Glossary 78 LIFETIME LIMITED WARRANTY. GREENLEE Phone: (International)

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1 A AC alternating current, or current that reverses direction at regular rate. When graphed, alternating current can appear as a series of curves, squares, or triangles. The shape of the graph is referred to as a wave or waveform. This term also identifies the voltage that drives such current (AC voltage) and the circuits through which alternating current flows (AC circuits) and other characteristics that pertain to alternating current. See cycle, frequency, hertz, and DC. AC Waveforms accuracy the degree to which an instrument correctly displays the measured value. ambient temperature the temperature of the surrounding air. ampere a measurement of current, often abbreviated amp. amplification the process of increasing the magnitude of a signal. amplitude the magnitude, or size, of a signal. analog data or information presented in a continuous form; changes in value over time. When graphed, may appear as a straight line or as a continuously changing curve. See digital. anode the positive pole of a device. See cathode. ANSI (American National Standards Institute) a national organization that identifies and responds to industrial and public standards needs. attenuation a loss of signal strength, or power, due to resistance or impedance; measured in db. autoranging the capability of a meter to automatically select the proper range for the selected measurement; a feature of most modern digital multimeters. See manual ranging. AWG (American Wire Gauge) a standardized system for sizing wires and cables; measurements are based on conductor diameter. B bandwidth a measure of the amount of information which can pass through a device per unit of time; measured in hertz. bar graph a display that conveys analog information; this type of display is the digital equivalent of the needle on an analog meter. BICSI (Building Industry Standard Consulting Service International) an industry association concerned with the design and installation of communication wiring systems. burden voltage in a current-measuring instrument, this is the voltage drop across the input terminals caused by internal shunt resistance; this characteristic is a potential source of error. An instrument with lower burden voltage has a lower potential for error than a similar instrument with higher burden voltage. bus a bundle or group of conductors; examples include ribbon cable or a grouping of copper traces on a circuit board. bus bar a large conductor, usually a length of solid copper, used to carry a large amount of current to various devices. C Canadian Standards Association (CSA) a Canadian organization, similar to UL in the United States, that tests products to ensure compliance with national standards. capacitance the ability of a component or circuit to hold an electrical charge; measured in farads. capacitor a component which consists of two conductors separated by an insulator, allowing it to temporarily hold an electrical charge. cathode the negative pole of a device. See anode. Certificate of Calibration a detailed report indicating values obtained against performance specifications. The calibration is performed using instruments traceable to NIST. Meters with Certificate of Calibration may be ordered through the Greenlee catalog. See NIST. Certificate of Conformance a printed certificate stating that the device conforms to listed specifications. circuit breaker a mechanical device that opens, or breaks, a circuit when an overload occurs. clamp-on a meter or accessory that closes around a conductor and makes noncontact measurements by sensing the magnetic field that surrounds the conductor. common mode voltages voltage that appears on both leads of a measuring instrument, which can cause digit rattle or offset. CMRR (Common Mode Rejection Ratio) a measure of the ability to filter out common mode voltages; CMRR is expressed in db. coil a winding of wire; examples include the wire wound around the armature of a motor and the wire that surrounds the core of a transformer. 78

2 conductance a measure of conductivity. conductivity the ability to allow current to flow; the inverse of resistance. contact thermometer a temperature-sensing device that requires physical contact to take a measurement. See noncontact thermometer. continuity refers to an uninterrupted path for current flow, or a closed circuit. diode an electrical component that allows current to travel in one direction only; usually used to control the flow of current. See LED. duty cycle the ratio that compares the amount of time an intermittent device is switched on to the amount of time it is switched off. This term also describes a continuous waveform the ratio that compares the amount of time the signal is high to the amount of time it is low. It is usually expressed as a percentage. copper loss loss of signal strength due to copper s resistance to current flow. E Square wave with a 50% duty cycle crest factor an AC term that refers to the ratio of a peak value to its corresponding RMS value; it is represented by the Greek letter χ. See RMS. current the flow of electrons in a circuit; measured in amperes, or amps. crosstalk a signal generated by one channel or circuit that interferes with the signal on another channel or circuit. Crosstalk is typically measured at the close end of the circuit (near-end crosstalk) or at the distant end (far-end crosstalk). cycle concerning electricity, this is one iteration of a regular repeated signal, such as AC voltage. See AC, frequency, and hertz. D One cycle each of a sine wave, square wave, and sawtooth wave db (decibels) the ratio between two quantities of power; this is a common measurement for gain or loss in telecom and audio applications. The db scale is not linear, but logarithmic an increase in three db represents a doubling of power. dbm a decibel measurement with a reference in milliwatts. DC direct current, or current that travels in one direction only. When graphed, DC current appears as a straight line. This term also identifies the voltage that drives such current (DC voltage) and the circuits through which direct current flows (DC circuits) and other characteristics that pertain to direct current. See AC. digital data or information presented in discrete segments; changes in value over time. When graphed, appears as a jagged curve (a series of steps). See analog. digital multimeter (DMM) a test instrument with a digital readout that measures and displays a variety of characteristics or properties (such as voltage, current, frequency, temperature, etc.). electromagnetic interference (EMI) unwanted signals that emanate from electric, electronic, and magnetic devices. F farad the unit of measure for capacitance. far-end crosstalk (FEXT) crosstalk measured at the distant end of a telecom circuit. See crosstalk and near-end crosstalk. fixed resistor a resistor with a fixed value. See resistor. full scale the maximum measurement to which an accuracy specification applies. fuse a device that opens a circuit and stops the flow of current when an overload condition occurs. frequency an AC term which measures the number of cycles per second, or hertz. Line voltage in the United States is 60 cycles per second, or 60 hertz. See AC. frequency response the frequency range within which an instrument can carry out measurement functions at the specified accuracy. G GFCI tester a device that intentionally disturbs the current flow through a GFCI. See ground fault circuit interrupter. ground a return path for current flowing in a circuit; also known as common, since a single conductor can provide the return path for many components or devices. In a power distribution network, this path is literally the earth. ground conductor an extra conductor intended to provide a low-resistance current path in case of a malfunction. ground fault an inadvertent connection to ground. 79

3 ground fault circuit interrupter (GFCI) a receptacle with an extremely fast circuit breaker built in; it monitors the difference between line current and neutral current. When line current exceeds the neutral current by a predetermined margin, the GFCI opens the circuit to stop the flow of current. Also known as a ground fault interrupter (GFI). H Hall effect a technology that allows accurate measurement of DC current with a clamp-on ammeter. See clamp-on. harmonic a signal with a frequency that is some multiple of the fundamental frequency. Harmonics can damage or degrade the performance of many electrical and electronic devices. harmonic distortion an increasingly common form of power corruption caused by nonlinear load devices, such as variable speed motor drives, computers, and lighting ballasts. headroom the extra capacity, or margin, by which a telecom system exceeds the minimum requirements; expressed in db. hertz the unit of measure of frequency; the technical term for cycles per second. See AC. I impedance total opposition to current flow in an AC circuit; includes resistance, capacitance, and reactance. interference unwanted signals that disrupt or degrade normal signal transmission. L LED (light-emitting diode) a semiconductor device that illuminates when current is flowing through it. Unlike a standard diode, an LED is usually used to indicate the flow of current. See diode. line filter a device that filters out electrical interference; prevents signals from motors and other devices from spreading throughout a circuit and disturbing other devices. liquid crystal display (LCD) an efficient, high-contrast readout; commonly used in DMMs and other test instruments. mechanical relay a device that uses a varying electrical input to open and close a set of mechanical contacts; an electromagnetic switch. See solid-state relay. megohmmeter a test instrument that evaluates the integrity of insulation by measuring the insulation s resistance. multimedia communication of information by multiple methods or formats. multimeter a test instrument that measures and displays a variety of characteristics or properties. multimode optical fiber optical fiber cable in which light travels in many bound modes. multiplexing a process of combining several communication channels so that the information can be transmitted over a single circuit; such methods include time division and frequency division. N near-end crosstalk (NEXT) crosstalk measured at the near end of a telecom circuit. See crosstalk and far-end crosstalk. network the interconnected pathways that allow communication among many computers and peripheral devices. neutral conductor a conductor that provides the normal return path for current in a power distribution system. NIST (National Institute of Standards and Technology) a federal agency that works with industry to develop measurements and standards. noise jargon for interference. noise rejection the ability to reject unwanted signals (noise). noncontact thermometer a temperature-sensing device that does not require physical contact to take a measurement; it senses infrared radiation to determine surface temperature. A noncontact thermometer can be a self-contained unit or an accessory that connects to a digital multimeter. See contact thermometer. nonsinusoidal wave an electrical signal that is not a pure sine wave; such signals include square wave and sawtooth wave. load any device that consumes power in a circuit. Square Wave Sawtooth Wave M manual ranging a characteristic of some test instruments by which the user selects the measurement range. See autoranging. normal mode voltages AC signals that can cause inaccurate DC measurements. NMRR (Normal Mode Rejection Ratio) a measure of the ability to filter out normal mode voltages; NMRR is expressed in db. 80

4 O ohm a unit of electrical resistance. Ohm s law the simple mathematic formula that ties together voltage, resistance, and current; E = I x R. E stands for electromotive force (voltage), I stands for current, and R stands for resistance. For example, one volt will push one ampere of current through a resistance of one ohm. optical fiber a thin strand of glass or plastic used for carrying information encoded in light. P pair two color-coded wires in network cabling, usually twisted around each other to reduce interference. peak the point of maximum amplitude of a signal; can be either positive or negative. peak-to-peak value the difference measured between a positive peak and a negative peak. phase an AC term that describes the time relationship between voltage and current. If the circuit is purely resistive, voltage and current will peak at the same time; and they will be in phase. A capacitive or inductive circuit will cause the current to peak before or after the voltage, and they will be out of phase. Also refers to the time relationship between two or more voltages in a three-phase system. Three-Phase Voltage phase shift an AC term that describes the amount by which voltage and current are out of phase with each other. Typically measured at a peak or zero point of the wave, phase shift is measured in degrees. Voltage and Current Out of Phase polarity refers to the proper electrical connection of a device or component. For example, the positive and negative terminals of a battery are connected to the positive and negative terminals of a circuit, respectively. R range the domain of values, with specific upper and lower limits, over which a test instrument can take reliable measurements with specified accuracy. rectifier a device which converts AC current to DC current by allowing the current to flow in one direction only. Registered Communications Distribution Designer (RCDD) professional certification from BICSI. relative measurement the difference between a reference measurement and measurements that follow. For example, the relative measurement function of a DMM allows the user to easily subtract the resistance of the test leads from the resistance measurement of a device or circuit. resistance opposition to current flow, measured in ohms. See ohm and Ohm s law. resistor a device that limits the flow of current in a circuit. See ohm and Ohm s law. resolution the minimum incremental value a test instrument can measure and display. return loss a measurement of the noise or interference cause by the impedance of a cable; rendered in db. RMS (root mean squared) refers to some of the methods for displaying AC measurements. Two AC measurement methods common to DMMs are average responding RMS calibrated and true RMS reading. The average-responding RMS calibrated method takes the average value of the input signal, multiplies it by 1.11, and displays the result. This method is accurate if the input signal is a pure sine wave. The true RMS-reading method uses internal circuitry to read the true RMS value. This method is accurate, within the specified crest factor limitations, whether the input signal is a pure sine wave, a square wave, sawtooth wave, half wave, or signal with harmonics. The ability to read true RMS provides much more measurement versatility. The Waveforms and Crest Factors table shows some typical AC signals and their RMS values. Waveforms and Crest Factors Power Factor the ratio of True Power (expressed in watts) to Apparent Power (expressed in volt-amps) in an AC circuit. power sum a test method for four-pair cable that compares the sum of the pair-to-pair crosstalk from three pairs to the fourth pair. Waveform RMS Value Average Value Crest Factor * (χ) * The crest factor is the ratio of the peak value to the RMS value; it is represented by the Greek letter χ. 81

5 S sampling the process of making or displaying measurements at regular intervals. sampling rate the time interval at which sampling occurs; expressed as the number of samples per second. sine wave the shape of a perfect AC signal. When graphed, an undulating, regular wave. Because one revolution of an electrical generator produces one cycle of power, a sine wave is usually measured in degrees; one cycle equals 360 degrees. See AC, cycle and hertz. single-mode fiber optical fiber which permits only one mode to propagate. Generally used for long-distance telephone transmission. solid-state relay a relay with no moving parts; it has electronic switching devices instead of mechanical contacts. See mechanical relay. T temperature coefficient a factor or formula used to calculate the ambient temperature s effect on a test instrument s accuracy. thermocouple a device which converts heat into DC voltage; used to measure temperature. topology the physical configuration of a network. transformer a device that uses electromagnetism to increase or decrease an electrical property. transient voltage any temporary, unwanted voltage level. twisted pair see pair. U unshielded twisted pair (UTP) a twisted pair of copper conductors with no metallic braid shielding; used for networks which carry high-speed voice and data transmission. V volt the measurement unit of voltage. See Ohm s law. voltage also known as electromotive force, this is the electrical pressure that causes current to flow in a circuit; measured in volts. voltage dip a temporary decrease in voltage. voltage spike a temporary increase in voltage, usually of very short duration. voltage surge a temporary increase in voltage; usually of longer duration. volt tick a small, pen-like noncontact voltage detector. W watt a unit of measure for electrical power; in DC circuits or purely resistive AC circuits, power (in watts) is the product of volts multiplied by amps. 82