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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. A..4 Appendix A A..4 Appendix A 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. Jump Frequency A jump frequency is a point on the inverter output frequency range that you want the inverter to skip around. This feature may be used to avoid a resonant frequency, and you can program up to three jump frequencies in the inverter. Line Reactor A three-phase inductor generally installed in the AC input circuit of an inverter to minimize harmonics and to limit short-circuit current. Momentum The physical property of a body in motion that causes it to remain in motion. In the case of motors, the rotor and attached load 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. The Hitachi inverters have 16 preset speeds. 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. NEC 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. Open-collector Outputs A common logic-type discrete output that uses an NPN transistor that acts as a switch to a power supply common, usually ground. The transistor’s collector is open for external connection (not connected internally). Thus, the output sinks external load current to ground. 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 setpoint (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. A..5 Appendix A A..5 Appendix A Process Variable A physical property of a process that 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 (pulsewidthmodulating), 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 that converts AC power into DC power. Rectifiers are usually used in combination with capacitors to filter (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 either store the energy internally, deliver the braking energy back to the main power input, or dissipate it with a resistor. 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 torque applied in the direction opposite to motor shaft rotation. 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 current no longer results in an increase in the output current. The saturation voltage is the vo...