Heat Sensitive Switch

A project report on Heat Sensitive Switch

DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME

SVKM’s NMIMS

Heat Sensitive Switch

By

SUROVIT ROY (ROLL NO.743)

RAHUL VIRMANI (ROLL NO. 727)

HONEY SONI (ROLL NO.714)

Under the guidance of:

PROF. SHASHIKANT S. PATIL

Department of Electronics and Telecommunication Engineering

SVKM’s Mukesh Patel School of Technology Management and Engineering

Academic Year 2011-12



SVKM’s NMIMS

DESCRIPTION

The project idea put forth here can be used to turn on (or

off) the load connected across the relay at a predetermined

temperature. At the heart of this heat sensitive switch is IC

LM35, which is a linear temperature sensor and linear

temperature to voltage converter circuit.

The converter provides accurately linear and directly

proportional output signal in millivolts over temperature

range of 0 deg. C to 155 deg. C. It develops an output voltage

of 10mV per degree centigrade change in the ambient

temperature. Therefore the output voltage varies from 0 mV

at 0 deg. C to 1V at 100 deg. C at any voltage measurement

circuit connected across the output pins can read the

temperature directly.



SVKM’s NMIMS

CIRCUIT DIAGRAM



SVKM’s NMIMS

CONCEPT

IC 1 temperature tracking output is applied to the non-inverting

input (pin3) of the comparator IC 2. The inverting input (pin 2)

of IC 2 is connected across the positive supply rails via a

voltage divider network formed by potentiometer VR1.The

voltage at pin 2 is used as reference level for comparator

against the output supplied by IC 1.

So, if pin 3 of IC 2 receives a voltage lower than the set level, its

output goes low (approximately 650 mV). This low level is

applied to the input of load-relay driver comprising NPN

transistors T1 and T2 and they are in cut-off. Hence, relay RL1

is in the de-energized state, keeping mains supply to load ‘off’ as

long as the temperature at the sensor is low. Conversely, if pin 3

input receives a voltage higher than the set level, its output goes

high (approximately 2200 mV) and the load is turned ‘on’. This

happens when IC 1 is at a higher temperature and its output

voltage is also higher than the set level at pin 2 of IC 2.

Suppose, we want to switch on the load at 50 C. Heat the sensor

with soldering iron until 50 mV is obtained at pin 2 of the

sensor. Simultaneously, we have to vary VR1 such that pin 6 of

CA3130 becomes high. This will enable to energize the relay

and turn on the load. Keep the setting of VR1 at this position for

future use, so that whenever the temperature reaches 50 C, the

circuit will automatically switch on the load.



SVKM’s NMIMS

COMPONENTS USED

SEMICONDUCTORS :- IC1 LM35 temperature sensor IC2 CA3130 comparator IC3 7805 DC voltage regulator T1 BC 549 NPN transistor T2 BD 139 NPN transistor D1-D5 1N4007 rectifier diode LED1, LED2 5mm light emitting diode LED1, LED2 5mm light emitting diode

RESISTORS :- (all 1/4-watt,+ 5% carbon) R1 1.2 kilo-ohm R2 1.0 kilo-ohm R3 12 kilo-ohm R4 680 kilo-ohm R5 15 kilo-ohm R6,R8,R9 1.5 kilo-ohm

R7 1.0 kilo-ohm

CAPACITORS :- C1 47 micro farad(electrolytic) C2 1 micro farad(electrolytic) C3 0.17 micro farad(ceramic dis) C4 1000 micro farad, 35V(electrolytic)

MISCELLANEOUS :-

X1 230V AC to 0-12V AC, 250mA secondary transformer RL1 12V, 200 ohm 1 C/o relay



SVKM’s NMIMS

DESCRIPTION OF COMPONENTS

TEMPERATURE SENSOR- THE LM35 :-

The LM35 is an integrated circuit sensor that can be used to measure

temperature with an electrical output proportional to the temperature. The LM35 series are precision integrated-circuit temperature sensors,

whose output voltage is linearly proportional to the Celsius (Centigrade)

temperature. The LM35 thus has an advantage over linear temperature

sensors calibrated in ° Kelvin, as the user is not required to subtract a

large constant voltage from its output to obtain convenient Centigrade

scaling. The LM35 does not require any external calibration or

trimming to provide typical accuracies of ±¼°C at room temperature

and ±¾°C over a full -55 to +150°C temperature range. Low cost is

assured by trimming and calibration at the wafer level. The LM35's low

output impedance, linear output, and precise inherent calibration make

interfacing to readout or control circuitry especially easy. It can be used

with single power supplies, or with plus and minus supplies. As it draws

only 60 μA from its supply, it has very low self-heating, less than 0.1°C

in still air. The LM35 is rated to operate over a -55° to +150°C

temperature range, while the LM35C is rated for a -40° to +110°C

range (-10° with improved accuracy). The LM35 series is available

packaged in hermetic TO-46 transistor packages, while the LM35C,

LM35CA, and LM35D are also available in the plastic TO-92 transistor

package. The LM35D is also available in an 8-lead surface mount small

outline package and a plastic TO-220 package.



SVKM’s NMIMS

OPERATION OF LM35 :-

It has an output voltage that is proportional to the Celsius

temperature.

The scale factor is .01V/oC

The LM35 does not require any external calibration or trimming

and maintains an accuracy of +/-0.4 oC at room temperature and

+/- 0.8 oC over a range of 0 oC to +100 oC.

Another important characteristic of the LM35DZ is that it draws

only 60 micro amps from its supply and possesses a low self-

heating capability. The sensor self-heating causes less than 0.1 oC

temperature rise in still air.

TYPICAL PERFORMANCE OF LM35 :-



SVKM’s NMIMS

TRANSISTOR :-

A Bipolar Transistor essentially consists of a pair of PN Junction Diodes

that are joined back-to-back. This forms a sort of a sandwich where one

kind of semiconductor is placed in between two others. There are

therefore two kinds of Bipolar sandwich, the NPN and PNP varieties.

The three layers of the sandwich are conventionally called the Collector,

Base, and Emitter. The reasons for these names will become clear later

once we see how the transistor works. Some of the basic properties exhibited by a Bipolar Transistor are

immediately recognisable as being diode-like. However, when the

'filling' of the sandwich is fairly thin some interesting effects become

possible that allow us to use the Transistor as an Amplifier or Switch.



SVKM’s NMIMS

LIGHT EMITTING DIODE :-

LED's are special diodes that emit light when connected in a circuit.

They are frequently used as "pilot" lights in electronic appliances to

indicate whether the circuit is closed or not. A a clear (or often colored)

epoxy case enclosed the heart of an LED, the semi-conductor chip. The two wires extending below the LED epoxy enclosure, or the "bulb"

indicate how the LED should be connected into a circuit. The negative

side of an LED lead is indicated in two ways: 1) by the flat side of the

bulb, and 2) by the shorter of the two wires extending from the LED. The

negative lead should be connected to the negative terminal of a battery.

LED's operate at relative low voltages between about 1 and 4 volts, and

draw currents between about 10 and 40 milliamperes. Voltages and

currents substantially above these values can melt a LED chip.



SVKM’s NMIMS

CAPACITORS :-

Capacitors store electric charge. They are used with resistors in timing

circuits because it takes time for a capacitor to fill with charge. They are

used to smooth varying DC supplies by acting as a reservoir of charge.

They are also used in filter circuits because capacitors easily pass AC

(changing) signals but they block DC (constant) signals.

Capacitance

This is a measure of a capacitor's ability to store charge. A large

capacitance means that more charge can be stored. Capacitance is

measured in farads, symbol F. However 1F is very large, so prefixes are

used to show the smaller values. Three prefixes (multipliers) are used, μ (micro), n (nano) and p (pico):

μ means 10-6 (millionth), so 1000000μF = 1F n means 10-9 (thousand-millionth), so 1000nF = 1μF p means 10-12 (million-millionth), so 1000pF = 1nF

There are many types of capacitor but they can be split into two groups,

polarised and unpolarised. Each group has its own circuit symbol. Polarised capacitors (large values, 1μF +)



SVKM’s NMIMS

TRANSFORMER :-

A transformer is an electrical device that transfers energy from one

circuit to another by magnetic coupling with no moving parts. A

transformer comprises two or more coupled windings, or a single tapped

winding and, in most cases, a magnetic core to concentrate magnetic

flux. A changing current in one winding creates a time-varying magnetic

flux in the core, which induces a voltage in the other windings. Michael Faraday built the first transformer, although he used it only to

demonstrate the principle of electromagnetic induction and did not

foresee the use to which it would eventually be put.



SVKM’s NMIMS

RELAYS :-

A relay is an electrical switch that opens and closes under control of

another electrical circuit. In the original form, the switch is operated by

an electromagnet to open or close one or many sets of contacts. It was

invented by Joseph Henry in 1835. Because a relay is able to control an

output circuit of higher power than the input circuit, it can be

considered, in a broad sense, to be a form of electrical amplifier.

Operation

When a current flows through the coil, the resulting

magnetic field attracts an armature that is mechanically

linked to a moving contact. The movement either makes

or breaks a connection with a fixed contact. When the

current to the coil is switched off, the armature is

returned by a force that is half as strong as the magnetic

force to its relaxed position. Usually this is a spring, but

gravity is also used commonly in industrial motor

starters. Relays are manufactured to operate quickly. In

a low voltage application, this is to reduce noise. In a

high voltage or high current application, this is to reduce

arcing.

If the coil is energized with DC, a diode is frequently

installed across the coil, to dissipate the energy from the

collapsing magnetic field at deactivation, which would

otherwise generate a spike of voltage and might cause

damage to circuit components. If the coil is designed to

be energized with AC, a small copper ring can be crimped

to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum

pull on the armature during the AC.



SVKM’s NMIMS

VOLTAGE REGULATORS :- A voltage regulator is an electrical regulator designed to

automatically maintain a constant voltage level. It may use an electromechanical mechanism, or passive or active

electronic components. Depending on the design, it may be used to

regulate one or more AC or DC voltages. With the exception of shunt regulators, all voltage regulators operate by

comparing the actual output voltage to some internal fixed reference

voltage. Any difference is amplified and used to control the regulation

element. This forms a negative feedback servo control loop. If the output

voltage is too low, the regulation element is commanded to produce a

higher voltage. If the output voltage is too high, the regulation element

is commanded to produce a lower voltage. In this way, the output

voltage is held roughly constant. The control loop must be carefully

designed to produce the desired tradeoff between stability and speed of

response.



SVKM’s NMIMS

COMPARATORS :-

In electronics, a comparator is a device which compares two voltages

or currents and switches its output to indicate which is larger. More

generally, the term is also used to refer to a device that compares two

items of data.

A standard op-amp without negative feedback can be used as a

comparator, as indicated in the following diagram. When the non-inverting input (V+) is at a higher voltage than the

inverting input (V-), the high gain of the op-amp causes it to output the

most positive voltage it can. When the non-inverting input (V+) drops

below the inverting input (V-), the op-amp outputs the most negative

voltage it can.



SVKM’s NMIMS

WORKING

At the heart of this heat-sensitive switch is IC LM35 (IC1), which is

linear temperature sensor and linear temperature-to-voltage converter

circuit.

The input and ground pins of this heat-to-voltage converter IC are

connected across the regulated power supply rails and decoupled by R1

and C1. Its temperature-tracking output is applied to the non-inverting

input (pin 3) of the comparator built around IC2. The inverting input

(pin 2) of IC2 is connected across the positive supply rails via a voltage

divider network formed by potmeter VR1.

Since the wiper of potmeter VR1 is connected to the inverting input of

IC2. The voltage presented to this pin is linearly variable. This voltage

is used as a reference level for the comparator against the output

supplied by IC1.

So if the non-inverting input of IC2 receives a voltage lower than the set

level, its output goes low(approximately 650mV). This low level is

applied to the input of load-relay driver comprising npn transistors T1

and T2. The low level presented at the base of the transistor T1 keeps it

non-conductive. Since T2 receives forward bias voltage via the emitter

of T1, it is also kept non-conductive. Hence, relay RL1 is de-energised

state, keeping mains supply to the load ‘off’ as long as the temperature

at sensor is low.

Conversely, if the non-inverting input receives a voltage higher than the

set level, its output goes high (approximately 220mV) and the load is

turned ‘on’. This happens when IC1 is at a higher temperature and its

output voltage also higher than the set level at the inverting input of IC2.

so the load is turned on as soon as the ambient temperature rises above

the set level. Capacitor C3 at this pin helps iron out any ripple that

passes through the positive supply rail to avoid errors in the circuit

operation.



SVKM’s NMIMS

By adjusting potmeter VR1 and thereby varying the reference voltage

level at the inverting input pin pf IC1, the temperature threshold at

which energisation of the relay is required can be set. As this setting is

linear, the knob of potmeter VR1 can be provided with linear dial

calibrated in degrees centigrade. Therefore any temperature level can

be selected and constantly monitored for external actions like turning on

a room-heater in winter or a room-cooler in summer. The circuit can

also be used to activate emergency fire extinguishers, if positioned at the

probable fire accident site.

The circuit can be modified to operate any electrical appliance. In that

case, relay RL1 must be heavy-duty type with appropriately rate

contacts to match the power demands of the load to be operated.



SVKM’s NMIMS

REFERENCE

www.google.com

www.wikipedia.org

www.pdfmachine.com

www.efymag.com

www.datasheets4u.com

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Heat Sensitive Switch