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| Resistors are ubiquitous. As a result of this their efficiency is taken for granted, supplied they're operated within their power, voltage and environmental ratings this really is sensible, considering the fact that just after millions of accumulated resistor-years experience there is certainly small left for their producers to find out. But there are actually nevertheless applications where specifying and applying resistors wants to become handled with some care. Resistor types - Surface mount chip The most prevalent general purpose resistor would be the thick film surface mount chip sort. Readily available in big quantities and incredibly low prices, it really is the workhorse of your resistor globe. The construction is very very simple and hardly varies from manufacturer to manufacturer. An alumina (aluminium oxide ceramic) substrate with nickel plated terminations features a resistive ink film printed or otherwise deposited on its leading surface. The terminations are coated with a solder dip to make sure ease of wetting when the part is soldered into spot, and the best on the element is IBM Certified Sales Specialist coated with an epoxy or glass layer to guard the resistive element. Distinct manufacturers make many claims for the ruggedness and overall performance of their parts however the fundamental features are similar. Energy dissipation is largely controlled by the thermal properties of the PCB pads to which the chip is soldered, and in case you are running close to the rated power on the element it's going to be necessary to confirm that your pad style agrees using the manufacturer's suggestions. You may also get metal film chip resistors for higher performance applications, but these are additional pricey than the common thick film. The resistive ink approach used for chips can also create normal axial-lead resistors (metal glaze) of small size, and can be utilised directly onto a substrate to generate printed resistors. This strategy is frequently used in hybrid circuits and is extremely cost-effective mainly when huge numbers of similar values are essential. It can be possible to print resistors straight onto fibreglass printed circuit board, even though the outcome is of extremely poor good quality and can't be utilized exactly where a stable, predictable worth (compared with conventional sorts) is required. Metal film The next most prevalent kind will be the metal film, in its numerous guises. This can be the common element for industrial and military purposes. By far the most well-known varieties of leaded metal film are hardly any more high priced than carbon film and, offered their superior characteristics, especially temperature coefficient, noise and energy handling ability, numerous equipment manufacturers usually do not obtain it worthwhile to bother with carbon film. Variants of your common metal film cater for high or low resistance wants. 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 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 enables the same film composition to be applied over really a wide range of nominal values. The entire part is then coated in epoxy and marked. The disadvantage on the helical trimming course of action is the fact 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's surely low cost - much less than a penny in quantity. It also has the least impressive overall performance when it comes to tolerance and temperature coefficient, but it is generally sufficient for common objective use. The other kind which makes use of pure carbon because the resistive element is carbon composition, which was the earliest variety of resistor but these days finds a use in particular applications which involve an assured pulse withstand capability. Wirewound For medium and high energy (greater than 2W) applications the wirewound resistor is virtually universally used. It's pretty affordable and readily obtainable. Its disadvantages are its bulk, although this will allow a lower surface temperature to get a given power dissipation; and that because of its construction it can be noticeably inductive, which limits its use in high frequency or pulse applications. Wirewound kinds are out there either using a vitreous enamel or cement coating, or in an aluminium housing which is usually mounted to a heatsink. Aluminium housings can supply energy dissipations exceeding 100W per unit. Precision resistors Once circuit requirements get started to call for accuracy and drift specifications exceeding the usual metal film abilities, the cost increases substantially. It's nevertheless feasible to have metal film resistors of "precision" overall performance up to an order of magnitude improved than the common, although at prices an order of magnitude or far more greater. Drift needs of less than ten parts-per-million per °C introduce a lot of a lot more considerable elements in to the efficiency equation, for instance thermal emf, mechanical and thermal pressure, and terminating resistance. These is usually dealt with, and also the resistive and substrate supplies may be optimised, but the unit expenses are now measured in pounds, and delivery times 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 once, that 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 decreased breakdown voltage and power handling capacity. Printed Circuit Passive Components Resistors are ubiquitous. Due to this their efficiency is taken for granted, provided they are operated inside their power, voltage and environmental ratings this really is reasonable, since after millions of accumulated resistor-years expertise there's little left for their producers to discover. But you can find still applications where specifying and applying resistors requires to be handled with some care. Resistor kinds - Surface mount chip The most common general objective resistor is definitely the thick film surface mount chip variety. Accessible in substantial quantities and incredibly low prices, it truly is the workhorse of your resistor world. The construction is pretty uncomplicated and hardly varies from manufacturer to manufacturer. An alumina (aluminium oxide ceramic) substrate with nickel plated terminations features 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, and also the top from the component is coated with an epoxy or glass layer to protect the resistive element. Diverse manufacturers make various claims for the ruggedness and overall performance of their parts however the standard capabilities are comparable. Energy dissipation is largely controlled by the thermal properties on the PCB pads to which the chip is soldered, and if you are operating close towards the rated power of the part it's going to 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 more highly-priced than the typical thick film. The resistive ink approach employed for chips may also produce common axial-lead resistors (metal glaze) of smaller size, and may be applied straight onto a substrate to generate printed resistors. This approach is frequently applied in hybrid circuits and is really cost-effective in particular when big numbers of comparable values are expected. It is actually feasible to print resistors straight onto fibreglass printed circuit board, although the outcome is of really poor excellent and can't be utilized where a stable, predictable worth (compared with conventional varieties) is required. Metal film The next most common type could be the metal film, in its various guises. This really is the typical element for industrial and military purposes. By far the most well-liked varieties of leaded metal film are hardly any a lot more pricey than carbon film and, provided their superior characteristics, especially temperature coefficient, noise and energy handling potential, a lot of gear manufacturers don't uncover it worthwhile to bother with carbon film. Variants in the typical metal film cater for high or low resistance requires. The "metal" in a metal film is a nickel-chromium alloy of varying composition for various resistance ranges. A film of this alloy is plated onto an alumina substrate. For leaded parts, the end caps and leads are force-fitted to the tubular assembly and also the resistance element is trimmed to worth by cutting a helical groove of controlled dimensions in it, which allows the identical film composition to be made use of over pretty a wide range of nominal values. The complete part is then coated in epoxy and marked. The disadvantage with the helical trimming method is that it inherently increases the resistor's stray inductance, and also limits its pulse IBM Certifications handling capability. Carbon The most widespread leaded resistor for commercial applications may be the carbon film. It really is certainly low cost - much less than a penny in quantity. It also has the least impressive overall performance when it comes to tolerance and temperature coefficient, but it is usually sufficient for general objective use. The other type which uses pure carbon because the resistive element is carbon composition, which was the earliest type 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 nearly universally used. It's pretty low-cost and readily out there. Its disadvantages are its bulk, although this enables a lower surface temperature for a offered power dissipation; and that as a result of its construction it really is noticeably inductive, which limits its use in high frequency or pulse applications. Wirewound types are available either with a vitreous enamel or cement coating, or in an aluminium housing which might be mounted to a heatsink. Aluminium housings can offer energy dissipations exceeding 100W per unit. Precision resistors Once circuit requirements start to call for accuracy and drift specifications exceeding the usual metal film abilities, the cost increases substantially. It is nonetheless possible to have metal film resistors of "precision" performance up to an order of magnitude far better than the standard, though at prices an order of magnitude or far more larger. Drift requirements of less than ten parts-per-million per °C introduce a lot of extra substantial variables in to the overall performance equation, including thermal emf, mechanical and thermal tension, and terminating resistance. These might be dealt with, along with the resistive and substrate supplies might be optimised, however the unit fees are now measured in pounds, and delivery times 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 once, which is then encapsulated to form a multi-resistor single package. The resulting resistors have the identical performance as a single thick film chip, though with lowered breakdown voltage and energy handling potential. |
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