International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
Smart Heater
N.BHAVANA #1,B.SURESH*2
#
Department of Electronics and Communication Engineering, K L University
Vaddeswaram, Guntur, AP, India
*
Asst Professor
Department of Electronics and Communication Engineering, K L University
Vaddeswaram, Guntur, AP, India
Abstract—Defining the problem: Having power cuts
of 7 to 8 hours in the villages showed me how server
power shortage was. Saving power is equal to
generating power.so we wanted to save power which
made me to take up this project.
Problem statement: In the process of saving
electricity we are controlling power consumption of
heater.The heater will be on till the water
temperature exceeds 60 degrees.when water attains
60 degrees the heater is made off. Now it remains off
till the temperature reaches 40 degrees.As soon as the
temperature attains 40 degrees the heater is made on.
Approach: We will construct the circuit on the bread
board and try to slove the problems.Since this circuit
is used to control heating of water heaters in home it
doesn't require much accuracy.Ideally if a heater is
designed to maintain water at 60 degrees,after
attaining 60 degrees water is maintained at that
temperature with some hysteresis.it requires heater
to be on as soon as temperature falls below hysteresis
voltage.this process consumes more power.it is not a
problem if heater temperature falls below some 10
degrees the required temperature for house hold
purposes.Accordingly in our system since the heater
still remains off though its temperature is 10 degrees
below the required temperature.Like this power is
saved.
Keywords— Smart Heater, Instrumentation
Amplifier,OperationalAmplifier,Transistor
,Difference Amplifier.
I.
INTRODUCTION
Due to increase in the industrialization,
increase in the population there is ever
growing need to electricity.but there is
large gap between production and
consumption of electricity in India.So
every industry every village is facing
power cuts.this is causing lot of loss to
both the industrialist and farmers.
We initially wanted to make our
home self sufficient. Saving electricity is
ISSN: 2231-5381
equal to generating electricity. So we
wanted to do modify some appliance in
our home to save electricity among
many appliance the first one is fan, where
we are using resistive regulators to control
its speed, It consumes the same power
wheatear we operate in full speed or the
slowest one. So we can modify this
system an save some power, the next
possibility is the tube light. We keep the
light on though we are not in the room. So
we can design a system to control the tube
light based on whether the room is
occupied or not. We can design a system
which will control the intensity of tube
light based on the ambient lightening in
the room. The other one is to save the
power by making the heater smart. I like
the heaters very much.
So we decide to make a smart
heater, the normal heaters are designed to
maintain water at a particular temperature.
But due to noise if a particular
temperature is fixed it will cause the
heater to on and off rapidly so a hysteresis
is introduced. Normally this hysteresis is
of 1 or 2 degrees variations from the
required temperature.For applications in
home
such
accurate
temperature
measurement is not required.So we
applied the hysteresis concept here to
achieve our target.
The previous system consumes more
power since it has to maintain the water at
the required temperature, it is not a
problem if heater temperature falls below
some10 degrees the required temperature
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
for house hold purposes.Accordingly in
our system since the heater still remains
off though its temperature is 10degrees
below the required temperature.Like the
power is saved.
II.
The
circuit
is
WORKING
given
below
fig.1.
resistor is connected to 9 volts.Voltage
across 1k ohm resistor is fed to a
operational amplifier acting as a emitter
follower.This output acts as a 1volt
reference voltage.A 1.5k ohm resistance is
obtained by adjusting the preset and 1k
ohm resistor in series is connected to
9volts.Voltage across 1k ohm resistor is
fed to a operational amplifier acting as a
emitter follower.This output acts as
a5.45volt reference voltage.
Pt 100 is connected in a wheat stone
bridge with other resistor values equal to
100ohms.This bridge is supplied with
1volt voltage. Two leads are taken out
from the bridge as shown in the
diagram.These two leads are taken out
from the bridge as shown in the
diagram.These two leads are fed to the
instrumentation amplifier.
The instrumentation amplifier 1st
stage is the emitter follower.The emitter
follower has ideally infinite input
resistance and zero output resistance. This
is used so that the latter stage resistances
will not affect the wheat stone bridge
resistance.The next stage is the difference
amplifier.
The difference amplifier amplifies
the gain so that low voltage variations that
occur at the bridge due to variation in the
temperature
can
be
measured.the
resistance of pt100 follows the equation:
R=R0*(1+AT+B(T^2))
basically it consists of temperature
measuring block, a comparator, relay
driving circuit.two reference voltage 1
volt and5.45volts are derived from resistor
divider circuit from 9 volts.
A 8k ohm resistor and 1k ohm
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A=3.9*(10^-3)PERDEGREES
CENTIGRADE
B=5.775*(10^-7)PERDEGREES
CENTIGRADE
R0 is the resistance of pt100 at 0 degrees
which is 100 ohms
The gain of the difference amplifier
are so adjusted that the voltage at its
output is one tenth of the room
temperature in degrees.
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
This difference amplifier output is
fed to a schmitt trigger. The hysteresis
curve is shifted to positive x-axis by
biasing it with5.45volts obtained from the
operational amplifier acting as emitter
follower.the upper and lower triggering
points are 6 volts and 4 volts respectively.
Initially when the temperature is less
than the schmitt trigger output is high.
When the temperature reaches 60 degrees
the output goes low when the temperature
now is decreasing if it were a normal
comparator it would be on but since it is a
schmitt trigger it will be again triggered
when voltage falls to lower triggering
point in this case it is achieved if the
temperature falls to 40 degrees and then
the voltage is volts.so now again
temperature keeps on increasing and when
it reaches 60 degrees the out again falls
low and thus the cycle continues.
If the output of the schmitt trigger is
high it will on the transistor.this will make
collector current to flow in the relay and
the relay is energized. The energized relay
connects the supply to the heater and
switches on the heater.The base current is
limited by base resistors.when the schmitt
trigger output is low it will off the
transistor and this will off the relay cutting
away supply to the heater which will
eventually turn off the heater.When the
relay is off high voltage is produced at
across the relay since inductor will oppose
sudden changes in the current.This voltage
may destroy the transistor.So a
freewheeling diode is used to limit the
voltage across relay to 0.7 volts and also
discharges the relay.
The transistor is operated in the saturation
region. The base current is so choose that
the transistor is well driven into saturation
region .Since this is a demonstration
circuit instead of a heater a light emitting
diode and current limiting resistor are
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used to show the operation..
The LM 258 is a dual operational
amplifier. It is given 9 volts to the positive
supply terminal and the negative supply
terminal is grounded .The saturation
voltage is 5.8volts .The gain of BC 547
is 4 in the active region .
III. DESIGN SPECIFICATIONS
HOW TO FIND R1 AND R2
We need to derive 1volt from 9volt so the
relation between R1 and R2 should be
R1 = 8*R2
CALCULATE THE RESISTANCE OF
R7 AND R9
In order to get output voltage of difference
amplifier proportional to temperature the
gain of the resistor R7 and R9 should
satisfy the relation
R9=51.4*R7
TO CALCULATE R11,R12,R13
We have to shift the hysteresis so that the
lower triggering point is 4 volts and upper
triggering point is 6 volts so the resistor
values R11,R12,R13 should be designed
according to the following relations
R13=2.75*R12
R12=0.733*R12
TO CALCULATE VALUES OF R16,R17
The gain of bc547 is about 5 so the values
R16,R17 should be designed so that the
transistor is driven into saturation.choose
base current as 8.25ma.the emitter and
base saturation voltage is 0.85 volts.from
this R16=R17 and they can be calculated
as
R16=2*(5.8-0.85)/(8.25*10^_3)
TO CALCULATE VALUE OF R18
The resistance of the 5 volts coil is 130
ohms.the collector emitter saturation
voltage is 0.74volts.so from this R18 can
be calculated as follow
R18=(9-4.7-0.74)/4.3*8.25*10^-3)
=100ohms
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
IV. CONCLUSION
The wheat stone bridge output voltage is
not stable it is varying with the variations
of supply. So only wheat stone bridge is
not giving faithful results.also the 100ohm
resistors in the bridge should be very
accurate.so use 3 presets in bridge instead
of the resistors and adjust them so that the
node voltage are obtained as required.
The hfe minimum of the BC547 as
mentioned in data sheets as 110 is not
practically obtainable the gain of the
transistor was approximately 4.the circuit
is very sensitive due to this the output of
the difference amplifier which should be
one tenth of temperature is not obtained.in
order to obtain this the bridge should me
modified so that supply variations and
sensitivity to noise should be reduced.
Self heating of the sensor should be
avoided by allowing only very less current
to flow through the sensor. The
freewheeling diode can be any diode
whose forward voltage drop is 0.7volts.the
reverse voltage rating is not of importance
since the operation of diode here is used in
forward biased mode.
REFERENCES
[1]
[2]
[3]
J.B.Gupta, Electronic Devices and Circuits, 3rd
edition, Katson books, 2009
A.Anand Kumar, Pulse and Digital Circuits, 2nd
edition, PHI Learning Private Ltd, 2008
Linear Integrated Circuits By
Salivahanan
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