CNMV 58 Page 1, Totally 9Pages
/Technical Specification for Verification and
Inspection of Sound Level Meters / S/N /CNMV 58
Rev. / 11. This Technical Specification is enactedpursuant to Paragraph 2, Articles 14 and 16 of the Weights and Measures Act.
2. The revision, date of promulgations, document No, date of enforcement and content of the amendment are listed as follows:
Rev. / Date ofPromulgation / Document No.
(Ching-Piao-Szu-Tsu) / Date of Enforcement / Content of Amendment
1 / 04.07.2003 / No.09240006030 / 01.08.2003
Date of Promulgation
04.07.2003 / Bureau of Standards, Metrology and Inspection, Ministry of Economic Affairs / Date of Enforcement
01.08.2003
1. Scope：Thisspecification applies to the verification and inspection of sound level meters.
2. Construction：
2.1The measure unit of sound level meters is“decibel” and the symbol is“dB”
2.2 The followings shall be marked on an easily visible position:
(1) Type ( type 1 or type 2).
(2) Manufacturer’s name or trademark.
(3) Type number and instrument number. If microphone and the main part are separable, serial number shall be provided both on microphone and the main part.
2.3Sound level meters shall have A frequency weighting characteristic.
2.4Sound level meters shall have a time weighting characteristic, such as fast ( F or FAST), slow (S or SLOW).
2.5Sound level meters shall have AC or DC signal output terminals, or shall have a function of keeping measuring the sound pressure level of maximum value.
2.6 When the amplifier of sound level meters reach saturation, sound level meters shall be equipped with a indicating device to indicate overload input.
2.7 The minimum scale interval for sound level meters with digital output indicators shall be less than 0.1 dB and for instruments with analog output indicators shall be less than 1 dB.
2.8No matter sound level meters are digital outputs or analog outputs, the range of indicators shall be at least 15 decibel.
2.9 The major graduation line of analog indicator of sound level meters shall be recorded indicating value obviously on sound level meters. The interval of two graduation lines shall be more than 1 mm.
2.10 If sound level meters use battery, a warning device should be provided to indicate low battery voltage.
3. Verification, inspection and maximum permissible errors
3.1Verification and inspection equipment：certificates of traceability and uncertainty of certified equipment should be provided.
（1）Pulse generator：pulse with: 50μs～10 ms; rise time: less than 10μs; polarity: positive/negative
（2）Standard microphone: frequency range: 20Hz～16 kHz; uncertainty of open circuit sensitivity: ±0.2dB( at referance frequency)
（3）Signal generator：frequency range: 20Hz～20 kHz; frequency deviation: within ±1 %; output voltage:1 mVrms～5 Vrms; harmonic distortion: less than 0.5%
（4）Anechoic apparatus: free field deviation: at the frequency over 125 Hz and within the range of 0.5 m～1.0m from the centerof sound source, free field deviation shall have the feature of deviation less than ±1.0 dB of the free field.
Frequency range shall include 125 Hz to 4000 Hz at least, and background noise shall be less than 20 dB(A).
（5）Test sound source: frequency range: 20Hz～20 kHz; maximum sound pressure level not less than 100 dB ( 1 m away from the reference point of sound source).
（6）RMS voltage meter: uncertainty of RMS measurement: 1%.
（7）Pre-amplifier: frequency range: 20Hz～16 kHz; harmonic distortion: less than 1% at frequencies between 20 Hz to 16 kHz.
（8）Measurement amplifier: uncertainty better than ±0.2 dB.
（9）Attenuator：uncertainty better than ±（1%+0.05）dB; frequency range: 20Hz～20 kHz; minimum change attenuation value: 0.1 dB.
（10）Filter: frequency range: 20Hz～20 kHz ( include function of 1/3 octave).
3.2 All the testing of sound level meters should be conducted under the following environmental conditions: temperature: (23 5) ℃; relative humidity: (55 15) %; atmosphere pressure: (101.3 5) kPa.
3.3 Sound level meters are tested under conditions prescribed in Section 3.2. After the meter warming up, use substitute method to conduct accuracy verification or inspection in noiseless roomsas shown in figure 1. In a free field, a sound level meter is 1 meter away from sound source. Read measurement results of sound level meters corresponding to frequency 125 Hz, 200 Hz, 250 Hz, 315 Hz, 400 Hz, 500 Hz, 630 Hz, 800 Hz, 1 kHz, 1.25 kHz, 1.6 kHz, 2 kHz, 2.5 kHz, 3.15 kHz and 4 kHz and measurement results of the sinusoidal wave for 94 dB sound pressure level. Compare the measure results of sound level meters with measurement results of standard microphone under the same conditions. For every frequency, there is a difference between two measurement results. Calculate the average of these differences. Then the average is the instrument error. For type 1 sound level meters, the instrument error shall not exceed 0.7 dB. For type 2 sound level meters, the instrument error shall not exceed 1.0 dB.
Figure 1 System for instrument error test of sound level meters
3.4 Sound level meters performs verification of the frequency weighting characteristic under the electric characteristic test as shown in figure 2. Apply 1kHz sinusoidal signal through the equivalent effective resistance the same as microphone to sound level meters and have the sound level meters display the indication 6 dB below upper limit of primary indicator range and use this indication as reference level. Then follow the frequency listed in table 1 to change signal frequency, calculate corresponding reference level and draw the response curve to get linear, A, B, C weighting characteristic. Follow therequirementsof the maximum permissible errors in Table 1 to decide if it is complied with the requirements.
Figure 2 Electrical characteristic testing system
Table 1 Frequency weighting characteristics relative free-field frequency response in the reference direction and maximum permissible errors (unit: dB)
Frequency(Hz) / Characteristics
of A / Characteristics
of C / Linearity / Maximum permissible errors
Type 1 / Type 2
20 / -50.5 / -6.2 / 0 / ±3.0 / ±3.0
25 / -44.7 / -4.4 / 0 / ±2.0 / ±3.0
31.5 / -39.4 / -3.0 / 0 / ±1.5 / ±3.0
40 / -34.6 / -2.0 / 0 / ±1.5 / ±2.0
50 / -30.2 / -1.3 / 0 / ±1.5 / ±2.0
63 / -26.2 / -0.8 / 0 / ±1.5 / ±2.0
80 / -22.5 / -0.5 / 0 / ±1.5 / ±2.0
100 / -19.1 / -0.3 / 0 / ±1.0 / ±1.5
125 / -16.1 / -0.2 / 0 / ±1.0 / ±1.5
160 / -13.4 / -0.1 / 0 / ±1.0 / ±1.5
200 / -10.9 / -0.0 / 0 / ±1.0 / ±1.5
250 / -8.6 / -0.0 / 0 / ±1.0 / ±1.5
315 / -6.6 / -0.0 / 0 / ±1.0 / ±1.5
400 / -4.8 / -0.0 / 0 / ±1.0 / ±1.5
500 / -3.2 / -0.0 / 0 / ±1.0 / ±1.5
630 / -1.9 / -0.0 / 0 / ±1.0 / ±1.5
800 / -0.8 / -0.0 / 0 / ±1.0 / ±1.5
1000 / 0.0 / 0.0 / 0 / ±1.0 / ±1.5
1250 / +0.6 / -0.0 / 0 / ±1.0 / ±1.5
1600 / +1.0 / -0.1 / 0 / ±1.0 / ±2.0
2000 / +1.2 / -0.2 / 0 / ±1.0 / ±2.0
2500 / +1.3 / -0.3 / 0 / ±1.0 / ±2.5
3150 / +1.2 / -0.5 / 0 / ±1.0 / ±2.5
4000 / +1.0 / -0.8 / 0 / ±1.0 / ±3.0
5000 / +0.5 / -1.3 / 0 / ±1.5 / ±3.5
6300 / -0.1 / -2.0 / 0 / +1.5
-2.0 / ±4.5
8000 / -1.1 / -3.0 / 0 / +1.5
-3.0 / ±5.0
10000 / -2.5 / -4.4 / 0 / +2.0
-4.0 / +5.0
-∞
12500 / -4.3 / -6.2 / 0 / +3.0
-6.0 / +5.0
-∞
3.5 Sound level meters performs the verification of the effective value characteristic under the electric characteristic test as shown in figure 3. Put sound level meters under“A-weighting”frequency weighting positionand time weighting is on“SLOW” position. Use serial tone burst and 2kHz continuous signal comparison method to carry out the test.
3.5.1 Apply 2kHz sinusoidal signal through the equivalent resistance the same as microphone to sound level meters. Adjust input signal amplitude to sound level meters display the indication 2 dB below upper limit of primary indicator range and use this indication asreference level.
3.5.2 Input tone burst for a duration of 5.5 ms, 2.0 ms, 0.5 ms separately that has 40Hz repeat frequency. The difference between indication of sound level meters and reference level shall comply with the requirements listed in table 2.
Table 2 Verification and inspection maximum permissible errorsfor
Crest factor (unit: dB)
Crest factorType / 1< CF ≦3 / 3< CF ≦5 / 5< CF ≦10
Type 1 / 0.5 / 1.0 / 1.5
Type 2 / 1.0 / 1.0 / --
Figure 3 System of effective value indication error
3.6 Sound level meters performs the verification of the time weighting characteristic under the electric characteristic test . Input duration of 200 ms time (F) and 500 ms (S) and 2k Hz single tone to sound level meters. The difference between maximum display value and the display value of sinusoidal wave that is continuous and has equal amplitude shall meet the requirements in table 3.
3.6.1 Apply 2k Hz sinusoidal signal through the equivalent resistance the same as microphone to sound level meters. Adjust input signal amplitude to sound level meters display the indication 4 dB below upper limit of primary indicator range and use this indication as reference level.
3.6.2 Apply a duration of 200ms (F) and duration of 500ms (S)at 2kHz tone burst to sound level meters.
Table 3 The response to test tone burst
Detector-indicator characteristic / Duration of test tone burst (ms) / Maximum response to test tone burst referred to response to continuous signal (dB) / Maximum permissible errors (dB)Type 1 / Type 2
Fast / 200 / -1.0 / 1.0 / +1.0
-2.0
Slow / 500 / -4.1 / 1.0 / 2.0
3.7 The time weighting characteristics of sound level meters respond to the suddenly signal is the overshoot of indicator. The verification method is conducted under electric characteristics test.
3.7.1 Apply 1kHz sinusoidal signal through the equivalent resistancethe same as microphone to sound level meters. Adjust input signal amplitude to sound level meters display the indication 4 dB below upper limit of primary indicator range and use this indication as reference level.
3.7.2 Apply above signal suddenly to the sound level meters and keep stable. The maximum permissible errors of overshoot shall meet the requirements in table 4.
Table 4 Maximum overshoot (unit: dB)
TypeDetector-indicator characteristics / Type 1 / Type 2
Fast / <1.1 / <1.1
Slow / <1.6 / <1.6
3.8 The system level linearity verification of major indication range of sound level meters and the linearity verification of points separated by 1dB and the linearity verification of points separated by 10dB can be done underthe electric characteristics. The maximum permissible errors of system level linearity and linearity separated by two different levelsas shown in table 5 and 6. The reference for linearity cerification is reference sound level. Put sound level meters in the range of reference sound level. Apply 31.5 Hz, 1kHz and 8kHz sinusoidal signal respectively. Then adjust attenuator to the indication of sound level meters on the test positions. Use fine attenuator adjustment to check the graduation of indicator.
Table 5 The maximum permissible errors of system level linearity (unit: dB)
TypeReading / Type 1 / Type 2
Major indication range / 0.7 / 1.0
Table 6 maximum permissible error of linearity separated by two different levels (unit: dB)
TypeReading / Type 1 / Type 2
Two testing points separated by 1 dB within major indicationrange / 0.2 / 0.3
Two testing points separated by 10 dB within major indicationrange / 0.4 / 0.6
3.9 The verification of level range control of sound level meters is under the electric characteristics. Apply 31.5 Hz, 1kHz, 8kHz sinusoidal signal through fine attenuator to sound level meters and change the type of level range control. Adjust attenuator again but do not change the indication of sound level meters. The difference between change of level rangecontrol and change of attenuator is the error of level range control. The value shall meet the requirements in table 7.
Table 7 maximum permissible errors of level range control (unit: dB)
TypeFrequency (Hz) / Type 1 / Type 2
31.5~8000 / 0.5 / 0.7
3.10 The verification of overload of sound level meters is carried out underelectric characteristics. Apply 1k Hz sinusoidal signal through the equivalent resistance the same as microphone to sound level meters. The frequency weighting of sound level meters is A, making signal indication value lower 5 dB than the sound level of maximum range that can be detected. Then reduce signal frequency to 20 Hz, and increase signal amplitude according to the weighting characteristics listed in the table 1. When signal weighting range is over, the overload indicationshould be shown.
3.11 The verification or inspection report of sound level meters shall record the instrument number of sound level meters under test. If microphone and sound level meters are separable, the instrument number of microphone and sound level meters shall also be recorded.
3.12 The inspection maximum permissible errors of sound level meters are the same as the verification maximum permissible errors.
3.13 The validity period of the verification of sound level meters is two years from the first day of the next month that sound level meters bear the verification compliance marks.
4. The verification compliance marks
4.1 The place of verification compliance tag of sound level meters shall be obvious andstuck on the cover of the main part.
4.2 A verification certificate shall be issued after the sound level meters pass the verification.