Ambient Temperature The air temperature in the chamber in which a powered electronic unit resides. A unit's heat sinks rely on a lower ambient temperature in order to dissipate heat away from sensitive electronics.

Auto-tuning The ability of a controller to execute a procedure that interacts with a load to determine the proper coefficients to use in the control algorithm. Auto tuning is a common feature of process controllers with PID loops.

Base Frequency The power input frequency for which an AC induction motor is designed to operate. Most motors will specify a 50 to 60 Hz value. The Hitachi inverters have a programmable base frequency, so you must ensure that parameter matches the attached motor. The term base frequency helps differentiate it from the carrier frequency. See also carrier frequency and frequency setting.

Braking Resistor Some variable speed drives can cause the motor to develop decelerating torque by

switching motor wiring so the motor becomes a generator, connected to an energy-absorbing resistor. See also four -quadrant operation and dynamic braking.

Break-away Torque The torque a motor must produce to overcome the static friction of a load, in order to

start the load moving.

Brushes A sliding electrical connection between a xed post inside the motor housing and a ring on the motor shaft. Typically used in DC motors or low-cost AC motors, brushes route current to windings on the rotor. AC induction motors with a squirrel-cage design do not have the need for brushes. See also commutation and squirrel cage.

Carrier Frequency The frequency of the constant, periodic, switching waveform that the inverter modulates to generate the AC output to the motor. See also PWM.

CE A regulatory agency for governing the performance of electronic products in Europe. Drive installations designed to have C.E. approval must have particular filter(s) installed in the application.

Choke An inductor which is tuned to react at radio frequencies is called a choke, since it attenuates (chokes) frequencies above a particular threshold. Tuning is often accomplished by using a movable magnetic core. In variable-frequency drive systems, a choke positioned around high-current wiring can help attenuate harmful harmonics and protect equipment. See also harmonics.

DC Braking The inverter DC braking feature stops the AC commutation to the motor, and sends

a DC current through the motor windings in order to stop the motor. Also called "DC injection braking," it has little effect at high speed, and is used as the motor is nearing a stop.

Dead Band In a control system, the range of input change for which there is no perceptible change

in the output. In PID loops, the error term may have a dead band associated with it. Dead band may or may not be desirable; it depends on the needs of the application.

Digital Operator Panel For Hitachi inverters, "digital operator panel" (DOP) refers first to the operator keypad on the front panel of the inverter. It also includes hand-held remote keypads, which connect to the inverter via a cable. Finally, the DOP Plus is a PC-based software simulation of the keypad devices.

Diode A semiconductor device which has a voltage-current characteristic that allows current

to ow only in one direction, with negligible leakage current in the reverse direction.

See also rectifi er.

Duty Cycle 1. The percent of time a square wave of xed frequency is on (high) versus off (low).

2. The ratio of operating time of a motor, braking resistor, etc. to its resting time. This

parameter usually is speci ed 0 in association with the allowable thermal rise for the


Dynamic Braking The optional dynamic braking unit shunts the motor-generated EMF energy into a special braking resistor. The added dissipation (braking torque) is effective at higher speeds, having almost no effect as the motor nears a stop.

Error In process control, the error is the difference between the desired value or setpoint (SP) and the actual value of a the process variable (PV). See also process variable and PID Loop.

EMI Electromagnetic Interference – In motor/drive systems, the switching of high currents and voltages creates the possibility of generating radiated electrical noise that may interfere with the operation of nearby sensitive electrical instruments or devices. Certain aspects of an installation, such as long motor lead wire lengths, tend to increase the chance of EMI. .

Four-quadrant operation Referring to a graph of torque versus direction, a four-quadrant drive can turn the motor either forward or reverse, as well as decelerate in either direction (see also reverse torque). A load that has a relatively high inertia and must move in both directions and change directions rapidly requires four-quadrant capability from its drive.

Free-run Stop A method of stopping a motor, caused when the inverter simply turns off its motor output

connections. This may allow the motor and load to coast to a stop, or a mechanical brake may intervene and shorten the deceleration time.

Frequency Setting While frequency has a broad meaning in electronics, it typically refers to motor speed

for variable-frequency drives (inverters). This is because the output frequency of the inverter is variable, and is proportional to the attained motor speed. For example, a motor with a base frequency of 60 Hz can be speed controlled with an inverter output varying from 0 to 60 Hz. See also base frequency, carrier frequency, and slip.

Harmonics According to Fourier Series mathematics, a periodic (repeating) function (waveform) can be expressed as a the summation of a series of pure sine waves of related frequencies. The lowest frequency is the fundamental, while all the other wave components are called harmonics. The square waves used in inverters produce high-frequency harmonics, even though the main goal is to produce lower-frequency sine waves. These harmonics can be harmful to electronics (including motor windings) and cause radiated energy that interferes with nearby electronic devices. A choke is sometimes used to suppress the transmission of harmonics in an electrical system. See also choke.

Horsepower A unit of physical measure to quantify the amount of work done per unit of time. You can directly convert between horsepower and Watts as measurements of power.

IEEE 519 An industry standard which specifies allowable current and voltage distortion levels in an electrical distribution system. The current distortion levels are defined by the ratio of ISC / IL. Where ISC is the short circuit current available from the source transformer and IL is the maximum load demand current. The resulting ratio defines the allowable TDD total demand distortion which ranges from 5% to 20%. The standard also defines the maximum allowable voltage distortion limits defined as 3% for special applications and 5% for general systems.

IGBT Insulated Gate Bipolar Transistor (IGBT) –  a semiconductor transistor capable of conducting very large currents when in saturation and capable of withstanding very high voltages when it is off.

Inertia The natural resistance a stationary object to being moved by an external force. See also momentum.

Intelligent Terminal A configured input or output logic function on the Hitachi invert ers. Each terminal may be assigned one of several functions.

Inverter A device that electronically changes DC to AC current through a alternating process of switching the input to the output, inverted and non-inverted. A variable speed drive such as the Hitachi L100 is also called an inverter, since it contains three inverter circuits to generate 3-phase output to the motor.

Isolation Transformer A transformer with 1:1 voltage ratio that provides electrical isola tion between its primary and secondary windings. These are typically used on the power input side of the device to be protected. An isolation transformer can protect equipment from a ground fault or other malfunction of nearby equipment, as well as attenuate harmful harmonics and transients on the input power.

Jogging Operation Usually done manually, a jog command from an operator's panel requests the motor/

drive system to run indefinitely in a particular direction, until the machine operator ends

the jog operation.

Matrix Filter A passive lter used to mitigate harmonics on the line side of a drive system.

Momentum The physical property of a body in motion that causes it to continue to move in a straight

line. In the case of motors, the armature and shaft are rotating and possesses angular momentum.

Multi-speed Operation The ability of a motor drive to store preset discrete speed levels for the motor, and control motor speed according to the currently selected speed preset.

Motor Load In motor terminology, motor load consists of the inertia of the physical mass that is moved by the motor and the related friction from guiding mechanisms. See also inertia.

N.E.C The National Electric Code is a regulatory document that governs electrical power and device wiring and installation in the United States.

NEMA The National Electric Manufacturer's Association. NEMA Codes are a published series of device ratings standards. Industry uses these to evaluate or compare the performance of devices made by various manufacturers to a known standard.

Power Factor A ratio that expresses a phase difference (timing offset) between current and voltage

supplied by a power source to a load. A perfect power factor = 1.0 (no phase offset). Power factors less than one cause some energy loss in power transmission wiring (source to load).

PID Loop Proportional - Integral - Derivative – a mathematical model used for process control. A process controller maintains a process variable (PV) at a set point (SP) by using its PID algorithm to compensate for dynamic conditions and vary its output to drive the PV toward the desired value. For variable-frequency drives, the process variable is the motor speed. See also error.

Process Variable A physical property of a process which is of interest because it affects the quality of

the primary task accomplished by the process. For an industrial oven, temperature is the process variable. See also PID Loop and error.

PWM Pulse-width modulation: A type of AC adjustable frequency drive that accomplishes

frequency and voltage control at the output section (inverter) of the drive. The drive output voltage waveform is at a constant amplitude, and by "chopping" the waveform (pulse width-modulating), the average voltage is controlled. The chopping frequency is sometimes called the carrier frequency.

Reactance The impedance of inductors and capacitors has two components. The resistive part is constant, while the reactive part changes with applied frequency. These devices have a complex impedance (complex number), where the resistance is the real part and the reactance is the imaginary part.

Rectifier An electronic device made of one or more diodes which converts AC power into DC power. Rectifiers are usually used in combination with capacitors to lter (smooth) the rectified waveform to closely approximate a pure DC voltage source.

Regenerative Braking A particular method of generating reverse torque to a motor, an inverter will switch internally to allow the motor to become a generator and will store the energy internally and/or deliver the braking energy back to the power input mains.

Regulation The quality of control applied to maintain a parameter of interest at a desired value. Usually expressed as a percent (+/-) from the nominal, motor regulation usually refers to its shaft speed.

Reverse Torque The force of available from some types of inverters to change the direction of rotation

of a motor shaft. As such, reverse torque is a decelerating force on the motor and its external load.

Rotor The windings of a motor that rotate, being physically coupled to the motor shaft. See also stator

Saturation Voltage For a transistor semiconductor device, it is in saturation when an increase in input

(gate) current no longer results in an increase in the output (source/drain) current. The saturation voltage is the voltage from the power source to the transistor output (Vsource to Vdrain). The ideal saturation voltage is zero.

Sensorless Vector Control A technique used in variable-frequency drives to rotate the force vector in the motor without the use of a shaft position sensor (angular). Benefits include an increase in torque at the lowest speed and the cost savings from the lack of a shaft position sensor.

Setpoint (SP) The set point is the desired value of a process variable of interest. See also Process

Variable (PV) and PID Loop.

Single-phase An AC power source consisting of Hot and Neutral wires. An Earth Ground connection

usually accompanies them. In theory, the voltage potential on Neutral stays at or near Earth Ground, while Hot varies sinusoidally above and below Neutral. This power source is named Single Phase to differentiate it from three-phase power sources.

Slip The difference between the theoretical speed of a motor at no load (determined by its inverter output waveforms) and the actual speed. Some slip is essential in order to develop torque to the load, but too much will cause excessive heat in the motor windings and/or cause the motor to stall.

Squirrel Cage A "nickname" for the appearance of the rotor frame assembly for an AC induction motor.

Stator The windings in a motor that are stationary and coupled to the power input of the motor.

See also rotor.

Tachometer 1. A signal generator usually attached to the motor shaft for the purpose of providing

feedback to the speed controlling device of the motor. 2. A speed-monitoring test meter which may optically sense shaft rotation speed and display it on a read out.

Thermal Switch An electromechanical safety device that opens to stop current ow when the temperature

at the device reaches a specific temperature threshold. In variable-speed drive systems, thermal switches are typically installed at or near the motor, in order to protect the windings from heat damage.

Transistor A solid state, three-terminal device that provides amplification of signals and can be used for switching and control. While transistors have a linear operating range, inverters use them as high-powered switches. Recent developments in power semiconductors has produced transistors capable of handling hundreds of volts and tens of Amperes or more, all with high reliability. The saturation voltage has been decreasing, resulting in less heat dissipation. Hitachi inverters use state-of-the-art semiconductors to provide high performance and reliability, all in a compact package. See also IGBT and

saturation voltage.

Trip An event which causes the inverter to stop operation is called a "trip" event (as intripping a circuit breaker). The inverter keeps a history log of trip events. They also requirean action to clear.

Twelve Pulse A type of drive system consisting of a phase shift input transformer, (2) six-pulse diode

module front ends and an inverter section, used to control a motor and reduce input side line harmonics.