What is Resistor?

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element.

The current through a resistor is in direct proportion to the voltage across the resistor's terminals. This relationship is represented by Ohm's law:

where I is the current through the conductor in units of amperes, V is the potential difference measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms.

The ratio of the voltage applied across a resistor's terminals to the intensity of current in the circuit is called its resistance, and this can be assumed to be a constant (independent of the voltage) for ordinary resistors working within their ratings.

Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-chrome). Resistors are also implemented within integrated circuits, particularly analog devices, and can also be integrated into hybrid and printed circuits.

Types of Resistor:

Resistors can be broadly classified based on the following criteria: the type of material used, the power rating and resistance value.

 Fixed resistors.

           In some scenarios, an electrical circuit may need a lesser amount of current to flow through it than the input value. Fixed resistors are used in these situations to limit the flow of current.

• Carbon Composition Resistors: 

            These resistors are cylindrical rods which are a mixture of carbon granules and powdered ceramic. The resistor value depends on the composition of the ceramic material. A higher quantity of ceramic content will result in more resistance. Since the rod is coated with an insulated material, there are chances of damage due to excessive heat caused by soldering.

High current and voltage can also damage the resistor. These factors bring irreversible changes in the resistance power of these resistors. This type of resistor is rarely used nowadays due to their high cost and are only preferred in power supply and welding circuits.

• Carbon film resistors: 

           This resistor is formed by depositing a carbon film layer on an insulating substrate. Helical cuts are then made through the carbon film to trace a long and helical resistive path. The resistance can be varied by using different resistivity carbon material and modifying the shape of the resistor. The helical resistive path make these resistors highly inductive and of little use for RF applications.

They exhibit a temperature coefficient between -100 and -900 ppm/ °C. The carbon film is protected either by a conformal epoxy coating or a ceramic tube. The operation of these resistors requires high pulse stability. 

• Metal Film resistor:

          These resistors are made from small rods of ceramic coated with metal (such as a nickel alloy) or metal oxide (such as tin oxide). The value of resistance is controlled mainly by the thickness of the coating layer (the thicker the layer, the lower is the value of resistance). A fine spiral groove can be cut along the rod using a laser to split the carbon or metal coating effectively into a long and spiral strip, which forms the resistor.

Metal film resistors can be obtained in a wide range of resistance values from a few Ohms to tens of millions of Ohms with a very small tolerance. For example, for a stated value of 100K Ohm, the actual value will be between 99K Ohm and 101K Ohm. Small carbon, metal and oxide resistors come in various colors such as dark red, brown, blue, green, grey or white. 

• Wire wound resistor:

          Wire wound resistors vary in size and physical appearance. Their resistive elements are commonly lengths of wire, usually an alloy such as Nickel/Chromium or Manganin wrapped around a small ceramic or glass fiber rod and coated in an insulating flameproof cement film. They are normally available in low values of resistance but are capable of dissipating large amounts of power.

These resistors can get very hot during use. For this reason, these resistors are housed in a finned metal case that can be bolted to a metal chassis to dissipate the heat generated. Protection from fire is important and fireproof cases or coatings are vital. Lead-out wires are normally welded rather than soldered to the resistor. Enamel resistors are used in scenarios where high power is involved and are encapsulated in heat proof bases.

Since wire wound resistors are primarily coils, they have more undesirable inductance than other types of resistor, although winding the wire in sections with alternately reversed directions can minimize inductance. Other techniques employ bifilar winding to reduce cross-section area of the coil. For the most demanding circuits, resistors with Ayrton-Perry windings are used.

• Thin film and thick film resistors: 

          The principal difference between thin film and thick film resistors is how the film is applied to the cylinder (axial resistors) or the surface (SMD resistors). Thin film resistors are made by sputtering (a method of vacuum deposition) the resistive material onto an insulating substrate whereas thick film are made using screen and stencil printing processes.

Ceramic conductors such as tantalum nitride (TaN), ruthenium dioxide (RuO₂), lead oxide (PbO), bismuth ruthenate (Bi₂Ru₂O₇), nickel chromium (NiCr), and bismuth iridate (Bi₂Ir₂O₇) are the materials commonly used for making thin film resistors. Thick film resistors are usually made by mixing ceramics with powdered glass. Thick films have tolerances ranging from 1 to 2% and a temperature coefficient between ±200 or ±250 ppm/K.

Thin film resistors are usually more expensive than thick film resistors. Thin film resistors are preferred for microwave passive and active power componentssuch as microwave power resistors, microwave power terminations, microwave resistive power dividers, microwave power attenuators.

• Surface mount resistor (SMT):

          This type of resistor helps to achieve very low power dissipation along with very high component density. Most modern circuits use tiny SMT resistors. These are made by depositing a film of resistive material such as tin oxide on a tiny ceramic chip. The edges of the resistor are then accurately ground or cut with a laser to give precise resistance across the device. Tolerances may be as low as 0.02%. Contacts at each end are provided, which are soldered directly onto the conductive print on the circuit board, usually by automatic assembly methods. These are mostly used where space is an important factor.

• Network resistors:

          These resistors are the combination of resistances which may be giving identical value at all pins, with one pin acting as a common terminal. These resistors are available in both single in line package and dual in line package and may be surface mount or through hole. These are used in applications such as pull up/pull down, DAC etc.

Variable resistors. 

                       Presets and potentiometers are commonly used types of variable resistors. These are mostly used for voltage division and setting the sensitivity of sensors. These have a sliding contact or wiper which can be rotated with the help of a screw driver to change the resistance value. In the linear type, the change in resistance is linear as the wiper rotates. In the logarithmic type, the resistance changes exponentially as the wiper slides. The value is meant to be set correctly when installed in some device, and is not adjusted by the device's user.

The variable may have three tabs where the middle tab is the wiper. If all the three tabs are used, it behaves as a voltage divider. If only wiper tab is used along with another tab, it becomes a variable resistor or rheostat. If only the side tabs are used, then it behaves as a fixed resistor. These are mostly used for tuning, voltage division and adjusting sensitivity of sensors.

The variable can have one or two switches in-built where the resistor operates for the ON state of the switch(s). Such resistors were mostly used for volume control in older TV and radio circuits. There may also be four-tab variables where the fourth lead is for feedback signal and placed near the first tab. Wire wound variable resistors are used for very precise control of resistance.

The wiper may also be rotary (as in most presets), sliding or disc shaped (as used in pocket radios for volume control).

Semi variable resistors  

                                 These are two terminal variable resistors designed for handling higher voltages and currents. These are constructed by resistive wire wrapped to form a toroid coil with the wiper moving over the upper surface of the toroid, sliding from one turn of the wire to the next. A rheostat is also made from resistance wire wound on a heat-resisting cylinder with the slider made from a number of metal fingers. The fingers can be moved along the coil of resistance wire by a sliding knob, thus changing the tapping point.

 Special resistors 

•  Thermistors:

            Thermistors are special resistors whose resistance changes with the temperature. If the resistance increases with increase in temperature, then it is called positive temperature coefficient (PTC) or posistors. If the resistance decreases with the increase in temperature, then it is called a negative temperature coefficient (NTC).

An NTC can be replaced by a transistor with a trimmer potentiometer. PTCs are mostly used as current limiter for circuit protection. As the heat dissipation of resistor increases, the resistance is increased thereby limiting the current. The NTCs are mostly used for temperature sensing, replacement of fuses in power supply protection and for low temperature measurements of up to 10K. These are constructed using sintered metal oxides in ceramic matrix.

• Light dependent resistors (LDR):

          LDRs have cadmium sulfide zigzag tack whose resistance decreases as the light intensity incident on it increases. In the absence of light, its resistance is in mega ohms but on the application of light, the resistance falls drastically. These resistors are used in many consumer items such as camera light meters, street lights, clock radios, alarms, and outdoor clocks.

Resistor Color Code / Resistance Measurement:

    By Color Codes

Chip resistors have a three digit numeric representation where the first two digits represent the number and the third digit is the multiplier. For example, on a chip resistor, the number 103 signifies that its resistance is 10K with 3 being the multiplication factor. 

                        

          

What is Engineering?

              Engineering is the application of scientific, economic, social, and practical knowledge in order to design, build, and maintain structures, machines, devices, systems, materials and processes. It may encompass using insights to conceive, model and scale an appropriate solution to a problem or objective. The discipline of engineering is extremely broad, and encompasses a range of more specialized fields of engineering, each with a more specific emphasis on particular areas of technology and types of application.

               Engineering is not science. Engineers generally don't "do" science. Science is about discovering the natural. Engineering is creating the artificial.

Types Of Engineering:

Just like music can be grouped into areas like rap, rock or country and western, there are different branches of engineering. According to my research, I found 200 types of Engineering! Whereas some common and renowned engineering are: 

• AEROSPACE
  Aerospace engineers design, analyze, model, simulate, and test aircraft, spacecraft, satellites, missiles, and rockets. Aerospace technology also extends to many other applications of objects moving within gases or liquids. Examples are golf balls, high-speed trains, hydrofoil ships, or tall buildings in the wind.
  
  As an aerospace engineer, you might work on the Orion space mission, which plans on putting astronauts back on the moon by 2020. Or, you might be involved in developing a new generation of space telescopes, the source of some of our most significant cosmological discoveries. But outer space is just one of many realms to explore as an aerospace engineer. You might develop commercial airliners, military jets, or helicopters for our airways. And getting even more down-to-earth, you could design the latest ground and sea transportation, including high-speed trains, racing cars, or deep-sea vessels that explore life at the bottom of the ocean. 

• AGRICULTURAL AND BIOLOGICAL
  Agricultural engineers apply knowledge of engineering technology and science to agriculture and the efficient use of biological resources. In addition to creating advances in farming and agriculture, agricultural engineers apply engineering design and analysis to protecting natural resources, develop power systems to support agriculture, and provide environmental controls.

• AUDIO
  Most people take the sounds we hear every day for granted. But it may surprise you to learn that the creation of audio is a unique endeavor that blends both art and science. Did you ever stop to think how they created the sounds in a video game, or in a move, TV show or at a concert? There are literally thousands of different jobs available in this field that are as rewarding as they are challenging.
  
  There are many career choices in the field of Audio Engineering. Perhaps you are a musician, are interested in electronics and sound, or like the idea of working with people who produce and perform in the many fields of entertainment. You will find challenging and fulfilling work in audio engineering.

• BIOENGINEERING AND BIOCHEMICAL
  Bioengineers study living systems and apply that knowledge to solve various problems. They study the safety of food supplies, keep desirable organisms alive in fermentation processes, and design biologically based sensors. Bioengineering is widely used to destroy wastes and clean up contaminated soil and water. These engineers contribute greatly to human health and the environment.

• BIOMEDICAL
  Biomedical Engineers study biology and medicine to develop technologies related to health care. They develop medical diagnostic machines, medical instruments, artificial organs, joint replacement parts, and prosthetic devices. Rapid advances in these areas will probably continue throughout your lifetime.

• CERAMIC AND MATERIALS
  Ceramic and Materials Engineers solve problems by relying on their creative and technical skills - making useful products in many forms from common as well as exotic materials. Every day we use a multitude of these products. Each time we talk on the phone, use a computer, or heat food in a microwave oven, we are using products made possible by the inventions and designs of engineers working with ceramics and other materials.

• CHEMICAL
  Everything around us is made of chemicals. Chemical changes can be used to produce all kinds of useful products. Chemical Engineers discover and manufacture better plastics, paints, fuels, fibers, medicines, fertilizers, semiconductors, paper, and all other kinds of chemicals. Chemical Engineers also play an important role in protecting the environment, inventing cleaner technologies, calculating environmental impacts, and studying the fate of chemicals in the environment.

• CIVIL
  What would it feel like to have the expertise to build a school that could withstand an earthquake, a road system that puts an end to chronic traffic jams, or a sports stadium that offers everyone a great view? As a civil engineer, your job would be to oversee the construction of the buildings and infrastructure that make up our world: highways, skyscrapers, railways, bridges, and water reservoirs, as well as some of the most spectacular and high-profile of all engineering feats—think of the world’s tallest building, the towering Taipei 101 in Asia, or the Chunnel, the 31-mile-long tunnel beneath the English Channel. Civil engineers are fond of saying that it’s architects who put designs on paper, but engineers who actually get things built.

• COMPUTER
  Computer Engineering is the design, construction, implementation, and maintenance of computers and computer controlled equipment for the benefit of humankind. Most universities offer Computer Engineering as either a degree program of its own or as a sub-discipline of Electrical Engineering. With the widespread use and intergration of computers into our everyday lives, it's hard to separate what an Electrical Engineer needs to know and what a Computer Engineer needs to know. Because of this, several universities offer a dual degree in both Electrical and Computer Engineering.

• ELECTRICAL
  As an electrical engineer, you could develop components for some of the most fun things in our lives (MP3 players, digital cameras, or roller coasters) as well as the most essential (medical tests or communications systems). This largest field of engineering encompasses the macro (huge power grids that light up cities, for example) as well as the micro (including a device smaller than a millimeter that tells a car’s airbags when to inflate). As an electrical engineer, you might work on robotics, computer networks, wireless communications, or medical imaging—areas that are at the very forefront of technological innovation.

• ENVIRONMENTAL
  Environmental Engineering is the study of ways to protect the environment.
  
  Most of us care deeply about stopping pollution and protecting our natural resources. Imagine yourself having more than just a passion for saving our environment, but also possessing the actual know-how to do something about these alarming problems! As an environmental engineer, you’ll make a real difference in the survival of our planet by finding ways of cleaning up our oceans, rivers, and drinking water, developing air pollution equipment, designing more effective recycling systems, or discovering safe ways to dispose of toxic waste.

• GEOLOGICAL AND GEOPHYSICAL
  Geological and Geophysical Engineers draw on the science of geology to study the earth, using engineering principles to seek and develop deposits of natural resources and design foundations for large buildings, bridges, and other structures. Related engineering fields include Civil, Mineral, Mining, and Petroleum.

• INDUSTRIAL
  Industrial engineers determine the most effective ways to use people,machines, materials, information, and energy to make a product or to provide a service. Sometimes they are called "efficiency experts."
  
  Do you think of yourself as super organized? Do you think you’re good at understanding the big picture and figuring out how things could work better? If so, you might make a great industrial engineer. Your job would involve organizing people, places, equipment, and information, ensuring that complex and large-scale systems operate safely and efficiently.
  
  For example, you might keep a hospital operating room running like clockwork. You might make sure an assembly line runs smoothly both for people and machines. Or you might be involved in adding a little extra fun and convenience to people’s lives by figuring out ways of making amusement park lines shorter, or by seeing to it that a big clothing chain always has every size of jeans in stock.
  
  Although most industrial engineers work in manufacturing industries, they may also work in consulting services, healthcare, and communications.

• MANUFACTURING
  Manufacturing means making things. Manufacturing engineers direct and coordinate the processes for making things - from the beginning to the end. As businesses try to make products better and at less cost, it turns to manufacturing engineers to find out how. Manufacturing engineers work with all aspects of manufacturing from production control to materials handling to automation. The assembly line is the domain of the manufacturing engineer. Machine vision and robotics are some of the more advanced technologies in the manufacturing engineers toolkit.
  
  The beginning of the manufacturing process often involves creating prototypes or models of the desired object. In the past, these prototypes were created from wood or clay (kind of like sculpting). Today rapid prototyping is the state of the art. There are a number of types of rapid prototyping systems currently available, but one of the coolest is called stereolithography. A computer-controlled laser shoots through a pool of liquid plastic and forms a solid plastic part which is literally pulled out of the liquid. Manufacturing engineers use rapid prototyping to reduce time to market for something new as well as reducing production cost.

• MARINE AND OCEAN
  These engineering fields are closely related, and deal with the design of ocean vehicles, marine propulsion systems, and marine structures such as harbors, docks, and offshore drilling platforms. These engineers are exploring and developing the natural resources and transportation systems of the ocean.
  
  Two hundred miles off the coast of Washington state, a research ship hovers on the sea's surface, manipulated by navigational satellites hundreds of miles above. A thin cable of fiber-optic strands and electrical conductors connects the ship to a remotely-piloted robotic vehicle on the seafloor 7,000 feet below as it shoots live, high-definition video of volcanic smoker vents and strange life-forms. The video is linked, real time, to a communications satellite 22,500 miles above and, from there, into classrooms coast to coast.

• MECHANICAL
  As a mechanical engineer, you might develop a bike lock or an aircraft carrier, a child’s toy or a hybrid car engine, a wheelchair or a sailboat—in other words, just about anything you can think of that involves a mechanical process, whether it’s a cool, cutting-edge product or a life-saving medical device. Mechanical engineers are often referred to as the general practitioners of the engineering profession, since they work in nearly every area of technology, from aerospace and automotive to computers and biotechnology.

• MINING
  Mining engineers study all phases of extracting mineral deposits from the earth. They design mines and related equipment and supervise their construction and operation. They also work to minimize the environmental effects of mining. These engineers supply energy and rare materials to meet the world's needs.

• NUCLEAR
  Nuclear engineers harness the power of the atom to benefit humankind. They search for efficient ways to capture and put to beneficial use those tiny natural bursts of energy resulting from sub-atomic particles that break apart molecules. As a nuclear engineer, you may be challenged by problems in consumer and industrial power, space exploration, water supply, food supply, environment and pollution, health, and transportation. Participation in these broad areas may carry you into many exciting and challenging careers. These may include interaction of radiation with matter, radiation measurements, radioisotope production and use, reactor engineering, and fusion reactors and materials.

• PETROLEUM
  Petroleum engineers study the earth to find oil and gas reservoirs. They design oil wells, storage tanks, and transportation systems. They supervise the construction and operation of oil and gas fields. Petroleum engineers are researching new technologies to allow more oil and gas to be extracted from each well. They help supply the world's need for energy and chemical raw materials.

Electronics and communication engineering, Electrical and electronics engineering and many more.........

Happy Engineering To You......