24-03-2011, 10:21 AM
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ABSTRACT
Ideal gas sensor is used to detect the presence of a dangerous LPG leak in your car or in a service station, storage tank environment. This unit can be easily incorporated into an alarm unit, to sound an alarm or give a visual indication of the LPG concentration. The sensor has excellent sensitivity combined with a quick response time. The sensor can also sense iso-butane, propane, LNG and cigarette smoke.
If the LPG sensor senses any gas leakage from storage the output of this sensor goes low. This low signal is monitored by the microcontroller and it will identify the gas leakage. Now the microcontroller is ready to make call. At first the dial relay is activated. It is the similar operation to speed dials the assigned number from the cell phone. Now our unit makes call to the saved speed dial cell number. The people who have the cell phone are accepting the call and send DTMF signal from the cell phone. That DTMF tone is received by our project and converts it to equivalent BCD number. This BCD is monitored by the microcontroller and gives output depending upon the BCD.
If we send DTMF for ‘1’ the exhaust fan is run in slow speed. If we send DTMF for ‘2’ the exhaust fan is operated in full speed. Other than this DTMF is sending the exhaust fan is stopped.
INTRODUCTION
The MQ5 Gas Vapor Monitor detects gas vapors at 10%, 20% or 30% of the concentration required for an explosion (LEL or Lower Explosive Limit). The desired sensitivity can be selected from the front panel and stored in the non-volatile memory. When activated, the MQ5 built-in 85 dB alarm will sound and make call to the stored cell number.
The alarm will continue to sound as long as the sensor detects a dangerous concentration of gas vapor or until the reset button is pressed. If the alarm is silenced by the use of the reset button, the MQ5 will automatically arm the alarm again as soon as the gas vapor has subsided.
BLOCK DIAGRAM DESCRIPTION
LPG SENSOR
It senses the leakage of LPG. The out put of this sensor is ‘high’ at normal condition. The output goes low, when it senses the LPG.
MICROCONTROLLER
It is the whole control of the project. It controls the cell phone, relay unit, when LPG leak occurs. The input/ output ports of the microcontroller is used for this.
SPEED DIAL RELAY
It gives speed dial function to the cell phone automatically.
CELL PHONE
It is an ordinary cell phone, which has head set. DTMF is receive by this cell phone.
DTMF DECODER
DTMF means Dual Tone Multi Frequency. It is the tone which two frequency of sinusoidal signals. It is different for different keys of phone key pad. DTMF transmitted by cell phone is converted to its equivalent BCD by this unit.
RELAY UNIT
Relays are not directly driven by the microcontroller. Hence relay drivers are used for this purpose. Relays are used to operate the exhaust fan.
EXHAUST FAN
This is used to send out the LPG to space and then the concentration of LPG is reduced.
CIRCUIT DESCRIPTION
If the LPG sensor senses any gas leakage from storage the out put of this sensor goes low. This low signal is monitored by the microcontroller and it will identify the gas leakage. Now the microcontroller is ready to make call.
At first the speed dial relay is activated. It is the similar operation to call the stored number and assigned as speed dial number. Now our unit makes call to the speed dialed cell number.
The people who have the cell phone are accepting the call and send DTMF signal from the cell phone. That DTMF tone is received by our project and converts it to equivalent BCD number. This BCD is monitored by the microcontroller and gives output depending upon the BCD.
If we send DTMF for ‘1’ the exhaust fan is run in slow speed. If we send DTMF for ‘2’ the exhaust fan is operated in full speed. Other than this DTMF is sending the exhaust fan is stopped.
LPG DETECTOR
OPERATION PRINCIPLE
The sensing material in TGS gas sensors is metal oxide, most typically SnO2. When a metal oxide crystal such as SnO2 is heated at a certain high temperature in air, oxygen is adsorbed on the crystal surface with a negative charge. Then donor electrons in the crystal surface are transferred to the adsorbed oxygen, resulting in leaving positive charges in a space charge layer. Thus, surface potential is formed to serve as a potential barrier against electron flow.
Inside the sensor, electric current flows through the conjunction parts (grain boundary) of SnO2 micro crystals. At grain boundaries, adsorbed oxygen forms a potential barrier which prevents carriers from moving freely. The electrical resistance of the sensor is attributed to this potential barrier. In the presence of a deoxidizing gas, the surface density of the negatively charged oxygen decreases, so the barrier height in the grain boundary is reduced. The reduced barrier height decreases sensor resistance.
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