Mini project presentation AUTOMATIC TEMPERATURE CONTROLLED FAN Abhilash.K.M(02) Abin Baby(03) Ajith Kumar R(04) Bineesh Babu P(10) College of Engineering Munnar
Automatic tempearture controlled fan
May 22, 2015
Here is a circuit through which the
speed of a fan can be linearly controlled
automatically, depending
on the room temperature. The circuit is
highly efficient as it uses thyristors for
power control. Alternatively, the same
circuit can be used for automatic temperature
controlled AC power control.
In this circuit, the temperature sensor
used is an NTC thermistor, i.e. one having
a negative temperature coefficient. The
value of thermistor resistance at 25°C is
about 1 kilo-ohm.
Op-amp A1 essentially works as
I to V (current-to-voltage) converter
and converts temperature variations
into voltage variations. To amplify
the change in voltage due to change in
temperature, instrumentation amplifier
formed by op-amps A2, A3 and A4
is used. Resistor R2 and zener diode
D1 combination is used for generating
reference voltage as we want to amplify
only change in voltage due to the
change in temperature.
Op-amp μA741 (IC2) works as a
comparator. One input to the comparator
is the output from the instrumentation
amplifier while the other input
is the stepped down, rectified and
suitably attenuated sample of AC voltage.
This is a negative going pulsating
DC voltage. It will be observed that
with increase in temperature, pin 2 of
IC2 goes more and more negative and
hence the width of the positive going
output pulses (at pin 6) increases linearly
with the temperature. Thus IC2
functions as a pulse width modulator
in this circuit. The output from the
comparator is coupled to an optocoupler,
which in turn controls the AC
power delivered to fan (load).
The circuit has a high sensitivity and
the output RMS voltage (across load) can
be varied from 120V to 230V (for a temp.
range of 22°C to 36°C), and hence wide
variations in speed are available. Also
note that speed varies linearly and not
in steps. Besides, since an optocoupler is
used, the control circuit is fully isolated
from power circuit, thus providing added
safety. Note that for any given temperature
the speed of fan (i.e. voltage across
load) can be adjusted to a desired value
by adjusting potmeters VR1 and VR2
appropriately.
Potmeter VR1 should he initially kept
in its mid position to realise a gain of approximately
40 from the instrumentation
amplifier. It may be subsequently trimmed
slightly to obtain linear variation of the
fan speed.
speed of a fan can be linearly controlled
automatically, depending
on the room temperature. The circuit is
highly efficient as it uses thyristors for
power control. Alternatively, the same
circuit can be used for automatic temperature
controlled AC power control.
In this circuit, the temperature sensor
used is an NTC thermistor, i.e. one having
a negative temperature coefficient. The
value of thermistor resistance at 25°C is
about 1 kilo-ohm.
Op-amp A1 essentially works as
I to V (current-to-voltage) converter
and converts temperature variations
into voltage variations. To amplify
the change in voltage due to change in
temperature, instrumentation amplifier
formed by op-amps A2, A3 and A4
is used. Resistor R2 and zener diode
D1 combination is used for generating
reference voltage as we want to amplify
only change in voltage due to the
change in temperature.
Op-amp μA741 (IC2) works as a
comparator. One input to the comparator
is the output from the instrumentation
amplifier while the other input
is the stepped down, rectified and
suitably attenuated sample of AC voltage.
This is a negative going pulsating
DC voltage. It will be observed that
with increase in temperature, pin 2 of
IC2 goes more and more negative and
hence the width of the positive going
output pulses (at pin 6) increases linearly
with the temperature. Thus IC2
functions as a pulse width modulator
in this circuit. The output from the
comparator is coupled to an optocoupler,
which in turn controls the AC
power delivered to fan (load).
The circuit has a high sensitivity and
the output RMS voltage (across load) can
be varied from 120V to 230V (for a temp.
range of 22°C to 36°C), and hence wide
variations in speed are available. Also
note that speed varies linearly and not
in steps. Besides, since an optocoupler is
used, the control circuit is fully isolated
from power circuit, thus providing added
safety. Note that for any given temperature
the speed of fan (i.e. voltage across
load) can be adjusted to a desired value
by adjusting potmeters VR1 and VR2
appropriately.
Potmeter VR1 should he initially kept
in its mid position to realise a gain of approximately
40 from the instrumentation
amplifier. It may be subsequently trimmed
slightly to obtain linear variation of the
fan speed.
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Transcript
Mini project presentation
AUTOMATIC TEMPERATURECONTROLLED FAN
Abhilash.K.M(02)Abin Baby(03)Ajith Kumar R(04)Bineesh Babu P(10)
College of Engineering Munnar
College of Engineering Munnar
Mini project byStudents of College of Engineering, Munnar
College of Engineering Munnar
INTRODUCTION
Ordinary fan regulatorsElectronic fan regulators
College of Engineering Munnar
Why automatic temperature controlled fan?
*Automatic speed control*Low power loss*Reduce Current Consumption*Allows fan to ramp up or down smoothly to new speed*Increase Fan Life*A single temperature or all temperatures can control the fan speed.*Small size and economic
College of Engineering Munnar
Thermistor
High Gain
Amplifier
Comparator
Bridge Rectifier
Triac Optocoupler
Increase intemperature
BLOCK DIAGRAM
AC supply230 V, 50Hz
230 VAC
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Components Used
*Thermistor*IC LM324*IC µA741*Resistors*Zener diodes*Optocoupler (MOC3011)*Triac(BT 136)
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CIRCUIT DIAGRAM
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LM324
* 4 OpAmps in a single IC
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NEED OF OPTOCOUPLER
* Basically an opto-isolator, designed to transfer electrical signals by utilizing light waves to provide coupling with electrical isolation between its input and output. *The main purpose of an opto-isolator is to prevent high voltages or rapidly changing voltages on one side of the circuit from damaging components or distorting transmissions on the other side.
Schematic diagram of an opto-isolator showing source of light (LED) on the left, dielectric barrier in the center, and sensor (phototransistor) on the right.
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THERMISTOR
• A thermistor is a type of resistor • resistance varies significantly with
temperature• used as current limiters,
temperature sensors, self-resetting overcurrent protectors, and self-regulating heating elements
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TRIAC
• speed controls for electric fans
• TRIACs are bidirectional and so current can flow through them in either direction.
• TRIACs can be triggered by either a positive or a negative current applied to its gate electrode.
• Once triggered, the device continues to conduct until the current drops below a certain threshold, called the holding current.
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OUR PROGRESS
We have designed and wired the circuit on the bread board level, and the output is obtained upto 2 stages.
REFERENCE
Wikipedia, electronicsforyou.com
COST250 rs
College of Engineering Munnar
THANK YOU
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