29-12-2014, 05:14 PM
PLEASE GIVE US PROJECT REPORT OF TOPIC AUTOMATIC
TEMPARATURE CONTROLLED FAN USING THERMISTOR
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automatic temperature controlled fan pdf report
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PLEASE GIVE US PROJECT REPORT OF TOPIC AUTOMATIC
TEMPARATURE CONTROLLED FAN USING THERMISTOR
04-04-2017, 11:11 AM
Here is a circuit through which the speed of a fan can be linearly controlled automatically, depending on the ambient temperature. The circuit is highly efficient, as it uses thyristors for power control. Alternatively, the same circuit may be used for automatic temperature controlled AC power control.
![[Image: 56C_Automatic-Temperature-_-efy.jpg]](http://electronicsforu.com/wp-contents/uploads/2016/04/56C_Automatic-Temperature-_-efy.jpg)
In this circuit, the temperature sensor used is an NTC thermistor, i.e. one having a negative temperature coefficient. The resistance value of the thermistor at 25 ° C is about 1 kilo-ohm.
Op-amp A1 essentially functions as an I to V (current-to-voltage) converter and converts temperature variations into voltage variations. To amplify the voltage change due to the temperature change, instrumentation amplifier formed by amplifiers op A2, A3 and A4 is used. The resistor R2 and the Zener diode combination D1 are used to generate reference voltage, since we want to amplify only the voltage change due to the change in temperature.
Op-amp μA741 (IC2) functions as a comparator. One input to the comparator is the output of the instrumentation amplifier while the other input is the staggered, rectified, and adequately attenuated sample of the AC voltage. This is a continuous negative pulse voltage. It will be noted that with increasing temperature, pin 2 of IC2 is increasingly negative and therefore the width of positive output pulses (at pin 6) increases linearly with temperature. Therefore, IC2 functions as a pulse width modulator in this circuit. The comparator output is coupled to an optocoupler, which in turn controls the AC power supplied to the fan (load).
The circuit has a high sensitivity and the RMS output voltage (via the load) can be varied from 120V to 230V (for a temperature range of 22 ° C to 36 ° C), and therefore large variations in speed They're available. Also keep in mind that speed varies linearly and not in steps. In addition, since an optocoupler is used, the control circuit is completely isolated from the power circuit, thus providing greater safety. Note that for any given temperature the fan speed (ie the voltage across the load) can be adjusted to a desired value by properly adjusting the potentiometers VR1 and VR2.
Potmeter VR1 must initially be held in its mid position to make a gain of approximately 40 from the instrumentation amplifier. It can then be trimmed slightly to obtain a linear variation of fan speed.
In this circuit, the temperature sensor used is an NTC thermistor, i.e. one having a negative temperature coefficient. The resistance value of the thermistor at 25 ° C is about 1 kilo-ohm.
Op-amp A1 essentially functions as an I to V (current-to-voltage) converter and converts temperature variations into voltage variations. To amplify the voltage change due to the temperature change, instrumentation amplifier formed by amplifiers op A2, A3 and A4 is used. The resistor R2 and the Zener diode combination D1 are used to generate reference voltage, since we want to amplify only the voltage change due to the change in temperature.
Op-amp μA741 (IC2) functions as a comparator. One input to the comparator is the output of the instrumentation amplifier while the other input is the staggered, rectified, and adequately attenuated sample of the AC voltage. This is a continuous negative pulse voltage. It will be noted that with increasing temperature, pin 2 of IC2 is increasingly negative and therefore the width of positive output pulses (at pin 6) increases linearly with temperature. Therefore, IC2 functions as a pulse width modulator in this circuit. The comparator output is coupled to an optocoupler, which in turn controls the AC power supplied to the fan (load).
The circuit has a high sensitivity and the RMS output voltage (via the load) can be varied from 120V to 230V (for a temperature range of 22 ° C to 36 ° C), and therefore large variations in speed They're available. Also keep in mind that speed varies linearly and not in steps. In addition, since an optocoupler is used, the control circuit is completely isolated from the power circuit, thus providing greater safety. Note that for any given temperature the fan speed (ie the voltage across the load) can be adjusted to a desired value by properly adjusting the potentiometers VR1 and VR2.
Potmeter VR1 must initially be held in its mid position to make a gain of approximately 40 from the instrumentation amplifier. It can then be trimmed slightly to obtain a linear variation of fan speed.
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