1. 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
2. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
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.
3. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
SVKM’s NMIMS
CIRCUIT DIAGRAM
4. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
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.
6. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
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.
7. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
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 :-
8. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
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.
9. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
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.
10. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
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 +)
11. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
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.
12. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
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.
13. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
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.
14. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
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.
15. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
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.
16. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
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.
17. A project report on Heat Sensitive Switch
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING,MPSTME
SVKM’s NMIMS
REFERENCE
www.google.com
www.wikipedia.org
www.pdfmachine.com
www.efymag.com
www.datasheets4u.com
