A Project Synopsis on
“Temperature Sensitive Fan"
ACKNOWLEDGEMENT
We express our deep sense of gratitude to Mr. Z and Z Project Incharge & Lecturer, Department of Electrical & Electronics Engg., for his fruitful guidance, supervision, constructive criticism and constant encouragement throughout this project.
Lastly, We would like to acknowledge our Department staff and all of our college Colleagues.
Date:
CONTENTS
· Aim
· Feasibility Study
· Block Diagram
· Circuit Diagram & Circuit Operation
· Design Issues
· Overview Image of Project
· Advantages
AIM
Automating the on/off state of a fan is useful in many ways - it prevents the waste of energy when it's not hot enough for a fan to be needed; it also makes it possible to monitor environments that are not comfortable, or possible, for humans to monitor, especially for extended periods of time. By connecting a temperature sensor to a PolyBlock in Compare Mode, it's quite simple to turn on a fan when the value from the temperature sensor exceeds a given threshold.
Connecting the necessary components for a Temperature Controlled Fan is straightforward. The idea is that the temperature sensor produces a voltage that is proportional to the temperature in degrees fahrenheit. The voltage is just the temperature divided by 100, so when it's 0 degrees fahrenheit, it outputs 0V, when it's 70 degrees the sensor outputs 0.70V, and so on. The idea is to use the Poly Block to compare the incoming voltage with a reference voltage of its own. This reference voltage can be set by using the trimpot dial on the Poly Block.
Feasibility Study
For this project, we want to activate a fan, so we connect the +V of the Poly Block to one side of the Fan, and the other side to the S1 output. When the Poly Block activates its Greater outputs (the low power O1 and the higher current S1), the fan is switched on and starts to run.
By setting the trimpot correctly, the fan can be made to come on at any temperature, and turn off again when the temperature falls below the reference point.
This set up assumes that the sensor will be located very close to the PolyBlock. If it is necessary to have the temperature sensor far away from the PolyBlock, consider using the Line Block to extend the signal range.
If the selected fan draws more than 2A at the voltage supplied, you may want to consider using the Switch Block, which takes would take a weak logical signal from the O1 output and use it to switch much higher currents (up to around 10A).
To connect an AC household fan with a standard power outlet, you could use the AC Switch Block connected to the O1 output, although this is more dangerous since AC voltages are present.
Block Diagram
Circuit Diagram
Circuit operation:
R3-R4 and P1-R1 are wired as a Wheatstone bridge in which R3-R4 generates a fixed two-thirds-supply "reference" voltage, P1-R1 generates a temperature-sensitive "variable" voltage, and Q1 is used as a bridge balance detector.
P1 is adjusted so that the "reference" and "variable" voltages are equal at a temperature just below the required trigger value, and under this condition Q1 Base and Emitter are at equal voltages and Q1 is cut off. When the R1 temperature goes above this "balance" value the P1-R1 voltage falls below the "reference" value, so Q1 becomes forward biased, pulse-charging C1.
This occurs because the whole circuit is supplied by a 100Hz half-wave voltage obtained from mains supply by means of D3-D6 diode bridge without a smoothing capacitor and fixed to 18V by R9 and Zener diode D1. Therefore the 18V supply of the circuit is not true DC but has a rather trapezoidal shape. C1 provides a variable phase-delay pulse-train related to temperature and synchronous with the mains supply "zero voltage" point of each half cycle, thus producing minimal switching RFI from the SCR. Q2 and Q3 form a trigger device, generating a short pulse suitable to drive the SCR.
P1 is adjusted so that the "reference" and "variable" voltages are equal at a temperature just below the required trigger value, and under this condition Q1 Base and Emitter are at equal voltages and Q1 is cut off. When the R1 temperature goes above this "balance" value the P1-R1 voltage falls below the "reference" value, so Q1 becomes forward biased, pulse-charging C1.
This occurs because the whole circuit is supplied by a 100Hz half-wave voltage obtained from mains supply by means of D3-D6 diode bridge without a smoothing capacitor and fixed to 18V by R9 and Zener diode D1. Therefore the 18V supply of the circuit is not true DC but has a rather trapezoidal shape. C1 provides a variable phase-delay pulse-train related to temperature and synchronous with the mains supply "zero voltage" point of each half cycle, thus producing minimal switching RFI from the SCR. Q2 and Q3 form a trigger device, generating a short pulse suitable to drive the SCR.
Design Issues
1) Temperature Sensor :-
The temperature sensor is a powered sensor, and has three wires - one for the +5V supply, a 0V or ground supply and a signal.
Sensors include thermistors Hall-effect sensors, and chip-on-board thermal-controller devices, and each fan comes with a linear ramp control featuring two temperature set points.
2) Poly Block :-
Poly Block is used to compare the incoming voltage with a reference voltage of its own. This reference voltage can be set by using the trimpot dial on the Poly Block.
3) Power Supply :-
A power supply is a device that supplies electrical energy to one or more electric loads.
Every power supply must obtain the energy it supplies to its load, as well as any energy it consumes while performing that task, from an energy source.
AC/DC supply :-
In the past, mains electricity was supplied as DC in some regions, AC in others. Transformers cannot be used for DC, but a simple, cheap unregulated power supply could run directly from either AC or DC mains without using a transformer. The power supply consisted of a rectifier and a filter capacitor. When operating from DC the rectifier was essentially a conductor, having no effect; it was included to allow operation from AC or DC without modification. Overview Image of the Project
Advantages
1) More Powerful Cooling :-
AC Switch Block can be used to control a household fan instead of one of its smaller relatives.
2) Oxygen Flow :-
Substitute a carbon dioxide (or other gas) sensor for the temperature sensor to allow the fan to turn on automatically when there's not enough oxygen in a room.
3) Temperature Monitor :-
Substitute a small alarm for the fan to create an alert that lets you know when the temperature has exceeded (or dropped below) a certain threshold.
Applications
Used as CPU Fan to control the Computer Processor Temperature
THANX GUYS
THANX GUYS
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