SIST EN 27779:1999
(Main)Acoustics - Measurement of airborne noise emitted by computer and business equipment (ISO 7779:1988)
Acoustics - Measurement of airborne noise emitted by computer and business equipment (ISO 7779:1988)
Specification of procedures for measuring and reporting the noise emitted by computer and business equipment
Akustik - Geräuschmessung an Maschinen - Luftschallemission, Hüllflächen- und Hallraumverfahren-Geräte der Büro- und Informationstechnik (ISO 7779:1988)
Acoustique - Mesurage du bruit aérien émis par les équipements informatiques et de bureau (ISO 7779:1988)
Akustika - Merjenje zračnega hrupa računalnika in pisarniške opreme (ISO 7779:1988)
General Information
Relations
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Akustik - Geräuschmessung an Maschinen - Luftschallemission, Hüllflächen- und Hallraumverfahren-Geräte der Büro- und Informationstechnik (ISO 7779:1988)Acoustique - Mesurage du bruit aérien émis par les équipements informatiques et de bureau (ISO 7779:1988)Acoustics - Measurement of airborne noise emitted by computer and business equipment (ISO 7779:1988)35.020Informacijska tehnika in tehnologija na splošnoInformation technology (IT) in general17.140.20Emisija hrupa naprav in opremeNoise emitted by machines and equipmentICS:Ta slovenski standard je istoveten z:EN 27779:1991SIST EN 27779:1999en01-november-1999SIST EN 27779:1999SLOVENSKI
STANDARD
SIST EN 27779:1999
SIST EN 27779:1999
SIST EN 27779:1999
INTERNATIONAL STANDARD 7779 INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXflYHAPOAHAR OPrAHM3A~Mfl I-IO CTAHAAPTM3A~MM Acoustics - Measurement of airborne noise emitted by Computer and business equipment Acoustique - Mesurage du bruit a&ien hmis par les hquipements informatiques et de bureau ISO First edition 1988-06-15 Reference number ISO 7779: 1988 (E) SIST EN 27779:1999
ISO7779:1988 (EI Foreword ISO (the International Organization for Standardization) is a worldwide federation of national Standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Esch member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with ISO, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISO Council. They are approved in accordance with ISO procedures requiring at least 75 % approval by the member bodies voting. International Standard ISO 7779 was prepared by Technical Committee ISO/TC 43, A cous tics. Users should note that all International Standards undergo revision from time to time and that any reference made herein to any other International Standard implies its latest edition, unless otherwise stated. 0 International Organkation for Standardization, 1988 Printed in Switzerland ii SIST EN 27779:1999
IsO7779:1988E) Contents Page 0 Introduction . 1 Scope and field of application . 2 Conformance . 3 References . 4 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Method for determining Sound power levels of equipment in reverberation rooms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Method for determining Sound power levels of equipment under essentially free-field conditions over a reflecting plane . . . . . . . . . . . . . . . . . . . . 7 Method for measuring Sound pressure levels at the Operator and bystander positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Annexes Standard test table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Alternative measurement surfaces for Sound power measurements in accordance with clause 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 26 Installation and operating conditions for specific equipment categories . . . . . Measurement of impulsive Sound pressure levels and discrete tones at the oberator position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 10 19 35 . . . Ill SIST EN 27779:1999
This page intentionally left blank SIST EN 27779:1999
INTERNATIONAL STANDARD ISO 7779 : 1988 (EI Acoustics - Measurement of airborne noise emitted by Computer and business equipment 0 Introduction This International Standard specifies methods for the measure- ment of airborne noise emitted by Computer and business equipment. Hitherto, a wide variety of methods has been ap- plied by individual manufacturers and users to satisfy particular equipment or application needs. These diverse practices have, in many cases, made comparison of noise emission difficult. This International Standard simplifies such comparisons and is the basis for declaration of the noise emission level of Computer and business equipment. In Order to ensure accuracy, validity and acceptability, this International Standard is based on the basic International Stan- dards for determining the Sound power level (ISO 3741, ISO 3742, ISO 3744 and ISO 3745) and the Sound pressure level at the Operator position(s) (ISO 6081). Furthermore, implementation is simplified by conformance to these Inter- national Standards. In many cases, free-field conditions over a reflecting plane are obtained by semi-anechoic rooms. These rooms may be par- ticularly useful during product design to locate and to improve individual contributing noise sources. Reverberation rooms may be more economical for production control and for obtain- ing Sound power levels for declaration purposes. The method for measuring the Sound pressure level at the Operator or bystander positions (see ISO 6081) is specified in a separate clause, as this level is not considered to be primary declaration information. The measurements tan, however, be carried out at the same time as those for Sound power deter- mination in a free field over a reflecting plane. For comparison of similar equipment it is essential that the installation conditions and mode of Operation be the Same. In annex C these Parameters are standardized for many categories of equipment. lt is intended to extend annex C to other categories in a future revision. 1 Scope and field of application 1.1 Scope This International Standard specifies procedures for measuring and reporting the noise emitted by Computer and business equipment. lt is based on the measurement procedures specified in ISO 3746, ISO 3741, ISO 3742, ISO 3744 and ISO 3745. The basic emission quantity is the A-weighted Sound power level which may be used for comparing equipment of the same type, but from different manufacturers, or for comparing different equipment. The A-weighted Sound power level is supplemented by the A-weighted Sound pressure level measured at the Operator position(s) or the bystander positions. This Sound pressure level is not a measurement of total occupational noise exposure of workers (noise immission). Two methods for determining the Sound power levels are specified in this International Standard in Order to avoid undue restriction on existing facilities and experience. The first method is based on reverberant room measurements (see ISO 3741 and ISO 3742); the second is based on measure- ments in an essentially free field over a reflecting plane (see ISO 3744 and ISO 3745). Either method may be used in accord- ante with this International Standard. They are comparable in accuracy and yield the same A-weighted Sound power level within the tolerante range of the methods specified in this International Standard. 1.2 Field kf application This International Standard is suitable for type tests and pro- vides methods for manufacturers and testing laboratories to obtain comparable results. The method specified in clause 5 provides a comparison pro- cedure for determining Sound power levels in a reverberation room. The method specified in clause 6 provides a direct pro- cedure for determining Sound power levels using essentially free-field conditions over a reflecting plane. The method specified in clause 7 provides a procedure for measuring noise at the Operator or bystander positions. The procedures in this International Standard may be applied to equipment which radiates broad-band noise, narrow-band noise, noise which contains discrete-frequency components or impulsive noise. The methods specified in this International Standard allow the determination of noise emission levels for a unit tested individually. The Sound power levels and Sound pressure levels are used for noise emission declaration and comparison purposes. They are not to be considered as installation noise levels; however they may be used for installation planning. If Sound power levels obtained are determined for several units of the same production series, the result tan be used to deter- mine a statistical value for that production series. SIST EN 27779:1999
ISO 7779 : 1988 (El 2 Conformance 4 Definitions Measurements are in conformance with this International dard if they meet the following requirements: Stan- a) The measurement procedure, the installation and the operating conditions specified by this International Stan- dard are fully taken into account. b) For the determination of Sound power levels, the method specified in clause 5 or the method specified in clause 6 is used. c) For the measurement of Sound pressure level at the Operator or bystander positions, the method specified in clause 7 is used. 3 References ISO 266, Acoustics - Preferred frequencies for measure- men ts. ISO 3746, Acoustics - Determination of Sound power levels of noise sources - Guidelines for the use of basic Standards and for the preparation of noise test Codes. ISO 3741, Acoustics - Determination of Sound power levels of noise sources - Precision methods for broad-band sources in reverberation rooms. ISO 3742, Acoustics - Determination of Sound power levels of noise sources - Precision methods for discrete-frequency and narrow-band sources in reverberation rooms. ISO 3743, Acoustics - Determination of Sound power levels of noise sources - Engineering methods for special reverberation test rooms. ISO 3744, Acoustics - Determination of Sound power levels of noise sources - Engineering methods for free-field conditions over a reflecting plane. ISO 3745, Acoustics - Determination of Sound power levels of noise sources - Precision methods for anechoic and semi- anechoic rooms. ISO 6081, Acoustics - Noise emitted b y machinery and equip- ment - Guidelines for the preparation of test Codes of engin- eering grade requiring noise measurements at the operator’s or b ys tander’s Position. ISO 6926, Acoustics - Determination of Sound power levels of noise sources - Charac teriza tion and calibra tion o f reference Sound sources. 1) ISO 9295, Acoustics - Measurement of high- frequency emitted by Computer and business equipment. noise ISO 9296, Acoustics - Declared noise emission values of com- Puter and business equipment. IEC Publication 225, Octave, half-octave and third-octave fIters in tended for the analysis of Sounds and vibrations. band IEC Publication 651, Sound level meters. IEC Publication 804, lntegrating-averaging Soundlevel meters. For the purposes definitions apply. of this International Standard, the following 4.1 level of background noise: The Sound pressure level at specified locations when the equipment being tested is neither operating nor idling. 4.2 bystander: An individual who is not the Operator of the equipment, but whose Position lies within the Sound field pro- duced by the equipment, either occasionally or continuously. 4.3 bystander Position : A measurement typical location occupied by a bystander. Position at a 4.4 Computer and business equipment: Equipment and components thereof which are primarily used in offices or off ice-like environments and in Computer installations. 4.5 floor-standing equipment : A functional unit that its own stand and is intended to be installed on the floor. has 4.6 frequency range of interest: This range normally extends from the 100 Hz one-third octave band to the 10 000 Hz one-third octave band. The 16 kHz octave band shall be included if a preliminan/ investigation indicates that it may affect the A-weighted Sound pressure or Sound power levels. The range and centre frequencies of the octave bands are spe- cified in ISO 266. NOTES 1 If the 16 kHz octave band is included in the measurements, the pro- cedures of this International Standard may yield measurement uncer- tainties greater than those stated. 2 For equipment which emits Sound only in the 16 kHz octave band, the procedures specified in ISO 9295 should be used. 4.7 functional unit: An entity of physical equipment, which has been allocated an identification number, capable of accom- plishing a specified task. A functional unit may be supported by a frame or frames and may be self-enclosed or designed to be attached to another device. 4.8 idling mode: A condition in which the equipment being tested, after any necessary warm-up period, is energized but is not operating. 4.9 measurement surface: A hypothetical surface of area S enveloping the equipment being tested on which the measur- ing Points are located. 4.10 operating mode: A condition in which the being tested is pe lrforming its intended function(s). ew ipment 4.11 Operator: An individual who operates a piece of equipment from a Position in the immediate vicinity of the equipment. 1) At present at the Stage of draft. 2 SIST EN 27779:1999
ISO 7779 I 1988 (EI 4.12 Operator Position : Measurement Position at the 5 Method for determining Sound power assigned work-Station of the Operator. levels of equipment in reverberation rooms 4.13 rack-mounted equipment : One or more sub- assemblies installed in an end-use enclosure. 5.1 General 4.14 reference box: A hypothetical reference surface which is the smallest rectangular parallelepiped that just encloses the equipment being tested and terminates on the reflecting plane. The method specified in this clause provides a comparison pro- cedure for determining the Sound power levels produced by Computer and business equipment using a reverberation room. lt applies to equipment which radiates broad-band noise, narrow-band noise, or noise which contains discrete-frequency components or impulsive noise. 4.15 reference Sound Source: A device which is intended for use as a stable Source of Sound which has a known, calibrated broad-band Sound power spectrum over the fre- quency range of interest and which conforms to ISO 6926. The measurements shall be carried out in a qualified reverbera- tion room. The volume of the equipment being tested should preferably be not greater than 1 % of the volume of the reverberation room. 4.16 Sound power level, Lw, in decibels: Ten times the logarithm to the base 10 of the ratio of a given Sound power to the reference Sound power. The weighting network (A-weight- ing) or the width of the frequency band used shall be indicated. The reference Sound power is 1 pW. NOTE - Measurements on equipment which has a volume of less than 1 m3 and emits broad-band noise may be carried out in a special reverberation test room (sec ISO 3743). 5.2 Measurement uncertainty NOTE - For the purposes of this International Standard, the Sound power is the time-average value of the Sound power during the measurement duration. Measurements carried out in accordance with this method yield Standard deviations which are equal to, or less than, those given in table 1. 4.17 Sound pressure level, L,, in decibels: Ten times the logarithm to the base 10 of the time-mean-Square Sound pressure to the Square of the reference Sound pressure. The weighting network (A-weighting) or the width of the frequency band used shall be indicated. The reference Sound pressure is 20 PPa. Ta ble d power 1 - Uncertainty in determining soun in a reverberation room Octave-band centre frequency HZ One-third octave- band centre frequency HZ Standard deviation dB NOTE - For the purposes of this International Standard, the Sound pressure is the Square root of the time average of the squared Sound pressure during the measurement duration. 100 to 160 3 200 to 315 2 500 to 4 000 4ooto 5000 L5 6300to 10000 3 4.18 Standard test table: A rigid table having a top surface of at least 0,5 m2 (length of the top plane > 700 mm). A suitable design for the Standard test table is shown in annex A. NOTES - 4.19 sub-assembly: A functional unit intended to be in- stalled in another unit or assembled with other units in a Single enclosure. The unit may or may not have its own enclosure and identification number. 4.20 surface-average Sound pressure level, L,,, in decibels : Space/time-average Sound pressure level averaged over a measurement surface, corrected for the environment. 4.21 table-top equipment: A functional unit that has a complete enclosure and is intended to be installed or used on a table, desk or separate stand. 4.22 time-average Sound pressure level, LpT, in decibels; equivalent continuous Sound pressure level during time T, in decibels: Ten times the logarithm to the base 10 of the ratio of a time-mean-Square value of instantaneous band- limited Sound pressure, during a stated time interval, to the Square of the Standard reference Sound pressure. 1 For most Computer and business equipment, the A-weighted Sound power level is determined by the Sound power levels in the 250 to 4 000 Hz octave bands. The A-weighted Sound power level is deter- mined with a Standard deviation of approximately 1,5 dB. A larger Standard deviation may result when the Sound power levels in other bands determine the A-weighted jevel. 2 The Standard deviations given in table 1 reflect the cumulative effects of all Causes of measurement uncertainty, including variations from laboratory to laboratory, but excluding variations in the Sound power level from equipment to equipment or from test to test which may be caused, for example, by changes in the installation or operating conditions of the equipment. The reproducibility and repeatability of the test results for the same piece of equipment and the same measure- ment conditions may be considerably better (i.e. smaller Standard deviations) than the uncertainties given in table 1 would indicate. 3 If the method specified in this clause is used to compare the Sound power levels of similar equipment that are omnidirectional and radiate broad-band noise, the uncertainty in this comparison yields a Standard deviation which is less than that given in table 1, provided that the measurements are carried out in the same environment. Os,3 Test environment 5.3.1 General 4.23 wall-mounted equipment: A functional unit which is normally mounted against or in a wall and does not have a stand of its own. Guidelines specified in ISO 3741 and ISO 3742 for the design of the reverberation room shall be used. Criteria for room absorp- tion and the procedure for room qualifications given in these same International Standards shall be used. SIST EN 27779:1999
ISO 7779 : 1988 (El 5.3.2 Test room volume The minimum test room volume shall be as stated in table 2. If frequencies above 3 000 Hz are included in the frequency range of interest, the volume of the test room shall not exceed 300 m3. The ratio of the maximum dimension of the test room to its minimum dimension shall not exceed 3: 1. Table 2 - Minimum room of the lowest frequenc olume as a functi band of interest on howest frequency band Minimum room of interest volume Hz m3 125 (octave) or 100 (one-third octave) 200 125 (one-third octave) 150 160 (one-third octave) 100 250 (octave) or 200 (one-third octave) or higher 70 53.3 Level of background noise The level of the background noise, including any noise due to motion of the microphone and/or rotating diffusers, shall be at least 6 dB, and preferably more than IO dB, below the Sound pressure level to be measured in each frequency band within the frequency range of interest. 5.3.4 Temperature and relative humidity The air absorption in the reverberation room varies with temperature and humidity, particularly at frequencies above 1 000 Hz. The temperature 8, in degrees Celsius, and the relative humidity (r.h.1, expressed as a percentage, shall be controlled during the Sound pressure level measurements. The product r.h. x (8 + 5) shall not vary by more than k 10 % during the measurements specified in 5.6, 5.7 and 5.8. For equipment the Sound pressure level of which varies with temperature, the test temperature shall be 23 + 2 OC. The following conditions are recommended : - barometric pressure: 86 to 106 kPa - temperature: 15 to 30 OC - relative humidity: 40 % to 70 % 5.4 lnstrumentation 5.4.1 General The instrumentation shall be designed to measure the space/ time-average Sound pressure level in octave and/or one-third octave bands; the space/time-average Sound pressure level is the level of the squared Sound pressure averaged over time and space. Alternatively, the space/time-average may be calculated in accordance with 5.9. The instruments used may perform the required averaging in one of two different ways : a) By integrating the Square of the Signal over a fixed time interval and dividing by the time interval. This integration may be performed by either digital or analogue means; digital integration is the preferred method (sec IEC Publica- tion 804). b) By continuous averaging of the Square of the Signal using RC-smoothing with a time constant of at least 1 s (“slow” meter characteristic). Such continuous averaging provides only an approximation of the true average and it places restrictions on the settling time and Observation time (see note to 5.7.2). 5.4.2 Microphone and its associated cable The microphone used shall comply with the requirements regarding accuracy, stability and frequency response for a type 1 instrument specified either in IEC Publication 651 or in IEC Publication 804 and shall have been calibrated for its random incidence response. The microphone and its associated cable shall be Chosen so that their sensitivity does not Change by more than 0,2 dB over the temperature range encountered during measurement. If the microphone is moved, care shall be exercised to avoid intro- ducing acoustical or electrical noise (e.g. from gears, flexing cables or sliding contacts) that could interfere with the measurements. 5.4.3 Frequency response of the instrumentation System The frequency response of the entire instrumentation System shall be flat over the frequency range of interest within the tolerantes given either in IEC Publication 651 or, preferably, in IEC Publication 804, for type 1 instruments. 5.4.4 Reference Sound Source The reference Sound Source shall meet the requirements specified in ISO 6926 over the frequency range of interest. 5.4.5 Filter characteristics An octave-band or one-third octave-band filter set complying with the requirements specified in IEC Publication 225 shall be used. The centre frequencies of the bands shall correspond to those specified in ISO 266. 5.4.6 Calibration During each series of measurements, an acoustical calibrator with an accuracy of & 0,5 dB shall be applied to the microphone to check the calibration of the entire measuring System at one or more frequencies over the frequency range of interest. The calibrator shall be checked at least once a year to verify that its output has not changed. In addition, an acoustical and an electrical calibration of the instrumentation System over the entire frequency range shall be carried out at least every two years. The reference Sound Source shall be checked annually to verify that its output Sound level has not changed. 4 SIST EN 27779:1999
ISO 7779 : 1988 (El 5.5 Installation and Operation of equipment - General requirements 5.5.1 Equipment installation The equipment shall be installed according to its intended use. If the normal installation is unknown or if several possibilities exist, the same conditions for a group of similar machines shall be Chosen and reported. Installation conditions for many dif- ferent categories of equipment are specified in annex C; these shall be followed when labelling information is to be obtained. a) Floor-standing equipment shall be located at least 1,5 m from any wall of the room and no major surfaces shall be parallel to a wall of the reverberation room. If the equipment being tested consists of several frames bolted together in an installation and is too large for testing purposes, the frames may be measured separately. In such circumstances, additional covers may be required for the frames during the acoustical evaluation. These additional covers shall be acoustically comparable with the other covers on the equipment. If a unit is mechanically or acoustically coupled to another unit so that the noise levels of one are significantly influenced by the other, the equip- ment being tested shall, where practicable, include all units coupled together in this way. b) Floor-standing equipment which is to be installed in front of a wall shall be placed on a hard floor in front of a hard wall (see note 2 in 6.3.1). The distance from the wall shall be in accordance with the manufacturer’s instructions or as specified in annex C. If such information is not available, the distance shall be 0,l m. c) Table-top equipment shall be placed on the floor at least 1,5 m from any wall of the room unless a table or stand is required for Operation according to annex C, e.g. Printers which take Paper from or Stack Paper on the floor. Such equipment shall be placed in the centre of the top plane of the Standard test table (see annex AI. d) Wall-mounted equipment shall be mounted on a wall of the reverberation room at least 1,5 m from any other reflec- ting surface, unless otherwise specified. Alternatively, if Operation permits, the equipment may be laid on its side and installed with its mounting surface attached to the floor at least 1,5 m from any wall of the room. e) Rack-mounted equipment shall be placed in an en- closure which camplies with the installation specifications for the equipment. The location of all units within the enclosure shall be described. The enclosure shall be tested as floor-standing or table-top equipment. Rack-mounted equipment which does not include, but requires the use of, air-moving equipment (i.e. cooling-fan assemblies) when in Operation shall be tested with such equipment, as supplied or recommended by the manufacturer. f) If the equipment is usually installed by being recessed into a wall or other structure, a representative structure shall be used for mounting during the measurements. g) Hand-held equipment shall be supported 0,l m above the reflecting plane by Vibration-isolating elements. The supports shall not interfere with the propagation of airborne Sound. h) A sub-assembly shall be supported 0,25 m above the reflecting plane by Vibration-isolating elements. The sup- ports shall not interfere with the propagation of airborne Sound. NOTE - If the equipment is mounted near one or more reflecting planes, the Sound power radiated by the equipment may depend strongly upon its Position and orientation. lt may be of interest to determine the radiated Sound power either for one pat-ticular equip- ment Position and orientation or from the average value for several positions and orientations. Care shall be taken to ensure that any electrical conduits, piping, air ducts or other auxiliary equipment connected to the equipment being tested do not radiate significant amounts of Sound energy into the test room. If practicable, all auxiliary equipment necessary for the Operation of the equipment shall be located outside the test room and the test room shall be cleared of all objects which may interfere with the measurements. 5.5.2 Input voltage and frequency The equipment shall be operated within 5 % of either a) the rated voltage (if any is stated), or Phase-to-Phase voltage variations shall not exceed 5 %. 5.5.3 Equipment Operation During the acoustical measurements the equipment shall be operated in a’manner typical of normal use. Annex C specifies such conditions for many different categories of equipment. The noise shall be measured with the equipment in both the idling and the operating modes. If several operating modes exist, e.g. reading and punching, the noise of each individual mode shall be determined and recorded. For equipment which, in normal functional Operation, has several operating modes, the mode producing the highest A-weighted Sound power level shall be determined, unless otherwise specified in annex C. In the case of rack-mounted equipment in which the Operation of several functional units is possible, the unit producing the highest A-weighted Sound power level shall be operated together with those other units required for its Operation. All other units shall be in the idling mode. Some equipment does not operate continuously because of its mechanical design or its mode of Operation under program con- trol. Long periods may occur during which the equipment is idling. The operating mode measurements shall not include these idling periods. If it is not possible to operate the equip- ment continuously during the acoustical evaluation, the time interval during which measurements have to be made shall be described in the test plan, equipment specifications or other documentation. Some equipment has operational cycles that are too short to allow reliable determination of the noise emissions. In such cases, a typical cycle shall be repeated several times. SIST EN 27779:1999
Iso 7779 : 1988 (El If the equipment being tested produces attention Signals, such 5.6.1.1 Select an array of six fixed microphones (or six as tones or bells, such intermittent Sound shall not be included microphone positions) spaced at least A/2 apart, where A. is the in an operating mode. During the acoustical evaluation in wavelength of the Sound corresponding to the centre fre- t
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.