Potentiometer

A potentiometer (short Poti, according to the new German spelling and potentiometer ) is an electrical resistance element whose resistance values ​​are changed mechanically ( by rotating or sliding ). It has at least two ports and is primarily used as a continuously adjustable voltage divider.

• 5.1 Resistance characteristic
• 5.2 characteristics

• 6.1 Active potentiometer

Basic structure and function

The voltage divider consists of an electrically non-conducting substrate on which a resistive material is applied, two terminals at both ends of the resistor element and a movable sliding contact (also referred to as a slider ), which divides the fixed total resistance electrically in two opposite partial resistors.

Application

Potentiometers are commonly used to control electronic devices, such as for the sound settings of a radio. In this role, other solutions are used (eg buttons or incremental ) in an increasing degree. The reasons are on the one hand in the progressive digitalisation of many electronic functions, on the other hand the fact that mechanical potentiometer due to the abrasion resistance of the material does not operate without wear through the grinder.

Electrical wiring

Depending on the external circuit results in either a variable resistor, an adjustable voltage tap ( voltage divider ) or - if significant load at the output - a so-called loaded voltage divider. Only in the circuit as a voltage divider but is ahead of the eponymous potentiometer; while a potential difference (voltage ) is represented by the angle of rotation of a (Precision) potentiometer.

Designs

Wirewound

Drahtdrehpotentiometer have a toroidal, wire shift resistors a helical coil of resistance wire on an insulator (usually made ​​of ceramic material ). This design is perfect when you want a high power dissipation must be implemented in the component. These components are also called rheostat; Strictly speaking, a rheostat, a variable resistor with two terminals, while a potentiometer ( as mentioned above ) represents a voltage divider, which has three ports.

Potentiometer

The potentiometer of the wire in the form of a double helix is placed on a helical insulating. Their grinder allows, for example, five or ten revolutions by and laterally the course of the spiral follows in rotation.

Film potentiometers

At Schichtpotentiometern is the resistance material consists of a carbon layer, a metal layer, a cermet layer or a conductive plastic ( conductive plastic ). The resistance of Schichtpotentiometern carrier is usually a circular segment, but can also be stretched when Schiebepotentiometern ( sliders ).

There are film potentiometers with linearly dependent on the rotation angle resistance ratio and those with logarithmic characteristic. The latter are particularly advantageous when the adjustment passes over several orders of magnitude (eg volume control ).

Potentiometers with logarithmic characteristic vice versa are also available and are suitable for example for setting the frequency of an astable multivibrator.

Rotary potentiometer with a small angle of rotation are used in joysticks.

Trimming potentiometer

Trimming potentiometers are designed for the comparison of a circuit and usually have only a screwdriver slot. They are set once and possibly fixed with varnish.

In the industrial sector and in the measurement technology, but more common trimming potentiometer find (so-called spindle trimmer) use. To be either a linear motion is produced by a spindle drive or a rotary motion with a screw drive.

Mehrfachpotentiometer

Mehrfachpotentiometer, usually twice ( tandem or Stereopotentiometer ), for example, be used to control the volume of both channels of a stereo amplifier. Higher-quality amplifiers often have a motorized potentiometer (potentiometer with drive ) for remote volume control.

In the sound very accurate and long (100 mm) Slide, also slider or fader for fine volume control called (of English. To fade ( fade ) ) used, which generally have a logarithmic curve. In newer consoles usually motorized slider ( motorized faders ) are used, which can move to stored settings reproducible by itself before.

Electronic potentiometer

Digital or electronic potentiometer consisting of series-connected individual resistors ( e.g., 100 ) as well, comprised of field effect transistors, electronic switches. This arrangement is combined with a digital control circuit for an integrated circuit. Such digital potentiometers are used as a trimming potentiometer ( they retain their value set for life ) or for setting on switch, an incremental encoder or a microcontroller. You therefore have a volatile and / or nonvolatile memory for the " wiper position ".

Membrane potentiometer

See: membrane potentiometer

Other features

Potentiometer is available as a control element having a shaft for a knob or a slide potentiometer (eg on consoles and in recording studios ). Particularly precise potentiometer also be used for linear or angular measurement ( encoders, angular encoders), see potentiometric.

Potentiometers are available with various connection types such as solder lugs, connectors, terminals and PCB mounting as Surface Mounted Device or for through-hole mounting.

The sliding tracks of potentiometers may be provided with taps to configure it for different characteristics can. Certain embodiments of an acoustically correct volume equalization ( Loudness Correction ) works with such taps.

Resistance curve

The angle or distance between feature and resistance potentiometers can also be non-linear (positive or negative logarithmic, exponential, or S- shaped).

Linear potentiometers have no or labeling lin, B (formerly A) or 1, for example, " 10 k 1" for a 10 - kOhm potentiometer with linear resistive track. Positive logarithmic potentiometer bear the mark log, A (formerly C ), audio or 2 behind the resistance value, for example " 10 K 2 ". A " " before the value is common. Here the resistance path is logarithmic increasing.

Negative logarithmic potentiometers with a - in front of the value or F or 3 behind the value " ".

Parameters

Characteristic of a potentiometer in addition to its nominal resistance ( resistance between the end terminals ) and its tolerance following features:

• Rated power ( power loss ); it is the angle of rotation depends
• With linear potentiometers linearity
• At Tandempotentiometern their synchronism
• Mechanical parameters: rotation angle or actuation distance, shaft diameter
• Mechanical life ( achievable number of operations )
• The maximum current that can be transferred from the grinder, without damaging the material or the sliding contact resistance

Incorrect use of the term " potentiometer"

Active potentiometer

For the control of dimmable fluorescent tubes sometimes a so-called " active potentiometer " is required. What is meant by this has little to do with a proper potentiometer. Instead, it is a controllable voltage source, which may be typically set to a value between 0V and 10V.