Pierre and Marie Curie in their laboratory prior to 1907.
Credit: Public domain
In many ways, the history of civilization is the history of chemistry — the study of matter and its properties. Humans have always sought to identify, use and change the materials in our environment. Early potters found beautiful glazes to decorate and preserve their wares. Herdsmen, brewers and vintners used fermentation techniques to make cheese, beer and wine. Housewives leached the lye from wood ash to make soap. Smiths learned to combine copper and tin to make bronze. Crafters learned to make glass; leatherworkers tanned hides.
In the eighth century A.D., Jābir ibn Hayyān, a Muslim astronomer, philosopher and scientist, became one of the first to use scientific methods to study materials. Also known by his Latinized name, Geber, he is known as the "father of chemistry." He is thought to be the author of 22 scrolls describing methods of distillation, crystallization, sublimation and evaporation. He invented the alembic, a device used to distill and study acids. He also developed an early chemical classification system using the properties of the materials he studied. His categories were:
“Spirits” — materials that would vaporize when heated.
"Metals" — including iron, tin, copper, and lead.
Non-malleable substances — materials that could be made into powders, such as stone.
Today we might call similar materials “volatile chemicals, metals and non-metals.”
Classical chemistry
In Europe, the study of chemistry was conducted by alchemists with the goals of transforming common metals into gold or silver and inventing a chemical elixir that would prolong life. Although these goals were never achieved, there were some important discoveries made in the attempt.
Robert Boyle(1627-1691) studied the behavior of gases and discovered the inverse relationship between volume and pressure of a gas. He also stated that “all reality and change can be described in terms of elementary particles and their motion,” an early understanding of atomic theory. In 1661, he wrote the first chemistry textbook, “The Sceptical Cymist,” which moved the study of substances away from mystical associations with alchemy and toward scientific investigation.
By the 1700s, the Age of Enlightenment had taken root all over Europe. Joseph Priestley (1733-1804) disproved the idea that air was an indivisible element. He showed that it was, instead, a combination of gases when he isolated oxygen and went on to discover seven other discreet gases. Jacques Charlescontinued Boyles’ work and is known for stating the direct relationship between temperature and pressure of gases. In 1794, Joseph Proust studied pure chemical compounds and stated the Law of Definite Proportions — a chemical compound will always have its own characteristic ratio of elemental components. Water, for instance, always has a two-to-one ratio of hydrogen to oxygen.
Portrait of Antoine and Marie-Anne Lavoisier, who helped develop the metric system and a system for naming chemical compounds.
Credit: Public domain
Antoine Lavoisier (1743-1794) was a French chemist who made important contributions to the science. While working as a tax collector, Lavoisier helped to develop the metric system in order to insure uniform weights and measures. He was admitted to the French Academy of Sciences in 1768. Two years later, at age 28, he married the 13-year-old daughter of a colleague. Marie-Anne Lavoisier is known to have assisted her husband in his scientific studies by translating English papers and doing numerous drawings to illustrate his experiments.
Lavoisier’s insistence on meticulous measurement led to his discovery of the Law of Conservation of Mass. In 1787, Lavoisier published "Methods of Chemical Nomenclature," which included the rules for naming chemical compounds that are still in use today. His "Elementary Treatise of Chemistry" (1789) was the first modern chemistry textbook. It clearly defined a chemical element as a substance that cannot be reduced in weight by a chemical reaction and listed oxygen, iron, carbon, sulfur and nearly 30 other elements then known to exist. The book did have a few errors though; it listed light and heat as elements.
Amedeo Avogadro (1776-1856) was an Italian lawyer who began to study science and mathematics in 1800. Expanding on the work of Boyle and Charles, he clarified the difference between atoms and molecules. He went on to state that equal volumes of gas at the same temperature and pressure have the same number of molecules. The number of molecules in a 1-gram molecular weight (1 mole) sample of a pure substance is called Avogadro’s Constant in his honor. It has been experimentally determined to be 6.023 x 1023 molecules and is an important conversion factor used to determine the mass of reactants and products in chemical reactions.
In 1803, an English meteorologist began to speculate on the phenomenon of water vapor. John Dalton (1766-1844) was aware that water vapor is part of the atmosphere, but experiments showed that water vapor would not form in certain other gases. He speculated that this had something to do with the number of particles present in those gases. Perhaps there was no room in those gases for particles of water vapor to penetrate. There were either more particles in the “heavier” gases or those particles were larger. Using his own data and the Law of Definite Proportions, he determined the relative masses of particles for six of the known elements: hydrogen (the lightest and assigned a mass of 1), oxygen, nitrogen, carbon, sulfur and phosphorous. Dalton explained his findings by stating the principles of the first atomic theory of matter.
Elements are composed of extremely small particles called atoms.
Atoms of the same element are identical in size, mass and other properties. Atoms of different elements have different properties.
Atoms cannot be created, subdivided or destroyed.
Atoms of different elements combine in simple whole number ratios to form chemical compounds.
In chemical reactions atoms are combined, separated or rearranged to form new compounds.
Dmitri Mendeleev (1834-1907) was a Russian chemist known for developing the first Periodic Table of the Elements. He listed the 63 known elements and their properties on cards. When he arranged the elements in order of increasing atomic mass, he could group elements with similar properties. With a few exceptions, every seventh element had similar properties (The eighth chemical group — the Noble Gases — had not been discovered yet). Mendeleev realized that if he left spaces for the places where no known element fit into the pattern that it was even more exact. Using the blank spaces in his table, he was able to predict the properties of elements that had yet to be discovered. Mendeleev’s original table has been updated to include the 92 naturally occurring elements and 26 synthesized elements.
Describing the atom
In 1896, Henri Becquerel discovered radiation. Along with Pierre and Marie Curie, he showed that certain elements emit energy at fixed rates. In 1903, Becquerel shared a Nobel Prize with the Curies for the discovery of radioactivity. In 1900, Max Planck discovered that energy must be emitted in discreet units that he called “quanta” (since named photons) not in continuous waves. It appeared that atoms were made up of still smaller particles, some of which could move away.
In 1911, Ernst Rutherford demonstrated that atoms consisted of a tiny dense positively charged region surrounded by relatively large areas of empty space in which still smaller, negatively charged particles (electrons) move. Rutherford assumed that the electrons orbit the nucleus in separate neat orbits, just as the planets orbit the sun. However, because the nucleus is larger and denser than the electrons, he could not explain why the electrons were not simply pulled into the nucleus thus destroying the atom.
Niels Bohr in 1922.
Credit: AB Lagrelius & Westphal, via American Institute of Physics
Niels Bohr’s (1885-1962) atomic model solved this problem by using Planck’s information. Photons are emitted from an electrically stimulated atom only at certain frequencies. He hypothesized that electrons inhabit distinct energy levels and light is only emitted when an electrically “excited” electron is forced to change energy levels.
Electrons in the first energy level, closest to the nucleus, are tightly bound to the nucleus and have relatively low energy. In levels more distant from the nucleus the electrons have increasing energy. Electrons in the energy level furthest from the nucleus are not bound as tightly and are the electrons involved when atoms bond together to form compounds. The periodic nature of the elemental properties is a result of the number of electrons in the outer energy level that can be involved in chemical bonds. Although Bohr models have been replaced by more accurate atomic models, the underlying principles are sound and Bohr models are still used as simplified diagrams to show chemical bonding.
Our understanding of the atom has continued to be refined. In 1935, James Chadwick was awarded the Nobel Prize for his discovery that there are an equal number of electrically neutral particles in the nucleus of an atom. Since neutrons are electrically neutral, they are not deflected by either electrons or protons. Furthermore, neutrons have more mass than protons. These facts combine to make it possible for neutrons to penetrate atoms and break apart the nucleus, releasing vast amounts of energy. In recent years, it is increasingly obvious that the protons, neutrons and electrons of classical chemistry are made up of still smaller subatomic particles. The sciences of chemistry and physics are becoming increasingly intertwined and theories overlap and conflict as we continue to probe the materials out of which our universe is made.
For further details log on website : http://www.livescience.com/46020-chemistry-history.html
Chemistry is the study of matter, its properties, how and why substances combine or separate to form other substances, and how substances interact with energy. Many people think of chemists as being white-coated scientists mixing strange liquids in a laboratory, but the truth is we are all chemists.
Doctors, nurses and veterinarians must study chemistry, but understanding basic chemistry concepts is important for almost every profession. Chemistry is part of everything in our lives.
Every material in existence is made up of matter — even our own bodies. Chemistry is involved in everything we do, from growing and cooking food to cleaning our homes and bodies to launching a space shuttle. Chemistry is one of the physical sciences that help us to describe and explain our world.
Five branches
There are five main branches of chemistry, each of which has many areas of study.
Analytical chemistry uses qualitative and quantitative observation to identify and measure the physical and chemical properties of substances. In a sense, all chemistry is analytical.
Physical chemistry combines chemistry with physics. Physical chemists study how matter and energy interact. Thermodynamics and quantum mechanics are two of the important branches of physical chemistry.
Organic chemistry specifically studies compounds that contain the element carbon. Carbon has many unique properties that allow it to form complex chemical bonds and very large molecules. Organic chemistry is known as the “Chemistry of Life” because all of the molecules that make up living tissue have carbon as part of their makeup.
Inorganic chemistry studies materials such as metals and gases that do not have carbon as part of their makeup.
Biochemistry is the study of chemical processes that occur within living organisms.
Fields of study
Within these broad categories are countless fields of study, many of which have important effects on our daily life. Chemists improve many products, from the food we eat and the clothing we wear to the materials with which we build our homes. Chemistry helps to protect our environment and searches for new sources of energy.
Food chemistry
Food science deals with the three biological components of food — carbohydrates, lipids and proteins. Carbohydrates are sugars and starches, the chemical fuels needed for our cells to function. Lipids are fats and oils and are essential parts of cell membranes and to lubricate and cushion organs within the body. Because fats have 2.25 times the energy per gram than either carbohydrates or proteins, many people try to limit their intake to avoid becoming overweight. Proteins are complex molecules composed of from 100 to 500 or more amino acids that are chained together and folded into three-dimensional shapes necessary for the structure and function of every cell. Our bodies can synthesize some of the amino acids; however eight of them, the essential amino acids, must be taken in as part of our food. Food scientists are also concerned with the inorganic components of food such as its water content, minerals, vitamins and enzymes.
Food chemists improve the quality, safety, storage and taste of our food. Food chemists may work for private industry to develop new products or improve processing. They may also work for government agencies such as the Food and Drug Administration to inspect food products and handlers to protect us from contamination or harmful practices. Food chemists test products to supply information used for the nutrition labels or to determine how packaging and storage affects the safety and quality of the food. Flavorists work with chemicals to change the taste of food. Chemists may also work on other ways to improve sensory appeal, such as enhancing color, odor or texture.
Environmental chemistry
Environmental chemists study how chemicals interact with the natural environment. Environmental chemistry is an interdisciplinary study that involves both analytical chemistry and an understanding of environmental science. Environmental chemists must first understand the chemicals and chemical reactions present in natural processes in the soil water and air. Sampling and analysis can then determine if human activities have contaminated the environment or caused harmful reactions to affect it.
Water quality is an important area of environmental chemistry. “Pure” water does not exist in nature; it always has some minerals or other substance dissolved in it. Water quality chemists test rivers, lakes and ocean water for characteristics such as dissolved oxygen, salinity, turbidity, suspended sediments, and pH. Water destined for human consumption must be free of harmful contaminants and may be treated with additives like fluoride and chlorine to increase its safety.
Agricultural chemistry
Agricultural chemistry is concerned with the substances and chemical reactions that are involved with the production, protection and use of crops and livestock. It is a highly interdisciplinary field that relies on ties to many other sciences. Agricultural chemists may work with the Department of Agriculture, the Environmental Protection Agency, the Food and Drug Administration or for private industry. Agricultural chemists develop fertilizers, insecticides and herbicides necessary for large-scale crop production. They must also monitor how these products are used and their impacts on the environment. Nutritional supplements are developed to increase the productivity of meat and dairy herds.
Agricultural biotechnology is a fast-growing focus for many agricultural chemists. Genetically manipulating crops to be resistant to the herbicides used to control weeds in the fields requires detailed understanding of both the plants and the chemicals at the molecular level. Biochemists must understand genetics, chemistry and business needs to develop crops that are easier to transport or that have a longer shelf life.
Chemical engineering
Chemical engineers research and develop new materials or processes that involve chemical reactions. Chemical engineering combines a background in chemistry with engineering and economics concepts to solve technological problems. Chemical engineering jobs fall into two main groups: industrial applications and development of new products.
Industries require chemical engineers to devise new ways to make the manufacturing of their products easier and more cost effective. Chemical engineers are involved in designing and operating processing plants, develop safety procedures for handling dangerous materials, and supervise the manufacture of nearly every product we use. Chemical engineers work to develop new products and processes in every field from pharmaceuticals to fuels and computer components.
Geochemistry
Geochemists combine chemistry and geology to study the makeup and interaction between substances found in the Earth. Geochemists may spend more time in field studies than other types of chemists. Many work for the U.S. Geological Survey or the Environmental Protection Agency in determining how mining operations and waste can affect water quality and the environment. They may travel to remote abandoned mines to collect samples and perform rough field evaluations, and then follow a stream through its watershed to evaluate how contaminants are moving through the system. Petroleum geochemists are employed by oil and gas companies to help find new energy reserves. They may also work on pipelines and oil rigs to prevent chemical reactions that could cause explosions or spills.
For further details log on website : http://www.livescience.com/45986-what-is-chemistry.html
A replica of a mass spectrometer used by the physicist J.J. Thompson in the 1910s.
Credit: Creative Commons | Jeff Dahl
Imagine plopping an atom down on a scale. As you do so, skin cells that are trillions of atoms thick flake off your hand and flutter down all around it, burying it in a pile of atomic doppelgangers. Meanwhile, moisture and atmospheric particles shoot about, bouncing on and off the scale and sending its atom-sensitive needle whipping back and forth like a windshield wiper. And by the way, how did you manage to isolate a single atom in the first place?
A moment's thought shows you can't weigh an atom on a traditional scale.
Instead, physicists do it using an instrument called a mass spectrometer. Invented in 1912 by physicist J.J. Thomson and improved incrementally over the past century, it works like this: First, physicists "ionize" a gas of atoms by firing a beam of particles at the gas, which either adds electrons to the atoms in it or knocks a few of their electrons off, depending on the type of particle beam used. This gives the atoms — now known as "ions" — a net negative or positive electric charge.
Next, the ions are sent through a tube in which they're subjected to electric and magnetic fields. Both of these fields exert a force on the ions, and the strengths of the two forces are proportional to the ions' charge (neutral atoms don't feel the forces). The electric force causes the ions to change speed, while the magnetic force bends their path.
The ions are then collected by "Faraday cups" at the end of the tube, generating a current in wires attached to the cups. By measuring where and when the stream of ions hits the Faraday cups, the physicists can determine how much they must have accelerated, and in what direction, as a result of the electric and magnetic forces. Lastly, by way of Newton's second law of motion, F=ma, rearranged as m=F/a, the physicists divide the total force acting on the ions by their resulting acceleration to determine the ions' mass.
The mass of the electron has also been determined using a mass spectrometer — in that case, electrons were simply sent through the instrument themselves. That measurement enables physicists to determine the mass of an atom when it has the correct number of electrons, rather than a dearth or surplus of them.
Using a mass spectrometer, physicists have determined the mass of a hydrogen atom to be 1.660538921(73)×10−27 kilograms, where the parenthetical digits are not known with complete certainty. That's accurate enough for most purposes.
Ye olde mass
What about before the days of mass spectrometers, when chemists were fuzzy about what an atom even was? Then, they primarily measured the weights of the atoms that composed various elements in terms of their relative masses, rather than their actual masses. In 1811, the Italian scientist Amedeo Avogadro realized that the volume of a gas (at a given pressure and temperature) is proportional to the number of atoms or molecules composing it, regardless of which gas it was. This useful fact allowed chemists to compare the relative weights of equal volumes of different gases to determine the relative masses of the atoms composing them.
They measured atomic weights in terms of atomic mass units (u), where 1 u was equal to one-twelfth of the mass of a carbon-12 atom. When in the second half of the 19th century, chemists used other means to approximate the number of atoms in a given volume of gas — that famous constant known as Avogadro's number — they began producing rough estimates of the mass of a single atom by weighing the volume of the whole gas, and dividing by the number.
For further details log on website : http://www.livescience.com/20581-weigh-atom.html
Atoms are the basic units of matter and the defining structure of elements. Atoms are made up of three particles: protons, neutrons and electrons.
Protons and neutrons are heavier than electrons and reside in the center of the atom, which is called the nucleus. Electrons are extremely lightweight and exist in a cloud orbiting the nucleus. The electron cloud has a radius 10,000 times greater than the nucleus.
Protons and neutrons have approximately the same mass. However, one proton weighs more than 1,800 electrons. Atoms always have an equal number of protons and electrons, and the number of protons and neutrons is usually the same as well. Adding a proton to an atom makes a new element, while adding a neutron makes an isotope, or heavier version, of that atom.
Nucleus
The nucleus was discovered in 1911, but its parts were not identified until 1932. Virtually all the mass of the atom resides in the nucleus. The nucleus is held together by the "strong force," one of the four basic forces in nature. This force between the protons and neutrons overcomes the repulsive electrical force that would, according to the rules of electricity, push the protons apart otherwise.
Protons
Protons are positively charged particles found within atomic nuclei. They were discovered by Ernest Rutherford in experiments conducted between 1911 and 1919.
The number of protons in an atom defines what element it is. For example, carbon atoms have six protons, hydrogen atoms have one and oxygen atoms have eight. The number of protons in an atom is referred to as the atomic number of that element. The number of protons in an atom also determines the chemical behavior of the element. The Periodic Table of the Elements arranges elements in order of increasing atomic number.
Protons are made of other particles called quarks. There are three quarks in each proton — two "up" quarks and one "down" quark — and they are held together by other particles called gluons.
Electrons
Electrons have a negative charge and are electrically attracted to the positively charged protons. Electrons surround the atomic nucleus in pathways called orbitals. The inner orbitals surrounding the atom are spherical but the outer orbitals are much more complicated.
An atom's electron configuration is the orbital description of the locations of the electrons in an unexcited atom. Using the electron configuration and principles of physics, chemists can predict an atom's properties, such as stability, boiling point and conductivity.
Typically, only the outermost electron shells matter in chemistry. The inner electron shell notation is often truncated by replacing the long-hand orbital description with the symbol for a noble gas in brackets. This method of notation vastly simplifies the description for large molecules.
For example, the electron configuration for beryllium (Be) is 1s22s2, but it's is written [He]2s2. [He] is equivalent to all the electron orbitals in a helium atom. The Letters, s, p, d, and f designate the shape of the orbitals and the superscript gives the number of electrons in that orbital.
Neutrons
Neutrons are uncharged particles found within atomic nuclei. A neutron's mass is slightly larger than that of a proton. Like protons, neutrons are also made of quarks — one "up" quark and two "down" quarks. Neutrons were discovered by James Chadwick in 1932.
Isotopes
The number of neutrons in a nucleus determines the isotope of that element. For example, hydrogen has three known isotopes: protium, deuterium and tritium. Protium, symbolized as 1H, is just ordinary hydrogen; it has one proton and one electron and no neutrons. Deuterium (D or 2H) has one proton, one electron and one neutron. Tritium (T or 3H) has one proton, one electron and two neutrons.
For further details log on website : http://www.livescience.com/37206-atom-definition.html
Penderia aliran jisim atau penderia aliran jisim udara (mass air flow sensor) ialah penderia yang bertindak balas kepada jumlah bendalir (biasanya gas) mengalir melalui kamar yang mengandungi penderia. Ia direka agar tidak sensitif kepada kepadatan bendalir.
Penderia jisim aliran udara digunakan bagi mengetahui jisim udara yang memasuki suntikan bahan-api engin pembakaran dalaman. Maklumat jisim udara diperlukan bagi unit kawalan enjin ("engine control unit - ECU") untuk mengimbangi dan menghantar jisim bahan api yang betul kepada enjin. Udara bertukar kepadatannya ketika ia mengambang dan mengucup dengan tekanan dan suhu. Bagi pengunaan kereta, kepadatan udara berbeza dengan suhu luaran, altitude, dan kegunaan pengecaj turbo dan ini merupakan penggunaan sesuai bagi penderia jisim.
Terdapat dua jenis biasa penderia jisim aliran udara yang digunakan dalam enjin kereta. Ia adalah meter vane dan wayar panas. Tidak satupun menggunakan teknologi yang mengujur jisim udara secara langsung. Bagaimanapun, dengan tambahan satu atau dua penderia, kadar aliran jisim udara ke enjin boleh ditentukan dengan tepat.
Kedua-dua pendekatan digunakan hampir sepenuhnya bagi enjin pancutan bahan api eletronik. Kedua-dua reka bentuk penderia memiliki output 0.0- 5.0 volt atau isyarat modulasi luas denyutan ("pulse-width modulation - PWM") yang berkadar dengan kadar aliran jisim udara, dan kedua penderia memiliki bukaan masuk penderia suhu udara ("intake air temperature - IAT") disepadukan ke dalam kerangkanya.
Apabila MAF digunakan bersama dengan penderia oksijen, kadar udara/bahanapi enjin dapat dikawal dengan amat tepat. Penderia MAF membekalkan maklumat jangkaan aliran udara sensor (aliran udara yang diukur) litar-buka kepada ECU, dan penderia oksijen membekalkan suap balas litar tutup bagi pembetulan kecil kepada jangkaan jisim udara. Lihat juga penderia MAP.
Vane, atau dayung, menonjol ke dalam aliran udara masuk ke enjin pada lengan berspring. Pergerakan vane adalah berkadar dengan aliran udara, dan voltan dihasilkan berkadar dengan jarak pergerakan vane, atau kadar pergerakan vane mengawal jumlah suntikan bahanapi, sebagaimana yang terdapat pada sistem K-Jetronic.
Pergerakan vane disebabkan oleh heretan aliran udara padanya, Ia tidak mengukur isipadu atau jisim secara langsung. Daya heretan bergantung kepada isipadu udara, had laju dan bentuk vane,
Pendekatan meter vane mempunyai kelemahannya:
ia menghadkan aliran udara yang menghadkan hasilan enjin
ie memiliki sambungan eletrik atau kekanikal yang boleh haus
mendapatkan ruang tengekan dalam ruang engin yang tertutup bermasaalah
Penderia aliran jisim udara wayar panas menentukan jisim udara mengalir ke dalam sistem masukan udara enjin. Teori operasi bagi penderia aliran jisim udara wayar panas adalah menyamai anemometer wayar panas (yang menentukan hadlaju udara). Ia dicapai dengan memanaskan wayar menggunakan arus eletrik yang tergantung dalam aliran udara enjin, seperti wayar pembakar. Rintangan eletrik wayar meningkat ketika suhu wayar meningkat, yang menghadkan arus eletrik mengalir melalui litar. Ketika udara mengalir melalui wayar, wayar menyejuk dan mengurangkan rintangannya, yang seterusnya membenarkan lebih banyak arus mengalir melalui litar. Ketika lebih banyak arus mengalir, suhu wayar meningkat sehinggakan rintangan mencapai keseimbangan semula. Jumlah arus yang diperlukan bagi mengekalkan suhu wayar adalah berkadar selaras dengan jisim udara mengalir melalui wayar. Litar eletronik bersepadu menukar ukuran arus kepada isyarat voltan yang kemudiannya dihantar ke ECU.
Sekiranya isipadu udara meningkat disebabkan peningkatan tekanan atau penurunan suhu, tetapi isipadu udara kekal sekata, udara yang lebih padat akan menyingkir lebih banyak haba dari wayar menunjukkan peningkatan aliran jisim udara. Tidak seperti unsur penderia meter vane, tindak balas wayar panas sejajar dengan kepadatan udara. Keupayaan penderia ini amat sesuai bagi menyokong proses pembakaran gasolin yang pada asasnya bertindak balas kepada jisim udara, bukannya isipadu udara.
Setengah kelebihan MAF wayar panas berbanding stail lama meter vane adalah:
bertindak balas dengan pantas kepada perubahan aliran udara
halangan aliran udaran rendah
paket keseluruhan lebih kecil
kurang sensitif kepada kedudukan tenggekan dan unjuran
tidak memiliki bahagian bergerak dengan itu meningkatkan ketahanannya
lebih murah
penderia suhu dan tekanan berasingan tidak diperlukan (untuk menentukan jisim udara)
Terdapat beberapa kekurangan:
kekotoran dan minyak mampu mencemarkan wayar panas dan menganggu ketepatannya
pemasangan memerlukan aliran laminar melalui wayar panas
Siri enjin LS GM (termasuk juga yang lain) menggunakan sistem MAF "wayar sejuk" (dihasilkan oleh AC Delco) di mana gelung penderia seni dalam aliran jisim udara melalui penderia tersebut. Penderia merupakan sebahagian litar oscilator yang frekuensi olengannya bertukar dengan gelung penderia; dengan itu frekuensi berkait dengan jumlah udara (kaki padu setiap minit) melalui unit tersebut. Isyarat eletrik olengan ini kemudiannya dimuat kepada ECU kereta. Unit MAF ini (seperti mana yang digambarkan) memiliki 3 pin, bertanda +, - dan F. F membawa frekuensi gelombang segi empat antara - dan F. Ia dikuasa oleh +5 VDC dari pengawal punca kuasa ECU.
Jaringan pada MAF digunakan untuk melancaran aliran udara untuk memastikan penderia mempunyai peluang terbaik bagi pembacaan stabil. Hal ini tidak digunakan untuk mengukur aliran udara se saat. Dalam situasi di mana pemilik menggunakan penapis udara kasa berminyak, terdapat kemungkinan minyak lebihan melapisi sensor MAF dan mempengaruhi bacaan. Malah, General Motors telah mengeluarkan Buletin Perkhidmatan Teknikal, yang menunjukkan masalah dari menanti yang kasar sehinggalah kerosakan transmisi akibat penderia yang tercemar. Untuk membersihkan bahagian penderia MAF halus, Pencuci MAF atau Eletronik tertentu perlu digunakan, bukannya pencuci karburator atau brek. Ini merupakan pelarut berasaskan alkohol atau CFC, bukan hasil penyulingan petrol yang keras yang digunakan dalam pencuci lain... Penderia perlu disemburkan dengan perlahan dari jarak tertentu untuk mengelakkan kerosakan fizikal pada mereka. Pengilang mendakwa bahawa ujian yang mudah tetapi sangat boleh diharap untuk memastikan ia berfungsi dengan betul adalah dengan mengetuk unit tersebut dengan pemegang pemutar skru ketika kereta hidup, dan sekiranya ini menyebabkan perubahan pada frekuensi keluaran maka unit tersebut perlu dibuang dan OEM gantian dipasang.
Animasi fenomena. Ehsan, Cesareo de La Rosa Siqueira.
Penderia vortex Kármán bertindak dengan membentuk lapisan arus udara. Arus udara terganggo oleh lekuk menegak pada penderia. Ini menyebabkan gelombang pada aliran udara dan seterusnya gelombang akan runtuh berulang dan menghasilkan vortex Kármán. Frekuensi ulang-alik tekanan udara yang terhasil berkadar dengan hadlaju udara.
Vortex ini boleh dibaca secara langsung sebagai denyutan tekanan pada penderia, atau ia boleh dibuat berlanggar dengan cermin yang kemudiannya akan mengganggu atau memancarkan suluhan cahaya dipantul untuk menhasilkan denyutan sebagai tindakbalas kepada vortex. Jenis pertama hanya boleh digunakan bagi udara ditarik masuk (sebelum turbo atau supercaj), sementara jenis yang kedua secara teori boleh digunakan bagi udara ditolak atau ditarik masuk (sebelum atau selepas penggunaan pencetus paksa seperti yang disebut sebelumnya super- atau turbocaj). Disebalik menghasilkan voltan sekata diubah oleh faktor rintangan, jenis keluaran MAF ini sebagai frekuensi kemudiannya perlu ditafsir oleh ECU. Jenis MAF ini terdapat pada Mitsubishi Lancers/EVO, kesemua "Diamond-Star Motors - DSM" (Mitsubishi Eclipse, Eagle Talon, Plymouth Laser) da sesetengah Toyota dan Lexuses. [1]
Unsur aliran Laminar mengukur aliran jisim gas secara langsung. Ia beroperasi pada prinsip bahawa, berdasarkan aliran laminar, perbezaan tekanan sepanjang paip adalah berkadar kepada kadar aliran. Keadaan aliran Laminar wujud pada gas apabila nombor Reynolds bagi gas adalah di bawah nombor kritikal. Kepekatan cecair perlu diimbangkan dalam keputusannya. Unsur aliran Laminar biasanya dibina daripada sejumlah besar paip selari bagi mencapai kadar aliran yang diperlukan.
For further information log on website :
https://ms.wikipedia.org/wiki/Penderia_aliran_jisim
