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Sound and Vibration Instrument Hire and Calibration

B&K 2250 BZ 7230 FFT - Fast Fourier Transform Specifications

To see the specifications for the various options available, click a link

Bruel & Kjaer Sound Level Meter
BZ 7222 : Sound Analysis Software
BZ 7223 : Frequency Analysis Software
BZ 7224 : Logging Software
BZ 7225 : Enhanced Logging Option
BZ 7226 : Sound Recording Software
BZ 7227 : Reverberation Time Option
BZ 7228 : Sound Insulation Option
BZ 7230 : FFT Analysis Option
BZ 7231 : Tone Assessment Option
B&K 2250 : Home Page
B&K 2250 : Specifications
B&K 2250 : Detailed Image
Bruel & Kjaer 2250 + FFT Narrow Band Software - BZ 7230 £ 36 a day *
Specifications for FFT analysis are given for the hand-held analyser with software BZ -7230 installed and fitted with one of the recommended transducers (see Table 2)

FFT Analysis

Sampling Frequency: Down sampling from 51.2 kHz
Frequency Span: 100 Hz, 200 Hz, 500 Hz, 1 kHz, 2 kHz, 5 kHz, 10 kHz, 20 kHz
Lines: 100, 200, 400, 800, 1600, 3200, 6400 ¹
Zoom Centre Frequency: Can be set so that the Frequency Span is placed in the range 0 to 20 kHz
Spectrum: Averaged and Maximum
Pre-weighting: Z (none), A, B or C

Measurement Control

Manual Start
Exponential Averaging: With an averaging time of up to 999 spectra, measured with Hanning window and 67% overlap
Linear Averaging: Up to 8388607 spectra measured with Hanning window and 67% overlap
Triggered Start
Transient Signal Type: Linear averaging of up to 32767 triggered spectra measured with rectangular window and 0% overlap
Continuous Signal Type: Linear averaging of up to 32767 spectra measured with Hanning window and 67% overlap. Up to 32767 spectra are averaged on each trigger.
Auto-start: A total of 10 timers allow set up of measurement start times up to a month in advance.
Each timer can be repeated.
Measurements are automatically stored when completed.


Delay: From 16383 samples before the trigger time to 300 seconds after
Hold Off: 0 to 300 s
Internal Trigger: Uses the time signal from the measurement transducer. The Internal Level is set in the relevant measurement units External Trigger: Uses the Trigger Input. The External Level is set in the range -18 to 18 V
Hysteresis (Only for External Trigger): 0 to 10 V
Slope (Only for External Trigger): Rising, Falling Pull-up (Only for External Trigger): For Type 2250 serial numbers above 2479653 the Trigger Input is pulled up to +5 V through a 7.5 k resistor when this parameter field is set to On
1. The actual number of lines is one more than stated, to provide symmetry around the centre frequency.

Measurement Range

(See Table 2)
The lower limit of the measurement range is influenced by self generated random noise and self-generated tones called spurious signals. The influence of the random part can be reduced to a level below the spurious signals by selecting a small analysis bandwidth (small span and many lines). Therefore, the lower limit is specified as the maximum Peak level of the spurious signal lines.
BZ-7230 has only one measuring range but the spurious level depends on the peak level of the signal. Therefore, two specifications are given. One for high levels, where the upper limit is the overload limit, and one for low levels.
The Typical Frequency Response shows the ±1 dB limits for Direct Input and microphones, and the ±10 % limits for accelerometers.

RPM Measurement

RPM is measured on the signal connected to Trigger input when Tacho is set to On
Range: 1 to 6000000 RPM
Instantaneous RPM: Instantaneous RPM is only displayed (and not stored)
Average RPM: Displayed and stored together with each Spectrum result. In Linear Averaging it is an average over the same time as the spectrum. In Exponential Averaging it is the last measured RPM
Gear Ratio: 10-5 to 1038. The displayed RPM's are the measured RPM's divided by the RPM Gear Ratio.


Instantaneous Overload: Displayed as an icon and indicated by the Traffic Light
Spectrum Overload: Displayed and stored with each Spectrum result

Display Spectra

Two spectra superimposed
Scaling: RMS, Peak, Peak-to-Peak, Power, PSD, ESD
Reference Spectrum: Compare spectrum to stored (measured) reference
Axis: Logarithmic and Linear Y-axis, Linear X-axis
X-axis: Display full frequency range or expand the X-axis until only 20 FFT lines are displayed. Scroll available
Y-axis Display Range: 5, 10, 20, 40, 60, 80, 100, 120, 140, 160, 180 or 200 dB. Auto-zoom or Auto-scale available
Digital Post-weighting: Z (none) or A-weighting

Display Parameters

Sound Pressure Level in dB

Table 2 Measurement ranges with the recommended transducers

Transducer Nominal Sensitivity Spurious Free Dynamic Range for High Levels Spurious Free Dynamic Range for Low Levels Typical Frequency Response Extended Low Frequency On Off
Direct Input1 V/V   3 µV - 14.1 V peak300 mV - 75 mV peak 1.5/6.3 Hz - 20 kHz
418950 mV/Pa10 dB - 143 dB peak-10 dB - 97.5 dB peak6.8/7.8 Hz - 20 kHz,
419112.5 mV/Pa22 dB - 155 dB peak2 dB - 109.5 dB peak3.6/6.6 Hz - 20 kHz
419312.5 mV/Pa22 dB - 155 dB peak2 dB - 109.5 dB peak0.56/6.3 Hz - 20 kHz
495050 mV/Pa10 dB - 155 dB peak-10 dB - 97.5 dB peak4.3/6.3 Hz - 19 kHz
495231.6 mV/Pa14 dB - 146 dB peak -6 dB - 101.5 dB peak4.3/6.3 Hz - 14 kHz
4397-A 1 mV/ms-23 mms-2 - 7.1 kms-2 peak300 µms-2 - 75 ms-2 peak1.25/6.3 Hz - 20 kHz
4513 1 mV/ms-23 mms-2 - 7.1 kms-2 peak300 µms-2 - 75 ms-2 peak1.25/6.3 Hz - 10 kHz
4513-00110 mV/ms-2300 μms-2 - 710 ms-2 peak 30 µms-2 - 7.5 ms-2 peak1.25/6.3 Hz - 10 kHz
4513-00250 mV/ms-260 μms-2 - 141 ms-2 peak 6 µms-2 - 1.5 ms-2 peak1.25/6.3 Hz - 10 kHz


Acceleration, velocity or displacement in dB or physical units. SI units (m/s2, m/s or m) or US/UK units (g, m/s or Mil)
Direct: Voltage in dB or V


Readings: Total level within the spectrum.
Frequency Correction: For spectra measured with a Hanning Window, spectral peaks are interpolated to a higher precision
Main: Reads level versus frequency
Symmetrical Delta and Delta: Defines lower and upper frequency limit for any part of the spectrum and calculates the level sum within that frequency range
Harmonic: Identifies fundamental frequency and harmonics in the spectrum and calculates the Total Harmonic Distortion 2 (THD)
Reference: Reads the difference between the main cursor Y-value and the reference cursor Y-value

Note 2. Total Harmonic Distortion (THD) is the sum (in %) of all the harmonics relative to the sum of the fundamental and all the harmonics.


Limit Level Check

Limit Level: Determines the level at which the spectrum is checked
Limit Range: Determines the frequency range for the limit level check
Indication: Two indicators are displayed, latched and instantaneous When the spectrum exceeds the limit level, a recording can be started (license for BZ-7226 required) and a 3.3 V DC signal can be output at the Output Socket

Sound Level Meter Parameters

Sound level meter (broadband) parameters are measured simultaneously with the FFT parameters. However, their measurement starts when the Start/Pause push button is pressed and ends at the nearest whole second after the end of the FFT measurement
Specifications for the Sound Level Meter parameters apply to Handheld Analyser Type 2250 fitted with Microphone Type 4189 and Microphone Preamplifier ZC-0032

Self-generated Noise Level

- typical values at 23°C for nominal microphone open-circuit sensitivity:
Weighting  Microphone   Electrical  Total  
"A" 14.6 dB 12.4 dB16.6 dB
"B" 13.4 dB 11.5 dB15.6 dB
"C" 13.5 dB 12.9 dB16.2 dB
"Z" 5 Hz - 20 kHz 15.3 dB 18.3 dB20.1 dB
"Z" 3 Hz - 20 kHz 15.3 dB 25.5 dB25.9 dB

Conforms with the following National and International Standards

Note: The International IEC Standards are adopted as European standards by CENELEC. When this happens, the letters IEC are replaced with EN and the number is retained. The analyser also conforms to these EN Standards


Parallel Detectors on every measurement:
A- or B-weighted (switchable) broadband detector channel with `Fast' time weighting, one linearly averaging detector and one peak detector
C- or Z-weighted (switchable) as for A- or B-weighted
Overload Detector: Monitors the overload outputs of all the frequency weighted channels


X = frequency weightings A or B
Y = frequency weightings C or Z
V = frequency weightings A, B, C or Z

For Display and Storage

Start TimeStop Time Overload %
Elapsed TimeLXeq LYeq
LXFmaxLYFmax LXFmax

Measuring Ranges

- when using Microphone Type 4189:
Dynamic Range: From typical noise floor to max. level for a 1 kHz pure tone signal, A-weighted: 16.6 to 140 dB
Primary Indicator Range: In accordance with IEC 60651, A-weighted: 23.5 dB to 123 dB
Linearity Range: In accordance with IEC 60804, A-weighted: 21.4 dB to 140 dB
Linear Operating Range: In accordance with IEC 61672, A-weighted: 1 kHz: 24.8 dB to 140 dB
Peak C Range: In accordance with IEC 61672: 42.3 dB to 143 dB
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E&OE - specifications subject to change without notice.