Low Temperature Sensor

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Mini Project Report

LOW TEMPERATURE DETECTOR

Submitted By:

T. Ravi Teja(07331A04B3)

V.V.H. Tejaswi(07331A04C9)N. Hemanth Kamesh(08335A0405)

Y.

Srinivas(07331A04D0)


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I

ABSTRACT

This project is being developed as a part of control

of temperature in an industry where a high

temperature is to be maintained. In a manufacture

industry where a metal or a chemical is to be dealt

a particular high temperature must be maintained,

when ever there is a error in the temperature theworkers must be made aware of that, so that they

can make the necessary arrangements to maintain

the required temperature. Therefore an efficient

LOW TEMPERATURE SENSOR must be placed which

detects the fluctuations and alarm the workers of

the error that has occurred and they maintain thetemperature employing the necessary

arrangements.

This circiut deals with a parallel

operation of a 555timer with the switching

characteristics of a thermistor ,whose impedance

varies with the temperature on it and provides theapt switching accordingly, on the basis of which

the timer operates the alarm.


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II

Candidate Declaration

We hereby declare that the work presented in this

project titledLOW TEMPERATURE DETECTORsubmitted towardscompletion of mini-project insixth Semester of B.Tech (ECE) at MaharajaVijayaramGajapathi Raja College OfEngineering.It

is anauthentic record of our original work pursuedunder the guidanceof SirSrinivasgaru.

T. Ravi

Teja(07331A04B3)V.V.H. Tejaswi(07331A04C9)

N. Hemanth

Kamesh(08335A0405)


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Y.


III

Acknowledgement

First and foremost, I would like to express mysinceregratitude to my project guide, Sir SrinivasGaru. Iwas privileged toexperience a sustained enthusiastic and involvedinterest from his side.This fueled my enthusiasmeven further and encouraged us to boldlystep intowhat was a totally dark and unexplored expansebefore us.

I would also like to thank my seniors who wereready with a positive comment all the time,whether it was an off-hand comment toencourages or a constructive piece of criticism anda special thank to IEEE organization who arrangeda good database for mines.

Last but not least, I would like to thank the MVGRCollege of Engineering, ECE staff members andtheinstitute, in general, for extending a helping handat every junctureof need.


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T. RaviTeja(07331A04B3)

V.V.H. Tejaswi(07331A04C9)

N. Hemanth

Kamesh(08335A0405)

Y.


Table Of Contents

Abstract

.ICandidate declaration

IIAcknowledgement

..III

Project

IntroductionCircuit diagram


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Circuit working

Components

Component description

Data sheets

Applications

Project applications

Improvisation

Bibliography

LOW TEMPERATURE DETECTOR

INTRODUCTION

The main motto of this project is to make the

workers aware of the temperature levels of themanufacture unit on which they are working on. Aparticular manufacture unit (like a furnace) is to bemaintained at a particular temperature, which is the dutyof the worker or the employee to look after thetemperature to be maintained. Every occasion an


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employee cant check the temperature manually. So aparticular electronic device is required to observe thetemperature levels and inform any error is detected

This device is designed in such a manner that itworks only belaow a particular temperature and all thetemperatures above that threshold, the circiut is in its offstate. As the temperature falls down to the threshold thecirciut slowly comes to its on state from its off condition.As the temperature further falllsbelaow the thresholdlevel the circiut switches on and alarms the workersindicating an error in the temperature levels of the

furnace or the manufacturing unit.

The temperature levels are different atdifferent levels based on the application of the industry orthe manufacturing unit. This level is can be altered by thedesigner of the circiut by varying the parameters likeimpedance and capacitance that provide the biasing tothe switching unit and timer that are employed in it to

actuate the alarm according to the raise and fall of thetemperature in the unit. The components may not changemuch due to the temperature levels and applications butthere exists variations in the values of the passivecomponents that are to be employed.

CIRCIUT DIAGRAM


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M:..Speaker (Audiooutput)C1,C2:..0.01UFC3: 100UF

TH: Thermistor(Temperature sensor)

CIRCIUT OPERATION


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The circiut works on the basic principle of the thermistor.A thermistor can be defined as a resistor whoseimpedance varies with the temperature of theenvironment in which it is placed. It can be of two types,they are the negative temperature coefficient and thepositive coefficient. The negative coefficient thermistorincreases the impedance with the decrease intemperature whereas the positive coefficient thermistorincreases the impedance with increase in temperature.

The thermistor here used depends on the design required

for he manufacture unit or furnace.

The temperature of the environment which is to bemeasured is exposed to the thermistor and the terminalsare connected to a 555 timer which is being operated asan astablemultivibrator. As the temperature of theenvironment varies the impedance of the thermistorvaries accordingly and thereby the supply to the timer

which generates the pulses if necessary.The thermistor is biased appropriately with a 1Kpotentiometer which maintains the design parameters,mainly the threshold level of temperature to which thefurnace or the manufacturing unit should not reduce.

The transistor BC547 used is an NPN transistor which actsas a switch with the potentiometer as the collector

resistance which manages the threshold level thatswitches the device on and off. The fluctuations inimpedance make the transistor operate in active andsaturation region instantaneously making the alarm onand off respectively, according to the pulses generatedby the timer.


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The thermistor having a linear relation withtemperature may either decrease or increase with thedecrease with temperature, so a thermistor with positive

temperature coefficient is selected in order to provide thepath low impedance when the temperature decreases inthe environment. This replaces a short circuit in place ofthermistor when ever the temperature of theenvironment reduces the threshold temperature designedby the potentiometer, as desired for the application. Thezener connected in reverse bias to the thermistor which isconnected to the speaker through the timer device.

Therefore the circuit is placed in the furnaceby exposing the thermistor to the environment to whichthe temperature is to be observed. The potentiometer isset in a designed manner to provide the necessarythreshold level. The timer provides the pulses to alarmaccording the switching conditions of the transistor whenever the temperature at the thermistor falls below the

threshold level set as per the design.


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COMPONENTS

Thermistor 3296-3/8 Square Trim pot trimming

potentiometer

BC547 Transistor

555Timer

3V Zener diode

Capacitors (100UF and 0.01UF)Resistors (1Kohms and 4Kohms)

Speaker(8ohms and 1watt)

Battery (power supply 3V-9V)


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COMPONENTS DESCRIPTION ANDDATASHEETS

1. THERMISTOR

A thermistor is a type ofresistor whose resistancevaries with temperature. The word is a portmanteau of

thermal and resistor. Thermistors are widely used asinrush current limiters, temperature sensors, self-resetting overcurrent protectors, and self-regulatingheating elements.

Thermistors differ from resistance temperaturedetectors(RTD) in that the material used in a thermistor isgenerally a ceramic or polymer, while RTDs use pure

metals. The temperature response is also different; RTDsare useful over larger temperature ranges, whilethermistors typically achieve a higher precision within alimited temperature range.

Assuming, as a first-order approximation, that therelationship between resistance and temperature islinear, then:

Where

R = change in resistanceT= change in temperaturek= first-order temperature coefficient of resistance
http://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Portmanteauhttp://en.wikipedia.org/wiki/Thermal_(disambiguation)http://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Sensorshttp://en.wikipedia.org/wiki/Heating_elementhttp://en.wikipedia.org/wiki/Resistance_temperature_detectorhttp://en.wikipedia.org/wiki/Linearhttp://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Portmanteauhttp://en.wikipedia.org/wiki/Thermal_(disambiguation)http://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Sensorshttp://en.wikipedia.org/wiki/Heating_elementhttp://en.wikipedia.org/wiki/Resistance_temperature_detectorhttp://en.wikipedia.org/wiki/Linear


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Thermistors can be classified into two types, dependingon the sign ofk. Ifkis positive, the resistance increaseswith increasing temperature, and the device is called apositive temperaturecoefficient (PTC) thermistor, or

posistor. Ifkis negative, the resistance decreases withincreasing temperature, and the device is called anegative temperature coefficient (NTC) thermistor.Resistors that are not thermistors are designed to have akas close to zero as possible (smallest possible k), sothat their resistance remains nearly constant over a widetemperature range.

Instead of the temperature coefficient k, sometimes thetemperature coefficient of resistance (alpha) or T isused.

Structure and Function of PTC Thermistor

PTC (Positive Temperature Coefficient of Resistance) thermistor is a

kind of positive temperature coefficient thermistor, mainly made up of

BaTiO3 ceramics. BaTiO3 ceramics is a kind of typical ferroelectric

material with the resistivity of greater than 1012.cm under normaltemperature, through semi-conductor doping, it has a strong PTC

efficacy, that means it has extremely low resistance under normal

temperature, but it experiences a sudden and large mutation around

Curie temperature (also called switch temperature, or reference

temperature) as ambient temperature rises. This is because a barrier layer

induced by the surface state exists on the crystal particle border of the

multicrystal BaTiO3 semiconductor material. Under Curie temperature,

the high-resistance crystal boundary has ferroelectric characteristics withgreat dielectric constant and low potential barrier, electrons can easily

penetrate the potential barrier and corresponding materials have low

resistivity. When above Curie temperature, crystal lattice occurs at the

high-resistance layer and the ferroelectric constant decreases quickly.

The potential barrier increases because the dielectric constant drops in
http://en.wikipedia.org/wiki/Positive_numberhttp://en.wikipedia.org/wiki/Temperature_coefficient#Positive_temperature_coefficient_of_resistancehttp://en.wikipedia.org/wiki/Temperature_coefficient#Negative_temperature_coefficienthttp://en.wikipedia.org/wiki/Positive_numberhttp://en.wikipedia.org/wiki/Temperature_coefficient#Positive_temperature_coefficient_of_resistancehttp://en.wikipedia.org/wiki/Temperature_coefficient#Negative_temperature_coefficient


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accordance with the Curie-Weiss Law. With the dramatic increase of the

barrier height, it becomes difficult for electrons to pass potential barrier

and the resistivity of the corresponding materials rises dramatically. This

behaves as the PTC efficacy of the material in a macro manner. Due to

this property, the PTC thermistor is widely used in industrial electronicequipment and household appliances. The field of its application is

classified in light of the three basic electric performances of the PTC

thermistors. The fundamental parameters are as indicated in the

following matrix diagram (Fig.1).

Rn - Room temperature zero-power

resistance

Rmin - Minimum zero-power resistance

Tb - Curie temperature

Rb - Switch resistance value Rb=2Rn

Rmax - Maximum resistance

Tp - Poise point temperature

- Lift-drag ratio is LgRmax/Rmin

Applications

PTC thermistors can be used as current-limitingdevices for circuit protection, as replacements forfuses. Current through the device cause a smallamount of resistive heating. If the current is largeenough to generate more heat than the device canlose to its surroundings, the device heats up, causing

Fig.1 PTC Thermistor Resistance vs.

Temperature Curve


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its resistance to increase, and therefore causing evenmore heating. This creates a self-reinforcing effectthat drives the resistance upwards, reducing thecurrent and voltage available to the device.

NTC thermistors are used as resistancethermometers in low-temperature measurements ofthe order of 10 K.

NTC thermistors can be used as inrush-currentlimiting devices in power supply circuits. Theypresent a higher resistance initially which preventslarge currents from flowing at turn-on, and then heatup and become much lower resistance to allow

higher current flow during normal operation. Thesethermistors are usually much larger than measuringtype thermistors, and are purposely designed for thisapplication.

NTC thermistors are regularly used in automotiveapplications. For example, they monitor things likecoolant temperature and/or oil temperature insidethe engine and provide data to the ECU and,

indirectly, to the dashboard. They can be also usedto monitor temperature of an incubator.
http://en.wikipedia.org/wiki/Resistance_thermometerhttp://en.wikipedia.org/wiki/Resistance_thermometerhttp://en.wikipedia.org/wiki/Resistance_thermometerhttp://en.wikipedia.org/wiki/Resistance_thermometer


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2. 3296-3/8 Square Trimpot TrimmingPotentiometer

A potentiometer (colloquially known as a "pot") is athree-terminalresistor with a sliding contact that forms anadjustable voltage divider. If only two terminals are used(one side and the wiper), it acts as a variable resistoror rheostat. Potentiometers are commonly used tocontrol electrical devices such as volume controls onaudio equipment. Potentiometers operated by amechanism can be used as position transducers, forexample, in ajoystick.

Potentiometers are rarely used to directly controlsignificant power (more than a watt). Instead they areused to adjust the level of analog signals (e.g. volume

controls on audio equipment), and as control inputs forelectronic circuits. For example, a light dimmer uses apotentiometer to control the switching of aTRIAC and soindirectly control the brightness of lamps.

APPLICATIONS
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Potentiometers are widely used as user controls, and maycontrol a very wide variety of equipment functions. Thewidespread use of potentiometers in consumerelectronics has declined in the 1990s, with digital controls

now more common. However they remain in manyapplications, such as volume controls and as positionsensors.

AUDIO CONTROL

One of the most common uses for modern low-power

potentiometers is as audio control devices. Both linearpots (also known as "faders") and rotary potentiometers(commonly called knobs) are regularly used to adjustloudness, frequency attenuation and other characteristicsof audio signals.

The 'log pot' is used as the volume control in audioamplifiers, where it is also called an "audio taper pot",

because the amplitude response of the human ear is alsologarithmic. It ensures that, on a volume control marked0 to 10, for example, a setting of 5 sounds half as loud asa setting of 10. There is also an anti-log potor reverseaudio taperwhich is simply the reverse of a log pot. It isalmost always used in a ganged configuration with a logpot, for instance, in an audio balance control.

TelevisionPotentiometers were formerly used to control picturebrightness, contrast, and color response. A potentiometerwas often used to adjust "vertical hold", which affected
http://en.wikipedia.org/wiki/Audio_amplifierhttp://en.wikipedia.org/wiki/Audio_amplifierhttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Earhttp://en.wikipedia.org/wiki/Audio_amplifierhttp://en.wikipedia.org/wiki/Audio_amplifierhttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Ear


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the synchronization between the receiver's internalsweep circuit and the received picture signal.

Transducers

Potentiometers are also very widely used as a part ofdisplacementtransducers because of the simplicity ofconstruction and because they can give a large outputsignal.

Computation

In analog computers, high precision potentiometers are used toscale intermediate results by desired constant factors, or to set initialconditions for a calculation. A motor-driven potentiometer may be used

as a function generator, using a non-linear resistance card to supply

approximations to trigonometric functions.

3. 555 Timer

The 555 Timer IC is an integrated circuit (chip)implementing a variety oftimer and multivibratorapplications. The IC was designed by Hans R. Camenzindin 1970 and brought to market in 1971 by Signetics (later

acquired by Philips). The original name was the SE555(metal can)/NE555 (plastic DIP) and the part wasdescribed as "The IC Time Machine.It has been claimedthat the 555 gets its name from the three 5k resistorsused in typical early implementations, but HansCamenzind has stated that the number was arbitrary. The
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part is still in wide use, thanks to its ease of use, low priceand good stability. As of 2003, it is estimated that 1billion units are manufactured every year.

Depending on the manufacturer, the standard 555package includes over 20 transistors, 2 diodes and 15resistors on a silicon chip installed in an 8-pin mini dual-in-line package (DIP-8). Variants available include the 556(a 14-pin DIP combining two 555s on one chip), and the558 (a 16-pin DIP combining four slightly modified 555swith DIS & THR connected internally, and TR falling edgesensitive instead of level sensitive).

Ultra-low power versions of the 555 are also available,such as the 7555 and TLC555. The 7555 requires slightlydifferent wiring using fewer external components and lesspower.

The 555 has three operating modes:

Monostable mode: in this mode, the 555 functions as

a "one-shot". Applications include timers, missingpulse detection, bounce free switches, touchswitches, frequency divider, capacitancemeasurement, pulse-width modulation (PWM) etc

Astable - free running mode: the 555 can operate asan oscillator. Uses include LED and lamp flashers,pulse generation, logic clocks, tone generation,security alarms, pulse position modulation, etc.

Bistable mode or Schmitt trigger: the 555 canoperate as a flip-flop, if the DIS pin is not connectedand no capacitor is used. Uses include bounce freelatched switches, etc.
http://en.wikipedia.org/wiki/1000000000_(number)http://en.wikipedia.org/wiki/1000000000_(number)http://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/DIP-8http://en.wikipedia.org/wiki/Monostablehttp://en.wikipedia.org/wiki/Astablehttp://en.wikipedia.org/wiki/Oscillatorhttp://en.wikipedia.org/wiki/LEDhttp://en.wikipedia.org/wiki/Pulse_position_modulationhttp://en.wikipedia.org/wiki/Bistablehttp://en.wikipedia.org/wiki/Schmitt_triggerhttp://en.wikipedia.org/wiki/Flip-flop_(electronics)http://en.wikipedia.org/wiki/1000000000_(number)http://en.wikipedia.org/wiki/1000000000_(number)http://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/DIP-8http://en.wikipedia.org/wiki/Monostablehttp://en.wikipedia.org/wiki/Astablehttp://en.wikipedia.org/wiki/Oscillatorhttp://en.wikipedia.org/wiki/LEDhttp://en.wikipedia.org/wiki/Pulse_position_modulationhttp://en.wikipedia.org/wiki/Bistablehttp://en.wikipedia.org/wiki/Schmitt_triggerhttp://en.wikipedia.org/wiki/Flip-flop_(electronics)


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4. 3V Zener diode

A Zener diode is a type ofdiode that permits current notonly in the forward direction like a normal diode, but alsoin the reverse direction if the voltage is larger than thebreakdown voltage known as "Zener knee voltage" or"Zener voltage". The device was named after ClarenceZener, who discovered this electrical property.

A conventional solid-state diode will not allow significant

current if it is reverse-biased below its reverse breakdownvoltage. When the reverse bias breakdown voltage isexceeded, a conventional diode is subject to high currentdue to avalanche breakdown. Unless this current islimited by circuitry, the diode will be permanentlydamaged. In case of large forward bias (current in thedirection of the arrow), the diode exhibits a voltage dropdue to its junction built-in voltage and internal resistance.

The amount of the voltage drop depends on thesemiconductor material and the doping concentrations.

A Zener diode exhibits almost the same properties,except the device is specially designed so as to have agreatly reduced breakdown voltage, the so-called Zenervoltage. By contrast with the conventional device, areverse-biased Zener diode will exhibit a controlledbreakdown and allow the current to keep the voltage

across the Zener diode at the Zener voltage. Forexample, a diode with a Zener breakdown voltage of 3.2V will exhibit a voltage drop of 3.2 V if reverse biasvoltage applied across it is more than its Zener voltage.

The Zener diode is therefore ideal for applications such asthe generation of a reference voltage (e.g. for an
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amplifier stage), or as a voltage stabilizer for low-currentapplications.

The Zener diode's operation depends on the heavy

doping of its p-n junction allowing electrons to tunnelfrom the valence band of the p-type material to theconduction band of the n-type material. In the atomicscale, this tunneling corresponds to the transport ofvalence band electrons into the empty conduction bandstates; as a result of the reduced barrier between thesebands and high electric fields that are induced due to therelatively high levels of dopings on both sides. The

breakdown voltage can be controlled quite accurately inthe doping process. While tolerances within 0.05% areavailable, the most widely used tolerances are 5% and10%. Breakdown voltage for commonly available zenerdiodes can vary widely from 1.2 volts to 200volts.

Current-voltage characteristic of a Zener diode with a breakdown voltage of

17 volt. Notice the change of voltage scale between the forward biased(positive) direction and the reverse biased (negative) direction.

5. Capacitor
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A capacitor (formerly known as condenser) is apassiveelectronic component consisting of a pair ofconductors separated by a dielectric (insulator). When apotential difference (voltage) exists across the

conductors, an electric field is present in the dielectric.This field stores energy and produces a mechanical forcebetween the conductors. The effect is greatest whenthere is a narrow separation between large areas ofconductor; hence capacitor conductors are often calledplates.

An ideal capacitor is characterized by a single constant

value, capacitance, which is measured in farads. This isthe ratio of the electric charge on each conductor to thepotential difference between them. In practice, thedielectric between the plates passes a small amount ofleakage current. The conductors and leads introduce anequivalent series resistance and the dielectric has anelectric field strength limit resulting in a breakdownvoltage.

Capacitors are widely used in electronic circuits to blockdirect current while allowing alternating current to pass,to filter out interference, to smooth the output ofpowersupplies, and for many other purposes. They are used inresonant circuits in radio frequency equipment to selectparticular frequencies from a signal with manyfrequencies.
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Capacitor packages: SMD ceramic at top left; SMD tantalum at bottom left;through-hole tantalum at top right; through-hole electrolytic at bottom right.Major scale divisions are cm.

6. Resistor

A resistor is a two-terminalelectronic component thatproduces a voltage across its terminals that isproportional to the electric current passing through it inaccordance with Ohm's law:

V= IR

Resistors are elements ofelectrical networks andelectronic circuits and are ubiquitous in most electronicequipment. Practical resistors can be made of variouscompounds and films, as well as resistance wire (wiremade of a high-resistivity alloy, such as nickel/chrome).

The primary characteristics of a resistor are theresistance, the tolerance, maximum working voltage andthe power rating. Other characteristics include

temperature coefficient, noise, and inductance. Less well-known is critical resistance, the value below which powerdissipation limits the maximum permitted current flow,and above which the limit is applied voltage. Criticalresistance is determined by the design, materials anddimensions of the resistor.
http://en.wikipedia.org/wiki/Surface-mount_technologyhttp://en.wikipedia.org/wiki/Through-holehttp://en.wikipedia.org/wiki/Terminal_(electronics)http://en.wikipedia.org/wiki/Terminal_(electronics)http://en.wikipedia.org/wiki/Electronic_componenthttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Proportionality_(mathematics)#Direct_proportionhttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Ohm's_lawhttp://en.wikipedia.org/wiki/Electrical_networkshttp://en.wikipedia.org/wiki/Resistance_wirehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Engineering_tolerance#Electrical_component_tolerancehttp://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Temperature_coefficienthttp://en.wikipedia.org/wiki/Electrical_noisehttp://en.wikipedia.org/wiki/Inductancehttp://en.wikipedia.org/w/index.php?title=Critical_resistance&action=edit&redlink=1http://en.wikipedia.org/wiki/Surface-mount_technologyhttp://en.wikipedia.org/wiki/Through-holehttp://en.wikipedia.org/wiki/Terminal_(electronics)http://en.wikipedia.org/wiki/Electronic_componenthttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Proportionality_(mathematics)#Direct_proportionhttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Ohm's_lawhttp://en.wikipedia.org/wiki/Electrical_networkshttp://en.wikipedia.org/wiki/Resistance_wirehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Engineering_tolerance#Electrical_component_tolerancehttp://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Temperature_coefficienthttp://en.wikipedia.org/wiki/Electrical_noisehttp://en.wikipedia.org/wiki/Inductancehttp://en.wikipedia.org/w/index.php?title=Critical_resistance&action=edit&redlink=1


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Resistors can be integrated into hybrid and printedcircuits, as well as integrated circuits. Size, and positionof leads (or terminals) are relevant to equipmentdesigners; resistors must be physically large enough not

to overheat when dissipating their power.

7. BC547 Transistor

A bipolar (junction) transistor (BJT) is a three-terminalelectronic device constructed ofdopedsemiconductormaterial and may be used in amplifying or switchingapplications. Bipolartransistors are so named becausetheir operation involves both electrons and holes. Chargeflow in a BJT is due to bidirectional diffusion ofchargecarriers across a junction between two regions ofdifferent charge concentrations. This mode of operation iscontrasted with unipolar transistors, such as field-effecttransistors, in which only one carrier type is involved incharge flow due to drift. By design, most of the BJT

collector current is due to the flow of charges injectedfrom a high-concentration emitter into the base wherethey are minority carriers that diffuse toward thecollector, and so BJTs are classified as minority-carrierdevices.

APPLICATIONS

The BJT remains a device that excels in someapplications, such as discrete circuit design, due to thevery wide selection of BJT types available, and because ofits high trans conductance and output resistancecompared to MOSFETs. The BJT is also the choice fordemanding analog circuits, especially for very-high-
http://en.wikipedia.org/wiki/Hybrid_circuithttp://en.wikipedia.org/wiki/Printed_circuit_boardhttp://en.wikipedia.org/wiki/Printed_circuit_boardhttp://en.wikipedia.org/wiki/Integrated_circuitshttp://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Doping_(Semiconductors)http://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Electronic_amplifierhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Electron_holehttp://en.wikipedia.org/wiki/Diffusionhttp://en.wikipedia.org/wiki/Charge_carriers_in_semiconductorshttp://en.wikipedia.org/wiki/Charge_carriers_in_semiconductorshttp://en.wikipedia.org/wiki/Field-effect_transistorhttp://en.wikipedia.org/wiki/Field-effect_transistorhttp://en.wikipedia.org/wiki/Drift_velocityhttp://en.wikipedia.org/wiki/Minority_carrierhttp://en.wikipedia.org/wiki/Transconductancehttp://en.wikipedia.org/wiki/MOSFEThttp://en.wikipedia.org/wiki/Very-high-frequencyhttp://en.wikipedia.org/wiki/Hybrid_circuithttp://en.wikipedia.org/wiki/Printed_circuit_boardhttp://en.wikipedia.org/wiki/Printed_circuit_boardhttp://en.wikipedia.org/wiki/Integrated_circuitshttp://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Doping_(Semiconductors)http://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Electronic_amplifierhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Electron_holehttp://en.wikipedia.org/wiki/Diffusionhttp://en.wikipedia.org/wiki/Charge_carriers_in_semiconductorshttp://en.wikipedia.org/wiki/Charge_carriers_in_semiconductorshttp://en.wikipedia.org/wiki/Field-effect_transistorhttp://en.wikipedia.org/wiki/Field-effect_transistorhttp://en.wikipedia.org/wiki/Drift_velocityhttp://en.wikipedia.org/wiki/Minority_carrierhttp://en.wikipedia.org/wiki/Transconductancehttp://en.wikipedia.org/wiki/MOSFEThttp://en.wikipedia.org/wiki/Very-high-frequency


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frequency applications, such as radio-frequency circuitsfor wireless systems. Bipolar transistors can be combinedwith MOSFETs in an integrated circuit by using a BiCMOSprocess of wafer fabrication to create circuits that take

advantage of the application strengths of both types oftransistor.

Temperature sensors

Because of the known temperature and currentdependence of the forward-biased baseemitter junctionvoltage, the BJT can be used to measure temperature by

subtracting two voltages at two different bias currents ina known ratio.

Logarithmic converters

Because baseemitter voltage varies as the log of thebaseemitter and collectoremitter currents, a BJT canalso be used to compute logarithmsand anti-logarithms. Adiode can also perform these nonlinear functions, but the

transistor provides more circuit flexibility.

PROJECT APPLICATIONS

The design model presented has a wide range ofapplication in the field of industry and manufacturingunits. The temperature maintenance plays a key role inany kind of industrial plant.

For example when a manufacturing unit like steelplant is considered we need the temperature of thefurnace to maintained at a high temperature.
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Though the parameters may change the design andcircuitry remains the same.

The temperature of the metal to be melted and thetemperature at which the chemical reaction takesplace can also be maintained by the circuit.

The temperature in room heaters and thermal unitscan use this circuit in order to check if the

temperature of the environment doesnt fall belowthe threshold level

The incubators require necessary warmth for theorganism to survive; this can be checked all the timeusing this circuit.

Storing a chemical at a particular temperature issometimes necessary, where the temperature shouldnot fall, this circuit is applicable.

IMPROVISATIONSThe circuit can be extended by adding a smoke detectorto it. If at all any case of excess heat exists, the workerswill be aware of it also. So the extension using a smokedetector will maintain the circuit at a very efficient


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condition avoiding over heat and also maintain theoperation at the required threshold level.


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Low Temperature Sensor

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Transcript of Low Temperature Sensor