Author: bbe

Know the Uses of Reaction Bonded Silicon Carbide
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Silicon carbide is popularly known as carborundum. The compound is made up of silicon and carbon elements and their chemical formula is SiC. The compound is naturally found as moissanite. This is used as an abrasive for which huge amounts of the compound is produced every year.

Do you know that this compound has varied uses? If not, continue reading this article to find out about the uses of the reaction bonded silicon carbide compound.

For Structural Materials

The compound is often used in bulletproof vests and composite armor. They also serve as shelving and support materials in high-temperature areas like kilns for glass fusing, firing ceramics, etc. The SiC kiln shelves are used because they are light in weight than the traditional alumina shelves.

As A Strong Catalyst Support

Reaction bonded silicon carbide exhibits a natural resistance property to oxidation. This, it is chosen as a heterogeneous catalyst to support oxidation reactions of hydrocarbons, like n-butane to maleic anhydride.

In Steel Production

When dissolved in basic oxygen furnace the compound can be used to make steel. The excess energy generated in the furnace allows processing of more scrap materials same as of hot metals.

As Abrasive Material and Cutting Tools

Silicon carbide is durable. Hence, they are used popularly as an abrasive in modern lapidary. The hardness of it makes it useful in the manufacturing industries for works like water-jet cutting, grinding, sandblasting and honing.

The finer particles of silicon carbide are fixed to paper to make sandpapers and grip tape for skateboards.

In Electric Systems

They are greatly used in the electric voltage purposes as silicon has a greater voltage acceptance. The earliest use of this compound was in the lightning arresters. Because of the voltage-dependent resistance, columns of carborundum pellets were used to connect the power lines with the earth. So, when lightning strikes the excess voltage will be passed to the earth harmlessly.

If switches are made out of them they can be placed in series. As they are good for high voltage requirements they can easily reduce the complexity of a system.

As Carborundum Printmaking

Another use of SiC compounds is collograph printmaking technique commonly known as Carborundum printmaking. On the surface of an aluminum plate, the Carborundum grit is applied to a paste. When the paste becomes dry the ink application is done. The ink gets trapped in the granular surface. When the ink is wiped off the bare areas the ink plate is printed onto paper. The painted marks embossed on the paper is the resultant print.

Irrespective of the above there are several other uses of a Silicon carbide compound. Thus, the industries are relying more on this cost-effective compound for their industrial needs.

Black Masterbatch Benefits And Uses
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Masterbatch is liquid of solid additive for plastic that is used for coloring or imparting different properties to plastic. It is a concentrated mixture of additives and pigments that are encapsulated in the heat process to carrier resin that is then cooled and then cut into granular shapes. Processors use masterbatch to economically color raw polymer in the plastic manufacturing process.

Masterbatch is preferred by many because it is less expensive compared to buying a material that is fully compounded. Such a material is not only expensive, but can also be less open to product color variability. The concentrates are also preferred over compounding raw materials on site because they do not have dispersion issues of additives and colorants as it is the case with the compounding process. They might require longer lead times and more storage space, but masterbatches are still advantageous in more ways than one. They offer excellent coverage power and dispersion so they are able to meet requirements for various end user applications and resins. Below are some of the benefits black masterbatch offers to final products.

· Excellent mechanical properties offering better tear and impact resistance and balance stiffness

· Excellent dyeing power

· Enhances appropriate stretching

· Suitable and compliant even for food packaging

· When combined with latest additives, black masterbatch offers thermal stability, UV radiation protection, electrical conductivity, bactericidal effects and flame propagation resistance, heat dissipation and thermal conductivity

These benefits are what makes black masterbatch excellent solution for different segments. Some of the segments that benefit and use the black concentrates include:

· Agriculture for irrigation pipes, agricultural tarpaulins and mulching purposes

· Automotive for technical parts production through polymer engineering

· Electric for electronics such as mixers, blenders, washing machines, coffee machines, vacuum cleaners, TVs and DVDs among many other items

· Packaging for blowing film, flatting film, coatings, injecting and blowing sheets and direct contact with fatty foods and dairy products

· Shoes for the production of blankets and EVA soles

· Raffia for the production of sacks meant for wheat flour, sugar, animal feed and raffia as well as other plasticulture applications

· Fibers to get multifilament and monofilaments

· Construction for wires, cables, geomembranes, hoses, plugs, profiles and fittings, corrugated tubes and water tanks

There are so many masterbatch manufacturers today and you would need to choose a reliable one to have a good experience purchasing and using the concentrates that you needs. Some of the questions that you should ask before placing your order are;

· What will I use the masterbatch for?

· Is it going to get in touch with potable water?

· Is FDA approval necessary?

· What directives need to be adhered to?

· Is it necessary that it is free from heavy metals?

· Does it need additives to enhance performance?

· Is it for outdoor or indoor use?

These questions will help you get the best supply form and material sample within a good time frame. You always work with a reliable manufacturer and supplier so you can have your needs met in the most professional manner possible.

Top 8 Major Elements of Personal Protection Equipment
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Personal protective equipment or PPC is now among the most common applications that can be seen in factory and working environments. PPE equipment can be easily worn by workers for minimizing exposure to different kinds of occupational hazards. Some PPE examples include fall protection, aprons, gloves, safety jackets, foot, eye and head protection. The use of PPE would only be a single element in a complete program safety that would employ different kinds of strategies for maintenance of healthy and safe working environment. However, total or permanent protection isn’t guaranteed by PPE as the hazard isn’t eliminated itself.

The major elements of personal protective equipment can be categorized through the body area of protected body, by the types of hazard, and the garment accessory. A single item, like safety shoes, would provide different types of protection: with steel insoles and steel toe cap you get different proper protection from puncture injuries or crushing, impervious rubber and protection lining from chemicals and water protection, high reflectivity and heal resistance through radiant heat protection, and high electrical resistivity protection through electric shock. Here lie the top 8 major elements of PPE-:

1. Noise

With the help of earmuffs and earplugs the damage extent to hearing can be significantly reduced thus increasing ear safety. High level noise exposure causes irreversible loss of hearing and impairment with psychological or physical stress.

2. Access and height protection

The range height and access protection is wide and includes things like fall-arrest systems, body harnesses, lowering harnesses, rescue lifting, lanyards, energy absorbers, etc. Such kind of PPE is specialized and needs thorough training through competent persons, in user checks and the right use as well.

3. Respirators

With respiratory mask it becomes simple to protect the worker from breathing contaminants in the polluted air, thus preserving respiratory tract and the heart’s health. Two main types of respirators are present. Type one functions through filtering gases, chemicals, and airborne particles, through air breathed by workers. The process of filtration would either be active or passive. Particulate respirators or gas masks are main examples of these kinds of respirators. The type two helps in protection of users by offering clean and respirable air through any other source. This type also includes self-contained breathing apparatus and respirators.

4. Protective clothing

Being one of the main PPE elements, it is all-encompassing and refers to different uniforms and suits that is worn for protection of users through any harm. Ballistic coats that are worn through law enforcement officials and lab coats or safety gloves that are worn by scientists daily at work would come under this category.

5. Ensembles

In personal protective equipment, many types of ensembles can be found for protecting you against different conditions and this work together for specific tasks or occupations. PPE equipment like safety helmets is usable for multiple tasks or occupation for offering maximum protection to users. Chainsaw protection can be done by wearing several equipment (especially hearing protection, face guard, anti-vibration gloves, Kevlar chaps and chainsaw safety boots. Additionally, other measures are also advisable for using this hazardous equipment

6. Bee-keepers

Different clothing equipment is worn depending on bee temperament and reaction of bees to availability of nectar. At the minimum, most of the bee keepers wear brimmed hats and veils made through hardware clothes that bear similarity with window-screen materials. Another level of protection would involve long gauntlets with leather gloves.

7. Eye protection

While eye protection equipment would vary per the occupation, the offered safety gets generalized. With safety glasses, you get long term protection from external debris and side protection is possible through side shields and wrap around designs. Eyes can be protected from welding, dust, splashes and other hazards by Safety Goggles. Face shields can be worn over standard eyewear for protection against blood, impact and chemical-borne hazards.

8. Skin protection

Second most common injuries are related to the skin and occupation related skin illnesses like skin cancers, contact dermatitis, infections and other skin injuries are second most common occupational diseases that are costly. Any skin protection PPE is of utmost importance at the workplace as it becomes a barrier between hazardous agent and the skin.

Cable Hipot Test: Safety Assurance of Electrical Installations
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Electricity in safe, closed systems brings convenience to modern life. When those systems fail, the result may not only be inconvenience, but also severe electric shock. The electrical industry has developed numerous practices to ensure safety. One such practice is the cable hipot test (high potential test).

This test is a method of testing the integrity of the insulation of electrical cables. It is performed to expose any potential problems in an electrical cable or system that could cause harm or shock.

This type of testing will expose weaknesses in electrical cables and insulation that may not be seen under normal operating conditions using standard voltage levels. These problems may appear in the cables themselves, as well as in splices and terminal connections. Potential weaknesses include cracked insulation, unattached wires, and conductive contaminants.

In order to find problems in a system, higher than normal voltage is sent through cables during this test. Testing units monitor the excess voltage being introduced through a system while simultaneously measuring the leakage current. Leakage indicates near shorts that leak voltage during the test due to the excessive current being applied. These near shorts can indicate trouble spots, such as poor insulation or installation errors.

There are different types of hipot testing. An insulation resistance test is used for cables to show the resistance of cable insulation. This test uses steady DC current. It is more accurate and safer to use DC current for such a test than to use AC current. In addition, DC testing equipment is more portable and much less expensive than AC testing equipment.

There are two specific situations when cable hipot tests are administered. One is to test new installations, and the other is to test existing systems.

Special consideration is required when testing older electrical systems. Excess current may damage the aging insulation of certain types of cables. This type of testing is not recommended by the electrical industry for cross-linked polyethelene (XLP) or ethylene propylene rubber (EPR) cables that have been in use for more than five years. However, paper insulated lead covered (PILC) cables with over five years of service may be tested with DC testing units.

By sending excess voltage through electrical cables, it is possible to find potential problems that would not appear during normal operation with standard current levels. The cable hipot test is an invaluable way to give electrical professionals a clear view of the quality and safety of their installations.

Smoked Flavor From Electric Grills
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With the advent of electric grills, it is possible to cook food outdoors without the mess of charcoal, lighter fluid, or blinding smoke. What can go missing is the smoky flavor that so many desire from food off the barbecue. Here are some tips to help you grill with electricity but still get that smoked food taste.

Safety is always the first priority in all outdoor cooking. Just because there is no flame, it doesn’t remove all fire risk. Follow clearance measurements stated in the owner’s manual to cook a safe distance from all structures. If you must use an extension cord with your grill, use the proper gauge or thickness and length to avoid overheating the cord from excess resistance. Never leave your grill unattended. A flare-up or grill knocked over from a gust of wind can quickly ruin your food or your day.

Your smoke source will be wood, of course, in the form of chips or a large chunk. The wood can be soaked in water beforehand, but that will only increase the time it takes to get smoke. Wrap a handful of chips in a double layer of heavy aluminum foil, and use a fork to poke a few holes in it. Poke too few holes, and the wood will not get enough air to burn. Poke too many, and the wood may burn up too quickly.

Whether wood chips or chunks, you will need to learn the nature of your particular grill to determine the best placement. The wood may be best suited to positions above, below, or beside the element. So long as you get a small but steady stream of smoke, it is enough.

If your electric grill cycles the element on and off based on the thermostat, it may be necessary to increase the heat setting to have enough heat to get wood smoking. The next consideration becomes how to avoid burning the food. Increase the distance between the element and the food when you’re smoking it. If you increase the heat setting but don’t get smoke, you may need to slightly alter the element control to allow turning it slightly higher. That option is beyond the scope of this article.

The smoke cannot be excessive from the wood, nor can it be allowed to accumulate around the food. The goal is a stream of smoke around the food and out the top area of grill. If your grill lid has a vent hole of some sort, it needs to be fully open or mostly so. Merely tilting the grill lid may not allow smoke to stream out. You may have a thermometer in the lid; this is an ideal place to put a vent hole for the smoke. Remove the thermometer and plug most of it with aluminum foil. Another solution is to use a metal can top screwed through the lid next to the hole to adjust the smoke exhaust.

Another obvious safety point is to remember the possibility of your wood flaming up. Keep a spray bottle of water handy to mist the wood. Remember that the smoking wood gets a large load of oxygen when you lift the lid, and you should be prepared to keep it safe.

Treadmill Fitness Equipment – Manual Treadmill Or Electric Treadmill, Which is Better?
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Looking to get some treadmill fitness equipment? When you’re looking for a treadmill, there are 2 main considerations, you need to decide on if you want a manual treadmill or an electric treadmill. This article will help you to distinguish between the two so that you pick up the treadmill fitness equipment that is right for you.

1. Manual Treadmill

A manual treadmill is often going to be the cheaper of the two options as there is no motor that powers it. It is run based off of momentum. In order to get it started, you need to apply your body weight to it to get the treadmill conveyor rolling. Once its rolling you can then resume running at a more even pace.

Not everyone likes having this kind of functionality though, it’s a bit primitive, however it does get the job done. This kind of treadmill is perfect for someone on a small budget.

2. Electric Treadmill

On the other hand, if you need the treadmill to come with bells and whistles, you had best look to an electric treadmill. Electric treadmills will give you things like heart rate monitors and intensity programs. You can even adjust the incline on the fly as well as the resistance.

This all comes at a premium though as electric treadmills are often double the cost, coming in at $500-$1000 at the cheapest levels.

When you’re deciding on the treadmill fitness equipment that is right for you, it’s essentially going to come down to price. I would look upon this as a long term investment though and go with the more expensive of the two, if you do it will last you at least a good 5 years.

Class of Protection in Electrical Appliances
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All electrical appliances using mains voltage have to provide at least 2 levels of protection to the user. This is to ensure that if one of the protection layers were to fail, there is the back-up of the second layer still in place. This makes electrical equipment very safe to use. Appliances can be Class 1 or Class 2.

When PAT testing, it is important to first identify the Class of the appliance as Class 1 appliances are tested differently from Class 2 appliances.

Depending on how exactly the protection is provided, electrical appliance are put into 5 Classes of equipment construction which are Class 1, 2, 3, 0, 01. Of these the most important are Class 1 & 2. For completeness all the Classes are described below.

CLASS 1

Here the protection is provided by a combination of insulation and use of the mains Earth. It is best shown by referring to an electric fire that has been taken apart.

In the open plug the three wires connecting to the LIVE, NEUTRAL and EARTH pins. Inside the fire, the brown LIVE wire and the blue NEUTRAL wire connect to a plastic connector. The green/yellow Earth wire connects to the metal case of the fire.

The user is protected from electric shock by the plastic insulation of the connector. This holds the LIVE and NEUTRAL wires in place and prevents them from touching the metal case of this electric fire. This plastic insulation of the connector is known as basic insulation.

If this basic insulation were to fail, say due to excessive movement of the cable where it touches the metal case then the user of the fire can receive an electric shock if not for the fact that the EARTH wire is present.

By connecting to the metal case of the electric fire, the EARTH wire keeps all this metal at EARTH potential. What this means is that it is impossible to get an electric shock even when the metal case of the fire is connected directly to the LIVE voltage. In practice a fuse would blow either in the plug or the main fuse box to protect the user.

In summary, in Class 1 appliances the user is protected by a combination of basic insulation and the provision of an EARTH connection, thus providing two levels of protection.

When PAT Testing Class 1 appliances, the Earth Continuity and Insulation Resistance tests are carried out.

CLASS 2

In a Class 2 appliance, the user is protected by at least two layers of insulation. For this reason, Class 2 appliances are also known as Double Insulated. They do not require an Earth connection.

This is best shown by looking inside a Class 2 electric drill which has been opened up. Inside one can see that as well as the plastic connector providing basic insulation, there is additional insulation provided by the plastic enclosure of the drill.

The user is therefore protected by two separate layers of insulation. When PAT testing Class 2 appliances, just the Insulation Resistance test is carried out.

Class 2 appliances are always indicated by the double box symbol on the rating plate.

CLASS 3

Equipment built to Class 3 standard are designed to be supplied from a special safety isolating transformer whose output is known as Safety Extra-Low Voltage or SELV. This must not exceed 50 V AC and is normally is below 24V or 12V. All Class 3 appliances are marked by a special symbol. There is no use of an Earth in Class III appliance

The electrical safety of Class 3 appliances are taken care of in the safety isolating transformer design where the separation between the windings is equivalent to double insulation. The transformer is marked as being suitable for use with Class III appliances.

CLASS 0 & 01

This type of equipment is not for normal use in business or residential environments. It is just presented here for completeness.

Class 0 appliances depend only on basic insulation for protection from electric shock. For this reason, they do not have 2 levels of protection built in and are not allowed for sale. The brass lamp shown here is an example of a two wire, metal cased appliance with only basic insulation. There is no provision for connection of an earth to the bulb holder.

In Class 01 appliances, there is provision for an Earth connection, but it is wired with either twin core cable or only has a 2-pin plug, so an Earth cannot be connected. AS in Class 0 equipment, one is dependent only on basic insulation for protection from electric shock. As they only have 1 level of protection, Class 01 appliances are not allowed for sale.

If during PAT testing one comes across a Class 0 or Class 01 appliance these can be failed.

IDENTIFYING CLASS I & CLASS II APPLIANCE

As the PAT testing carried on Class 1 and Class 2 appliances differ, it is important to identify one from the other. There is no other area of PAT testing that causes more confusion than this and there are many myths surrounding this. It will be informative to list some of these.

If there is a fuse in the plug, then it must be Class 1.

It is made of metal so it must be Class 1

The case is plastic so it must be Class 2

It has a three core cable so it must be Class 1

The plug has a metal Earth pin so it must be Class 1

None of the above statements is a fool-proof way to identify Class I and Class II appliances and some are quite misleading.

The easiest rule to apply is the one below.

If the rating plate has a double box then the appliance is Class 2. If it does not then it is Class 1.

Example – Kettle

The rating plate on this kettle clearly has no “double-box” symbol, so using our rule, it must be Class 1. The Earth connection from the plug is terminated on the outside metal casing of the heating element. When PAT testing this kettle the Earth Continuity and Insulation Resistance test has to be carried out.

Example – Plug-top power supply

The rating plate on this Plug-top transformer clearly shows the “double box” symbol, so this is a Class 2 appliance. Note that it has a plastic Earth pin, as this is not required for Class II. (Not all Class 2 appliances have a plastic earth pin). Just the Insulation Resistance test has to be carried out during PAT testing.

Example – Mains extension

The rating plate on this extension is moulded in the plastic. It clearly does not have a “double-box” symbol, so it must be a Class 1. When PAT testing this extension lead the Earth Continuity and Insulation Resistance test has to be carried out.

Example – Table lamp

The rating plate on this table lamp clearly shows the “double-box” so it is a Class 2 appliance. (Note that this is a Class 2 appliance that is largely in a metal enclosure). The bulb holder is made of plastic and provides the required double insulation. Just the Insulation Resistance test has to be carried out during PAT testing.

Example – Desk fan

The rating plate for this fan not only does not have a “double-box” symbol, it also says that the appliance must be earthed. So this is clearly a Class 1 appliance. Note that it does not have any user accessible metal.

Example – Metal Lamp

If this metal lamp had a rating plate, then it would be a Class 1 appliance as it has an earth point on the lamp holder. However, as the rating plate is missing, this would have to be failed.

Are Class 1 and Class 2 appliances just as safe?

As both have 2 levels of protection built in, they are both safe for general use.

However with Class 1 an appliance, one of the layers of safety is provided by the earth connection. For this to be effective, the wiring in the building has to be inspected regularly to check that the Earth in the mains socket is correctly taken to the local earth potential. This is usually picked off the Earth sheathing of the mains cable coming into the premises, or by driving a local stake into the ground. So Class 1 appliances depend on the external wiring in the building to fully provide the 2 levels of protection.

Class 2 appliances however always provide 2 levels of protection irrespective of the status of the wiring installation. Both layers of protection are built into the design making Class 2 appliances are a lot safer than Class 1 appliances.

How the Electric Guitar Revolutionized the Music Industry
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When you first listen to a song, with the exception of the lyrics, the first sound that you’re going to recognize is the sound of the guitar. No guitar has changed music, quiet like the electric guitar.

Before the electric guitar, there was America’s beloved acoustic guitar. It greatly changed music in that it allowed musicians alternatives to the mandolin and banjos. The acoustic guitar is a huge asset for songwriters because of its portability, which allowed musicians to write or perform their music almost anywhere.

When the electric was first built in the 1930’s, it was met with strong resistance. Critics actually believed that the sounds would not be appealing to music lovers and they didn’t believe the electric guitar would make it off the assembly line. Even the original creator couldn’t have imagined the impact that the electric guitar would have on the music industry. No one in those days could have. The very first electric to be manufactured and sold to the general public was built by the Electro String Company in 1931. These guitars were actually made from cast aluminum, and people actually referred to them as “frying pans”, which prompted the Gibson Guitar Corporation to create their ES-150 guitar. These guitars quickly became popular and this particular Gibson guitar became one of Gibson’s best sellers, ever. And when artists began to realize that the electric gave them the flexibility to create their own musical style, it started to change the sound of music.

The invention of the electric was a huge asset to concert halls. Before it, concert halls we’re smaller, accommodating smaller crowds. This was because the acoustic guitars’ sound was hard to hear from a distance. It allowed venues to expand because the sound could be amplified, allowing much more people to hear the concerts from a greater distance. Concerts started to change forever. Now, instead of a musician playing for a few hundred people, they were playing for a few thousand. And today, musicians are performing for a few hundred thousand fans and selling out every single seat!

Electrics have evolved from the original production. There are additional pickups on the modern guitars that allow artists to create unique, individual music styles. No guitar has been able to capture the emotions of a song or its musician like the electric guitar. What makes the guitar able to do this is that it can be amplified. You can’t have one without an amplifier. When used alone, it doesn’t create the mood changing sounds that the amplifier does. The electric guitar and amplifier go hand in hand. The amplifier to the electric guitar is the bread to the butter in the music industry.

No one can truly evaluate the way music has changed over the last several years. Great music has the power to change lives. Music expresses what simple words alone cannot. The electric guitar expresses the feelings that words cannot. The sounds of the electric guitar are electrifying (no pun intended). It has created some of the best performances ever. It has become the very definition of rock and roll. It will continue to revolutionize music for generations to come.

What’s the Difference Between a Tuned and an Untuned Oscillator Circuit?
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A tuned oscillator uses a LC (inductor-capacitor) tank-circuit, a frequency-selective RC (resistor-capacitor) circuit or a quartz crystal circuit in its feedback path. Generally, the output waveform shape from a tuned oscillator circuit is sinusoidal and for this to happen positive feedback is used around an amplifying device such as a transistor or op-amp.

If negative feedback is applied to an amplifier the gain of the amplifier is decreased but the stability is increased. With positive feedback however, the gain is increased but the stability is decreased. This increase in gain produces a situation where an alternating sinusoidal output is obtained without a signal input. The amplifier has now become an oscillator giving an alternating output with the energy required to maintain this oscillation is obtained from the d.c. supply.

A tank-circuit consisting of a parallel-tuned LC circuit or RC circuit is used as the frequency determining unit which is “tuned” to give oscillations around its resonant frequency, hence the name tuned oscillator. The output from this device is feedback to its own input in such a way that the feedback signal aids the change in input signal. No input signal is required because the frequency determining unit provides its own signal via the feedback network in such a way that the circuit is self-exciting. Then this type of circuit is known generally as a Feedback Oscillator (positive feedback) and oscillators which use this technique are:

LC Oscillators: As their name implies, LC oscillators consist of a parallel tuned inductor-capacitor tank circuit as their frequency determining unit. The capacitor is constantly charging and discharging through the inductor coil at its selected resonant frequency but due to the heavy losses in the resistive element of the coil, the dielectric of the capacitor, and in radiation from the circuit. So in a practicle LC circuit the amplitude of the oscillatory voltage decreases at each half cycle and these oscillations would eventually die away to zero. If sufficient energy is applied at the appropriate time from a d.c. power supply in the cycle to overcome these losses then oscillations will continue at a constant frequency and amplitude indefinitely. Resonant frequency occurs when the coils inductive reactance (XL) equals that of the capacitive reactance (XC). Oscillations are controlled by varying the value of the capacitor (varactor).

Tuned oscillator circuits which use an LC (Inductor/Capacitor) tank circuit include:

• Hartley Oscillator
• Clapp Oscillator
• Colpitts Oscillator
• Tuned Collector Oscillator
• Pierce Oscillator
• Miller Oscillator

RC Oscillators: RC oscillators are also known as “phase shift oscillators” because their oscillating elements are made up of resistor-capacitor circuits which produce a phase-shifting circuit which corresponds to positive feedback. RC networks are not naturally oscillating circuits but become oscillating elements when connected around transistor or operational amplifiers.

RC oscillators do not use inductors but instead produces oscillations at a frequency at which the RC network produces a 180 deg. phase shift. A single stage amplifier will produce 180 deg. phase shift between its input and output and which can be used as a stage to produce the required positive feedback. The output from the amplifier is fed back via the RC network to its input. The input is shifted 180 deg. through the amplifier and 180 deg. through the RC network and 180 deg. + 180 deg. = 360 deg. or zero phase shift.

One useful property of the RC oscillator is that output frequency is inversely proportional to capacitance which means that a change in capacitance produces a much higher frequency compared to the LC oscillator. However, the disadvantages are that the output power of the RC oscillator is low due to dissipation in the resistive elements and for positive feedback to occur the amplifier gain must be greater than 29.

Tuned oscillator circuits which use a RC (Resistor/Capacitor) phase shifting circuit include:

• Ladder Phase Shift Oscillator
• Relaxation Oscillator
• Quadrature Oscillator
• Wein Bridge Oscillator
• Switched Capacitor Oscillator
• Digitally Switched Oscillators
• Phase Advance Oscillator (current transfer)
• Phase Retard Oscillator (voltage transfer)

Crystal Oscillators: Quartz and some other crystalline substances exhibit the “piezo-electric” effect. When a mechanical stress or physical deformation is applied to two surfaces of a suitably cut crystal it will produce a voltage between the surfaces. Likewise, when a voltage is applied to the crystal it causes a small physical deformation to the actual shape of the crystal.

Then if the voltage produced by mechanical deformation is fed back in some way, it will itself produce mechanical distortion in the crystal which will produce a voltage, which will…continue forever. This forms the basis of a number of crystal oscillators, because this feedback occurs only at the natural frequency of vibration of the crystal with this natural frequency value being determined by the “cut” of the crystal. Then the crystal in fact behaves as a resonant circuit with a very narrow bandwidth.

There is a limit to the stability and frequency that can be obtained from normal LC or RC tuned oscillators. Quartz crystal oscillators operate at very high frequencies up to 10Mhz when operating in the parallel mode. They also have very high stability and a resonant frequency with a very high Q factor making them ideal for use in CPU, microcontroller and video applications.

“Untuned Oscillators”

Unlike the tuned oscillators above, an untuned oscillator has no LC tank-circuit, frequency-selective RC or crystal circuit in its feedback path. Instead, an untuned oscillator uses nonlinear feedback and generally, the output waveform from an untuned oscillator is non-sinusoidal such as square-wave, triangular-wave or pulse being characterised by a sudden transition from one condition of stability or state to the next. Untuned oscillators are more commonly known as relaxation oscillators. Types of untuned oscillators include:

Ring Oscillator: Ring oscillators consist of an “odd” number of logic gates or amplifiers connected together in a series chain so that the output of the last is connected to the input of the first producing a ring type circuit. The frequency of oscillation depends upon the proporgation delay of the components used and the number of odd “stages” that are within the ring. Oscillation frequency is very high as to is the power consumption. Ring oscillators are more of a novelty as their high frequency and use of components make them impractical as an oscillator.

Relaxation Oscillators: Relaxation oscillators are more commonly known as multivibrators. They are a class of oscillator in which the active devices (usually a transistor) in the circuit are driven well beyond their cut-off and saturation regions for a period of time. Relaxation oscillators are cheap and easy to build with the three main types of multivibrator being.

• Astable Multivibrator: – has no stable state.
• Monostable Multivibrator: – has one stable state.
• Bistable Multivibrator: – has two stable states.

555 and Timer Chips: As well as our old favourite the NE555 timer and its variations, there are a whole host of different chips available in both TTL and CMOS that can be used to generate a variety of different waveforms and signals with some of the most popular being the: 74LS121, 74LS123, 74LS221 and their variants.

Tankless Water Heater Information
electric resistance

Just like you wouldn’t leave the heating systems switched on in your home when you are away for a vacation, wouldn’t it be a whole lot wiser if you were using heating systems for water only when you were actually using the hot water? Conventional water heaters heat your water and then save it all up in a tank and wait for you to use it. This seems pretty convenient. After all, when you do need the water, it is all ready and available. However we rarely realize the amount of electricity that would be wasted in maintaining the hot water at its given temperature. also, there is only a limited supply of hot water at a go, when it finishes off, you must wait for another long while before more water becomes available. The solution to all of this? Tank-less water heater.

Tank-less water heaters can heat water without the need for any kind of a storage tank. They do so by being an intermediate step between the cold water line and the hot water tap. When you need hot water, you simply turn the tap on, as the water starts flowing through the pipe, sensors switch on the heater which then heats the water as it travels to the tap. Usually these units have a long coiled pipe inside of them which allows water to travel a greater distance inside the unit, hence allowing greater time to heat the water. The heating element can be electric or gas. In case of electric element, high resistance coils are wound along the length of the pipe, hence allowing the pipe to get heated up on demand, and hence heat the water as it flows through it. In the other case, gas is used in small burners which too in turn do the same thing by heating the pipe up.

Of course, there are limitations to using such devices. They do not allow fast flow of water which is possible with storage tank heaters, since they are just emptying the tank. The water flow may be slow, but it would be consistent and indefinite. Since there is no storage system, hot water would keep flowing as long as you need it. For a household, it would be wiser to get multiple units or booster units to ensure consistent supply of water because high requirements can take a toll on this system. The benefits of going through the trouble of installing these systems is immense, they can bring down the energy usage by 1/3rd for a house that uses 41 gallons of hot water in a day.

Which tank-less water heater you use would depend on your location and your requirement. Locations makes a difference because the incoming water temperature would play a major role in deciding which heater you need. Also if your necessary temperature rise is achievable by gas or electric heating element would decide the kind that you choose. But rest assured, whichever heating system you may use, using tank-less water heaters would help save energy.