ASA-S1.20-1988-R2003.pdf
《ASA-S1.20-1988-R2003.pdf》由会员分享,可在线阅读,更多相关《ASA-S1.20-1988-R2003.pdf(45页珍藏版)》请在三一文库上搜索。
1、ANSI S1.20-1988 (ASA 75-1 988) (Revision of ANSI S1.20-1972) REAFFIRMED BY ANSI ON: MAY 2 8 AMERICAN NATIONAL STANDARD PROCEDURES FOR CALIBRATION OF UNDERWATER ELECTmw ACOUSTIC TRANSDUCERS/CiWPipTeTd2) xexpU(o/c)(d, +d3-d2)Y2. (11) The SI derived unit of free-field current sensitivity (Mi H is the a
2、mpere per pascal ( M a ) . The free-field current sensitivity level is expressed in decibels, re: one ampere per micropascal ( 1 NpPa = l Npbar). See Sec. 4 of American National Standard S1.8-1969 (R1974). 5.3.2.4 Transmitting Current Response See 7.16 of American National Standard S 1.1- 1960 (R197
3、61.1 The magnitude of the transmitting current response of a projector P at frequency f and at the distance 1 m in a specified direction is given by The S I derived unit of transmitting current re- sponse (Si is the pascal meter per ampere (Pa.m/ A). The transmitting current response level is ex- pr
4、essed in decibels, re: one micropascal meter per am- pere ( 1 pPa-m/A). See Sec. 4 of American National Standard S 1.8- 1969 (R 1974). 3 i FIG. 2. Measurement framework for supporting the three transducers in-line. Copyright Acoustical Society of America Provided by IHS under license with ASA Licens
5、ee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/18/2007 04:52:51 MDTNo reproduction or networking permitted without license from IHS -,-,- ANSI S1.20-1988 5.3.2.5 Transmitting Voltage Response See 7.15 of American National Standard S1.l-1960 (R1976). With the arrangements shown in
6、Fig. 1 and the vol- tage and current measurements of 5.3.2.3, the trans- mitting voltage response (Se ) , , of projector P at fre- quency f and at the distance 1 m in a specified direction is given by The SI derived unit of transmitting voltage response (Se is the pascal meter per volt (Pa.m/V). The
7、 transmitting voltage response level is expressed in decibels, re: one micropascal meter per volt (1 pPa*m/V). See Sec. 4 of American National Stan- dard S1.8-1969 (R1974). 5.3.2.6 Sources of Error in Reciprocity Calibrations There are several possible sources of error besides those that can be iden
8、tified by the tests for free field (5.3.1) and for a reciprocal transducer (5.3.2.1), and these must be examined. In a reciprocity calibration, three currents and three voltages must be measured, as seen in the foregoing sections. Generally, the current is measured by the voltage generated in the se
9、condary of a current transformer or it is measured as the voltage drop across a standard resistance placed in series with the transducer whose current is to be measured (5.3.2.6.1). Thus a voltmeter can be used for all elec- trical measurements. Because the equations for sensi- tivity and response t
10、hen show an equal number of vol- tages in the numerator and the denominator, the voltmeter need not be a standard. It must, however, be linear, stable, and should have an impedance that is very large with respect to that of all measured voltage sources. All electrical measurements must be made at th
11、e same terminals of the transducer. Because three experimental arrangements are required for a calibra- tion, stability of the measuring equipment is essential. 5.3.2.6.1 Current Measure. Two methods for measur- ing transducer currents are in general use. In the better method, the current is measure
12、d by the voltage genera- ted in the secondary of a current transformer when the primary is placed in series with the transducer and of- ten in the high side of the circuit. A shielded trans- former of toroidal configuration having a primary of low impedance and low capacitance to the secondary and t
13、o the ground is recommended. In the other meth- od, the current is measured as the voltage drop across a standard resistance in series with the transducer and 7 generally in the ground side of the circuit. This resistor must be located at the transducer terminal, its value must be less than 1% of th
14、e value of the resistive com- ponent of the complex impedance, and it must never be more than a few ohms in order to avoid noticeable errors resulting from additional currents through dis- tributed capacitance to ground. A third method has been used to measure the current in small, low-fre- quency,
15、coupler projectors. A large standard capacitor is placed in series with the projector, and the current is computed from the measured voltage across the ca- pacitor and its reactance. The method can be used to l Hz or less provided the capacitor is of sufficiently low dissipation. 5.3.2.6.2 Hydrophon
16、e Output Voltage. The impedance of the voltmeter should be greater than approximately loo0 times the impedance of the hydrophone for mea- surements involving phase and greater than approxi- mately 100 times the impedance of the hydrophone if only magnitude is desired; if it is not, a correction to o
17、pen-circuit voltage must be made (see 5.8 1. The mea- sured voltages may range from a few microvolts to volts. Acoustic and electrical interference should be eliminated, if possible, by modifying the measuring conditions. The undesired, interfering signals are those transmitted electromagnetically a
18、nd acoustically by in- direct paths. The pulse technique can be used to sepa- rate the desired, direct-path acoustical signal from the undesired, interfering signals. A gated receiving sys- tem measures the direct-path acoustical signal and blocks out the interference. The measured signal can be det
19、ected by means of an oscilloscope. In sweep-fre- quency, continuous-wave measurements, the interfer- ence that results from two signals from a common source (acoustic reflections or electromagnetic trans- mission and the desired signal) can be resolved by computation (see 5.1 1.2). 5.3.2.6.3 Efectiv
20、e Acoustic Center. American National Standard S1.1-1960 (R1976) defines the effective acoustic center of a projector as “the point from which spherically divergent sound waves, observable at re- mote points, appear to diverge.” In practice, the acoustic center is the point used for positioning the p
21、rojector and measuring distances, and through which any axis of rotation must pass. Except for spherical projectors, the acoustic center must be determined ex- perimentally. Some logical point is selected and then tested by a distance-loss experiment; that is, the sound pressure from the projector m
22、ust be inversely propor- tional to the distance from the acoustic center to the point of measurement, or the 6-dB-per-double-distance rule must apply, for all orientations. Copyright Acoustical Society of America Provided by IHS under license with ASA Licensee=IHS Employees/1111111001, User=Wing, Be
23、rnie Not for Resale, 04/18/2007 04:52:51 MDTNo reproduction or networking permitted without license from IHS -,-,- STD=ASA SI-20-ENGL L788 9 0181440 UOh42Al O74 D 8 AMERICAN NATIONAL STANDARD Most projectors are symmetrical in an up-down and right-left sense; therefore, errors in selecting the acous
24、tic center usually are in the axial direction (x axis in 5.7.2.1). Such position errors usually are only a few percent or less of the projector-to-hydrophone dis- tance, and, therefore, cause measurement errors of only a few tenths of a decibel. For this reason, the se- lection of the acoustic cente
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- ASA S1 20 1988 R2003
链接地址:https://www.31doc.com/p-3729899.html