1565-B SERIES Sound-Level Meter User and Service Manual
Contents
1. ajd 10 Figure 2 2 The sound level meter fitted with the Type 1560 P96 Adaptor and the Type 1560 P52 Vibration Pickup 2 2 USE A VIBRATION METER Installation Figure 2 2 shows the Sound Level Meter fitted with the Type 1560 P96 Adaptor and the Type 1560 P52 Vibration Pickup The microphone is replaced with the adaptor as in paragraph 3 6 but in this case the adaptor requires no modification The vibration pickup includes a short cable fitted with a three terminal microphone connector that mates with the adaptor Calibration One method of calibrating the SLM uses the Type 1557 A Vibration Calibra tor as follows Remove one of the 50 gram disks from the calibrator and mount the pickup in its place Two other pickups are also available the Type 1560 P53 with a greater frequency range than the Type 1560 P52 and the Type 1560 P54 with greater sensitivity 5 7 4 Meter Window Care The clear acrylic meter window can be come susceptible to electrostatic charge build up and can be scratched if improperly cleaned If static charge problems occur possibly as the result of frequent cleaning the window should be carefully polished with a soft dry cloth such as cheesecloth or nylon chiffon Then a coating of Statnul should be applied with the polishing cloth CAUTION Do not use any kind of solvent Kleenex or paper towels can scratch the window surface Available from Mancib Co Bu2. Figure 5 2 Type 1562 Calibrator mounted over SLM Microphone a Remove the microphone para 5 3 steps b and c and replace it with the equivalent impedance see Figure 5 3 and para 3 6 b Connect the Type 1309 Oscillator OUT PUT to the input of the Type 1450 TB Atten uator Figure 5 3 The microphone is removed and its equivalent impedance connected to the SLM input 35 l d GR 274 NP PATCH CORD ALL LEADS Figure 5 1 Test equipment setup 3 3 2 Overload Prevention An important possible source of error in SLM measurements arises from strong noise fields that overload the instrument causing distortion in the meter amplifier circuit This circuit is capable of handling signals more than 11 dB above full scale meter indication Ex cept for very high crest factor spiked sig nals an on scale meter indication will yield a valid reading Analysis of noise signals containing large low frequency components may cause overload of circuits prior to the output amplifier when these signals are weighted by the A and B net works The SLM guards against this type of overload by partially weighting the signal be fore the active circuits can be overloaded Fig ure 3 3 shows the maximum sinewave input before overload occurs for each weighting The curves may be used as follows a Measure the C weighted sound level b Now measure the A or B weighted sound level c Compare th
3. ture coefficient of 2 2 pF C over the range of The following accessories are supplied with the Type 1565 B Sound Level Meter cidence at frequencies from 5 Hz to 12 5 kHz 1 4 ACCESSORIES SUPPLIED 5 o Bis og z VAD 05 M 8 1 X13 ux 9z z MP si f6Lf ST8 S06S 115 BASIL VAD SILT 0Sco M 8 1 His OA Sz wg btu LbLS 89 S06S Kis OAM VAD C OSL 05 9 M 8 1 Xe UA o zz wT ni 619ft 6L2 S06S Est OATS SLA 167 6609 M F T SSF Ux r6 dwog zn 8f8f 89 S06S 518 SLCt 6609 M F T ux z dwog mu Kors 0097 66610 6077 1909 ya z 1eoui n32ay punom tim 10d 6H Mis 66t VAD 66 0 0S79 M 8 1 Xiz U 66 una su 00T 789 S06S XS BAT SIA Z9T 6609 M 1 1 Ss dwog n 9480 82S S06S XIF UA OET VHD OfTE 0E79 M 8 1 HIF WA OET uia 09 AWd 88860 LTIH ISZ9 M 8 1 XSF UW LTT wta su MIF OW LIT LT IS 0SE9 M T UIN Z TT dwog eu Is OW VED 0S79 M 8 1 EIz OW wia pr Eis OW VED T OSTO M 8 1 Sts OW upra ni SYO LSISAY azs 7008 SthT 0 46 wsy 29294 IOTN VZ UL 6878 OLTT 097F ammu uoisauuo sxovf X6EGOLLASN corro 160L Tt S X6 60L29SN 9dAL 0 SLINDYID GBS VYOR LNI MOONS 54 itd Say POD SW ON MEd UD wodduseg
4. 200 1 CEA 8 06 ti BTS 68 kN 25 1565 0410 1984 2200 23 021 114 75042 75042 75042 75042 75042 75042 75042 75042 75042 75042 75042 75042 71590 PB 10 24655 24655 05568 6250 0715 6250 0332 6250 0205 6250 9619 6099 3515 6250 3200 6250 1178 75042 1565 0410 1984 2200 7910 1900 7880 2120 Im 1 78 13 1 8 W Comp 6 2 kM 59 1 4 W Film 7 15 13 1 8 W Film 105 21 1 8 W Film 3 48 t1 Film 8 06kQ 21 1 8 W Comp 68 25 1 4 W SWITCHES Push Button 1 2 Subminiature Oak Rotary Bat Con and SW Block Asm Slide DPDT F Used in units with meter stamped 1770 on rear of case All others take the 7 15 resistor R29 51 1983 0400 1 A frequency characteristic see Figure 1 5 carefully controlled in manufacture to give 4 Low temperature coefficient of internal impedance cable correction is not affected by Figure 1 5 Typical response characteristics for the 1560 2133 Microphone a flat response to sound waves of random in 2 Rugged dependable design capable of withstanding wide climate changes from 40 to 95 C from 0 to 100 relative humidity 3 Low temperature coefficient of sensitivity 0 02 dB C gives minimal change in output voltage from 10 to 50 C temperature at the microphone The nominal internal impedance of the microphone is 381 pF at 23 C with a tempera
5. PRECISION INSTRUMENTS FOR TEST AND MEASUREMENT e 1565 B SERIES Sound Level Meter User and Service Manual Copyright 2001 IET Labs Inc 1565 B im January 2002 LOW ENO OF SOUNO LEVEL MICROPHONE RANGE SET BY LEVEL RANGE CONTROL INSTALL A GR WINDSCREEN P N 1560 9521 TO MAKE OUTDOOR MEASUREMENTS 10 dif PORTION OF IN PRESENCE OF WIND SCALE FOR SOUND LEVEL COMPARISONS ON 2 RANGE FULL SCALE SOUND LEVEL RANGE SET BY LEVEL RANGE CONTROL CALIBRATION ADJUSTMENT TOOL SUPPLIED LEVEL RANGE CONTROL SELECTS SOUND LEVEL RANGE LEVEL RANGE CONTROL LOCK SLIDE DOWN TO RELEASE SIGNAL OUTPUT JACK DEPRESS NEEDLE witt GO TO BATTERY REGION IF OK DEPRESS TO SELECT WEIGHTING NETWORK METER SPEED DOWN FOR SLOW UP FOR FAST BATTER tn port RY COV ONOFF SOUEEZE BOTH Sipes OO SWITCH TO RELEASE Figure 1 1 Sound Level Meter Controls and Indicators CONDENSED OPERATING INSTRUCTIONS e Remove and retain protective cap on micro phone 8030 1631 e Set LEVEL RANGE control to the 110 120 dB Range e Slide power switch to right ON 7550 1753 e Depress and hold BAT CHECK button meter should indicate in BATTERY portion of scale If not turn power off and squeeze ears of battery cover together to remove and replace batteries Depress the appropriate weighting and meter speed buttons A B or C up for fast down for slow NOTE The Occupational Safety and He
6. The observ er facing the sound from directly behind the instrument acts as a reflector to produce errors of several dB in the frequency range above 100 Hz A more uniform frequency response is obtained with the meter in front of the observer but with the sound grazing the micro phone coming from the side rather than from the front When out of doors hold the instrument with the microphone pointing up ward to avoid interference from reflected high frequencies and as far from the body as is convenient Do not point the microphone toward a source of background noise any source other than the one being measured The sound level meter can be mounted on a tripod see para 2 1 3 to reduce further the effects of the observer s presence His position should be similar to that for hand held opera tion a line between the observer and the instrument should be approximately perpendic ular to a line from the instrument to the sound source 21 LJ aT 4 t t t umm 4 4 4 48 ERROR TO BE FROM TOTAL NOISE H 144 8 io DIFFERENCE BETWEEN TOTAL NOISE ANO BACKGROUND ALONE Figure 3 4 Effect of background noise on measurements 3 5 BACKGROUND NOISE Measurements should be made with as little background noise as possible For all weightings the background level should be at least 10 dB below the total measured level
7. red scale only the low end of the SLM range setting SECTION 4 PRINCIPLES OF OPERATION 4 1 GENERAL The all solid state circuit contains 2 transis tors and 1 IC package and is carried by a single flexible etched circuit board The circuitry con sists of two amplifiers an attenuator weighting networks a meter circuit and a power supply as depicted by Figures 4 1 and 5 8 SIS Im Figure 4 1 Block diagram of the Sound Level Meter e oer er arrest meur amen psano arrewuarce tman meree cers ourrur t 1 ri on CATTERY SWITCH a ak C eR CowPiovr Tec Qe esm Sw OCUTIF ICH FIOR Secreu s c o E SCHEMATIC SHOWN ON 4068 CWIG FAST Figure 5 8 Schematic diagram for Type 1565 C SLM Detail of 55 LEVEL RANGE control shown on facing page
8. 83 115 141 52 84 116 1 59 53 85 117 178 54 86 118 200 55 87 119 2 24 56 88 120 251 57 89 121 282 58 90 122 3 16 59 91 123 3 55 60 92 124 398 61 93 125 447 62 94 126 5 01 63 95 127 5 62 64 96 128 6 31 65 97 129 7 08 130 794 b Adjust the 1309 controls for a 0 1 V 1 kHz output c Connect the 1309 OUTPUT terminals to the SLM input d Adjust the SLM controls for C weighting and 110 120 dB range e Turn the SLM on and observe the meter indication The correct indication depends on the sensi tivity of the microphone refer to its calibration certificate as given by Table 5 2 If the indication is incorrect adjust CAL control If the correct indication cannot be obtained refer to para 5 7 Table 5 2 ELECTRICAL CALIBRATION DATA Microphone Meter Sensitivity Indication re 1V N m dBre20uN m 110 120 dB range In SI units 20 uN m 20 micropascal 5 7 TROUBLE ANALYSIS 5 7 1 Battery Check If the SLM cannot meet minimum perfor mance standards para 5 2 the first step of trouble analysis should be to check the batter 41 Figure 5 4 Circuitry removed from case If a part is obviously faulty or damaged clip the leads close to the part and then remove the leads from the opposite side 5 6 ELECTRICAL CALIBRATION An electrical calibration can be performed by the following procedure 8 Remove the microphone para 5 3 and connect a 390 pF capacitor to the microph
9. Health Act require use of the A network hence the symbol dB A for sound level decibels on the A scale When no standard test procedure is involved measurements should be made with each of the three weighting charac teristics For a full discussion of weighting net works refer to the General Radio Handbook of Noise Measurement R W Young Journal of the Acoustical Society of America Vol 36 pp 289 2985 1964 D P Love Noise Control Vol 5 pp 230 235 July 1959 17 18 B anoc 4 ELECTRICAL FREQUENCY RESPONSE FOR THE USA WEIGHTING pil Ege 2000 000 0000 RELATIVE MESPONSE OC CIEL r RO a went 1 Figure 3 2 A B and C weighted responses of the SLM The frequency response of the SLM for each weighting characteristic is shown in Figure 3 2 The C weighting curve is nearly uniform over the frequency range from 32 Hz to 8 kHz thus giving an indication of the over all sound pressure The A weighting characteristic dis criminates heavily against low frequency sounds to give an indication closely correlated with subjective estimates of loudness annoyance and speech interference The B weighting char acteristic between the A and C curves is sometimes used in place of A weighting when the subjective effects of noise are of interest When a frequency analyzer is to be used with the SLM set the weighting switch to C
10. Output gt 1 2 V rms behind 6200 N with meter at full scale will drive Octave Band Noise Analyzer recorders oscilloscopes or low impedance headphones HARMONIC DIS TORTION lt 0 5 0 1 typical from 32 Hz to 8 kHz C weighted with meter at full scale Calibration Can be pressure calibrated at 125 250 500 1000 and 2000 Hz with 1562 Sound Level Calibrator Environmental TEMPERATURE 10 to 50 C operating 40 to 60 C storage with batteries removed coefficient of sensitivity 0 02 dB C at 6 dB below full scale meter reading HUMIDITY 9096 RH MAGNETIC FIELD 1 Oersted 80 A m 50 or 60 Hz field causes 45 dB C weighted indication when meter is oriented to maximum sensitivity to field Supplied Carrying pouch miniature phone plug to connect to output and screwdriver for calibration adjustment Also hex wrench Power Two 9 V batteries Burgess 2U6 or equal supplied provide 50 h operation Mechanical Shielded plastic case DIMEN SIONS wxhxd 3 63x6 5x2 09 in 92x165x53 mm WEIGHT 130210 45 kg net 3 Ib 1 4 kg shipping Warranty see page 30 Figure 5 7 Main circuit etched circuit board 52 Figure 5 6 Meter switch etched circuit board SECTION 1 INTRODUCTION 1 1 GENERAL Sound or noise is basically a rapid varia tion in atmospheric pressure and a sound level meter SLM is an instrument that measures weighted sound pressure level A measurement of sound is accompl
11. Pu pes 402 1511 S18 Vd 1v21812313 Screwdriver P N 1565 0440 Micro Plug Switchcraft 850 P2 Two batteries Burgess 2U6 or equal Allen wrench P N 7985 1680 050 in 1 5 ACCESSORIES AVAILABLE Following are some of the accessories that are available for use with the SLM consult the GR catalog information for others 1 Type 1562 Sound Level Calibrator P N 1562 9701 for accurate field calibration of microphones and sound measuring instruments 2 Type 1560 P96 Adaptor P N 1560 9696 to adapt the input socket to mate with a stand ard 3 terminal male aud o connector Switch craft Type A3M for connection to a vibration pickup or other transducer 3 Type 1560 P52 Vibration Pickup P N 1560 9652 refer to para 2 2 4 Type 1560 P83 Earphone Coupler P N 1560 9683 for connecting an audiometer ear phone to the SLM 5 Type 1560 P73 Extension Cable P N 1560 9673 for use between the microphone and instrument input 25 ft 6 Adaptor cables Type1560 P77 Micro plug to 3 4 in spaced banana plug pair GR274 P N 1560 9677 Type 1560 P78 Micro plug to std in phone plug P N 1560 9678 Type 1560 P79 Micro plug to BNC P N 1560 9679 Type 1560 P80 Micro plug to std 1 4 in phone jack P N 1560 9680 7 Type 1560 9590 Tripod 8 GR Microphone Windscreen P N 1560 9521 for reducing the effects of wind noise and protecting the diaphragm ELECTRICAL PARTS LIST GR PartNo Mfg Code Fed Stoc
12. When this cannot be done apply the corrections given in Figure 3 4 3 6 USE OF AN EXTENSION CABLE The sound level meter can be operated at some distance from its microphone if a low noise extension cable such as the Type 1560 P73 is used In fact this is a good practice when measuring high intensity fields However several factors must be considered The use of the cable will change the source impedance as seen by the input terminals of the SLM thereby changing the weighting character istics To compensate for this a capacitor must 22 be added in series with the input to the SLM SECTION 5 SERVICE AND MAINTENANCE 5 1 FIELD SERVICE The General Radio warranty attests the quality of materials and workmanship in our products When difficulties do occur our ser vice engineers will assist in any way possible If the difficulty cannot be eliminated by use of the following service instructions please con tact our Service Department see ear cover giving full information of the trouble and of steps taken to remedy it Be sure to mention the serial and type numbers of the instrument Before returning an instrument to General Radio for service please contact our Service Department or nearest office requesting a Returned Material tag Use of this tag will ensure proper handling and identification For instruments not covered by the warranty a purchase order should be forwarded to avoid unnecessary delay 5 2 MINIMU
13. of incidence between the microphone and the sound source When measurements are made on a source in a free field an angle of incidence of 70 degrees between the axis of the microphone and the sound source will approximate random response 3 8 USE AS A PREAMPLIFIER The SLM can be used as a preamplitier for the GR 1558 Octave Band Noise Analyzer to make low level octave band measurements i e below the low end of the 1558 sound level range Following is a recommended procedure a Connect the SLM output to the 1558 INPUT SLM jack with the GR 1560 P78 P N 1560 9678 adaptor cable b Adjust the SLM controls as follows Level range control 110 120 Meter speed SLOW om oo oy go ov a onc QN c Adjust the 1558 controls as follows Function SW s Fast Band CPS ALL PASS BAND LEVEL dial 12 00 o clock BAND LEVEL knob Fully cw d Use the GR 1562 Calibrator to make the SLM read 114 dB adjust the 1558 CAL con trol for a 4 meter indication The setup is now calibrated so that a 1558 meter indication of O equals the low end of the SLM range setting e Set the SLM level range control for an on scale indication or the lowest range f Set the BAND CPS control to the desired band Set the BAND LEVEL knob for an on scale reading The band level in dB is the alge braic sum of the 1558 meter indication the BAND LEVEL knob setting
14. short the input as shown in Figure 5 3 Set the 1565 to the de sired range and check the noise level for any of the bands given in the table The cable must be free and unrestricted Set the calibrator on a level surface and turn it ON Adjust the LEVEL control so that the meter indicates 100 Depress the SLOW button on the SLM and set the level range control to the 110 120 dB range Adjust the SLM indication to 112 dB by means of the CAL control The meter will now indicate a level of 112 dB when the pickup is subjected to an acceleration of 1 g rms 386 inches per second per second Use Table 2 1 to convert indicated levels in dB to acceleration in g s rms The SLM can also be calibrated by electrical means when the sensitivity of the Type 1560 P52 Vibration Pickup is known Install the Type 1560 P96 Adaptor then apply a voltage numerically equal to the pickup sensi tivity in volts per g between terminals No 1 and No 3 of the adaptor input Terminal No Figure 2 3 Frequency response of the Type 1560 P52 Vibration Pickup with the SLM 12 Table 2 1 ACCELERATION IN g s CORRESPONDING TO VARIOUS INDICATED LEVELS Level Accel Level Accel Level Accel in dB in a s in dB in g s in dB in g s 34 98 200 35 99 224 36 100 251 37 101 282 38 102 316 39 103 355 40 104 398 41 105 447 42 106 501 43 107 562 44 108 631 45 109 708 46 110 794 47 78 111 891 48 80 112 1 00 49 81 113 1 12 50 82 114 1 26 51
15. Calif 37942 P R Mallory amp Co Inc Indianapolis Ind 56289 Sprague Electric Co N Adams Mass 72982 Erie Technological Products Inc Erie Penn 75042 IRC in Philadelphia Penn 19108 Lighting Products Division Selem Mass 01971 51 Mfg Part No Fed GR PartNo Mfg Code ELECTRICAL PARTS LIST cont 2222 Fon STA A wan Figure 1 3 Typical response characteristics of 3 the SLM with C weighting 4 1 3 2 Microphone General Radio s lead zirconate titanate cera mic microphone cartridge P N 1560 2133 was developed as a measurement grade microphone With a diameter of 0 936 in it fits into any fix ture designed to accept the current industry standard Western Electric 640 AA Condenser Microphone The following features make it excellent for sound level measurements X H Le VSS M 2n Figure 1 4 Directional patterns of the 1560 2133 Microphone ELECTRICAL PARTS LIST cont Fed GR Part No Mfg Code Fed Stock No Mfg Part No Ret Des RESISTORS Cont 5905 681 8757 5905 827 3332 5905 682 4103 5905 824 3077 5905 682 4100 5905 815 3793 5905 686 3385 5905 279 4619 5905 815 3793 CEA 61 9 Q t1 BTS 51 kN t5 CEA 1 78 kQ 21 BTS 6 2 25 CEA 7 15 tig CEA 105 kQ tI CEA 3 48 kf 117 BTS 9 1 kM 5 75042 CEA 7 15 118 6250 1806 75042 CEA 715 N 13 CEA 332 fj 21 CEA 205 CEA
16. M PERFORMANCE STANDARDS 5 2 1 General The equipment methods and criteria for verifying the specified performance of the SLM are presented in the following paragraphs Table 5 1 lists the necessary equipment and Figure 5 1 shows an equipment setup for making performance tests 31 EN GenRad This product i warranted to be free from detects in material and workman ship and when property used will perform in accordancs with specifications Any GA menutectured instrument module or pert found not to meet this standard within a period of one year after original shipment will be repsired or replaced st no charge when returned to GR service facility QR policy Is to maintain repair capability for a period of ten years after the original shipment and 1o make this capability available at the then prevailing schedule of charges for any product returned to a GR service facility Changes in the produet not approved by GA shail vold this warranty GA is not liable for consequential damage This warranty ls in lie of aft other warranties expressed or implied including but not limited to the implied warranties of merchantability and fitness for particule purpose CAPACITANCE TO BE INSERTED IN ADAPTOR pF CABLE LOSS 8 CAPACITANCE OF CABLE pF Figure 3 5 The chart shows the compensation required for the capacitance of various exten sion cables and the corresponding cable loss Also cable losses will cause the m
17. Observe the 334 A meter indication the distortion should be less than 0 596 5 3 DISASSEMBLY ASSEMBLY CAUTION This instrument should be serviced by skilled service personnel The procedure outlined below is intended as a guide for skilled service personnel only a Remove the batteries and retain the foam insert see para 3 1 b Using Allen wrench turn setscrew acces sible through top rear of case fully clockwise to release microphone then pull it straight out Place the SLM face down and remove the four screws from the back half of the case d Turn the instrument over and remove the front half of the case Be careful not to break microphone leads or lose the LEVEL RANGE control slide bar lock e Grasp the ON OFF switch assembly with a thumb and forefinger and pull straight up to dislodge it from the mounting post Retain the insulating strip f Carefully remove the circuitry from the back half of the case and remove the tape that 37 c Connect the 2540 DVM to the oscilla tor output and the Type 1192 Counter to the attenuator input d Connect a 600 2 1 resistor across the OUTPUT terminals of the attenuator then connect the attenuator OUTPUT to the input of the SLM e Connect the HP 334A with a 600 2 load across the input to the SLM output jack f Adjust the SLM controls as follows Level range control 80 90 dB WOE 6 BOWW g Adjust the 1309 cont
18. ROPHONE BASE Figure 3 6 Installation of an extension cable between sound level meter and the microphone a Insert the 050 in Allen wrench through the access hole at the top rear and turn the screw clockwise b Pull the microphone straight out from the top Note that the L molded inside the potential is indicated by the meter unless the negative battery is below 7 0 V If this lower negative voltage limit is exceeded Q3 turns on causing the meter to indicate that the negative battery potential is low Both batteries should be replaced at the same time Meter readings for false weightings such as all buttons up or 2 adjacent buttons down are prevented by short circuiting the meter via Q4 Since the microphone capacitance serves as part of the weighting network the spectrum is partly weighted before it is introduced to the preamplifier which reduces the likelihood of overloading the amplifier The source capaci tance cannot be changed however without affecting the weighting characteristic 4 3 POWER SUPPLY The power supply consists of two 9 V tran sistor radio batteries used to supply positive and negative voltages and circuitry for check ing the level of charge Approximately 50 hours of operation are obtained when the instrument is operated for two hours per day 4 2 MAIN CIRCUITRY Transistors Q1 and Q2 comprise the active elements of the preamplifier Q1 is a low noise N channel fi
19. alth Act regulations re quire A weighting and SLOW meter response 8120 0150 2 5210 4109 7550 1745 1984 4750 Point the microphone at right angles to the direction of the noise path keeping your body out of the path see Figure 3 1 9 Adjust the LEVEL RANGE control for a reading For readings below 40 dB read the meter below the low end range mark and subtract the reading in dB from 40 e f the pointer fluctuates more than 3 dB depress the SLOW button CAUTION If continuous noise exceeds 115 dB A slow immediate RESISTANCE IS IN OHMS K 10 M z 10 CAPACITANCE 1S IN FARADS u 10 p 107 VOLTAGES EXPLAINED IN INSTRUCTION BOOK SERVICE NOTES use of protective ear muffs CPANEL CONTROL Emaar Tp REAR CONTROL SCREWDRIVER CONTROL WT WIRE TIE TP TEST POINT or plugs is indicated E COMPLETE REFERENCE DESIGNATION INCLUDES SUBASSEMBL Y LETTER C A BRI For best results use the GR 1562 SLM 54 Calibrator periodically see para 5 2 2 n SPECIFICATIONS Sound Level 30 to 130 dB re 20 uN m A weighted 35 to 130 dB B and C weighted Weighting A B and C Conforms to ANSI 51 4 1971 Type 2 and IEC 123 1961 Meter Rims response with fast and slow speeds Input MICROPHONE Lead zirconate titanate ceramic 1560 P96 Adaptor converts input to 3 pin male A3 connector for correct weighting source impedance must be 380 pF 5 INPUT IMPEDANCE 13 MQ 15 pF
20. cations 5 5 SERVICING ETCHED CIRCUIT The SLM contains a single etched circuit board which is flexible and transparent The electrical components are on one side and all solder connections are on the other CAUTION When removing or replacing parts use a low heat soldering iron and a small diameter rosin core solder Do not subject the parts or board to prolonged heat holds the etched circuit in a folded configura tion The LEVEL RANGE detent spring will pull out of the case with the circuitry Reinstall it in the case Also make sure that the OUT PUT jack ground clip is still in place g Remove the c ring ground contact springs and 2 washers from the left end of the level range control shaft and pull the knob and shaft out of the assembly Be careful not to lose the spring and nylon washer on the shaft Figure 5 8 shows details All of the components are now easily accessible See para 5 5 for component replace ment instructions To reassemble the instrument reverse the above procedure B fore inserting the LEVEL RANGE shaft position the tab on each switch S2A and S2B Figure 5 4 at 12 o clock with the meter facing you Notice that the knob has two mechanical stops on the inside surface Turn the knob so that these stops are adjacent to the meter face then insert the shaft through switch S2B Place the right hand drum highest number 130 on the shaft with the number 90 appearing in the window Place the o
21. chinery traffic noise and other noises of 8 reasonably constant character 1 3 DESCRIPTION 1 3 1 General The instrument is housed in a high impact molded plastic case that is shaped for comfort able hand held operation and tapered at the microphone end to minimize the effect of case diffraction It consists of the following ele ments a microphone to pick up sound an amplifier to raise the microphone output to useful levels a calibrated attenuator to adjust the amplification to a value appropriate to the sound level being measured an indicating me ter to exhibit the measured sound level net works to adjust the frequency characteristic of the response A B or C weighting and an output connection to accommodate additional measuring equipment It covers the sound level range from 30 to 130 dB above the standard reference level of 20 uN m 0 0002 jubar Figure 1 2 shows a polar plot of the angle of incidence responses and Figure 1 3 shows the frequency response as a function of incidence of the SLM FEDERAL MANUFACTURER S CODE From Federal Supply Code for Manufacturers Cataloging Handbooks H4 1 Name to Code and H4 2 Code to Name as supplemented through August 1968 04713 Motorola Phoenix Ariz 86008 07263 Fairchild Camera Mountain View Calif 07999 Borg Inst Delavan Wisc 63115 24446 G E Schenectady N Y 12306 24655 General Radio Co W Concord Mass 01781 28959 Hoffman Electronics Corp E Monte
22. e C weighted reading with the maximum input level for the level range selected in b If possible select the next high er level range If the sound level drops 10 dB the reading in b is valid 19 0 A WEIGHTING Figure 3 3 Relative maximum input sound pressure levels that can be measured in the various weighting modes 5 2 2 Calibration A quick reliable sound pressure level cali bration can be performed at specific frequen cies by means of a Type 1562 Sound Level Calibrator The calibrator like the SLM is small light and battery operated making it ideal for field use The procedure is as follows a Set the SLM level range control to the 110 120 dB range b Slide the power switch to the ON position and depress the C weighting network button c Turn the calibrator on and set the desired calibrating frequency 500 Hz for example d Place the calibrator with the Type 1560 6100 Adaptor 15 16 in installed over the microphone of the SLM as in Figure 5 2 e Observe the SLM meter indication to be 114 dB 0 5 dB If the meter indication is incorrect by more than 0 5 dB adjust the CAL control to obtain 114 dB Use the screwdriver supplied P N 1565 0440 f Check the meter indication at the other calibrator frequencies It should be 114 dB 1 dB at 125 250 and 1000 Hz and 2 dB at 2000 Hz 5 2 3 Output Voltage Figure 5 1 The SLM will supply at least 1 2 V ac at the output jack when
23. eighting Gain for 60 dB microphone re 1 V ubar Table 5 4 DESIGN CENTER AC VOLTAGES Full Scale Mike input Input Gain Output 2nd Input Gain Output dB Output Atten 1stAmp IstAmp Ist Amp Atten 2nd Amp 2ndAmp 2nd Amp 50 0 0603mV 1 0 008mV 26 4 1 67mV 1 1 67 mV 750 1 25 V 60 O 2mV 0 2 mV 426 4 5 28 mV 3 16 1 67 mV 750 1 25 V 70 0 63mV 1 0 63 mV 26 4 16 7 mV 10 1 67 mV 750 1 25 V 80 20mV 1 2 0 mV 426 4 52 8 mV 31 6 1 67 mV 750 1 25 V 90 6 3mV 6 3 mV 426 4 167mV 4100 1 67 mv 750 1 25 V 100 0 02V 10 20mv 426 4 52 8 mV 31 6 1 67 mV 750 1 25 V 110 0 008V 10 63mV 426 4 167mV 100 1 67mV 750 1 25 V 120 02V 100 20mV 426 4 52 8 mV 731 6 1 67mV 750 1 25 V 130 0 63V 100 6 3 mv 426 4 167mV 100 1 67mV 750 1 25 V Microphone sensitivity level 60 dB re 1 V pber kHz signal and C weighting T Actual voltages may differ slightly due to gain variations of the amplifier BAND LEVEL 48 819195 BAWLD0 E 1 1H Bnd ajqnop pue Ong 6njd euoud paepuels 149AU02 ase spJoo yed ueo12spuim auoudouoiu ou jo osn Aq pesneo AuAnisues WIS U seBueu qL z NB jo pui 104 uaasaspum M oudouan Aq pasnes suonanpe puiM EL Z oun6r4 wexe Jo4 edAj jeujoue JO IBUU0D indjno y WeAUOD SpJOO yned asn S uonosuuoo jo sue aw Joujouy 19110 POD 49ed 0896 0981 H9 eui esn xoel euoud Puepueys WIS Parod
24. el range control to the 110 120 dB range If the control will not turn use a pointed object such as the end of a paper clip to slide the level range control lock see Figure 1 1 away from the knob 16 Stand with the instrument in front of you with the sound coming from the side Point the microphone in a direction perpendicular to the noise path keeping your body out of the path See Figure3 1 Depress one of the weighting buttons see para 3 3 and turn the level range control until an on scale reading is obtained ores Figure 3 1 Proper positioning of meter with respect to noise source The left window indicates the dB reading at the lower end of the scale while the right window indicates the full scale reading for the range set by the level range control For ex ample if the level range control is set to the 60 70 dB range the left window will indicate 60 and the right window 70 If the meter pointer is 4 divisions to the right of the first major meter scale division the indicated sound level is 64 dB for the particular weighting selected When using fast meter speed an average level should be estimated if the meter pointer b Adjust the 334 A controls as follows FUNCTION sw SET LEVEL METER RANGE sw 100 FREQUENCY RANGE sw X100 HIGH PASS FILTER sw OUT c Adjust the 334 A SENSITIVITY controls for a full scale reading d Set the 334 A FUNCTION switch to DISTORTION e
25. eld effect transistor and operates in conjunction with a high gain bipolar transis tor Q2 to stabilize the gain R9 a potentiom eter in the preamplifier feedback loop is used to calibrate the instrument The main amplifier consists of one inte grated circuit that provides low output imped ance and high gain gain is stabilized via the feedback loop This amplifier drives both the meter detector circuit and the output terminals The attenuator is divided into two sections for best signal to noise ratio One section pre cedes the input amplifier the other is between the amplifier stages The attenuation is adjust able in 10 dB steps Each coupling and feedback path in the SLM serves double duty by forming part of the weighting network The main amplifier feed back loop shapes the 733 Hz and 8 kHz rolloff for A weighting and A B and C weighting respectively Rolloff at 107 Hz for A weighting 160 Hz for B weighting and 32 Hz for C weight ing is accomplished by the combination of transducer capacitance and input load resis tance The 32 Hz rolloff for A and B weighting is formed by the preamplifier output coupling circuit and the second section of the attenua tor The battery check circuit utilizes the meter and a sensing circuit consisting of Q3 CR4 CR5 and associated resistors When the BAT CHECK button is depressed the positive battery microphone and engraved on the SLM jack indicates mating connectors c Pl
26. eter to read low by an amount that varies with the cable length Figure 3 5 shows the loss and the value of the compensating capacitor for cable capaci tances between 150 and 1500 pF The Type 1560 P73 Extension Cable P N 1560 9673 for use with the SLM is a 25 foot cable fitted with standard 3 terminal micro phone connectors A Type 1560 P96 Adaptor P N 1560 9696 and a Type 1560 3040 Micro phone Base P5 base or P5 microphone com plete are needed to mate the SLM and the microphone with the connectors The capaci tance of the Type 1560 P73 Extension Cable is approximately 550 pF Figure 3 Sshows that a series capacitor of 640 pF is required for this 23 cable capacitance This capacitor can be in stalled in the Type 1560 P96 Adaptor as follows a Remove the outer shell of the adaptor by turning the setscrew in the side of the shell in a clockwise direction and pulling the shell off the adaptor b Remove the lead connecting terminal No 3 of the microphone connector to one of the teflon insulated pin plugs and replace the lead with a small mica or ceramic capacitor of about 640 pF c Replace the outer shell The value of capacitance to be used with other cables can be determined from Figure 3 5 To connect an extension cable proceed as follows see Figure 3 6 TYPE 1560 P96 ADAPTOR MODIFIED TO INCLUDE SERIES CAPACI MICROPHONE REMOVED FROM SOUND LEVEL METER SOUND LEVEL METER TYPE 1560 MIC
27. ished by changing a noise into an electrical signal and displaying it on an indicator in terms of decibels dB The apparent loudness that we attribute toa sound varies not only with the sound pressure but also with the frequency or pitch of the sound How it varies with frequency depends on the sound pressure This effect is taken into account to some extent for pure tones by weighting networks included in the SLM The above points are illustrated briefly in A Primer of Noise Measurement a 34 page book let free upon request from General Radio Co For 8 more comprehensive work on noise our Handbook of Noise Measurement for 7 50 contains 328 pages of detailed information on how to solve your noise problems Our Primer of Plant Noise Measurement and Hearing Test ing free explains conformance to the Federal Regulations of 1971 1 2 PURPOSE The basic instrument of the General Radio sound measuring equipment line is the sound level meter SLM Theunit Figure 1 1 is a Type 2 i e general purpose SLM A Type 2 instrument has tolerances required by the Amer ican National Standards Institute ANSI stand ard specification S1 4 1971 for sound level meters These tolerances are generally more stringent than those required for Type 3 in struments The chief use of the SLM is making noise measurements in a working or living environ ment such as routine measurements of office building ventilator systems typewriters ma
28. k No Mfg Part No CAPACITORS 5910 080 9646 4400 2050 80183 4404 0335 5013 1 pF 5201 831 33 pF t5 150D476X0006B2 12954 831 IS pF 153 72982 4450 5500 56289 4450 4303 4450 5100 56289 Ceramic 0 1 uF 180 203 100 V Ceramic 33 pF 155 500 V Tantalum 47 0 uF 220 6 V Tantalum 15 pF 5 15 V 5910 855 6343 150D106X002082 831 82 pF 58 8111 200 YSD 101 831 1 pF 25 OG 80 uF 220 150D685X0010A2 72982 72982 76149 37942 4404 0825 4410 1213 4400 6442 4450 4302 4450 6300 Ceramic 27 pF 5 100 V NPO Ceramic 100 pF 553 200 V Tantalum 10 0 pF 220 20 V Tantalum 1 0 uF 53 35 V Ceramic 82 pF 558 500 V oo 80 pF 2208 15 V 5910 936 1332 4450 4800 56289 pw Dunne dU 8111 A100 Y5S 102M 56 MF 210 15760 MTP 300 pF 220 72982 76149 4450 5724 4450 5520 4400 6422 P 6 8 pF 202 6 V Tantalum 56 uF 210 6 V Ceramic 001 pF t20 100 V 02 Tantalum 300 pF t20 10 V 5910 727 3562 1N4009 IN34A S 25440 58854 28959 6082 1012 Type 1N4009 Type IN34A 5961 170 4430 6082 1003 1N958B 6083 1057 Type 1N958B 7 5 V Figure 5 5 Mechanical parts front view MECHANICAL PARTS LIST Fig Ret Ont Descrippon GR Part No 1 1 Knob ON off 1565 7310 2 5 Pushbutton knob A B C SLOW 5511 0403 BAT CHECK 3 1 Case front 1565 1510 4 l Microphone MK101 1560 2133 5 Level range contr
29. ling air across the site of the microphone see Figure 2 1a Any attenuation of monitored noise result ing from use of the windscreen occurs over only a portion of the frequency spectrum being monitored The loss of system sensitivity oc casioned by use of the windscreen is shown in Figure 2 1b For normally encountered noises the influence of the windscreen on measured sound level is negligible 2 1 5 Output Connector It may be desirable to drive other equip ment with the SLM such as a recorder or an oscilloscope Therefore a connector near the level range control is available to supply volt ages proportional to the meter response A Switchcraft Type 850 P2 Micro plug connec tor is supplied with the SLM to complete this end of a patch cord The other end can be ter minated with whatever connection is necessary The output voltage is 1 2 V for a full scale reading into an open circuit with a 6200 2 source impedance Table 5 5 TYPICAL INTERNAL SIGNAL TO NOISE RATIOS Octave Band Noise Levels in dB Below Full Scale setting of level range control 140 130 110 100 90 80 70 60 120 Center Freq Hz Band 0 0 0 HH 9958558323 HHH ouo 599999923 mH oy 3358838888 Ro855888r 29 E BSLLLKLLKKAK 0 0 9 5888889988 1010 SSERXRRBB oN L258888888 o 100 SSRELKENA 15 18 21 24 27 30 33 36 39 31 5 63 125 250 500 1000 2000 4000 8000 SLM set for C w
30. ol knob 1565 1230 6 Battery cover 1565 7430 1 Case rear 1565 5010 46 SECTION 2 INSTALLATION 2 1 INSTALLATION 2 1 1 General The sound level meter should be stored in the vinyl pouch supplied when not in use It can be carried conveniently at waist level by slipping your belt through the loop on the back of the pouch 2 1 2 Operating Environment The SLM operates over the range of environ mental conditions that are normally encoun tered in industrial applications CAUTION Remove the batteries before storing to avoid the corrosive effects of battery leakage 2 1 3 Tripod Mounting Any tripod that has a standard 1 4 20 thread will fit the insert on the back of the instrument case To tripod mount the SLM screw the threaded end of the pan head into the insert and hand tighten GR has a tripod avail able P N 1560 9590 2 1 4 Microphone Windscreen To attenuate ambient wind noises use a GR Microphone Windscreen P N 1560 9521 The windscreen may 850 be used to cushion the microphone from accidental shocks and pro tect the microphone diaphram from accumu lations of oil vapor and dust The windscreen is a 3 in diameter sphere that fits snugly over the microphone It is made of reticulated polyurethane foam and can be conveniently removed and washed or replaced if it becomes soiled This is in addition to the obvious advantage of attenuating ambient wind noises such as might emanate from a fan blowing coo
31. one leads as shown in Figure 5 3 1 is grounded to the instrument case Depress the SLOW button on the SLM and set the level range control to the 110 120 dB range The oscillator frequency should be between 100 and 1000 Hz Adjust the CAL control for a meter indication of 112 dB Install the pickup and use Table 2 1 to convert indicated dB levels to acceleration in g s rms The technique for measuring vibration is given in the GR Handbook of Noise Measure ment The frequency response for the combina tion of the sound level meter and the Type 1560 P52 Vibration Pickup is shown in Figure 2 3 2 3 DETERMINATION OF NOISE EXPOSURE According to the Occupational Safety and Health Act of 1970 noise that measures above 115 dB A is automatically too high for any length of exposure over about 1 second The SLM can be used to estimate the actual per sonnel exposure by measuring the noise level in various areas of the plant and measuring the time that personnel are present All noises between 90 dB A and 115 dB A should be recorded and combined to obtain equivalent continuous levels Notice in Table 2 2 that the permissible exposure for high level noise is for much shorter periods than for low level noise An instrument that will automati cally measure and compute the total exposure is the GR Type 1944 Noise Dosimeter Its digital readout not only tells you the per centage of the exposure limit that has been ac cumulated but al
32. rlington MA 01803 Table 5 3 TEST VOLTAGES dc 10 Component Terminal To Ground avo t 8 B c 2 B c 2 3 4 6 7 Do not measure high impedance ies Replace them with fresh units if the check doesn t give an indication in the BATTERY region 5 7 2 Electrical Check Next isolate the problem to either the microphone or the rest of the instrument To do this replace the microphone with its equiva lent impedance para 5 2 3 and drive the input with a 0 63 V 1 kHz signal Check the SLM indication to be 130 3 dB If this indication is satisfactory the microphone is defective and should be replaced If it is not satisfactory use the DVM to check the voltage at the output jack It should be gt 1 25 V If this voltage is in Correct use Tables 5 3 and 5 4 to further iso late the problem 5 7 3 Internal Noise Table 5 5 gives the typical internal noise levels measured in octave bands for each attenu ator setting and is intended as a reference for making octave band noise measurements To reproduce this table use the setup shown in Figure 5 1 Apply a 1 kHz calibration signal 2 V nominal to the input of the SLM to give a full scale reading on the 130 140 dB range The microphone is replaced with its equivalent impedance see Figure 5 3 Calibrate the 1933 for a full scale reading with the controls set for octave band response Remove the equipment connected to the 15658 SLM input and then
33. rols as follows FREQUENCY 1 kHz OUTPUT VOLTAGE 1 h Adjust the 334A controls as follows Function sw VOLTMETER METER RANGE sw M i Adjust the 1450 TB so that the SLM reads full scale j Observe the 334 A meter indication it should be greater than0 11 V With the 600 2 resistor removed from the 334 A input the voltage should be greater than 1 2 V rms 5 2 4 Output Distortion Figure 5 1 Following is a procedure that can be used to check the distortion of the output voltage a Use the same equipment setup as ex plained in para 5 2 3 fluctuates by 3 dB or less When the fluctua tions are greater than 3 dB depress the meter speed button down for SLOW NOTE The Occupational Safety and Health Act regulations require A weighting and slow meter response The same measurement procedure is used for A B or C weighting the weighting charac teristic should always be stated otherwise the measurement will be meaningless Com mon practice is to assume A weighting unless otherwise stated ANSI S1 4 1971 3 3 WEIGHTING NETWORKS 3 3 1 Choosing the Proper Weighting Noise codes and acceptance test procedures frequently specify the weighting characteristics to be used For example A weighting is often used for the measurement of motor vehicle appliance office or plant noise Except for impact noise Federal Regulations such as the Walsh Healey Act and the Occupational Safety and
34. so indicates whether the in 13 14 Stantaneous 115 dB A and impact 140 d8 peak levels have been exceeded The SLM can be used in conjunction with the 1944 Refer to the 1944 Instruction Manual for operating instructions Table 2 2 PERMISSIBLE NOISE EXPOSURES 1 4 or less Tat the time of printing an added exposure of 16 hours at 85 dB A is under active consider ation Check regulations in force Under Part 1910 95 Occupational Noise Ex posure Dept of Labor of the Code of Fed era Regulations Chap XVII of Title 29 39 F R 7006 See also Guidelines to the Dept of Labor s tional Noise Standards Bulletin 334 GPO 1971 O 484 782 3 C Check that the flex circuit lays properly in the case Be sure it does not interfere with the front case screw holes d Place the LEVEL RANGE lock in its groove in the lower case with the locking tab facing the microphone and down e After case assembly check the alignment of CAL pot R9 in the access hole and opera tion of LEVEL RANGE control and lock f Replace battery foam insert if it becomes detached g Remount microphone with the L on the socket mating the L pin on the microphone Tighten the microphone by adjusting the set screw counterclockwise h Instali batteries After disassembly the SLM should be re calibrated 5 4 MAJOR COMPONENTS Figure 5 4 identifies the major components of the SLM with their corresponding lo
35. the meter is at full scale deflection This output is sufficient to drive an analyzer recorder oscilloscope headphones etc Following is a procedure that can be used to check the amplitude Table 5 1 TEST EQUIPMENT Recommended Item Requirements Type Range 20 Hz 8 kHz GR 1309 Output 1 V oe a Voltage 0 10 V rms 2540 D Freq 10 Hz 50 kHz Accuracy 2 Data Impedance gt 100 Precision Calibrator OUTPUT V GR 1562 FREQUENCY 125 250 500 1 kHz and 2 kHz Digital Counter 10 Hz 50 kHz GR 1192 Attenuator 0 100 dB in 0 1 dB steps GR 1450 TB Distortion Meter 10 Hz 50 kHz HP 334 A Precision Meets ANSI 1 4 1971 GR 1933 SLM and Type 1 Octave Band Noise Analyzer Patch Cord GR874 to banana plugs GR874 R33 Patch Cord 2 GR 274 to 274 GR 274 NP Adaptor cable Micro plug to Std phone GR 1560 9678 plugs Adaptor cable Micro plug to GR274 GR 1560 9677 Adaptor cable Micro plug to GR 1933 GR 1933 9602 mast Resistor 600 1 2 GR 500 G Capacitor 390 pF 11096 Mica Or equivalent 3 4 EFFECT OF THE OPERATOR When the sound is coming mainly from one direction the sound level reading may be some what affected by the relative positions of instrument and observer The SLM should not be held in front of the observer with the microphone pointed toward the source of the sound although this is perhaps the most logical manner This position gives a marked increase in the response at high frequencies
36. ther drum on the shaft with the number 80 appear ing in the window Place the spring and washer on the shaft and insert the end of the shaft into switch S2A Continue with steps f through a of the above procedure in reverse order To Remount The Microphone a Insert its socket in the lower half case with the setscrew facing access hole Be sure tab of OUTPUT jack is mating with the ground clip in the lower case b Insert the insulating strip in front of the 38 ON OFF switch post then insert the switch SECTION 3 OPERATING PROCEDURE 3 1 BATTERIES Two 9 V carbon zinc transistor batteries are supplied and should be checked each time the instrument is used To check the batteries slide the power switch to the right depress and hold the BAT CHECK pushbutton The meter should indicate in the region marked BAT TERY If it does not the batteries must be replaced To replace the batteries first turn the instrument off Then with a thumb and fore finger grasp the knurled edges of the bottom cover squeeze and remove Pull the batteries out of the compartment and disconnect them from the clip Replace with Burgess 2U6 Eveready 216 or equivalent 3 2 BASIC OPERATION Remove and retain the protective cap on the microphone Slide the power switch to the ON position Check the batteries by depressing the BAT CHECK button If the meter does not indicate in the BATTERY region the batteries must be replaced Set the lev
37. ug the modified P96 Adaptor into the microphone connector Make sure the adaptor pin marked G mates with the connector L pin and that the setscrew access holes line up Turn the Allen setscrew counterclockwise to lock the adaptor in place d Connect the microphone to the Type 1560 3040 Microphone Base black lead to pin L on the microphone Fasten the microphone base to the cartridge with the setscrews in the base e Install the extension cable between the SLM and the microphone base para 3 6 The loss for the Type 1560 P73 25 ft Extension Cable is found from Figure 3 5 to be 7 8 dB This value must be added to the reading of the SLM to obtain the actual sound level Or the correction can be determined with the Type 1562 Sound Level Calibrator set to produce a level of 114 dB at the microphone Using the 1560 2133 Microphone with base at the end of an extension cable allows sound field intensity measurements up to 140 dB To do this calibrate the sound level meter to read 104 dB instead of 114 dB with the 1562 Calibrator and add 10 dB to all readings NOTE When replacing the micro phone on the SLM make sure the L hole on the socket mates with the L terminal on the microphone cartridge 3 7 PREFERRED ANGLE INCIDENCE When measurements are made on sounds in reverberant fields the angle of incidence of sounds reaching the microphone is indetermi nant In this case there is no preferred argle
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