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Glossary of Terms

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Abbe Error

The angular error that occurs when the measuring point of interest is displaced from the actual measuring scale location.

Absolute Encoder

A mechanical to electrical conversion device which provides position information. This device outputs a specific discrete address throughout 360 degrees

AC motor

A type of motor which, when energized with an AC signal, provides shaft rotation.


Occurs when a system or motor changes operating speed. The time rate of change of velocity. Normally expressed in radians/second2.

Acceleration Torque

The torque required to change a system or motor operating speed. May also be termed peak torque. To accelerate a system, the load (and motor) inertia and friction levels must be overcome.


Measure of discrepancy between the expected and the actual position. Accuracy is indicated as the maximum deviation from the target location.


Microsoft's specification for reusable software components. ActiveX is based on COM, the Component Object Model. The basic idea is to define exactly how software components interact and interoperate so developers can create components that work together using the definition. ActiveX components were originally called OLE Servers and ActiveX Servers and this renaming (actually for marketing rather than technical reasons) has created a lot of confusion about what they are. A lot of languages and applications support ActiveX in some way or another and Visual Basic supports it very strongly since it's one of the cornerstones of the Win32 environment

Air Gap

Distance required between the linear motor stationary and moving members. Or, The space between the rotating and stationary member in an electric motor.

Alternating Current


Current that reverses at regularly recurring intervals of time and has alternately positive and negative values.

Ambient Temperature

The temperature of air surrounding a device.


Practical unit of electrical current. One ampere of current is equal to 6.28 x 1018 electrons passing one point in one second. Abbreviated as amp. One amp is equal to one coulomb per second.


A device which increases voltage and current from low levels (millivolt/milliamp) to higher levels (volts/amps). May also be called a power amplifier or servodriver.

Analog Device

An apparatus that measures continuous information (i.e. voltage – current). The measured signal has an infinite number of possible values. The only limitation on resolution is the accuracy of the measuring device.

Analog Signal

A signal that seems to be continuous and changes smoothly, instead of making abrupt changes.


Terminal by which current enters, i.e., the positive terminal.


Cogging in a motor refers to certain preferred stopped positions. The motor appears to “jump” from position to position. Anticogging refers to smooth rotation as opposed to preferred stopping positions.


A small opening placed over the photo receiver lens.


Short for Application Program Interface, API is a set of routines, protocols, and tools for building software applications. A good API makes it easier to develop a program by providing all the building blocks. A programmer puts the blocks together. Most operating environments, such as Microsoft Windows, provide an API so that programmers can write applications consistent with the operating environment. Although APIs are designed for programmers, they are ultimately good for users because they guarantee that all programs using a common API will have similar interfaces. This makes it easier for users to learn new programs.

ABB’s Mint products have an API as part of the Active control that accompanies the product. This provide access to Mint commands from any ActiveX compliant application such as Visual Basic, Visual C++, LabVIEW etc.

Application Layer

The top layer of the ISO/OSI reference model comprising seven stacked layers. This layer handles issues like network transparency, resource allocation and problem partitioning. The application layer is concerned with the user's view of the network (e.g. formatting electronic mail messages).


Application Specific Integrated Circuit
A custom designed integrated circuit for specific purposes.

Asynchronous Data



Data in an ETHERNET Powerlink network which is not time critical. There is a specific time slot reserved for asynchronous data shared by all nodes. Each node connected to the network can send asynchronous data by requesting it to the Managing Node. The Managing Node keeps a list of all asynchronous data requests and will subsequently grant the bus to one node after each other. Asychronous data transfer are unicasts i.e. sent from point to point.


Loss or reduction of signal intensity.


An abbreviation for American Wire Gauge, a scale of wire sizes.



Back EMF

A motor characteristic which indicates an approximate amount of voltage to be applied to reach a speed. This is usually expressed in volts per 1000 RPM (volts/kRPM). May also be called “voltage constant.”

Backlash Deadband

(lost motion) caused by clearances between mechanical motion components which may occur when starting or reversing direction.


A measurement of the range which a package (or amplifier, or motor) can respond. Expressed in frequency or Hertz.

Base Speed

The speed a motor attains when rated voltage is applied (with rated load applied).


The DC voltage applied to establish a desired operating point. Bias point may be adjustable in some cases when interfacing with other equipment.

Bode Plot

A graphic plot or picture of gain versus frequency. This provides servo system designers with a graph illustrating areas of resonant free responses, and therefore indicates where resonant points are located.

Braking Torque

The torque required to bring a motor down from running speed to a standstill. The term is also used to describe the torque developed by a motor during dynamic braking conditions.


A device that works on Layer 2 of the OSI reference model and connects 2 similar networks to each other. In this connection, data packets are transferred from one subnetwork to another subnetwork through the analysis of the MAC address.


Conducting material through which current is passed. In a DC motor, it interfaces between the external circuit and the commutator.

Brushless Motor

A motor which uses “electronic” commutation instead of a mechanical commutator and brushes. An electric feedback device is used to electronically switch current from winding to winding. Also known as AC Servo or Brushless DC motor.

Brushless Resolver

An indication type feedback device which does not use brushes or slip rings. Signals are fed in (or out) of the rotor assembly via transformer action.


The power supply voltage available from an amplifier.



Cantilever Load

A load which tends to impose a radial force (perpendicular to the shaft axis) on a motor.


Controller Area Network, developed by Bosch and Intel. It is an inter-module bus that links controlled devices.

ABB makes use of the CAN interface for I/O expansion, communicating with HMI panels and peer-to-peer communications.


An open standard that operates over a CAN based network. Devices that confirm to CANopen standard will operate in the same way and allow for interoperability between devices from different vendors. The CANopen specification is controlled by the CAN in Automation group (

Carrier Sense Multiple Access

The ability of a node to detect whether the medium is currently in use.


Category 5 cable, commonly known as Cat 5, is an unshielded twisted pair type cable designed for high signal integrity. The actual standard defines specific electrical properties of the wire, but it is most commonly known as being rated for its Ethernet capability of 100 Mbit/s.


Terminal by which current leaves, i.e. the negative terminal.

Centralized Control

Typically referred to a system where a single controller controls an entire machine, including all axes and I/O. ABB’s NextMove motion controllers are examples of centralized controllers.

The opposite of centralized control is decentralized control where multiple “intelligent” units share the system responsibilities. ABB’s e100 drives can be networked together for a decentralized control system.

Circulating Circuit

The current in armature conductors which are short circuited during commutation.


A circuit that keeps the voltage output from exceeding a preset value.

Closed Loop

A package which has a control signal and a feedback signal. The feedback signal is used to correct package (speed or position) errors.

Closed Loop Gain

The gain, measured with feedback, is the ratio of the voltage appearing across the output terminal to the voltage at the input.

Closely Coupled

Closely coupled axes will start together and typically stop together. Consider an XY system that must draw complex shapes. The X and Y axes must be closely coupled in order to draw the shapes. A robot arm is another example of axes that are closely coupled.


Low speed, nonuniform rotation which shows up as jerky motion. Most observable at speeds below 50 RPM.

Collision Detection

An alteration to CSMA that gives a node the ability to detect a collision the moment one occurs.

Collision Domain

The domain in which a collision will occur if two nodes attempt to transmit data at the same time.

The CSMA/CD access process limits the runtime of a data package from one participant to another. Depending on the data rate, what results is a spatially limited network, the so-termed collision domain. The maximum diameter of a collision domain is 512 m at 10Mbit/s (Ethernet) and 512m at 100Mbit/s (Fast Ethernet). Full duplex operation with switches or bridges precludes collisions, thus enabling network expansion beyond these limits.


When two nodes on a network attempt to transmit data on the same medium at the same time.


This is a mechanical cylinder device consisting of segments of conductive material (usually copper) interspaced with insulation material (to isolate each separate segment). A commutator passes current from brushes into the motor’s rotor assembly, and performs switching of currents from winding to winding as the motor rotates.

Commutation (electronic)


The sequence at which the controller switches the drive voltage/current among the various motor windings to ensure smooth linear motion of the motor. Commutation can be achieved through the use of brushes, Hall Effect sensors, or with a sinusoidal current.


Adjusting a package to obtain optimum operation.

Computer Interface

Circuitry designed to allow communication between a computer and some other processor, such as the programmable controller’s Central Processing Unit.


Any material which tends to make the flow of electric current relatively easy.

Constant Current Power Supply


Current regulator. A power supply capable of maintaining a preset current through a variable load. This is achieved by automatically varying the load voltage in order to maintain the ratio V load/load constant.

Constant Voltage Power Supply


Voltage regulator. A power supply that is capable of maintaining a present voltage across a variable load. This is achieved by automatically varying the output current in order to maintain the product of load current times load resistance constant.

Continuous Torque

This is the torque that a motor can generate at stall without exceeding its armature temperature rating. controller The “brains” of a drive package. It monitors and makes any needed corrections to accomplish the desired task.

Controlled Node

Standard station in an ETHERNET Powerlink network without the abilty to manage the SCNM mechanism.

Cooling, Convection

A method of heat transfer which uses the natural upward motion of warmed air.

Coordinated Motion

See closely coupled.

Crossover Frequency

The point at which a Bode plot crosses zero gain. Expressed in frequency or Hertz.


Carrier Sense Multiple Access Collision Detection is a network access method in which devices that are ready to transmit data first check the channel for a carrier. If no carrier is sensed, a device can transmit. If two devices transmit at once, a collision occurs and each computer backs off and waits a random amount of time before attempting to retransmit. This is the access method used by Ethernet.


Time value of movement of free electrons. One ampere equals one coulomb per second. Conventional reference is opposite to direction of actual electron movement.

Current at Peak Torque

This is the current required to obtain peak stall torque from the motor. It is given in amperes and is the same as the demagnetization current rating of the motor.

Current Foldback

A method used by a control to reduce its output current during overload conditions, thus protecting itself.

Current Limiting

A method used by a control to limit its maximum output current to a preset value.

Current Sensing Resistor

A resistor placed in series in order to sense a voltage which is proportional to load current.

Current Sinking

A sensor output type such that when it is ON, current flow is from the load into the sensor output, then to ground. Output is normally high.

Current Sourcing

A sensor output type such that when it is ON, current flow is from the sensor into the load. Output is normally low.

Current, Demagnetization

The level of current which can damage a PM motor.

Cycle Time

The time between two consecutive starts of a cyclic – i.e. repeating – process. The cycle time includes the time for processing a task and some idle time before the beginning of the next cycle.



DC Motor

A type of motor which when energized with a DC voltage provides shaft rotation.

Dead Band

A range of input that gets no package response.


A decentralized system will consist of two or more programmable controllers that operate a machine.

ABB’s e100 drives can be networked together for a decentralized control system.


A measure of system gain. Gain in db = 20 LOG10A.

Delay Logic

Signal modification of various types. ON delay logic energizes output only if the input signal duration exceeds a preselect time daily.


A programming language developed by Borland. Based on the Pascal programming language, Delphi competes with Microsoft Visual Basic as a RAD (Rapid Application Development) Windows tool.


A partial loss of magnetic strength, either temporary, or permanent.


The practice of reducing output power of a unit due to high temperature.


Referring to events that have no random or probabilistic aspects but proceed in a fixed predictable fashion.

Deterministic Communication

Describes a communication process whose time evolution can be predicted exactly. I.e. the time by when a message reaches the recipient is predictable.

Digital Circuit

A circuit that has only two stable states, operating in the manner of a switch, i.e. either “on” or “off”.

Digital Encoder

See Encoder.

Digital Signal

A signal which is either “on” or “off”. May be stated as “high” or “low”. This signal appears like “pulses”.


A device used to permit current flow in one direction and to inhibit current flow in other direction.

Direct Current (DC)

A unidirectional current in which changes in value are so small that they may be neglected. As ordinarily used, the term describes a practically nonpulsating current.


To stop or disconnect a response.


Power losses inside a device which give rise to heat.


Dual Port RAM. An area of RAM (Random Access Memory) that is shared between two processors.

Duty Cycle

An indication or measurement of the time which power may be applied onto a motor. A “continuous duty” motor may have rated power applied all the time; whereas an “intermittent duty” motor must have cool down time.

Dynamic Brake

A technique used to stop a motor. The motor’s windings are essentially shorted together (thru a resistor). The motor declines to a stop exponentially.

Dynamic Routing

Dynamic routing means that with the help of routing protocols, a router continuously calculates rules and parameters for path selection through the network, which are stored in routing tables. It ensures path selection adapted to the current topology and load distribution of a network.




A measure of how effectively a motor converts electrical energy into mechanical rotation. Ratio of output power to input power represented as a percentage.

Electrical Time Constant

Time in seconds for a step current input to reach 63% of its final value.

Electronic Commutation  

When magnetic fields of a motor are switched on and off via electronics (such as transistors), as opposed to a mechanical commutator, the technique is known as electronic commutation.

EMI Electromagnetic Interference

Signals which are radiated and result in interference.


To allow or permit an output response. (This is the opposite of disable).


The encoder is a mechanical to electrical conversion device. The output signal shown shaft/load position (or location). May also be called an “optical encoder”, “digital encoder”, “rotary encoder”, “incremental encoder”, or “digital tachometer”.


The conditions in which a device operates. This may include high temperature, shock, moisture, oil splash, etc.

Error Signal

The difference between desired, or command signal and actual, or feedback signal. This signal forces a correction to occur in a servo or vector drive.


The most widely-installed local area network (LAN) technology.

ETHERNET Powerlink

An extension to standard Ethernet on layer 2, to exchange data under hard real-time constraints. It was developed for deterministic data exchange, short cycle times and isochronous operation in industrial automation.

Ethernet Specification

Developed by Xerox, DEC and Intel in 1980, sometimes referred to as Ethernet II.


Eurocard is a European standard format for PCB cards, which can be plugged together into a standardized chassis. The chassis consists of a series of slots on the top and bottom, into which the cards are slid so they stand on end, like books on a shelf. At the "back" of each card is one or more DIN 41612 (or other DIN) connectors, which plug into similar connectors on a backplane at the rear of the chassis.



Fall Time

A measure of the time required for the output voltage of a circuit to change from a high voltage level (90%) to a low voltage level (10%).

Fast Ethernet

The family of Ethernet specifications which operate at 100 Mb/s.


A signal which provides information back to the controller or drive


Composed of and/or containing iron. Exhibits magnetic characteristics as opposed to nonferrous materials which do not.


Software or programs that are loaded into Read Only Memory (ROM) or are embedded into a control system.

Flash Memory

A type of programmable memory chip that retains data even when the power is turned off.

Floating Point

A computer representation of a real number, for example 1234.567.

Integers can only represent whole numbers, for example 1234.

Force Ripple

The periodic force variation that occurs when the motor is in operation.

Forcer Linear

stepper motor component that contains the coil assembly.


Field Programmable Gate Array. A programmable logic chip with a high density of gates. Allows very complex functions to be programmed, eliminating or reducing other logic devices.

Frame Size

A term referring to a set of physical motor dimensions established by NEMA and IEC.


Directly related to time, i.e. frequency = 1/time. Expressed in Hertz or cycles per second (cps).

Front End

For software applications, front end is the same as user interface.


File Transfer Protocol. A standard protocol for transferring large files across the internet or Ethernet.

Full Duplex

A mode of data transmission in which each device is able to transmit and receive data simultaneously

Full Step

Longest distance that a stepper motor moves during one pulse. Typically 50 full steps per rev.

Fully Switched Ethernet

Term for an Ethernet network where for each node there is one dedicated port on a switch. Thus, collisions are avoided and full duplex data exchange is possible.




A comparison (or ratio) of the output signal and the input signal.


A device that operates above the Layer 2 of the OSI reference model and converts protocols. At Layer 3, these devices are generally designated as routers.

Gravity (Gravity Constant)

1G is equal to 386 in/sec2 = 9.81 m/sec2.



Hall Effect

Describes what happens when a semiconductor, through which a current is flowing, is placed in a magnetic field. A difference in potential (voltage) is generated in the field and the conductor. Typically used to sense magnetic fields.

Half Duplex

A mode of data transmission in which each device alternately receives and transmits data.

Hall Effect Sensor

A magnetic device that senses changes in a magnetic field and generates an output voltage.

Home Position

Unique position used as the initialization location from which all other programmable locations are referenced. Also known as the reference marker or datum.




Resistance and inductance limit the amount of current drawn from an alternating current line. The vectorial sum of these two factors is called impedance.

IEEE 802.3

The standard specification for Ethernet.

Incremental Motion System Incrementing

A mode in which a system or a motor is operating in a stop–stop velocity profile. That is, running (or operating) for a given time, and remaining idle for a given time.


A programmable motion controller that sends step or step and direction signals to the linear stepper motor driver.


The property of an electronic circuit by which an electromotive force is induced in it by a variation of current, either 1) in the circuit itself, or 2) in a neighboring circuit.

Induction Motor

An AC motor in which the currents flowing in the stator winding induce a current in the rotor assembly. Inductance motors have slip and therefore the rotor rotates slower than the stator’s magnetic field.


The property of a body that resists changes in movement.

Inertia Match

This occurs when the load inertia equals the motor inertia. This can be made to occur by choosing a coupling ratio.

Insulation Resistance

Megger check. A measure of a motor’s insulation system. A high test voltage is applied between each motor terminal (leadwire) and ground and the resistance (usually in megohms) is measured.


A nonconducting support for an electric conductor. A material that does not conduct electricity.

Integrated Circuit (IC)

An interconnected array of active and passive elements integrated within a single semiconductor substrate or other compatible material, and capable of performing one complete electronic function.


A common boundary between electronic systems, or parts of a single system.

Interface Circuit

A circuit that links one type of device with another. Its function is to produce the required current and voltage levels for the next stage of circuitry from the previous stage.

Iron Core Motor

A DC motor which has steel laminations in the rotating armature.


Industry Standard Architecture. A bus standard used in IBM compatible PC’s. Allows devices such as modems, sound cards, video cards to be added. Now superseded by PCI bus.


Pertains to processes that require timing coordination to be successful. Isochronous data transfer ensures that data flows continuously and at a steady rate in close timing with the ability of connected devices.

Isochronous Data

Data in an ETHERNET Powerlink network which is to be transmitted every cycle.




A high level object orientated programming language developed by Sun Microsystems. Java is platform independent, i.e. a Java application can run on many different hardware platforms and operating systems.



Lag Network

An electrical network which increases the delay between input signal and output signal.


Thin metal sheets of steel stacked together to form the core of an electromagnet.

Laser Interferometer

Feedback device used to measure the distance between the incident and reflected light beam. Provides the highest degree of resolution and accuracy.

Lead Screw

A device for translating rotary motion into linear motion.

Leakage Current

Small current flowing through the output device in the OFF state.


Abbreviation for “light emitting diode”; a semiconductor device which when energized emits waves, either visible, invisible, or infrared radiation.

Linear Characteristic

A straight line characteristic which usually is predictable when outside disturbances are considered (i.e. voltage, temperature, etc.)

Linear Circuit

A circuit whose output is a continuous amplified version of its input. That is, the output is a predetermined variation of the input.

Linear Motor

Type of motor that converts electric current into direct linear motion without ball screws, gears, or other mechanical transmission systems.


A measure of how close the actual output is to the ideal or theoretical output.


Linux is a free operating system that runs on many kinds of hardware including PCs and Macintoshes. Linux is a group effort: thousands of developers around the world contribute to Linux, adding new features and fixing bugs. Linux competes with Microsoft Windows.

Loosely Coupled

Multiple axes that move together but not in synchronization. Axes may start within a few micro-seconds of each other and stop at different times.

Low Pass Filter

A digital which passes slow changing, low frequency information, while attenuating high frequency, detailed edge information. The filter allows the tuning out of mechanical resonance. Useful for systems with ball screws or other devices. Low pass filters are supported on ABB’s MicroFlex, MicroFlex e100 and EuroFlex servo drives.



Maximum Terminal Voltage

This is the maximum voltage of the amplifier that should be applied to a motor.


Medium Access Control. A term used in Ethernet netoworks. For broadcast networks, it is the method which devices use to determine which device has line access at any given time


A unique identifier that identifies an Ethernet device on the network. All Ethernet devices have a unique 48-bit address.

Managing Node

A node capable to manage the SCNM mechanism in an ETHERNET Powerlink network.

Maximum Segment Length

The maximum length of cable that can be used in the network before signals become lost or corrupt due to attenuation of the medium.


A finer unit of displacement that is achieved by proportioning the current in each phase of the linear stepper motor. It provides smoother motion and higher resolution.


ABB’s automation programming language for their range of multi-axis motion controllers and servo drives.


Mean time between failures. This is a measure of how long a product will perform, before a failure or problem occurs. A measure of product life.

Multi Speed Resolver

multi speed resolver Similar to resolver, except numerous electrical cycles are produced for each 360 degrees of mechanical shaft revolution. A simple resolver produces only one electrical cycle per one mechanical shaft rotation.

Multiplexed Isochronous Data

Data from various ETHERNET Powerlink nodes which is multiplexed to a limited number of isochronous slots. Thus, multiplexed data is not transmitted every cycle but at a multitude of cycles. A proper mixture of Isochronous Data and Multiplexed Isochronous Data provide for a better load-balance of the entire network.



No Load Speed

How fast the motor will run with no load when the maximum rated voltage is applied.

Networking Stack

This refers to the “stacked” layers (TCP, IP, or others) through which all data passes at both ends of a data exchange. A clear picture of layers is provided in the ISO/OSI reference model of the layers involved in any network communication.


Network Interface Card – provides computers with a connection to Ethernet networks.


A specific device on a network.


Random, unwanted electrical signals.

Notch Filter

A filter that only lets everything BUT a certain notched portion of frequencies through. The filter allows the tuning out of mechanical resonance. Useful for systems with ball screws or other devices. Low pass filters are supported on ABB’s MicroFlex, MicroFlex e100 and EuroFlex servo drives.


Sinking/Pull Down where 0 volts = Active. NPN transistor is one of the two types of bipolar transistors, the second being PNP. The letters “N” and “P” refer to the majority charge carriers inside the different regions of the transistor.

NPN transistors consist of a layer of P-doped (the doping agent is often boron) semiconductor (the “base”) between two N-doped (often made with arsenic) layers. NPN resistors are commonly operated with the emitter at ground and the collector at a positive voltage.




The unit of electrical resistance. Resistance through which a current of one ampere will flow when a voltage of one volt is applied.

Open Loop

A package that has a control signal only. This package cannot make any corrections.

Open Mode

An ETHERNET Powerlink operation mode. The real-time nodes and regular Ethernet nodes don’t need to be seperated in protected network domains. In open mode, deterministic communication is still guaranteed, however timing constraints like cycle time (typically miliseconds) and jitter (typically 10th of microseconds) are more relaxed than in protected mode and depending on the IEEE 1588 implemetation (hardware or software clocks).

Operating Temperature

The range of temperatures a device can operate within.


Measure of squareness (90 degree relationship) between motion axes. The value of error is typically expressed in arc seconds.


A vibration or ringing typical of an unstable condition.

Output Ripple

Unwanted variations in the output signal.

Over Temperature Protection

A thermal sensitive circuit that automatically turns off if it gets too hot.

Overload Protection

A circuit that protects a device by shutting down when levels (voltage or current or temperature) reach a maximum.


How much a signal goes over the desired level during a change. Usually shown in percent (%) such as, the ratio of level to the desired level.



Peak Torque

The maximum useful torque that can be generated at the maximum recommended current. Usually it is the torque produced by the maximum demagnetization current.


Programmable Automation Controller. A new term for a sophisticated PLC combining the flexibility of a PC architecture with the robustness of a PLC.


Peripheral Component Interconnect. A standard describing how the peripheral components of a computer system may be connected together.


Two way communications from one node to another, or any other node on the network. The slave nodes can communicate with one another and do not have to go through the master node to distribute the data.

Permanent Magnet (PM) Motor

A DC motor having a permanent magnet to produce a field as opposed the electromagnetic.

Permanent Magnet Material  

A piece of ferromagnetic material that having once been magnetized, shows definite resistance to external demagnetizing forces; that is, it requires a high demagnetizing force to remove the resultant magnetism.

PFM Pulse Frequency Modulation

A technique used to turn transistors on and off. The amplitude of the voltage is held constant. The applied voltage is turned on and off at a variable frequency, i.e. turned on and off at various times. Thus by varying the frequency of the applied voltage, the motor speed is varied.

Photo Receiver

A unit consisting of photo sensor, focusing lens, and protective enclosure.

Photo Sensor

A light sensitive portion of a photoelectric control that converts a light signal into an electrical signal.

Photo Transistor

A type of photo sensor.


Proportional Integral Derivative. A mathematical method for closed loop control based upon a measured feedback and control set point.


The long stationary component of the linear stepper motor.


Programmable Logic Controller. A device that handles machine I/O (digital and analog) using simple programming techniques such as Ladder Logic and Function Block Diagrams. Can also handle motion and communications.

Plug Reverse

The immediate reversal of a motor. This is done by reversing motor voltage immediately without waiting for the motor’s rotation to stop.


Permanent Magnet Direct Current.

PMDC Motor

Permanent Magnet Direct Current Motor. This type of motor uses permanent magnets to set up the stator field. The rotor field is set up by passing current through brushes, then through a commutator, and into the rotor assembly.


Sourcing/Pull-up where 24V = Active. PNP transistor is one of the two types of bipolar transistors, the second being NPN. The letters “N” and “P” refer to the majority charge carriers inside the different regions of the transistor.

PNP transistors consist of an n-type semiconductor between a p-type semiconductor that serves as an emitter and a p-type semiconductor that serves as a collector.


Also referred to as index move. Axis moves from one position to another.

In communications these refers to a direct link between one node and another on a network.

Poles, Motor

A term which refers to the number of magnetic poles inside a motor, i.e., a 2 pole or a 4 pole motor.


The time rate at which work is done, or transferred. Written as: power = force times distance divided by time. In electrical terms: power = voltage times current. Express in watts.

Power Output

The power available at the output shaft. It is equal to the power applied minus motor losses, such as: copper, brush, windage, and friction losses.

Power Supply

A device which converts power from one form to another, for example, from AC to DC. It supplies the necessary voltage and current to system circuits and the motor.

PPR Pulses per Revolution.

A term used with encoders to show the number of pulses sent out when the encoder rotates through 360 degrees. Also called line count.


The linear motor component that contains the coil assembly.

Primary Winding

That winding of a motor, transformer or other electrical device which is connected to the power source.


A momentary sharp change in current, voltage, or other quantity that is normally constant. A pulse is characterized by a rise and fall, and has a finite duration.

PWM Pulse Width Modulation.

A way to turn transistors on and off. The amplitude of applied voltage is held the same while the width of the applied voltage pulse is changed (modulated). By changing the width, the “average” voltage applied to the motor changes, so motor speed changes.



Radial Play

The shaft displacement perpendicular to the shaft due to a side force applied perpendicular to the shaft axis. Usually specified as a reversal of a given force.

Rated Current

The current required of the servo amplifier to provide the continuous stall torque rating of a motor.

Real Numbers

Decimal numbers, for example 3.14, 0.25. Sometimes referred to as Floating Point numbers.


A Real-Time System responds in a timely, predictable (=deterministic) way to unpredictable external stimuli arrivals.


A device that converts alternating current into direct current.


A control that can absorb power (generated by the motor) resulting in quick stops.

Regulated Power Supply

A power supply which maintains a constant output voltage (or current) for changes in the line voltage, output load, ambient temperature, or time.


The maximum amount that the output will change as a result of a specified change in line voltage, output load, temperature, or time.


The discrepancy between two successive approaches of a motor to a target position. Approaching the target position from the same direction twice and determining the discrepancy between them provides unidirectional repeatability. Approaching the target position from two different directions and determining the discrepancy between them provides bidirectional repeatability.


The opposition that a device offers to the flow of electrical current, measured in ohms.


A device that introduces resistance into an electric circuit.


The smallest displacement that a motor is able to move or the smallest displacement an encoder is able to detect.


The smallest detectable increment of measure.


An induction type feedback device which output signal is in proportion to the angle it rotates through.

Resolver to Digital Converter

An electronic circuit which transforms or converts the resolver angle into a signal which is meaningful to the control electronics.


The rotor’s component parts are elastic and tend to deflect under torque (i.e. output shaft of motor lags internal motor shaft). This elasticity stores mechanical energy resulting in angular vibrations called resonance.

Resonant Point

Any electrical or mechanical device with mass has a point at which it is unstable when subjected to an alternating driving force or signal. This unstable point is termed the resonant point.

Response Time

The time it takes for a device to respond to an input signal.


Radio Frequency Interference.


A variation or small change in an output signal. An ideal DC output would be smooth or constant. Stated in either peak–to–peak or RMS value.

Rotary Motor

Type of motor that converts electric current into rotational motion.


A device working on Layer 3 of the ISO/OSI reference model, connecting different network segments, or splitting up networks into subnetworks. A router sends data packets onward based on routing table information. Routing tables are either fixed or dynamically determined by using routing protocols.

Routing Protocol

Used by routers during dynamic routing in order to exchange information about connected networks amongst each other. The information is then stored in the router’s routing tables.


An industry standard for sending signals over a twisted wire pair less than 15m (50 feet). It defines pin assignments and signal levels for receiving and sending devices. Other standards cover sending data over distances more than 15m (50 feet).


An industry standard for sending signals over distances up to 1200m (4000 feet).



Saturation Voltage

The voltage drop appearing across a switching transistor or SCR that is fully turned ON.

SCNM – Slot Communication Network Management

In an ETHERNET Powerlink network, the managing node allocates data transfer time for data from each node in a cyclic manner within a guaranteed cycle time. Within each cycle there are slots for Isochronous Data and Multiplexed Isochronous Data, as well as Asynchronous Data for ad-hoc communication. The SCNM mechanism ensures that there are no collisions during physical network access of any of the networked nodes thus providing deterministic communication via Standard Ethernet.

SCR Silicon Control Rectifier.

A semiconductor type device that can be turned on with a DC signal. It controls turning on and turning off rectified power to a motor.


Linear motor component that contains the steel and permanent magnets or aluminum plates.


A material whose resistivity is between that of conductors and insulators, and whose resistivity can sometimes be changed by light, and electric field, or a magnetic field.


A sensing element. The basic element that usually changes some physical parameter to an electrical signal.

Service Factor

A multiplier that shows how much more (than the horsepower rating on the nameplate) a motor can be driven without overheating, expressed in percent.

Servo Drive

Several devices which control or regulate speed/position of a load. Such a drive controls the load with respect to a reference input signal, by comparing the feedback signal. It outputs an error signal which makes any necessary corrections.

Servo Motor

A motor and feedback device. Servo motors are used in closed loop systems.

Set Point

An input variable, which sets the desired value of the controlled variable. The input variable may be manually set, automatically set or programmed. It is expressed in the same units as the controlled variable.

Settling Time

Amount of time required for a signal (or motor) to stop oscillating. Usually expressed in milliseconds (ms).

Short Circuit Protection

Output circuit protection made to protect a device from damage due to a short circuit. This does not protect against overload problems.

Slip Ring

A conductor band, mounted on an armature and insulated from it. A conductor strip slides on the band as the armature rotates. The function of the slip ring system is essentially the same as a commutator and brushes in a brush type motor.

Slot Telegram

Data telegram used in an SCMN time slot

Starting Torque

The amount of torque delivered by a motor when first energized.

Static Routing

Static routing means that data transmission paths are fixed in the routing tables of a router and, a specific bandwidth is reserved for each connection. Data packets always take the same path between two terminal devices. It is therefore not possible to respond automatically to changes in the topology or in the case of overloads of connections.


That part of a motor structure which does not rotate.

Steady State

A stable condition, such as when a motor is sitting idle, or when it is rotating at a continuous rate. An unchanging condition.

Stepper Motor

A motor that moves in predetermined steps. The stepper motor’s position is determined by the number of step pulses that are supplied to the motor. Typically, this type of motor operates as an open loop system. Although a position verification sensor is available.


Ability of an object to resist displacement. A measure of deflection for a positioning axis under load.Expressed in pound per inch.


A device working on Layer 2 of the ISO/OSI reference model. In contrast to hubs, switches analyze the incoming data packets and only relay them to ports at which the receiver is registered. Multicast and broadcast messages are sent to all ports. Data transmission on several ports can be done simultaneously and full duplex. Switches provide for a better load balance on a network.

Switched Network

Term for an Ethernet network that is made up of switches.




The feedback device which provides a signal out proportional to speed of rotation of the input shaft.


Transmission Control Protocol/Internet Protocol A protocol for communication between computers, used as a standard for transmitting data over networks and as the basis for standard Internet protocols.

Temperature Operating

The range of environmental temperature in which a unit can safely be operated.

Temperature Rise

The increase in temperature above ambient.


Force is the action of one body on another tending to create or change the motion of the second body. A rotating force is one which produces a turning movement about a central point (shaft). This turning movement is torque. torque constant An expression of the relationship between input current and output torque. For each ampere of current, a fixed amount of torque is produced.

Torque Friction

All motors have some inherent friction. The two main sources are bearing friction and brush friction. Each one will vary with speed.

Torque Ripple

A variation of small change in torque delivered. This may be caused by nonlinearities in the motor or by the controller.

Total Indicated Runout (TIR)

A shaft rotates in a nonconcentric manner. The amount of eccentricity or wobble is termed TIR

Transient Protection

Circuitry to guard against spikes on the supply lines. Spikes are caused by inductive sources such as heavy motors or solenoids turning on and off.

Transient State

May be referred to as dynamic condition. Caused by an input command which results in a change of state, i.e., not settled, but changing.


In electronic usage usually refers to an unwanted, temporary, large increase or decrease in a current or supply voltage that only occurs occasionally.


A timing pulse used to initiate the transmission of signals through the appropriate circuit paths.




User Datagram Protocol. A communications protocol for the Internet network layer, transport layer, and session layer, which makes it possible to send a datagram message from one computer to an application running in another computer. Like TCP (Transmission Control Protocol), UDP is used with IP (the Internet Protocol). Unlike TCP, UDP is connectionless and does not guarantee reliable communication; the application itself must process any errors and check for reliable delivery.


A plug-and-play interface between a computer and add-on devices such as mobile devices (PalmOS®, PocketPC®), printers, keyboards etc. New devices can be added without adapter cards or without the computer being off.

User Interface

The means by which an operator can interact with a machine. Often based around PC based systems such as Windows and Linux.



Velocity Ripple

Periodic velocity fluctuation that occurs when the motor is in operation.


Visual Basic for Applications. Used as a macro language to add functionality to Windows-based applications such as Microsoft Excel, Word, Powerpoint etc.


A subset of the Visual Basic for Applications (VBA) programming language that is used to create dynamic web pages.

Visual Basic

A Windows-based programming language and environment developed by Microsoft. Visual Basic is based on the BASIC programming language. Primarily used to develop Windows-based applications.

Visual C++

A Windows-based programming language and environment developed by Microsoft. Visual C++ is based on the C++ programming language. Primarily used to develop Windows-based applications.


The unit of voltage, potential, or electromotive force. One volt will send a current of one ampere through a resistance of one ohm. Commonly abbreviated as V (or E).


Term used to designate the electrical energy differential that exists between two points and is capable of producing a flow of current when a closed path is connected between the two points.

Voltage at Peak Torque

The voltage required to produce peak torque when the motor is at a standstill and the winding temperature is 25 degrees centigrade.

Voltage Constant

The relationship between applied voltage and output motor speed. Expressed as V/kRPM or volt/radian/second. May also be called “Back EMF”.

Voltage Drop

The voltage developed across the component or conductor by the flow of current through the resistance or impedance of the component or conductor.

Voltage, Rated

A value provided to show at conditions rated speed and rated load are measured.




The amount of power required to maintain a current of one ampere at a pressure of one volt. One horsepower is equal to 746 watts.


A geometric shape as obtained by displaying a characteristic of voltage or as a function of time. AC line voltage produces a sine wave form.

Web Server

A computer that delivers (serves up) Web pages.

Wound Field Motor

A type of DC motor in which the stator field is created via a winding (as opposed to a permanent magnet). The rotor field is set up by passing current through the brush/commutator/rotor assembly.




XML (Extensible Markup Language) is a standard for creating markup languages which describe the structure of data. See for details.