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Acceleration/Deceleration The time rate of change in velocity; acceleration refers to an increase in velocity, while deceleration refers to a decrease in velocity. Generally expressed as radians/sec/sec. Board-mounted trimmer potentiometers let users adjust the time it takes for the motor to reach set speed.
Actuator A device that converts various forms of energy, when given an input, to rotating or linear mechanical motion such as a motor.
Air-Gap The area between the rotating and stationary members of an electric motor.
Alternating Current (AC) Electrical current flow, usually generated by the utilities at 60 Hz, which continuously reverses direction in the middle of its cycle. Mathematically, it follows a sine wave; it travels from zero, then reaches a maximum in one direction, decreases to zero, then reverses to reach a maximum in the opposite direction.
Ambient Temperature The temperature of the medium, usually air, around a device such as a motor or drive.
Ampere (AMP) The standard unit of electrical current, or rate of electron flow. A closed-loop electrical circuit with one volt of potential difference across one Ohm of resistance causes one ampere of current to flow.
Armature The armature is the rotating member of an electric motor. In brush-type DC motors, it consists of the main current carrying windings (conductors) in the rotor. The commutator switches the power supply to the armature windings to generate a magnetic field.
Back-Emf Also known as counter emf (cemf), it is the voltage produced across motor windings, due to the winding turns being cut by a magnetic field, during rotation of the motor. The back-emf is directly proportional to rotor velocity and opposite in polarity to the applied voltage. This static voltage arises from the generator action in a motor, even if the motor windings are not energized.
Backlash In a mechanical system, backlash is the relative motion between two devices, connected by a coupler, gear, screw, etc.
Bridge Rectifier A section of the DC drive that converts the AC power supply into a DC source.
Brushes The current conducting material, usually carbon or graphite, which rests directly on the commutator of brush-type DC motor. They transmit current from the power supply to the armature.  
Capacitor A device which holds electrical charge for a period of time, prevents the flow of direct current and allows the flow of alternating current. These components serve as filters in DC drives to provide a “cleaner” DC signal to the motor.
Chassis Open construction of a drive for mounting within a customer’s existing enclosure or control console.
Choke A filter device consisting of an inductor and a resistor. Although more expensive than a typical RC filter, they exhibit better performance.
Closed-loop A system that uses feedback information to regulate the output response. The output feeds back to a controller for comparison to the input command; any difference results in a corresponding change in the input command. Thus, the accuracy increases.
Cogging Cogging refers to shaft rotation occurring in jerks or increments rather than smooth continuous motion. The non-uniform (“jerky”) rotation results from the armature’s propensity to certain discrete angular positions. The interaction of the armature coils entering and leaving magnetic fields, produced by the field coils or permanent magnets, causes speed changes. The armature tends to speed up and slow down as it cuts through the fields during rotation. Cogging is very apparent at low speeds, and determines a motor’s speed range.
Commutator A device mounted on the armature shaft and consisting of a number of wedge shaped copper segments arranged around the shaft. These segments are insulated from the shaft and from each other. The motor brushes ride on the periphery of the commutator, and electrically connect and switch the armature coils to the power source.
Conductor Any material, such as copper or aluminum, which offers little resistance to the flow of electric current.
Current Limit (Torque Limit) This feature permits the operator to adjust the maximum current the motor can draw. This, in effect, limits the maximum torque the motor will produce.
Dynamic Braking A way of quickly stopping a motor by disconnecting the power source. The rotating motor then becomes a generator. When connected to a resistor, the energy of rotation is then dissipated as heat in the resistor.
Duty Cycle The ratio of operating time versus total cycle time of a motor. A motor has a continuous duty rating if it continues to operate for an indefinite amount of time and its normal operating temperature remains within the temperature limits of its insulation system. A motor has an intermittent duty rating if it never reaches a steady temperature, but is allowed to cool between operations.
Enclosure A description of the motor or drive housing. The selected enclosure depends on the application’s environment and heat generated by the device.
Filter An electrical device used to suppress electrical noise, or to improve the DC output to a DC motor.  
Flyback Diode This is a super fast recovery diode that snubs current and voltage spikes as a result of the fast transients that occur when IGBT, and MOSFETS are turned on and off quickly. Form Factor Form factor indicates how much AC component resides in the DC output from DC drives. Represented mathematically as the ratio of a signal’s root-mean square current value to its average current value. Any form factor value greater than one means that some of the current produces heat instead of torque.
Four-quadrant This term refers to a drive’s ability to control the velocity and torque of a motor in either direction of rotation. The direction of torque can be in the opposite direction of the velocity for applications requiring braking or deceleration. Single-quadrant drives, on the other hand, only produce torque and velocity in the same direction of rotation.
Frequency Frequency refers to how often a complete cycle occurs in a unit of time. Frequency is usually measured in cycles per second, or Hertz, where 1 cycle/second equals 1 Hz. The standard AC power supply in the USA is 60 Hz, while 50 Hz remains common in many other countries of the world.
Friction The resistance to motion between surfaces.
Fuse A device connected to an electrical circuit designed to melt and open the circuit in the event of excess current flow. Gearhead A mechanical device that converts speed and torque to values required by the application. Output torque increases, and output speed decreases proportionally to the gear ratio. Generator A machine that converts mechanical energy into electric energy.
Hall Effect Sensor These feedback devices, commonly used in brushless motors, provide information for the amplifier to electronically commutate the motor. The sensors generate commutation signals by sensing the position of a magnetized wheel on the rotor.
Horsepower The rate at which work is performed. It equals the speed multiplied by torque, and a constant, depending on the units selected.
Inductance A property of an electric circuit that represents its ability to resist changes in current flow.  
Inertia A function of the mass and shape of an object. The inertia represents the property of an object that resists a change in motion. An object’s inertia increases directly with an increase in the object’s mass; also, increasing inertia loads require more force to accelerate and decelerate them.
Inverter (Variable Frequency Drives) AC drive that varies the frequency and voltage applied to an AC motor to vary motor speed.
IR Compensation It varies the mount of voltage to the armature in response to current (load) changes. It is adjustable via aboard mounted trimmer potentiometer.
Isolated Gate Bipolar Transistor gate (IGBT) A power transistor with a gate similar to the base of BJT. The difference is that the gate is electrically insulated from the collector-emitter circuit. This allows high voltages and currents to be conducted.
Jogging This feature provides a means of momentarily moving the motor at a different speed (normally slower) from the normal operating speed. Operators access this function using a separate control input.
Load A term used to describe work require form a motor to drive equipment attached at the shaft. Usually defined in units of horsepower, or torque at a certain speed.
Mosfet A Metal-Oxide-Semiconductor-Field-Effect-Transistor is similar to standard field-effect transistors. MOSFETs can be a N or P type. They will or will not conduct from source to drain unless a voltage is applied to the gate of the MOSFET. They have turn-on and turn-off capability, as well as fast reaction times.
NEMA The acronym stands for the National Electrical Manufacturers Association. The agency provides specification standards for motors and drives.
Noise (EMI/RFI) Electrical disturbances that interfere with proper transmission of electrical signals. Noise can have adverse effects on the system performance.
Non-volatile Memory A memory storage system that maintains information during the loss of power. Ohm Unit of electrical resistance of a circuit in which a potential difference of one volt produces a current of one ampere.
Open-Collector An output signal, provided by a transistor, where the “open-collector output” acts like a switch closure to ground when activated.
Open-Loop A system that does not use feedback information to regulate performance.
Phase Lock Loop (PLL) Used for error correction, PLL refers to an external digital controller that monitors digital feedback proportional to velocity. It compares that to a known number of counts that should be seen within a specified time frame, and calculates error based on its feedback. Minarik uses Phase Lock Loop on digital front-ends such as the DLC Series.
PLC A programmable logic controller (PLC) uses programmed logic instructions to control banks of inputs and outputs which interface timed switch actuation to external electro-mechanical devices.  
 Plugging A method to provide quick stopping or reversing of a motor by applying partial or full reverse voltage on the motor terminals during operation. Not recommended for DC systems since the life of the motor and drive reduces, while permanent damage may result.
Proportional-Integral-Derivative The act of recognizing a velocity or position error in a system, and applying correction (or voltage change) to the system amplifier, thereby changing the motor’s speed or altering position. PID refers to a group of gain parameters that tune or optimize the response of a closed-loop system.
Poles The magnetic poles in an electric motor that result from connection and placement of the windings in the motor. Besides poles created by electricity, permanent magnets mounted in specific areas are poles with a constant orientation.
Potentiometer (Pot) A passive device (variable resistor) used to vary voltage between a minimum and maximum level. The standard speed pot is a 300° or single-turn. Operators control the speed of a motor from the potentiometer connected to a drive. Also, board-mounted trimmer pots allow users to make calibrations.
Rated Values The rated value of a parameter (voltage, temp, etc.) is the maximum value that the parameter can reach in an electric device operating continuously without undue degradation, loss of its basic properties, or safety hazards.
Regenerative Regenerative drives, often used interchangeably with four quadrant drives, applies to the regeneration of energy from the motor and drive, back to the power source. A motor generates when the load forces the motor to go faster than the drive has set. Four quadrant drives can prevent motors from over speeding. A four quadrant drive is regenerative when it puts the generated energy back into the source, like a battery or the AC line. Also, the energy could be dumped across a dynamic brake resistor or a dump resistor, as is the case in a non-regenerative, four quadrant drive.  
 Relay These electronic components control other devices in a circuit. A set of contacts, the switching mechanism, open or close when the relay’s magnetic coil becomes energized. Resistance The opposition to current flow through a conductor in a closed circuit.
Rotor The rotating assembly of a motor. Usually includes a shaft, fan and rotor core.
Silicon Controlled Rectifier (SCR) Also known as a thyristor, a SCR is basically a diode with an extra junction tied to a third leg, known as the gate between the cathode and anode. SCRs prevent current flow in either direction until the gate receives a voltage signal. After receiving this trigger signal, the SCR then becomes a diode. It remains on, regardless of what happens at the gate, until the zero crossing, at which point current cease to flow.
Servo A system consisting of an amplifier, actuator, and feedback element. Servos tend to control one or combination of the following variables: position, velocity and torque.  
 Speed Regulation Defined as the deviation in motor speed from No Load to Full Load; usually expressed as a percentage of base speed. Feedback devices, like a tachometer or digital closed loop control, provide increased regulation.
Stator The stationary part of a motor. A PM DC motor holds its magnets in the stator.
Surge Suppressors These devices, like a metal oxide varistor (MOV), suppress voltage transients that can occur on the AC line.
Tachometer Feedback A tachometer (tach) generates a voltage proportional to speed. Tachs provide a closed-loop system with excellent speed regulation.
Torque A rotational force equal to an equivalent linear force applied at a right angle to a radius of r.  
Torque-to-Inertia Ratio The rated motor torque divided by its rotor inertia. Helps determine a motor’s ability to accelerate loads.
Transformer A passive device that raises or lowers AC voltage by induction.
TTL (Transistor-Transistor Logic) A popular family of integrated circuit devices that operate from logic level voltages, 5 to 12 VDC.
Voltage Voltage is electric pressure. A volt is a unit of electromotive force which causes 1 Amp of current to flow through a 1 Ohm resistor.
Watts The power required to maintain one ampere of current at a pressure of one volt when the two components are in phase with each other. A unit of horsepower is equal to 746 watts.
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