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| Resistors are ubiquitous. Because of this their overall performance is taken for granted, supplied they're operated within their energy, voltage and environmental ratings this is affordable, given that following millions of accumulated resistor-years experience there is certainly little left for their producers to discover. But you can find still applications where specifying and applying resistors requirements to become handled with some care. Resistor varieties - Surface mount chip The most widespread general goal resistor would be the thick film surface mount chip kind. Offered in enormous quantities and pretty low costs, it is actually the workhorse with the resistor planet. The construction is really uncomplicated and hardly varies from manufacturer to manufacturer. An alumina (aluminium oxide ceramic) substrate with nickel plated terminations includes a resistive ink film printed or otherwise deposited on its leading surface. The terminations are coated using a solder dip to make sure ease of wetting when the part is soldered into place, plus the top on the portion is IBM Certified Sales Specialist coated with an epoxy or glass layer to shield the resistive element. Unique producers make a variety of claims for the ruggedness and overall performance of their parts however the standard attributes are comparable. Power dissipation is largely controlled by the thermal properties of the PCB pads to which the chip is soldered, and should you be operating close for the rated power from the part it will be necessary to confirm that your pad style agrees using the manufacturer's suggestions. You can also get metal film chip resistors for greater performance applications, but these are extra costly than the typical thick film. The resistive ink technique employed for chips may also produce common axial-lead resistors (metal glaze) of modest size, and can be utilised straight onto a substrate to create printed resistors. This approach is often utilized in hybrid circuits and is very cost-effective specially when significant numbers of related values are needed. It's attainable to print resistors straight onto fibreglass printed circuit board, although the outcome is of incredibly poor high quality and cannot be applied exactly where a stable, predictable value (compared with conventional types) is required. Metal film The subsequent most popular kind is definitely the metal film, in its many guises. This really is the regular element for industrial and military purposes. Essentially the most well-liked varieties of leaded metal film are hardly any more costly than carbon film and, given their superior characteristics, particularly temperature coefficient, noise and power handling potential, many equipment producers usually do not discover it worthwhile to bother with carbon film. Variants from the standard metal film cater for high or low resistance desires. The "metal" in a metal film is usually a nickel-chromium alloy of varying composition for diverse resistance ranges. A film of this alloy is plated onto an alumina substrate. For leaded parts, the finish caps and leads are force-fitted to the tubular assembly as well as the resistance element IBM Certified Integration Developer is trimmed to value by cutting a helical groove of controlled dimensions in it, which permits the same film composition to be employed more than really a wide range of nominal values. The complete part is then coated in epoxy and marked. The disadvantage on the helical trimming procedure is the fact that it inherently increases the resistor's stray inductance, and also limits its pulse handling capability. Carbon The most prevalent leaded resistor for commercial applications may be the carbon film. It's undoubtedly cheap - less than a penny in quantity. It also has the least impressive efficiency in terms of tolerance and temperature coefficient, however it is ordinarily adequate for general purpose use. The other variety which utilizes pure carbon because the resistive element is carbon composition, which was the earliest variety of resistor but these days finds a use in certain applications which involve an assured pulse withstand capability. Wirewound For medium and high energy (greater than 2W) applications the wirewound resistor is pretty much universally applied. It is actually pretty inexpensive and readily out there. Its disadvantages are its bulk, although this will allow a lower surface temperature for any offered power dissipation; and that due to its construction it is actually noticeably inductive, which limits its use in high frequency or pulse applications. Wirewound kinds are offered either using a vitreous enamel or cement coating, or in an aluminium housing which could be mounted to a heatsink. Aluminium housings can give energy dissipations exceeding 100W per unit. Precision resistors Once circuit needs start out to call for accuracy and drift specifications exceeding the usual metal film abilities, the price increases substantially. It's nonetheless possible to acquire metal film resistors of "precision" performance as much as an order of magnitude improved than the standard, although at rates an order of magnitude or a lot more larger. Drift specifications of much less than 10 parts-per-million per °C introduce many more substantial aspects in to the performance equation, which include thermal emf, mechanical and thermal tension, and terminating resistance. These could be dealt with, plus the resistive and substrate supplies is often optimised, but the unit fees are now measured in pounds, and delivery instances stretch to months. Resistor networks Thick film resistor networks are manufactured like chips. A resistive ink is screen printed onto a ceramic substrate to form quite a few resistors at once, which is then encapsulated to form a multi-resistor single package. The resulting resistors have the same performance as a single thick film chip, even though with lowered breakdown voltage and energy handling capability. Printed Circuit Passive Components Resistors are ubiquitous. Because of this their performance is taken for granted, provided they may be operated inside their energy, voltage and environmental ratings this is affordable, since right after millions of accumulated resistor-years expertise there's small left for their manufacturers to learn. But there are actually still applications where specifying and applying resistors needs to be handled with some care. Resistor kinds - Surface mount chip The most typical general purpose resistor would be the thick film surface mount chip type. Out there in enormous quantities and very low prices, it is actually the workhorse in the resistor world. The construction is very easy and hardly varies from manufacturer to manufacturer. An alumina (aluminium oxide ceramic) substrate with nickel plated terminations includes a resistive ink film printed or otherwise deposited on its best surface. The terminations are coated having a solder dip to make sure ease of wetting when the element is soldered into place, along with the best from the part is coated with an epoxy or glass layer to safeguard the resistive element. Different producers make many claims for the ruggedness and performance of their parts but the fundamental capabilities are related. Energy dissipation is largely controlled by the thermal properties of your PCB pads to which the chip is soldered, and if you are operating close for the rated energy from the part it'll be essential to confirm that your pad style agrees using the manufacturer's suggestions. You can also get metal film chip resistors for larger overall performance applications, but these are far more expensive than the common thick film. The resistive ink strategy made use of for chips may also create typical axial-lead resistors (metal glaze) of modest size, and may be employed directly onto a substrate to create printed resistors. This strategy is regularly employed in hybrid circuits and is very cost-effective in particular when huge numbers of related values are essential. It can be possible to print resistors directly onto fibreglass printed circuit board, even though the result is of incredibly poor superior and can not be utilised exactly where a stable, predictable value (compared with conventional forms) is essential. Metal film The subsequent most popular variety is the metal film, in its different guises. This really is the typical part for industrial and military purposes. Probably the most well known varieties of leaded metal film are hardly any much more expensive than carbon film and, offered their superior characteristics, especially temperature coefficient, noise and power handling capability, many equipment producers don't uncover it worthwhile to bother with carbon film. Variants with the common metal film cater for high or low resistance requires. The "metal" inside a metal film is usually a nickel-chromium alloy of varying composition for different resistance ranges. A film of this alloy is plated onto an alumina substrate. For leaded parts, the finish caps and leads are force-fitted to the tubular assembly along with the resistance element is trimmed to worth by cutting a helical groove of controlled dimensions in it, which will allow the identical film composition to be utilised over very a wide range of nominal values. The whole element is then coated in epoxy and marked. The disadvantage in the helical trimming course of action is the fact that it inherently increases the resistor's stray inductance, as well as limits its pulse IBM Certifications handling capability. Carbon The most popular leaded resistor for commercial applications would be the carbon film. It truly is undoubtedly inexpensive - much less than a penny in quantity. It also has the least impressive overall performance in terms of tolerance and temperature coefficient, but it is ordinarily sufficient for common goal use. The other variety which utilizes pure carbon because the resistive element is carbon composition, which was the earliest variety of resistor but today finds a use in specific applications which involve an assured pulse withstand capability. Wirewound For medium and high power (greater than 2W) applications the wirewound resistor is almost universally employed. It is actually fairly inexpensive and readily available. Its disadvantages are its bulk, even though this permits a lower surface temperature for any provided energy dissipation; and that because of its construction it can be noticeably inductive, which limits its use in high frequency or pulse applications. Wirewound varieties are available either with a vitreous enamel or cement coating, or in an aluminium housing which is often mounted to a heatsink. Aluminium housings can offer energy dissipations exceeding 100W per unit. Precision resistors Once circuit specifications start off to call for accuracy and drift specifications exceeding the usual metal film skills, the cost increases substantially. It really is still feasible to acquire metal film resistors of "precision" overall performance up to an order of magnitude far better than the standard, although at prices an order of magnitude or far more higher. Drift requirements of much less than 10 parts-per-million per °C introduce several much more significant aspects in to the performance equation, such as thermal emf, mechanical and thermal pressure, and terminating resistance. These might be dealt with, and the resistive and substrate materials might be optimised, however the unit costs are now measured in pounds, and delivery instances stretch to months. Resistor networks Thick film resistor networks are manufactured like chips. A resistive ink is screen printed onto a ceramic substrate to form several resistors at once, which is then encapsulated to form a multi-resistor single package. The resulting resistors have exactly the same overall performance as a single thick film chip, even though with lowered breakdown voltage and power handling ability. |
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