www.bksv.com

Brüel & Kjær Sound & Vibration Measurement A/S.

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2250, 2270 & Measurement Partner Suite: Transducers, Calibration & Signal Recording

The 2250 and 2270 can support accelerometers, hydrophones, and various microphones. The webinar

looks at the setup and calibration of these transducers and the signal recordings that can be made using the optional

BZ7226 Recording application..

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Sound Meters

Most SOUND meters come with a microphone.

Microphone Types: Free Field, Diffuse Field, Pressure Field

Free Field Microphones are optimized to measure highest frequencies accurately pointed at a noise source.

In a diffuse field a Free Field Microphone will underestimate the sound pressure at high frequencies – unless compensated for.

pm D

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4189 Free Field Microphone

Max RMS – 146dB @3% distortion @ 1kHz

2250 / 2270 limit is 144dB peak (14Volts)

Typ. Noise Floor 16.6 dBA (20.1 dBZ)

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Types of Microphones

Random incidence

Pressure

Free field

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Measuring in Accordance with Standards:

IEC ANSI

70° – 80°

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IEC 61672 Class 1 (Type 1)?

While it is an accuracy rating for a sound meter – often it is attributed to a microphone

For Microphones and Meters Frequency Response might look like this:

-4

-3

-2

-1

0

1

2

3

4

100 1000 10000 100000

Reality is a lot different: A LOT more involved…

LD8312250/70

IEC 61672 CLASS 1 Tolerance Levels

(Free Field Frequency Response)

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When is a Sound Meter Not a Sound Meter?

Vibration measurements

Acceleration measurements in dB? Reference Value: 1µm/s² (1 g ~ 140dB) or 1µg (1g = 120dB) Occasionally, 10-5 m/s² (~1µg) is used (USA military) FFT Application BZ7230 Allows direct read out of units in G’s,

in/sec, mils, mm, m/s, m/s²

Pressure Measurements Reference dB level is Pa, or µPa

Hydrophone measurements in water are in µPa.

(When using a hydrophone – select transducer Type “Accelerometer)

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Calibration

When do you Calibrate?– Traceable Calibration

– Record the Calibration Value

– Maintain a Calibration History

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Acoustic Calibrators

AcousticalCalibrator

Pistonphone

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Pistonphone and Acoustical Calibrator

860577/1e

Pistonphone Acoustical Calibrator

f = 250 HzL = 124 ± L [dB]

f = 1000 HzL = 94 dB = 1 Pa

Microphoneto be calibrated

Acoustical Calibrator

Microphoneto be calibrated

1/2” Adaptor

Battery

Lid

ReferenceMicrophone

PressureEqualization

Loud-speaker

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Signal Recording

Recording Control

Recording Quality

Recorded Signal Weighting

Automatic Gain Control

Setting the Peak Level

2250/2270

Measurement

Range

16 Bit

Wav

Range

Signal

Range

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Summary

We’ve learned about Microphone Types and Accuracy We’ve seen how to enter new transducers (microphones and

accelerometers) We’ve looked calibration procedure for transducers We’ve examined how to set-up signal recording option BZ7226

– Under Compressed “Automatic Gain”

– Or optimizing the dynamic range of the recording with automatic gain off

– Playing and saving recordings in BZ5503 Measurement Partner Suite