BRUEL & KJAER 1405 Instruction Manual Download | Manualshive

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Summary of Contents for 1405

Page 1: ...d pink noise up to 50 kHz All three random signals can be stopped without extraneous noise either manually or remotely The instrument contains a 3 dB Octave filter and a Compressor circuit both of which can be used independently BRilEL K IAER Power Compr Voltage Compr lnput Compr dS 1405 Noiie Generator Type 1405 Compression WI leNo Pinl No u 20 kJot t 50 HI Gen StOP Output Output ...

Page 2: ...RANDOM NOISE GENERATOR TYPE 1405 January 1974 ...

Page 3: ... 3 3 OPERATION AND APPLICATIONS 7 Mode1 Wh ite Noise 100 kHz 7 Mode 2 White Noise 20 kHz 8 Mode 3 Pink Noise 50 kHz 9 Mode 4 Pink Noise 10 dB 12 Mode 5 Filter 3 dB Octave 13 Calibration pf Power Spectral Density Levels 13 Mode Compressor Only 15 Setting up of the Compressor Loop 15 4 DESCRIPTION 17 4 1 RANDOM NOISE OUTPUTS 17 4 2 THE 3 dB OCTAVE FILTER 19 4 3 THE COMPRESSOR CIRCUIT 20 ...

Page 4: ...r other weighting purposes such as automatic bandwidth com pensation The generator also con tains a compressor amplifier which is useful when performing frequency response measurements in various applications within the fields of sound and vibration In such cases the noise generator is often com bined with a filter in order to obtain a narrow band signal which is then used to control the compresso...

Page 5: ...evel Used when 1405 is combined with 1 3 Octave Filter Set 1616 I I Compres sor Integrator Voltage r Rectifier r Reference Regulator Fig 1 Block diagram of Type 1405 Specifications 1405 5 Use as a 3 dB octave filter 6 Use as a compressor amplifier Amplitude Distribution Symmetrical Gaussian with crest factor up to five Output level Calibrated output 3 16 V RMS in 100 kHz pos Continuously variable ...

Page 6: ... on the meter lamp should light Knob for adjustment of the compressor voltage Turning the knob anti clockwise will increase the compressor voltage increase the degree of compression and decrease the output signal level B K co axial socket which accepts plug JP 0101 for input of the com pressor control signal This socket is also used for input to the 3 dB Octave filter Knob for adjustment of the co...

Page 7: ... adjustment of the random noise output level In the position Cal fully clockwise if the instrument is in either of the two white noise modes the instrument will output a signal of spectral density 10 4 V2 Hz Push button operated noiseless switch for turning the instrument s Random Noise Generator off Indicates the degree of Compression between 0 and aOdB 2 White Noise 20 kHz 3 Pink Noise 50 kHz 4 ...

Page 8: ...e Fig 2 4 GEN OUTPUT BNC socket for output of random noise signals output from 3 dB Octave filter and input of signal from an external generator for compression as selected by the MODE SWITCH OUTPUT BNC socket in parallel with B K socket on front panel for output of the compressed signal COMPRESSOR INPUT BNC socket in parallel with B K socket on front panel for input of compressor control signal 2...

Page 9: ...of the instruments should be connected to mains ground The 1405 has an internal switch which enables the connection between signal ground and chassis ground to be removed if necessary The switch is shown in Fig 3 1 Fig 3 1 The Signal Grounding switch The switch can be located by standing the instrument on its left side as viewed from the front releasing the knurled nut on the front panel and remov...

Page 10: ...e given in this sec tion 3 3 1 Mode 1 White Noise 100 kHz The application given for this mode is the determination of the response to random noise of an electronic circuit A typical set up is shown in Fig 3 3 The 1405 controls should be set as follows POWER COMPR SPEED MODE SWITCH OUTPUT On Compr Off White Noise 100 kHz Cal The response of the test circuit to random noise is shown analyzed in Fig ...

Page 11: ...ing different analyzers are the determination of the frequency response of tape recorders including crqss talk measurement of the frequency response of microphones allowing third octave sensitivities to be obtained and the de termination of the effective noise bandwidth of filter systems 3 3 2 Mode 2 White Noise 20 kHz 8 The application given for this mode is that of reverberation measurement for ...

Page 12: ...OL socket can be used in two ways First a simple switch con nected as shown in Fig 3 5 a can be used contact closure stopping the generator or a DC voltage between 2 5 and 20V connected as shown in Fig 3 5 b Opening the con tact will stop the generator and closing the contact will start the generator The genera tor returns to full output 10 ms after restarting 12 5 20V a b 173581 Fig 3 5 Connectio...

Page 13: ...86 For further information on this application for instance Level Recorder settings use of paper loops to save paper and the reading of Reverberation Time from the decay curves the relevant Level Recorder Instruction Manual should be consulted 3 3 3 Mode 3 Pink Noise 50 kHz 10 The application given in this mode is the measurement of transmission loss through a partition in an open plan office or t...

Page 14: ... the bandwidth of consecutive filters increases with fre quency at 3 dB Octave The Sound Source is thus given the best possibility of produ cing a flat frequency output spectrum Placed in front of the partition under test is a Half Inch Microphone which detects the sound pressure falling on it This signal is returned via a Measuring Amplifier to the COMPRESSOR INPUT socket on the 1405 The compress...

Page 15: ...Octave Filter Set 1616 Tape Recorder 7004 173592 Fig 3 8 Set up for Reverberation Measurements using Portable Instruments If required the 1405 can be battery powered in this application two batteries of between 22 and 30 V being necessary which are connected via the REMOTE CONTROL socket on the rear panel as shown in Fig 3 2 The 1405 controls should be set as follows POWER COMPR SPEED MODE SWITCH ...

Page 16: ...quency Analyzer Type 2120 which permits a continuously swept analysis with 1 3 10 or third octave bandwidth As the bandwidth selected on the Analyzer increases at the rate of 3 dB Octave the signal fre quency weighting at 3 dB Octave is equivalent to division by the bandwidth as re quired for a PSD plot The signal is finally passed to a Level Recorder for tracing out on suitable frequency cali bra...

Page 17: ...73598 Fig 3 10 Correction Graph for Power Spectral Density For the example already given the upper line of the Level Recorder paper corresponds to 40 dB re 1 V 2 If the analysis was made with third octave filtering 23 effec tive noise bandwidth then the number of dB to be subtracted from Fig 3 10 is 22 Thus the upper line of the Level Recorder paper corresponds to 62 dB re 1 V2 Hz 4 If the origina...

Page 18: ...via a Preamplifier and a Measuring Amplifier Setting up the Compressor Loop The object of the compressor loop is to counteract any unevenness in the frequency re sponse of the Exciter by regulating the excitation signal and thus maintaining a constant level over the full test frequency range Most Exciters generally show a similar frequency characteristic relatively low response at low frequencies ...

Page 19: ...hence the Measuring Amplifier meter deflection to the required value This ad justment should be done slowly so as to allow the compressor to keep up with the change and not overshoot 6 The settings should now be checked by manually sweeping the generator slowly across the test frequency range The COMPRESSION meter deflection must always stay between 0 dB and 80 dB If a large Exciter resonance give...

Page 20: ...4 Pink Noise 10 dB 5 Filter 3 dB Oct 6 Compr Only Fi lter 1 30_ ____ 0 1 3 dB oct j 40 Filter 5 06 I Compr 7 2 1 Gen Output 3 1 D O 5 O _ R T L Integrator __ AGC Voltage ectl ler r Reference h Ampl ifier Regulator I Fig 4 1 Block Diagram 4 1 RANDOM NOISE OUTPUTS I ompressor Speed I ompreSSio Meter I Outpu L 40 173593 The heart of the 1405 is a White Noise Generator which consists of a matched pair...

Page 21: ...Hz Low Pass Filter obtained from a swept sine test is shown in Fig 4 2 The spectral density is constant at 10 4 V2 Hz within 1 dB up to 75 kHz The effective noise bandwidth of 100 kHz for the Low Pass Filter results in a 3 16 V RMS output in this mode a 10 CD c 2a 3a 4a a 5 10 100 1k 10k Frequency Hz 1 1 1SdS Octave 1 1 1 lOOk 1M 173596 Fig 4 2 Frequency Characteristic of the 100 kHz Low Pass Filt...

Page 22: ...ectral density S f in this mode will follow the formula 1 S f 2 or S f 4 2 THE 3 dB OCTAVE FILTER 0 0810 JT 0 00656 f 1 V Hz 2 The 3 dB Octave filter can be isolated from the rest of the instrument and used sepa rately by setting the MODE SWITCH to mode 5 Filter 3 dB Oct This mode is useful for converting a constant percentage bandwidth analysis of a noise signal into a con stant bandwidth analysi...

Page 23: ...for the com pressor to attempt to suppress peaks in the random or sinusoidal signal being com pressed This introduces distortion into the signal which is passed to the test exciter re sulting in reduced excitation at the fundamental test frequency and spurious excitation at the higher harmonics As a guide in restricting this effect the variation of second and third harmonic distortion with frequen...

Page 24: ...sducers Impedance Heads Accelerometer Preamplifiers Vibration Meters Accelerometer Calibrators Magnetic Transducers Capacitive Transducers Complex Modulus Apparatus VIBRATION TESTING Exciter Controls Sine Exciter Controls Sine Random Exciter Equalizers Random or Shock Exciters Power Amplifiers Programmer Units Stroboscopes STRAIN MEASUREMENTS Strain Gauge Apparatus Multi point Panels Automatic Sel...

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