1、 flIL-STD-7LIO -2 HF W 7797711 0035233 3 MIL-STD-740-2(SH) 30 December 1986 SUPERSEDING MIL-STD-i40B(SHIPS)(IN PART) 13 January 1965 (See 6.6) MILITARY STANDA?ZJ 5V3JCTUREBOR.NE VIBRATORY ACCELERATION MEASUREMENTS AND ACCEPTANCE CRITERIA OF SHIPBOARD EQUIPMENT AMSC N4009 AREA HFAC DISTRIBUTION STATE
2、MENT _I_ A Approved for public release; distribution unlimited 7 THIS DOCUMENT CONTAINS ,3 General Specifications and Tests for (Shipboard Application). MIL-“17508 - Mounts, Resilient; Types 6E2000, 6E900, 6E900BB, 7E450, 7E450BB, 6E150, and 6E100. MIL-“19379 - Mounts, Resilient, Mare Island Types l
3、lM15, llM25, and 1OM50. MIL-“19863 - Mounts, Resilient: Type 5B5000H. MIL-“21649 - Mount, Resilient, Type 5M10,OOO-H. STANDARD MILITARY MIL-STD-1621 - Acoustical and Vibrational Standard Reference Quantities. (Copies of specifications and standards required by contractors in connection with specific
4、 acquisition functions should be obtained from the contracting activity or as directed by.the contracting officer.) 2.2 Other publications. The following documents form a part of this standard to the extent specified herein. Unless otherwise specified, the issues of the documents which are DoD adopt
5、ed shall be those listed in the issue of the DoDISS specified in the solicitation. The issues of documents which have not been adopted shall be those in effect on the date of the cited DoDISS. AMERICAN NATIONAL STANDARDS INSTITUTE (ANSI) S1.6 - Preferred Frequencies and Band Numbers for Acoustical S
6、1.ll - Octave, Half-Octave, and- Third-Octave Band Filter Sets. S2.2 - Calibration of Shock and Vibration Pickups; Methods for. Measurements. (Application for copies should be addressed to Publication Sales, Dept. STD, American Institute of Physics, 335 East 45th Street, New York, NY 10017.) (Nongov
7、ernment standards are generally available for reference from libra- ries. They are also distributed among nongovernment standards bodies and using Federal agencies.) 2.3 Order of precedence. In the event of a conflict between the text of this standard and the references cited herein, the text of thi
8、s standard shall take precedence. 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-STD-740 -2 HF W 77779LL 0035238 4 M MIL-STD-740-2(SH) 30 December 1986 3. DEFINITIONS 3.1 Symbols. Symbols used herein are as follows: ao = Reference vibratory ac
9、celeration (see 3.2.3) FFT = Fast Fourier Transform fc = Band-center frequency (see 3.2.8) fl = Lower band-edge frequency (see 3.2.7) f2 = Upper band-edge frequency (see 3.2.7) gn = International standard acceleration of free fall (see 3.2.3) La = Structureborne vibratory acceleration level (see 3.2
10、.4) DIM = Distributed isolation material (see 3.14.2) 3.2 Terminology. 3.2.1 Frequency. The frequency of a function periodic in time is the reciprocal of the period. The unit of frequency is the hertz (Hz). One Hz is equa-l to one cycle per second. 3.2.2 Level. The level of a vibratory quantity is t
11、he logarithm of the ratio of that quantity to a reference quantity of the same kind. The base of the logarithm, the reference quantity, and the kind of level shall be indicated. 3.2.3 Reference vibratory acceleration (ao)-. The reference quantity is 10 micrometers per second squared (pm/sz) root mea
12、n square (rms) (10 pm/s2 = centimeters per second squared (cm/s2) = 393.7 x inches per second squared (in/s2). Units of the International System (SI) as specified in MIL-STD-1621 are prescribed for the measurement of vibrational quantities. The-acceleration of 10 pm/s2 is nearly one millionth of the
13、 in ernational standard acceleration of free fall gn = 9.80665 m/s2 = 386.089 in/s . Therefore, for reporting in accordance with this standard, the reference vibratory acceleration may be described as ao = 1 1.18, (rms). For calibration purposes use 1 gn (rms) = 120 dB re ao. I 3.2.4 Structureborne
14、vibratory acceleration level (La). La, in decibels (dB) is 20 times the logarithm to base 10 of the ratio of the measured structure- borne vibratory acceleration to ao; that is, measured acceleration in pm/s2 (rms) 10 pm/2 (ms) La in dB = 20 log 10 3.2.5 Band. A band is a continuous spread of freque
15、ncies. 3.2.6 Band level. Band level is the vibratory level in a particular band. 3.2.7 Band-edge frequencies. The upper (f2) and lower (fl) band-edge frequencies are those frequencies above and below the frequency of maximum response of a filter at which the response to a sinusoidal signal is 3 dB b
16、elow the maximum response. 3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-STD-740-2(SH) 30 December 1986 3.2.8 Nominal band-center frequency ( f r). The nominal band center fre- quency may be either the arithmetic or geometric mean between the
17、 band-edge frequencies of a band, the arithmetic mean being fc = (fl 3- f2)/2 and the geometric mean being fc = (fl x f2) /. The arithmetic mean is normally used when constgnt bandwidth filters, such as 50 Hz are specified. The geometric mean is normally used for filters of constant percentage bandw
18、idth, such as one-third octave band filters. 3.2.9 Bandwidth. The bandwidth of a filter is the difference between fl and f2. This difference may be expressed in Hz, as a percentage of the band- center frequency, or as the interval between the band-edge frequencies, in terms of octaves or parts there
19、of, such as one-third, one-fifteenth, etc. 3.2.10 One-third octave band. The one-third octave bands designated in this standard are those whose band-center frequencies are preferred one-third octave bands specified in ANSI S1.6. The width of a one-third octave band is approximately 23 percent of its
20、 band-center frequency. 3.2.11 Narrowband. Narrowband, when used in this specification, refers to that measurement bandwidth obtained with the use of a 400 line fast fourier transform. The preferred increments are zero Hz to 400 Hz, 400 Hz to 2000 Hz, and 2000 Hz to approximately 10,000 Hz. Other ba
21、ndwidths, not to exceed 10 percent of the center frequency, may be used if approved by the contracting activity. 3.2.12 Equipment. The term “equipment“, when used in this standard, refers to any equipment such as a system, subsystem, or part thereof which is being measured to determine compliance wi
22、th the structureborne acceptance criteria. 3.2.13 _I_ Type. The term “type“ is used to divide equipment into groups for the purpose of specifying structureborne noise criteria. 3.2.13.1 Type I. Type I designates reciprocating compressors and internal combustion engines. 3.2.13.2 Type II. Type II des
23、ignates pumps, valves, and life support equipment. 3.2.13.3 Type III. Type III designates equipment not covered by types I, II and IV. 3.2.13.4 Type IV. Type IV designates vaneaxial fans. 3.2.14 Mounting. 3.2.14.1 Resiliently mounted equipment. Resiliently mounted equipment is equipment which is iso
24、lated from a support structure by Navy approved resilient mounts. For equipment which is not isolated by Navy approved resilient mounts, the criteria for solidly mounted equipment shall apply. Approved resilient mounts are mounts in accordance with MIL-M-17185, MIL-M-17508, MIL-M-19379, MIL-“19863,
25、or MIL-“21649. For the purposes of this standard, DIM mounted equipment is considered to be solidly mounted equipment. 4 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-STD-7qO -2 HF 7777733 00352qO 2 MIL-STD-740-2(SH) 30 December 1986 3.2.14.2 C
26、ompound mounts. A compound or two stage mount is a three element device consisting of an intermediate mass contained between resilient elements. I 3.2.14.3 Solidly mounted equipment. Solidly mounted equipment is equipment which is attached directly to the supporting structure. For the purposes of th
27、is standard, DIM mounted equipment is considered to be solidly mounted equipment. 3.2.15 Contracting activity. Contracting activity, when used in this standard is the Government or its authorized representative. 4. GENERAL REQUIREMENTS 4.1 Equipment sampling. If sampling is called for by the acquisi
28、tion specifications or the contract or order (see 6.3), selection of equipment for test shall be on the basis of conformance to the drawing requirements for that equipment, and shall not consider advance measurements, observations, or opinions about the acoustical performance of the particular equip
29、ment sample. 4.2 Equipment evaluation plan. When specified in the contract or order, an equipment structureborne vibratory acceleration measurement plan shall be prepared (see 6.4). 4.3 Testing. The Government shall have the option to witness all tests con- ducted to meet contractual requirements. N
30、otification of tests letters shall be prepared in accordance with the data ordering document included in the contract or order (see 6.4) as specified (see 6.3). 4.4 Reporting standards. 4.4.1 Reference quantity identification. The applicable reference quantity shall be indicated on every table, figu
31、re, and graph, and at least once in the text. The reference quantity may be introduced by “re“ which indicates that the level is “with reference to“. For example, the 100 Hz one-third octave band level re 10 pm/s2 is 85 dB. 4.4.2 Measurement bands. The bandwidths of the measurement bands shall be re
32、ported together with the measured levels. Normal procedure for reporting measured levels shall include the bandwidth and the band-center frequency with the level. For example: one-third octave 100 Hz band level was 85 dB re 10 pm/s2; the 10 Hz bandwidth 100 Hz band level was 85 dB; or, the 6 percent
33、 bandwidth 100 Hz band level was 85 dB re 10 vm/s2. 4.4.3 Plotting format. Plotting formats shall be in accordance with MIL-STD-1621. That is, all plots of data in which a level in dB is plotted against frequency on a logarithmic scale shall be made on graphs in which a factor of ten in frequency is
34、 equal in length to 25 dB (preferred) or 50 dB. Where the bandwidth of analysis is one-third octave or larger, one factor of ten in frequency shall be 50 mm (preferred) or 2 inches in length. The ordinate and abscissa of all graphs shall be labeled so that levels and frequencies can be readily unher
35、stood without need to refer elsewhere in the report. Narrowband data shali be plotted using a linear frequency scale and the vibration level in decibels. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-STD-7LI0 -2 HF m 77777LL 00352LIL LI m MIL-S
36、TD-740-2( SH) 30 December 1986 5. DETAILED REQUIREMENTS 5.1 Structureborne acceptance criteria. Structureborne acceptance criteria shall be in accordance with figure 2 for the type of equipment specified (see 3.2.13 and 6.3). The one-third octave band levels that must be compared to the specified le
37、vels shall be measured in accordance with 5.2 for the locations specified in 5.3.1. Equipment which fails to meet the acceptance criteria shall not be installed in the ship until the following have been accomplished: (a) When specified in the contract or order, a sound test failure notification and
38、recommendations report shall be prepared for each deficient equipment item measured (see 6.4). deficient equipment or directed the specific course of action. (b) The Government or the contracting activity has accepted the 5.1.1 Figure 2 correction factors. Certain correction factors, shown in the no
39、tes on figure 2, apply only for some specific equipment, anticipated ship- board mounting and system connection configurations, or combinations thereof. For example, 15 dB shall be subtracted from the type II curve for solidly mounted non-sea connected pumps. No correction factor shall be applied fo
40、r other than the specific conditions or combinations shown on figure 2. For example, no correction to the type II curve shall be made for resiliently mounted sea connected pumps. 5.2 Measurements. The measurements required by this standard are normally made using an accelerometer attached to the equ
41、ipment or its supporting structure, as outlined in 5.3, which covers measurement locations, and 5.4, which covers the details of accelerometer attachment. These measurements are normally made during steady state operating conditions. 5.2.1 Required measurements. Unless otherwise specified (see 6.3),
42、 the following measurements shall be made: 5.2.1.1 General. Measurements in accordance with 5.2.2 shall be made at the specified locations in three mutually perpendicular directions , one of which shall be vertical. Additionally, for equipment with horizontally oriented shaft, one other direction sh
43、all be perpendicular to the equipment shaft. For valves, measurements in two directions are required; perpendicular and parallel to the flow for outlet flanges or nozzles, and three mutually perpendicular directions for other structural connections, except the inlets. 5.2.1.2 One-third octave band m
44、easurements. One-third octave band measure- ments in accordance with 5.2.2.1 shall be made at the locations specified in 5.3. 5.2.1.3 Narrowband measurements. These measurements may be required by the contracting activity and shall also be made whenever the equipment fails the one- third octave band
45、 criteria at the location and in the direction of the failure. When narrowband analyses are required they shall be made in accordance with 5-2.2.2. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-STD-740-2( SH) 30 December 1986 5.2.2 Measurement
46、procedures. 5.2.2.1 One-third octave band measurement procedure. One-third octave band La shall be measured for the ambient (nonoperating) condition and for the condi- tions specified in 5.8 using accelerometers, preamplifiers, meters, connecting cable, and actual or synthesized one-third octave ban
47、d filters, a graphic level or X-Y recorder or digital printer, and connecting cables. The one-third octave band filters shall cover band-center frequencies over the range specified (unless otherwise specified (see 6.3), this range shall include the 10-Hz band or the fundamental forcing frequency of
48、the equipment, whichever is lower through the 10,000-Hz band) and have rejection characteristics beyond the band-edges at least as good as those specified in ANSI S1.11, for class II filters. The recorder shal1,provide a permanent reproducible copy conforming to 4.3.3. The complete system shall howe
49、ver, the optional mounting pads and clamps shown on figure 1 may.be used to attach the items. If, in specific cases, the mounting fixture of figure 1 cannot be used, the alternative mounting fixture shall be approved by the contracting activity. The combined assembly of equipment item and mounting fixture shall be resiliently mounted and oriented so that the item is in its normal shipboard installation position. 5.7 Calibration of instrumentation. Instrumentation used shall hav
