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In many circuit applications, resistance must be inserted into the circuit in the purpose of reducing the current or to produce a desired IR voltage drop. The component used for this are resistor and labeled with the letter R in the circuit diagrams. Resistor are the most commonly found component in all electronic equipment, from a small AM radio to a color television receiver. The common type of resistor is the carbon resistor as shown in the image.
TYPE OF RESISTORS:
The two main characteristics of a resistor are its R in ohms and the wattage rating. Resistors available values ranges from a fraction of an ohms up to many mega ohms. The power rating can be as high as several watts or as low as 1/10 W.
The power rating of a resistor is important because it specifies the maximum wattage the resistor can dissipate without producing excessive heat that can damage the component and or other components in the circuit. Dissipation means that the power is wasted as I2R loss. Since the result heat is not used, the generated heat which is usually too much can make the resistor burn open.
When power dissipation is about 5 watts or more wirewound resistors are used, specially in devices that require high current handling capability, heat dissipation and resistance stability and accuracy. For 2W or less, carbon resistor are preferable because they are smaller and cost less.
Carbon resistors are most common in electronic equipment because they are smaller and cost less as compared to wirewound resistor, Usually higher R values have smaller wattage because they have less current.
Both carbon and wirewound resistors can be either fixed or variable. A fixed resistor have a specific R that cannot be adjusted, while a variable resistor can be adjusted for any value between zero ohms up to its maximum R value.
Carbon composition variable resistors are commonly used for control, such as the volume control in a radio receiver or the contrast control in a television receiver. An application for a variable resistor is to divide the voltage from a power supply.
1. WIREWOUND RESISTOR: Resistance wire such as manganin wrapped around an insulating core, Commonly used insulating materials are cement, porcelain, or just plain compressed paper.
The wire is bare, but usually the entire unit is encased in an insulator. The length of wire used and its specific resistivity determine the resistance of the unit.
Wirewound ResistorSince wirewound resistors are generally for low-resistance high-power applications, wirewound resistors are available in power ratings from 5W to several hundred watts, with resistance range of less than 1Ω to several thousand ohms. In addition, wirewound precision resistors are used where accurate, stable resistance values are require.
2. CARBON COMPOSITION RESISTOR: This type of resistor are made of finely divided carbon or graphite mixed with a powdered insulating material in the proportions needed for the desired value. The resistor element is usually enclosed in a plastic case for insulation and mechanical strength.
Joined to the two end of the carbon resistance elements are metal caps with leads of tinned copper wire for soldering the resistor connections into a circuits. Carbon resistors are commonly available in resistance values of 1/10, 1/8, ¼, ½, 1 or 2 watts.
3. CARBON FILM RESISTOR: Carbon film resistors are manufactured by depositing a carbon film on a ceramic substrate. In many ways semilar to carbon composition resistors, they can be interchange with each other, the cost is less than for the hot-molded carbon-composition type.
4. METAL-FILM RESISTORS: These are form by means of vacuum deposition, a process by which any of the number of different metal or metal oxide films are deposited on a suitable insulating mandrel or core.
Nickel and chromium are deposited on the alumina ceramic core and the unit is then subjected to laser trimming. Metal film resistors are laser trimmed or helixed to obtain the desired resistance value before the protective insulation coat is applied.
TYPES OF METAL FILMS RESISTORS
- METAL-OXIDE DEPOSITION — This process makes use of a chemical vapor deposite to a tin-oxide film onto a glass substrate. Although this tin oxide resistor is similar in performance to evaporated or sputtered metal film, the technique is obviously not capable of achieving the level of precision possible with other thin-film process.
- BULK METAL. — This process produces a flat instead of cylindrical elements. It is an expensive process but produces resistor with a tight tolerance and excellent temperature coefficient of resistance characteristics, used exclusively for ultra-precision applications. This process entails the laminations of metal foil to a substrate and later etched chemically to produce a serpentine rather than helical conduction path.
- THICK FILM — This process coats ceramic substrate with a glass-metal matrix material. Later, it is fired at an extremely high temperature to produce a metallic film. Unlike in other processes wherein the resistive elements are subjected to a very temperature in order to vaporize materials, the thick film process does it to cure.
- VACUUM DEPOSITION — Also known as evaporated metal film, it is the original metal film resistor manufacturing process. This techniques superheats a nickel chromium alloy wire by resistance or electron — beam heating in a vacuum. As the alloy evaporizes, it is deposited on ceramic substrates which are then loaded into a vacuum container. To achieve the resistance ranges, manufacturers make use of contaminants called dopants.
- SPUTTERING — This is a more recently developed techniques and closely related to vacuum deposition. It is likewise yields a product consisting of nichrome resistor on a ceramic substrate.5. CERMIT-FILM RESISTORS: These have a carbon coating fired onto a solid ceramic substrate. The purpose is to have a exact or precise R values and greater stability with heat. They are often made in a small square, with leads to fit a PC board. A flat package with multiple leads can be used for several resistors in one unit.
- VARIABLE RESISTORS:
Variable resistors can be wirewound or a carbon type. Inside the metal case, the control has a circular disk that is the carbon-composition resistance element. Joined to the two end are the outside soldering-lug terminals 1 and 3. The middle lug 2 is connected to the variable arm contacting the resistor element by a metal spring wiper. As the shaft of the control is rotated, the variable arm moves the wiper to make contact at different points.
When the contact moves closer to one end, the resistance decreases between this end and the variable arm. The variable resistance is zero when the wiper contacts this end but is maximum with the variable arm at the opposite end. Between the two outside ends, the resistance is not variable but always has the maximum resistance of the control.
RESISTORS COLOR CODING :
In addition to having the required resistance value in ohms, a resistor should have a wattage rating high enough to dissipate the I2R power produced by the current flowing through the resistance, without becoming too hot. If a resistor becomes too hot because of excessive power dissipation, it can change appreciably in resistance value or burn.
The power rating is a physical property depending on the resistor construction, specifically physical size.
1. The larger the physical size of the resistor indicates a higher power rating.
2. Higher-wattage resistors can operate at higher temperature.
3. Wirewound resistors are physically larger with higher wattage rating than carbon resistor.
For both types, a higher power rating allows a higher voltage rating. The rating gives the highest voltage that may be applied across the resistor without internal arching. In wirewound resistors, excessive voltage can produce an arc between turns; in carbon resistors, the arc is between carbon granules.
SERIES AND PARALLEL COMBINATION:
In some cases two or more resistors are combines in series or parallel to obtain a desired resistance value with a higher wattage rating as shown.
series parallel resistors
The total resistance depend on the series and parallel connections. However, the combination has a power rating equal to the sum of the individual wattage ratings, whether the resistors are in parallel or series. The reason is that the total physical size increases with each added resistor, Such combinations can be used to obtain a higher power rating.
Figure a, the two equal resistors in series double the resistance. Also the power rating of the combination is twice the value for one resistor.Figure b, the two equal resistor in parallel have one-half the resistance. However the combined power rating is still twice the value for one resistor.
Figure c, the series parallel combination of four resistors makes RT the same on each resistor. However, the total power rating is four times the value for one resistor.
CHECKING RESISTOR WITH OHMMETER :
An open resistor reads infinitely high ohms. For some reason, infinite ohms is often confused with zero ohms. Remember though that infinite ohms means an open circuit. The current is zero but the resistance is infinitely high. Furthermore, it is practically impossible for a resistor to become short-circuited in itself. The resistor may be short circuited by some other part of the circuit, however, the construction of resistors is such that the trouble they develop is an open circuit, with infinitely high resistance in ohms.
An ISO image file is an exact representation of a CD, DVD or Blu-Ray Disc in a single archive file, these files are either downloaded online or created through an ISO image file app such as ImgBurn, BurnAware, ISODisk, ISO Recorder or other ISO image file creation apps. After creating or downloading ISO image file you can then mount it on a virtual CD/DVD drive as if it’s a real disc or burn it to disc and use it in replace of your original disc
If you often visit YouTube to watch online videos then you probably want to view it offline too or want to view it on other devices such as your phone. You want to view YouTube video offline especially if you have a very slow internet connection at home or want to view the video in HD format. Unfortunately, YouTube is designed to be viewed or watched on their website and not to be downloaded, that’s why you can’t find any download link for downloading videos on YouTube. Fortunately for us there are lots of software and websites that we can use as a downloader for YouTube videos.
Saving YouTube Video Using Online YouTube Download site
There are websites that caters in downloading YouTube video, all you have to do is copy the video URL and paste it on their download bar then clicking on the download button. To download video from YouTube follow these simple steps.
- Go to YouTube and play the video you want to download, copy the video URL from the YouTube webpage address bar as shown in the sample below.
- Go to saveFrom.net and paste the YouTube video URL on the download bar and click on the download button, after clicking the download button you will be shown with available video format that you can select from as the video format to save such as FLV, MP4, 3GP and other video format. Click on the Video format you want on the Download link column and select where you want to save your video download.
Aside from online YouTube download site, you can also download YouTube downloader software and install it on your computer, during installation watch out for any attempt to install toolbars by the installer. You can uncheck any checkbox that wants you to install toolbar that can possibly change your default search page.
Free YouTube Downloader
Free YouTube Downloader is a free tool that will let you download YouTube video. To install the app you have to visit Free YouTube Downloader website and download the app. After Installing the app all you have to do is copy the YouTube video URL from youtube.com and paste it on the YouTube URL box downloader then select the output format such as MP4, FLV, Xvid or other video format you want. You can also download video as an mp3 audio instead of video format.
YTD Video Downloader
YTD Video Downloader is also a free tool for downloading video from YouTube, but if you want additional functionality of YTD Video Downloader such as automatic conversion of video and want to download multiple videos simultaneously then you have to upgrade the software to PRO version. The basic free functionality of the software is good enough for you to download videos unless you want additional downloading functionality then upgrade to PRO version. Downloading video in YTD YouTube Downloader is almost the same with any other video downloader all you have to do is copy the video URL from YouTube and paste it in the Paste URL box then click on download.
How to download YouTube Video using YTD video downloader
After downloading your video from YouTube try VLC Media Player to play your videosbecause this software support almost all video format.
An ISO image file is an exact representation of a CD, DVD or Blu-Ray Disc in a single archive file. When you create an ISO image using optical disc utility programs such as ImgBurn what it does is it duplicate the disc precisely into a single achieve file.
To Mount the ISO Image in Windows 7 and Older Operating System
Mounting ISO file in Windows 7 and older Operating System such as Windows Vista and Windows XP requires you to use third party software such as magiciso. In Windows 8 and Windows 8.1 mounting iso and some virtual disc image is easy and you don’t have to install third party software because iso image mounting utility is already integrated to the operating system.
To begin mounting your iso image in Windows 7 and older operating system, download a virtual CD/DVD disc mounting utility such as magiciso from their website and be sure to select the correct operating system you’re using. We’ll be using magiciso for mounting iso or any other CD/DVD image like .BIN (CDRWin), .NRG (Nero-Burning Rom), MDF/MDS (Fantom CD) or any other CD/DVD image created from different software manufacturer. Magiciso is a freeware, light-weight and very helpful utility designed for creating and managing virtual CD drives and CD/DVD disc.
After downloading magiciso install it on your computer, there’s no need to restart your computer after completing the installation.
You’ll see a magiciso icon at your desktop taskbar after the installation.
Magicdisc icon on Windows taskbar
Right click on the magiciso icon and hover your mouse on Virtual CD/DVD-ROM and select the virtual drive you want your ISO image to use and click on the Mount on the dropdown menu.
Browse the iso image file on your computer and click Open to mount the image file.
The mounted iso image will autorun, you can now use the mounted image as if it is a real disc on a virtual optical drive. To unmount the iso image from the virtual drive, again right click on the magiciso icon on your desktop taskbar, hover your mouse to Virtual CD/DVD ROM and select the drive you want to unmount then click on the Unmount on the context menu.
Mounting ISO in Windows 8 and Windows 8.1
In Windows 8 and Windows 8.1 theres no need to worry about installing a third-party software for mounting ISO image because ISO image mounting is already built-in to the operating system. All you have to do is find your ISO image file and right click on it then click on Mount, once you’ve click the mount option on the context menu you’ll see a new drive with the iso image mounted.
To unmount the iso image right click on the virtual drive where the iso image is mounted then click on Eject.
Note: Procedures in mounting and unmounting iso image file are the same in Windows 8 and Windows 8.1