Resistors will be divided into development varieties in addition to resistance materials. The next breakdown for the sort will be made.
The selection of fabric expertise is restricted to the aim. Usually it’s a trade-off between prices, precision, and different necessities. For instance, carbon composition is a really previous approach with low precision however remains to be used for particular purposes the place excessive power pulses happen. Carbon composition resistors have a physique of a mix of advantageous carbon particles and a non-conductive ceramic.
The carbon movie approach has higher tolerance. These are product of a non-conductive rod with a skinny carbon movie layer round it. This layer is handled with a spiral minimize to extend and management the resistance worth. Steel and metallic oxide movies are extensively used these days and have higher properties for stability and tolerance. Moreover, they’re much less influenced by temperature variations. They’re simply as carbon movie resistors constructed with a resistive movie round a cylindrical physique.
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The metallic oxide movie is usually extra sturdy. Wirewound resistors are most likely the oldest kind and can be utilized for each excessive precision in addition to excessive energy purposes. They’re constructed by winding a particular metallic alloy wire, reminiscent of nickel-chrome, round a non-conductive core. They’re sturdy, correct, and may have very low resistance worth. A drawback is that they endure from parasitic reactance at excessive frequencies. For the best necessities on precision and stability, metallic foil resistors are used. They’re constructed by cementing a particular alloy cold-rolled movie onto a ceramic substrate.
Mounted worth resistors have an outlined ohmic resistance and will not be adjustable. Mounted resistors are probably the most generally used resistors and normally probably the most used digital elements. Mounted resistors can be found in axial leaded and floor mount packages in addition to extra personalized packages relying on their software. Whereas axial leaded resistors was once probably the most used resistors, these days the benefits of floor mount units make the SMD resistors the preferred.
A set resistor has a static, outlined electrical resistance which isn’t adjustable. In an excellent world, an ideal resistor would have a continuing ohmic resistance below all circumstances.
This resistance could be unbiased of for instance frequency, voltage or temperature. In follow no resistor is ideal and all resistors have a sure stray capacitance and inductance, leading to an impedance worth completely different from the nominal resistance worth. The resistor supplies have a sure temperature coefficient, leading to a temperature dependency of the resistor worth.
The completely different resistor varieties and supplies decide the dependency of the resistance worth on these exterior elements. Relying on e.g. the required accuracy, energy dissipation, and noise necessities, the sort and materials of the resistor are chosen. Some widespread kinds of mounted resistors are displayed beneath. A set resistor has a static, outlined electrical resistance which isn’t adjustable.
In an excellent world, an ideal resistor would have a continuing ohmic resistance below all circumstances. This resistance could be unbiased of for instance frequency, voltage, or temperature. In follow no resistor is ideal and all resistors have a sure stray capacitance and inductance, leading to an impedance worth completely different from the nominal resistance worth.
The resistor supplies have a sure temperature coefficient, leading to a temperature dependency of the resistor worth. The completely different resistor varieties and supplies decide the dependency of the resistance worth on these exterior elements. Relying on e.g. the required accuracy, energy dissipation, and noise necessities, the sort and materials of the resistor are chosen. Some widespread kinds of mounted resistors are displayed beneath.
IDENTIFYING FIXED VALUE RESISTORS
Within the subsequent desk an outline of basic goal resistors is given. The categories listed below are among the many most used resistors normally. The carbon movie is the commonest axial leaded resistor which is used for purposes the place an excellent tolerance and temperature coefficient will not be obligatory. The metallic movie is the overall axial leaded resistor of alternative for larger precision purposes.
For top energy purposes, wire wound resistors are sometimes used, the aluminum housing as proven within the image is commonly used for energy rankings from 10-250W. Floor mount or SMD resistors are normally constructed from thick or thin-film materials. The properties listed on this desk point out widespread ranges for the values adopted by the commonest worth between brackets. Nevertheless these values shouldn’t be seen as limiting, a number of particular goal resistors with very completely different traits exist.
A variable resistor is a resistor of which the electrical resistance worth will be adjusted. A variable resistor is in essence an electromechanical transducer and usually works by sliding a contact (wiper) over a resistive ingredient. When a variable resistor is used as a possible divider by utilizing 3 terminals it’s known as a potentiometer.
When solely two terminals are used, it features as a variable resistance and known as a rheostat. Electronically managed variable resistors exist, which will be managed electronically as an alternative of by mechanical motion. These resistors are known as digital potentiometers. A variable resistor has an adjustable ohmic resistance worth. This may be performed both mechanically (potentiometer, rheostat) or electronically (digital potentiometer).
A potentiometer is a manually adjustable variable resistor with 3 terminals. Two terminals are related to each ends of a resistive ingredient, and the third terminal connects to a sliding contact, known as a wiper, shifting over the resistive ingredient. The place of the wiper determines the output voltage of the potentiometer.
The potentiometer primarily features as a variable voltage divider. The resistive ingredient will be seen as two resistors in collection(potentiometer resistance), the place the wiper place determines the resistance ratio of the primary resistor to the second resistor.
A potentiometer can be generally often called a potmeter or pot. The commonest type of potmeter is the one flip rotary potmeter. Any such pot is commonly utilized in audio quantity management (logarithmic taper) in addition to many different purposes. Completely different supplies are used to assemble potentiometers, together with carbon composition, cermet, wirewound, conductive plastic or metallic movie.
A potentiometer is a manually adjustable, variable resistor with three terminals. Two terminals are related to a resistive ingredient; the third terminal is related to an adjustable wiper. The place of the wiper determines the output voltage. All kinds of potmeters exist. Manually adjustable potmeters will be divided in rotary or linear motion varieties. The tables beneath checklist the obtainable varieties and their purposes. In addition to manually adjustable pots, additionally electronically managed potentiometers exist, typically known as digital potmeters.
The commonest kind of potentiometer has a wiper that strikes alongside a round path.
|Single rotation of|
roughly 270 levels or
3/4 of a full flip
|Commonest pot, utilized in|
purposes the place a single flip
gives sufficient management
|A number of rotations (largely 5,|
10 or 20), for elevated
constructed both with a
wiper that follows a spiral or
helix kind, or by utilizing a
|Used the place excessive precision and|
decision are required. The
worm-gear multi-turn pots are
typically used as trim pots on PCB.
|Two potentiometers mixed|
on the identical shaft, enabling
the parallel setting of two
channels. Commonest are
single flip potentiometers
with equal resistance and
taper. Greater than two gangs
are attainable however not very
|Utilized in for instance stereo|
audio quantity management or different
purposes the place 2 channels
need to be adjusted in parallel.
|Twin potmeter, the place the 2|
individually adjusted by means
of concentric shafts. Permits
using two controls on one
|Usually encountered in a (older) automobile|
radios, the place the amount and
tone controls are mixed.
|Servo pot||A motorized potmeter which|
can be routinely
adjusted by a servo motor.
|Used had been guide and|
automated adjustment is
required. Usually seen in audio
gear, the place the distant management
can flip the amount
Linear potentiometers have a wiper that strikes alongside a linear path. They’re also referred to as slider, slide pot or fader.
|Slide pot||Single linear slider|
audio purposes additionally
often called a fader. Excessive
high quality faders are
|For single-channel management or|
measurement of distance.
|Twin-slide pot||Twin slide|
slider controlling two
|Usually used for stereo management in|
skilled audio or different
purposes the place twin parallel
channels are managed.
|Multi-turn slide||Constructed from a|
spindle which actuates
a linear potentiometer
wiper. A number of
rotations (largely 5, 10
or 20), for elevated
|Used the place excessive precision and|
decision is required. The multi-turn
linear pots are used as trim pots on
PCB, however not as widespread because the
worm-gear trimmer potentiometer.
|Motorized fader||Fader which will be|
by a servo motor.
|Used the place guide and automated|
adjustment is required. Widespread in
studio audio mixers, the place the servo
faders will be routinely moved to
a saved configuration.
Digital potentiometers are potentiometers that are managed electronically. Generally they exist of an array of small resistive elements in collection. Each resistive ingredient is supplied with a swap which might function the tap-off level or digital wiper place. A digital potmeter will be managed by for instance up/down alerts or protocols like I²C and SPI.
MATERIALS USED FOR POTMETERS
|Carbon composition ink molded on a substrate|
(phenolic resin). Commonest materials, low value, and affordable noise and put on traits.
|Wirewound||Wirewound pots can deal with excessive energy, are long-lasting, and will be very exact. They’ve nevertheless a restricted decision and tough really feel. Most utilized in excessive energy purposes (rheostats are sometimes wirewound) or as precision pots.|
|Very easy really feel and excessive decision will be constructed to carry out hundreds of thousands of cycles. Can solely deal with a restricted energy and are costly. Usually utilized in high-end (audio) gear the place a excessive decision and low noise are vital.|
|Cermet||Very steady, low temperature coefficient and handles excessive temperatures effectively. Alternatively fairly costly and sometimes restricted quantity of cycles allowed (particular long-life cermet pots additionally exist). They’re extensively used for trimpots which do not need to be adjusted typically.|
The potentiometer taper is the connection between the mechanical place and resistance ratio. Linear taper and logarithmic (audio) taper are the commonest types of taper. For extra data go to the devoted web page about potentiometer taper.
Potentiometers values are sometimes marked with a readable string indicating the overall resistance, reminiscent of “100k” for a 100 kOhm potentiometer. Typically a 3 digit coding system just like smd resistor coding is used. On this system the primary digits point out the worth and the final digit signifies the multiplier. For instance a 1 kOhm could be coded as 102, that means 10Ω x 102 = 1 kΩ.
The taper of a potentiometer is often indicated with a letter. The next desk lists the used coding for potentiometer taper, completely different requirements use the identical letters which will be complicated. It’s at all times a good suggestion to double-check the taper by measurement.
|Log / Audio||LOG||A||C||A||L|
The decision of a potentiometer is the smallest attainable change in resistance ratio. Wirewound resistors typically have a decrease decision as a result of the wire turns introduce discrete steps in resistance. Conductive plastic potmeters have the very best decision. The decision will be influenced by the wiper configuration; a wiper consisting of a number of unfold contact factors will increase the potentiometer decision.
Hop-on and Hop-off resistance
At first and finish of journey, the resistive observe of a potentiometer is related to low resistance metallic elements which join the resistive ingredient to the top terminals. The change in resistance when the wiper enters or exits the resistive observe is named the hop-on and hop-off resistance
- FIXED RESISTORS
- IDENTIFYING FIXED VALUE RESISTORS
- VARIABLE RESISTORS
- DIGITAL POTENTIOMETER
- MATERIALS USED FOR POTMETERS