TRIAC

Triacs are widely used in AC power control applications. They are able to switch high voltages and high levels of current, and over both parts of an AC waveform. This makes triac circuits ideal for use in a variety of applications where power switching is needed. One particular use of triac circuits is in light dimmers for domestic lighting, and they are also used in many other power control situations including motor control.

The triac is a development of the thyristor. While the thyristor can only control current over one half of the cycle, the triac controls it over two halves of an AC waveform. As such the triac can be considered as a pair of parallel but opposite thyristors with the two gates connected together and the anode of one device connected to the cathode of the other, etc..

Triac symbol

The basic triac symbol used on circuit diagram indicates its bi-directional properties. The triac symbol can be seen to be a couple of thyristor symbols in opposite senses merged together.

Like a thyristor, a triac has three terminals. However the names of these are a little more difficult to assign, because the main current carrying terminals are connected to what is effectively a cathode of one thyristor, and the anode of another within the overall device. There is a gate which acts as a trigger to turn the device on. In addition to this the other terminals are both called Anodes, or Main Terminals These are usually designated Anode 1 and Anode 2 or Main Terminal 1 and Main Terminal 2 (MT1 and MT2). When using triacs it is both MT1 and MT2 have very similar properties.

How does a triac work?

Before looking at how a triac works, it helps to have an understanding of haow a thyristor works. In this way the basic concepts can be grasped for the simpler device and then applied to a triac which is more complicated. The operation of the thyristor is covered in the article in this section and accessible through the "Related Articles" box on the left of the page and below the main menu.

For the operation of the triac, it can be imagined from the circuit symbol that the triac consists of two thyristors in parallel but around different ways. The operation of the triac can be looked on in this fashion, although the actual operation at the semiconductor level is rather more complicated.

When the voltage on the MT1 is positive with regard to MT2 and a positive gate voltage is applied, one of the thyristors conducts. When the voltage is reversed and a negative voltage is applied to the gate, the other thyristor conducts. This is provided that there is sufficient voltage across the device to enable a minimum holding current to flow.

Using triacs

there are a number of points to note when using triacs. Although these devices operate very well, to get the best performance out of them it is necessary to understand a few hints on tips on using triacs.

It is found that because of their internal construction and the slight differences between the two halves, triacs do not fire symmetrically. This results in harmonics being generated: the less symmetrical the triac fires, the greater the level of harmonics that are produced. It is not normally desirable to have high levels of harmonics in a power system and as a result triacs are not favoured for high power systems. Instead for these systems two thyristors may be used as it is easier to control their firing.

To help in overcoming the problem non-symmetrical firing ad the resulting harmonics, a device known as a diac (diode AC switch) is often placed in series with the gate of the triac. The inclusion of this device helps make the switching more even for both halves of the cycle. This results from the fact that the diac switching characteristic is far more even than that of the triac. Since the diac prevents any gate current flowing until the trigger voltage has reached a certain voltage in either direction, this makes the firing point of the triac more even in both directions.

diac

A diac is a full-wave or bi-directional semiconductor switch that can be turned on in both forward and reverse polarities. The name diac comes from the words Diode AC switch. The diac is an electronics component that is widely used to assist even triggering of a triac when used in AC switches and as a result they are often found in light dimmers such as those used in domestic lighting. These electronic components are also widely used in starter circuits for fluorescent lamps.

Although the term is not often seen, they may also be called symmetrical trigger diodes - a term resulting from the symmetry of their characteristic curve.

Diac symbol

The diac symbol used to depict this electronic component in circuit diagrams can be remembered as a combination of what may appear to be two diodes in parallel with each other but connected in opposite directions.Owing to the fact that diacs are bi-direction devices the terminals cannot be labelled as anode and cathode as they are for a diode. Instead they may be labelled as A1 and A2 or MT1 ("Main Terminal") and MT2.

Diac operation

Diac circuits use the fact that a diac only conducts current only after a certain breakdown voltage has been exceeded. The actual breakdown voltage will depend upon the specification for the particular component type.

When the diac breakdown voltage occurs, the resistance of the component decreases abruptly and this leads to a sharp decrease in the voltage drop across the diac, and a corresponding increase in current. The diac will remain in its conducing state until the current flow through it drops below a particular value known as the holding current. When the current falls below the holding current, the diac switches back to its high resistance, or non-conducting state.

Diacs are widely used in AC applications and it is found that the device is "reset" to its non-conducting state, each time the voltage on the cycle falls so that the current falls below the holding current. As the behaviour of the device is approximately equal in both directions, it can provide a method of providing equal switching for both halves of an AC cycle, e.g for triacs.

Most diacs have a breakdown voltage of around 30 volts, although the exact specifications will depend upon the particular type of device.. Interestingly their behaviour is somewhat similar to that of a neon lamp, although they offer a far more precise switch on voltage and thereby provide a far better degree of switching equalisation.

Diac applications

One of the major uses of diacs within triac circuits. The diac is placed in series with the gate of a triac to provide a more symmetrical switching characteristic. It is found that triacs do not fire symmetrically as a result of slight differences between the two halves of the device. This results in harmonics being generated, and the less symmetrical the device fires, the greater the level of harmonics produced. It is generally undesirable to have high levels of harmonics in a power system.

To help in overcoming this problem, a diac is often placed in series with the gate. This device helps make the switching more even for both halves of the cycle. This results from the fact that the diac switching characteristic is far more even than that of the triac. Since the diac prevents any gate current flowing until the trigger voltage has reached a certain voltage in either direction, this makes the firing point of the triac more even in both directions. In view of their usefulness, diacs may often be built into the gate terminal of a triac.

fluorescent starter

A fluorescent light not have the usual glowing filament of an incadent bulb, but instead contains a mercury vapor that gives off ultraviolet light when ionized. The ultraviolet light makes particles that coat the inside of the tube, and these particles glow or fluoresce.

Fluorescent starters are used in several type of fluorescent lights. The starter is there to help the lamp light. When voltage is applied to the fluorescent lamp, here's what happens:

1. The starter (which is simply a timed switch) allows current to flow through the filaments at the ends of the tube.
2. The current causes the starter's contacts to heat up and open, thus interrupting the flow of current. The tube lights.
3. Since the lighted fluorescent tube has a low resistance, the ballast now serves as a current limiter.

When you turn on a fluorescent tube, the starter is a closed switch. The filaments at the ends of the tube are heated by electricity, and they create a cloud of electrons inside the tube. The fluorescent starter is a time-delay switch that opens after a second or two। When it opens, the voltage across the tube allows a stream of electrons to flow across the tube and ionize the mercury vapor.

Without the starter, a steady stream of electrons is never created between the two filaments, and the lamp flickers। Without the ballast, the arc is a short circuit between the filaments, and this short circuit contains a lot of current. The current either vaporizes the filaments or causes the bulb to explode.

The most common fluorescent starter is called a "glow tube starter" (or just starter) and contains a small gas (neon, etc.) filled tube and an optional radio frequency interference (RFI) suppression capacitor in a cylindrical aluminum can with a 2 pin base. While all starters are physically interchangeable, the wattage rating of the starter should be matched to the wattage rating of the fluorescent tubes for reliable operation and long life.

The glow tube incorporates a switch which is normally open। When power is applied, a glow discharge takes place which heats a bimetal contact. A second or so later, the contacts close and provide current to the fluorescent filaments. Since the glow is extinguished, there is no longer any heating of the bimetal and the contacts open. The inductive kick generated at the instant of opening triggers the main discharge in the fluorescent tube. If the contacts open at a bad time, there isn't enough inductive kick and the process repeats.

Tube light requires two things to function . Very high starting voltage , and high voltage to continue the operation . The starter is a circuit which breaks at regular intervals . When you break a circuit and start again , high voltage spark takes place . This voltage is further amplified through the choke which is a transformer . Thus at the beginning the starter gives high voltage sparks . Due to this the current begins to flow through the tube and the tube begins to glow. Once the tube starts , the required voltage to sustain is quite low , which is provided by the choke .

If the starter is bad the tube does not start . If the choke is bad or if the gas is low , the tube does not sustain its light .

telephone

telephone triage is more than answering health questions. Telephone triage nurses must be able to ass
ess a client's health concerns without the advantage of visual inspection or face-to-face interaction. Nurses must rely on their communication skills, knowledge of disease processes, and normal growth and development for all age groups in order to ascertain an accurate understanding of the client's symptoms. Triage nurses must have impeccable listening skills to notice the non-verbal clues the client is giving regarding pain, anxiety, fear, and level of comprehension.

There is a difference between health advice lines and triage lines. Health advice lines are usually a community-based information service that offers answers to general healthcare questions. Triage services are typically offered by healthcare facilities and are used in association with a physician's office. They take calls from patients who are attempting to contact the physician or other healthcare provider after usual office hours, for specific health concerns, or urgent medical needs. The triage nurse must assess the severity of the patient's symptoms and then guide the patient to the appropriate level of care.

Triage nurses do not diagnose clients over the phone. The function of the telephone triage nurse is to determine the severity of the caller's complaint using a series of algorithms developed by a coordinated effort of physicians and nurses, direct the caller to the appropriate emergency services if necessary, recommend the suggested medical follow-up based on their assessments and established triage protocols, and provide health information. This process is called the "disposition" in triage settings.

In addition to addressing specific caller complaints, many tele-nurse programs also book appointments for the physicians' offices with which they are associated, both during and after office hours. Furthermore, some programs review and triage the lab/x-ray results received in the office and notify the medical practitioner of critical values. Making follow-up calls to high-risk patients may also involve allowing the triage nurse to assess changes of status or to ensure that the patient sought the appropriate treatment. In addition, there are interpretation services ओफ्फेरेड

A traditional landline telephone system, also known as "plain old telephone service" (POTS), commonly handles both signaling and audio information on the same twisted pair of insulated wires: the telephone line. Although originally designed for voice communication, the system has been adapted for data communication such as Telex, Fax and Internet communication. The signaling equipment consists of a bell, beeper, light or other device to alert the user to incoming calls, and number buttons or a rotary dial to enter a telephone number for outgoing calls. A twisted pair line is preferred as it is more effective at rejecting electromagnetic interference (EMI) and crosstalk than an untwisted pair.

The telephone consists of an alerting device, usually a ringer, that remains connected to the phone line whenever the phone is "on hook", and other components which are connected when the phone is "off hook". These include a transmitter (microphone), a receiver (speaker) and other circuits for dialing, filtering, and amplification. A calling party wishing to speak to another party will pick up the telephone's handset, thus operating a button switch or "switchhook", which puts the telephone into an active (off hook) state by connecting the transmitter (microphone), receiver (speaker) and related audio components to the line. This circuitry has a low resistance (less than 300 Ohms) which causes DC current (48 volts, nominal) from the telephone exchange to flow through the line. The exchange detects this DC current, attaches a digit receiver circuit to the line, and sends a dial tone to indicate readiness. On a modern telephone, the calling party then presses the number buttons in a sequence corresponding to the telephone number of the called party. The buttons are connected to a tone generator circuit that produces DTMF tones which end up at a circuit at the exchange. A rotary dial telephone employs pulse dialing, sending electrical pulses corresponding to the telephone number to the exchange. (Most exchanges are still equipped to handle pulse dialing.) Provided the called party's line is not already active or "busy", the exchange sends an intermittent ringing signal (about 90 volts AC in North America and UK and 60 volts in Germany) to alert the called party to an incoming call. If the called party's line is active, the exchange sends a busy signal to the calling party. However, if the called party's line is active but has call waiting installed, the exchange sends an intermittent audible tone to the called party to indicate an incoming call.

The phone's ringer is connected to the line through a capacitor, a device which blocks the flow of DC current but permits AC current. This constitutes a mechanism whereby the phone draws no current when it is on hook, but exchange circuitry can send an AC voltage down the line to activate the ringer for an incoming call. When a landline phone is inactive or "on hook", the circuitry at the telephone exchange detects the absence of DC current flow and therefore "knows" that the phone is on hook with only the alerting device electrically connected to the line. When a party initiates a call to this line, and the ringing signal is transmitted. When the called party picks up the handset, they actuate a double-circuit switchhook which simultaneously disconnects the alerting device and connects the audio circuitry to the line. This, in turn, draws DC current through the line, confirming that the called phone is now active. The exchange circuitry turns off the ring signal, and both phones are now active and connected through the exchange. The parties may now converse as long as both phones remain off hook. When a party "hangs up", placing the handset back on the cradle or hook, DC current ceases to flow in that line, signaling the exchange to disconnect the call.

Calls to parties beyond the local exchange are carried over "trunk" lines which establish connections between exchanges. In modern telephone networks, fiber-optic cable and digital technology are often employed in such connections. Satellite technology may be used for communication over very long distances.

In most telephones, the transmitter and receiver (microphone and speaker) are located in the handset, although in a speakerphone these components may be located in the base or in a separate enclosure. Powered by the line, the transmitter produces an electric current whose voltage varies in response to the sound waves arriving at its diaphragm. The resulting current is transmitted along the telephone line to the local exchange then on to the other phone (via the local exchange or a larger network), where it passes through the coil of the receiver. The varying voltage in the coil produces a corresponding movement of the receiver's diaphragm, reproducing the sound waves present at the transmitter.

A Lineman's handset is a telephone designed for testing the telephone network, and may be attached directly to aerial lines and other infrastructure components.

mic

The MIC is the lowest concentration of antimicrobial agent which inhibits the growth of the microorganism.

A current definition of the Minimum Inhibitory Concentration, MIC, is "the lowest concentration which resulted in maintenance or reduction of inoculum viability"।

Antibiotic resistance is the ability of a microorganism to withstand the effects of an antibiotic. Antibiotic resistance develops through mutation or plasmid exchange between bacteria of the same species. If a bacterium carries several resistance genes, it is called multiresistant or, informally, a superbug.

Antibiotic resistance is a consequence of evolution via natural selection। The antibiotic action is an environmental pressure; those bacteria which have a mutation allowing them to survive will live on to reproduce. They will then pass this trait to their offspring, which will be a fully resistant generation.

A microphone is an example of a transducer, a device that changes information from one form to another. Sound information exists as patterns of air pressure; the microphone changes this information into patterns of electric current. The recording engineer is interested in the accuracy of this transformation, a concept he thinks of as fidelity.

A variety of mechanical techniques can be used in building microphones। The two most commonly encountered in recording studios are the magneto-dynamic and the variable condenser designs.

This is a measure of how much electrical output is produced by a given sound. This is a vital specification if you are trying to record very tiny sounds, such as a turtle snapping its jaw, but should be considered in any situation. If you put an insensitive mic on a quiet instrument, such as an acoustic guitar, you will have to increase the gain of the mixing console, adding noise to the mix. On the other hand, a very sensitive mic on vocals might overload the input electronics of the mixer or tape deck, producing distortion.

An electret microphone is a relatively new type of capacitor microphone invented at Bell laboratories in 1962 by Gerhard Sessler and Jim West. The externally-applied charge described above under condenser microphones is replaced by a permanent charge in an electret material. An electret is a ferroelectric material that has been permanently electrically charged or polarized. The name comes from electrostatic and magnet; a static charge is embedded in an electret by alignment of the static charges in the material, much the way a magnet is made by aligning the magnetic domains in a piece of iron।

Due to their good performance and ease of manufacture, hence low cost, the vast majority of microphones made today are electret microphones; a semiconductor manufacturer estimates annual production at over one billion units. Nearly all cell-phone, computer, PDA and headset microphones are electret types. They are used in many applications, from high-quality recording and lavalier use to built-in microphones in small sound recording devices and telephones. Though electret microphones were once considered low quality, the best ones can now rival traditional condenser microphones in every respect and can even offer the long-term stability and ultra-flat response needed for a measurement microphone. Unlike other capacitor microphones, they require no polarizing voltage, but often contain an integrated preamplifier which does require power (often incorrectly called polarizing power or bias). This preamp is frequently phantom powered in sound reinforcement and studio applications. Microphones designed for Personal Computer (PC) use, sometimes called multimedia microphones, use a stereo 3.5 mm plug (though a mono source) with the ring receiving power via a resistor from (normally) a 5 V supply in the computer; unfortunately, a number of incompatible dynamic microphones are fitted with 3.5 mm plugs too. While few electret microphones rival the best DC-polarized units in terms of noise level, this is not due to any inherent limitation of the electret. Rather, mass production techniques needed to produce microphones cheaply don't lend themselves to the precision needed to produce the highest quality microphones, due to the tight tolerances required in internal dimensions. These tolerances are the same for all condenser microphones, whether the DC, RF or electret technology is used.

Light-emitting diode

An LED is a special semiconductor which emits light when current is passed through it. There are many different physical styles. The emitted color spectrum is usually very narrow. It can generally be specified as a specific wavelength in the electromagnetic spectrum. The emitted color selection is somewhat limited. The most commonly available colors are red, green, amber, yellow, blue and white. The red, green, yellow and amber have a working voltage of approximately 1.8 volts. You can refer to the data sheet for each LED to find the exact value. The actual working voltage is determined by the breakdown voltage of the particular semiconductor material.

When using an LED in a circuit, the exact working voltage is not extremely important. The most important thing is the current flow through the LED. The current through the diode must be limited by a series resistor. An LED has a specified maximum continuous current rating. Most LEDs can pass 20 milliamps continuously without damage but it is not necessary to use the maximum rated current. An LED will light with much less current. The difference between high current and low current will be the brightness of the LED. To decide what resistor value is needed, you subtract the working (forward) voltage from the power supply voltage and divide that number by the desired current flow.

Working voltage (Vf)=1.8 volts

Desired current flow=15ma (.015 amps)

Power supply voltage=12 volts

12-1.8=10.2

10.2/.015=680 ohms

A light-emitting diode (LED) is an electronic light source. The LED was first invented in Russia in the 1920s, and introduced in America as a practical electronic component in 1962. Oleg Vladimirovich Losev was a radio technician who noticed that diodes used in radio receivers emitted light when current was passed through them. In 1927, he published details in a Russian journal of the first ever LED.

All early devices emitted low-intensity red light, but modern LEDs are available across the visible, ultraviolet and infra red wavelengths, with very high brightness.

LEDs are based on the semiconductor diode. When the diode is forward biased (switched on), electrons are able to recombine with holes and energy is released in the form of light. This effect is called electroluminescence and the color of the light is determined by the energy gap of the semiconductor. The LED is usually small in area (less than 1 mm²) with integrated optical components to shape its radiation pattern and assist in reflection.

LEDs present many advantages over traditional light sources including lower energy consumption, longer lifetime, improved robustness, smaller size and faster switching. However, they are relatively expensive and require more precise current and heat management than traditional light sources.

Applications of LEDs are diverse. They are used as low-energy indicators but also for replacements for traditional light sources in general lighting and automotive lighting. The compact size of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are useful in communications technology.

Water cooler

A concurrent use water cooler capable of simultaneously dispensing a single fluid to two or more users is presented. The invention includes a container having a single reservoir therein, a lid contacting and removable from the container, at least two spigots disposed about and attached to the container, a vent hole, and a plug to close the vent hole. Spigots communicate with the single reservoir and enable the gravity-fed dispensing of a single fluid. At least one spigot has a threaded spout allowing attachment of a fluid supply line. The threaded spigot is biased to resist the static pressure associated with fluid within the supply line so as to remain closed unless actuated by the user. An optional stand contacts and supports the water cooler. One or more cup dispensers may be attached to the container or stand. The present invention has immediate applicability to sports teams, military units, construction crews, and the like, where two or more persons consume a potable liquid.

A water cooler (commonly spelled "watercooler" ) is a devise that cools and dispenses water. They are generally broken up in two categories: bottle-less and bottled water coolers. Bottle-less water coolers are hooked up to a water supply, while bottled water coolers require delivery (or self pick up) of water in large bottles from vendos.

The most common form of the watercooler is wall mounted and connected to the building's water supply for a continuous supply of water and electricity to run a refrignation unit to cool the incoming water, and to the building's waste disposal system to dispose of unused water. Some versions are free standing floor models, which are becoming more popular in countries where it is not common to drink water straight from the tap.

A newer, free-standing design involves bottles of water, usually treated in some way, placed spout-down into the dispensing machine. To install the bottle, the bottle is tipped upside down and set onto the dispenser, a probe punctures the cap of the bottle and allows the water to flow into the machine's internal reservoir. These machines come in different sizes and vary from table units, intended for occasional use to floor-mounted units intended for heavier use. Bottled Water normally is delivered to the household or business on a regularly basis, where empty bottles are exchanged for full ones. Commonly a cup dispenser can be mounted to the side of the unit to keep disposable paper or plastic cups handy for use. The bottle size varies with the size of the unit with the larger versions in the u.s using 5 gallon bottles. The standard size elsewhere is 18.9litters. Some units offer a refrigeration function to chill the water. These units do not have a place to dump excess water, only offering a small basin to catch minor spills. On the front, a lever or push button dispenses the water into a cup held beneath the spigot. When the water container is empty, it is lifted off the top of the dispenser, and automatically seals to prevent any excess water still in the bottle from leaking.

These gravity-powered systems have a device to dispense water in a controlled manner. Some versions also have a second dispenser that delivers room temperature water or even heated water that can be used for tea,hot chocolate, or instant coffee. The water in the alternate hot tab is generally heated with a heating elements a hot tank (much like the traditional hot water heaters used in residential homes). Additionally, the hot tap is equipped with a push-in safty valvs to prevent burns from an accidental or inadvertent pressing of the lever.

Table top or kitchen worktop versions are available which utilise readily available five liter water bottles from supermarkets. For example the one by design house Warwick Design shown. These coollers use air pumps to push the water into the cooling chamber and peltier devices to chill the water.

Refrigerator

Freezers keep their contents frozen. They are used in households and in industry and commerce. Most freezers operate around 0 °F (-18 °C). Domestic freezers can be included as a separate compartment in a refrigerator, or can be a separate appliance. Domestic freezers are generally upright units resembling refrigerators, or chests resembling upright units laid on their backs. Many upright modern freezers come with an ice dispenser built into their door.

In the kitchen of nearly every home in America there is a refrigerator. Every 15 min­utes or so you hear the motor turn on, and it magically keeps things cold. Without refrigeration, we'd be throwing out our leftovers instead of saving them for another meal.

The refrigerator is one of those miracles of modern living that totally changes life. Prior to refrigeration, the only way to preserve meat was to salt it, and iced beverages in the summer were a real luxury.

The basic idea behind a refrigerator is very simple: It uses the evaporation of a liquid to absorb heat. In this article, you'll find out how your refrigerator performs its magic based on this simple principle. We'll also look at cold packs, electronic coolers and the propane refrigerators found in RVs.

The fundamental reason for having a refrigerator is to keep food cold. Cold temperatures help food stay fresh longer. The basic idea behind refrigeration is to slow down the activity of bacteria (which all food contains) so that it takes longer for the bacteria to spoil the food.

For example, bacteria will spoil milk in two or three hours if the milk is left out on the kitchen counter at room temperature. However, by reducing the temperature of the milk, it will stay fresh for a week or two -- the cold temperature inside the refrigerator decreases the activity of the bacteria that much. By freezing the milk you can stop the bacteria altogether, and the milk can last for months (until effects like freezer burn begin to spoil the milk in non-bacterial ways).

Refrigeration and freezing are two of the most common forms of food preservation used today. For more information on other ways to preserve food.

Soldering Iron

This soldering iron system includes the only iron to use switching technology allowing the closest possible monitoring and correcting of extremely small temperature variations of the tip, thus resulting in a soldering iron that is in a state of constant temperature under varying thermal loads. This compact soldering system with its modern style takes up little space on the workbench. It is stackable so that two or more control bases and/or iron holders can be attached together where two different soldering tips and soldering iron temperatures can be maintained and used for one single job. Control base and the iron holder can be separated if needed.

Soldering Iron Systems
A soldering iron is a device for applying heat to melt solder for soldering two metal parts together.

Vineet Electric Company was founded by Mr. Dinesh Vineet in 1982.At that time good quality soldering irons with international specifications were not available in India. Mr. Dinesh Vineet, himself an Electronics Engineer, was working with a reputed Electronics PSU. He designed a soldering iron with international specifications and incorporated a novel coating procedure for copper bits which till date remain unique. Our siron range of products are far ahead of competition and are perceived highly by users.

A soldering iron is a tool used for applying heat to two adjoining metal parts such that solder may melt and flow between those parts, binding them securely and conductively.

A soldering iron is composed of a heated metal tip and an insulated handle. Heating is often achieved electrically, by passing a current, supplied through an electrical cord or a battery, through a heating element. Another heating method includes combustion of a suitable gas, which can either be delivered through a tank mounted on the iron (flameless), or through an external flame.

Some soldering irons heat up and cool down in a few seconds, but others take minutes.

For electrical work, wires and various electronic components are soldered to printed circuit boards, other wires, and small terminals. A low-power iron (15-30watts) is suitable for this work. In earlier days wires were frequently soldered to large chassis made of heavy metal, but this high-power requirement is now rare. Higher power is used for non-electrical metal-work.

Small battery-operated or gas soldering irons are useful when there isn’t a convenient source of electricity.

Some soldering irons have interchangeable tips for different types of work. Pyramid tips with a triangular flat face are useful for soldering sheet metal. Fine round or chisel tips are typically used for electronics work.

A soldering iron stand keeps the iron away from flammable materials, and often also comes with a sponge and flux pot for cleaning the tip. Some soldering irons for continuous and professional use come as part of a soldering station, which allows the exact temperature of the tip to be adjusted, kept constant, and displayed.

Heat the work piece as well as the solder applied to it. This helps to prevent "cold joints", where hot solder is applied by the iron to a relatively cold target, shrouding it in solder to look like a good joint, but without wetting it properly, and without forming a good connection.

Some electrical solder contains flux cores (the purpose of the flux is to clean the oxides off the metals to permit a good joint). If the solder is applied to the iron first then the flux is rapidly burnt off (the wispy white smoke you get from the tip of the iron) and cannot serve its purpose on the joint. In heavier applications, including plumbing, flux is normally applied completely separately.

VACUUM CLEANERS

When you sip soda through a straw, you are utilizing the simplest of all suction mechanisms. Sucking the soda up causes a pressure drop between the bottom of the straw and the top of the straw. With greater fluid pressure at the bottom than the top, the soda is pushed up to your mouth. ­

This is the same basic mechanism at work in a vacuum cleaner, though the execution is a bit more complicated. In this article, we'll look inside a vacuum cleaner to find out how it puts suction to work when cleaning up the dust and debris in your house. As we'll see, the standard vacuum cleaner design is exceedingly simple, but it relies on a host of physical principles to clean effectively.

It may look like a complicated machine, but the conventional vacuum cleaner is actually made up of only six essential components:

• An intake port, which may include a variety of cleaning accessories
• An exhaust port
• An electric motor
• A fan
• A porous bag
• A housing that contains all the other components.

When you plug the vacuum cleaner in and turn it on, this is what happens:

1. The electric current operates the motor. The motor is attached to the fan, which has angled blades.
2. As the fan blades turn, they force air forward, toward the exhaust port.
3. When air particles are driven forward, the density of particles (and therefore the air pressure) increases in front of the fan and decreases behind the fan.

This pressure drop behind the fan is just like the pressure drop in the straw when you sip from your drink. The pressure level in the area behind the fan drops below the pressure level outside the vacuum cleaner (the ambient air pressure). This creates suction, a partial vacuum, inside the vacuum cleaner. The ambient air pushes itself into the vacuum cleaner through the intake port because the air pressure inside the vacuum cleaner is lower than the pressure outside.

As long as the fan is running and the passageway through the vacuum cleaner remains open, there is a constant stream of air moving through the intake port and out the exhaust port. But how does a flowing stream of air collect the dirt and debris from your carpet? The key principle is friction.

A vacuum's suction is caused by a difference in air pressure. An electric motor reduces the pressure inside the machine. Atmospheric pressure then pushes the air through the carpet and into the nozzle, and so the dust is literally pushed into the bag.

Tests have shown that vacuuming can kill 100% of young fleas and 96% of adult fleas.

Hairdryer

hairdryer is an electromechanical device designed to blow cool or hot air over wet or damp hair, in order to accelerate the evaporation of water particles and dry the hair. Blowdryers allow to better control the shape and style of hair, by accelerating and controlling the formation of temporary hydrogen bonds inside each strand. These hydrogen bonds are very powerful (allowing for stronger hair shaping than even the sulfur bonds formed by permanent waving products), but are temporary and extremely vulnerable to humidity. They disappear with a single washing of the hair.

Hairstyles using blowdryers usually have volume and discipline, which can be further improved by the use of styling products and hairbrushes during drying to add tension, hold and lift.

Blowdryers were invented around the end of the 19th century. The first model was created by Alexandre F. Godefoy in his salon in France. The handheld, household hair-dryer first appeared in 1920.

What is ion Technology?
Ion technology is a stream of ions produced by the device which are blown onto the hair in the air stream. These ions seperate free water molecules into micro drops (Smaller drops) which are easier to dry which means less time that the hair is subject to heat. Also these microdrops are more easily absorbed by the hair producing more hydrated healthier hair. These negative ions also cancel out the harmful positive static charges created from brushing the hair.

What are ceramics in hairdryers?
the ceramics are to isolate the ionic generators and to group the ions at the tip where the air stream takes them to the hair

What does Wattage matter?
The wattage is the general guide to the power output of the hair dryer. Higher wattage means more power that produces more heat suitable for heavier thicker hair. The hotter the temperature of the airstream the faster the hair will dry but the more damage that can be caused without ionic protection.

Which of these are professional and what is the difference?
The professional dryers have the highest wattage for use in salons and fast drying. The best dryers are the highest wattage but also have a temperature control and/or coolshot

So which is the best dryer for me?
The best dryers are the ones with a combination of all the best features. Higher wattage but temperature control means that the dryer is suitable for all hair types. Ionic technology is also recommended to protect your hair during drying.

Most models use coils of wire that have a high electric resistivity and heats rapidly with an electric current. A fan usually blows ambient air past the hot coils resulting in heated air effective for drying. The heating element in most hairdryers is a bare, coiled nichrome wire that is wrapped around insulating mica heating boards. Nichrome wire is used in heating elements, because of two important properties: it is a poor conductor of electricity and it does not oxidize when heated.

A survey of stores in 2007 showed that many hair dryers have ceramic heating elements (like ceramic heaters) - because of their "instant heat" capability.

Many of these hair dryers have "cool shot" buttons which turn off the heater and just blow room temperature air while the button is pressed.

Many also feature "ionic" operation, to reduce the amount of static electricity build-up in the hair. Manufacturers also claim this makes the hair "smoother".

Electric Toaster

the toaster is made of a series of heating elements mounted on mica frames and supported on a porcelain base. It is an example of heating by exposed wires and direct radiation. The heaters H are coils of flat resistance wire that are wound on wedge-shaped pieces of mica. They are supported on a wire frame that is formed to receive slices of bread on each side of the heaters. The attachment piece A and the material of the heater is similar in construction to that of the flat-iron. The electric circuit may be traced from the contacts at A and B in the attachment plug by the dotted lines which indicate the wires in the porcelain base. The current traverses each coil in turn and connects with the next, alternately at the top and bottom. The resistance is such as will permit the voltage of the circuit to send through the coils current sufficient to raise the heaters to a red heat. The added resistance of the hot wires decreases the flow of current to keep the temperature at the desired degree.

In a heater of this kind the resistance of the wire may increase with age and the coils fail to glow with a sufficient brightness. The reason for the lack of heat is that of decrease in current, due to the increased resistance of the wires. This condition may be corrected by the removal of a little of the heater coils. If a turn or two of the heater wire is removed, the resistance of the circuit is reduced and the effect of the increased current will produce a higher temperature in the heater.

The toaster is typically a small electric kitchen appliance designed to toast multiple types of bread products. A typical modern two-slice toaster draws anywhere between 600 and 1200 W and makes toast in 1 to 3 minutes. There are also non-electrical toasters that can be used to toast bread products over an open fire or flame.

Modern toasters are typically one of three varieties: pop-up toasters, ovens and conveyors.

In pop-up or automatic toasters, bread slices are inserted vertically into the slots (generally only large enough to admit a single slice of bread) on the top of the toaster. A lever on the side of the toaster is depressed, activating the toaster. When an internal device determines that the toasting cycle is complete, the toaster turns off and the toast pops up out of the slots. The heating elements of a pop-up toaster are usually oriented vertically, parallel to the bread slice - although there are some variations.

In earlier days, the completion of the toasting operation was determined by a mechanical clockwork timer; the user could adjust the running time of the timer to determine the degree of "doneness" of the toast, but the first cycle produced less toasted toast than subsequent cycles because the toaster was not yet warmed up. Toasters made since the 1930s frequently use a thermal sensor, such as a bimetallic strip, located close to the toast. This allows the first cycle to run longer than subsequent cycles. The thermal device is also slightly responsive to the actual temperature of the toast itself. Like the timer, it can be adjusted by the user to determine the "doneness" of the toast. By comparison, toaster ovens are small electric ovens with a door on one side and a tray within. To toast bread with a toaster oven, one lays down slices of bread horizontally on the tray, closes the door, and activates the toaster. When the toast is done, the toaster turns off, but the door must be opened manually. Most toaster ovens are significantly larger than toasters, but are capable of performing most of the functions of electric ovens, albeit on a much smaller scale. They can be used to cook toast with toppings, like garlic bread or cheese, though they tend to produce drier toast and require longer operating times, since their heating elements are located further from the toast (to allow larger items to be cooked). They may also heat less evenly than either toasters or larger electric ovens, and some glass cookware cannot be used in them.

toaster oven

Conveyor toasters are designed to make many slices of toast and are generally used in the catering industry, being suitable for large-scale use. Bread is toasted 350-900 slices an hour, making conveyor toasters ideal for a large restaurant that is constantly busy with growing demand. However, such devices have occasionally been produced for home use as far back as 1938, when the Toast-O-Lator went into limited production. [See www.jitterbuzz.com/indtol.html for a detailed history of the Toast-O-Lator company]

As with so many home appliances, more elaborate toasters and toaster ovens now utilize computer-controlled mechanisms in place of electromechanical controls. Toasters are usually freestanding, counter-top appliances, although some toaster ovens may be hung beneath cabinets.

Sometimes toast gets stuck in a toaster, particularly pop-up toasters, and must be freed manually. As most toasters are in the kitchen, metal knives and forks are typically an easily available tool but can cause risk of electric shock, unless the appliance is disconnected from the main electrical outlet.

Some toasters also have a small round griddle on them for making eggs with toast.

Washing Machine

When you use a washing machine, you generally select the length of wash time based on the amount of clothes you wish to wash and the type and degree of dirt you have. To automate this process, we use sensors to detect these parameters (i.e. volume of clothes, degree and type of dirt). The wash time is then determined from this data. Unfortunately, there is no easy way to formulate a precise mathematical relationship between volume of clothes and dirt and the length of wash time required. Consequently, this problem has remained unsolved until very recently. People simply set wash times by hand and from personal trial and error experience. Washing machines were not as automatic as they could be.

To build a more fully automatic washing machine with self determining wash times, we are going to focus on two subsystems of the machine: (1) the sensor mechanism and (2) the controller unit. The sensor system provides external input signals into the machine from which decisions can be made. It is the controller's responsibility to make the decisions and to signal the outside world by some form of output. Because the input/output relationship is not clear, the design of a washing machine controller has not in the past lent itself to traditional methods of control design. We address this design problem using fuzzy logic and FIDE.

For particularly dirty clothing covered with mud or dirt, it was necessary to constantly rub and flex the cloth to break apart solids and help the soap penetrate through thick, dry, or sticky layers of soil on the cloth. At first this was done by pounding or rubbing the clothing with rocks in a river, and later developed into the corrugated wash board. In Roman times a fuller would whiten clothing by stomping on it in a bucket full of fermented urine.

Washing machine technology was developed as a way to reduce the drudgery of this scrubbing and rubbing process, by providing an open basin or sealed container with paddles or fingers to automatically agitate the clothing. The earliest machines were often hand-operated but were built with the belief that the machine itself was faster and easier to operate than washing the clothing by hand directly. As electricity was not commonly available until at least 1930, these early machines were often operated by a low-speed single-cylinder hit and miss gasoline engine.

Because water usually had to be heated on a fire for washing, the warm soapy water was precious and would be reused over and over, first to wash the least soiled clothing, then to wash progressively dirtier clothing. The load of soaking wet clothing would be removed, and another load of dirty clothes added to the machine. While the earliest machines were constructed entirely from wood, later machines made of metal permitted a fire to burn below the washtub, to keep the water warm throughout the day's washing.

Removal of soap and water from the clothing after washing was originally a separate process. The soaking wet clothing would be formed into a roll and twisted by hand to extract water. To help reduce this labour, the wringer/mangle was developed, which uses two rollers under spring tension to squeeze water out of the clothing. Each piece of clothing would be fed through the wringer separately. The first wringers were hand-operated, but were eventually included as a powered attachment above the washer tub. The wringer would be swung over the wash tub so that extracted wash water would fall back into the tub to be reused for the next wash load.

The modern process of water removal by spinning did not come into use until electric motors were developed. Spinning requires a constant high-speed power source, and was originally done in a separate device known as an extractor. A load of washed clothing would be transferred from the wash tub to the extractor basket, and the water spun out. These early extractors were often dangerous to use since unevenly distributed loads would cause the machine to shake violently. Many efforts have been made to counteract the shaking of unstable loads, first by mounting the spinning basket on a free-floating shock-absorbing frame to absorb minor imbalances, and a bump switch to detect severe movement and stop the machine so that the load can be manually redistributed. Many modern machines are equipped with a sealed ring of liquid that works to counteract any imbalances.

What is now referred to as an automatic washer was at one time referred to as a washer/extractor, which combines the features of these two devices into a single machine, plus also includes the ability to fill and drain water by itself. It is possible to take this a step further, to also merge the automatic washing machine and clothes dryer into a single device, but this is generally uncommon because the drying process tends to use much more energy than using two separate devices; a combined washer/dryer not only must dry the clothing, but also need to dry out the wash chamber itself.

In 2009, L'Osservatore Romano, the semi-official newspaper of the Holy See, pronounced the washing machine an important milestone in the liberation of women, as it freed them from the drudgery of household chores.

Right now the statistics say that this machine could perform the same task by using less than 90 per cent of the water of conventional machines and 30 per cent less energy. This machine can have the environmental impact of taking two million cars off the road.

How could that be possible? Here the work of water is replaced by using thousands of tiny reusable nylon polymer beads. These plastic beads attract and absorb dirt under humid conditions. Stephen Burkinshaw said: “We’ve shown that it can remove all sorts of everyday stains including coffee and lipstick while using a tiny fraction of the water used by conventional machines.”

How does this washing machine function? This technology requires a small amount of water and detergent to dampen the clothes and loosen stains. This device also creates the water vapor that allows the beads to work. Once washing is finished, the beads fall through a mesh in the machine’s drum. These beads are reusable. One can reuse them up to a hundred times. One needs 20kg of the beads along with a cup of water and detergent. The chips can be used up to 100 times, the equivalent of six months’ washing.

A demonstration was held at the Clean Show in New Orleans between June 18th and 21st. The beads are placed inside the smaller of two concentric drums along with the dirty laundry, a spew of detergent and a little water. As the drums spin, the water wets the clothes and the detergent gets to work loosening the dirt. Then the nylon beads mop it up.

The beads have a crystalline structure. This structure makes the surface of beads with an electrical charge that attracts dirt. When the beads are heated in humid conditions to the temperature they lose their crystalline structure and acquire an amorphous structure. Now the dirt is drawn into the core of the bead where it remains locked in place.

The whole process takes about 30 minutes and the outer drum stops rotating. The inner drum has the clothes and the beads. The inner drum also has a small slot. As it keeps on rotating, the beads fall through the slot; some 99.95% of them are collected in the outer drum. The remaining that are trapped in the folds of the clothes normally fall into a collection trough while the laundry is being removed, and a vacuum wand can be used to remove them from pockets etc.

Xeros chief executive Bill Westwater said: “We’ve got an eye on the consumer but it will take time and we hope commercial success could act as a springboard to move into the consumer market. We’ve been very encouraged by the response from people, but the proof is in the pudding and that means putting a machine into someone’s operations and justifying the savings.”

We can draw the conclusion that when so little water is used and the warm beads help dry the laundry, less tumble drying is needed. An environmental consultancy, URS Corp, estimates that this washing machine’s carbon footprint was 40% smaller than the most efficient existing systems for washing and drying laundry.