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Electrical Engineering Terms Glossary

AC Signal: The time variant portion of a voltage or current.

Alternate Sweep: A vertical mode of operation for a dual-trace oscilloscope. The signal from the second channel is displayed after the signal from the first channel. Each trace has a complete trace, and the display continues to alternate. This mode is used for SEC/DIV settings of less than 1 ms/div (faster than 1 kHz).

Alternating Current (AC): An electric current whose instantaneous value and direction change periodically. The term usually refers to sinusoidally shaped current or voltage waves.

Amplitude: Height of a waveform above ground (1/2 peak-peak value)

Attenuation: The decrease in signal amplitude during its transmission from one point to another.

Bandwidth: The oscilloscope frequency range within which performance of a particular characteristic falls within specified limits, commonly defined as the difference between the upper and lower frequency at which the response is .707 (-3dB) of the response at the reference frequency.

Blanking: The process of making the trace, or parts of a trace, invisible.

Bypass: A capacitor placed from a dc signal to ground will remove any ac component of the signal by creating an ac short circuit to ground.

Calibration: The process of comparing an instrument or device against a standard to determine instrument accuracy or to make a correction.

Capacitance: The property of a system of conductors to and dielectrics which enables the system to store electricity when a voltage is applied between the conductors, expressed as a ratio of the electrical charge stored and the voltage across the conductors. The basic unit is the Farad .

Capacitor: A device consisting of two conducting materials separated by an insulating material (dielectric), which can store an electrical charge when a potential difference exists between the two conductors.

Cathode-ray-tube: An electron-beam tube in which the beam can be focused to a small cross-section on a luminescent screen and varied in both position and intensity to produce a visible pattern.

Chop: A vertical mode of operation for dual-trace oscilloscopes in which the display is switched between the two channels at some fixed rate. This mode should be used for slow sweep rates.

Common: The potential level serving as ground for the entire circuit.

Comparator: A component which satisfies, for input Vin and reference voltage Vr the equations

if Vin > Vr then Vout = Vcc.
if Vin < Vr then Vout = -Vcc.

Compensation: The controlling elements that compensate, or, offset the undesirable characteristics of the process being controlled in a system.

Coupling: The association of two or more circuits or systems in such a way that power or information may be transferred from one to the other.

Crosstalk: "Leakage" of signal from one source into another.

Current: The rate of change of charge (electrons) or flow of charge/second (dQ/dt) through a circuit.

Detent: A stop or other device (such as a pin or lever) on a ratchet wheel. Switch action is typified by a gradual increase in force to a position at which there is an immediate and marked reduction in force.

Diode: The diode is the simplest and most fundamental non-linear circuit element. It is a two terminal device which only allows current to flow in one direction.

Direct Current (DC): An electric current that flows in only one direction with essentially constant value.

Display: The visual representation of a signal on a CRT screen.

Distortion: An undesired change in waveform.

Dual Channel (Dual-trace) Oscilloscope: An oscilloscope that has two independent input connectors and vertical sections and can display them simultaneously.

Dual-sweep (Dual-timebase) Oscilloscope: An oscilloscope that can display a signal with two independent SEC/DIV settings.

Duty Cycle: The ratio of the lengths of the positive to negative halves of a waveform expressed in percentages.

Farad" Unit of measure of capacitance. Named after Farad.

Feedbac: Voltage from the output of a circuit is channeled (or "fed") back into the input of the circuit.

Focus: The oscilloscope control that converges the CRT electron beams to produce a sharp display.

Free-running Trace: A trace that is displayed without being triggered and either with or without an applied signal.

Frequency: The inverse of time (1/seconds). How often an event occurs within a second.

Graticule: The CRT grid lines that facilitate the location and measurement of oscilloscope traces.

Ground: 1. A conducting connection that by which an electric circuit or equipment is connected to the earth to establish and maintain a reference potential level. 2. The voltage reference point in a circuit.

Hertz: Unit of frequency, one cycle per second.

Hysteresis: An output voltage Vcc does not change to -Vcc until the input increases above B*Vcc, B being a constant value. Conversely, -Vcc does not change to Vcc until the input decreases below -B*Vcc.

Impedance: The total apparent opposition a circuit offers to the flow of alternating current in an electrical circuit.

Inductance: The voltage across an inductor is directly proportional to the rate of change of the current through it divided by the rate of change of time (difference current/difference time = di/dt). The proportionality constant which makes this true is L, the inductance of the inductor component. It is denoted by L and its units are the Henry (H). Therefore, the voltage v across an inductor is given by v = L*(di/dt).

Inductor: Circuit element which is a conductor wrapped into a coil to create a magnetic field.

LED: Light Emitting Diode, emits light when current is passed through it.

Megahertz (MHz): A frequency of one-million Hertz, or 106 cycles per second.

Microphone (Condenser): An electromechanical transducer that converts sound pressure into an electrical signal. Condenser mics require power to charge a capacitor used to sense changes in sound pressure levels (SPL).

Noise: An unwanted voltage or curent in an electrical circuit.

Oscilloscope: An instrument for making visible the instantaneous values of one or more rapidly varying electrical quantities as a function of time or of another electrical or mechanical quantity.

Period: Duration between repetitions of a waveform cycle. (1/frequency).

Potentiometer: A three terminal device with a wiper that is positioned along a resistive element; effectively making a voltage divider.

Probe: An oscilloscope input device, usually having a pointed metal tip for making electrical contact with a circuit element and a flexible cable for transmitting the signal to the oscilloscope.

Rise Time: The time taken for the leading edge of a pulse to rise from 10% to 90% of its final value.

Resistance: A measurement of the impedence of a substance to charge movement.

Schmitt Trigger: A circuit devised of an op-amp configured as a comparator and given a positive feedback. The Schmitt trigger employs hysteresis in order to create a switching voltage which is less susceptible to noise than a straight switch.

Scope: Short for oscilloscope.

Screen: The surface of the CRT upon which the visible pattern is produced; the display area.

Sensitivity: The ratio of the output value to the input value.

Short Circuit: Include a wire or other component into a circuit which effectively nullifies a component of that circuit, or leaves the voltage across the component unchanged in its AC or DC signal.

Signal: A visual, audible, electrical or other indication used to convey information.

Single Sweep: The ability of an oscilloscope to display just one window of time, thus preventing unwanted multiple displays. Useful for trace photography.

Slope: The ratio of change in the vertical quantity (Y) to the change in the horizontal quantity (X).

Spot: The illuminated area that appears where the electron beam strikes the screen of a CRT.

Sweep: Time-dependent information created by the electron beam moving across a CRT screen.

Time Base: Oscilloscope circuitry that controls the time dependence for the sweep. Time dependence is set by the SEC/DIV control.

Trace: The visual representation of an individual signal on a CRT.

Transducer: A device that provides a usable output in response to a specific physical quantity, property, or condition which is measured.

Transient: A phenomenon caused by a sudden change in conditions that persist for relatively short time after the change.

Trigger: The signal used to initiate a sweep on an oscilloscope and determine the beginning point of the trace.

Trigger Holdoff: A front-panel control that inhibits the trigger circuit from looking for a trigger for some specified time after the end of the trace.

Trigger Level: The instantaneous level that a trigger source signal must reach before a sweep is initiated by the trigger circuit.

URL: Universal resource locator. This is the address of something on the web. Examples include http//ece.wpi.edu/~frontier, ftp//ftp.wpi.edu, mailtonatalie@wpi.edu.

Volt: The unit of electric potential difference that and electromotive force equal to the difference of potential between two points on a conductor carrying a constant one-ampere current when the power dissipated between these two points is equal to one watt.

Voltage: The difference in electric potential, expressed in volts, between two points.

Watt: The SI unit of power, it stands for 1 Joule/sec.

Waveform: Graphic representation of the variation of a quantity (such as volts) as a function of some variable, usually time.

X-Y: A graphic representation of the relationship of the X signal, which controls the horizontal position of the beam in time, and the Y signal, which controls the vertical position of the beam in time.

Z-axis: Refers to the signal in an oscilloscope that controls electron-beam brightness as the trace is formed.