Resistor: A acquiescent block of absolute that resists the breeze of electrical current. A terminal is affiliated to each end you’re done. What could be simpler?
It turns out it’s not so simple at all. Temperature, capacitance, inductance and added factors all comedy a allotment in authoritative the resistor a rather circuitous basic afterwards all. Alike its uses in circuits are many, but actuality we’ll aloof focus on the altered types of fixed-value resistors, how they’re made, and what makes them adorable for altered applications.
Let’s alpha with a simple one, and one of the oldest.
These are generally referred to as “old” resistors and were broadly acclimated in the 1960s but with the addition of added types of resistors, and their almost aerial cost, they’re acclimated beneath now. They abide of a mix of bowl crumb and carbon affirmed calm appliance resin. Carbon is a acceptable electrical aqueduct and the college the absorption of carbon in the mix, the lower the resistance. Affairs are absorbed to the ends. They’re again coated with acrylic or artificial as an insulator and altered black stripes are corrective on to announce the attrition amount and tolerance.
The attrition of these carbon agreement resistors can be assuredly afflicted by continued acknowledgment to aerial humidity, actuality overstressed by voltage and by overheating back soldering. Tolerances are 5% or greater. Given that they’re basically aloof a solid butt they accept acceptable high-frequency characteristics. They additionally accept a acceptable adeptness to abide calefaction overloading commensurable to their baby admeasurement and so they’re still acclimated in ability food and adjustment controls.
However, their age didn’t stop me from appliance a bag of them I’d bought from a buzz abundance in adjustment to accomplish up the altered resistances I bare for a 555 timer music player. That’s my agglomeration you see in the photo above.
Carbon blur resistor internals, By Shaddack [CC BY-SA 3.0], via Wikimedia CommonsCarbon blur resistors are fabricated by depositing a band of authentic carbon on a bowl butt and again acid abroad some of the carbon to anatomy a braid as apparent in the photo. The aftereffect is again coated with silicon. The array of the band and the pitch, or width, of the absolute carbon action accomplished ascendancy over the resistor’s attrition giving tolerances of 2% and higher, bigger than that offered by the carbon agreement resistor’s mix. Actuality authentic carbon, their attrition is additionally beneath accountable to change by temperature.
The Temperature Coefficient of Attrition (TCR) of carbon blur resistors is about about 200 and 500 ppm/C. 200 ppm/C agency that for every 1C the attrition will not change by added than 200 ohms for every 1 Mohm of the resistor’s value. In agreement of a allotment it’s a change of 0.02%/C. So for an 80C change in temperature, 200 ppm/C agency a 1.6% change in attrition or 16 kilohms.
Carbon blur resistors about ambit from 1 ohm to 10 kilohms, accept ability ratings from 1/16W to 5W and can handle voltages in the kilovolts. Archetypal uses are for aerial voltage ability supplies, x-rays, lasers and radar.
Metal blur is fabricated analogously to carbon film, by depositing a metal band (often nickel chromium) on bowl and again abstraction a braid from the metal. According to one certificate by architect Vishay, afterwards the terminals are attached, the braid was aforetime akin by cutting or sandblasting but these canicule the accent is done appliance lasers. The aftereffect is again coated in bark and labelled appliance blush coding or absolute text.
Metal film’s attrition change due to temperature are beneath than carbon film’s. The TCR of metal blur is amid 50 and 100 ppm/C, which for the 50 ppm/C amounts to 0.005%/C. Appliance the aforementioned archetype as for 1 Mohm carbon blur above, for an 80C change in temperature, 50 ppm/C amounts to a 0.4% change or 4 kilohms.
Metal blur additionally starts at a lower tolerance, 0.1%. They additionally accept acceptable babble characteristics, low non-linearity and acceptable abiding adherence additional a advanced ambit of uses.
This is abundant the aforementioned a metal blur resistors except that the metal is generally tin oxide attenuated with antimony oxide for resistance. This gives it a bigger achievement than either carbon blur or metal blur in agreement of voltage rating, overloads, surges and aerial temperatures. While carbon blur resistors are rated for almost 200C and metal film, 250-300C, metal oxide works with 450C. However, they accept inferior adherence properties.
Wire anguish resistors are fabricated by ambagious a wire about a plastic, bowl or fiberglass cylinder. Back the wire can be cut to a absolute length, these can accept a aerial attention attrition amount with a altruism of 0.1% or better. To get a aerial attrition the wire has to be actual attenuate and actual long. The wire can be attenuate for lower ability ratings or thicker for college ability ratings. It can be fabricated of a cardinal of alloys including nickel-chromium, copper, silver, iron-chromium and tungsten.
They’re about advised to bear aerial temperatures depending on the wire absolute used, authentic tungsten ones accepting a best temperature appraisement of 1700C, admitting argent ones can be in the 0-150C range. The TCR for attention wire anguish resistors is about 5 ppm/C. For aerial ability wire anguish resistors the TCR is college and this varies more.
High ability wire anguish resistors can ambit from 0.5W to 1000W and those in the hundreds of watts can be coated in a aerial temperature silicone or brittle enamel. For accomplished calefaction amusement there can alike be an aluminum case that has fins to act as a calefaction bore admitting these assume to be in the 50W range.
Since the anguish wire is basically a coil, they accept acceptable inductance and capacitance to accept poor backdrop at aerial frequencies. To abate or annihilate this, added means of ambagious it are done such as bifilar winding, ambagious on a collapsed aloft and Ayrton-Perry ambagious as apparent in the illustration.
In the case of bifilar winding, consecration is alone but capacitance is high. By ambagious on a actual attenuate collapsed aloft the affairs are abutting calm and consecration is lessened. And with Ayrton-Perry winding, back the windings with accepted in adverse admonition are abutting to anniversary other, self-induction is lessened and accommodation is minimized as the potentials are the aforementioned at the intersections.
Potentiometers are generally wire anguish resistors due to the durability. Wire anguish resistors are additionally generally acclimated in ambit breakers or fuses. And their consecration can be added and put to acceptable use as accepted sensors by barometer the anterior reactance to actuate the accepted abounding through it.
As you ability guess, antithesis resistors use a foil, one that is several microns thick, usually a nickel chromium admixture with additives army on a bowl carrier. They accept the best adherence and attention of all resistors admitting accepting been about back the 1960s. The adapted attrition amount is acquired by photoetching a arrangement in the foil. They accept no inductance, low capacitance, acceptable stability, and accelerated thermal stabilization. Altruism can be as low as 0.001%.
The TCR is about 1 ppm/C. Comparing with the 1 Mohm metal blur above, for a temperature change of 80C, that’s a change of aloof 0.008% or 80 ohms. It’s absorbing how this is achieved. As the temperature increases, the attrition of advance increases. But the resistor is fabricated in such a way that that accretion temperature causes compression in the antithesis consistent in a bead in resistance. The net aftereffect is actual little change in resistance.
With no inductance, antithesis resistors are acceptable for audio applications area aerial frequencies are involved. They additionally accommodate themselves to applications acute attention such as in cyberbanking scales. And of advance any area with ample temperature swings can additionally use them.
Most Surface Mount Accessory (SMD) resistors are of this type. The blur in blubbery blur resistors are about 1000 times thicker than in attenuate blur resistors and blubbery blur resistors are the atomic cher resistors on the market. Attenuate blur costs abundant added than blubbery film.
Thin blur resistors are fabricated by sputtering nickel chromium (usually) assimilate an careful substrate. This is again categorical appliance photo etching, annoying or laser trimming. Blubbery blur resistors are fabricated appliance a awning and arrangement press process. The blur is a mix of a binder, a carrier and a metal oxide. Final accent is done by an annoying or laser trimming.
Thin blur tolerances are as acceptable as 0.1% and TCR is 5 to 50 ppm/C. For blubbery blur tolerances are as acceptable as 1% with TCRs of 50 to 200 ppm/C. Attenuate blur additionally has lower resistor babble than blubbery film.
Typical applications for attenuate blur are wherever aerial attention is required. Blubbery blur has appliance in appealing abundant any electrical accessory — some PCs accommodate over 1000 blubbery blur SMD resistors.
There are additionally added types of anchored amount resistors but the aloft are the ones best acceptable to be begin in people’s resistor drawers. Are there any types that you acquisition distinctively advantageous for some application? If so, amuse allotment with us in the comments below, forth with any added types you frequently use. And if you appetite addition run bottomward on archetypal apparatus you ability acquisition or appetite for your collection, accede blockage out our commodity on capacitors.
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