Potentiometer: Working and Types Essay Example

intended interaction. They are typically smaller than user-accessible potentiometers and may require a screwdriver for operation instead of a knob. These types are often referred to as "preset potentiometers."

Some presets can be accessed using a small screwdriver inserted through a hole in the case for easy maintenance without dismantling. Multiturn potentiometers also operate by rotating a shaft, but they require several turns instead of less than one full turn. Certain multiturn potentiometers feature a linear resistive element with a sliding component that moves along it, propelled by a worm gear. Others have a helical resistive element with a wiper that completes 10, 20, or more revolutions, moving along the helix as it rotates. Both user-accessible and preset multiturn potentiometers allow for more precise adjustments. Rotating them through the same angle results in a setting change typically one-tenth as much as that of a simple rotary potentiometer. A string potentiometer is a multi-turn potentiometer where an attached wire reel turns against a spring, converting linear position into variable resistance.

Rotary potentiometers that can be accessed by the user may have a switch that is activated when the rotation reaches its counter-clockwise extreme. This switch was previously used to turn on radio, television receivers, and other equipment at minimum volume with an audible click. Then, the volume could be increased by turning a knob. In stereo audio amplifiers used for volume control, multiple resistance elements can be grouped together and controlled with the same shaft. The manufacturer determines the relationship between slider position and resistance, which is called the "taper" or "law". Linear or logarithmic (also known as "audio taper") potentiometers are generally sufficient for most applications, although

any type of relationship is possible. The taper used can be identified by a letter code; however, these definitions are not standardized. More recent potentiometers usually have an 'A' label indicating logarithmic taper or a 'B' indicating linear taper.

Older potentiometers can be identified by various markings. An 'A' indicates a linear taper, a 'C' indicates a logarithmic taper, and an 'F' indicates an anti-logarithmic taper. When a non-linear taper is mentioned with a percentage, it refers to the resistance value at the midpoint of the shaft rotation. For instance, if a 10% logarithmic taper is applied to a 10K ohm potentiometer, it would result in 1K at the midpoint. The higher the percentage, the steeper the logarithmic curve. A linear taper potentiometer describes its electrical characteristic rather than its resistive element's geometry as it has a resistive element with consistent cross-section. This leads to a device where the resistance between the contact (wiper) and one end terminal varies proportionally to their distance.

Linear taper potentiometers are used when the division ratio of the potentiometer needs to be directly proportional to the angle of shaft rotation or slider position, as seen in controls for adjusting an analog cathode-ray oscilloscope's centering. On the other hand, a logarithmic taper potentiometer has a resistive element that either tapers from one end to the other or is made from a material with varying resistivity along its length. This type of potentiometer produces an output voltage that follows a logarithmic function based on the position of the slider. Cheaper "log" potentiometers may not accurately follow a logarithmic law but approximate it by using two regions of different resistance with constant resistivity. Alternatively,

a linear potentiometer can be used with an external resistor to simulate, albeit inaccurately, a logarithmic potentiometer.

Logarithmic potentiometers are pricier but commonly employed in audio amplifiers due to the logarithmic nature of human volume perception. In addition, a high-power wire-wound potentiometer can serve as a rheostat.

The most common way to vary resistance in a circuit is by using a rheostat, which is a two-terminal variable resistor. In low-power applications (less than approximately 1 watt), a three-terminal potentiometer is often used, with one terminal unconnected or connected to the wiper. For higher power handling (more than around 1 watt), the rheostat can be constructed with a resistance wire wound around a semicircular insulator, and the wiper sliding from one turn of the wire to the next. Another option is winding a resistance wire on a heat-resisting cylinder to create a rheostat, with several metal fingers serving as the slider that lightly grip a small portion of the resistance wire turns. A sliding knob allows these "fingers" to move along the coil of resistance wire, thereby changing the "tapping" point.

Wire-wound rheostats with ratings up to several thousand watts are utilized in various applications, such as DC motor drives, electric welding controls, and controls for generators. A digital potentiometer is an electronic component that replicates the functions of analog potentiometers. It can adjust the resistance between two terminals through digital input signals, similar to an analog potentiometer. Additionally, a membrane potentiometer employs a conductive membrane that is deformed by a sliding element to make contact with a resistor voltage divider. The linearity of a membrane potentiometer can vary from 0.5% to % depending on the material, design, and

manufacturing process.

The typical repeat accuracy of these potentiometers is between 0.1 mm and 1 mm, with a resolution that is theoretically infinite. Depending on the materials used and the actuation method (contact or contactless), the service life of these potentiometers can range from 1 million to 20 million cycles. Manufacturers of membrane potentiometers offer linear, rotary, and application-specific variations, with linear versions ranging from 9mm to 1000mm in length and rotary versions ranging from 0° to multiple full turns. Various material options such as PET (foil), FR4, and Kapton are available for these potentiometers, each having a height of 0.

5mm.Membrane potentiometers can be used for position sensing. [4] [edit]Potentiometer applications Potentiometers are seldom employed for directly controlling substantial amounts of power (more than a watt or so). Rather, they are utilized for adjusting the level of analog signals (such as volume controls on audio equipment), and as control inputs for electronic circuits. For example, a light dimmer utilizes a potentiometer to manage the switching of TRIAC and thereby indirectly control the brightness of lamps. Preset potentiometers find extensive use in electronics for various adjustments to be made during manufacturing or servicing. User-actuated potentiometers are widely employed as user controls and have the ability to regulate a diverse range of equipment functions. The prevalent use of potentiometers in consumer electronics experienced a decline during the 1990s, with rotary encoders, up/down pushbuttons, and other digital controls now being more predominant.

However, potentiometers are still utilized in various applications, such as volume controls and position sensors. [edit]Audio control Potentiometers, both linear and rotary, with low power consumption, are employed to regulate audio equipment. They enable adjustments in loudness,

frequency attenuation, and other characteristics of audio signals. The 'log pot', also known as an "audio taper pot", serves as the volume control in audio amplifiers. It is referred to as an audio taper pot because the human ear perceives sound on a logarithmic scale. This ensures that a setting of 5 on a volume control marked from 0 to 10 sounds subjectively half as loud as a setting of 10. In audio balance control, an anti-log pot or reverse audio taper potentiometer is used, which is the inverse of a logarithmic potentiometer. This type is almost always used in conjunction with a logarithmic potentiometer. Potentiometers combined with filter networks function as tone controls or equalizers. In the past, potentiometers were utilized in television to regulate picture brightness, contrast, and color response.

A potentiometer is commonly utilized to adjust "vertical hold" and impact the synchronization between a receiver's internal sweep circuit and the received picture signal. It also affects other aspects, such as audio-video carrier offset and tuning frequency (for push-button sets).

Motion Control Potentiometers can function as position feedback devices, enabling the creation of "closed-loop" control, particularly in servomechanisms.

Transducers commonly employ potentiometers as part of displacement transducers due to the simplicity of their construction and the ability to generate a large output signal.

In analog computers, high-precision potentiometers play a role in scaling intermediate results by desired constant factors or establishing initial conditions for calculations.

A motor-driven potentiometer can serve as a function generator by utilizing a non-linear resistance card to provide approximations of trigonometric functions. For example, when the shaft rotates, it represents an angle, and the voltage division ratio can be

made proportional to the cosine of the angle.

- [edit]Theory of operation A potentiometer is commonly used as a voltage divider to obtain a manually adjustable output voltage at the slider (wiper) from a fixed input voltage. The voltage across can be calculated using the equation: If is large compared to the other resistances, the output voltage can be approximated using the simpler equation: (dividing throughout by and canceling terms with as denominator) For example, if and , the output voltage will be approximately: However, due to the load resistance, it will actually be slightly lower, around 6.23 V. One advantage of using a potential divider instead of a variable resistor in series with the source is that a potential divider can vary the output voltage from maximum 0 to ground (zero volts) as the wiper moves from one end of the potentiometer to the other.

However, there is always a small amount of contact resistance.