Post on 08-Apr-2018
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Resistor Types
PRECISION WIREWOUNDThe Precision Wire wound is a highly accurateresistor with a very low TCR and can be accuratewithin .005%. A temperature coefficient ofresistance (TCR) of as little a 3 part per millionper degree Celsius (3ppm/oC) can be achieved.However these components are too expensive forgeneral use and are normally used in highlyaccurate DC applications. The frequency responseof this type is not good. When used in an rfapplication all Precision Wire wound Resistors will
have a low Q resonant frequency. The powerhandling capability is very small. These are generally used in highlyaccurate DC measuring equipment, and reference resistors for voltageregulators and decoding networks.
The accuracy is maintained at 25oC (degrees Celsius) and will changewith temperature. The maximum value available is dependent upon
physical size and is much lower than most other types of resistor. Theirpower rating is approximately 1/10 of a similar physical size in a carboncomposition. They are rated for operation at +85oC or +125oC withmaximum operating temperature not to exceed +145oC. This means thatfull rated power can be applied at +85 ( 125) oC with no degradation in
performance. It may be operated above +125 (85) oC if the load isreduced. The derating is linear, rated load at +125(85) oC and no load at+145oC. Life is generally rated for 10,000 hours at rated temperature andrated load. The allowable change in resistance under these conditions is0.10%. Extended life can be achieved if operated at lower temperaturesand reduced power levels. End of life requirements are generally definedby the manufacturer or in some case by user specification. Somedegradation in performance can be expected. In some cases, particularlyif the tolerance is very low and the TC is low, the rated power is reducedto improve resistor stability through life. Precision Resistors regardless oftype, are designed for maximum accuracy and not to carry power. The
materials used in these resistors are highly stable heat treated materialsthat do change under extended heat and mechanical stress. Themanufacturing processes are designed to remove anystresses induced during manufacture. There is littledetectable noise in this type of resistor. The stabilityand reliability of these resistors is very good andtheir accuracy can be enhanced by matching theabsolute value and the temperature coefficient over
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their operating range to achieve very accurate voltage division.
NIST STANDARDThe NIST (National Institute of Standards and
Technology) Standard can be as accurate as .001%
with roughly the same TCR as Precision Wire woundResistors and are very stable. These are used as astandard in verifying the accuracy of resistivemeasuring devices. They are normally the Primary Standards of acompany's test lab.
They are returned to the NIST for measurement and their accuracy istracked through out the standards life to determine the Standard'sstability. Most companies will have two sets of standards so that they cancontinue to measure while one set of standards are being measured bythe NIST . They will alternate returning these NIST Standards to the NIST, one set one year and the other set the next year. For extremely
accurate measurements, the Standard with the longest history and thebest stability will be used. If erratic readings are received from the NISTover a period of years, the Standard is retired. Also, if the reading hassignificantly changed since the last NIST reading, the standard is suspect
and all measurements made using that standardmust be checked. Normally, a standard will takeabout 3 years to stabilize and becomes morestable with time unless it has had excessivepower applied or has been dropped. Thesestandards are generally stored in an oil bath at+25oC. During measurement, a thermometer is
placed in a cavity in the top of the Standard,called the oil well, and the temperature isrecorded for each measurement so that theexact value can be determined. That is the
value at +25oC plus or minus the change in value caused by thetemperature coefficient. Each standard will have a temperaturecorrection chart for exact values. Being stored in the oil bath preventsthe Standard from being stressed by changes in room temperature. Theseare highly precision devices and are expensive to buy and expensive tomaintain, but they are the primary resistor reference for any test lab.
These resistors are furnished in a totally enclosed metal case and for
values above 1 ohm, this enclosure is filled with mineral oil (other typeof oil may contain additives that can cause corrosion in later life). Thevalues below 1 ohm may be built in an enclosure that is perforated andthese must be submersed in oil. If power is applied without it beingsubmersed, the Standard will be ruined.
All NIST Type Standards are equipped with provisions for two, three, orfour terminal measurements. The applied power is calculated and thetemperature of the Standard is monitored during test. The lowest power
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level consistent with sufficient resolution to get the desiredmeasurement is used (in the area of 0.01 watts) and any appreciable risein temperature will dictate that the measurement should be suspendedand the test set-up reviewed for ways to reduce the power level. TheseStandards are rated for operation at room temperature only but their
other characteristics are the same as Precision Wire wound Resistors.
POWER WIREWOUND RESISTORSPower Wire wound Resistors are used when it is
necessary to handle a lot of power. They will handle morepower per unit volume than any other resistor. Some ofthese resistors are free wound similar to heater elements. These requiresome form of cooling in order to handle any appreciable amount ofpower. Some are cooled by fans and others are immersed in various typesof liquid ranging from mineral oil to high density silicone liquids. Mostare wound on some type of winding form. These winding forms vary.
Some examples are ceramic tubes, ceramic rods, heavily anodizedaluminium, fibreglass mandrels, etc.To achieve the maximum power rating in the smallest package size,
the core on which the windings are made must have a material with highheat conductivity. It may be Steatite, Alumina, Beryllium Oxide, or insome cases hard anodized Aluminium. Theoretically, the anodizedAluminium core has a better heat conductivity than any other insulatedmaterial, with Beryllium Oxide being very close. There are specificproblems with the anodized aluminium cores such as nicks in the coating,abrasion during capping and controlling the anodized thickness. Thereare various shapes, oval, flat, cylindrical, and most shapes are designed
to optimize heat dissipation.The more heat that can beradiated from the resistor, themore power that can be safelyapplied.
There is a group of thesecalled "Chassis MountedResistors". These are generallycylindrical power resistorswound on a ceramic coremoulded and pressed into an
aluminium heat sink and usuallywith heat radiating fins. Theseare designed to be mounted to
metal plates or a chassis to further conduct heat. This result in a ratingapproximately 5 times or more its normal rating.
These resistors come in a variety of accuracy's and TCRs. They can becustom made as a cross breed between a Precision Resistor and a PowerResistor; capable of handling more power than the standard Precision
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tolerances, low TCRs, and the range of values is extremely limited. Theyare often found as surge resistors in TVs and other electronic /electricalequipment. Their main selling point is low cost. They are often sold withan enamel coating for a low power precision wirewound resistor that iseven lower in cost.
One more item to consider, Power Wire wounds are made using alloyswith melt temperatures ranging from +1200o C to +1500o C and may beoperated cherry red without failure for short periods of time, howeverthe resistance value and TCR will change significantly and the insulatingmaterial will severely degrade. The bathtub boat type cannot besubjected to this type of overload, the fibre glass winding form willdisintegrate.
FUSE RESISTORSFuse Resistors serve a dual
purpose, a resistor and a fuse. They
are designed so that they will openwith a large surge current. Thefusing current is calculated based onthe amount of energy required tomelt the resistive material (the melttemperature plus the amount ofenergy required to vaporize theresistive material).
These resistors will normally run hotter than a normal precision orpower resistor so that a momentary surge will bring the resistive elementup to fusing temperature. Some designs create a hot spot inside the
resistor to assist in this fusing. Calculations are made and samples areproduced to verify the calculations. The major unknown is the heattransfer of the materials, which can be quite significant for pulse of longduration, and is very difficult to calculate. Mounting of these devices iscritical because it will effect the fusing current. These are quite oftenmade to mount in fuse clips for more accurate fusing characteristics.
CARBON COMPOSITIONCarbon composition resistors were once the most common resistor on
the market. They still have a very large market and prices are highlycompetitive. They are made from carbon rods cut in the appropriate
length then moulded with leads attached. The mix of the carbon can bevaried to change the resistivity for the desired values.
High values are much more readily available. Very low values are moredifficult to achieve. A 5% tolerance is available. This is usually done bymeasuring and selecting values. Normal tolerances withoutmeasurement and selection is in the area of 20%.
The temperature coefficient of resistance is in the range of 1000ppm/oC and is negative, that is when the temperature goes up the
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resistance goes down and when the temperature goes down, theresistance goes up. This is due to the carbon particles being relaxed(with increase in temperature) and being compressed (with the reductionin temperature).
These resistors also has a voltage coefficient. That is the resistance
will change with applied voltage, the greater the voltage, the greaterthe change. In addition to a power rating, they also have a voltagerating. (The wire wound voltage rating is determined by the value andthe wattage rating). The voltage rating of Carbon Composition Resistorsis determined by physical size as well as the value and wattage rating.
One more item to consider is that due to their construction, theygenerate noise and this noise level varies with value and physical size.The power capability in relation to physical size is greater than PrecisionWire wounds but less than Power Wire wounds.
CARBON FILM RESISTORS
Carbon Film Resistors have many of thesame characteristics as carbon compositionresistors. The material is similar thereforethey have noise, a voltage coefficient, the TCRcan be much lower because the formula can be varied to achieve this,the tolerance is much tighter due to the difference in manufacturingprocesses.
The Carbon Film Resistor is made by coating ceramic rods with amixture of carbon materials. This material is applied to these rods in avariety of means, the one most familiar to me are dipping, rolling,printing , or spraying the rods in the appropriate solution. The thickness
of the coating can be determined by the viscosity of the solution. This aswell as the material composition will determine the ohms / square. Someof you may not be familiar with this term. It simply means that if amaterial has a resistivity of 100 ohms / square, one square inch withhave the same resistance as 1 square mm, or 1 square foot or 1 squareyard or 1 square mile all equalling 100 ohms but the power handlingcapability is proportional to the size.
One batch of material can produce resistors in a wide range of values.These rods are cut to the length required for a specific size of resistor.These rods can then be spiral cut to a wide range of values. The originalmethod of spiralling these was done with grinding wheels on a machine
similar to a lathe. I am sure that later processes use lasers that areprogrammed to cut to specific values. The maximum ohmic value of thisgroup is the highest in the discrete resistor group.
Tolerance of 1% can be achieved with out measuring and selecting.Tolerance of less than 1% can be achieved by measuring and selecting.You should use caution in getting tight tolerances in this type becausethe temperature coefficient, voltage coefficient and stability may meanthat it is only good for that tolerance at the time it was installed. The
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TCR of carbon film resistors is in the neighbourhood of 100 to 200 ppmand is generally negative. Measuring and selecting can yield even tighterTCRs.
The frequency response of this type of resistor is among the best, farbetter than Wirewounds, and much better that carbon composition. The
wirewound resistors are inductive at lower frequencies and values andsomewhat capacitive at higher frequencies regardless of value. Alsowirewound resistors will have a resonant frequency. Carbon CompositionResistors will be predominately capacitive .
METAL FILM RESISTORSMetal Film resistors are the best
compromise of all resistors. They arenot as accurate and have a highertemperature coefficient of resistanceand are not as stable as Precision
Wirewounds. They are moreaccurate, do not have a voltagecoefficient, have a lowertemperature coefficient than CarbonFilm. TCRs of 50 to 100 ppm can be achieved.
They have a very low noise level when properly manufactured. In factsome of the screening processes measure the noise level to determine ifthere are problems in a particular batch of resistors.
Metal film resistors are manufactured by an evaporation/depositionprocess. That is the base metal is vaporized in a vacuum and depositedon a ceramic rod or wafer. Several attempts have been made to vaporize
low TCR materials and deposit on these substrates, but to my knowledge,these attempts have not been successful. This is partially due to thedifferent boiling points of the various base metals in these alloys (I usethe word alloy not entirely accurately, for these materials are not truealloys but amalgamations --- they do not bond to form a molecule as doesa true alloy). The very low TCR resistive materials are heat treated toachieve the resistivity and low TCR. This is not compatible with anevaporation process.
The frequency characteristics of this type are excellentand better than Carbon Films. The one area that carbonfilms exceed metal films is the maximum values. Carbon
films can achieve higher maximum values than any othergroup.
FOIL RESISTORSFoil resistors are similar in characteristics as metal films. Their main
advantages are better stability than metal films and lower TCRs. Theyhave excellent frequency response, low TCR, good stability, and veryaccurate. They are manufactured by rolling the same wire materials as
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used in precision wirewound resistors to make thin strips of foil. This foilis then bonded to a ceramic substrate and etched to produce the valuerequired. They can be trimmed further by abrasive processes, chemicalmachining or heat treating to achieve the desired tolerance. Their maindisadvantage is the maximum value is less than Metal Film Resistors.
The accuracy is about the same as metal film resistors, the TCR andstability approaches Precision Wirewounds but somewhat less becausethe rolling process and the packaging process produce stresses in the foil.The resistive materials used in Precision Wirewound Resistors is verysensitive to stresses which result in instability and higher TCRs. Anystresses on these material will result in a change in the resistance valueand TCR, the greater the stress, the larger the change. This type can beused as strain gauges, strain being measured as a change in theresistance. When used as a strain gauge, the foil is bonded to a flexiblesubstrate that can be mounted on a part where the stress is to bemeasured.
FILAMENT RESISTORSThe Filament Resistors are similar to the Bathtub Boat Resistor except
they are not packaged in a ceramic shell (boat). The individual resistiveelement with the leads already crimped is coated with an insulatingmaterial, generally a high temperature varnish. These are used inapplications where tolerance, TCR, and stability are not important butthe cost is the governing consideration. The cost on this type is slightlyhigher that carbon composition and the electrical characteristics arebetter.
POWER FILM RESISTORSPower film resistors are similar in manufacture to their respective
metal film or carbon film resistors. They are manufactured and rated aspower resistors, with the power rating being the most importantcharacteristic. Power Film Resistors are available in higher maximumvalues than the Power Wirewound Resistors and have a very goodfrequency response. They are generally used in applications requiringgood frequency response and/or higher maximum values. Generally forpower applications, the tolerance is wider, the temperature rating ischanged so that under full load resistor will not exceed the maximumdesign temperature, and the physical sizes are larger, and in some cases,
the core may be made from a higher heat conductive material and othermeans to help radiate heat.
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CapacitorCapacitor is defined as device to store electric charge .The capacity of acapacitor to store charge is known as capacitance.
Types of capacitor
Structure of a surface mount (SMT) film capacitor.
Capacitors have thin conducting plates (usually made of metal), separated by alayer of dielectric, then stacked or rolled to form a compact device.
Many types of capacitors are available commercially, with capacitance ranging fromthe picofarad, microfarad range to more than a farad, and voltage ratings up to
hundreds of kilovolts. In general, the higher the capacitance and voltage rating, thelarger the physical size of the capacitor and the higher the cost. Tolerances incapacitance value for discrete capacitors are usually specified as a percentage ofthe nominal value. Tolerances ranging from 50% (electrolytic types) to less than 1%are commonly available.
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Another figure of merit for capacitors is stability with respect to time andtemperature, sometimes called drift. Variable capacitors are generally less stable
than fixed types.
The electrodes need round edges to avoid field electron emission. Air has a low
breakdown voltage, so any air inside a capacitor - especially at plate edges - willreduce the voltage rating. Even closed air bubbles in the insulator or between theinsulator and the electrode lead to gas discharge, particularly in AC or Highfrequency applications. Groups of identically constructed capacitor elements areoften connected in series for operation at higher voltage. High voltage capacitorsneed large, smooth, and round terminals to prevent corona discharge.
Types of dielectric
CapacitorPolarized
Capacitor
Variable
Capacitor
Fixed capacitor comparisons
Capacitor type Dielectric used Features/applications Disadvantages
Paper CapacitorsPaper or oil-
impregnated paper
Impregnated paper was extensively
used for older capacitors, using
wax, oil, or epoxy as an impregnant.
Oil-Kraft paper capacitors are still
used in certain high voltage
applications. Has mostly been
Large size. Also, paper
is highly hygroscopic,
absorbing moisture from
the atmosphere despite
plastic enclosures and
impregnates. Absorbed
moisture degrades
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replaced by plastic film capacitors. performance by
increasing dielectric
losses (power factor)
and decreasing
insulation resistance.
Metalized Paper
CapacitorsPaper
Comparatively smaller in size than
paper-foil capacitors
Suitable only for lower
current applications. Has
been largely superseded
by metalized film
capacitors
PET film
CapacitorPolyester film
Smaller in size when compared to
paper or polypropylene capacitors
of comparable specifications. Mayuse plates of foil, metalized film, or
a combination. PET film capacitors
have almost completely replaced
paper capacitors for most DC
electronic applications. Operating
voltages up to 60,000VDC and
operating temperatures up to
125C. Low moisture absorption.
Temperature stability is
poorer than paper
capacitors. Usable at low
(AC power) frequencies,
but inappropriate for RF
applications due to
excessive dielectric
heating.
Kapton CapacitorKapton polyimide
film
Similar to PET film, but significantly
higher operating temperature (up to
250C).
Higher cost than PET.Temperature stability is
poorer than paper
capacitors. Usable at low
(AC power) frequencies,
but inappropriate for RF
applications due to
excessive dielectric
heating.
Polystyrene
CapacitorPolystyrene
Excellent general purpose plasticfilm capacitor. Excellent stability,
low moisture pick-up and a slightly
negative temperature coefficient
that can be used to match the
positive temperature co-efficient of
other components. Ideal for low
power RF and precision analog
Maximum operating
temperature is limited to
about +85C.
Comparatively bigger in
size.
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applications
Polycarbonate
Plastic Film
Capacitor
Polycarbonate
Superior insulation resistance,
dissipation factor, and dielectric
absorption versus polystyrenecapacitors. Moisture pick-up is less,
with about +/- 80 ppm temperature
co-efficient. Can use full operating
voltage across entire temperature
range (-55C to 125C)
Maximum operating
temperature limited to
about 125C.
Polypropylene
Plastic Film
Capacitors
Polypropylene
Has become the most popular
capacitor dielectric[citation needed]
.
Extremely low dissipation factor,
higher dielectric strength thanpolycarbonate and polyester films,
low moisture absorption, and high
insulation resistance. May use
plates of foil, metalized film, or a
combination. Film is compatible with
self-healing technology to improve
reliability. Usable in high frequency
applications due to very low
dielectric losses. Larger value and
higher voltage types from 1 to
100F at up to 440V AC are used
as run capacitors in some types of
single phase electric motors.
More susceptible to
damage from transient
over-voltages or voltage
reversals than oil-
impregnated Kraft paper
for pulsed power energy
discharge applications.
Polysulphone
Plastic Film
Capacitors
Polysulfone
Similar to polycarbonate. Can
withstand full voltage at
comparatively higher temperatures.
Moisture pick-up is typically 0.2%,
limiting its stability.
Very limited availability
and higher cost
PTFE
Fluorocarbon
(TEFLON) Film
Capacitors
Polytetra-
fluoroethylene
Lowest loss solid dielectric.
Operating temperatures up to
250C, extremely high insulation
resistance, and good stability. Used
in stringent, mission-critical
applications
Large size (due to low
dielectric constant), and
higher cost than other
film capacitors.
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Polyamide Plastic
Film CapacitorsPolyamide
Operating temperatures of up to
200C. High insulation resistance,
good stability and low dissipation
factor.
Large size and high cost.
Metalized Plastic
Film Capacitors
Polyester or
Polycarbonate
Reliable and significantly smaller in
size. Thin metalization can be used
to advantage by making capacitors
"self healing".
Thin plates limit
maximum current
carrying capability.
Stacked Plate
Mica CapacitorsMica
Advantages of mica capacitors
arise from the fact that the dielectricmaterial (mica) is inert. It does not
change physically or chemically
with age and it has good
temperature stability. Very resistant
to corona damage
Unless properly sealed,
susceptible to moisture
pick-up which will
increase the powerfactor and decrease
insulation resistance.
Higher cost due to
scarcity of high grade
dielectric material and
manually-intensive
assembly.
MetalizedMica or
SilverMicaCapacitors
Mica
Silver mica capacitors have the
above mentioned advantages. Inaddition, they have much reduced
moisture infiltration.
Higher cost
Glass Capacitors Glass
Similar to Mica Capacitors. Stability
and frequency characteristics are
better than silver mica capacitors.
Ultra-reliable, ultra-stable, and
resistant to nuclear radiation.
High cost.
Class-I
Temperature
Compensating
Type Ceramic
Capacitors
Mixture of complex
Titanate
compounds
Low cost and small size, excellent
high frequency characteristics and
good reliability. Predictable linear
capacitance change with operating
temperature. Available in voltages
up to 15,000 volts
Capacitance changes
with change in applied
voltage, with frequency
and with aging effects.
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Class-II High
dielectric strength
Type Ceramic
Capacitors
Barium titanate
based dielectrics
Smaller than Class-I type due to
higher dielectric strength of
ceramics used. Available in
voltages up to 50,000 volts.
Not as stable as Class-I
type with respect to
temperature, and
capacitance changes
significantly with appliedvoltage.
Aluminum
Electrolytic
Capacitors
Aluminum oxide
Very large capacitance to volume
ratio, inexpensive, polarized.
Primary applications are as
smoothing and reservoir capacitors
in power supplies.
Dielectric leakage is
high, large internal
resistance and
inductance limits high
frequency performance,
poor low temperature
stability and loose
tolerances. May vent or
burst open when
overloaded and/or
overheated. Limited to
about 500 volts.
Lithium IonCapacitors
Lithium ion
The Lithium Ion Capacitors have a
higher Power Density as compared
to batteries and LICs are safer in
use than LIBs in which thermal
runaway reactions may occur.
Compared to Electric Double Layer
Capacitor (EDLC), the LIC has a
higher output voltage. They both
have similar Power Densities, but
Energy Density of an LIC is much
higher.
New technology.
Tantalum
Electrolytic
Capacitors
Tantalum oxide
Large capacitance to volume ratio,
smaller size, good stability, wide
operating temperature range, long
reliable operating life. Extensivelyused in miniaturized equipment and
computers. Available in both
polarized and unpolarized varieties.
Solid tantalum capacitors have
much better characteristics than
their wet counterparts.
Higher cost than
aluminum electrolytic
capacitors. Voltagelimited to about 50 volts.
Explodes quite violently
when voltage rating,
current rating, or slew
rates are exceeded, or
when a polarized version
is subjected to reverse
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voltage.
Electrolytic
double-layer
capacitors (EDLC)
Supercapacitors
Thin Electrolyte
layer and Activated
Carbon
Extremely large capacitance to
volume ratio, small size, low ESR.
Available in hundreds, orthousands, of farads. A relatively
new capacitor technology. Often
used to temporarily provide power
to equipment during battery
replacement. Can rapidly absorb
and deliver larger currents than
batteries during charging and
discharging, making them valuable
for hybrid vehicles. Polarized, low
operating voltage (volts per
capacitor cell). Groups of cells are
stacked to provide higher overall
operating voltage.
Relatively high cost.
Alternating
current oil-filled
Capacitors
Oil-impregnated
paper
Usually PET or polypropylene film
dielectric. Primarily designed to
provide very large capacitance for
industrial AC applications to
withstand large currents and high
peak voltages at power line
frequencies. The applications
include AC motor starting and
running, phase splitting, power
factor correction, voltage regulation,
control equipment, etc..
Limited to low frequency
applications due to high
dielectric losses at
higher frequencies.
Direct current oil-
filled capacitors
Paper or Paper-
polyester film
combination
Primarily designed for DC
applications such as filtering,
bypassing, coupling, arc
suppression, voltage doubling, etc...
Operating voltage rating
must be derated as per
the curve supplied by the
manufacturer if the DC
contains ripple.
Physically larger than
polymer dielectric
counterparts.
Energy StorageKraft capacitor
paper impregnated
Designed specifically for intermittent
duty, high current discharge
Physically large and
heavy. Significantly
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Capacitors with electrical
grade castor oil or
similar high
dielectric constant
fluid, with
extended foilplates
applications. More tolerant of
voltage reversal than many polymer
dielectrics. Typical applications
include pulsed power,
electromagnetic forming, pulsed
lasers, Marx generators, and pulsedwelders.
lower energy density
than polymer dielectric
systems. Not self-
healing. Device may fail
catastrophically due to
high stored energy.
Vacuum
Capacitors
Vacuum capacitors
use highly
evacuated glass or
ceramic chamber
with concentric
cylindrical
electrodes.
Extremely low loss. Used for high
voltage high power RF applications,
such as transmitters and induction
heating where even a small amount
of dielectric loss would cause
excessive heating. Can be self-
healing if arc-over current is limited.
Very high cost, fragile,
physically large, and
relatively low
capacitance.
A 12 pF, 20 kV fixed vacuum capacitor
Two 8 F, 525 V paper electrolytic capacitors in a 1930s radio.
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Colour coding
ColorSignifica
nt digits
Multipli
er
Capacitan
ce
tolerance
Characteris
tic
DC
workin
g
voltag
e
Operating
temperatu
re
EIA/vibrati
on
Black 0 1 20% 55 C to
+70 C10 to 55 Hz
Brow
n1 10 1% B 100
Red 2 100 2% C 55 C to
+85C
Orang
e3 1,000 D 300
Yello
w 4 10,000 E
55 C to
+125C
10 to
2000 Hz
Green 5 5% F 500
Blue 6 55 C to
+150 C
Violet 7
Grey 8
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White 9 EIA
Gold 0.5%* 1000
Silver 10%
*Or 0.5 pF, whichever is greater.