Rheostats at a glance


Rheostats are variable or adjustable resistors used to divide voltage in applications that require the adjustment of resistance in an electrical circuit. Rheostats, like potentiometers, are generally used in applications that demand variable control for higher amounts of voltage.
As a result of the reduction of size and power consumption in many of today’s electrical devices, rheostats, are not as frequently found in commercial and industrial products and have been replaced by potentiometers, triacs and SCRs. However, rheostats are still commonly used for applications requiring a large amount of current or high voltage. Common utilization of rheostats include light dimmers, motor speed regulators, arc lamps, pumps, fans, respirators, x-ray devices and medical apparatus.

Rheostat Construction.
Many rheostats are wire-wound and have a lengthy conductive material (usually a wire) wrapped into a spiral. Its resistance element can be a ribbon or metal wire, a conducting liquid, or carbon, completely dependent on the application. For average current flow, the metallic type is most common; for very small current flow, the carbon form is used; and for large amounts of current the electrolytic type, whereby electrodes are placed in a conducting fluid, is most suited. The contacts and the coil are sealed within the casing to sheild them from dirt, grime, dust and other impurities. These often lead to an open circuit and form moisture ,which ultimately, causes a short circuit. Rheostats have 3 terminals that are made up of a resistive wire wrapped to create a toroid coil with a wiper that glides along the surface of the coil. It is most often designed with a ceramic center.
When choosing a rheostat for a certain function, the current rating is usually a more crucial factor than the wattage rating. If using a rheostat for motor control it is essential to understand that all types of direct current motors could be speed-controlled, however, a small amount of AC motors are controllable with a rheostat. Therefore, it is essential to obtain the appropriate type of AC motor when speed control is needed. Most rheostats have either a round or flat shaft that enables you to attach a knob to the rheostat. The smaller sized rheostats have screw-driver slots that make for easy adjustments.
Switches can be attached to a rheostat in order to open the circuit or to access a self-regulating circuit. Rheostats can be equipped with a fixed or an adjustable stop. The stop can be set to limit the angle of rotation to any desired part of the total possible rotation. Normally, this specific type of rheostat is used in operations where keeping a set amount of resistance within the circuit is very important.

How Rheostats Work.
The basic fundamentals that apply to the effect of a rheostat in a circuit is Ohm’s law, which explains that, current is inversely proportional to resistance for a given voltage. This means the current diminishes as the resistance escalates or current increases as the resistance decreases. Current enters the rheostat by means of one of its terminals, flows through the wire coil and contact, and exits through the other terminal. Rheostats do not have polarity and behave the same when the terminals are reverted.

Some light dimmers use rheostats to limit the current going through a light bulb so as to vary the illumination. The more the resistance of the rheostat, the dimmer the light bulb will glow. Some lights will not work effectively with dimmers, including fluorescent and gas discharge lamps. These lights use resistive, inductive or electronic ballasts which restrict and maintain a constant current for the lighting circuit. Rheostats may have no effect on varying the brightness of the lamps and may even harm the ballasts.
Motor controllers also use rheostats to control a motor’s velocity by limiting the flow of current. They are used in many small devices such as blenders, mixers, fans, and power tools. Rheostats are also used as test devices to provide a reference resistance value. While rheostats can be used to manage electric ovens and cook-tops, thermostats or temperature controllers are favored because they have additional controls and temperature feedback capabilities that enable a more consistent temperature regulation.
The rheostat is still a common and fundamental electronic component used to control the outflow of current in a circuit. However, it has largely been superseded by solid state devices such as triacs and silicon controlled rectifiers (SCR). A triac is more energy competent than a rheostat and is more reliable because of the absence of mechanical components. Rheostats commonly fail because their contacts become unclean or the coil wire corrodes and breaks, while solid state devices are reasonably immune to these external conditions.

Rheostat vs Potentiometers.
Both rheostats and potentiometers offer the same function in an electronic circuit, with the primary variance in terminology being used to describe the current capacity and composition of the devices. Rheostats are typically rated at 5 watts or more and are wire-wound, while potentiometers are usually less than 5 watts and are of carbon composition. Through their diversified structures, potentiometers and rheostats are utilized in different applications where voltage, current, range, tolerance, operating AC and DC voltage and environment are key factors. Potentiometers and rheostats also differ in regards to performance specifications, mounting, packaging and attributes.

Environmental Protection and the Emergent Market of e-Book Readers

From an environmental standpoint, introducing e-ink technology into home use, school curriculum, library facilities, and business use provides a win-win scenario with benefits to be had at all angles. Green reading reduces an individual’s literary carbon footprint intertwining human interaction and the planet’s lifespan together on a favorable level. Traditional reading involves a greater cost on so many levels including production, storage, transport, and disposal. Not only must one consider the cost of making and keeping the book, but one must also consider the getting rid of the book once it is no longer wanted.

Electronic Books as an Alternative to Paper Books

Up until recently, electronic books have only been a temporary alternative to paper books. In fact, the creation of e-Books is simply another facet to improvements in digital technology and the need to reach more people more quickly. Nonetheless, developed partially as a means to obtaining a book more quickly than waiting for it to be published in paper format, eBooks were not originally intended to replace hard copies be they paper or fully bound versions in hard cover.

All of that is about to change as authors are beginning to sign on for eBook versions of their books only. Perhaps one of the most famous of these authors is Stephen King who recently agreed to an eBook-only version of his latest publication, “Riding the Bullet.” His eBook-only novella has met with tremendous success and is promoting the way for other such books to follow. Once a novel, novella, magazine, newspaper, or children’s story can only be read as an e-Book, the choice will be an easy one. The use of e-Book readers will become commonplace as a matter of course. According to Digital Book Readers, the changes it would provide for the people and the nature are immense and vast, and certainly worth consideration.

Benefits to Green Reading: Storage and Disposal

Since storage and disposal of e-Books is more environmentally friendly than storage and disposal of traditional books, the environment will benefit greatly from the incorporation of e-Books into daily living patterns. Not only will landfills grow at a less alarming rate, but trees will be cut down less frequently as the need for paper diminishes.

The world’s forests will continue to grow while continuing to provide cleaner, oxygen-rich air. Even if these forests are allowed to grow once they have been cleared for their timber, the result is not as good as it would have been had the forest been allowed to grow. Studies have shown that older, established forests retain more carbon than their newer counterparts. Hence, the environment is better if human interaction with it changes through more responsible use of its resources.

Plus, there are other benefits to be had as well, especially where the production of traditional ink-on-paper books is concerned. Not only does the use of e-Books reduce the need to produce ink, paper, and bindings, but it also reduces the pollution associated with such activity. Moreover, e-Books are easier to transport at a lower financial and physical cost than traditional book transport.

The Facts about Paper Production of Books and Newsprint

According to the Green Press Initiative, the United States is responsible for using more than twenty million trees to produce books each and every year and that figure doesn’t take into account the 95 million trees estimated to be consumed by the newsprint industry each year. As eBook reading grows in popularity, it is hoped that these numbers will be reduced significantly.

The Green Press Initiative has also stated that landfills hold a large amount of paper products to the tune of approximately one fourth of the landfill’s content. As if taking up so much space isn’t bad enough, the decomposition of paper products produces a highly toxic greenhouse gas known as methane gas. So not only does paper production create carbon dioxide emissions during their manufacture, but they also produce methane when they fall into a state of decay. These facts certainly point to a better world with the production of eBooks on a global level.

The Harry Potter series of books, one of the most popular series ever and enjoyed by children and adults alike, is projected to reach a total of 290,000 tons of paper in its production of more than 370,000 million books as estimated by Prime View Inrternational. At a cost of 20 trees to produce one ton of paper to be used in the manufacture of books, this comes at the high cost of 5.8 million trees.

According to the U.S. Book Industry Study Group, more than 12.4 million tons of carbon dioxide are released into the atmosphere on an annual basis due to the mass production of books in hard copy format. This boils down to almost 9 pounds of carbon per book that is produced. Talk about leaving a carbon footprint on the world! While significant changes such as increasing the use of recycled paper are being implemented, they cannot compare to the benefits that eBooks and eBook readers can produce.

According to the Green Press Initiative, many of the world’s forests are becoming endangered due to the logging that continues to occur. Indonesia’s tropical forests lose about 4.5 million acres each year to logging, some of it illegally culled. More than 2 million acres of Canada’s Boreal Forest are logged each year with 65% of that going for paper reading and writing products. In the southeastern United States, at least 6 million acres of forests fall prey to logging companies while this area along with 26 million plantation acres is known as the largest paper producing area in the world.

Digital Cameras

Photography — a creative art, an essential tool for some and a hobby for many others. Today, we have reached a stage where everyone should have a camera.

Photography started with film cameras and they were always thought of as difficult devices to use and rightly so for many reasons. They were difficult to maintain and operate. You had to truly understand photography to be able to take good photographs. For the rest who wanted a camera as a utility, something to keep memories as prints, there were the simple handheld cameras of their time. These were compact cameras and they were certainly cheap, and they made taking photographs much simpler, but not totally foolproof. There were still problems common to both SLR and point-and-shoot users. Film developing was a costly affair and plenty of photos were lost due to mistakes during shooting — this was a time before digital sensors or preview LCD screens.

Digital Cameras gained significant acceptance quite quickly. They fixed many of the problems associated with film cameras — the instant ability to view your shot, most importantly, but they did so at a price. Even the really early digital cameras that lacked the refinements and the automation that we see today were much costlier than the then-available decent film SLRs that were generally considered to be great cameras for professional and amateurs alike. As we’ve seen in the past with every new technology, users should perhaps have delayed purchasing these expensive gadgets, but instead the take-up of digital cameras was fast, and the market has continued to grow ever since.

It has been years now since point-and-shoots (P&S) were developed, and the pace at which developments and improvements have taken place has been staggering. Within a decade, we’ve gone from film cameras that couldn’t guarantee a proper set of photos in a film to digital point-and-shoots that can detect faces, store them, click photos when people smile and there’s hardly any cost involved in using them!

What else could anyone want? There are those who look at point-and-shoots and think of them as toys and consider the only proper cameras to be the dSLRs. Speaking practically, point-and-shoots are actually pretty decent. Prosumer point-and-shoot cameras, such as the Sony DSC H5, the Canon SX 10 IS, the Canon PowerShot S5 IS and many more, have closed the gap between standard point-and-shoots and dSLRs. Easy operation, and the ability to take macro photos to telephoto shots on a single camera without the need for changing any lens or settings. For hassle-free photographs, these prosumer cameras are very good.

However, if you are serious about photography and are analytical about quality and perfection, then we and other enthusiasts will tell you that you ought to buy a dSLR. If you are a professional photographer using a P&S camera, then we honestly aren’t sure why….

dSLRs bring a lot to the table, and there are good reasons for their weight, size and the number of knobs and settings they carry. You don’t just go out and buy a dSLR and walk around with it in your pocket. They require a rather more considered approach. They are meant for those who’ll sit an entire weekend in a nursery taking photos of flowers, go out and do some wild life photography, sports photography and will take that kind of dedicated time on the camera trying out all kinds of shots. dSLRs are modular gadgets. So over time, you’ll be drawn into buying an extra lens or two. The type you buy and the amount you spend will obviously depend on your requirements. We take a look at two such cameras.