative Coefficient of Resistance type and Positive temperature Coefficient

of resistance type.

4.1 NEGATIVE COEFFICIENT OF RESISTANCE TYPE

NTC thermistors have temperatures that vary inversely with resistance such that as the

temperature increases, the resistance decreases, and vice versa. These types of thermistors are

very often used for temperature control and indication. Mostly nickel, manganese, copper, iron

and cobalt are materials which are used for their construction.

Fig no 15: NTC Thermistor

APPLICATIONS

Resistance thermometers

Inrush-current limiting devices

Automotive applications

Digital thermostats

POSITIVE TEMPERATURE COEFFICIENT TYPE

PTC thermistors are the opposite of NTCs that is they have resistance increases with rise oftemperature and the resistance decrease with the fall of temperature. PTCs are constructed using

semiconductors combined with ceramics or polymers.

APPLICATIONS

Used in overload protect circuits


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Used in thermal switches

Ordinary thermometers

Fig no 16: PTC thermistors


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6.0 THERMOCOUPLE

The thermocouple is the most commonly used type of temperature sensing device.

Thermocouple is a simple device, easy to use and speed of response to changes in temperature,

also its small size. Thermocouples also have widest temperature range of all temperature sensors

from below -200 0C to well over 2000 0C.

Fig no 17: The Thermocouple

The principle of operation is that the junction of two dissimilar metals such as copper and

constantan, produce a thermo-electric effect that produce a few millivolts of potential

difference between two terminals. There are six types of thermocouples can be seen. Those are

E, J, K, N, T and U types. Each type of thermocouple construct by using different materials for

withstand on a specific temperature range.

APPLICATIONS

Thermic fluid heaters

Ovens

Boilers

Duct lines


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Thermocouple Sensor Color CodesExtension and Compensating Leads

CodeType

Conductors (+/-) SensitivityBritish

BS 1843:1952

E Nickel Chromium /Constantan

-200 to 900oC

J Iron / Constantan 0 to 750oC

KNickel Chromium /Nickel Aluminum

-200 to 1250oC

N Nicrosil / Nisil 0 to 1250oC

T Copper / Constantan -200 to 350oC

UCopper / Copper Nickel

Compensating for"S" and "R"

0 to 1450oC

Fig no 18: Thermocouple types and color codes


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7.0 STRAIN GAUGE

Strain gauges are used for the measurement of tensile and compressive strain in a body and can

therefore pick up expansion as well as contraction. Strain is caused in a body by internal or

external forces, pressures, moments, heat, or structural changes in the material. In general, most

types of strain gages depend on the proportional variance of electrical resistance to strain: thepiezoresistive or semi-conductor gage, the carbon-resistive gage, the bonded metallic wire, and

foil resistance gages.

Fig no 19: Strain Gauge

APPLICATIONS

Axial loading

Torsional bending

Bending beam

Torsional loading

Pressure diaphragm


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8.0 LOAD CELL

A load cell is a device that is used to convert a force in to electrical signal. This conversion is

indirect and happens in two stages through a mechanical arrangement, the force being sensed by

deforms a strain gauge. The strain gauge measures the deformation as an electrical signal,

because the strain changes the effective electrical resistance of the wire. A load cell usuallyconsists of four strain gauges in a Wheatstone bridge configuration. Also load cells of one strain

gauge are also available. The electrical signal output is typically in the order of a few millivolts

and requires amplification by an instrumentation amplifier before it can be used. The output of

the transducer is plugged into an algorithm to calculate the force applied to the transducer. There

are several types of load cells. Such as,

Compression load cells

S beam load cells

Platform and single point load

cells

Compression / tension load cells

Low profile load cells

Bending beam load cells

Canister load cells

Hydraulic load cells

Pneumatic load cells

The typical load cell is as shown below.

Fig no 20: Load cell

APPLICATIONS

used in tension controllers

Platform scales Hopper scales

Forklift

Wheel load

Automotive seat weight


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9.0 PROXIMITY SENSORS

A proximity sensor can detect metal targets approaching the sensor, without physical contact

with the target. Proximity sensors are roughly classified into the following three types according

to the operating principle: the high-frequency oscillation type using electromagnetic induction,

the magnetic type using a magnet, and the capacitance type using the change of capacitance.Among them the induction type and the capacitance type sensors are most commonly used.

INDUCTIVE PROXIMITY SENSORS

Inductive proximity sensors respond to ferrous and non - ferrous metal objects. They will also

detect metal through a layer of non - metal material. An inductive sensor consists of an oscillator

circuit and an output circuit including a switching device, all housed in a resin encapsulated

body. An essential part of the oscillator circuit is the inductance coil creating a magnetic field in

front of the sensing face. When the magnetic field is disturbed, the output circuit responds by

either closing the output switch (normally open version type NO) or by opening the outputswitch (normally closed version type NC).

Fig no 21: inductive proximity sensor

APPLICATIONS

High speed process control systems for the detection

In control systems for positioning and counting of ferrous and non-ferrous objects Used as limit switches


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CAPACITIVE PROXIMITY SENSORS

Capacitive sensors respond to any substance with a high dielectric constant (water, oil, fuel,

sugar, paper) without necessarily making physical contact. They are less suitable for polystyrene

and similar low density substances. Operation is based on an internal oscillator with two

capacitive plate-electrodes, tuned to respond when a substance approaches the sensing face.When the target is sensed, the output switch will either close to activate a load for a normally

open option or the switch will open to de-activate the load for a normally closed option. The

LED will illuminate when the output switch closes.

Fig no 22: Capacitive proximity sensor

APPLICATIONS

Level control of non-conductive liquids

Level control of granular substances

Sensing substances through a protective layer


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11.0 GYRO SENSOR

Gyro sensors, also known as angular rate sensors or angular velocity sensors are devices that

sense angular velocity. Also these sensors are used for primarily for navigation. The gyro sensors

can be measured the rotational velocity in 1, 2, or 3 directions. 3-axis gyroscopes are often

implemented with a 3-axis accelerometer to provide a full 6 degree-of-freedom motion trackingsystem.Gyroscopes have evolved from mechanical-inertial spinning devices consisting of rotors,

axles, and gimbals to various incarnations of electronic and optical devices.Each exploits some

physical property of the system allowing it to detect rotational velocity about some axis. There

are three types of gyro sensors are available.

Rotary gyro sensors

Vibrating structure gyro sensors

Optical gyro sensors

Fig no 24: Gyro sensor

The gyro sensors have following specifications,

Measurement range

Number of sensing axes

Nonlinearity

Shock survivability

Working temperature range

Bandwidth

Angular Random Walk (ARW)

Bias Drift

Bias Instability

APPLICATIONS

Used to maintain direction in tunnel mining

Inertial navigation systems

Stabilization of flying vehicles like radio-controlled helicopters or unmanned aerial

vehicles


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13.0 INFRARED SENSORS

The sensors which are detecting the infrared rays are known as infrared sensors. There are two

major types of infrared sensors can be seen. They are thermal detectors and photonic detectors.

Fig no 26: infrared sensors

In thermal detector type IR sensors, it sense the infrared radiations which are emit from heatsources and gives electric output according to the detected concentration of the IR rays.

Therefore it is used in thermal detection applications. Such as,

Flame detection

Gas detectors

Petroleum exploration

In temperature measuring equipment

Other type of IR detector is the photonic detectors. Mostly these types of applications must

consist with both IR senders and receivers. There applications can be mentioned as below,

In object detection

Wheel encoders

Contact-less tachometers

Component positioning applications

In remote controllers

Security devices


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14.0 MOTORS

In today motors are used for fulfill the rotary motion applications. There are several types of

motors. Mainly they can be categorized into two groups such as AC motors and DC motors.

14.1 DC MOTORS

Direct current motors are widely used in applications where the adjustable speeds required. And

also in dc motors can minimize the size of the mechanical brake so that it is used in where the

quick stop is needed. This is happen due to the dynamic breaking of dc motors. Also by using dc

motors it can be controlled speed smoothly quickly down to zero by accelerating in to the

opposite direction. The dc motors respond quickly to control signal changes because of the

property of high torque to inertia ratio. There are several types of dc motors,

Permanent magnet type dc motors

DC shunt motors

Dc series motors

DC compound motors

When the selecting a dc motor following factors should be considered.

Speed range of motor

Allowable speed variation

Torque requirement

Reversing

Duty rating

Peak torque

Heating

The prices of dc motors spread in vast range, price of the general permanent magnet type dc

motor are about 25 rupees. A typical dc motor is as shown below.

Fig no 27: DC motor


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DC MOTOR APPLICATIONS

DC shunt motors are used in lathes, fans, pumps disc and band saw drive requiring moderate

torques. The DC series motors are used in electric traction and high speed machines. Also the

DC compound motors are used in rolling mills and other loads requiring large momentary

torques.

14.2 AC MOTORS

As the name says these type motors works by using alternative current. The ac motors can be

dividing in to two major groups, which is asynchronous and synchronous. AC motors are widely

used in industry because of their simple design, low cost, reliable operation, easily found

replacements and variety of mounting.

The most common type of asynchronous motor is ac induction motor. And there are several

types of induction motors, such as single phase induction motors, three phase induction motors,

and polyphase motors. Their most common applications as below,

Conveyers

Steel mills machines

Polyethylene printing and laminating machines

Compressors

Centrifugal pumps

Centrifugal fans

There are two main types of synchronous motors, non-excited motors and DC-excited motors

and also the applications can be mentioned as bellow,

Constant speed requirement applications

Positioning machines

Robot actuators

Electric clocks


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14.3 STEPPER MOTORS

Stepper motor is device that converts electrical pulses in to mechanical movements. The normal

motors have continuous rotations but in steeper motors it rotates fixed angular increments. When

selecting stepper motor have to consider step size or step angle. Normally step resolutions have

90 degrees to a fraction of a degree, though 15 degrees to 1.8 degrees has been most common.There are three types of stepper motors,

Variable-reluctance

Permanent-magnet

Hybrid

The stepper motors are most widely used in whenever a controlled movement is required.


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15.0 PNEUMATIC ACTUATORS

Pneumatics is the most commonly used control type in the industry. In this case it is used

compressed air also the maximum air pressure must be below 10 bars. There are number of

pneumatic actuators can be seen. The function of the pneumatics actuators are converts energy

from the compressed air in to motions. There are several types of pneumatic actuators such ascylinders, rotary actuators, grippers and vacuum generators. Among them pneumatic cylinders

and rotary actuators are important.

15.1 PNEUMATIC CYLINDERS

Pneumatic cylinders are type of linear actuators and it converts fluid power into mechanical

power. Also they are used at high pressure and produce large force and precise movement. There

are three major types of cylinders,

Single acting cylinders

Double rod cylinders

Telescopic cylinders

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