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From armature to zero setting: 

Brief explanation of terminology.

It is not absolutely necessary to know what an armature is. One could even ask where this term originates from man. Or one can simply look up the meaning of the term. The CDS motor lexicon offers an easy and understandable explanation of all technical terms relating to electrical motors. You learn, for instance, that the term incremental encoder is easier to understand than to pronounce or that a magnet wheel works without pedals. And that is a CDS DURADRIVE service that goes without saying.

From asynchronous to zinc coating.

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In electrical engineering and in particular in electrical motors, armature refers to the moveable part in an electromagnetic field. The armature is also often referred to as rotor or inductor. This applies, however, only to DC motors. In AC motors the rotating part is not the armature but the so-called magnet wheel. The name armature would in this case also be misleading, as AC motors also have an armature current and an armature winding. Both terms are, however, not technically linked to the armature referred to in DC motors.

Asynchronous generator:

In order for an asynchronous machine to be operated as a generator, it must be magnetically excited and mechanically driven. The latter is, for instance, the case when used in a wind turbine generator system, where the asynchronous generator is driven by the rotor blades via a gearbox. In general, the following applies: Where an inductor of an asynchronous machine moves quicker than the rotary field surrounding it, energy is returned to the grid. In this case, the asynchronous machine operates as an asynchronous generator. The same effect occurs during braking of asynchronous machines. For instance when an elevator moves down with a respective braking of the asynchronous machine. In this case, the braking energy is returned to the grid. The magnetic excitement of an asynchronous machine required for operating the generator is either produced by a capacitor or as separate excitation from a grid supplied by the synchronous generators. Asynchronous generators are, for instance, used in small – mostly unmanned – hydroelectric plants.

Asynchronous motor:

Asynchronous motors are AC motors and are amongst the most frequently used electric motors, partly because of their special advantage: they do not require a commutator, carbon brushes and slip rings, i.e. wear and tear is reduced and brush sparking is avoided. Asynchronous motors can therefore also be used as drives in potentially explosives environments. Asynchronous motors also have the advantage of producing a constant output, requiring little maintenance and offering a long service life. Because of their sturdy design, they are often used for applications exposed to considerable mechanical loading. For instance as vibratory drives in the construction industry. In pumps, the inductor can run even in liquids, gasses or in a vacuum as no voltage is applied to it. Apart from in pumps, asynchronous motors are also used in conveyor belts or fans. In general, asynchronous three-phase motors are amongst the most cost effective motors, provided no particular size requirements have to be met.



Also known as storage battery. A battery is a store for electrical energy. It converts electrical energy into chemical energy that can be stored. As soon as a battery is used, e.g. when switching on a laptop, the chemical energy is converted back into electrical energy by an electro-chemical reaction caused by various materials. From lithium-ion to zinc bromine batteries.

Bell-shaped rotor motor:

Bell-shaped rotor motors are permanent magnet excited DC motors. The peculiarity of these motors is their design: the rotor is hollow and ironless. Consequently the motors have no detent torque and can be easily rotated. Bell-shaped rotor motors achieve higher levels of efficiency at high speeds. At the same time the moment of (rotation) inertia is lower.  This allows the construction of drives offering the advantages of a low weight and high dynamics. These motors are, for instance, used in electrical model railways.

Breakdown spark:

See brush sparking


See carbon brushes

Brush sparking:

Brush sparking refers to sparking at the commutator or on the carbon brushes of an electrical motor. There are various reasons for sparking. Carbon brushes may be excessively worn and thus only provide an inadequate contact to the rotor, resulting in brush sparking. At high speeds it can, however, also occur that two commutator segments are charged differently and short-circuit. This can also cause sparking. Irrespective of the cause, brush sparking results in a higher wear of the carbon brushes and produces high-frequency voltage peaks.

Built-in encoders / built-in rotary encoders:

Built-in rotary encoders are a special type of rotary encoders. They are also referred to as integral encoders, gear-wheel encoders or MiniCoders. Their magnetic scanning system allows a complete non-contact operation. When used with a gear wheel, rotating movements can be incrementally recorded. Using additional piston rods, longitudinal movements can also be measured. Built-in rotary encoders require less space than incremental encoders, making them particularly suitable for use in machine tools.



The word capacitor derives from the Latin “condensare“, meaning “to compact“. In electrical engineering, capacitors are used for storing electrical charges. A capacitor consists of two electrically conductive surfaces (electrodes), which in the most basic form are arranged as smooth plates parallel to each other. The so-called dielectric with, in particular, its insulating property is located between these electrodes. In order to store an electric charge, a constant voltage is applied to the still uncharged capacitor. Current flows for a brief time and one electrode is charged positively and one electrode negatively. This charge remains as soon as the capacitor is disconnected from power.  Capacitors are, for instance, used in capacitor motors. Or also in flashlights used for photography. The power required for generating a flash cannot be directly retrieved from the battery as its internal resistance is too high. A charged capacitor, on the other hand provides an output of several kilowatts in fractions of a second.

Capacitor motor:

Capacitor motors are asynchronous motors. In contrast to the asynchronous motors operated by three-phase current they do, however, operate with a single-phase alternating current. Although the motor has a higher mass compared to three-phase motors and also a lower starting torque, it does offer a quiet operation, a long service life and requires little maintenance. A decisive factor is, however, its high efficiency for the single-phase operation. Because of this advantage, it is often used in domestic applications from roller shutters to lawn mowers.

Carbon brushes:

Carbon brushes are used in electric motors and generators. They provide the electric contact to the collector or the slip rings of the moveable part of an electric motor or generator. In most cases they are made from graphite but can also contain copper, silver or other metals, depending on the respective application. Because of the varied fields of application in DC and AC motors, carbon brushes are available in nearly any size. From particularly small brushes for model railways up to brushes used for generators in power plants, weighing several kilograms. Carbon brushes are also referred to as brushes, motor carbon or sliding carbon.


See commutator


The term commutator derives from the Latin “commutare“, meaning “to interchange“. Commutators are also referred to as current reversers, polarity reversers or collectors. In any case, they refer to a mechanical switching device with in most cases a cylindrical design, for reversing the direction of a current in a circuit. Commutators consist of copper segments connected to the armature winding and of two or more carbon brushes, in contact with the surface of the commutator in order to effect a conversion of the either incoming or outgoing current. This is, in particular, important for DC motors. Without conversion, no torque could be generated during rotational movements.

Compound motor:

See compound wound motor

Compound wound motor:

Compound wound motors combine the advantages of shunt wound and serial wound motors. Due to their balanced relationship between speed and torque they are, for instance, used for driving presses and punching machines. Compound wound motors are DC motors and are also referred to as compound motors.


DC motor:

DC motors include shunt, serial wound and series motors, as well as permanent magnet excited motors. The general advantages offered by this type of motor are a smooth start-up and excellent controllability. Each type does, however, also have its very own advantages. DC motors are generally used in wind turbine generator systems as blade adjustment or pitch drives. They are, however, also used as winding drives in the textile industry.


A dielectric is a substance that is not conductive or conducts only little electricity. The substance is non-metallic and thus not magnetic and can be a gas, a liquid or a solid. In capacitors, the insulation material between the two capacitor plates or electrodes is for instance referred to as a dielectric. The term dielectric is also used in high-voltage and high frequency engineering. Here, a dielectric refers to the insulation material separating, for instance, the conductors in a coaxial cable.

Disc motor:

The name of this type of motor derives from the fact that its rotor is disc shaped. This special rotor also results in a special motor shape: its diameter exceeds its length, making the disc motor easily recognisable. Disc motors run very evenly and smoothly even at low speeds. As a result, a reduction gear is often not required. Due to the striking thin design of its windings the motor offers a high power density. Disc motors are particularly suited for dynamic applications, such as electric bikes and electric cars or in smaller, brushless applications, such as video recorders. With the exception of electricity meters, disc motors are always DC motors.



Energy, chemical:

Chemical energy is, for instance, contained in fuels such as petrol or Diesel. The fuel is burnt in car engines and the chemical energy contained therein is released and converted into mechanical energy, driving the car. Chemical energy can, however, also be directly converted to electrical energy. In fuel cells, for instance, the chemical reaction energy of a combustion process is directly converted to electrical energy.

Energy, electrical:

Energy is first and foremost a physical dimension. In electrical motors its output is measured in joule or kWh. Energy can occur in various forms with electrical energy being one of them. Electrical energy can be converted to other forms of energy, e.g. to chemical or mechanical energy. An electric motor, for instance, converts its used electrical energy to mechanical energy. This means that the electric motor generates a magnetic field, exerting in turn a force on conductors containing electricity or a permanent magnet.



Frequency converters:

Frequency converters are a special type of inverters, used for changing the frequency of an alternating current. A thus converted voltage allows infinitely variable speeds from zero to the rated speed without reducing the torque. Economical asynchronous motors can thus be used in an extended speed range. But not only the speed behaviour is improved. Frequency converters can also be used to ensure the smooth start-up of machines, a major advantage in lifting equipment or for the operation of conveyor belts. Another important area of application for frequency converters is in the pump and in the ventilation technology.




From a purely technical point of view a generator is identical to an electric motor although it works exactly the opposite way round. Whilst the electric motor generates kinetic energy from the electrical energy with which it is operated, the generator converts mechanical energy to electrical energy. This mechanical energy is supplied to the generator via a shaft, as for instance in a wind turbine generator system.




Illgner converter:

The Illgner converter generally operates like a Leonard set but also contains a flywheel. This flywheel is directly connected to a three-phase motor and offers the option of storing kinetic energy. A feature particularly advantageous for heavy industry applications. The stored energy can, for instance, be used to even out load peaks that can occasionally occur in steel works when starting up steel rollers. Although already patented in 1901 and despite of the enormous progress made in the area of frequency converters, some systems are still using the benefits of this technology today. The Illgner converter was named after its inventor, the German electrical engineer Karl Illgner.

Incremental encoder:

Incremental encoders are sensors used for recording positional changes on, for instance, machine tools. In industry these are, in particular, used for measuring speed, angels of rotation or distances. The measuring is always based on a count and a determination of direction. In industrial applications, incremental encoders are used for machine tools and in automation technology or on test stations. Incremental encoders are also referred to as rotary encoders or rotary pulse encoders. A special form of rotary encoders that has become increasingly popular is built-in rotary encoders. These space-saving encoders can, in particular, be found in machine tools.


See armature



See rectifier inverter






Leonard set (Ward-Leonard converter):

The Leonard set is a combination of a converter and a DC motor. The converter first of all consists of an asynchronous motor and a direct-current based generator connected thereto.  In this way, a controllable DC voltage is generated from a three-phase current with which the DC motor can then be operated. In particular very large drives that must also offer a variable speed can be operated with the Leonard set with a low loss, such as drives in rolling mills. A Leonard set also has a regenerative capability. This means that the energy generated, for instance, during braking can be recovered. Named after the inventor, the American Harry Ward Leonard, the Leonard set is sometimes also referred to as Ward-Leonard converter.

Leyden jar:

The Leyden jar can certainly be regarded as the forerunner of capacitors. It consisted of a glass jar coated internally and externally by metal foil. Based on the functional principle of a capacitor, the glass had the function of the isolator (dielectric). This functional principle was discovered rather by accident. Two scientists including the physicist Pieter van Musschenbroek, received electric shocks whilst working with glass and metal parts. The name Leyden jar is derived from the place where Pieter van Musschenbroek was born and worked: the Dutch town of Leyden.



Magnetic field:

Magnetism refers to the force effective between magnets or magnetised objects and the movement of electrical charges. The area between these magnets or objects through which the force is transferred is called the magnetic field. The magnetic field is, on one hand generated by these objects and acts, on the other hand, on these objects. Magnetic fields are not only created by magnetic material but also by electric currents. Just like in a coil through which a current flows.

Magnet wheel:

In electric motors, the magnet wheel is the rotating part of an electromagnetic action. This does, however, only apply to three-phase motors. In DC motors, the moveable part is called the armature. For three-phase motors, the name armature would also be misleading as these types of motors also have an armature current and an armature winding. Both terms are, however, not technically linked to the armature referred to in DC motors.


See built-in rotary encoders

Motor carbon:

See carbon brushes

Motor-generator set:

A motor-generator set converts the type of current, for instance direct current to alternating current. It consists of an electric motor driving, in turn, a generator to produce the desired type of current. The motor and generator are linked by their shafts and form the so-called motor-generator set. A special type of motor-generator set is the rotary converter. Compared to the motor-generator set it has no exposed shaft and only consists of one machine. Whereas in the past motor-generator sets were also used for smaller applications, today they are almost exclusively used in large industrial applications, as for instance in railroad transformer stations.






Permanent magnet:

Permanent magnets permanently maintain their static magnetic field and do not depend on the flow of electric current like electromagnets. A permanent magnet consists of a piece of iron, nickel, cobalt or another material that can be magnetised. Irrespective of the material, the permanent magnet has one or several North and South poles on its surface. But always in equal numbers. Permanent magnets are also referred to as perma magnets.

Permanent magnet excited motors:

Permanent magnet excited motors are DC motors. They offer the advantage of not requiring any energy for generating a magnetic field. This improves their effectiveness, in particular, in case of a low overall output. These motors also require little space. Also there are no losses from the excitation windings, as these are replaced by magnets.

Power converter:

Equipment that changes one type of current to another is called a power converter. Power converters include rectifiers, rectifier inverters, transformers and frequency converters. Power converters changing alternating current to direct current are called rectifiers. Converters converting direct current to alternating current are called rectifier inverters or inverters. Where a generator operated by an electric motor is involved in the conversion, the power converter is called a transformer. The frequency converter is a special form of rectifier inverter and is used for changing the frequency of an alternating current. Especially when the speed should be infinitely variable without reducing the torque.

Power commutator:

See commutator







Rectifiers convert alternating current into direct current, for instance where a DC motor is to be operated in an alternating current system. They are part of the group of converters generally used for converting one type of current to another. In the drive engineering sector, controllable rectifiers are mainly used as they not only convert the voltage but can also control the output or speed of a drive. And that in nearly all areas of application. From industrial plants to domestic appliances and electrical locomotives.

Rectifier inverter:

Rectifier inverters belong to the group of power converters. They convert direct voltage to alternating voltage or direct current to alternating current. Depending on their setting, they can generate single-phase or three-phase alternating current (three-phase current). A conversion to alternating current is required where only direct voltage is available as the voltage source. For instance in car batteries or where direct current from photovoltaic systems is fed into the grid. Rectifier inverters are, however, most frequently used for driving synchronous and asynchronous motors. In this case, a direct voltage is first converted to an alternating voltage. The frequency of this voltage is, however, variable allowing it to be used for the precise control of drives. This special form of a rectifier inverter is therefore called a frequency converter.

Rotating field:

In electrical engineering, magnetic fields rotating around a rotating axis are referred to as rotating fields. They are generated to drive the shafts of three-phase motors and self-starting AC motors. The rotor, secured to the shaft of the motor, is in this case pulled along by magnetic force.

Rotary encoder:

See incremental encoder

Rotary pulse encoder:

See incremental encoder


See armature



Serial wound motor:

Serial wound motors are DC motors. They do not have a defined idling speed and, under loading, their speed reduces more than that of shunt wound motors. These motors do, however, offer a high starting torque. They therefore withstand high loads during short operations and are thus also used in starter motors of, for instance, electric locomotives. Serial wound motor are also referred to as series machines.

Series machine:

See serial wound motor


Servo motor:

DC motors, synchronous motors and asynchronous motors can all be used as servo motors. Together with a servo amplifier (or servo controller) they then form the so-called servo drive. This drive allows the precise control of the torque, speed or position. As part of this process the current position of the rotor is constantly measured by a rotary encoder, e.g. an incremental encoder. The determined value is then compared with the set value and adjusted in case of any deviation. Servo motors were initially used as auxiliary drives, resulting in the name “servo“, which derives from the Latin “servus“ or “slave“. Servo motors are, for instance, used in machine tools or industrial robotic applications.

Shunt wound motor:

Shunt wound motors are DC motors. The name shunt wound originates from the fact that the excitation winding and the armature winding are connected in parallel or next to each other. The magnetic field is only dependant on the operating voltage. Even if the current fluctuates, this operating voltage remains near constant. Compared to serial wound motors for instance, shunt wound motors offer a lower starting torque but offer the advantage of considerable speed stability. Shunt wound motors are, for instance used where several machines are operated in parallel to each other or for charging batteries.

Slip ring motor:

The slip ring motor is an asynchronous three-phase current motor. In this type of motor the rotor winding is not short-circuited but is connected to the outside via the slip rings. These motors are used for applications requiring a high starting torque and a low starting current. For a smooth start under high or full loading for instance, such as in large mills, stone breakers or crane systems. The efficiency of these motor is, however, somewhat lower. They are also amongst the motors requiring the most maintenance.

Sliding carbon:

See carbon brushes


The stator is the fixed and unmoveable part of an electric motor, generator or even of a pump. The stator is often also the housing of the electric motor.

Synchronous generator:

Apart from asynchronous generators, the synchronous generator is another version of an alternating current generator. Compared to the asynchronous generator it has a more complex design. In order to be able to provide a constant frequency and voltage it must be controlled extremely quickly and precisely. This is achieved with two regulating stages. The first regulating stage maintains the constant speed of the generator. The second regulating stage generates the desired output voltage. This voltage is not speed-dependant but is influenced by the current flowing through the armature of the synchronous generator. The higher the current, the greater the magnetic field and thus the output voltage. The second regulating stage permanently misses this output voltage and adapts the value of the current flowing through the armature accordingly. As the current flowing through the armature is transferred via the slip rings – and thus parts susceptible to wear –  synchronous generators require more maintenance. The two regulating stages also mean that the design is somewhat more elaborate. Synchronous generators are therefore all in all more expensive than asynchronous generators. Synchronous generators are mainly used in power plants, but also as alternators in cars.

Synchronous motor:

Synchronous motors are three-phase motors. They offer a particularly high level of efficiency, making them particularly suitable for continuous-operation applications. The frequency controlled speed, not depending on the loading, ensures that the driving axles of conveyor belts are always synchronised. One advantage ensuring that synchronous motors are, amongst others, used in the beverage industry.


Three-phase machine:

Three-phase machines can be operated in two ways. As electric motors they convert electrical energy – in this case three-phase current – into mechanical energy. This is exactly the opposite in the generator operation, where mechanical energy is converted into electrical energy. Three-phase current is also referred to as three-phase alternating current. Three phases because in three-phase current, the voltage is supplied to precisely three independent coils via three separate conductors. These coils are arranged in a circle offset by 120° from each other, resulting in an overall magnetic field. As the voltage is alternately supplied to the three coils, the rotor arranged in the overall magnetic field turns accordingly. Three-phase machines are available as synchronous and asynchronous models.







Ward-Leonard converter:

See Leonard set







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