1、5HDIILUPHGE$16,-XO5HDIILUPHGE$16,0DUFK5HDIILUPHGE$16,0DUFK5HDIILUPHGE$16,0DUFKAMERICAN NATIONAL STANDARDS ON ACOUSTICS The Acoustical Society of America provides the Secretariat for Accredited Standards Committees S 1 on Acoustics, 52 on Mechanical Shock and Vibration, 53 on Bio acoustics, and S 12
2、on Noise. These committees have wide representation from the technical community (manufacturers, consumers, and general-interest representa tives). The standards are published by the Acoustical Society of America through the American Institute of Physics as American National Standards after approval
3、 by their respective standards committees and the American National Standards Institute. These standards are developed and published as a public service to provide stan dards useful to the public, industry, and consumers, and to Federal, State, and local governments. This standard was approved by th
4、e American National Standards Institute as ANSI S1.25-1991 on 24 October 1991. An American National Standard implies a consensus of those substantially concerned with its scope and provisions. An American National Standard is intended as a guide to aid the manufacturer, the umwmer, and the general p
5、ublic. The existence of an American National Standard does not in any respect preclude anyone, whether he has approved the standard or not, from manufacturing, market ing, purchasing, or using products, processes, or procedures not conforming to the standard. Ameri can National Standards are subject
6、 to periodic review and users are cautioned to obtain the latest editions. Cwtion Nottf:e: An American National Standard may be revised or withdrawn at any lime. The proce dure of the American National Standards Institute require that action be taken to reaffirm, revise, or withdraw this standard no
7、 later than five years from the dare of publication. The American National Standards Institute, Inc. (ANSI) is the national coordinator of voluntary standards development and the clearing house in the U.S. for information on national and international standards. The Acoustical Society of America (AS
8、A) is an organization of scientists and engineers formed in 1929 to increase and diffuse the knowledge of acoustics and to promote its practical applications. Published by the Acoustical Society of America through the American Institute of Physics 1992 by Acoustical Society of America. This standard
9、 may not be reproduced in whole or in part in any form for sale, promotion, or any commercial purpose, or any purpose not falling within the fair-use provisions of the Copyright Act of 1976, without prior written permission of the publisher. For permission, address the Standards Secretariat of the A
10、coustical Society of America. FOREWORD comfort. At the time this standard was submitted to Accredited Standards Committee S 1, Acoustics, for final approval, the membership was as follows: G. S. K. VVong, Cha R. L. McKinley, Vice-Chairman A. Brenig, Secretary Acoustical Society of America T. F. W. E
11、mbleton, G. S. K. Wong !A/t) Air-Conditioning and Refrigeration Institute S. Wang, ). Clukey !Ait) American Industrial Hygiene Association C. D. Bohl AT the criterion level is 90 dB, the threshold level is 80 dB and the exchange rate is 5 dB. The options for class designation are: Frequency Weightin
12、g Time Constant Criterion Level Threshold Level Exchange Rate A orC F (FAST); S (SLOW) 90, 85, 84, 80, V (Variable) 90, 80, V (Variable) 5, 4, 3 NOTE: For dosimeters with variable criterion and threshold lev els, the selected levels shall be specified in order to obtain a valid reading. 4. GENERAL C
13、HARACTERISTICS 4.1 General A noise dosimeter is generally a combination of a microphone, an amplifier with specified frequency weighting, a squaring device, an exponential averaging device with a specified time constant, a holding upper limit indicator, an exponent circuit with a specified ex-ANSI 5
14、1.25-1992 3 AMPLIFIER AND SQUARING MICROPHONE : FREQUENCY DEVICE WEIGHTING EXPONENTIAL EXPONENT THRESHOLD AVERAGING DEVICE CIRCUIT CIRCUIT HOLDING UPPER ILIMIT INDICATOR INTEGRATOR ! 1 INDICATOR j FIG. 1. Block diagram of functional elements of a noise dosimeter. ponent, a threshold circuit, a devic
15、e that integrates with respect to time, and an indicator. The actual in strument need not be separable into such individual functional elements since the primary basis of accept ability of the instrument is the overall performance. For convenience of description of the required charac teristics of t
16、he device, however, the instrument is treat ed as if it were a cascade of separable individual ele ments. (See Fig. 1.) 4.2 Relative Frequency Response The frequency characteristics of the overall instru ment are specified in Table 1. The relative response level is given at discrete preferred freque
17、ncies, but the response must be that corresponding to a smooth curve at the specified frequencies. The tolerances are identical to those for a Type 2 sound-level meter (ANSI S 1.4-1983). The specified tolerances are abso lute tolerances at the criterion level and at the refer ence ambient conditions
18、 specified in Sec. 7.1. Above 10 kHz, the roJl-off rate must not be Jess than 6 dB/oc tave. 4.3 Exponential Averaging The time constant of the exponential averaging de vice connected to the output of the squaring device is nominaJly 1 s, corresponding to the SLOW response of a standard sound level m
19、eter, or 0.125 s, correspond ing to the FAST response. NOTE: For dosimeters based on the 3 dB exchange rate, the ex ponential averaging device is optional. 4.4 Threshold The threshold circuit shall be placed after the expo nential averaging device in order that the integrator will properly integrate
20、 over sensed sound levels that exceed the threshold. 4.5 Integration The integrator integrates a power function of the mean square signal over time. This function is deter mined by the exponent circuit (see the block dia gram). The exponent depends on the exchange rate, being 0.6 for the 5 dB rate,
21、0. 75 for the 4 dB rate, and 1.0 for the 3 dB rate. The integrated output over time of the exponential circuit as modified by the threshold circuit is proportional to the percentage criterion expo sure. 4.6 Indicator The indicator may be built into or separate from the dosimeter. The number displaye
22、d shall be a percen tage. The resolution of the display shall be sufficient to express this percentage rounded to the nearest integer. 4 AMERICAN NATIONAL STANDARD TABLE l. Random incidence relative response level as a function of frequency for A- and C-weighting. (Type 2 Tolerances. ANSI Sl.4-1983)
23、. Nominal Exact A- C-Frequency Frequency Weighting Weighting Hz in Hz dB dB 20 25 31.5 40 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000 19.95 25.12 31.62 39.81 50.12 63.10 79.43 100.0 125.9 158.5 199.5 251.2 316.2 398.1 501.2 631.0 794.3 100
24、0 1259 1585 1995 2512 3162 3981 5012 6310 7943 10000 -50.5 -44.7 -39.4 -34.6 -30.2 -26.2 -22.5 -19.1 -16.1 - 13.4 - 10.9 -8.6 -6.6 -4.8 -32 - 1.9 -0.8 0 + 0.6 + 1.0 +1.2 +1.3 + 1.2 + 1.0 + 0.5 -0.1 -1.1 -2.5 -6.2 -4.4 -3.0 -2.0 -1.3 -0.8 -0.5 -0.3 -0.2 -0.1 0 0 0 0 0 0 0 0 0 -0.1 -0.2 -0.3 -0.5 -0.8
25、 -1.3 -2.0 - 3.0 -4.4 Tolerance 3 3 3 2 2 2 2 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 2 2 2.5 2.5 3 3.5 4.5 5 + 5- 00 Nominal frequencies are as specified in ANSI Sl.6-l984 (R 1990), American National Standard Preferred Frequencies and Band Numbers for Acoustical Measurements. Exact frequenc
26、ies are given above to four significant figures and are calculated from frequency equals 10“ IN, where N is an integer band number from 10 to 43 (I Hertz corresponds toN= 0). Above 10kHz, the roll-off rate must not be less than 6 dB/octave. 4.7 Principle of Operation The principle of operation of th
27、e dosimeter is de scribed in mathematical terms below. T D(Q) = (100/T,) i 10(L- L,)!q)dt (I) where: D( Q) = percentage criterion exposure for exchange rate Q; T, = criterion sound duration = 8 hours T = measurement duration in hours; t = time in hours; L =SLOW (or FAST) A-weighted sound lev-el, a f
28、unction of time, when the sound level is greater than or equal to L, or equals - oo when the A-weighted sound level is less than Lt; L, = threshold sound level specified by the manufacturer; L, =criterion sound level specified by the man-ufacturer; Q = exchange rate in decibels; and q = parameter th
29、at determines the ex-change rate, where q = 10 for a 3 dB exchange rate q = 5/log 2 for a 5 dB exchange rate q = 4/log 2 for a 4 dB exchange rate NOTE: The factor of 100 in the equation produces a result that is a percentage. If the sound level is greater than the threshold level and it is held cons
30、tant, as during testing, D( Q) = 100( TIT,) 10 ( L L, llql (2) The average sound level during the sample time, T, over which a percentage criterion exposure is mea sured, is L v = L, + q log D(Q) X Tj100T (3) If the sound level is held constant during a test, the average sound level is that constant
31、 level. 4.8 Electrical Test Signal The manufacturer shall provide the means to sub stitute an electrical signal for the microphone for the purpose of performing tests on the complete instru ment without the microphone. The manufacturer shall also provide suitable test points when required by the tes
32、t procedures recommended in this standard. 5 INSTRUMENT CHARACTERISTICS AND TOLERANCES 5.1 Frequency Characteristics The complete instrument, with the microphone mounted in a manner specified by the manufacturer, shall have the frequency response at the criterion level as specified in Table 1, withi
33、n the absolute tolerance limits there listed, in a random incidence sound field (See Sec. 7.2.2). The manufacturer shall state the up per and lower values of sound level L and duration T over which the instrument satisfies the requirements of this standard. A controlled, abrupt cutoff in response sh
34、all be provided for sounds having a level less than ANSI 51.25-1992 5 the threshold level as defined in Sec. 3.10. It is strongly recommended that the threshold level shall be at least 5 dB below the criterion sound level. The actual threshold level must be specified by the manufacturer. 5.2 Directi
35、onal Characteristics The maximum deviation of the free-field relative re sponse level with respect to the random-incidence rela tive response level as a function of angle of incidence shall not exceed the values given in Tables 2 and 3. The specification applies for sound incident on the mi crophone
36、 and whatever part of the instrument case is to be exposed to the sound field when the microphone is mounted relative to the dosimeter in a manner speci fied by the manufacturer, but without an observer present. 5.3 Operating Range Characteristics The instrument shall have an operating range of at l
37、east 50 dB. 5.4 Pulse Range The instrument shall have a pulse range of at least 53 dB. The manufacturer shall state the actual pulse range for tone bursts of 1.0 ms as well as that for the shortest tone burst that meets the accuracy require ment of 2.5 dB. (See Sec. 7.5). 5.5 Amplifier Characteristi
38、cs When a sensitivity range control is included in a noise dosimeter, it shall introduce an error less than 0.5 dB over the frequency range from 63 to 2000 Hz and less than l dB in the frequency ranges from 22.4 to 63 Hz and from 2000 to 11200 Hz for all set tings, relative to a range setting specif
39、ied by the manu facturer as the reference range. The amplifier shall have a pulse range sufficiently large to allow it to drive the detector system to meet the tests given in Sec. 7 .5. 5.6 Linearity The linearity of the system shall be within 0.5 dB over a 30 dB range above the criterion level spec
40、ified by the manufacturer, with a steady sine-wave test sig nal. Over the full operating range, specified by the manufacturer, the linearity shall be within 1.0 dB. Linearity tests are described in Sec. 7. 7. TABLE 2. Maximum allowable deviation of free-field relative response level with respect to
41、random-incidence relative response level when the angle of incidence is varied by 22.5“ from the calibration angle of inci dence (Type 2, ANSI S 1.4-1983). These allowances are added arithmetically to the tolerance limits in Table I. Frequency Allowance (hz) (dB) 31.5 to 2000 2 2000 to 4000 2.5 4000
42、 to 5000 3 5000 to 6300 3.5 6300 to 8000 4.5 5.7 Square Law and Averaging Characteristics The dosimeter shall be calibrated using sine-wave signals. Tests of the accuracy of the detector system (squaring device and exponential averaging device) employing steady state and transient signals are pre sc
43、ribed in Sec. 7.5. 5.8 Power Supply If the instrument is battery operated, the manufac turer shall prescribe a battery test method that ensures the battery voltage is adequate to operate the instru ment within specifications. It is highly desirable that the test method be such as to ensure operation
44、 for a time period of eight hours. TABLE 3. Maximum allowable deviation of free-field relative response level for sounds arriving at any angle of incidence with respect to random-incidence relative response level (Type 2, ANSI Sl.4-1983). These allowances are added arithmetically to the tolerance li
45、mits in Table I. Frequency (Hz) 31.5 to 2000 2000 to 4000 4000 to 5000 5000 to 6300 6300 to 8000 Allowance (dB) 3 + 3, -4 +4, -6 + 5,-8 + 8,-9 6 AMERICAN NATIONAL STANDARD 5.9 Field Calibration A method to confirm that the dosimeter is oper ational shall be prescribed by the manufacturer. This metho
46、d shall constitute an acoustical calibration so that the microphone is included in the test. This test shall have the capability of verifying all circuits includ ing the integrator and display. A single sound level at I kHz at least 3 dB above the criterion sound level and threshold level (if used)
47、is acceptable for the test. 5.10 Holding Upper Limit Trigger Level If a holding upper limit indicator is provided, its root-mean-square (rms) trigger level shall be stated by the manufacturer and it shall be tested by the methods given in Sec. 7.6. 6. SENSITIVITY TO VARIOUS ENVIRONMENTS 6.1 Static P
48、ressure The sensitivity of the instrument shall not change by more than 0.5 dB for a variation of 10% in static pressure, stated in 7 .1. 6.2 Noise When the microphone is replaced by an equivalent electrical impedance and the dosimeter is placed in a sound field equal to the upper limit of the operating range for the period of time corresponding to a crit erion exposure of 100%, the indication shall be I% or less. For very high operating ranges, the time period shall not be shorter than 5 seconds. In a quiet environ ment (lower than the threshold level) when the micro phone is replaced by an
