GB/T 4130-2000 Low frequency calibration method for acoustic hydrophones
Some standard content:
ICS17.140.01
National Standard of the People's Republic of China
GB/T4130—2000
Acoustics--Low frequency calibration methods of hydrophones2000-03-16 issued
2000-12-01 implementation
State Administration of Quality and Technical Supervision issued
GB/T4130—2000
Reference standards
3 Coupled cavity reciprocity method
Piezoelectric compensation method
Vibrating liquid column method
6 Closed cavity comparison method
Appendix A (standard appendix)
Appendix B (suggestive appendix)
Appendix C (suggestive appendix)
Appendix D (suggestive appendix)
Determination of voltage coupling loss of hydrophone
Under different temperatures and different hydrostatic pressures Density and sound velocity of several liquids measured with standard volume blocks Reciprocity constant
Uncertainty analysis of calibration results of coupled cavity reciprocity method 12
GB/T4130--2000
This standard has revised GB4130-1984 according to the current development of underwater acoustic measurement and testing in my country. The main contents of the revision are: 1) At present, computers have been introduced into the vibration liquid column calibration devices of major underwater acoustic units in my country. While program-controlled measurement, high-frequency correction factors can be conveniently used to correct the calibration results, and the calibration accuracy has been significantly improved. Therefore, the original secondary calibration was defined as primary calibration during the revision, which is equivalent to IEC565A (1980) "Calibration of Hydrophones". The piston generator is the low-frequency calibration method recommended in IEC565A, and it is also used to varying degrees in major domestic underwater acoustic units. Therefore, it is added to the secondary calibration method during this revision. 2) In the coupled cavity reciprocity method, during this revision, this standard uses a current sampler to replace the original standard resistor to measure the current, which improves the signal-to-noise ratio of low-frequency current measurement and extends the calibration frequency to low frequencies. The volume of the coupled cavity is measured using the standard volume block measurement method, which improves the calibration accuracy.
3) In the piezoelectric compensation method, the measurement of the characteristic constant, during the revision, this standard introduces the correction term of equivalent height, eliminates the influence of vibration acceleration on gravity acceleration, and improves the measurement accuracy. From the date of entry into force, this standard will replace GB4130-1984. This standard was proposed by the Chinese Academy of Sciences.
This standard is under the jurisdiction of the National Technical Committee for Acoustic Standardization. The drafting units of this standard are: No. 715 Institute of China Shipbuilding Industry Corporation and Institute of Acoustics, Chinese Academy of Sciences. The main drafters of this standard are Xue Yaoquan, Shuai Wenjun, and Zhu Houqing. National Standard of the People's Republic of China
Acoustics-Lowfrequency calibration methods of hydrophones
Acoustics-Lowfrequency calibration methods of hydrophones1 Scope
This standard specifies the methods for calibrating hydrophones in the frequency range of 1Hz to 3.15kHz. The methods specified in this standard are divided into primary calibration methods and secondary calibration methods. GB/T4130-2000
Replaces GB/T4130-1984
The calibration uncertainty of the primary calibration method is not more than 0.5dB, and it is mainly used to calibrate standard hydrophones. It includes the coupled cavity reciprocity method, the piezoelectric compensation method, and the vibrating liquid column method.
The calibration uncertainty of the secondary calibration method is not more than 1.0dB, and it is mainly used to calibrate measurement hydrophones. It includes the closed cavity comparison method and the pistonphone calibration method.
2 Referenced Standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard was published, the versions shown were all valid. All standards are subject to revision, and parties using this standard should explore the possibility of using the latest version of the following standards. GB/T3223-1994 Acoustics Hydroacoustic Transducer Free Field Calibration Method 3 Coupled Cavity Reciprocity Method
3.1 Principle
The calibration principle of the coupled cavity reciprocity method is the same as the free field reciprocity calibration principle of the hydroacoustic transducer in GB/T3223, except that the transmitter (F), reciprocity transducer (H), and receiving hydrophone (J) are placed in a rigid cavity filled with liquid and calibrated under a uniform pressure field. The schematic diagram of the coupled cavity is shown in Figure 1. According to the calibration steps in Figure 2, three measurements are made to measure the excitation currents Ip, I'F, IH of the transmitter (F) and the reciprocal transducer (H) and the open circuit voltages UH, Un, UHI at the output ends of the reciprocal transducer (H) and the hydrophone (J) respectively. When I=I\, the sound pressure sensitivity of the hydrophone can be obtained as follows:
Wherein: Mp-sound pressure sensitivity of the hydrophone, V/Pa; rUnUH
Uk-open circuit voltage at the output end of the hydrophone (J) when the transmitter (F) sends, V; UH-open circuit voltage at the output end of the reciprocal transducer (H) when the transmitter (F) sends, V; Uu-open circuit voltage at the output end of the hydrophone (J) when the reciprocal transducer (H) sends, VIH
-excitation current of the reciprocal transducer, A;
J coupling cavity reciprocity constant, m\/(Pa·s). When the size of the coupling cavity is much smaller than the wavelength of the acoustic wave of the liquid in the cavity, its reciprocity constant is: J=uC.
@=2 yuan f
Where: f—frequency, Hz;
Approved by the State Administration of Quality and Technical Supervision on March 16, 2000·(1)
(2)
Implemented on December 1, 2000
GB/T4130—2000
C. The acoustic compliance of the liquid in the coupling cavity and its boundary, m\/Pa. When the wall and transducer of the coupling cavity are rigid, and there is no material or bubble that releases pressure in the cavity, this acoustic compliance is the acoustic V
Where: V-volume of the liquid in the cavity, m;
—speed of sound in the liquid, m/s
—density of the liquid, kg/m.
Therefore, the reciprocity constant of the coupling cavity can be calculated using formula (4): ov
per shielding net
Figure 1 Schematic diagram of the coupling cavity
3.2 Design requirements of the coupling cavity
Figure 2 Calibration steps
The coupling cavity is required to have a rigid boundary. To this end, the thickness of the cavity wall should be at least greater than the inner radius of the cavity, and the sound velocity in the cavity is close to the free field sound velocity.
In order to meet the requirement that the sound field in the cavity is basically uniform, the maximum dimension in the cavity should be less than one tenth of the wavelength of the sound wave in the liquid in the cavity, and there should be no pressure relief material in the cavity, then the non-uniformity of the sound pressure in the cavity will not be greater than 0.3dB. The transmitter (F) and hydrophone (J) used in the coupling cavity must be linear, and the reciprocal transducer (H) must be linear, passive, and reversible. All three transducers must meet the requirements of acoustic rigidity. 3.3 Measurement
3.3.1 Voltage measurement
The principle block diagram of a typical coupled cavity reciprocity calibration device is shown in Figure 3. The output terminals of the reciprocity transducer, hydrophone and excitation current sampler are connected to the electronic switch respectively. Um, Un and UH are amplified by the same preamplifier and measuring amplifier and measured by a digital voltmeter with an allowable limit error of no more than 0.5%. The input impedance of the preamplifier should be greater than 100 times the equivalent impedance of the hydrophone, and the resulting voltage coupling loss will be no more than 1%. If this requirement is not met, the insertion voltage method should be used for correction (see Appendix A). 2
3.3.2 Current measurement
Frequency synthesizer
Power amplifier
Current sampling
GB/T4130—2000
Preamplifier
Electronic switch
Measuring amplifier
Digital voltmeter
Oscilloscope
Computer
Figure 3 Block diagram of coupled cavity reciprocity calibration principle
The excitation current I of the reciprocal transducer can be measured by a current sampler connected in series in the reciprocal transducer circuit. The value of the current sampler's impedance must be less than one percent of the transducer's impedance value, and its allowable limit error is not more than 0.3%: the measurement of the current sampler's output voltage is the same as Article 3.3.1.
Note: If the transfer impedance between the transmitter and the hydrophone is measured by an attenuator to obtain the sound pressure sensitivity of the hydrophone, please refer to GB/T3223. 3.3.3 Determination of reciprocity constant
The reciprocity constant of the coupling cavity can be calculated according to formula (4) by measuring the volume, sound velocity and density of the liquid in the cavity. It can also be determined by measuring the reciprocity constant using a standard volume block (see Appendix C). The density β and the sound velocity c are functions of temperature and pressure (see Appendix B). The allowable limit error of measuring density should not be greater than 0.5%, and the allowable limit error of measuring sound velocity should not be greater than 1.5%. The volume V should be measured with a liquid with low adhesion, such as anhydrous ethanol. During measurement, bubbles should be prevented from entering the liquid. The allowable limit error of the measured volume should not exceed 0.5%.
The frequency should be measured with a digital frequency meter with an allowable limit error of no more than 0.1%. If the measurement is performed according to the above requirements, the allowable limit error of the reciprocity constant will not exceed 3.1%. 3.3.4 Measurement requirements
a) The liquid in the cavity must be degassed before calibration. Calibration can also be performed at a pressure not exceeding 0.5MPa to eliminate the influence of residual air in the cavity on the measurement.
b) The frequency of the signal used for calibration should include the frequency specified by the 1/3 frequency doubling sequence. During calibration, the change in signal frequency shall not exceed 0.1%.
c) Before calibration, the transmitter, reciprocal transducer and hydrophone should be linearly checked, and the deviation should not exceed 0.5%. The reciprocal transducer should also be tested for linearity. Reciprocity test is carried out, and the deviation should not be greater than 0.5%. For the test method, please refer to the relevant clauses in GB/T3223. d) During calibration, the signal-to-noise ratio should be greater than 30dB. At the same time, the excitation power applied to the transmitter and the reciprocal transducer should be as small as possible to prevent the transmitter and the reciprocal transducer from heating up and causing changes in the temperature and pressure of the liquid in the cavity and introducing errors. e) In order to avoid electrical crosstalk between the transmitter, reciprocal transducer and the hydrophone, electrical shielding should be considered between them. 3.4 Frequency Limit and Calibration Uncertainty
3.4.1 Frequency Limit
The maximum size of the coupling cavity is not greater than one tenth of the wavelength, which gives the high-frequency limit of the coupling cavity calibration. When the system is compliance controlled, the open-circuit voltage at the output of the hydrophone is equal to the transmitter or reciprocal transducer. The ratio of the input voltage of the transducer is a constant. By measuring this ratio, the upper limit of the frequency that can be calibrated can be determined.
In theory, there is no low-frequency limit, but in practice, since the transmitter in the coupling cavity emits very low sound levels at low frequencies, the calibration cannot meet the requirement of a signal-to-noise ratio greater than 30dB. The low-frequency limit is thus determined. 3.4.2 Calibration uncertainty
If this method is measured according to the requirements of Section 3.3, the Class B uncertainty will not be greater than 2.1%. If the Class A uncertainty is controlled within 1.5% during the measurement, then within the frequency range of 3.15kHz, the expanded uncertainty (K=2) will not be greater than 5.2% or 0.5dB (calibration The calibration uncertainty analysis is shown in Appendix D).
4 Piezoelectric compensation method
4.1 Principle
The calibration principle of the piezoelectric compensation method is shown in Figure 4. It is a closed cavity with the compensation transducer as the main body, the source transducer is installed at the bottom, and the hydrophone to be calibrated is placed near the center of the compensation transducer. The compensation transducer is composed of a piezoelectric ceramic tube, the inner wall of which serves as the wall of the closed cavity, and the outer tube is a displacement sensor, which is acoustically coupled with the compensation transducer through the elastic coupling material filled between the inner and outer tubes to detect its displacement. During calibration, the source transducer is driven to generate an acoustic pressure in the cavity, and then the driving voltage U of the compensation transducer is adjusted. The amplitude and phase (the driving voltages of the two transducers are supplied by the same signal generator) make the output voltage U of the displacement sensor. is zero, that is, the vibration displacement of the compensation transducer is zero at this time, reaching the compensation state, so the sound pressure in the cavity is: dE
Where: K—characteristic constant of the compensation transducer, Pa/V—piezoelectric constant of the circular tube material, m/V,
E—elastic modulus of the circular tube material, Pa;
—average radius of the compensation transducer, m;
U. Compensation voltage, V.
Electronic switch
Elastic filler
Compensation transducer
Source transducer
The sound pressure sensitivity of the hydrophone is:
Preamplifier
Filter
Hydrophone to be calibrated
Displacement sensor
Figure 4 Principle of the calibration device of the piezoelectric compensation method
Where: U—open circuit voltage at the output end of the hydrophone, V. If the sound pressure sensitivity [level] is used, then equation (6) becomes: 4
Lock-in amplifier
Frequency synthesizer
Power amplifier
Computer and peripherals
（5）
（6）
GB/T4130—2000
M = 20lg(U.)
20lg(K)
Where: Mj—sound pressure sensitivity [level] (reference value: 0dB=1V/uPa). Note: If the piezoelectric compensation method calibration is performed manually, the electronic switch in Figure 4 can be replaced by a manual switch, and the computer and peripherals can be omitted. 4.2 Design requirements for piezoelectric compensation method calibration device (7)
The two ends of the compensation transducer are clamped with metal flanges to form a closed cavity. In order to reduce the influence of the longitudinal deformation of the compensation transducer caused by the transverse piezoelectric effect on the displacement sensor, the seal between the flange and the compensation transducer should be made of compliant material, and the annular gap between the inner and outer tubes should be filled with elastic material. The inner tube is used as a compensation transducer, and the outer tube is used as a displacement sensor. The source transducer is installed on the bottom flange, which can generate a sufficiently high sound pressure level in the cavity so that the signal-to-noise ratio is greater than 30dB during measurement. The hydrophone is installed on the upper flange, and its acoustic center should basically coincide with the geometric center of the compensation transducer. In order to meet the requirement that the sound pressure in the cavity is basically uniform, the maximum size in the cavity should be less than one-tenth of the wavelength of the sound wave in the cavity wave body, and there should be no pressure relief material in the cavity, so that the non-uniformity of the sound pressure in the cavity will not be greater than 0.3dB. In the design of the cavity, the thickness of the cavity wall (inner piezoelectric ceramic tube and upper and lower flanges) should also be considered to avoid bending vibration. 4.3 Measurement
4.3.1 Zero displacement indication and voltage measurement
The principle block diagram of the typical piezoelectric compensation calibration device is shown in Figure 4. A dual-channel frequency synthesizer with independently adjustable amplitude and phase is used as the signal source for the excitation source transducer and the compensation transducer. A frequency-selective voltage measuring instrument with high anti-interference performance (such as a low-frequency phase-locked amplifier) not only indicates Ua, but also reads U, and U. . The state selection is carried out through a multi-channel electronic switch, and the allowable limit error of the voltage measuring instrument should not be greater than 0.1dB. The input impedance of the preamplifier should be greater than one hundred times the electrical impedance of the hydrophone, and the resulting voltage coupling loss will not be greater than 0.1dB. If this requirement is not met, the insertion voltage method can be used for measurement (see Appendix A). The signal-to-noise ratio should be kept greater than 30dB during the measurement. 4.3.2 Measurement of characteristic constants
The method for measuring the characteristic constants of the compensation transducer is established according to the Pascal principle of fluid statics. Since the potential difference at the output end of the transducer under static pressure is difficult to measure accurately, the characteristic constant is usually measured at a very low frequency (for example, below 1 Hz) that is at least 20 times lower than the resonance frequency of the "compensation chamber-connecting pipe-open container" system used for measurement. The measurement principle diagram is shown in Figure 5. The open container is connected to the compensation chamber through a connecting pipe, and the liquid in the container performs low-frequency sinusoidal vibration (below 1 Hz) in the vertical direction, so that alternating static water pressure is generated in the compensation chamber. At the same time, the excitation voltage and phase of the compensation transducer are adjusted at the same frequency to achieve a compensation state. The characteristic constant K of the compensation transducer is calculated by formula (8).
In the formula: p-liquid density, kg/m
g——gravitational acceleration, m/s*,
h-—liquid vibration amplitude, m;
f——liquid vibration frequency, Hz;
H. Liquid surface equivalent height, m: bzxz.net
（8）
U-Peak value of compensation transmitter driving voltage in compensation state, V. Liquid surface equivalent height H. Calculated from formula (9): S-AH
In the formula, △H is the difference between the liquid surface height when the alternating static pressure in the compensation chamber is equal to zero and the liquid surface height during actual measurement. (9)
Preamplifier
Phase-locked amplifier
Voltmeter
GB/T4130—2000
Phase and amplitude controller
Frequency synthesizer
Figure 5 Schematic diagram of characteristic constant measurement
Vibration mechanism
Zero static pressure liquid level line
The allowable limit error of liquid vibration amplitude measurement shall not exceed 0.2%, and the compensation voltage shall be measured using a digital voltmeter with an allowable error of not more than 0.5%. The allowable limit error of liquid density shall not exceed 0.5%. If measured according to the above requirements, the uncertainty of the characteristic constant will not exceed 2.3% or 0.2dB.
4.3.3 Measurement requirements
The liquid in the container shall be degassed and ensure that there are no bubbles attached to the container wall. 4.4 Frequency limit and calibration uncertainty
4.4.1 Frequency Limit
The maximum dimension in the cavity is not greater than one tenth of the wavelength, which gives the high-frequency limit of the calibration device. However, if the hydrophone is axisymmetric and the acoustic center of the hydrophone and the geometric center of the compensation transducer are basically coincident when the hydrophone is installed, the influence of the inhomogeneity of the sound pressure in the cavity on the calibration result can be minimized, so the upper frequency limit of the calibration can be expanded upward. At the highest calibration frequency, the maximum dimension in the cavity should not be greater than one third of the wavelength.
The low-frequency limit is caused by the decrease in the signal-to-noise ratio at low frequencies in the compensation detection system and the difficulty in achieving balance in the compensation status indication system, which makes the measurement difficult. This lower frequency limit is generally around 1Hz. 4.4.2 Calibration Uncertainty
If this method is measured according to the requirements of Article 4.3, the expanded uncertainty will not be greater than 0.5dB (K=2). 5 Vibrating liquid column method
5.1 Principle
The principle block diagram of the vibrating liquid column method calibration device is shown in Figure 6. It is a rigid cylindrical container with an inner diameter smaller than the wavelength and an open top. It contains a certain height of liquid. The entire container is driven by a vibration table that performs sinusoidal vibration. The hydrophone is fixed on a bracket and vertically suspended on the central axis of the liquid column in the container. The sound pressure sensitivity of the hydrophone can be calculated based on the ratio of the pressure change at the depth of the liquid column where the hydrophone is located and the open circuit voltage at the output end of the hydrophone. 6
Accelerometer
Vibration table
Power amplifier
Frequency synthesizer
GB/T4130—2000
Hydrophone
Charge amplifier
Electronic switch
Digital voltmeter
Preamplifier
Measuring amplifier
Filter
Computer and peripherals
Figure 6 Schematic diagram of the calibration device of the vibrating liquid column method Assuming that the entire liquid column vibrates vertically as a whole relative to its equilibrium position, the sound pressure p generated by the pressure change at a depth of h below the liquid surface is:
p=prlg -hw2]
Where: p
Liquid density, kg/m;
Vibration displacement of the bottom of the container, m;
Gravity acceleration, m/s,
FFrequency of liquid vibration, Hz
When the frequency is high enough to make h>g, then equation (10) becomes: p=phrwpzh
Where:
Vibration acceleration of the bottom of the container, m/s?, If the vibration acceleration of the bottom of the container is measured by an accelerometer, then from equation (11) we can get the sound pressure sensitivity of the hydrophone: M
At high frequency, the sound pressure in the liquid column is:
Then equation (12) should be:
Where: Mr-
-Sound pressure sensitivity of the hydrophone, V/Pa;|| tt||Uf—open circuit voltage at the output end of the hydrophone, V; p—density of the liquid, kg/m;
h-——depth from the sound center of the hydrophone to the liquid surface, m; M.—sensitivity of the accelerometer, Vs/m; U—open circuit voltage at the output end of the accelerometer, V; sinkh
khcoskL
hcoskL
（10）
（11）
（12)
（13）
（14）
——wave number (-0/c, w=2f)), mf—frequency of liquid vibration, Hz
c-speed of sound in the liquid column, m/s;
GB/T4130—2000
L——height of the liquid column, m.
Note: If the vibration liquid column method calibration is performed manually, the electronic switch in Figure 6 can be replaced by a manual switch, and the computer and peripherals can be omitted. 5.2 Design requirements for the vibration liquid column container
The bottom and wall of the liquid column container should be rigid, and the lowest resonance frequency of the container should be higher than the lowest resonance frequency of the liquid column, and the calibration frequency should be lower than the lowest resonance frequency of the liquid column.
When designing the container, the sound pressure at the same depth in the liquid column should be the same, so the height of the liquid column should be greater than its diameter. In order to prevent the influence of the liquid dynamic flow when passing through the hydrophone, the diameter of the liquid column should be much larger than the diameter of the hydrophone. The suspension of the hydrophone should also be considered in the design to avoid the influence of the vibration source on the hydrophone. 5.3 Measurement
5.3.1 Sensitivity measurement
When measuring, the height L of the liquid column in the calibration container is less than one-fourth of the wavelength corresponding to the calibration frequency, and the water entry depth h of the sound center of the hydrophone is usually between one-half and two-thirds of the height of the liquid column. The electronic switch selects the hydrophone signal U from the preamplifier and the acceleration signal U from the charge amplifier, and simultaneously measures the corresponding known constants, and calculates the sensitivity value according to equation (12) or equation (14). In general, the position of the acoustic center of the hydrophone is known. If it is unknown, the following method can be used to eliminate the influence of the acoustic center position of the hydrophone on the measurement, that is, first set a reference point on the hydrophone, and measure the difference △U of the open circuit voltage at the output end of the hydrophone at two different depths hl and h2 in the liquid column while keeping the vibration table driving acceleration unchanged, and the ratio of the depth difference h. According to formula (14), the sound pressure sensitivity of the hydrophone can be obtained:
·15)
Measurement voltage U., U. The allowable limit error of the voltmeter is not more than 1%, and the input impedance of the preamplifier and the charge amplifier should be greater than 100 times the electrical impedance of the hydrophone and the accelerometer, respectively. The resulting voltage coupling loss will not be more than 1%. The signal-to-noise ratio should be kept greater than 20dB during the measurement, and the allowable range of the measurement depth is not more than 1%. The allowable limit error of the accelerometer is not more than 0.3dB. The allowable limit error of liquid density measurement is not more than 0.5%. 5.3.2 Measurement requirements
a) The calibration container is installed on the vibration table and calibrated with a spirit level to ensure that the container is installed horizontally. The liquid in the container should be degassed and no bubbles should be attached to the container wall. b) The accelerometer should be rigidly fixed to the bottom of the container. The ratio of the lateral vibration to the longitudinal vibration of the vibration table shall not be greater than 3%. c) The hydrophone is vertically suspended on the central axis of the liquid column in the container. The water depth of the sound center of the hydrophone should not be too shallow to meet the signal-to-noise ratio greater than 20dB. However, it should not be close to the bottom of the container. The water depth of the sound center of the hydrophone is usually between one-half and three-thirds of the length of the liquid column.
5.4 Frequency limit and calibration uncertainty
5.4.1 Frequency limit
The provision that the height of the liquid column should not be greater than one-quarter of the wavelength gives the high-frequency limit of this calibration method. In order to ignore the static drop, ha*>g must be satisfied. This condition constitutes a low-frequency limit. For example, when h=10cm, in order to make the error introduced by ignoring the drop pressure no more than 3%, the calibration frequency should be higher than 10Hz. 5.4.2 Calibration uncertainty
If this method is measured according to the requirements of Article 4.3, the Class B uncertainty will not be greater than 3.6% (K=2). If the Class A uncertainty is controlled within 2.0% during the measurement, the expanded uncertainty will not be greater than 0.5dB (K=2) in the frequency range of 10Hz to 1kHz.
6 Closed cavity comparison method
6.1 Principle
6.1.1 Simultaneous comparison method
GB/T41302000
In a rigid closed cavity filled with liquid, a transmitter establishes an acoustic field in the cavity, as shown in Figure 7. The hydrophone to be calibrated and the standard hydrophone are placed in the area with the same sound pressure in the cavity at the same time, and the open-circuit voltage at the output end of the hydrophone is measured. The sound pressure sensitivity of the hydrophone to be calibrated is:
Where: Mx
-sound pressure sensitivity of the hydrophone to be calibrated, V/Pa; sound pressure sensitivity of the standard hydrophone, V/Pa: Ux
-open-circuit voltage at the output end of the hydrophone to be calibrated, V; Us
-open-circuit voltage at the output end of the standard hydrophone, V. Ux
Hydrophone to be calibrated
Transmitter
Schematic diagram of simultaneous comparison method
6.1.2 Substitution comparison method
Standard hydrophone
（16）
In a rigid closed cavity filled with liquid, a sound field is established in the cavity by a transmitter, as shown in Figure 8. First, place the hydrophone to be calibrated into the cavity and measure the open-circuit voltage Ux at the output end of the hydrophone to be calibrated. Then replace the hydrophone to be calibrated with the standard hydrophone. Under the condition that the sound pressure in the closed cavity remains unchanged, measure the open-circuit voltage at the output end of the standard hydrophone. The sound pressure sensitivity of the hydrophone to be calibrated is obtained, and the calculation formula is the same as that of formula (16). UxUs
Transmitter
6.1.3 Pistonphone method
Figure 8 Schematic diagram of substitution comparison method
Hydrophone to be calibrated
Standard hydrophone
In a rigid closed cavity filled with liquid, an air piston generates alternating pressure, and a uniform alternating pressure field is established in the liquid cavity within the infrasonic frequency range, as shown in Figure 9. The hydrophone to be calibrated and the standard hydrophone are sealed in the liquid in the cavity in the same direction. When the piston moves, the open circuit voltage Ux of the hydrophone to be calibrated and the open circuit voltage Us of the standard hydrophone are measured respectively. Substituting them into formula (16) can obtain the sound pressure sensitivity of the hydrophone to be calibrated.
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.