1、 Access to Additional Content for SAE J247, Dated: April 2013 (Click here to view the publication) This Page is not part of the original publication This page has been added by IHS as a convenience to the user in order to provide access to additional content as authorized by the Copyright holder of
2、this document Click the link(s) below to access the content and use normal procedures for downloading or opening the files. J247 Information contained in the above is the property of the Copyright holder and all Notice of Disclaimer such high slew rates are mainly due to energy at frequencies far ab
3、ove those intended to be measured and are rightfully truncated by properly set filters. 4.10 Transducer Resonance Transducers should have an internal resonance above 100 kHz. When using a transducer with resonances below 100 kHz, it is recommended that a 25 kHz filter be installed by the manufacture
4、r between the sensing element and the first amplifier circuit. Caution should be exercised to assure that the noise floor remains at or below that specified elsewhere in this document. ( m V / P a )y s e n s i t i v i t t r a n s d u c e r a n d r a t e s l e w r e q u i r e d w h e r e, msk P a1600
5、 SdtdVSdtdVSAE J247 Revised APR2013 Page 10 of 23 FIGURE 4 - DATA CHANNEL FREQUENCY RESPONSE FIGURE 5 - FREQUENCY CONTENT OF IN-VEHICLE TEST -20 0 0-10 0 0010002000300040000 .0 0 0 0 .0 5 0 0 .1 0 0 0 .1 5 0 0 .2 0 0 0 .2 5 0 0 .3 0 0Time (se c onds)Pressure(Pa)P - t Da ta Sho w in g Fr equ ency C o
6、ntent- Cou pe w i th W indo ws Cl ose dUn filtere d Da taDa ta F il tere d a t CFC 18 0SAE J247 Revised APR2013 Page 11 of 23 5. DATA ACQUISITION SPECIFICATIONS 5.1 A/D Conversion Analog to Digital signal conversion can be performed using an analog-to-digital converter with a minimum of 16 bits (24
7、bit converters are preferred). 5.2 Sampling Rate The human ear can hear air pressure fluctuations with frequencies from 20 Hz to 20 kHz. While it may not be discernable to the human ear, low frequency air pressure fluctuations (DC to 20 Hz), may still affect damage to the hearing mechanism. Therefor
8、e, given Nyquist frequency considerations, the minimum sampling rate should be greater than 40 kHz. Because it has been shown that collecting data at different frequencies can result in different ARU value calculations from AHAAH, the sampling rate shall be specified at 48 kHz (Binseel, Kalb, and Pr
9、ice, “Using the AHAAH Software, Beta Release W93e“, 2009). This will allow comparisons of data from different labs without concern for different sampling rate effects. 6. HEADFORM DIMENSIONS In order to facilitate measurement consistency, repeatability, and best correspondence to the human hearing s
10、ystem, binaural measurements should be made using a headform meeting the dimensional guidelines and tolerances defined in the appropriate standards listed below. These minimum acceptable headform requirements and tolerances are required to ensure that measurements may best capture the acoustic input
11、 as would occur at the human ear canal. 6.1 ANSI S 3.36-1985 and ITU-T P.58 give guidelines for the acceptable dimensions of the headform itself. Table 1 below is a modified version of Table 1/P.58, excluding only the mouth dimensions, since a mouth is not required for measurements in the receiving
12、direction. Many of the dimensions, given in mm, are referenced to the ear canal entrance point (EEP), which is the point located at the geometric center of the ear canal opening. Please note: The nominal values correspond to P.58, but the tolerances have been enlarged to cover a wider range of exist
13、ing headforms. The minimum and maximum values for headforms meeting the P.58 specification are added in brackets ( ). 6.2 ITU-T P.58 gives guidelines for the acceptable directional characteristics of a complete head and torso simulator. These characteristics are specified below in Table 2, a non-mod
14、ified version of Table 4/P.58. The table provides monaural right ear frequency response and tolerance values for three directions (azimuth angles) in the horizontal plane (0 degrees elevation). In each case, the frequency response values are referenced to the frequency response for direct frontal so
15、und incidence (0 degrees azimuth and elevation). Increasing azimuth angle values are measured to the right of direct frontal incidence, i.e., 90 degrees is to the right, 180 degrees points directly to the rear, and 270 degrees is to the left. 6.3 ITU-T P.57 gives example guidelines for suitable earf
16、orms. The pinna, shapes described in ITU-T P.57 section 5.3.3 (Type 3.3) and section 5.3.4 (Type 3.4), are examples only and are not intended to be comprehensive. For in-vehicle measurements which are not close-coupled to the ear (i.e., sealed headphone or earplug), it is not necessary to use comple
17、te artificial ears with extended ear canals intended to match the acoustic impedance of the human ear. However, it is necessary to use a complete artificial ear, including a pinna that meets the directional characteristics specified in Table 2. 6.4 To accurately reproduce geometrically-imparted head
18、 related transfer functions and correct pressure measurement at the eardrum location, the pinnas should include cavum conchae and ear canals of minimum 4 mm depth. Longer ear canals are acceptable, but not mandatory. The ear canals should be terminated by calibrated transducers. It is strongly recom
19、mended that cavum conchae with minimum 5 mm depth be used; however, others may be used as long as the directional criteria in Table 2 are met. The pinna can be made of a solid or deformable material as in ITU-T P.57 Guidelines. 6.5 If binaural measurements, made according to the Section 6 guidelines
20、 herein, are intended for input into the AHAAH hearing model, the measurements should be made without binaural equalization. The unequalized time-domain data should be provided as input to the AHAAH model using the “Microphone relative to ear” setting of “3:eardrum”. If, on the other hand, measureme
21、nts are intended for reduced-level playback or other pre-listening analysis purposes, then an equalization, appropriate to the measured sound field, should be used. SAE J247 Revised APR2013 Page 12 of 23 TABLE 1 - HEAD AND TORSO DIMENSIONS (LINEAR DIMENSIONS IN MM) ACCORDING TO ITU-T P.58 Dimension
22、Nominal Minimum Maximum Head breadth 152 147 (147) 160 (154) Head length 191 190 (190) 220 (205) EEP to vertex 130 120 (128) 136 (136) EEP to EEP distance 132 130 (130) 150 (133) EEP to occipital wall 94 92 (92) 100 (100) EEP to shoulder a) 170 167 (167) 200 (181) Chin-to-vertex length 224 216 (216)
23、 240 (225) Shoulder breadth 420 400 (400) 455 (455) Chest depth 235 178 (178) 272 (272) Shoulder depth b) 110 108 (108) 161 (161) Shoulder location c) 10 -4 (-4) 46 (46) Head and torso height 600 (600) a) Measured from the shoulder surface, 175 mm sideways from the vertical plane which bisects the l
24、ine joining the ear canal entrance points and divides the head and torso into symmetrical halves, upward to the horizontal plane which contains the line joining the ear canal entrance points. b) Measured between front and back shoulder points, 175 mm sideways from the vertical plane (as described ab
25、ove). c) Measured from the point of the shoulder section, 175 mm sideways from the vertical plane (as described above), to the head and torso vertical plane which contains the line joining the ear canal entrance points (positive direction is rearward, behind this plane). SAE J247 Revised APR2013 Pag
26、e 13 of 23 TABLE 2 - MONAURAL FREQUENCY RESPONSE (dB) RIGHT EAR ACCORDING TO ITU-T P.58 Frequency (Hz) Azimuth angle Tolerance (dB) 90 180 270 100 0.0 0.0 0.0 1.0 125 0.5 0.0 0.0 1.0 160 1.0 -0.5 0.0 1.0 200 1.5 -0.5 -1.0 1.0 250 1.5 -0.5 -1.0 1.0 315 2.0 -0.7 -1.0 1.5 400 2.5 -1.0 -1.0 2.0 500 3.5
27、1.0 -1.0 2.0 630 4.5 0.0 -0.5 2.0 800 4.0 0.5 -1.0 2.0 1 000 4.5 1.5 -1.0 2.0 1 250 5.8 2.5 -0.5 2.5 1 600 5.0 1.0 -0.5 2.0 2 000 -0.5 -2.0 -4.0 2.0 2 500 0.0 -2.5 -6.0 2.0 3 150 1.5 -3.0 -8.0 2.0 4 000 1.5 -3.0 2.0 5 000 3.5 -4.0 4.5 6 300 12.0 -1.0 4.5 8 000 12.0 3.5 6.0 (10 000) 6.0 -3.0 7. CALI
28、BRATION GUIDELINES 7.1 Microphone Laboratory Calibrations Laboratory calibrations should be conducted on a periodic basis, to documented procedures, and with standards and test equipment traceable to the National Institute for Science and Technology (NIST), DIN, ECE or similar organization. 7.1.1 Fr
29、equency response calibration should be conducted with a free-standing microphone (not in the headform), at the highest amplitude practical, preferably within 3 dB of full-scale when feasible. 7.1.2 Amplitude linearity checks should be made at full-scale and at -20, -40, -60 dB when feasible. 7.1.3 W
30、henever it is impossible to include the transducer in tests under 7.1.1 and 7.1.2, the transducers may be simulated and voltage insertion calibration techniques used. However, the transducers should then be calibrated for amplitude and frequency response according to the manufacturers recommendation
31、s. Then, after installation, the data channel should be checked with an acoustic calibrator at the highest level possible. 7.1.4 Checks should be made to determine the effects of any anticipated test site conditions (for example, temperature, barometric pressure, mechanical shock, acceleration, phot
32、ographic lighting, electrical interference, etc.). SAE J247 Revised APR2013 Page 14 of 23 7.2 Microphone Test-Site Calibrations Test-site calibrations are end-to-end data channel calibrations. 7.2.1 Closed-coupler acoustic calibration techniques should be used to check the operation and calibration
33、of the microphone transducers. In the case of binaurally-housed transducers, a specially designed adapter should be used. The adapter should be capable of forming an airtight seal to the ear canal on one hand and the calibrator source on the other hand. The calibration correction, if any, due to the
34、 modified volume should be published or otherwise known. 7.2.2 Calibrations should be conducted at the highest amplitude practical, preferably a level equal to or greater than 50% (-6 dB) of data channel full-scale when feasible. Voltage insertion techniques using transducer laboratory calibration d
35、ata may be used. 7.3 Pressure Transducer Calibrations Piezoelectric pressure transducers are dynamic devices and require dynamic calibration. The most accurate method of doing this is with a shock tube. However, field calibrations can be carried out with a closed coupler-acoustic calibration techniq
36、ue as in 5.2.1 or other techniques described in ISA-37.16.01: “A Guide for the Dynamic Calibration of Pressure Transducers“. Calibrations may also be carried out with a closed volume high speed valve technique described in Appendix A of International Test Operations Report (ITOP) 4-2-822, “Electrica
37、l Measurement of Airblast Overpressure and Impulse Noise“. 8. TEST GUIDELINES The following are suggested when conducting acoustic impulse tests: 8.1 General Test Guidelines 8.1.1 Instrumentation used should be properly documented showing latest laboratory calibration dates. 8.1.2 Transducer calibra
38、tions should be conducted at the test-site before and after each test. 8.1.3 Several seconds of ambient noise should be recorded to establish the noise floor at the time of the test. 8.1.4 “Initiation Time“ (1 ms) should be recorded along with the acoustic data. A minimum of 5 ms of acoustic data be
39、fore initiation time should also be recorded (see Section 9). 8.1.5 Data channel full-scale should be selected so that anticipated maximum sound pressure level will be within 3 dB (30%) of full scale for a 16 bit digital measurement system. For measurement systems with more resolution (higher bit le
40、vels) this is not a concern, provided the measurement systems dynamic range includes both the anticipated maximum sound pressure level and the minimum sound pressure level of interest, 93 dB. In any case, should the actual sound pressure level limit exceed the full scale measurement capabilities (an
41、 “out of range” condition), the data is of course invalid and cannot be used. 8.1.6 Acceleration of the Instrumentation 8.1.6.1 If using free standing pressure transducers or microphones, care should be exercised to mechanically isolate the transducers from acceleration inputs, consistent with the t
42、est vehicle environment. When the transducer is subjected to accelerations, output compensation may be required. 8.1.6.2 Even if the transducer is isolated, it should be mounted in such a way as to orient the axis least sensitive to acceleration along the direction expected for the largest component
43、 of the acceleration vector. SAE J247 Revised APR2013 Page 15 of 23 8.1.6.3 For all test conditions, care should be taken to avoid contact between the airbag and the transducer or headform. In some cases, for example, with some head curtain airbags, contact avoidance may not be possible. In such cas
44、es, the signal must be carefully examined for influence of acceleration. For such circumstances data from a headform mounted accelerometer could be beneficial. In cases where the headform is contacted by the airbag, a new test should be considered with the headform repositioned just enough to avoid
45、the contact. 8.1.7 Cable capacitance and cable length, which effectively governs cable capacitance, and can have a resulting effect on slew rate and maximum recordable sound pressure, should be carefully controlled. Manufacturers recommendations should be followed. In addition, cable lengths should
46、not be changed without recalibration once a transducer is calibrated with a given cable (see discussion on slew rate in 4.9). 8.1.8 Cables should be routed carefully, and fastened, taped down, or otherwise fixed, to avoid pinching and whipping. Cable whipping has been shown to cause microphonics, wh
47、ich is the generation of a spurious electrical signal that resembles a pressure impulse, but is actually electrical noise associated with the motion of the cable. 8.1.9 Airbag deployment has been shown to generate significant amounts of electrostatic charge. As such, the vehicle, headform electronic
48、s, and any dummy or mannequin used to position the pressure transducers within the vehicle or reverberation chamber, must be properly grounded to a reliable earth ground (see Figure 6; see also IEST RD-DTE012.2, Handbook for Dynamic Data Acquisition and Analysis). 8.1.10 Rouhana et al. (1994), Rouha
49、na et al. (1998), and Banglmaier and Rouhana (2003) showed that even nominally identical airbag modules can exhibit large variations in the pressure-time histories and ARUs predicted by the AHAAH model. Therefore, the test engineer should consider statistical significance before deciding on the number of modules to be tested. 8.1.11 Many different headforms have been used in the past for measuring airbag impulse noise. Some meet minimum acceptable requirements for the external ear, transducer
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