Absolute Feedback
With the shaft in any position at motor start, the data from an absolute feedback mechanism always relays the position of the shaft. A non-absolute feedback mechanism must start from a known rotational position, such as the index pulse.
Absolute Move
A positioning mode in which all moves are referenced to a fixed origin position. for examble, if a stage is at +5 inches, an absolute move to +3 inches would result in a move of 2 inches toward the origin.
Absolute Positioning
Refers to a motion control system enploying position feedback devices (absolute encoders) to maintain a given mechanical location.
Absolute Programming
A positioning coordinate reference where all positions are specified relative to some reference, or "home" position. This is different from incremental programming, where distances are specified relative to the current position.
AC (Alternating Current)
The commonly available electric power supplied by an AC generator and is distributed in single- or three-phase forms. AC current changes its direction of flow (cycles).
AC Motor
A motor operating on AC current that flows in either direction (AC current). There are two general types: induction and synchronous.
A change in velocity as a function of time. Acceleration usually refers to increasing velocity, and deceleration to decreasing velocity.
A measure of the difference between expected position and actual position of a motor or mechanical system. Motor accuracy is usually specified as an angle representing the maximum deviation from expected position.
Acme Screw
A leadscrew which uses a threaded screw design with sliding surfaces between the screw and nut.
A device which creates mechanical motion by converting various forms of energy to mechanical energy. Also known as a self contained leadscrew system which converts rotary motion (from a motor) to linear motion.
Adaptive Control
A technique to allow the control to automatically compensate for changes in system parameters such as load variation.
Automated Instrument Manager
Automated mapping/facilities maintenance
Ambient Temperature
The temperature of the cooling medium, usually air, immediately surrounding the motor or another device.
Electronics which convert low-level command signals to high power voltages and currents to operate a servo motor. Electronics that convert low level command signals into high power voltages and currents to operate an electrical device.
Amplifier, PWM
A device which draws power from an independent source to produce a magnified pulse width modulated power signal form of a controlling input signal.
A device or circuit in which the output varies as a continuous function of the input.
Angular accuracy
The measure of shaft positioning accuracy on a servo or stepping motor.
Armature Reaction
The production of a magnetic field shifted 90 electrical degrees with respect to the stator magnetic field. The magnetic field is resultant of the armature current flow.
ASCII (American Standard Code for Information Interchange)
This code assigns a number to each numeral and letter of the alphabet. In this manner, information can be transmitted between machines as a series of binary numbers.
Asynchronous Machine
Any machine in which the output speed is not dependent of the excitation frequency.
Asynchronous transfer mode; a communications standard


B. EMF Harmonic Distortion
Root sum squares of the rms values of non fundamentals as a percentage of fundemental rms values.
Back EMF
The voltage generated when a permanent magnet motor is rotated. This voltage is proportional to motor speed and is present regardless of whether the motor winding(s) are energized or de-energized.
Torque created by the applied load on a drive nut causing the nut to reverse rotation
The amount of play (lost motion) between a set of moveable parts when changing the direction of travel. Typically seen in gears, drive trains, leadscrews, and bearings.
Ball Screw
Essentially power screws with a train of ball bearings riding between the screw and nut in a recirculating track. The screw has a rounded shape to conform to the balls. A ballscrew is highly efficient, has predictable service live, and a low rate of wear.
The frequency range in which the magnitude of the system gain expressed in dB is greater than -3 dB.
Base Speed
Response range is the command pulse range over which the unloaded motor can accelerate to command pulse rate from standstill, decelerate from command pulse rate to standstill, and reverse direction (on command) without loss of synchronism.
Base Speed, RPM
The speed in revolutions per minute (RPM), which a DC motor develops at rated armature and field voltage with rated load applied.
Baud Rate
Serial communication speed measured by the number of binary bits transmitted per second. Used for serial communication protocols such as RS232 and RS485.
BCD (Binary Coded Decimal)
A binary numbering system in which the decimal digits 0 to 9 are represented by a 4 bit binary number. Each digit in a decimal number assigned a four bit binary code.
Example: 156 = 0001 0101 0110.
An accordion style cover that can be mounted to a slide assembly for better protection of components in dirty environments. Note that bellows covers reduce travel and size considerations must be made to accommodate required travel and the cover.
Bi-Directional Repeatability
The difference in absolute position reached on returning to a given leadscrew angle from opposite directions.
Bifilar Winding
The term Bifilas Winding refers to the winding configuration of a step motor where each stator pole has a pair of winding, (4 electrical phases), the motor will have either 6 or 8 lead wires depending on termination. This winding configuration can be driven from a unipolar or bipolar drive design.
Base two numbering system. Each number being expressed in the powers of two, by 0 or 1.
Bipolar chopper driver
A class of step motor driver which uses a switch mode (chopper) technique to control motor current and polarity. Bipolar indicates the capability of providing motor phase current of either polarity (+ or -).
Bit (Binary Digit)
A unit of information equal to 1 binary decision or having only a value 0 or 1.
Block Diagram
A simplified representation of a system, with each component represented by a block, and each block positioned in order of signal flow through the system.
Bode Plot
A plot of the magnitude of system gain in dB and the phase of system gain in degrees versus the sinusoidal input signal frequency in logarithmic scale.
Bits per second
Braking Torque
The torque required to bring a motor down to a standstill. The term is also used to describe the torque developed by a motor during dynamic braking conditions.
Breakaway torque
The torque required to start a machine in motion. Almost always greater than the running torque.
A piece of current conducting material (usually carbon or graphite) which rides directly on the commutator of a commutated motor and conducts current from the power supply to the armature windings.
Brushless motor
Class of motors that operate using electronic commutation of phase currents, rather than electromechanical (brush-type) commutation. Brushless motors typically have a permanent magnet rotor and a wound stator.
Brushless Servo Drive
A servo drive used to control a permanent magnet synchronous AC motor. May also be referred to as an AC Servo Drive.
Brushless Servomotor
A class of servomotors which operates using electronic commutation of phase currents rather than electromechanical (brushes) commutation. Commutation is a function of rotor position. These motors typically have a permanent magnet rotor and wound stator. An "inside-out" DC motor with a permanent magnet rotor and electrical coils in the stator. Commutation of current in the windings is typcially achieved via external switching transistors and Hall-effect detectors. This type of motor avoids the limited life of brushes and their radiated EMI.
A group of parallel connections carrying pre-assigned digital signals. Buses usually consist of address and data information and miscellaneous control signals for the interconnection of microprocessors, memoris, and other computing elements.


C-face mounting
A standard NEMA mounting design, where the mounting holes in the face are threaded to receive the mating mount.
CAM Profile
A technique used to perform non-linear motion electronically similar to that achieved with mechanical cams.
Cantilevered Load
Any load not symmetrically mounted on a stage. Such loads exert torque moments upon the ways, and the resulting deformations can degrade accuracy.
A device which, when connected in an alternating-current circuit, causes the current to lead the voltage in time phase. The peak of the current wave is reached ahead of the peak of the voltage wave. This is the result of the successive storage and discharged of electric energy used in single-phase motors to start, or in three-phase motors for power factor correction.
The designation shows that a product such as a motor or control meets European Standards for safety and environmental protection. A CE mark is required for products used in most European Countries.
Characteristic Equation
1 + GH = 0, where G is the transfer function of the forward signal path and H is the transfer function of the feedback signal path.
Circular Coordinated Move
A coordinated move where the path between enpoints is the arc of a circle.
Class B insulation
A NEMA insulation specification. Class B insulation is rated to an operating (internal) temperature of 130°C.
Class F insulation
A NEMA insulation specification. Class F insulation is rated to an operating (internal) temperature of 155°C
Class H insulation
A NEMA insulation specification. Class H insulation is rated to an operating (internal) temperature of 180°C.
Closed loop
A broadly applied term, relating to any system in which the output is measured and compared to the input. The output is then adjusted to reach the desired condition. In motion control, the term typically describes a system utilizing a velocity and/or position transducer to generate correction signals in relation to desired parameters.
Closed Loop Positioning
The use of information from external feedback devices, such as encoders, in controlling a motor's movement to reach a desired position.
A mechanical device for engaging and disengaging a motor. It is often used when many starts and stops are required.
Cogging (Cogging torque)
A term used to describe non-uniform angular velocity. Cogging appears as a jerkiness, especially at low speeds.
Coil (Stator or Armature)
The electrical conductors wound into the core slot, electrically insulated from the iron core. These coils are connected into circuits or windings, which carry independent current. It is these coils that carry and produce the magnetic field when the current passes through them. There are two major types: "Mush" or "Random" wound, round wire found in smaller and medium motors where coils are randomly laid inslot of stator core: and formed coils of square wire individually lain in, one on top of the other, to give an evenly stacked layered appearance.
Command Position
The desired angular or linear position of an actuator. The command position is typically a signal that represents a realization of a motion control strategy.
Command Signal Generator
A device that supplies a command position signal to an automatic control system. This signal represents the desired motion of the actuator that is required to accomplish a task such as making a part. This signal is usually in the form of an electrical signal.
  1. A term which refers to the action of steering currents or voltages to the proper motor phases so as to produce optimum motor torque. In brush type motors, commutation is done electromechanically via the brushes and commutator. In brushless motors, commutation is done by the switching electronics using rotor position information obtained by Hall sensors, a Tachsyn, or a resolver.
  2. Commutation of step motors is normally done open loop. Feedback from the motor is not required to hold rotor position precisely.
A cylindrical device mounted on the armature shaft and consisting of a number of wedge-shaped copper segments arranged around the shaft (insulated from it and each other). The motor brushes ride on the periphery of the commutator and electrically connect and switch the armature coils to the power source.
A device where the feedback signal is subtracted from the command signal. The difference output of the comparator is called the error signal.
The adjustment of gain and requency parameters in a closed-loop system to achieve the desired dynamic response and also to insure a stable (non-oscillating) condition.
Compensation, Feed-forward
A control action which depends on the command only and not the error to improve system response time.
Compensation, Integral
A control action which is proportional to the integral or accumulative time error value product of the feed back loop error signal. It is usually used to reduce static error.
Compensation, Lag
A control action which causes the lag at low frequencies and tends to increase the delay between the input and output of a system while decreasing static.
Compensation, Lead
A control action which causes the phase to lead at high frequencies and tends to decrease the delay between the input and output of a system.
Compensation, Lead-Lag
A control action which combines the characteristics of lead and lag compensations.
Compensation, Proportional
A control action which is directly proportional to the error signal of a feedback loop. It is used to improve systems accuracy and response time.
The amount of displacement per unit of applied force.
Compliant Coupling
The limited motion of one coupled shaft without causing motion of the other coupled shaft that does not permit permanent displacement of one shaft with respect ot the other.
Computer Numerical Control
A computer-based motion control device programmable in a numerical word address format. A computer numerical control (CNC) product typically includes a CPU section, operator interface devices, input/output signal and data devices, software and realted peripheral apparatus.
A material such as copper or aluminium which offers low resistance or opposition to the flow of electric current.
Continuous rated current (ICR) (Amperes)
The maximum allowable continuous current a motor can handle without exceeding the motor temperature limits
Continuous rated torque (TCR) (lb-in.)
The maximum allowable continuous torque a motor can handle without exceeding the motor temperature limits
Continuous Rating
The limiting amount of Torque, Current, etc. that a device is capable of operating on or producing without thermal failure over an extended period of time.
Continuous stall current (ICS) (Amperes)
Amount of current applied to a motor (at locked rotor conditions), which results in rated temperature rise. Refer also to description of "Continuous stall torque"
Continuous stall torque (TCS) (lb-in.)
The amount of torque at zero speed, which a motor can continuously deliver without exceeding its thermal rating. Determined by applying DC current through two windings with rotor locked, while monitoring temperature. Specified with motor windings at maximum rated temperature, with motor in 25 degrees C ambient, mounted to a heat sink. Refer to individual specs for heat sink size.
Control Systems or Automatic control Systems
An engineering or scientific field that deals with controlling or determining the performance of dynamic systems such as servo systems.
A term describing a functional block containing an amplifier, power supplies, and possibly position-control electronics for operating a servomotor or step motor.
Controller / Microncontroller
A device that incorporates many or all functions of a computer in a single integrated circuit. Used to perform and logic required to do motion or process control.
Coordinated Motion
Multi-axis motion where the position of each axis is dependent on the other axis such that the path and velocity of a move can be acurately controlled. (Requires coordination between axes.)
The iron portion of the stator and rotor made up of cylindrical laminated electric stee. The stator and rotor cores are concentric and separated by an air gap, with the rotor core being the smaller of the two and inside to the stator core.
Coupling Ratio
The ratio of motor velocity to load velocity for a coupled to motor through a gear or similar mechanical device.
Critical Damping
A system is critically damped when the response to a step change is desired velocity or position is achieved in the minimum possible time with little or no overshoot.
Critical Speed
Speed of lead screw at which it begins to oscillate or whip.
Canadian Standards Authority
Carrier sense multiple-access, with collision detection; a communications method most often for Ethernet
The measure of electrical flow, measured in Amps.
Current at peak torque (IPK) (Amperes)
The amount of input current required to develop "peak torque". This is often outside the linear torque/current relationship.
Current, Rated
The maximum allowable continuous current a motor can handle without exceeding motor temperature limits.


D-flange mounting
This type of mount has clearance holes on the flange, and the mounting bolts stick out through the flange from the motor side. This mount is common in cases where the motor is integral to the machine.
Daisy Chain
A term used to describe the linking of several RS232C devices in sequence such that a single data stream flows through one device and on to the next. Daisy-chained devices usually are distinguished by device addresses which serve to indicate the desired destination for data in the stream.
The reduction or elimination of step overshoot is defined as damping. It is used in application where settling time is important. Types of damping are: mechanical, electronic and viscous (fluid). The electronic method includes series resistance, capacitance, back-phasing, delayed last-step excitation, and others. Mechanical damping is accomplished by adding friction in various schemes including fluid dampers.
Damping Ratio
Ratio of actual damping to critical damping. Less than one is an under-damped system and greater than one is an over-damped system.
Data base format; data base file
DC (Direct Current)
A current that flows only in one direction in an electric circuit. It may be continuous or discontinuous and it may be constant or varying.
DC Adjustable-speed Drive
All equipment required to adjust the speed or torque of DC motor(s) by controlling the voltages applied to the armature and/or field of the motors.
DC Drive
An electronic control unit for running DC motors. the DC drive converts AC line current to a variable DC current to cotnrol a DC motor. The DC drive has a signal input that controls the torque and speed of the motor.
Distributed control system; computers and I/O that control the real world in real time
Dead Band or Dead Range
The angle between clockwise and counter clockwise limits to which the rotor of an energized step motor can stop due to internal and external friction. Also known as a range of input signals for which there is no system response.
Deadbeat (Response)
Critically damped. Moving from one step position to another without overshoot or oscillation.
The rate velocity decreases as a function of time.
Decibel (db)
A logarithmic measurement of gain. If G is a systems gain (ratio of output to input) then 20 log G = gain in decibels (db)
Demag current
The current level at which the motor magnets will start to be demagnetized. This is an irreversible effect, which will alter the motor characteristics and degrade performance. Also known as peak current.
Detent Position
A step position is the static angular position which the shaft of an unloaded stepping motor assumes when it is energized as specified.
Detent torque
The maximum torque that can be applied to an unenergized step motor without causing continuous rotating motion.
Dielectric Test
A high voltage breakdown test of insulation's ability to withstand an AC voltage. Test criterion limits the leakage current to a specified magnitude and frequency, applied between the specified test points.
An electrical input or output signal which uses two lines of opposite polarity referenced to the legal signal ground.
A device or circuit in which the output varies in discrete steps, i.e., pulses or on-off operation.
Distributed Processing
A technique to gain increased performance and modularity in control systems utilizing multiple computers or processors.
Document management system
DNC, Direct Numerical Control
Technique of transforming part program data to a numerical control system via direct electrical connection in place of paper tapes.
Desktop network interface
DPBV - Dripproff Blower Ventilated
Type of motor cooled by blowing air through the inside fo the motor using an attached blower.
DPBV - Dripproof Blower Ventilated
Type of motor cooled by blowing air through the inside of the motor using an attached blower.
An electronic device that controls torque, speed and/or position of an AC or brushless motor. Typically a feedback device is mounted on the motor for closed-loop control of current, velocity and position.
Drive, Analog
Usually refering to any type of motor in which the input is an analog signal.
Drive, Digital
Usually referring to any type of motor drive in which the tuning or compensation is done digitally. Input may be an analog or digital signal.
Drive, Linear
A motor drive in which the output is directly proportional to either a voltage or current input. Normally both inputs and outputs are analog signals. This is a relatively inefficient drive type.
Drive, PWM
A motor drive utilizing Pulse-Width Modulation techniques to control power to the motor. Typically a high efficiency drive that can be used for high response applications.
Drive, SCR
A DC motor drive which utilizes internal silicon controlled rectifiers as the power control elements. Usually used for low bandwidths, high power applications.
Drive, Servo
A motor drive which utilizes internal feedback loops for accurate control of motor current and/or velocity.
Drive, Stepper
Electronics which convert step and direction inputs to high power currents and voltages to drive a stepping motor. the stepping motor driver is analogous to the servo motor amplifier.
Electronics which convert step and direction inputs to high power currents and voltages to drive a step motor. The step motor driver is analogous to the servomotor amplifier's logic.
Duty cycle
For a repetitive cycle, the ratio of on time to total cycle time. Duty cycle (%) = [On time / (On time + Off time)] × 100%
Dynamic braking
A passive technique for stopping a permanent magnet brush or brushless motor. The motor windings are shorted together through a resistor which results in motor braking with an exponential decrease in speed.
Dynamic Load
The actual working load applied to a bearing during operations.
A device which places a load on the motor to accurately measure its output torque and speed by providing a calibrated dynamic load. Helpful in testing motors for nameplate information and an effective device in measuring efficiency.


Eddy Current
Localized currents induced in an iron core by alternating magnetic flux. These currents translate into losses (heat) and their minimization is an important factor in lamination design.
Electrically Erasable Programmable Read Only Memory. Re-writable non-volatile memory chip. The contents of the EEPROM is not lost after power is turned off.
Effective Torque
The root mean square value of the instantaneous torque value over a given cycle.
The ratio of power output to power input.
Environmental information management system
Electrical Degree
A unit of measurement of time as applied to alternating current. One complete cycle equals 360 electrical degrees. Once cycle in a rotating field moves from one pole to the next pole of the same polarity. There are 360 electrical degrees in this time period. Therefore, in a two pole machine there are 360 degrees in one revolution, and the electrical and mechanical degrees are equal. In a machine with more than two poles, the number of electrical degrees per revolution is obtained by multiplying the number of pairs of poles by 360.
Electrical time constant (te) (Seconds)
The time required for current to reach 63.2% of its final value for a fixed voltage level. Can be calculated from the relationship te=L/R where L is inductance (henries) and R is resistance (ohms).
Electronic Damping
A means of suppressing oscillation of the step motor output by switching the motor winding in sequence such that the motor and load have come to rest when the final step position has been reached.
Electronic Gearing
A technique used to electrically simulate mechanical gearing. Causes one closed loop axis to be slaved to another open or closed loop axis with a variable ratio.
EMI (Electro-Magnetic Interference)
EMI is noise which, when coupled into sensitive electronic circuits, may cause problems.
A signal that permits a circuit to be activated.
A feedback device which converts mechanical motion into electronic signals. The most commonly used, rotary encoders, output digital pulses corresponding to incremental angular motion. For example, a 1000-line encoder produces 1000 pulses every mechanical revolution. The encoder consists of a glass or metal wheel with alternating transparent and opaque stripes, detected by optical sensors to produce the digital outputs.
Encoder Resolution
A measure of the smallest positional change which can be detected by the encoder.
Encoder, Absolute
A digital position transducer in which the output is representative of the absolute position of the input shaft within one (or more) revolutions. Output is usually a parallel digital word.
Encoder, Incremental
A position encoding device in which the output represents incremental changes in position.
Encoder, Linear
A digital position transducer which directly measures linear position.
Encoder, Marker
A one-per-revolution signal provided by some incremental encoders to specify a reference point within that revolution. Also known as Zero Reference signal or index pulse.
Enterprise Resource Planning
Ethernet Hub
A device for combining multiple Ethernet segments (typically 10BaseT) into a single segment. All traffic appearing on any port of a hub will be echoed to all of the other ports instantaneously.
Ethernet Switch
A device for connecting multiple Ethernet segments, while maintaining them as separate segments. Unlike a hub, a switch will intelligently route packets to the appropriate port (only) based on the MAC-level (OSI Layer 2) address in the packet.
A motor classification that indicates a motor is capable of withstanding internal explosions without bursting or allowing ignition to reach beyond the confines of the motor frame.


Fall Time
The time for the amplitude of systems response to decay to 37% of its steady-state value after the removal of steady-state input signal.
Fiber distributed data interface; a communications standard for networks
Feed Forward
A technique used to pre-compensate control a loop for known errors due to motor, drive, or lead characteristics. Provides improved response.
A signal which is transferred from the output back to the input for use in a closed loop system.
A type of permanent magnet consisting of ceramic compounds made up of oxides of iron, barium and strontium.
A term commonly used to describe the stationary (stator) member of a DC motor. the field provides the magnetic field with which the mechanically rotating (armature or rotor) member interacts.
Field Weakening
A method of increasing the speed of a wound field motor by reducing stator field intensity by reducing winding current.
Filter (control systems)
A transfer function used to modify the frequency or time response of a control system.
Facilities information management
Flatness OT Travel
The extent to which the straight line movement of a linear actuator is parallel to the base of the unit.
Flutter is an error of the basic cycle of an encoder per one revolution.
The magnetic field which is established around an energized conductor or permanent magnet. The field is represented by flux lines creating a flux pattern between opposite poles. The density of the flux lines is a measure of the strength of the magnetic field.
Following Error
The positional error curing motion resulting from use of a position control loop with proportional gain only.
The action of one body on another which tends to change the state of motion of that body. Typically described in terms of magnitude, direcion, and point of application.
Form factor
The ratio of RMS current to average current. This number is a measure of the current ripple in a SCR or other switch-mode type of drive. Since motor heating is a function of RMS current while motor torque is a function of average current, a form factor greater than 1.00 means some fraction of motor current is producing heat but not torque.
Four quadrant
Refers to a motion system which can operate in all four quadrants; i.e., velocity in either direction and torque in either direction. This means that the motor can accelerate, run, and decelerate in either direction.
Fricitonal Losses
The loss of energy due to the friction of moving parts.
A resistance to motion caused by contact with a surface. Friction can be constant with varying speed (Coulomb friction) or proportional to speed (viscous friction).
Full Load Current
The armature current of a motor at its full load torque and speed with rated voltage applied
Full Load Speed
The speed of a motor operated with rated voltage and full load torque.


The ratio of system output signal to system input signal. The control loop parameter that determines system performance characteristics.
The portion of a gearmotor, which cotnains the actual gearing which, converts the basic motor speed to the rated output speed.
A gearhead and motor combination to reduce the speed of the motor to obtain the desired speed or torque.
GIB Force
It is a clamping force between two devices.
Geographical information system, a system used to combine different types of geographical related information, such as water mains, sewers, power lines and roads.
global positioning system; satellites that continually transmit timing signals that allow a receiver to find its position.
Gravitational Constant
The acceleration of a free falling body due to the earth's gravitational pull. Equal to 9.8 m/s2, 32.2 ft/sec2
Graphical user interface; a program that lets users select icons representing commands and prompts for parameter entries through dialog boxes


Hall sensor
A feedback device which is used in a brushless servo system to provide information for the amplifier to electronically commutate the motor. The device uses a magnetized wheel and hall effect sensors to generate the commutation signals.
human-machine interface; discriminatory term
Holding torque
Sometimes called static torque, holding torque specifies the maximum external torque that can be applied to a stopped, energized motor without causing the rotor to rotate. Generally used as a figure of merit when comparing motors.
A reference position in a motion control system. Often designated as the zero position.
Home Limit Switch
Any device which locates the position of the zero reference.
Home Position
A reference position for all absolute positioning movements. Usually defined by a home limit switch and/or encoder marker. Normally set at power up and retained for as long as the control system is operational.
An index of the amount of work a machine or motor can perform. One horsepower is equal to 746 watts. Since power is equal to torque multiplied by speed, horsepower is a measure of a motor's torque and speed capability; e.g., a 1 HP motor will produce 36 lb-in. at 1,750 rpm.
HP = Torque (lb-in.) x Speed (RPM)/63,025
HP = Torque (lb-ft.) x Speed (RPM)/5,252
HP = Volts x Amps x Efficiency/746
Host Computer
An auxiliary computer system which is connected to a controller or controllers. The host computer in distributed control systems is frequently involved with controlling many remote and distributed motion control devices. It may also be used for off-line tasks such as program preparation, storage, supervisory control and evaluation.
hypertext markup language
HTTP (Hypertext Transfer Protocol)
A simple extensible protocol used for data exchange over the Internet. Browsers use HTTP to communicate with servers.
The oscillation of the system response about a theoretical steady-state value.
Hybrid step motor
A motor designed to move in discrete increments of steps. The motor has a permanent magnet rotor and a wound stator. Such motors are brushless. Phase currents are commutated as a function of time to produce motion.
The counter-force stored in an elastic material or mechanism after the outside forces acting on it have been changed. Commonly referred to as the difference between the position when approached from one direction and the same position when approached from the opposite direction. An example is the mechanical wind-up in the lead screw assembly.


information and control
I/O (Input/Output)
The reception and transmission of information between control devices. In modern control systems, I/O has two distant forms: switches, relays, etc. which are either an on or off state, or analog signals that are continuous in nature such as speed, temperture, flow, etc.
Losses due to current flowing in a conductor caused by resistance (equals the current squared times the resistance).
Idle current reduction
A step motor driver feature that reduce the phase current to the motor when no motor motion is commanded (idle condition) for a specified period of time. Idle current reduction reduces motor heating and allows high machine throughputs from a given motor.
integrated information management system, a system that links two or more client computer systems to automatically exchange information
Information management system
Incremental Motion
A motion control term that is ued to describe a device that produces one step of motion for each step command (usually a pulse) received.
Incremental Move
A move referenced from the current set position.
Electronics which convert high level motion commands from a host computer, PLC or operator panel into step and direction pulse streams for use by the step motor driver. Indexers can be broadly divided into two classes. A preset indexer typically accepts distance, velocity and ramp time inputs only. The more sophisticated programmable indexer is capable of complex motion control and includes program memory.
The characteristic of an electric circuit by which varying current in it produces a varying magnetic field which causes voltages in the same circuit or in a nearby circuit.
Inductance (L) (mH - millihenries line-to-line)
The electrical equivalent to mechanical inertia; that is, the property of a circuit, which has a tendency to resist current flow when no current is flowing, and when current is flowing has a tendency to maintain that current flow. Electromate® measures inductance (line-to-line) with a bridge at 1000 Hz and with the rotor positioned so the back-EMF waveform is at the peak of the sinusoid.
Inductance (mutual)
Mutual inductance is the property that exists between two current carrying conductors or coils when magnetic lines of force from one link with those of the other.
Inductance (self)
The self-inductance of a coil is the constant by which the time rate of change of the current in the coil must be multiplied to give the self-induced counter EMF.
The property of an object to resist change in velocity unless acted upon by an outside force. Higher inertia objects require larger torques to accelerate and decelerate. Inertia is dependent upon the mass and shape of the object.
Inertia Match
An inertial match between motor and load is obtained by selecting the coupling ratio such that the load moment of inertia reflected to the motor shaft is equal to the motor moment of inertia.
Inertial match
For most efficient operation, the system coupling ratio should be selected so that the reflected inertia of the load is equal to the rotor inertia of the motor.
A signal that prevents the circuit from functioning.
Inrush Current
The current surge generated when a piece of equipment such as a servo amplifier is connected to an AC line. This surge is typically due to the impulse charging of a large capacitor located in the equipment.
Undesirable motion of an actuator that is different from the command motion. Instability can take the form or irregular speed or hunting of the final rest position.
Instantaneous Start-Stop Rate
The maximum switching rate at which an unloaded step motor can run without losing synchronism, or missing steps from a stanstill, or stop without taking more steps than pulses.
Insulation Class
The rating assigned to the maximum temperature capability of the insulating components in a motor or other piece of equipment.
Intermittent Duty Zone
The RMS torque applied over a period of time that is not greater than the rated torque. The peak torque should not exceed the intermittent duty zone.
Intermittent-Duty Rating
The output rating of a device operated for a limited interval rather than continuously.
Internet Protocol, the transport protocol used on the Internet and many private networks.
IP Security Architecture, a proposed Internet standard for providing security services at the IP layer level. Some early implementations exist, for example in Cisco routers.
Integrated Services Digital Network
International Standards Organization
Information Solutions Practice; Internet Service Provider; Interoperable System Project
Intelligent Transportation Systems


No terms available.


kilobps, one thousand bps
An authentication protocol employing "tickets" generated with private key encryption to authorize transactions between a user and a remote server.
An authentication protocol employing "tickets" generated with private key encryption to authorize transactions between a user and a remote server.


Layer 2 Tunneling Protocol, an emerging standard for "tunneling" a variety of protocols across an IP connection. It is being forged as a compromise between Cisco's Layer 2 Forwarding (L2F) and Microsoft's (et al) PPTP.
The steel portion of the rotor and stator cores make up a series of thin laminations (sheets) which are stacked and fastened together by cleats, rivets or welds. Laminations are used instead of a solid piece in order to reduce eddy-current losses.
Local area network
The linear distance a nut on a leadscrew will travel with one revolution of the leadscrew.
Lead Ball Screw
A lead screw which has its threads formed as a ball bearing race; the carriage contains a circulating supply of balls for increased efficiency.
Lead Screw
A device for translating rotary motion into linear motion, consisting of an externally threaded screw and an internally threaded carriage (nut).
Lead Screw Pitch
The number of full rotations required to advanced a nut by 1" inch. lead is reciprocal to pitch. Metric screws are specified by lead only.
Least Significant Bit
The bit in a binary number that is the least important, or having the least weight.
The life of an actuator as a function of load and stroke length.
Limit Switch
A sensor, typically hall effect, optical, eddy current, or mechanical, which is used to sense the end of travel of a linear motion assembly. In addition to preventing over travel, it is frequently used to establish a precision reference. A sensor that signals the control to do something when a preset location is reached.
Motion control systems may have sensors called limits that alert the control electronics that the physical end of travel is being approached and that motion should stop.
laboratory information management system
Line Shaft
A shaft rotated by the primary motor drive. The line shaft transmits power from the motor to a load or series of loads. In the multiple load case, the loads are synchronized to one another because they are connected to the common shaft.
Linear Coordianted Move
A coordinated move where the path between endpoints is a line.
Linear Position Accuracy
The error between desired move and actual position achieved by a linear positioning components or stage system. The linear accuracy of components: motor accuracy, leadscrew accuracy, stage accuracy (Pitch and Yaw), and thermal expansion.
For a speed control system it is the maximum deviation between actual and set speed expressed as a percentage of set speed.
A device or mass to be moved or manipulated.
The burden imposed on a motor by the driven machine. It is often stated as the torque required to overcome the resistance of the machine it drives. Sometimes "load" is synonymous with "required power."
Load Angle - Dynamic
The angle between the loaded and unloaded position (theoretical zero) of the rotor at a given instant under otherwise identical conditions at a specified command pulse rate, mode of winding excitation and phase current.
Load Angle - Static
The angle between the magnetic axis of the stator and rotor magnetic fields with the motor driving a specified load.
Logic Ground
An electrical potential to which all control signals in a particular system are referenced.
Loop Gain, Open
the product of the forward path and feedback path gains.
Loop, Feedback Control
A control method that compares the input from a measurement device, such as an encoder or tachometer, to a desired parameter, such as a position or velocity and causes action to correct any detected error. Several types of loops can be used in combination (i.e. velocity and position together) for high performance requirements.
Loop, PIC (Proportional, Integral, and Derivative Loop)
Specialized very high performance control loop which gives superior response.
Loop, Position
A feedback control loop in which the controlled parameter is motor position.
Loop, Velocity
A feedback control loop in which the controlled parameters is mechanical veloctiy.
A motor converts electrical energy into a mechanical energy and in so doing, encounters losses. These losses are all the energy that is put into a motor and not transformed to usable power but are converted into heat causing the temperature of the windings and other motor parts to rise.


The quantity of matter that an object contains.
Master Slave Motion Control
A type of coordinated motion control where the master axis position is used to generate one or more slave axis position commands.
Matched Load
A load inertia equal to the driving element (motor rotor) inertia.
Maximum reversing Rate
The maximum pulse rate at which an unloaded step motor is able to reverse and remain in synchronism.
Maximum Slew Range
The maximum rate at which the step motor will run and remain in synchronism. This velocity is usually defined in the full step mode of 1.8 degree steps or as shaft speed in revolutions per second.
Megabps, one million bps
management consulting services
Mechanical Damper
A device of known inertia which attaches to the step motor shaft for damping step oscillations and preventing resonance's.
Mechanical time constant (tm) (Seconds)
In a simple first order system, the time required for the motor's speed to attain 63.2% of its final value for a fixed voltage level. Can be calculated from: where: J is inertia in lb-in./s2 R is resistance in ohms KT is torque constant in lb-in./amp. 8.87 is a conversion factor tM is calculated in seconds
A miniaturized computer system that executes instructions in a sequential manner. The sequential instructions form a control strategy for devices that may be connected to the system. The sequential instructions are loaded into microprocessor and can be easily changed or modified. Modern microprocessors are small electronic devices that execute a wide range of instructions at speeds as high as 1,000,000 instructions per second.
An electronic technique for increasing a step motor's position resolution and velocity smoothness by appropriately scaling the phase currents. Microstepping is also a technique used to reduce or eliminate the effects of system resonance at low speeds.
Mid-range instability
A phenomenon in which a step motor can fall out of synchronism due to a loss of torque at mid-range speeds. The torque loss is due to the interaction of the motor's electrical characteristics and the driver's electronics. Some drivers have circuitry to eliminate or reduce the effects of mid-range instability.
million instructions per second; a measure of computational speed
management information system; the suite of applications used by management to coordinate results from other subsystems such as LIMS and SCADA
mind-machine interface
maintenance management system
A protocol used for Modbus messaging in an Internet or Intranet environment.
Moment Load
Pitch, Roll, and Yaw.
Most Significant Bit
The bit in a binary number that is the most important or that has the most weight.
Motion Profile
A method of describing a move operation in terms of time, position, and velocity. Typically velocity is characterized as a function of time or distance which results in a triangular or trapezoidal profile.
A device that takes electrical energy and converts it into mechanical energy to turn a shaft.
Motor Constant
The ratio of the motor torque to motor input power.
Motor, AC
A device that converts electrical alternating current into mechanical energy. requires no commutation devices such as brushes. Normally operated off commercial AC power. Can be single or multiple phase.
Motor, AC Asynchronous or Induction
An AC motor in which speed is proportional to the frequency of the applied AC. Requires no magnets or field coil. Usually used for non-precise constant speed applications.
Motor, AC Synchronous
Another term for brushless DC motor.
Motor, DC
A device that converts electrical direct current into mechanical energy. It requires a commutating device, either brushes or electronic. Usually requires a source of DC power.
Motor, DC Brushless
A type of direct current motor that utilizes electronic commutation rather than brushes to transfer current.
Motor, DC Permanent Magnet
A motor utilizing permanent magnets to produce a magnetic field. Has linear torque speed characteristics.
Motor, DC Wound Field
A direct current utilizing a coil to produce a magnetic field. Usually used in high power applications where constant horsepower operation is desired.
Motor, Stepping
A specialized AC motor that allows discreter positioning without feedback. Normally used for non-critical, low power applications, since positional information is easily lost if acceleration or velocity limits are exceeded. Load variations can also cause loss of position. If encoders are used, these limitations can be overcome.
MOV: Metal Oxide Varistor
A device that suppresses the voltage transients occurring on an AC line.
Multi-axis Control System
Is a system designed to control more than one actuator. This type of controller allows the actuators to work independently or as a coordinated group to perform more complex tasks.
Multi-turn Encoder
A multi-turn encoder stores the number of rotations made by the shaft in non-volatile memory. See also Single-turn encoder.


NC, Numerical Control
Usually refers to any type of automated equipment or process used for contouring or positioning.
National Electric Code
Negative Feedback
The type of feedback's used in a closed loop system where the output value is inverted and combined with the input to be used to stabilize or improve system characteristics. The difference is used by the system to move the actuator in such a ways as to force the difference to zero.
NEMA - National Electrical Manufacturer's Association
Acronym for an organization which sets standards for motors and other industrial electrical equipment.
Neodymium iron boron
A type of rare-earth permanent magnet material.
network interface card; PCB that interfaces a computer to a network
National Institute of Government Planning
No Load Speed
Motor speed with not external load and full voltage applied.
Non-Volatile Memory
Information that is stored on a device that does not require continuous power to be maintained. Typically associated with an EEPROM (Electrically Erasable Programmable Memory) chip for memory storage.
NTC - Negative Temperature Coefficient
A negative temperature coefficient thermistor is used to detect and protect a motor winding from exceeding its maximum temperature rating. Resistance of the device decreases with an increase in temperature.


open database connectivity
operator interface; the hardware and software that shows an operator the state of a process
operator interface station; operational intercomm system
object linking and embedding; a way of combining information from different files
Object Oriented Programming
Open Collector (NPN)
An output signal which is provided by a transistor where the "open collector output" acts like a switch closure to ground when activated.
A system in which there is no feedback. Motor motion is expected to faithfully follow the input command. Stepping motor systems are an example of open-loop control.
Open-Loop Systems
A system where the command signal results in actuator movement but because the mvoement is not sensed, there is no way to correct the error. Open loop means no feedback.
Operator Interface
A device that allows the operator to communicate with a machine. This device typically has a keyboard or thumbwheel to enter instructions into the machine. It also has a display device that allows the machine to display messages.
Optical Encoder
A position or angular feedback device typically producing two pulse trains, phase shifted 90 degrees from each other providing positioning and directional information.
Optical Isolation
An interface circuit that transmits a signal with not direct electrical connection.
Optically Coupled
An interface circuit that transmits a signal with not direct electrical connection except for the logic ground.
Optically Isolated
A system or circuit that transmits signals with not direct electrical connection. Used to protectively isolate electrically noisy machine signals from the low-level control logic.
A method of sending a signal from one piece of equipment to another, which provides electrical isolation. Signals are transmitted optically.
Undesirable motion of an actuator that is different from the command motion. See Instability.
open system interconnection
Output Key
A key at the output end of the shaft that enbales connection to a compatible machine. The key is IEC 72 part 1 compatible.
Overload capacity
The ability of a drive to withstand currents above its continuous rating. It is defined by NEMA as 150% of the rated full-load current for "standard industrial DC motors" for one minute.
The amount that the parameter being controlled exceeds the desired value for a step input.
Overshoot (Permanent)
The amount the shaft of a step motor remains beyond the final commanded position.
Overshoot (Transient)
The maximum amount the shaft of a step motor rotates beyond the commanded position before coming to a stable rest.


process and instrumentation drawing/diagram
personal computer
printed circuit board
project delivery system
Peak Rating
Teh maximum value obtained over a complete cycle, usually intermittent within the system limits.
Peak torque (Tpk) (lb-in.)
The maximum torque a brushless motor can deliver for short periods of time. Operating PacTorq motors above the maximum torque value can cause demagnetization of the rare-earth magnets. This is an irreversible effect that will alter the motor characteristics and degrade performance. This is also known as peak current.
Not to be confused with system peak torque, which is often determined by
plifier peak current limitations, where peak current is typically two times continuous current.
Is a set of electrically excited stator poles, consisting of one or more pairs of oppositely polarized poles. Step motor manufacturers provide 4 lead motors with bifilar ratings and 6 or 8 lead motors with unifilar ratings.
Phase and Phase Angle
The separation in electrical degrees between any specified transitions of any two channels of an encoder.
Phase Angle Rotor-Stator
The angle of lag of the rotor to the axis of the stator magnetic field under load. The angle of lag between rotor and stator teeth under load.
Phase Margin
The difference between 180 degrees and the phase angle of a system at the frequency where the open loop gains is unity.
Phase-Locked Servo System
A hybrid control system in which the output of an optical tachometer is compared to a reference square wave signal to generate a system error signal proportional to both shaft velocity and positions errors.
PID (Proportinal-Intergral-Derivative)
An Acronym that describes the compensation structure that can be used in a closed-loop system.
The measurable distance between screw grooves or threads.
PLC (Programmable Logic Controller)
A programmable device which utilizes userdefined logic to control a bank of inputs and outputs which are interfaced to external devices.
PMDC Motor (Permanent Magnet Direct Current)
A motor comprising a wound iron-core armature and a permanent magnet stator. These brushed motors operate on DC power.
Point to Point Move
A multi-axis move from one point to another where each axis is controlled independently. (NO coordination between axis is required.)
A frequency at which the transfer function of a system goes to infinity.
Pole Pair, Electromechanical
The number of cycles of magnetic flux distribution in the air gap of a rotary electromechanical device.
Refers to the number of magnetic poles arranged on the rotor of the brushless motor. Unlike an AC motor, the number of poles has no direct relationship to the base speed of the motor.
Position Error
The difference between the present actuator (feedback) value and the desired position command for a position loop.
Position Feedback
Present actuator position is measured by a position transducer.
Plain Old Telephone System (see PSTN), a commonly used acronym for dial-up analog telephone lines.
  1. The rate at which work is done. In motion control, power is equal to torque multiplied by speed.
  2. The rate of doing work or expending energy. It may be written as: Power (watts) = force x distance/time. Expressed in electrical terms it is voltage x current = power (watts)
Power factor
Ratio of true power (kW) to apparent power (kVA).
Point-to-Point Tunneling Protocol, a standard developed jointly by Microsoft, U.S. Robotics, 3Com, and others, for tunneling PPP packets across IP connections. This protocol, incorporated into Windows NT, Windows 95/98, and other products, is now being merged with Cisco's Layer 2 Fowarding (L2F) into a new Internet standard called Layer 2 Tunneling Protocol (L2TP).
The compression of a bearing used to remove play with the anticipation of a load.
Primary Winding
The winding of a motor, transformer or other electrical device, which is connected to the power source.
Process Control
A term used to describe the control of machine or Manufacturing processes, especially in continuous production environments.
Programmable Logic Controller
An electronic device that scans on/off type inputs and controls on/off type outputs. The relationship between the input and outputs are logical statements that are programmable by the user.
Public Switched Telephone Network, typically refers to common dial-up telecommunications, often extended to include ISDN.
PTC - Positive Temperature Coefficient
A positive temperature coefficient thermistor is used to detect and protect a motor winding from exceeding its maximum temperature rating. Resistance of the device increases with an increase in temperature.
Pull In Step Rate
The (constant) maximum pulse rate at which the energized stepping motor will start driving a specified load without missing steps under specified drive conditions.
Pull In Torque
The maximum torque at which an energized stepping motor will start driving a specified load and run without losing steps, on application of a fixed pulse rate.
Pull Out Step Rate
The (constant) maximum pulse rate at which the energized stepping motor can run driving a specified load under specified drive conditions without losing steps.
Pull-out torque
The maximum friction load, at a particular inertial load, that can be applied to the shaft of a synchronous motor (running at constant speed) and not cause it to lose synchronism.
Pull-Up Torque
The minimum torque developed by an AC motor druing th period of acceleration from zero to the speed at which breadkown occurs. For motors, which do not have a definite breakdown torque, the pull-up torque is the minimum torque developed during the process of achieving rated speed.
Pulse rate
The frequency of the step pulses applied to a step motor driver. The pulse rate, multiplied by the resolution of the motor/driver combination (in steps per revolution), yields the rotational speed in revolutions per second.
Pulse Width Modulation (PWM)
  1. A PWM controller (amplifier) switches DC supply voltage on and off at fixed frequencies. The length of the on/off interval or voltage waveform is variable.
  2. Pulse width modulation (PWM), describes a switch-mode (as opposed to linear) control technique used in amplifiers and drivers to control motor voltage and current. PWM offers greatly improved efficiency compared to linear techniques.


Refers to signal characteristics of interfaces to positioning devices such as encoders or resolver's. Specifically, that property of position transducers that allows them to detect direction of motion using the phase relationship of two signal channels.


Rack & Pinion
A toothed bar (rack) which engages a gear (pinion) to convert rotary to linear motion.
redundant array of inexpensive devices; usually a group of similar devices such as disc drives that provide 100 percent back up and can survive failure of any single component without losing functionality
RAM (Ram Access Memory)
A memory chip that can be read from and written to. Used for temporary information storage. Data is lost after power loss.
The acceleration and deceleration of a motor. May also refer to the change in frequency of the applied step pulse train.
Rated Torque
The torque producing capacity of a motor at a given speed. This is the maximum continuous torque the motor can deliver to a load and is usually specified with a torque/speed curve.
RDC: Resolver-to-Digital Converter
An electronic component that converts the analogue signals from a resolver into a digital word representing angular position. R to D (Resolver to Digital) is sometimes used.
Reed Switch
A sealed, magnetically operated switch that, when positioned over a magnet, will provide a signal to the controls either by contact closure or contact release.
The action during motor braking, in which the motor acts as a generator and takes kinetic energy from the load, converts it to electrical energy, and returns it to the amplifier.
Regeneration Resistance
A resistive device which purpose is to shunt excess voltage developed during a motor being in a generation mode.
Relay Ladder Logic
This programming language expresses a program as a series of "coils" and "contacts", simulating the operation of electromechanical relays. The resultant program is the equivalent of a boolean equation, which is executed continuously in a combinatorial manner. The advantage of this language is the familiarity many electricians have with the simple operation of relays. Disadvantages include the complexity of large, cross-connected programs, and the difficulty of expressing such non-binary functions as motion control and analog I/O. An alternative technique now being widely used is State Language control.
The characteristic of a magnetic material which resists the flow of magnetic lines of force through it.
The degree to which a parameter such as position or velocity can be duplicated.
Repeatability (Bi-Directional)
The difference in the final position reached by moving away and then returning to a common point from both plus and minus directions. The error or non-repeatability is usually the sum of the backlash, hysteresis, and one unit of the system resolution.
Repeatability (Uni-Directional)
The ability of a system to repeat to a desired location, approaching that location from both plus and minus directions.
The degree of obstacle presented by a material to the flow of electric current is known as resistance and is measure to Ohms.
Resistance, Hot (RH)(Ohms line-to-line)
The motor's terminal resistance value specified at the hot winding temperature, which is at the motor's maximum rated temperature.
The smallest increment into which a parameter can be broken down. For example, a 1000 line encoder has a resolution of 1/1000 of a revolution.
An electromagnetic feedback device which converts angular shaft position into analog signals. These signals can be processed in various ways, such as with an RDC (resolver-to-digital converter) to produce digital position information. There are two basic types of resolvers; transmitter and receiver. A transmitter-type is designed for rotor primary excitation and stator secondary outputs. Position is determined by the ratio of the sine output amplitude to cosine output amplitude. A receiver-type is designed for stator primary excitations and rotor secondary output. Position is determined by the phase shift between the rotor output signal and one of the primary excitation signals.
Oscillatory behavior caused by mechanical limitations.
Restart torque
The maximum friction load, at a particular inertial load, that can be applied to the shaft of a synchronous motor without causing it to lose synchronism when accelerating to a constant speed from standstill.
Radio Frequency Interference.
Oscillation of a system following a sudden change in state.
reduced instruction set computer/chip
Rise Time
The time required for a signal to rise from 10% of its final value to 90% of its final value.
RMI (Remote Method Invocation)
A Java-based messaging protocol standard that can interrogate, change and control one or more CTC controllers.
RMI (Remote Method Invocation)
A Java-based messaging protocol standard that can interrogate, change and control one or more CTC controllers.
RMS (Root Mean Square)
The square root of the average of the squares of the values of a periodic quantity taken throughout one complete period.
RMS Current - Root Mean Square Current
In an intermittent duty cycle application, the RMS current is equal to the value of steady state current which would produce the equivalent motor heating over a period of time.
RMS Torque - Root Mean Square Torque.
In an intermittent duty cycle application, the RMS torque is equal to the value of steady state torque which would produce the equivalent motor heating over a period of time.
A re-programmable multifunctional manupulator designed to mvoe material, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks.
Robot Control
A computer-based motion control device to control the servo-axis motion of a robot.
ROM (Read Only Memory)
A memory chip that can be read but not altered.
The moving part of the motor, consisting of the shaft and magnets. These magnets are analogous to the field winding of a brush-type DC motor.
A device for intelligently switching traffic between multiple networks, based on a stored configuration and sophisticated routing software. Routers can switch traffic based on either MAC-level (OSI Layer 2) or Protocol-level (OSI Layer 3) addresses. These capabilities allow routers to perform security functions, as well as adaptive network reconfiguration
Revolutions Per Minute
RPM (Revolutions Per Minute)
The number of times per minute the shaft of the motor (machine) rotates. This is a function of design and the power supply.
A popular protocol for transmitting digital data over two lines in a bit-serial format. RS232C specifies signal levels, data formats, maximum transmission distances...etc.
A high speed, differential method of serial communication that allows for multiple network "drop", or "nodes", to share the transmit and receive lines. rS485 is commonly used in automation due to its extended range (4000 ft) and its outstanding noise immunity.
Remote terminal unit


Samarium Cobalt
A type of rare-earth permanent magnet material.
supervisory control and data acquisition [system]
SCR (Silicon Controlled Rectifier)
A semiconductor device which can be used to control motor power. Common SCR controls are used to control adjustable speeds of a PMDC motors. Motors designed for operation from the form factor produced by a full wave SCR control are called SCR rated motors and are usually rated at 90 Volts(DC) and 180 Volts(DC).
Secondary Winding
Winding which is not connected to the power source, but which carries current induced in it through its magnetic linkage with the primary winding.
Serial Port
A digital data communications port configured with a minimum number of signal lines. This is achieved by passing binary information signals as a timed series of "1"s and "0"s on a signal line.
A system consisting of several devices which continuously monitor actual information (position, velocity), compares those values to desired outcome and makes necessary corrections to minimize that difference.
Servo Amplifiers/Servo Drive
An electronic device which produces the winding current for a servo motor. The amplifier converts a low level control signal into a high voltage and current levels top produce torque in the motor.
Servo Motor
A DC motor in which position is achieved by precise linear or duty cycle control of motor current and accurate monitoring of an external feedback device. Converts electrical energy (winding current)into mechanical energy (torque).
Servo System
An automatic feedback control system for mechanical motion in which the controlled or output quantity is position, velocity, or acceleration. Servo systems are closed loop systems.
Settling time
The time required for a parameter to stop oscillating or ringing and reach its final value.
Shock loading
A load that produces extremely high peak torques for very short durations. This type of load is associated with conveyorized grinding, crushing and separation processes.
Shunt Regulator
A device located in a servo amplifier for controlling the regenerative energy that is generated when a motor brakes. This device dissipates the kinetic energy as heat.
Shunt Resistor
A device located in a servo amplifier for controlling regenerative energy generted when braking a motor. This device dissipates or "dumps" the kinetic energy as heat.
Single Point Ground
The common connection point for signal grounds in a control wiring environment.
Single-turn Encoder
A single-turn encoder cannot distinguish between one turn and the next without the aid of external circuitry. See also Multi-turn encoder.
In motion control, the portion of a move made at a constant non-zero velocity.
Slew Speed
The maximum velocity at which an encoder will be required to perform.
Switched Multi-Megabit Data System
SMTP (Simple Mail Transfer Protocol)
A standard protocol for transporting email messages between servers.
system network architecture
A "sniffer" is a program that is surreptitiously installed on a computer within a local network. The purpose of the program is to put the computer's network interface into "promiscuous mode" (yes, it's really called that), so that it will receive every packet that appears on the network. The sniffer creates a logfile on the computer's disk containing this network data, which may later be retrieved by the perpetrator and analyzed for information such as passwords or proprietary information
Simple Network Management Protocol
SOAP (Simple Object Access Protocol)
Based around XML, SOAP is a lightweight, cross-platform protocol for data exchange and control in a distributed environment. It can interrogate, change and control one or more CTC controllers.
Describes the linear or rotational velocity of a motor or other object in motion.
Speed Regulation
For a speed control systems, speed regulation is the variation in actual speed expressed as a percentage of set speed.
SPS (Steps-Per-Second)
A measure of velocity used with stepping motors.
SQL (Structured Query Language)
A standard interactive and programming language for getting information from and updating a database via queries. Queries take the form of a standard command language that lets you select, insert, update, or find out the location of data.
Stall Torque
The amount of torque developed with voltage applied and shaft locked, or not rotating. Also known as locked-rotor torque.
Starting Current
Amount of current drawn at the instant a motor is energized. Same as locked rotor current.
Starting Torque
The torque of twisting force delivered by a motor at the instant it is energized. Starting torque is often higher than rated running or full load torque.
State Languages
State languages are used primarily for expressing sequences of operations in the real world. Typically, these languages divide a program into a series of "states," or steps - the program executes wholly in one step until some transition event occurs which causes the program to move to a new step. As such, it represents a reasonable way to express the operation of machinery, which itself must transit through a series of mechanical states as it operates. Practical state languages used for automation must allow multitasking, whereby multiple threads of steps may be in operation at once.
Static Load
A load that is applied to a bearing while stationery.
The non-moving part of the motor. Specifically, it is the iron core with the wire winding in it that is pressed into the frame shell. The winding pattern determines the voltage constant of the motor.
The non-rotating part of a magnetic structure. In a motor the stator usually contains the mounting surface, bearings, and non-rotating windings or permanent magnets.
Step angle
The angular distance the shaft rotates upon receipt of a single step command.
Stepper Motor
Motor that receives electric pulses to command a move in discrete angular increments (steps). Through appropriate drive circuitry, controlling the rate and quantity of pulses will control the motor's velocity and position.
The ability to resist movement induced by an applied torque. Stiffness is often specified as a torque displacement curve, indicating the amount a motor shaft will rotate upon application of a known external force when stopped.
Straightness Of Travel
The deviation from ideal straight-line motion of a linear motion assembly. This can result from rotation around any of three perpendicular axes or translation in two linear axes.
A motor rotating at a speed corresponding correctly to the applied step pulse frequency is said to be in synchronism. Load torques in excess of the motor's capacity (rated torque) will cause a loss of synchronism. This condition is not damaging to a step motor.
The condition under which a motor runs at a speed which is directly related to the frequency of the power applied and is not dependent on other variables.


A device attached to a moving shaft that generates a voltage signal directly proportional to rotational speed. Tachometers are typically attached to the ouput shaft of DC or AC variable-speed motor requiring close speed regulation. The tachometer feeds its signal to a control which adjusts its output to the DC or AC motor accordingly.
A brushless, electromagnetic feedback transducer which produces an analog velocity feedback signal and commutation signals for a brushless servo motor. The tachsyn is functionally equivalent to hall sensors and a tachometer.
transmission control protocol/internet protocol
Totally Enclosed Fan Colled. A type of motor enclosure.
TENV - Totally Enclosed Non-Ventilated
Acronym describing a type of motor enclosure, which has no outside air going into it. It is cooled only by convection to the frame, which is usually finned.
Thermal protection
A thermal sensing device mounted to the motor to protect it from overheating. This is accomplished by disconnecting the motor phases from the drive in an over temperature condition.
Thermal resistance (Rth) (°C/watt)
An indication of how effectively a unit rids itself of heat; a measure of temperature rise per watts lost. In Pacific Scientific literature, it is the specified value from the motor windings to the ambient, under locked rotor conditions.
Thermal time constant (tth) (minutes)
The time required for a motor to attain 63.2% of its final temperature for a fixed power input.
Thermistor (Thermally Sensitive Resistor)
A semiconductor used to measure temperature that can be attached to an alarm or meter to detect motor overheating.
Thermocouple (Thermal Detection DEvice)
A temperature-detecting device made of two dissimilar metals, which generates a voltage as a function of temperature. Thermocouples can be attached to a meter or alarm to detect overheating of motor windings or bearings.
A temperature sensitive pilot duty device mounted on the interior of the motor to protect it from overheating.
Measurement of linear force. The total force required to move the load, including gravity, friction, and acceleration.
A measure of angular force which produces rotational motion. This force is defined by a linear force multiplied by a radius; e.g. lb-in. Torque is an important parameter of any motion control system. Formula: Torque (lb-ft.) = 5,250 x HP/RPM
Torque Constant (KT = lb-ft./A)
An expression of the relationship between input current and output torque. For each ampere of current, a fixed amount of torque is produced.
Torque Ripple
The cyclical variation of generated torque given by the products of motor angular velocity and number of commutator segments.
Torque-to-inertia ratio
Defined as the motor's holding torque divided by the inertia of its rotor. The higher the ratio, the higher a motor's maximum acceleration capability will be.
Any device that translates a physical parameter into an electrical parameter. Tachometers and encoders are examples of transducers.
Transfer Function
The ratio of the Laplace transforms of a system output signal and a system input signal.
A device which converts electrical power (alternating current) to electrical power of a different voltage. In this device, both primary and secondary windings are usually stationary and are wound on a common magnetic core.
Trapezoidal Profile
A motion profile in which the velocity vs. time profile resembles a trapezoid. Characterized by constant acceleration, constant velocity, and constant deceleration.
TTL (Transistor-Transistor-Logic)
Refers to a family of integrated circuit devices used for control. Typically using 5VDC logic threshold.


Underwriters Laboratory
Ultimate Winding Temperature
The maximum allowable temperature of a motor winding for a given class insulation.
Unipolar driver
A step motor driver configuration that uses a unipolar power supply and is capable of driving phase current in only one direction. The motor phase winding must be center tapped (6 or 8 lead) to operate with a unipolar driver. The center tap is used instead of providing the current reversal of a bipolar driver.


Variable Frequency drives
An electronic device used to control the speed of a standard AC induction motor. The device controls the speed by varying the frequency of the winding current used to drive the motor.
Vector Control
A method of obtaining servo type performance from an AC motor by controlling two components of motor current.
The change in position as a function of time. Velocity has both a magnitude and sign.
Viscous Damping (KDV) (lb-in./kRPM)
Inherent losses are present in all motors which result in lower torque delivered at the output shaft than developed at the rotor. Losses which are proportional to speed (i.e. speed dependent terms such as windage, friction, eddy current) are related through the motor's "viscous damping" constant, measured as the slope of the damping curve.
Difference in electrical potential between two points.
Voltage constant (KE) (V/kRPM peak, line-to-line)
May also be termed back-EMF constant. When a motor is operated, it generates a voltage proportional to speed, but opposing the applied voltage. The shape of the voltage waveform depends upon the specific motor design. For example, in a brushless motor, the waveshape may be trapezoidal or sinusoidal in nature. All Pacific Scientific brushless motor designs have a sinusoidal voltage constant. For a sine waveform, the voltage constant can be measured from line-to-neutral or line-to-line and expressed as a peak value or "RMS" value.
Voltage constant (or Back EMF Constant)
A number representing the relationship between Back EMF voltage and angular velocity. Typically expressed as V/KRPM.
Voltage Drop
Loss encountered across a circuit impedance from power source to applicable point (motor) caused by the resistance in conductor. Voltage drop across a resistor takes the form of heat released into the air at the point of resistance.
Virtual Private Network, a term typically used to refer to the creation of a protected network channel over public networking conduits such as the Internet. Technologies used to create VPNs include L2TP and PPTP.
Virtual Private Network, a term typically used to refer to the creation of a protected network channel over public networking conduits such as the Internet. Technologies used to create VPNs include L2TP and PPTP.


Wide-area network
One horsepower equals 746 watts.
Watts Loss
The amount of lost power due to inefficiencies of a device.
Force of gravity acting on a body. Determined by multiplying the mass of the object by the acceleration due to gravity.


XML (Extensible Markup Language)
A World Wide Web Consortium -(W3C) endorsed standard for document markup and data exchange. Highly user-configurable means of defining data and its structure.


No terms available.


No terms available.

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