Fabrication and design of a gas leakage detector

CHAPTER 1INTRODUCTION1.1 IntroductionIn many works of life people make use of gas as a generic term thou the purpose to which it serves each individual and chemical composition may vary. For example In homes as cooking gas, to power some generators in industries, as a tool in generating welding flame and in chemical laboratories. The usefulness of gas cannot be overemphasized and as such it has become quite indispensable in our society today.Everything in this world that has an advantage equally has disadvantages also and so is the situation with gas. Many a times due to human carelessness, forgetfulness or due to wear out of mechanical parts a leakage might occur. Gas leakages are difficult to detect until it too late and this might lead to catastrophic damages and loss of lives and property if the gas meets with a naked flame and ignites.The best approach in which this situation can be prevented is if the leakage can be quickly detected and immediately contained. This challenge has been solved in different ways in the past each of them having their varying pitfalls. This project is aimed at taking advantage of those weaknesses and developing them into strengths by application of the knowledge of embedded systems. The design will be simple and portable within the confines of an undergraduate student. The system will help notify in case of a leakage by giving an alarm once a gas leakage is detected or printing a message to a liquid crystal display or by employing both methods for effectiveness thereby helping to save lives.

1.2 Statement of the ProblemOne of the properties of gas is the ability to fill the surrounding space and do it quickly. The molecules of a gas move chaotically colliding with themselves and the walls of the container. There are three basic hazards that gases possess, flammable, toxic and asphyxiant Honeywell Analytics (2009). So due to the fact that a gas quickly fills up a space it could pose a danger to humans in the surrounding area, so a system that quickly detects the leakage of gas and warns the residents will be instrumental in safeguarding the lives and properties of the people in that area.1.3 Background and History of studyThe word gas comes from the word chaos. Gas is a swarm of molecules moving randomly and constantly colliding with themselves and the walls of the container; while a detector is a device used for sensing the presence of changes in something. So a gas sensor is a device that spots the existence of gas contained in vicinity in order to alert observers of a potentially dangerous situation through audible and visual indicators such as light or alarms or the combination of both. Gas detectors are usually installed as fixed (stationery) or portable unit depending on the application.Before the advent of modern electronic sensors, early means of gas detection relied on less precise methods. Coal miners would bring canaries down to the tunnels as an early gas detection system against life threating gases. The canary is usually a very songful bird and would stop singing and eventually die indicating the presence of life threating gases to the miners, a sign that they should quickly exit the vicinity. The major step in the development of gas detection technology was the use of a chemically infused paper that turned brown when exposed to carbon monoxide (Wikipedia, 2012, Gas leak detection).Since then many advance technologies have been developed to detect gas leakages effectively and indicate the type of gas detected on a display.Gas detectors are broadly divided into two categories by the type of gas they detect either combustible or toxic; this is further divided by the technology used. Catalytic and infrared sensors detect combustible gases and electrochemical and metal oxide semiconductor technologies are used to detect toxic gases. (Thomas, 2012, how gas detectors work).Catalytic sensorsrepresent a large number of gas detector devices that are manufactured today. This technology is used to detect combustible gases such as hydrocarbon, and works via catalytic oxidation. The sensors of this type of detector are typically constructed from a platinum treated wire coil. As a combustible gas comes into contact with the catalytic surface, it is oxidized and the wiring resistance is changed by heat that is released. A bridge circuit is typically used to indicate the resistance change.Infrared sensors or IR detectorswork via a system of transmitters and receivers to detect combustible gases, specifically hydrocarbon vapors. Typically, the transmitters are light sources and receivers are light detectors. If a gas is present in the optical path, it will interfere with the power of the light transmission between the transmitter and receiver. The altered state of light determines if and what type of gas is present.Electrochemical sensorsor cells are most commonly used in the detection of toxic gases like carbon monoxide, chlorine and nitrogen oxides. They function via electrodes signals when a gas is detected. Generally, these types of detectors are highly sensitive and give off warning signals via electrical currents. Various manufacturers produce these detectors with a digital display.Metal Oxide Semiconductors, or MOS,are also used for detecting toxic gases (commonly carbon monoxide) and work via a gas sensitive film that is composed of tin or tungsten oxides. The sensitive film reacts with gases, triggering the device when toxic levels are present. Generally, metal oxide sensors are considered efficient due their ability to operate in low-humidity ranges. In addition, they are able to detect a range of gases, including combustibles.1.4 Application of Gas Detection Systems1. In the oil and gas industry they are quite indispensible because they handle a large amount of highly flammable hydrocarbons. They are used in exploration drilling rigs, production platforms, onshore oil and gas terminals and refineries.2. In manufacturing semi-conductors highly toxic and flammable materials are used phosphorus, arsenic, and boron are used as doping agents. Typical applications are close to the wafer reactors, wafer dryers, gas cabinets, and chemical vapor deposition.3. In chemical plants in their raw materials storage, process areas, laboratories, pump rows, compressor stations and loading and unloading areas.4. In power stations where coal and oil are used as fuels and nowadays natural gas. It is used around the boiler pipe work and burners, in and around the turbine packages, in coal silos and conveyor belts in coal and oil fired stations.5. In hospitals in their laboratories, refrigeration plants and boiler rooms.6. In welding shops where oxyacetylene flame is being used.7. In homes where liquefied petroleum gas is used as a fuel for cooking.8. In enclosed areas used as car parks or underground parking lots, to detect the presence of toxic fumes produced by the exhaust the vehicles. The output may then be used to drive a ventilation fan in modern parking lots.1.5 Aims and Objectives of the projectThe aim of the project is to design and fabricate a gas detection system for domestic purposes.The objectives of the project are to:a) Design a compact and portable gas leakage detectorb) Evaluate the performance of the designed equipment

CHAPTER TWOLITERATURE REVIEWThis chapter will attempt to discuss the related literature under the following topics:i) Microcontrollersii) Gas sensorsiii) Liquid crystal displayiv) Light emitting diodev) Buzzervi) Power supply

2.1 MicrocontrollersA microcontroller is a single chip, self-contained computer which incorporates all the basic components of a personal computer on a much smaller scale (Byte Craft Limited, 2002, Pg. 5). Microcontrollers are often referred to as single chip devices or single chip computers. The main consequence of the microcontrollers small size is that its resources are far more limited than those of a desktop personal computer. In functional terms, a microcontroller is a programmable single chip which controls a process or system. Microcontrollers are typically used as embedded controllers where they control part of a larger system such as an appliance, automobile, scientific instrument or a computer peripheral. Microcontrollers are designed to be low cost solutions; therefore using them can drastically reduce part and design costs for the project. Physically, a microcontroller is an integrated circuit with pins along each side. The pins presented by a microcontroller are used for power, ground, oscillator, I/O ports, interrupt request signals, reset and control. You can find microcontrollers in all kinds of things these days. Any device that measures, stores, controls, calculates, or displays information is a candidate for putting a microcontroller inside.There are a variety of microcontrollers depending on the different architectures and the manufacturers such as PIC, ATMEL and MOTOROLA to mention a few. This write-up however will be concentrating on the PIC microcontrollers.

PIC stands for peripheral interface controller, it is made by Microchip Technology, and its architecture is based on the reduced instruction set computers (RISC). It has a wide range of microcontrollers broadly divided into the low end, mid-range and the high end microcontrollers. Table 2.1 shows the various classes of PIC microcontrollers highlighting their key features.

MCUPINSDATAWORD(BITS)PROGRAMMEMORY(BYTES)TYPICALINSTRUCTIONSSETSPEEDMIPSDESCRIPTION

10FXXX=68