automatic tempearture controlled fan
DESCRIPTION
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.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)
College of Engineering Munnar
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.
College of Engineering Munnar
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
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THANK YOU