A
Potentiometer is basically a resistor that can be manually adjusted. A
Potentiometer is essentially a bridge circuit that measures voltages. It is
designed for accurate measuring of unknown voltage in comparison with a
known voltage. A Potentiometer also proves to be useful for ascertaining
current. This is done by simply measuring the voltage drop produced by the
unknown current via the known resistance.
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Do
You Know?
Potentiometer is derived from the phrase voltage potential. “Potential"
referred to is the strength. |
Besides being an useful physics lab tool, a Potentiometer has multi-various
applications. For establishing output in most of the analog & digital devices potentiometers are commonly used like audio potentiometer in loud speakers for direct adjustment of volumes, digital potentiometer in a television set for controlling the brightness. Other potentiometers are like electronic potentiometer, ohm potentiometer, control potentiometer, turn potentiometer are also used for such purposes.
Functioning of a Potentiometer
The functioning of a Potentiometer is very simple. As already stated a
Potentiometer basically measures an unknown voltage in comparison with a
known voltage. This comparison technique of measurement can give a very high
degree of accuracy. This is due to the fact that the results thus obtained
is independent of actual pointer deflection. This is unlike a moving-coil
instrument. Here the accuracy of the known voltage standard is the crucial
factor to which the comparison is actually made.
A voltage (or current) is first put through a Potentiometer from one end to
the other. A portion of the resistance is then used as output on connection
by the tap. The output thus provided is a small fraction of the voltage
across the Potentiometer circuit. The tap can be connected to any one one
end of the Potentiometer. This causes the total Potentiometer resistance
varying from zero ohms to its full resistance capacity. Thus a Potentiometer
ascertains how much current is flowing through a circuit by controlling the
resistance. One thing is important to understand here is that while
regulating current, a Potentiometer is limited to the extent of the maximum
resistivity of the strip. A potentiometer is also utilized for controlling
the voltage or potential difference across a circuit. Contrary to the
current regulation, voltage regulation by the Potentiometer is not
restricted by the maximum resistivity of the strip.
Selecting a
Potentiometer
A gist of the important factors to consider in a Potentiometer is given
here. However these broad points are only meant to make the buyer aware of
the different parameters in a Potentiometer.
- Design of a Potentiometer: There are many types of mechanical
variations available in a Potentiometer such as special mounts, shaft
configurations etc. These days manufacturers of Potentiometers are
manufacturing customised Potentiometers in non-standard sizes also.
- Element Design: Varied and unique elements like linear or functional
potentiometric elements are available for mounting in systems.
- Direction of Actuation: Bi-directional Potentiometers with
insignificant errors during clockwise(CW) or counterclockwise (CCW)
shaft actuation are preferred.
- Life expectancy of the Potentiometer: In plastic Potentiometers
following things are important to prolong their life cycle
» Conductive film with a low contact resistance component
» For minimum wear and friction, the wiper attack angle
should be matched to the surface
» Wiper pressure below 8gm can also contribue to prolong the
life.
» Common life degradation tolerance for a Potentiometer is
1.5x initial specifications
- Actuation Speed: It has been seen that lower the actuation speed,
longer is thew life of a Potentiometer.
- Resolution : Resolution is the smallest increment of shaft
movement that results in a corresponding charge of the output.
Resolution can also be said to be the minimum detectable voltage change
that takes place with a shaft movement. In case of non-linear
Potentiometers, resolution is uniform in spite of variations in output
voltage slope. In case of Wirewound units of Potentiometers there is a "staircase"
output. The amplitude here of each of the steps is basically a function
of the winding.
- Taps of the Potentiometer:A tap of a Potentiometer is essentially an
electrical connection, that is joined to the resistance element. The
connection can be made at any point between the end terminals. There can
be two types of taps a Zero-Width Tap and Zero Resistance or Semi-Power
Taps.
- Reliability Considerations: Last but not the least a Potentiometer's
reliability is also of paramount importance. Reliability of a
Potentiometer essentially means its capacity to continue executing its
intended function. Primary reliability considerations include
tinuity and proportional » Convoltage output
» Wiper contact to conductive surface
» Continuous conductive surface
» Wiper (output) and continuity of excitation terminal
Types of Potentiometer
A wide range of potentiometers depending upon applications and technologies are available in the market, such as digital potentiometer, electronic potentiometer, audio potentiometer,ohm potentiometer, control potentiometer, etc.Here we will discuss only three of them.
Single Turn Potentiometers
Single turn Potentiometers generally have a circular configuration that
includes an element which is quite adept in carrying a contact via a single
revolution along a resistive member. A Single turn potentiometer is made
using a flat graphite annulus (ring) that serves as the resistive element, A
wiper( sliding contact) is then made to slide around this annulus. The wiper
is joined to an axle and then through another rotating contact, is brought
out for use as the third terminal. In case of single turn pots or
Potentiometer, the wiper normally moves under one revolution around the
contact. A Digram of a Single turn Potentiometer is shown containing all the
latest features.
Multiturn Potentiometer
In comparison to a Single turn Potentiometer Multiturn potentiometers
display the ability to output a higher usable resolution. That is the reason
for their use in many applications as Single turn Potentiometer gets
restricted to a resolution achievable in a single turn. In a Multiturn
potentiometer the resistor element can be helically shaped and the wiper can
undergo 10, 20 or even more complete revolutions.
Linear potentiometers
A
linear potentiometer or pot consists a resistive element that is of uniform
cross-section. In Linear Potentiometers the resistance between the one end
terminal and the contact (wiper) is just proportional to the space between
them. The term Linear in a Linear potentiometer is for describing the
electrical characteristic of the instrument and has got nothing to do with
the geometry of the Potentiometer.
