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10/04/23 DIF/DASE/B.ALCOVERRO 1
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
Infrasound Sensor Infrasound Sensor Dynamic CalibratorDynamic Calibrator
ALCOVERRO Benoît
DASE/TMG
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10/04/23 DIF/DASE/B.ALCOVERRO 2
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
Dynamic CalibrationDynamic Calibration
Dynamic calibration requires an infrasonic source with:– precise pressure signal applied to the sensor (some percent).
– no phase distortion introduced by the calibrator (or measured error).
– [0.001 Hz - 100 Hz] linear frequency range needed to verify the CTBT band [0.02 Hz - 4 Hz] (flat in amplitude and smooth phase).
– Low sensitivity to noisy signals.
Solution to generate a pressure:– Variation of a sealed volume at constant
temperature.– If V/V0 small, at first order,
P = P0 . P = P0 . VV P is static pressure dependant.
Volume variation V
Sealed volume V0
Static pressure
P0
Pressure generated P0+ P
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10/04/23 DIF/DASE/B.ALCOVERRO 3
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
The sensor is connected to a sealed cavity where the pressure is generated.
The use of small volumes (< 50 l) & light piston (< 100 g ) could increase the linearity up to 100 Hz (linear amplitude & smooth phase responses up to 10 Hz).
Low energy required to generate the pressure ( < 5 W for 10 Pa generated by Electro-mechanical driver)
Small size portable solution.
Basic Acoustical PrincipleBasic Acoustical Principle
V
Small sealed volume (30 l)
External pressure
P0
P0+ P
Displacementof piston
Sensor to be calibrated
Connection pipe P0+ P
pg
Driver
FrontCavity
Connexion Pipe
RearCavity
SensorP Cal
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10/04/23 DIF/DASE/B.ALCOVERRO 4
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
P0+ P
Sensor to be calibrated
pg
Driver
FrontCavity
RearCavity
SensorP Cal
Actual solutionActual solution
Cavities without leaks : low frequencies generation.
Sensor inlet inside the front cavity & small volumes : extend the high frequencies response. (resonant frequency could be around 100 Hz : flat amplitude & phase 30 Hz)
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10/04/23 DIF/DASE/B.ALCOVERRO 5
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
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10/04/23 DIF/DASE/B.ALCOVERRO 6
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
Leaks VerificationLeaks Verification
Verification by the mean of a Static pressure calibrator. Measurement over 1 hour must be stable.(P < 0.2 hPa for 5 hPa over pressure) Could be made before calibration
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10/04/23 DIF/DASE/B.ALCOVERRO 7
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
Accurate pressure adjustmentAccurate pressure adjustment
Pressure generated is temperature & static pressure dependant:
– the displacement of the piston must be adjusted before each calibration.
The solution: use a calibrated microphone:– measure the pressure at high frequency
(> 10 Hz)– attach to an absolute pressure reference
The frequency used for adjustment must be in the overlap band between microphone & calibrator:
– < 30 Hz for calibrator– > 10 Hz for current capacitance
microphones
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10/04/23 DIF/DASE/B.ALCOVERRO 8
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
Microphone CalibrationMicrophone Calibration The microphone used is flat & currently calibrated from 20 Hz to 2 kHz within (+/- 2.3 %). A 1kHz calibrator allows the measurement chain calibration at 10 Pa (+/- 1%) 16 bits digitizers used in control device allows 1 LSB error ( < 0.01 %)
This is the link with absolute reference Pressure (Quality procedures)
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10/04/23 DIF/DASE/B.ALCOVERRO 9
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
Complete systemComplete system Precise pressure generation requires adjustments before calibration: The calibrator accuracy depends on the microphone calibration:
– currently < 3 % but < 1% possible by specific calibration
SIGNALGENERATOR
16 bits
PowerAmplifier
PressureMeasurement
16 bitsCALCULATOR
Sync GPSPCLogicalcommands
Pref
Calibrated Microphone
Sensor to be calibrated
FEEDBACK LOOP & COMMAND CALIBRATORMLS + / - Vref
Sinus + / - Vref
Response of calibrated sensor
Gain Narrow band filter mean value
calculation
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10/04/23 DIF/DASE/B.ALCOVERRO 10
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
Calibration BenchCalibration Bench
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10/04/23 DIF/DASE/B.ALCOVERRO 11
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
Calibration FeaturesCalibration Features Signals generated:
– Sine Waves at finite frequencies [0.025 - 50] Hz
– Positives Pulses from [1 - 200] ms width
– Maximal length sequences with order [10 - 14] & [1 - 100] Hz sample rate for Transfer functions measurements.
Amplitude from [1 - 50] Pa (with on board power amplifier & 12 V DC supply)
Stimulus could be synchronized to an external trigger (1PPS for ex.)
Self calibration at 20 Hz is used to reach less than 3 % in absolute amplitude error (if no specific microphone calibration used) but could be < 1 %.
High frequency calibrator response could be measured by microphone & M.L.S. to precise H.F. measurements.
Frequency response : flat in Amplitude & Time over [DC - 30 Hz]. Temperature stability: < 3 °C for < 1% error in amplitude.
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10/04/23 DIF/DASE/B.ALCOVERRO 12
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
For calibration, pseudo-random sequences are used. The pseudo-random sequences characteristics:
– Binary sequences between +/- maxi.
– Random like distribution but identical sequences (depending on order)
– Spectral density = 1 over bandwidth
– maximal energy applied to the sensor
– Ref VANDERKOOY JAES Vol 42, N° 4 April 1994 Transfer function measurements:
Full range Calibration Full range Calibration using Pseudo-random sequences using Pseudo-random sequences
SENSOR TO BE TESTED
DIGITISER(one channel)
Pseudo-randomsequence(order n)Generated by calibrator
Correlation
Pseudo-randomsequence(order n)locally generated
Sensorresponse(Amplitude & Phase)
Possibility to be distant
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10/04/23 DIF/DASE/B.ALCOVERRO 13
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
Self Calibration & Sine Wave Self Calibration & Sine Wave
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10/04/23 DIF/DASE/B.ALCOVERRO 14
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
M.L.S. M.L.S.
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10/04/23 DIF/DASE/B.ALCOVERRO 15
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
Ex: Sensor sensitivity response Ex: Sensor sensitivity response
1 measurement 16384 pts MLS S.R. = 25 Hz duration = 2614
s 10 Pa excitation
Sensor Nominal sensitivity: 20 mV/Pa
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10/04/23 DIF/DASE/B.ALCOVERRO 16
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
Ex: Sensor response + tolerances Ex: Sensor response + tolerances
- 1.0 % / static calibration
20 mV/Pa nominal sensitivity
19.75 mV/Pa in static calibration
19.55 mV/Pa in dynamic calibration
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10/04/23 DIF/DASE/B.ALCOVERRO 17
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
Ex: MB2000 DC output responseEx: MB2000 DC output response
The calibrator is flat from 0.005 up to 10 Hz
(1.005 mV/Pa in static calibration)
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10/04/23 DIF/DASE/B.ALCOVERRO 18
INFRASOUND SENSOR CALIBRATION DEVICE 13/11/2001
Conclusion Conclusion Effective broadband infrasound calibrator Internationally patented On board MLS allows amplitude & phase measurements with
1 channel digitizer Self calibration requires no adjustments
Laboratory calibrator
On the field calibrator
remarks
Size (h x ) 0.55 x 0.40 0.30 x 0.2 (m)
Freq. response [0.001 – 30] Hz [0.01 – 10] Hz With flat amplitude & linear phase
Pressure range [1 – 50] Pa [1 – 10] Pa 12 V powered (< 5 W)
Absolute pressure Accuracy:
3 % < 1 %
3 % < 1 %
If currently mic. calibration If specific mic. calibration
State Industrialization Under dev.