Test Equipment Terms and Definitions

• Optical Terms
• RF Terms
• Communication Terms
• Bench Terms
• Mechanical Terms

Optical Terms

Term	Definition
Absolute Wavelength Accuracy	Absolute Wavelength Accuracy is the maximum difference between the actual wavelength and the displayed wavelength of the Optical Source. Wavelength is defined as wavelength in vacuum.
Amplified Spontaneous Emission Source (ASE)	ASE, a process where spontaneously emitted radiation (luminescence) is amplified. In lasers and particularly in high-gain erbium-doped amplifiers, amplified spontaneous emission is usually an unwanted effect. It tends to limit the gain achievable in a single stage of a fiber optic amplifier to the order of 40–50 dB.
Bandwidth	Bandwidth is the difference between the upper and lower frequencies in a contiguous set of frequencies within which a fiber optic component, link or network will operate.
Bit Error Ratio (BER)	Bit Error Ratio (BER) is the ratio of errors caused by the number of bits in a data stream that have been altered due to noise, interference, distoriton or bit synchronization errors.
Broadband Source (BBS)	A Broadband Source is a spectrally large source that emits a signal which contains a continuous range of frequencies with a broad optical bandwidth (usually 100 nm or more). Sometimes called a white light source, there are two different meanings of this term. Visible white light and a source which does not necessarily emit in the visible spectral region.
Chirp	A change in the optical frequency caused by direct modulation of the laser. A chirp is a signal in which the frequency increases ('up-chirp') or decreases ('down-chirp') with time. In some sources, the term chirp is used interchangeably with sweep signal.
Chromatic Dispersion	Chromatic Dispersion is a broadening of the input signal as it travels down the length of the fiber. Chromatic Dispersion results from a variation in propagation delay with wavelength, and is affected by fiber materials and dimensions.
Coherence	Coherence is the pattern and or relationships of waves due to phase properties.
Coherence Length	Average distance over which superimposed waves lose their phase relationships
Coherence Time	Average time for the wave train to lose its phase realtionships
dBm	Optical power referenced to 1 millimatt
Decibel (dB)	A unit of measurement of optical power which indicates relative power. A -10 dB means a reduction in power by 10 times, -20 dB means another 10 times or 100 times overall, -30 means another 10 times or 1000 times overall and so on.
Detector	A Detector is a signal conversion device that converts power from one form to another, such as from optical power to electrical power
Dynamic Range	In a transmission system, the ratio of the overload level to the noise level of the system, usually expressed in dB. Ratio of the highest to lowest detectable signal of a system, expressed in dB.
Extinction Ratio (ER)	Extinction Ratio is the ratio of two optical power levels, of a digital signal generated by an optical source, (example a laser diode), where P1 is the optical power level generated when the light source is "on," and P0 is the power level generated when the light source is "off." The extinction ratio may be expressed as a fraction, in dB, or as a percentage.
Fiber Bragg Grating (FBG)	A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by adding a periodic variation to the refractive index of the fiber core, which generates a wavelength specific dielectric mirror. A fiber Bragg grating can therefore be used as an inline optical filter to block certain wavelengths, or as a wavelength-specific reflector.
Flatness	Variation of insertion loss on the passband of an optical device.
Isolation	The extent to which optical power from one signal path is prevented from reaching another signal path.
Jitter	Jitter in technical terms is the deviation in or displacement of some aspect of the pulses in a high-frequency digital signal. Jitter is the time variation of a periodic signal in electronics and telecommunications, often in relation to a reference clock source. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of periodic signals. Jitter is a significant, and usually undesired, factor in the design of almost all communications links (e.g., USB, PCI-e, SATA, OC-48). In clock recovery applications it is called timing jitter.
Linearity	Linearity is the relative difference between the displayed power ratio, Dx/D0, and the actual (true) power ratio Px/P0 caused by changing the displayed power level from the reference level, D0, to an arbitrary displayed level, Dx.
Linewidth	Linewidth is the width of a spectral line in terms of wavelength, wave number and frequency.
Modulation	Modulation is the process by which the characteristic of one wave (the carrier) is modified by another. Adding information into pulses of light.
Multimode Fiber	Multimode Fiber has a large core (almost always 62.5 microns - a micron is one one millionth of a meter - but sometimes 50 microns) and is used with LED sources at wavelengths of 850 and 1300 nm for short distance, lower speed networks like LANs. Both multimode and singlemode fiber have an outside diameter of 125 microns - about 5 thousandths of an inch - just slightly larger than a human hair.
Nanometer (nm)	A unit of measure used to measure wavelength of light, meaning one one-billionth of a meter
Optical Power	Optical Power is usually measured in "dBm", or decibels referenced to one miliwatt of power. while loss is a relative reading, optical power is an absolute measurement, referenced to standards. You measure absolute power to test transmitters or receivers and relative power to test loss.
Optical Signal-to-noise Ratio (OSNR)	Optical Signal-to-noise ratio is the ratio between the signal power and the noise power in a given bandwidth. Most commonly a reference bandwidth of 0.1 nm is used. This bandwidth is independent from the modulation format, the frequency and the receiver. For instance a OSNR of 20dB/0.1nm could be given, even the signal of 40 GBit DPSK would not fit in this bandwidth. OSNR is measured with a Optical Spectrum Analyzer. It is generally measured at the wavelength of interest.
Polarization Dependent Loss (PDL)	Polarization Dependent Loss is the difference between the maximum and minimum values of loss due to the variation of the polarization states of light propagating through a device. PDL is expressed in decibels. Calculated by; PDL = 10 log10 (Ep/Es), where EP and ES are the measured diffraction efficiencies for P- and S-plane polarized incident light, respectively.
Polarization Extinction Ratio	Polarization Extinction Ratio is the ratio of optical power in the slow axis of the polarization maintaining fiber to optical power in the fast axis within a specified wavelength range.
Polarization Mode Dispersion (PMD)	Polarization mode dispersion (PMD) is a form of modal dispersion where two different polarizations of light in a waveguide, which normally travel at the same speed, travel at different speeds due to random imperfections and asymmetries, causing random spreading of optical pulses. It is he difference between the maximum and minimum values of loss typically measured in ps/km^1/2.
Power Flatness Over Modulation	When changing the wavelength and modulation frequency, and measuring the differences between actual and displayed power levels (in dB), the power flatness is ± half the span between the maximum and the minimum value of all differences.
Power Flatness Versus Wavelength	When changing the wavelength at constant power setting and recording the differences between actual and displayed power levels, the power flatness is ± half the span (in dB) between the maximum and the minimum of the measured power levels.
Power Linearity	When changing the power level and measuring the differences (in dB) between actual and displayed power levels, the power linearity is ± half the span (in dB) between the maximum and the minimum value of all differences.
Power Repeatability	Power Repeatability is the random uncertainty in reproducing the power level after changing and re-setting the power level. The power repeatability is ± half the span (in dB) between the highest and lowest actual power. Note: - The long-term power repeatability can be obtained by taken the power repeatability and power stability into account.
Refractive Index	The refractive index or index of refraction of a substance is a measure of the speed of light in that substance. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium. The velocity at which light travels in vacuum is a physical constant, and the fastest speed at which energy or information can be transferred. However, light travels slower through any given material, or medium, that is not vacuum.
Relative Intensity Noise (RIN)	Relative intensity noise (RIN), describes the instability in the power level of a laser. The noise term is important to describe lasers used in fiber-optic communication and LIDAR remote sensing. It is the square of the (spectrally resolved) RMS optical power amplitude divided by the measurement bandwidth and the square of the average optical power, expressed in dB/Hz.
Relative Wavelength Accuracy	When randomly changing the wavelength and measuring the differences between the actual and displayed wavelengths, the relative wavelength accuracy is ± half the span between the maximum and the minimum value of all differences.
Repeatability	Repeatability is the variation in a number of repeated measured quantities when measurement conditions are changed and restored. The value corresponds to half the spread between the minimum and maximum value measured.
Return Loss (RL)	Return Loss (RL) is the ratio of the incident power to the reflected power expressed in dB. RL = 10log (Pin/Pback)
Sidemode Suppression Ratio	Sidemode Suppression Ratio is the ratio of average signal power to the optical power of the highest sidemode within a distance from 0.1 to 6 GHz to the signal’s optical frequency, expressed in dB.
Singlemode fiber	Singlemode Fiber has a small core, only about 9 microns, and is used for telephony and CATV with laser sources at 1300 and 1550 nm. It can go very long distances at very high speeds. Both multimode and singlemode fiber have an outside diameter of 125 microns - about 5 thousandths of an inch - just slightly larger than a human hair.
Spectral Width	Spectral Width is the wavelength interval over which the magnitude of all spectral components is equal to or greater than a specified fraction of the magnitude of the component having the maximum value. In optical communications applications, the usual method of specifying spectral width is the full width at half maximum. This is the same convention used in bandwidth, defined as the frequency range where power drops by less than half (at most -3 dB).
Stability	Stability is the extent to which a specified property, characteristic, or parameter of a substance, device, or apparatus, such as a fiber optic transmission system, remains fixed with the passage of time or with varying environmental conditions.
Telecom Bands	Optical fiber communications typically operate in a wavelength region corresponding to one of the following Bands. O Band (original): 1260–1360 nm. E Band (extended): 1360–1460 nm. S Band (short wavelengths): 1460–1530 nm. C Band (conventional): 1530–1565 nm. L Band (long wavelengths): 1565–1625 nm. U Band (ultralong wavelengths): 1625–1675 nm
Total insertion loss	A measure of the loss of light within an optical component
Total Return loss	In an optical fiber, the loss that takes place at any discontinuity of refractive index, especially at an air-glass interface such as a fiber endface, at which a fraction of the optical signal is reflected back toward the source. RL = - 10log10 (Preflected/Preference)
Wavelength	Wavelength is a term for the color of light, usually expressed in nanometers (nm) or microns (m). In Fiber Optics the wavelenghts mostly used are in the infrared region where the light is invisible to the human eye.
Wavelength Repeatability	Wavelength Repeatability is the random uncertainty in reproducing a wavelength after detuning and re-setting the wavelength. The wavelength repeatability is ± half the span between the maximum and the minimum value of all actual values of these wavelengths. Example test condition: uninterrupted TLS output power, constant power level, temperature within operating temperature range, coherence control off, short time span. Note: NOTE The long-term wavelength repeatability can be obtained by taken the wavelength repeatability and wavelength stability into account.
Wavelength Resolution	Wavelength Resolution is the smallest possible displayed wavelength increment/decrement.
Wavelength Stability	Wavelength Stability is the change of wavelength during given time span, expressed as ± half the span between the maximum and the minimum of all actual wavelengths.

RF Terms

Term	Definition
Adjacent Channel Power	Adjacent Channel Power is the power from a modulated communications channel that leaks into an adjacent channel. This leakage is usually specified as a ratio to the power in the main channel, but is sometimes an absolute power.
Available Gain	Available Gain is the ratio, at a specific frequency, of power available from the output to the power in from the source.
Average Power	Average power means that the energy transfer rate is to be averaged over many periods of the lowest frequency involved. For a CW signal, the lowest frequency and highest frequency are the same, so average power and power are the same. For an amplitude modulated wave, the power must be averaged over many periods of the modulation component of the signal as well.
Averaging	Averaging is a mathematical process to reduce the variation in a measurement by summing the data points from multiple measurements and dividing by the number of points summed.
Carrier Wave (CW)	Carrier Wave or Continuous Wave is a sinusoidal signal without modulation.
Channel Bandwidth	Channel Bandwidth is the bandwidth over which power is measured. This is usually the bandwidth in which almost all of the power of a signal is contained.
Clipping	Clipping is the limiting of a signal so that it never exceeds some threshold.
dBc	dBc (decibels relative to the carrier) is the power ratio of a signal to a carrier signal, expressed in decibels. If the dBc figure is positive, then the relative signal strength is greater than the carrier signal strength. If the dBc figure is negative, then the relative signal strength is less than carrier signal strength.
dBm	dBm (sometimes dBmW) is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW). Zero dBm equals one milliwatt. A 3 dB increase represents roughly doubling the power, a 3 dB decrease, the power is reduced by about one half.
Dynamic range	Dynamic range the ratio of a specified maximum level of a parameter, such as power, current, voltage or frequency, to the minimum detectable value of that parameter.
Fall Time	Fall time is the time required for the amplitude of a pulse to decrease (fall) from a specified value (usually 90 percent of the peak value exclusive of overshoot or undershoot) to another specified value (usually 10 percent of the maximum value exclusive of overshoot or undershoot).
Frequency Span	Frequency Span specifies the range between the start and stop frequencies, also referred to as bandwidth
Harmonic	A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc.
Jitter	Jitter in technical terms is the deviation in or displacement of some aspect of the pulses in a high-frequency digital signal. Jitter is the time variation of a periodic signal in electronics and telecommunications, often in relation to a reference clock source. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of periodic signals. Jitter is a significant, and usually undesired, factor in the design of almost all communications links (e.g., USB, PCI-e, SATA, OC-48). In clock recovery applications it is called timing jitter.
Millimeter-wave	Millimeter-wave is a term that generally refers to frequencies of 26.5 GHz and above. That is where signal wavelengths fall below approximately 10 mm, and thus the terminology changes from centimeters to millimeters.
Mismatch Uncertainty	Mismatch Uncertainty is caused by re-reflections between one device (the source) and the device that follows it (the load).
Modulation	Modulation is the coding of information onto the carrier frequency. This includes amplitude, frequency, or phase modulation techniques.
Noise Density	Noise Density is the amount of noise within a defined bandwidth, usually normalized to 1 Hz.
Noise Figure	Noise Figure the ratio of the signal-to-noise power ratio at the input to the signal-to-noise power ratio at the output.
Noise Floor	Noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system.
Overshoot	Overshoot is the distortion that follows a major transition; the difference between the peak power point and the pulse-top amplitude computed as a percentage of the pulse-top amplitude.
Peak Envelope Power	Peak envelope power is the maximum value of the envelope power. Envelope power is measured by making the averaging time much less than 1/fm where fm is the maximum frequency component of the modulation waveform. The averaging time is therefore limited on both ends: (1) it must be small compared to the period of the highest modulation frequency, and (2) it must be large enough to be many RF cycles long.
Phase Noise	Phase noise is the frequency domain representation of rapid, short-term, random fluctuations in the phase of a waveform, caused by time domain instabilities. Phase noise (L(f)) is typically expressed in units of dBc/Hz, representing the noise power relative to the carrier contained in a 1 Hz bandwidth centered at a certain offsets from the carrier.
Pulse Power	Pulse Power, the energy transfer rate is averaged over the pulse width. Pulse width is considered to be the time between the 50 percent risetime/falltime amplitude points. Pulse power averages out any aberrations in the pulse envelope such as overshoot or ringing.
Resolution Bandwidth (RBW)	Resolution Bandwidth (RBW) is the minimum bandwidth over which you can separate two signals and still see them.
Rise Time	Rise time refers to the time required for a signal to change from a specified low value to a specified high value, usually 10 and 90 percent of pulse-top amplitude (vertical display is linear power).
Sensitivity	Sensitivity is the smallest signal that can reliably detected. Sensitivity specifies the strength of the smallest signal at the input that causes the output signal power to be M times the output noise power where M must be specified. M=1 is very popular
Spurious Signals	Spurious signals are undesired signals. They can be considered in two classes. They can be stationary; their frequency and amplitude do not change significantly, or non-stationary, where the frequency and/or amplitude change significantly over short time periods.
Standing Wave Ratio (SWR)	Standing wave ratio (SWR) is the ratio of the amplitude of a partial standing wave at an antinode (maximum) to the amplitude at an adjacent node (minimum).
White Noise	White noise is noise whose power spectral density (watts/hertz) is constant for the frequency range of interest.

Communication Terms

Term	Definition
Accuracy	Accuracy is the degree of closeness of measurements of a quantity to that quantity's actual (true) value.
ATM	Asynchronous Transfer Mode (ATM) is a switching technique for telecommunication networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from networks such as the Internet or Ethernet LANs that use variable sized packets or frames.
Bandwidth	Bandwidth is the difference between the upper and lower frequencies in a contiguous set of frequencies within which a fiber optic component, link or network will operate.
Bit Error Ratio (BER)	Bit Error Ratio (BER) is the ratio of errors caused by the number of bits in a data stream that have been altered due to noise, interference, distoriton or bit synchronization errors.
Chirp	A change in the optical frequency caused by direct modulation of the laser. A chirp is a signal in which the frequency increases ('up-chirp') or decreases ('down-chirp') with time. In some sources, the term chirp is used interchangeably with sweep signal.
Data Rate	Data Rate is the maximum number of bits of information which can be transmitted per second, as in a data transmission link. Typically expressed as megabits per second (Mbps).
dBm	Optical power referenced to 1 millimatt
Decibel (dB)	A unit of measurement of optical power which indicates relative power. A -10 dB means a reduction in power by 10 times, -20 dB means another 10 times or 100 times overall, -30 means another 10 times or 1000 times overall and so on.
Dynamic Range	In a transmission system, the ratio of the overload level to the noise level of the system, usually expressed in dB. Ratio of the highest to lowest detectable signal of a system, expressed in dB.
Extinction Ratio	Extinction ratio is the ratio of two optical power levels, of a digital signal generated by an optical source, where P1 is the optical power level generated when the light source is "on," and P0 is the power level generated when the light source is "off." The extinction ratio may be expressed as a fraction, in dB, or as a percentage. Extinction ratio = P1/P0
Jitter	Jitter in technical terms is the deviation in or displacement of some aspect of the pulses in a high-frequency digital signal. Jitter is the time variation of a periodic signal in electronics and telecommunications, often in relation to a reference clock source. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of periodic signals. Jitter is a significant, and usually undesired, factor in the design of almost all communications links (e.g., USB, PCI-e, SATA, OC-48). In clock recovery applications it is called timing jitter.
Linearity	Linearity is the relative difference between the displayed power ratio, Dx/D0, and the actual (true) power ratio Px/P0 caused by changing the displayed power level from the reference level, D0, to an arbitrary displayed level, Dx.
Multimode Fiber	Multimode Fiber has a large core (almost always 62.5 microns - a micron is one one millionth of a meter - but sometimes 50 microns) and is used with LED sources at wavelengths of 850 and 1300 nm for short distance, lower speed networks like LANs. Both multimode and singlemode fiber have an outside diameter of 125 microns - about 5 thousandths of an inch - just slightly larger than a human hair.
Multiplexing	Multiplexing (also known as muxing) is a method by which multiple analog message signals or digital data streams are combined into one signal over a shared medium. Multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred.
Nanometer (nm)	A unit of measure used to measure wavelength of light, meaning one one-billionth of a meter
Optical Signal-to-noise Ratio (OSNR)	Optical Signal-to-noise ratio is the ratio between the signal power and the noise power in a given bandwidth. Most commonly a reference bandwidth of 0.1 nm is used. This bandwidth is independent from the modulation format, the frequency and the receiver. For instance a OSNR of 20dB/0.1nm could be given, even the signal of 40 GBit DPSK would not fit in this bandwidth. OSNR is measured with a Optical Spectrum Analyzer. It is generally measured at the wavelength of interest.
Optical Time Domain Reflectometer (OTDR)	Optical Time Domain Reflectometer (OTDR) is a device for characterizing a fiber wherein an optical pulse is transmitted through the fiber and the resulting backscatter and reflections to the input are measured as a function of time. Useful in estimating attenuation coefficient as a function of distance and identifying defects and other localized losses.
PDH	Plesiochronous Digital Hierarchy (PDH) is a transmission system for voice communication using plesiochronous synchronisation. The transmitter adds dummy information bits to allow multiple channels to be bit interleaved. The receiver discards these bits once the signals have been demultiplexed. PDH combines multiple 2 Mb/s (E1) channels in Europe and 1.544 Mb/s (DS1) channels in the US and Japan.
POS	Packet over SONET/SDH (POS), is a communications protocol for transmitting packets in the form of the Point to Point Protocol (PPP) over SDH or SONET, which are both standard protocols for communicating digital information using lasers or light emitting diodes (LEDs) over optical fibre at high line rates.
Receiver	A receiver is a detector and electronic circuitry to change optical signals into electrical signals.
Receiver Sensitivity	Receiver Sensitivity is the optical power required by a receiver for low error signal transmission. In the case of digital signal transmission, the mean optical power is usually quoted in Watts or dBm (decibels referred to 1 milliwatt).
Return Loss (RL)	Return Loss (RL) is the ratio of the incident power to the reflected power expressed in dB. RL = 10log (Pin/Pback)
SDH	Synchronous Digital Hierarchy (SDH) is an international digital telecommunications network hierarchy which standardises transmission around the bit rate of 51.84 megabits per second, which is also called STS-1. Multiples of this bit rate comprise higher bit rate streams. Thus STS-3 is 3 times STS-1, STS-12 is 12 times STS-1, and so on. STS-3 is the lowest bit rate expected to carry ATM traffic, and is also referred to as STM-1 (Synchronous Transport Module-Level 1). The SDH specifies how payload data is framed and transported synchronously across optical fibre transmission links without requiring all the links and nodes to have the same synchronized clock for data transmission and recovery.
Sensitivity	Sensitivity is the minimum magnitude of input signal required to produce a specified output signal having a specified signal-to-noise ratio, or other specified criteria.
Singlemode Fiber	Singlemode Fiber has a small core, only about 9 microns, and is used for telephony and CATV with laser sources at 1300 and 1550 nm. It can go very long distances at very high speeds. Both multimode and singlemode fiber have an outside diameter of 125 microns - about 5 thousandths of an inch - just slightly larger than a human hair.
SONET	Synchronous Optical NETwork (SONET) is a fiber-optic transmission system for high-speed digital traffic. Employed by telephone companies and common carriers, speeds range from 51 Mbps to 40 Gbps. SONET is an intelligent system that provides advanced network management and a standard optical interface. Specified in the Broadband ISDN (B-ISDN) standard, SONET backbones are widely used to aggregate T1 and T3 lines. The European counterpart to SONET is the Synchronous Digital Hierarchy, and the term "SONET/SDH" is widely used when referring to SONET
Spectral Width	Spectral Width is the wavelength interval over which the magnitude of all spectral components is equal to or greater than a specified fraction of the magnitude of the component having the maximum value. In optical communications applications, the usual method of specifying spectral width is the full width at half maximum. This is the same convention used in bandwidth, defined as the frequency range where power drops by less than half (at most -3 dB).
Synchronous Transport Module (STM)	STM-1 (Synchronous Transport Module level-1) is the SDH ITU-T fiber optic network transmission standard. It has a bit rate of 155.52 Mbit/s. Other levels are STM-4, STM-16 and STM-64.
TDMA: Time Division Multiple Access	Time Division Multiple Access (TDMA) is a method of sharing a communications carrier by assigning separate time slots to individual users. A channel is defined by a carrier frequency and time slot.
Telecom Bands	Optical fiber communications typically operate in a wavelength region corresponding to one of the following Bands. O Band (original): 1260–1360 nm. E Band (extended): 1360–1460 nm. S Band (short wavelengths): 1460–1530 nm. C Band (conventional): 1530–1565 nm. L Band (long wavelengths): 1565–1625 nm. U Band (ultralong wavelengths): 1625–1675 nm

Bench Terms

Term	Definition
Available Gain	Available Gain is the ratio, at a specific frequency, of power available from the output to the power in from the source.
Average Power	Average power means that the energy transfer rate is to be averaged over many periods of the lowest frequency involved. For a CW signal, the lowest frequency and highest frequency are the same, so average power and power are the same. For an amplitude modulated wave, the power must be averaged over many periods of the modulation component of the signal as well.
Averaging	Averaging is a mathematical process to reduce the variation in a measurement by summing the data points from multiple measurements and dividing by the number of points summed.
Bandwidth	Bandwidth is the difference between the upper and lower frequencies in a contiguous set of frequencies within which a component, link or network will operate.
Carrier Wave (CW)	Carrier Wave or Continuous Wave is a sinusoidal signal without modulation.
Channel Bandwidth	Channel Bandwidth is the bandwidth over which power is measured. This is usually the bandwidth in which almost all of the power of a signal is contained.
Clipping	Clipping is the limiting of a signal so that it never exceeds some threshold.
Crest Factor	Crest factor or peak-to-average ratio (PAR) is a measurement of a waveform, calculated from the peak amplitude of the waveform divided by the RMS value of the waveform
dBc	dBc (decibels relative to the carrier) is the power ratio of a signal to a carrier signal, expressed in decibels. If the dBc figure is positive, then the relative signal strength is greater than the carrier signal strength. If the dBc figure is negative, then the relative signal strength is less than carrier signal strength.
dBm	dBm (sometimes dBmW) is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW). Zero dBm equals one milliwatt. A 3 dB increase represents roughly doubling the power, a 3 dB decrease, the power is reduced by about one half.
Decibel (dB)	A unit of measurement of power which indicates relative power. A -10 dB means a reduction in power by 10 times, -20 dB means another 10 times or 100 times overall, -30 means another 10 times or 1000 times overall and so on.
Dynamic range	Dynamic range the ratio of a specified maximum level of a parameter, such as power, current, voltage or frequency, to the minimum detectable value of that parameter.
Fall Time	Fall time is the time required for the amplitude of a pulse to decrease (fall) from a specified value (usually 90 percent of the peak value exclusive of overshoot or undershoot) to another specified value (usually 10 percent of the maximum value exclusive of overshoot or undershoot).
Frequency Span	Frequency Span specifies the range between the start and stop frequencies, also referred to as bandwidth
Harmonic	A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc.
Jitter	Jitter in technical terms is the deviation in or displacement of some aspect of the pulses in a high-frequency digital signal. Jitter is the time variation of a periodic signal in electronics and telecommunications, often in relation to a reference clock source. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of periodic signals. Jitter is a significant, and usually undesired, factor in the design of almost all communications links (e.g., USB, PCI-e, SATA, OC-48). In clock recovery applications it is called timing jitter.
Line Regulation	Line regulation is the capability to maintain a constant output voltage level on the output channel of a power supply despite changes to the input voltage level.
Linearity	Linearity is the relative difference between the displayed power ratio, Dx/D0, and the actual (true) power ratio Px/P0 caused by changing the displayed power level from the reference level, D0, to an arbitrary displayed level, Dx.
Load Regulation	Load regulation is the capability to maintain a constant voltage (or current) level on the output channel of a power supply despite changes in the supply's load (such as a change in resistance value connected across the supply output).
Millimeter-wave	Millimeter-wave is a term that generally refers to frequencies of 26.5 GHz and above. That is where signal wavelengths fall below approximately 10 mm, and thus the terminology changes from centimeters to millimeters.
Mismatch Uncertainty	Mismatch Uncertainty is caused by re-reflections between one device (the source) and the device that follows it (the load).
Modulation	Modulation is the process by which the characteristic of one wave (the carrier) is modified by another.
Noise Density	Noise Density is the amount of noise within a defined bandwidth, usually normalized to 1 Hz.
Noise Figure	Noise Figure the ratio of the signal-to-noise power ratio at the input to the signal-to-noise power ratio at the output.
Noise Floor	Noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system.
Overshoot	Overshoot is the distortion that follows a major transition; the difference between the peak power point and the pulse-top amplitude computed as a percentage of the pulse-top amplitude.
Peak Envelope Power	Peak envelope power is the maximum value of the envelope power. Envelope power is measured by making the averaging time much less than 1/fm where fm is the maximum frequency component of the modulation waveform. The averaging time is therefore limited on both ends: (1) it must be small compared to the period of the highest modulation frequency, and (2) it must be large enough to be many RF cycles long.
Phase Noise	Phase noise is the frequency domain representation of rapid, short-term, random fluctuations in the phase of a waveform, caused by time domain instabilities. Phase noise (L(f)) is typically expressed in units of dBc/Hz, representing the noise power relative to the carrier contained in a 1 Hz bandwidth centered at a certain offsets from the carrier.
Power Linearity	When changing the power level and measuring the differences (in dB) between actual and displayed power levels, the power linearity is ± half the span (in dB) between the maximum and the minimum value of all differences.
Power Repeatability	Power Repeatability is the random uncertainty in reproducing the power level after changing and re-setting the power level. The power repeatability is ± half the span (in dB) between the highest and lowest actual power. Note: - The long-term power repeatability can be obtained by taken the power repeatability and power stability into account.
Pulse Power	Pulse Power, the energy transfer rate is averaged over the pulse width. Pulse width is considered to be the time between the 50 percent risetime/falltime amplitude points. Pulse power averages out any aberrations in the pulse envelope such as overshoot or ringing.
Repeatability	Repeatability is the variation in a number of repeated measured quantities when measurement conditions are changed and restored. The value corresponds to half the spread between the minimum and maximum value measured.
Resolution Bandwidth (RBW)	Resolution Bandwidth (RBW) is the minimum bandwidth over which you can separate two signals and still see them.
Ringing	Ringing is an unwanted oscillation of a voltage or current.
Ripple	Ripple is the small unwanted residual periodic variation of the direct current (dc) output
Rise Time	Rise time refers to the time required for a signal to change from a specified low value to a specified high value, usually 10 and 90 percent of pulse-top amplitude (vertical display is linear power).
RMS	RMS or root mean square is a statistical measure of the magnitude of a varying quantity
Sensitivity	Sensitivity is the minimum magnitude of input signal required to produce a specified output signal having a specified signal-to-noise ratio, or other specified criteria.
Settling Time	Settling time of an output device is the time elapsed from the application of an ideal instantaneous step input to the time at which the amplifier output has entered and remained within a specified error band, usually symmetrical about the final value.
Stability	Stability is the extent to which a specified property, characteristic, or parameter of a substance, device, or apparatus, remains fixed with the passage of time or with varying environmental conditions.

Mechanical Terms

Term	Definition
Accuracy	The accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual (true) value.
Balance	A balance is a measuring instrument for determining the weight or mass of an object. In its traditional form, it consists of a pivoted horizontal lever with arms of equal length arms.
Ball Micrometer	Ball micrometers have ball-shaped (spherical) anvils. They may have one flat and one ball anvil, in which case they are used for measuring tube wall thickness, distance of a hole to an edge, and other distances where one anvil must be placed against a rounded surface.
Beam Type	Beam type is the simplest form of torque wrench consists of a long lever arm between the handle and the wrench head, made of a material which bends elastically in response to applied torque. The deflection at the handle is proportional to the applied torque and material constants of the cantilever arm.
Click Type	Click type is an advanced method of presetting torque with a calibrated clutch mechanism. At the point where the desired torque is reached, the clutch slips, signaling the desired torque and preventing additional tightening.
Compression	Compression is the application of balanced inward ("pushing") forces to different points on a material or structure, that is, forces with no net sum or torque directed so as to reduce its size in one or more directions.
Deflection	Deflection is the degree to which a structural element is displaced under a load. It may refer to an angle or a distance.
Force Gauge	A force gauge (also force gage) is a small measuring instrument used across all industries to measure the force during a push or pull test.
Friction	Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.
ft-lb	Foot-pound is a measurment of torque expressed as a force (pound) multiplied by (i.e. “times”) a distance (foot). It is the amount of force applied in the direction of turning by one pound on a one foot lever. To convert Foot-pound (ft-lb) to Inch-ounce multiply by 192. To convert Foot-pound (ft-lb) to Inch-pound multiply by 12.
Gauge Block	A gauge block is a metal or ceramic block that has been precision ground and lapped to a specific thickness. Gauge blocks come in sets of blocks with a range of standard lengths. In use, the blocks are stacked to make up a desired length.
in-lb	Inch-pound is a measurment of torque expressed as a force (pound) multiplied by (i.e. “times”) a distance (inch). It is the amount of force applied in the direction of turning by one pound on a one inch lever. To convert Inch-pound to Inch-ounce multiply by 16. To convert Inch-pound to Foot-pound (ft-lb) multiply by 0.0833.
in-oz	Inch-ounce is a measurment of torque expressed as a force (ounce) multiplied by (i.e. “times”) a distance (inch). It is the amount of force applied in the direction of turning by one ounce on a one inch lever. To convert Inch-ounce to Inch-pound multiply by 0.0625. To convert Inch-ounce to Foot-pound (ft-lb) multiply by 0.0052.
Lever	A lever is a machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum. A lever amplifies an input force to provide a greater output force, which is said to provide leverage. The ratio of the output force to the input force is theideal mechanical advantage of the lever.
Load Cell	A load cell is a transducer that is used to create an electrical signal whose magnitude is directly proportional to the force being measured. The various types of load cells include hydraulic load cells, pneumatic load cells and strain gauge load cells.
Optical Comparator	An optical comparator is a device that applies the principles of optics to the inspection of manufactured parts. In a comparator, the magnified silhouette of a part is projected upon the screen, and the dimensions and geometry of the part are measured against prescribed limits.
Piezometer	A piezometer is either a device used to measure static liquid pressure in a system by measuring the height to which a column of the liquid rises against gravity, or a device which measures the pressure of groundwater at a specific point.
Precision	The precision of a measurement system, related to reproducibility and repeatability, is the degree to which repeated measurements under unchanged conditions show the same results.
Pressure	Pressure is force per unit area applied in a direction perpendicular to the surface of an object.
Resolution	The resolution of a sensor/ instrument is the smallest change it can detect in the quantity that it is measuring. Often in a digital display, the least significant digit will fluctuate, indicating that changes of that magnitude are only just resolved
Significant Figures	The significant figures of a number are those digits that carry meaning contributing to its precision.
Snap Gauge	A snap gauge has four anvils or jaws, the first one or pair (outermost) are set using the upper limit (tolerance) of the part and the inner set adjusted to the lower limit of the part. A correctly machined part will pass the first set of jaws and stop at the second, the end of test.
Strain	A strain is a normalized measure of deformation representing the displacement between particles in the body relative to a reference length.
Strain Gauge	A strain gauge is a device used to measure strain on an object. The most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate. As the object is deformed, the foil is deformed, causing its electrical resistance to change.
Stress	Stress is a physical quantity that expresses the internal forces that neighbouring particles of a continuous material exert on each other.
Tension	Tension is the pulling force exerted by each end of a string, cable, chain, or similar one-dimensional continuous object, or by each end of a rod, truss member, or similar three dimensional object
Thermal Expansion	Thermal expansion is the tendency of matter to change in volume in response to a change in temperature, through heat transfer.
Torque	Torque is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist to an object. Mathematically, torque is defined as the cross product of the lever-arm distance vector and the force vector, which tends to produce rotation.
Transducer	A transducer is a device that converts a signal in one form of energy to another form of energy.
Vernier Scale	A vernier scale is a device that lets the user measure more precisely than could be done unaided when reading a uniformly-divided straight or circular measurement scale. It is scale that indicates where the measurement lies in between two of the marks on the main scale.

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