Definitions, Terms, Units and Parameters

C

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Calibration

: the process of measuring to determine the accuracy of your measurement chain. This result can then be used to offset measured values and take account of this inaccuracy.

Capacitor

: an electrical component that passes alternating currents but blocks direct currents. Also called a condenser, it is capable of storing electrical energy

Carpal Tunnel Syndrome

: pain, numbness and tingling sensation in the hands and fingers, see also hand arm vibration syndrome

CB : Critical Band

CCLD : Constant Current Line Drive

CE Marking

: a label to show an instrument conforms to the specification of a European Directive.

Centre Frequency

: the frequency in the middle of a band of frequencies, for example 1 kHz octave band.

centimetre : cm

: 0.01 metre

Centimetre-gram-second : CGS

: a system of measurement using the centimetre, the gram and the second as basic units of length, mass and time

See also the SI Units.

Charge Amplifier

: an amplifier with low input impedance whose output voltage is proportional to the output charge from a piezoelectric transducer. Has the advantage that the voltage output is not affected by length of connecting cable to the meter / analyser, and may also be normal screened cable not expensive accelerometer cable.

Charge Sensitivity

: the charge sensitivity of an accelerometer is independent of the cable length. The voltage sensitivity on the other hand is for the accelerometer when used with its standard length of cable.

To take into account different cable lengths or to convert from charge sensitivity to voltage sensitivity, divide the charge sensitivity by the total capacitance of the accelerometer and the cable, for example :-

a 1 pC/ms^-2 and 9.8 pC/g accelerometer with a capacitance of 900 pF and a 1.2 m cable (100 pF)

would give 1 pC / (900+100) pF = 1 mV/ms^-2

or 9.8 pC / (900+100) pF = 9.8 mV/g

by definition 1 g = 9.807 ms^-2 and conversely 10 ms^-2 = 1.01 g

Many accelerometers are supplied with a built-in preamplifier to transform the high impedance charge output to a low impedance voltage signal that can be transmitted over longer distances - see IEPE - Integrated Electronics Piezo Electric

CIC : Charge Injection Calibration

: is a technique patented by Bruel & Kjaer for on-line verification of the integrity of the entire measurement chain, for example, microphone, preamplifier and cabling. Manual CIC may be performed anytime a measurement is not running or automatically at the start and end of a logging measurement.

Class 1

: precision grade meters for laboratory and field use - also known as Type 1.

Class 2

: general grade meters for field use - also known as Type 2.

Classes

: Octave and third-octave filters used for sound level measurements are also required to meet Classes 0, 1 or 2.

Clipping

: an electrical signal is clipped if the signal level exceeds the capabilities of the amplifier. It is a distortion of the signal.

cm : centimetre

: 0.01 metre

CNEL : see Community Noise Equivalent Level below

Coherence

: is a number between one and zero, and is a measure of the degree of linearity between two related signals, such as the excitation force (input) of a structure related to the vibration response to that force (output).

Coincidence Effect

Coherent Output Power Spectrum

: a measure of what part of the (output) power spectrum is fully coherent with the input signal.

Community Noise Equivalent Level : CNEL

: the 24 hour average noise level of all hourly Leq measurements with a 10 dB penalty added to the levels between 2200 and 0700 hours and a 5 dB penalty added to the levels between 1900 and 2200 hours to reflect people's extra sensitivity to noise during the night and the evening.

Also known as Lden - Day-evening-night Noise Indicator

Condenser Microphones

: are widely used in noise measurements because they offer the best linearity, frequency range and high stability.

Because of their importance we have prepared more details Measurement Microphones

Constant Current Line Drive : CCLD

: with built-in electronics to transmit the output signal over 'long' cables. also known as IEPE

Constant Bandwidth Filter

: a filter with fixed frequency bandwidth, expressed in Hertz (Hz), regardless of centre frequency.

Constant Percentage Bandwidth Filter

: a filter whose bandwidth is a fixed percentage of centre frequency. The width of the individual filters is defined relative to their position in the range of interest. The higher the centre frequency of the filter, the wider the bandwidth. The bandwidth is defined in octaves or as a fixed percentage of the centre frequency of the filter.

Control of Noise at Work Regulations

: under the Noise at Work Regulations see also Noise Exposure and Noise Dose

Control of Vibration at Work Regulations

: under Vibration at Work Regulations .

see also the Aeq - acceleration equivalent value and Hand Arm Vibration Syndrome and Whole Body Vibration

Correlation

: measures the degree to which two time domain signals. The higher the correlation, the stronger the relationship between both signals. See also autocorrelation and cross-correlation.

Correlation Coefficient

: when the correlation is 1 or -1, a perfectly linear positive or negative relationship exists; when the correlation is 0, there is no relationship between the two sets of data.

Coulomb : C

: a coulomb is a unit of electrical charge, defined as the quantity of electrical charge transferred by 1 ampere in 1 second. Symbol C.

1 microcoulomb = 1 x 10^-6 C = 1 μC
1 picocoulomb = 1 x 10^-12 C = 1 pC.

CPB Filter see Constant Percentage Bandwidth Filter

Crest Factor

: the crest factor is peak amplitude of a waveform divided by the RMS value of the waveform. For example a sine wave has a crest factor of 1.414 or 3 dB. For a square wave the crest factor is 1.

Criterion Level

: is the maximum Leq sound level allowed for an 8-hour period and corresponds to the 100% noise dose value. Used for calculating Dose and ProjDose.

Critical Band

: the human ear combines sounds of similar frequency into frequency bands, called 'critical bands'. Zwicker divided the audio spectrum into 24 critical bands and named the units bark, see also loudness. The notion of critical bands explains the auditory masking of a narrow band (sinusoidal) signal by a wideband noise source. Critical Band Frequencies

Critical Frequency

Cross-correlation

: cross-correlation is a measure of the similarity of two time domain signals. If the signals are identical, the cross correlation will be one, and if they are completely dissimilar, the cross correlation will be zero.

Cross Power Spectrum

: measurement of two signals with an amplitude that is the product of the two signal amplitudes and a phase that is the difference of the two phases.

Cross-spectrum

: the cross-spectrum is the forward Fourier transform of the cross-correlation function. Generally, the cross-spectrum is a complex function.

Crosstalk

: the signal on one channel, track, or circuit interfering with another.

Ctr : under Sound Insulation.

cubic metre : m³

: volume.

cubic metre per kilogram : m³/kg

: specific volume.

cubic metre per second : m³/s

: volumetric flow.

Cumulative Distribution

: a method of representing time-varying noise by indicating the percentage of time that the noise level is present above (or below) a series of amplitude levels.

Cursor

: a thin hairline that can be positioned on a spectrum or time signal graphs to obtain a readout. Various types of cursor are available. For example, single cursor - a line, delta cursor - selects a band, harmonic cursor - marks a set of harmonics.

Cut-off Frequency

: the frequencies that mark the ends of a band, or the points at which the characteristics of a filter change from pass to no-pass.

Cycle

: the complete sequence of values of a periodic quantity that occurs during one period.

cycle per second : c/s.

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