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| Resistors are ubiquitous. Because of this their performance is taken for granted, offered they are operated within their power, voltage and environmental ratings this really is sensible, given that right after millions of accumulated resistor-years knowledge there is tiny left for their manufacturers to learn. But there are actually nevertheless applications exactly where specifying and applying resistors wants to be handled with some care. Resistor kinds - Surface mount chip The most widespread general purpose resistor is definitely the thick film surface mount chip variety. Readily available in big quantities and incredibly low rates, it really is the workhorse in the resistor world. The construction is extremely 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 with a solder dip to make sure ease of wetting when the component is soldered into place, and also the top from the element is IBM Certified Sales Specialist coated with an epoxy or glass layer to safeguard the resistive element. Distinct manufacturers make numerous claims for the ruggedness and overall performance of their parts however the simple attributes are related. Power dissipation is largely controlled by the thermal properties with the PCB pads to which the chip is soldered, and for anyone who is running close for the rated energy in the component it'll be necessary to confirm that your pad design agrees with all the manufacturer's recommendations. You may also get metal film chip resistors for higher performance applications, but these are much more pricey than the frequent thick film. The resistive ink method employed for chips can also produce typical axial-lead resistors (metal glaze) of tiny size, and can be utilised directly onto a substrate to create printed resistors. This technique is regularly utilized in hybrid circuits and is pretty cost-effective in particular when big numbers of comparable values are required. It really is feasible to print resistors straight onto fibreglass printed circuit board, although the result is of extremely poor good quality and cannot be utilized exactly where a stable, predictable value (compared with conventional forms) is required. Metal film The subsequent most popular sort would be the metal film, in its different guises. This can be the common component for industrial and military purposes. The most well known varieties of leaded metal film are hardly any far more costly than carbon film and, given their superior characteristics, especially temperature coefficient, noise and power handling capability, lots of gear manufacturers don't discover it worthwhile to bother with carbon film. Variants of the typical metal film cater for high or low resistance desires. The "metal" within a metal film is usually a nickel-chromium alloy of varying composition for unique resistance ranges. A film of this alloy is plated onto an alumina substrate. For leaded parts, the end caps and leads are force-fitted towards the tubular assembly as well as the resistance element IBM Certified Integration Developer is trimmed to worth by cutting a helical groove of controlled dimensions in it, which permits exactly the same film composition to be utilised more than quite a wide range of nominal values. The entire part is then coated in epoxy and marked. The disadvantage with the helical trimming approach is that it inherently increases the resistor's stray inductance, as well as limits its pulse handling capability. Carbon The most widespread leaded resistor for commercial applications will be the carbon film. It really is definitely low-cost - much less than a penny in quantity. It also has the least impressive efficiency in terms of tolerance and temperature coefficient, but it is normally adequate for general goal use. The other sort which uses pure carbon because the resistive element is carbon composition, which was the earliest kind of resistor but nowadays finds a use in specific applications which involve an assured pulse withstand capability. Wirewound For medium and high power (higher than 2W) applications the wirewound resistor is almost universally utilised. It's fairly inexpensive and readily readily available. Its disadvantages are its bulk, though this permits a lower surface temperature to get a given energy dissipation; and that due to its construction it is actually noticeably inductive, which limits its use in high frequency or pulse applications. Wirewound sorts are available either having a vitreous enamel or cement coating, or in an aluminium housing which may be mounted to a heatsink. Aluminium housings can offer you power dissipations exceeding 100W per unit. Precision resistors Once circuit needs start out to call for accuracy and drift specifications exceeding the usual metal film skills, the price increases substantially. It is nonetheless possible to get metal film resistors of "precision" efficiency as much as an order of magnitude improved than the typical, though at rates an order of magnitude or far more higher. Drift requirements of much less than ten parts-per-million per °C introduce quite a few extra important components into the performance equation, like thermal emf, mechanical and thermal anxiety, and terminating resistance. These might be dealt with, as well as the resistive and substrate supplies might be optimised, but the unit charges are now measured in pounds, and delivery occasions 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 numerous resistors at the moment, which can be then encapsulated to form a multi-resistor single package. The resulting resistors have the identical performance as a single thick film chip, even though with decreased breakdown voltage and power handling ability. Printed Circuit Passive Components Resistors are ubiquitous. Because of this their overall performance is taken for granted, supplied they may be operated within their power, voltage and environmental ratings this can be reasonable, considering the fact that soon after millions of accumulated resistor-years encounter there is small left for their producers to discover. But you'll find nonetheless applications where specifying and applying resistors desires to become handled with some care. Resistor forms - Surface mount chip The most common general goal resistor could be the thick film surface mount chip variety. Available in huge quantities and quite low rates, it is actually the workhorse of your resistor planet. The construction is incredibly very simple 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 top surface. The terminations are coated using a solder dip to ensure ease of wetting when the portion is soldered into spot, and the best with the component is coated with an epoxy or glass layer to defend the resistive element. Different producers make numerous claims for the ruggedness and efficiency of their parts but the simple functions are similar. Power dissipation is largely controlled by the thermal properties of your PCB pads to which the chip is soldered, and if you're running close for the rated power on the portion it will be essential to confirm that your pad design agrees together with the manufacturer's suggestions. You may also get metal film chip resistors for greater overall performance applications, but these are additional costly than the widespread thick film. The resistive ink method used for chips may also generate normal axial-lead resistors (metal glaze) of tiny size, and may be utilised straight onto a substrate to generate printed resistors. This technique is often utilised in hybrid circuits and is very cost-effective specifically when huge numbers of related values are needed. It can be attainable to print resistors straight onto fibreglass printed circuit board, even though the result is of quite poor excellent and can not be utilised where a stable, predictable value (compared with conventional kinds) is required. Metal film The subsequent most widespread sort is the metal film, in its many guises. This really is the common portion for industrial and military purposes. By far the most well known varieties of leaded metal film are hardly any far more high-priced than carbon film and, offered their superior characteristics, particularly temperature coefficient, noise and energy handling potential, a lot of gear manufacturers don't obtain it worthwhile to bother with carbon film. Variants of your regular metal film cater for high or low resistance requires. The "metal" in a metal film is actually a nickel-chromium alloy of varying composition for distinct resistance ranges. A film of this alloy is plated onto an alumina substrate. For leaded parts, the finish caps and leads are force-fitted for the tubular assembly and also the resistance element is trimmed to worth by cutting a helical groove of controlled dimensions in it, which makes it possible for exactly the same film composition to be utilised over really a wide range of nominal values. The entire element is then coated in epoxy and marked. The disadvantage in the helical trimming method is 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 may be the carbon film. It really is surely affordable - much less than a penny in quantity. It also has the least impressive efficiency when it comes to tolerance and temperature coefficient, nevertheless it is typically sufficient for general purpose use. The other sort which uses 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 energy (higher than 2W) applications the wirewound resistor is practically universally utilized. It is pretty cheap and readily accessible. Its disadvantages are its bulk, though this will allow a lower surface temperature for any offered power dissipation; and that because of its construction it really is noticeably inductive, which limits its use in high frequency or pulse applications. Wirewound sorts are obtainable either having a vitreous enamel or cement coating, or in an aluminium housing which can be mounted to a heatsink. Aluminium housings can present energy dissipations exceeding 100W per unit. Precision resistors Once circuit specifications start out to call for accuracy and drift specifications exceeding the usual metal film abilities, the expense increases substantially. It can be still doable to have metal film resistors of "precision" performance up to an order of magnitude greater than the normal, even though at costs an order of magnitude or much more greater. Drift needs of less than 10 parts-per-million per °C introduce numerous far more important factors into the overall performance equation, which include thermal emf, mechanical and thermal tension, and terminating resistance. These may be dealt with, and the resistive and substrate materials can be optimised, however the unit expenses are now measured in pounds, and delivery occasions 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 lots of resistors at after, which is then encapsulated to form a multi-resistor single package. The resulting resistors have the same efficiency as a single thick film chip, even though with reduced breakdown voltage and power handling capacity. |
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