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Brüel & Kjær 4423, Instructions And Applications, Page: 29 / 32

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Summary of Contents for 4423

Page 1: ... give the Equivalent Continuous L evel Leq calculated on the Equal Energy Principle The Weighting Network is selected on the Sound Level Meter and the Time Constant on the Noise Dose Meter 1 ms Fast Slow or Impulse being available The entire system from microphone to Noise Dose Meter can be calibrated using a Sound Level Calibrator or Pistonphone ...

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Page 3: ...NOISE DOSE METER TYPE 4423 September 1972 ...

Page 4: ...Conversion Slide Rule 13 3 2 Operation from a 12 V Battery 13 3 3 Supply of Power to the Sound Level Meter 14 3 4 Remote Control 14 3 5 Analysis of Tape Recorded Noise 15 4 MODE OF OPERATION 17 4 1 Principle 17 4 2 Input Amplifier 17 4 3 Squaring Network 18 4 4 Time Constants 18 4 5 Noise Dose Counter 20 4 6 Elapsed Time and Overload Duration Counters 22 5 SPECIFICATIONS 24 ...

Page 5: ...vel but also the duration of the exposure thus introducing the concept of Noise Dose For a steady continuous noise it is a simple matter to define the Noise Dose as being the sound level for the specified duration Time varying sound levels are however more difficult to define and some trading relationship between level and duration must be specified Such a relationship would allow the reduction of...

Page 6: ...onsulted Dl N ISO and the Code of Practice all operate with q 3 i e a noise Jevel must be increased by 3 dB to give the same Noise Dose when the duration is halved This corresponds to energy averaging and is often refer red to as the Equal Energy Principle The Walsh Healey Act however speci fies q 5 5 dB increase in level for half the duration Comparison on the basis of 90 dB A for an 8 hour day s...

Page 7: ...ROLS BrUel Kj er NOISE c _ DOSE COUI IT INHIBIT FUNCTION Fig 2 1 Front Panel Counts the number of hours for which the overload limit of the instrument was exceeded For the effect of OVER LOAD DURATION on measurement ac curacy see section 4 6 Counts the measurement duration in hours 5 ...

Page 8: ...nter This RESET button will only operate with the FUNCTION knob on Reset An orange lamp which lights when the overload limit of the instrument has been exceeded A white lamp which lights when a level 20 dB lower than the overload limit has been exceeded Acts as an On Off switch and allows switching between Calibration Re set Stand by and Measurement modes FINE and COARSE screw adjustments for cali...

Page 9: ...SLM POWER SIGNAL INPUT SIGNAL OUTPUT For connection of AC mains supply For selection of the correct AC mains supply voltage unscrew the central fuse holder unplug the black annular por tion and rotate it until the protruding metal piece is adjacent to the required voltage setting and replace Only the required voltage should be visible Re place the fuse holder For switching between AC mains power s...

Page 10: ...ry supply and remote control leads The connections are given in Fig 2 3 12 V DC Remote 172287 Control Switch Fig 2 3 External View of 4423 12 V DC POWER REM CONTR socket with connections FUSE 0 5 A For protection of the Sound Level Meter when powered by the Noise Dose Meter 4 5V I 1 5v To SLM 172288 Fig 2 4 External View of 4423 SLM POWER socket with connections 8 ...

Page 11: ... the Sound Level Meter For connections see Fig 2 4 A standard B K socket and a minia ture socket for signal input from the Sound Level Meter Measuring Amplifier or Frequency Spectrometer These sock ets can be used instead of the similar pair on the front panel For output of the DC Level from the Time Constant circuitry 9 ...

Page 12: ...cision Sound Level Meter A B C 2208 Noise Event Meter A 072040 Table 3 1 Classification of Sourrl Level Meters Group a contains the larger Sound Level Meters which can be used with Octave Filter Sets Type 1613 and group b contains the smaller pistol grip Sound Level Meters The Weighting Network facility of each instrument is also included as this determines the method of calibration which will be ...

Page 13: ... Batt can be used but the same switch position must be used for both calibration of the Noise Dose Meter and measurement The switch setting should not be altered during the measure ment 1 The Sound Level Calibrator or Pistonphone should be applied to the microphone and started The Sound Level Meter should then be ad justed to give a meter scale deflection of 4 0 dB 2204 use METER SWITCH position o...

Page 14: ...select BATT REC 3 Adjust the RANGE knob on the Sound Level Meter until the OVER LOAD 20 dB lamp flashes intermittently This procedure ensures that the sound level is varying about the centre of the dynamic range of the Noise Dose Meter If the OVERLOAD 20 dB lamp is perma nently on then the RANGE setting is too low and overload condi tions could occur during the measurement If the lamp is permanent...

Page 15: ...o the Sound Level Meter RANGE setting in dB to give the required equivalent continuous level Leq 3 2 OPERATION FROM A 12 V BATTERY The Noise Dose Meter may be powered using a 12 V battery The current drawn will be 1 5 A and hence for a full 8 hour working day measurement of Lew 12 Ah minimum battery capacity will be required Connections to the 12 V DC POWER REM CONTR socket should be made as in Fi...

Page 16: ...bly inserting the required length of cable checking that the correct polarity is maintained The connections to the Noise Dose Meter are shown in Fig 2 4 Plug the 7 pin Dl N plug of the battery adaptor into the SLM POWER socket at the rear of the Noise Dose Meter and screw or slide the Adaptor into the Sound Level Meter The Sound Level Meter should now operate when the Noise Dose Meter is switched ...

Page 17: ...ation if this is required The tape recording should consist of a calibration tone using either a Sound Level Calibrator or Pistonphone on the Sound Level Meter Microphone followed by the signal to be ana lyzed The Power Amplifier ATTENUATOR and GAIN CONTROL knobs should be adjusted to give a reasonable sound level from the loudspeaker Also a sound level scale should be inserted in the Measuring Am...

Page 18: ...mount The Noise Dose Meter FUNCTION knob should now be switched to Calibration 4 dB and the count adjusted to 99 The Measuring Amplifier should now be recalibrated to give a deflection corresponding to the exact level emitted by the Calibrator or Pistonphone The system is now calibrated The Noise to be analyzed should now be played back and the INPUT SECTION ATTENUATOR and if necessary the OUTPUT ...

Page 19: ...ain the Noise Dose The analysis time is also measured to give the Noise Dura tion T and these two values are used to calculate the value of Leq A block of diagram of the Noise Dose Meter is shown in Fig 4 1 4 2 INPUT AMPLIFIER The signal to the Noise Dose Meter is assumed to have no DC level as this will lead to clipping The output from the B KSound Level Meters Frequency Spectrometers and Measuri...

Page 20: ...e pending on the signal size By this process the accuracy of squaring of small signal levels is increased and the dynamic range extended to 40 dB 4 4 TIME CONSTANTS The output from the Squaring circuitry is fed to the Time Constant circuitry The time constants available are 1 ms Fast Slow and Im pulse The modes Fast and Slow are basically defined in terms of meter deflection on a Sound Level Meter...

Page 21: ... of the Impulse Time Constant switching to Impulse will give a different result depending on the signal wave form As an illustration of this two tape recorded samples of noise were analysed The first recording was of traffic noise from a four lane Motorway and the second punch press noise Examples of the variation of the levels of the two samples are shown in Fig 4 2 00 DOD DO 0 DO 0000000000 0000...

Page 22: ...t stage of the Converter is a straight forward Integrator consisting of an integrated circuit operational amplifier with capacitor feedback The variable voltage fed to the Integrator results in a ramp of variable negative slope negative because of the sign changing characteristics of the Integra tor The Integrator output is fed to a Level Detector which as soon as the output reaches 10V triggers a...

Page 23: ... fed to the Calibrator Control circuit which allows selection of either Measure Calibration or Re set modes In the Measure mode the pulse is fed directly to the NOISE DOSE COUNTER circuitry In the Calibration mode only the two light emitting diode Digits operate alternately reading the count for a 0 72 s period and then reading zero The ratio P t P Att in Eqn 3 is represented in the Noise Dose met...

Page 24: ...ERLOAD 20 dB lamps are pre heated and maintained just off so providing longer life Once they have lit they are kept on by means of a latch until the next pulse is emitted by the Oscillator This pulse stretching technique provides a longer light period The effect of Overload Duration on the accuracy of the Noise Dose Meter is shown in Fig 4 4 The two samples of noise analyzed are those previously d...

Page 25: ...ive greater errors for the same relative Overload Duration If the Overload Duration Count becomes large for a particular measure ment then the Sound Level Meter or Measuring Amplifier attenuator setting should be increased to lower the signal to the Noise Dose Meter If such a procedure fails to remove the occurence of a relatively large Overload Duration Count it is possible that the signal being ...

Page 26: ...djust ment setting B K Standard and Miniature con nectors at front and rear panels 10 kQ 20Hz to 20kHz 40 dB input range Can be increased to 80 dB by using a second 4423 in parallel see section 4 6 Any within dynamic range Determined by SLM attenuator Continuous squaring function RC 35 ms followed by separate RC 1 5 s discharge Effectively 3 s due to squaring RC 100 ms RC 500 ms RC 1 ms Circuitry ...

Page 27: ...y better than 1 Noise Dose Count 8 digit counter 2 light emitting diode digits plus 6 digit mechanical counter Max count rate approx 750Hz Calibration End to end from microphone calibrator to Noise Dose counter Correct calibra tion gives 99 read out at end of 0 72 s gate period repeated every 1 8 s Stand by Front panel or remote control contact closure Operating Ambient Temperature 10 to 55 C 14 t...

Page 28: ...plug JP 0101 1 7 pin DIN plug JP 0703 1 8 pin DIN plug JP 0802 1 Cable AO 0007 1 Cable AO 0037 Mains cable European AN 0005 or American AN 0006 Spare Fuses Protective case KA 0037 SLM Battery adaptors UA 0363 for Type 2203 UA 0364 for Type 2204 09 UA 0365 for Type 2205 06 08 ...

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