HP 427A User's Manual
Contents
1. 1106 eee 1 1 211 __ METER CORRECTION DBM 5 8 0477 IMPEDANCE 5 Figure 3 2 Impedance Correction Graph 01791 1 3 3 FEE TEEN er ee EE cS EM S UNS EE Pv Omm P rue 9 I da lt weraq yora periduns 10319 S lt T gt vYOH 912 S110A 9 S39V110A NONINO AHILLVE ATddNS 1 SITOA 9 2v LINDYID HOLVNNILLV HOLVNNILLV 5 ONINILIN 27 1508 27 JONVY DV 10 NOILdO vo SWHO 9 172 SAHO ov MOLYNNILIV 90193735 IndNI SL OA 5752 0997 SWHO NOLLAN 192 50 2 Lsnrav HOLVNNILLV 135440 20 39474 20 gt m E o o ul 4 0 r A ph po Model 427A Section IV SECTION IV THEORY OF 4 1 GENERAL 4 2 The Model 427A measuresac voltage dc voltage and resistance It is battery operated but with Op tion 01 can be powered by line voltage Figure 4 1 shows a simplified block diagram of the 427A 4 3 The Battery Regulator 1 regulates the bat tery output and provides 6 7 and 6 7 volt bias sup ply to the amplifiers The 427A uses two amplifiers the DC Amplifier 1 and the AC Metering Circuit A2 The former is a high input impeda2. 427A SM 94 opp YP OPERATING AND SERVICE MANUAL PROPERTY OF ELECTRICAL ENGINEERING VANDERBILT UNNER SITY VOLTMETER 421A HEWLETT p PACKARD Vilt dH K4XL s 8 BAMA This manual is provided FREE OF CHARGE from the BoatAnchor Manual Archive as a service to the Boatanchor community lt was uploaded by someone who wanted to help you repair and maintain your equipment If you paid anyone other than BAMA for this manual you paid someone who is making a profit from the free labor of others without asking their permission You may pass on copies of this manual to anyone who needs it But do it without charge Thousands of files are available without charge from BAMA Visit us at http bama sbc edu OPERATING AND SERVICE MANUAL hp Part No 00427 90004 MODEL 427A VOLTMETER Serials Prefixed 947 Appendix C Manual Backdating Changes adapts manual to serials prefixed 550 621 731 4 3 1 3 Copyright Hewlett Packard Company 1969 P O Box 301 Loveland Colorado 80537 U S A Printed JAN 1970 a a e e Table of Contents TABLE OF CONTENTS Model 427A Section Page I GENERAL INFORMATION 1 1 1 1 Description 1 1 1 5 1 1 1 7 Instrument and Manual Identification 1 1 1 10 Available Accessories 1 1 1 12 Cables and Adapters 1 1 1 13
3. da Section I Model 427A a HEWLETT PACKARD 4274 VOLI FUNCTION 3 EEE Figure 1 1 Model 427A Voltmeter Table 1 1 Specifications DC VOLTMETER Voltage Ranges 100 mV to 1000 full scale 1 3 10 sequence 9 ranges AC VOLTMETER Cont d bl Input Impedance 10 megohms shunted by 40pF on 10 mV to 1 V ranges 20 pf on 3 V to 300 V ranges Response Responds to the average value of the in put calibrated in rms voltsfor sine wave input Overload 300 V rms momentarily 1 V range and Accuracy 2 of full scale on any range 09C to 50 C Input Resistance 10 megohms on all ranges below AC Rejection Superimposed peak ac voltages 60 M Hz and above 100 times greater than full scale 425 V rms maximum above 1 V range affects reading less than 1 Maximum 450 OHMMETER volts peak Overload 1200 Vdc on any range AC VOLTMETER Voltage Ranges 10 mV to 300 V rms full scale in a 1 3 10 sequence 10 ranges Frequency Range 10 Hz to 1 MHz Accuracy 0 C to 50 C RANGE 2 OF FULL SCALE 0 01 V 30 V 10 Hz 1 100 V 300 V 10 Hz 100 KHz Frequency Response Resistance Ranges 10 ohms center scale to 10 meg ohms center scale 7 ranges Accuracy 5 of reading at midscale 00C to 50 C Polarity Common terminal negative source Current
4. I 1 i TO 1 R35 B M 5 5 VOLTGE i LEVELS CR4 1 I beat V E x S2C R IO R5 REG 222 len 5 R I TO I R36 AMI COPYRIGHT 1966 BY HEWLETT PACKARD COMPANY e 01 Model 427A V 528 8 2 R35 FROM 188K PWR SUP VIA S2E R IO e METERING CIRCUIT ASSEMBLY 00427 66502 25 1 6 46 7 ASSEMBLY MOUNTING SCREW 6 7 6 7 TPI 4750 t I 3 5 qe 2 8V 400 CPS IO MV 2 5 5 0 5V ew B8 7V RI4 IM 91 100 s RISS Ris 7500 35 59 0 6 7V Q BV RIO 68 1 200 6 7 01791 2 R36 158K Section V I I DC CAL PWR SUP SIC R 1 52 6 X IE zl 21 5 2l 4 o SiC F F gure 6 3 Schematic Diagram 6 3 Section 1 0 427 RO it 4274 8 05404 MPI3 MPI4 Figure 7 1 Model 427A Location of Mechanical Parts OPTION Ol ONLY 01791 1 an 1 2 cat tog fol 01791 P Model 427 Section SECTION REPLACEABLE PARTS 7 1 INTRODUCTION 7 2 This section contains information for ordering replacement parts Table 7 1 lists parts in alpha meric order of thei
5. IO WHT BLK ORN 2 RU 6 9 WHT BLK YEL 2 lt O WHT RED VIO OFF CRI ES 8 WAT RED YEL T WHT BLK BRN i 6 95 M T RED GRN CRAE wur BRN BLU ERS 4814 5 WHT BRN GRN C5 Cas rE ACRI T A T e RARE AURI 62 O WHT GRN VIO O IMC O us ADJ CRED AD lt gt 4274 8 05354 ANY PC PLUG ON BOARDS ARE FOR FACTORY TEST ONLY NUMBERS BY STAND OFF PINS APPEAR ON SCHEMATICS t en E Em 27 427A B 0540A ORN WHT BLU YEL WHT BLK C5 TO TO TO voirs 6 comm 52 2 CRI TI Figure 6 2 Component Location Sg OPTION O ONLY 7 10 SCHEMATIC NOTES PARTIAL REFERENCE DESIGNATIONS ARE SHOWN PREFIX WITH ASSEMBLY OR SUBASSEMBLY DESIGNATION S OR BOTH FOR COMPLETE DESIGNATION COMPONENT VALUES ARE SHOWN AS FOLLOWS UNLESS OTHER WISE NOTED RESISTANCE IN OHMS CAPACITANCE IN MICROFARADS CONNECTED TO A IN OPTION 01 INSTRUMENT CONNECTED TO B IN STANDARD INSTRUMENT DENOTES ASSEMBLY DENOTES OPTION 01 DENOTES MAIN SIGNAL PATH DENOTES DC FEEDBACK e DENOTES AC FEEDBACK PATH DENOTES POWER LINE GROUND VOLTMETER CHASSIS 57 DENOTES SIGNAL GROUND CIRCUIT GROUND TT DENOTES FRONT PANEL MARKING PT DENOTES REAR PANEL MARKING m DE
6. Adjust the set level control REF SET on Test Oscillator for convenient meter indi cation Record set level indication for use as reference in step d Adjust oscillator frequency to I MHz and adjust the amplitude vernier to the set level indication established in step DO NOT readjust the set level control Adjust A2C3 1 MC ADJ for exactly 0 01 volt indication the Model 427A If the range of adjustment A2C3 is insufficient refer to Paragraph 5 76 f Rotate 427A RANGE switch to 3 set 51 to position A Adjust the voltmeter calibrator for an output of 3 V at 400 Hz and record indication on 427A meter Change 51 to position Set the oscillator to 400 Hz and adjust amplitude for 427A meter indication recorded in step f h Adjust the set level control REF SET for a convenient reference i Increase oscillator frequency to 100 kHz and readjust oscillator amplitude to set level reference established in step h i Adjust C3 100 kHz ADJ for exactly a3 volt indication on the 427A 5 36 RESISTANCE INFINITY ADJUSTMENT 5 37 The resistance calibration is affected by the amplifier balance zero offset and regulator adjust ments Perform the steps in Paragraph 5 30 and 5 81 before makingthe resistance infinity adjustment Set FUNCTION to OHMS and RANGE to X10 b Short OHMSto COM and adjust theDC ZERO Qe for zero indication Open the input and adjust A1R18 X10 OHMS CAL for
7. Figure 1 2 11096 High Frequency Probe 01791 2 1 1 e e Mode1 427 Section SECTION II INSTALLATION 2 1 INTRODUCTION 2 2 This section contains information and instruc tions necessary for installation and shipping of Model 427A Voltmeter Included are initial inspection pro cedures power and grounding requirements install ation and instructions for repackaging for shipment 2 3 INITIAL INSPECTION 2 4 This instrument was carefully inspected both mechanically and electrically before shipment It should be physically free of mars or scratches and in perfect electrical order upon receipt To confirm this the instrument should be inspected for physical damage in transit Also test the electrical perform ance of the instrument using the procedure outlined in Paragraph 5 5 If there is damage or deficiency see the warranty on the inside front cover of this manual 2 5 POWER REQUIREMENTS 2 6 The Model 427A uses 22 5 volt dry cell battery for its primary power source However if Option01 is included the Model 427A can be operated from any source of 115 or 230 volts 420 at 50 to 400 Hz With the instrument disconnected from the ac power source move the slide switch located on the rear panel until the desired line voltage appears Power dissipation is less than 1 2 watt maximum 2 7 GROUNDING REQUIREMENTS 2 8 To protect operating personnel the National Electrical Ma
8. T O A1R8 0757 0453 fxd prec met flm 30 1K 1 1 8 W 15042 obd A1R9 0757 0454 R fxd prec met flm 33 2K 1 1 8 W 75042 CEA obd A1R10 0698 4199 fxd prec met flm 2800 ohms 1 1 4 W 19701 MF6C 1 11 Not assigned A1R12 0757 0439 R fxd prec met fim 6810 ohms 1 1 8 W 75042 CEA A1R13 0757 0440 fxd prec met 7500 ohms 1 1 8 W 75042 CEA T O obd A1R14 0684 3321 fxd comp 3300 ohms 10 1 4 W 01121 CB3321 1815 2100 0394 var ww 300 ohms 20 1 1 2 W 71450 110 A1R16 0698 4205 R fxd prec met flm 21K 1 1 8 W 75042 CEA T O obd A1R17 0698 4207 fxd prec met flm 44 2K 1 1 8 W 75042 CEA T O obd A1R18 2100 0328 var ww 500 ohms 10 1 1 2 W 71450 110 obd A1R19 0757 0408 fxd prec met flm 250 ohms 1 1 8 W 75042 CEA See Paragraph 5 73 A1R20 2100 0205 R var ww 5000 ohms 10 1 1 2 W hp 1 21 0698 4202 met flm 8870 18 1 1 8 W 75042 CEA T O obd A1R22 0684 3911 fxd comp 390 onms 10 1 4 W 01121 CB3911 Assembly board AC Metering Circuit includes hp C1 thru C9 Q1 thru Q3 CR1 thru CR4 R1 thru R17 A2 00427 66502 30D 107G012DC4M1 obd 0180 0039 0160 0356 fxd elect 100 12 vdcw fxd mica 18 5 300 vdew See Paragraph 5 75 var cer 8 50 pF 557 019 U2P0 34R 0130 0017 0180 0060 fxd elect 200 uF 100 10 3 30D207G003DC
9. A2R11 0757 0419 fxd prec met flm 681 ohms 1 1 8 W CEA T O obd 2885 PIPPP PPPH A2R12 0684 2731 fxd comp 27K 10 1 4 W CB2731 A2R 13 0757 0437 fxd prec met 4750 ohms 1 1 8 W CEA T O obd A2R14 0683 9105 fxd comp 91 ohms 5 1 4 W CB9105 See Paragraph 5 77 fxd prec met fim 7500 ohms 1 1 8 W A2R15 0757 0440 CEA obd A2R16 CEA T O obd R fxd prec met fim 59 0 ohms 1 1 8 W See Paragraph 5 80 var ww 1000 ohms 20 1 1 2 W 0698 4386 A2R17 2100 2069 110 BI 1420 0030 Battery 22 1 2 V dry cell No 763 0170 0022 C fxd 0 1 pF 20 600 HEW 27 0132 0003 var trimmer 0 7 to 535 016 4R 0140 0152 fxd mica 1000 pF 5 300 DM16F102J 0170 0022 C fxd 0 1 20 600 HEW 17 obd J1 See Option 01 J2 See MP16 and MP18 Mi 1120 0903 Meter 100 R1 0684 1031 fxd comp 10K 10 1 4 W CB1031 R2 0698 4217 fxd prec carbon 6 837 meg 1 2 W DC2 obd R3 0730 0113 fxd prec carbon 2 163 meg 1 1 W DC1 obd R4 0698 4214 fxd prec met flm 683 7K 0 55 1 4 W R5 0898 4212 fxd prec met flm 216 0 5 1 4 W T O R6 0698 4209 fxd prec met flm 68 37K 0 5 1 4 W CEB RT 0698 4206 fxd prec met
10. 2 I2 0268 i A Sl t 2 6 8 2 9 Z OZ 5198 1 9 9 201 06 B O8 PARES MMM TORE BADE 422 2642227277777227220722022227222222222727272022202220227220722227267 66066 LB 5 NDS ZZZZ7z727777727777722Z727ZZ7Z77227ZZ272727772Z772277777272Z27Z2Z727777777727Z7772Z7Z7772ZZ72Z2Z7Z727ZZ772Z27777772277272277227222222 2 SS SSS ra 8 2 L 826 Shi H 158 7 06 5 16 n 19 4 7 706 95 z I 69 26 Q 1 26 I 8 E d 0 pos T ze 5 U313W 1178 D 5 d nr TA 2 s 2 7 O AVHO c ss o 816 89 HOD Rp 7 916 50700 DNIEN e I 806 206 SALONIKI 6 5 d S310N 206 si 2 OL 256 o J 01791 2 n WHT BLK BLU 3 WHT BRN RED 4 9 A WHT BRN YEL 5 ORN J WHT RED 7 cu MINES 8 WHT ui REG vio 108 O 2 a ACR9 Y RI 4275 B 0538B
11. 683 7K R5 216 3 R6 60 37K RANGE ATTENUATOR SIAR OHMS ADJ cw 6 7 S2E F FROM Al 7 o lee le P70 A2 P DC OFFSET 50K FUNCTION FUNCTION P O S2A R s 5Y MIN 7 FUNCTION FUNCTION p DC FILTER P O R6 RT S2C RO 12 499K 499 amp S2C F 934 1 9 I z 227 O GO 09 ad e le gt o 2D F 956 ele Se 9 9 0 50 6 OPTION Ji wi 222 1 IMPEDAN CONVER 96 5 5 15 c 2800 15 15 3 I ASSEMBLY MOUNTING SCREW FUNCTION P O S2E R PWR SUP T VIA SZE R IO DC AMPLIFIER 8 BATTERY REGULATOR ASSEMBLY 00427 66501 AC METERING CIRCUIT ASSEMBLY 00427 FUNCTION P O 647V S2C R o 0 9 ASSEMBLY MOUNTING SCREW IMPEDANCE CONVERTER CTION a6 ab 4 5 DIR 2 RI use SIGIR AMP BAL 250 ASSEMBLY MOUNTING yl SCREW RI Q2 6 7V 100 92 6 7 9 49 9
12. 1 6 The battery used in the Model 427A is a 22 1 2 volt dry cell Eveready No 763 or an RCA VS102 Typical battery life is morethan 300 hours continuous operation or 700 hours intermittent operation 1 7 INSTRUMENT AND MANUAL IDENTIFICATION 1 8 Hewlett Packard uses a two section eight digit serial number 000 00000 If the first three digits prefix of the serial number on your instrument do not agree with those on the title page of this manual INFORMATION change sheets supplied with the manual will define differences between your instrument and the Model 427A described in this manual 1 9 If a letter prefixes the serial number the instrument was manufactured outside the United States 1 10 AVAILABLE ACCESSORIES 1 11 The following accessories are available to in crease the test capabilities of the Model 427A 1 12 CABLES AND ADAPTERS hp 110014 45 test lead dual banana to BNC male hp 11002 5 test lead dual banana to alligator clips hp 110034 5 test lead dual banana to pencil probe and alligator clip hp 10111A shielded BNC female to banana plug adapter 1 13 PROBES hp Model 11074A 10 1 Voltage Divider Probe extends the voltage range of Model 427 by a factor of 10 hp Model 11039A 1000 1 Capacitive Voltage Divider for measuring voltages up to 24 KV hp Model 11096A High Frequency Probe ex tends the frequency range ofthe 427A to 500 MHz The voltage range is 0 25V to 30V
13. mise electronic part M meter T transformer network ABBREVIATIONS Ag silver inside diameler ns nanosecond 8 1079 sl slide Al aluminum impg impregnaled seconds SPDT single pole double A alnpere s ined incandescent nsr not separalely replace throw Au gold ins insulation able SPST single pole single throw capacitor kilohm 3 103 ohms Q ohm 3 ceramic 43 bd ipti Ta tanlalum coef coefficient kHz Kilohertz 107 hertz res ke TC lemperature coefficient com common ala meter 7 tilanium dioxide vomp composition L inductor _ k cann connection lin linear taper ted circuit Lag toggle dep deposited log logarithmic taper pe printed circu lol lolerance 12 trim trimmer DPDT double pole double _ 1473 picofarad 5 10 E throw m milli 10 d farada transistor DPST double poic single mA milliampere s 10 piv peak inverse voltage volt 8 throw amperes 48 p o part of vacw alternating current MHz megahertz 10 heriz pos position 8 working vollage elect electrolytic megohm s 10 9 ohms poly polystyrene var variable encapsulated met flm metal pot potentiometer vdew direct current working mfr manufacturer peak to peak voltage F farad mig mounting 3 ppm parts per million FET field
14. 2 6 1 6 1 Introduction 6 1 Section Page REPLACEABLE PARTS 7 1 1 1 Introduction 7 1 7 4 Ordering Information 7 1 7 6 Non Listed Parts 41 1 Appendix CODE LIST OF MANUFACTURERS B SALES AND SERVICE OFFICES MANUAL BACKDATING CHANGES Number Page 5 3 1 Resistors Ux 5 7 5 4 Troubleshooting 5 7 5 5 Power Supply Voltages 5 8 5 6 AC Metering Circuit Voltages 5 8 7 1 Replaceable Parts 7 1 iii Table of Contents Model 427A Voltmeter 11096A High Frequency Probe Location of Front Panel Controls and Indicators Impedance Correction Graph Simplified Block Diagram DC Ohms Operation AC Operation DC Offset Circuit AC Accuracy and Frequency Response Check 427 OF ILLUSTRATIONS Page Number Page 1 0 5 9 Resistance Accuracy 5 2 1 1 5 3 DC Accuracy and Linearity Check 5 2 5 4 AC Rejection 5 3 3 0 5 5 Input Impedance Check 5 4 3 3 5 6 Location of Internal Adjustments 5 5 4 0 5 7 Battery 5 7 4 1 4 2 6 1 Location of Switch Components 6 2 4 2 6 2 Component 6 3 4 3 6 3 Schematic Diagram 6 3 5 0 1 1 Location of Mechanical 7 0 01791 2
15. 3 9 STANDARD INSTRUMENT a Rotate the FUNCTION Switch to BATT 1 5 MIN position b meter should read 1 5 or higher on the 0 3 scale on any range indicating that the battery voltage is 15 volts or higher the reading is below 1 5 replace the battery according to the steps in Paragraph 5 54 01791 2 Section 3 10 OPTION 01 INSTRUMENT 3 11 b 3 12 Select either battery line operation withthe rear panel BATT LINE slide switch H bat tery operation is selected check the battery according to Paragraph 3 9 If line operation is selected set the 115 230 slide switch to indicate the proper line volt age Rotate the FUNCTION switch to the desired function During line operation the BATT 1 5 MIN check position displays the output of the Option 01 power supply The reading should be 1 5 or higher on the 0 3 scale any range indicating power supply output of 15 volts or more This serves as venient check of the Option 01 power supply DC MEASUREMENTS Rotate the FUNCTION switch to DCV or DCV depending on the polarity of the input Short the VOLTS input tothe COM input tate RANGE to 0 1 and adjustthe DC ZERO thumbwheel for zero meter deflection Remove shorting connection there is a zero offset with COM and VOLTS open refer to Paragraph 4 16 and Paragraph 5 30 Select approximate range of input with RANGE
16. Not assigned 1750 A 64A Holder trimmer capacitor used with C3 00427 00601 Shield switch 7 4 01791 3 am c s ak 3 LL ila BEDR fm Model 427A Section VII Table 7 1 Replaceable Parts Cont d REFERENCE hp DESIGNA TOR PART NO a DESCRIPTION 00427 05501 Shield can Option 01 only 1510 0009 Assembly binding post black COM w o solder turret brass J2 0340 0099 Insulator binding post single grey plastic 0 500 OD x 0 200 ID x 0 090 thick with anti rotation boss P O J2 1510 0008 Assembly binding post VOLTS red w o solder turret brass 72 1510 0037 Assembly binding post OHMS blue w o solder turret brass 12 0370 0077 Knob skirted bar 5 8 diameter black for 1 4 diameter shaft 00427 06401 Holder battery 00427 90004 Manual operating and service 01791 2 7 5 MANUAL CHANGES MODEL 427A VOLTMETER Manual Serial Prelixed 947 hp Part No 00427 90004 Instrument Serial Number Make Manual Changes Instrument Serial Number Make Manual Changes Section Replaceable Parts Delete A2R21 and A2R22 Change hp Part No of MP3 Panel rear Option 01 only from 00427 00204 to 00427 00205 m Supplement A for 00427 90004 26 February 1970
17. OPEN CIRCUIT SHORT CIRCUIT RANGE VOLTAGE CURRENT X10 3d8 edB IdB GENERAL Floating Input May be operated up to 500 Vdc above ground Ohms input open in any function except ohms volts input open when instrument is in off position Power 22 1 2 volt dry cell battery Eveready No 763 RCA VS102 Option 01 Battery operation and ac line opera tion selectable on rear panel 115 or 230 V 20 50 Hz to 400 2 1 2 W IHz SHz lOHz IMHz eMHz 3MHz 4MHz Frequency response 10 mV to 30 V ranges 1 0 01791 2 44 e p Model 427A Section I SECTION 1 GENERAL 1 1 DESCRIPTION 1 2 The Hewlett Packard Model 427A is a versatile compact self contained voltmeter It is capable of making de measurements from 1 mV to 1000 volts ac measurements from 0 3 300 volts at frequencies from 10 Hz to 1 MHz and resistance measurements from 0 2 ohms to 500 megohms With the 01 option the Model 427A may be powered either by a 115 or 230 volt line or by an internal 22 1 2 volt dry cell battery 1 3 The use of solid state components throughout gives the Model 427A both ruggedness and reliability Battery operation makesthe instrument ideal for field use or isolation from common mode ground loops 1 4 Figure 1 1showsthe Model427A and Table 1 1 contains list of the Model 427A Specifications 1 5 BATTERY
18. 1 8W 0698 4190 fxd prec met 50 ohms 0 25 1 8 W 0698 4196 fxd prec met flm 1070 ohms 1 1 8 W 0757 0418 fxd prec met flm 619 ohms 1 1 8 W 0757 0422 fxd prec met flm 909 ohms 1 1 8 W 0698 4195 0698 4211 2100 1990 fxd prec met 1020 ohms 1 1 8 W fxd prec 158K 1 1 8 W var ww 200 ohms 20 DC 2 FAP AAAAA 00427 61902 00427 61901 00427 69501 Switch Switch FUNCTION Conversion Kit to Option 01 OPTION 01 0180 1802 fxd Al elect 150 uF 100 10 40 vdew 1901 0025 Diode Si 100 mA at 1 100 piv 12 pF 1251 2357 Connector ac power cord receptacle 3101 1234 3101 0011 Switch slide DPDT 115 230 Switch slide DPDT LINE BATT 9100 1328 Transformer ac power 8120 1348 Power cord KH 7041 MECHANICAL PARTS SEE FIGURE 7 1 5060 5918 5060 0702 00427 00204 00427 00202 5000 0702 Cover top with handle Assembly frame 6 x 8 sm Panel rear Option 01 only Panel rear Cover side 6 x 8 sm 5060 0727 5040 0700 1490 0031 5000 0710 00427 00204 Assembly foot third module Hinge Stand tilt third module stainless steel rod Cover bottom 5 x 8 sm Panel front 5020 5388 0370 0311 Meter trim third module Thumbwheel DC ZERO 9
19. 427A B 05654 P Figure 5 7 Battery Replacement 01791 3 Section V 5 56 TROUBLESHOOTING 5 57 Whenthe Model 427A operates improperly first adjust and calibrate it according to the procedures in Paragraph 5 25 If calibration is impossible then proceed with the troubleshooting steps 5 58 Check the instrument for obvious evidence of trouble such as loose or broken wires or broken connectors Check the printed circuit boards for cracks and separations and ensure that all connectors and pins are clean and tight 5 59 Isolatethetrouble to a particular circuit using the troubleshooting table Table 5 4 and the Theory of Operation Section IV Then refer to the Trouble Shooting steps for that circuit in the following para graphs Table 5 4 Troubleshooting PROBABLE TROUBLE Battery ok no re Power Supply See sponse to input Paragraph 5 60 DC offset circuit Check 2 1 Then check 106 DC Amplifier Check A1Q8 and associated circuit Check value of range resistors Check A1R14 and 199 DC Amplifier See Paragraph 5 63 All DCV ranges pegged with no input ACV and OHMS ok Nonlinear tracking on voltage ranges Constant upscale deflec tion on lower DCV ranges voltage at TP1 low Meter pegs on DCV and OHMS ranges DC Amplifier check A1Q6 A1Q8 and A1Q9 See Paragraph 5 65 Range resistor Ra in Fi
20. B shown in Figure 5 5 hp 427A VOLTMETER Figure 5 4 AC Rejection Check 01791 3 Section Model 427A TEST OSCILLATOR VOLTMETER CALIBRATOR hp738BR og ae M D 814 INPUT CAPACITANCE CHECK INPUT RESISTANCE CHECK hp427A VOLTMETER 100K 061 0460 hp427A VOLTMETER MEG 0 1 hp 0811 0473 Figure 5 5 Input Impedance Check d The voltmeter reading should drop to 0 91 indicating an input resistance of 10 The input resistance may vary slightly and tolerance of 2 should be allowed 5 23 INPUT CAPACITANCE CHECK 5 24 10 input resistance is shunted with 40 pF on the 0 01 through 1 volt ac ranges and with 20 pF on the 3 through 300 volt ac ranges For this input capacitance check 100 resistor is placed in ser ies with the meter input At known frequency reactance of the shunt capacitance will be equal to 100 At this point the voltage across the input re sistance and shunt capacitance will be equal to 0 707 times the input voltage The input capacitance may be checked by finding the frequency at which the dis played voltage drops to 0 707 times the input As in put capacitance decreases the roll off frequency in creases and vice versa a Connect oscillator and Model 427A to position A of the input capacitance check Figure 5 5 and set the Model 427A FUNCTION to ACV and RANGE to 1V b Se
21. Page Response Check 5 1 5 14 Resistance 2 Check 5 2 5 16 DC Accuracy 4 4 50 5 2 5 18 AC Rejection Check s aaa des 5 20 Input Impedance Check 5 3 5 25 Adjustment and Calibration LIST OF TABLES Number Page 1 1 Specifications 1 0 3 1 Effects of Harmonic Distortion 3 2 3 2 DB Range Identification 3 2 5 1 Required Test Equipment 5 0 5 2 Resistance Accuracy Check 5 2 01791 2 Procedures 5 4 5 21 Cover Removal 5 4 5 30 Amplifier Balance and Zero Offset Adjustment 5 5 5 31 Regulator Adjust 5 5 5 32 AC Calibration 5 5 5 36 Resistance Infinity Adjustment 5 6 5 38 DC Calibration 5 6 9 40 Alternate Performance Checks and Calibration Procedures 5 6 5 42 AC 5 6 5 45 Resistance Circuits 5 6 5 47 DC Circuitfs 32 22 xxx 5 7 5 50 Rejection 5 7 5 52 Input Impedance Check 5 7 5 54 Battery Replacement 5 7 5 56 Troubleshooting 5 7 5 60 Power Supply 5 8 5 63 DC Amplifier 5 8 5 67 AC Metering Circuit 5 8 5 71 Adjustment of Factory Selected Components 5 8 5 13 MRI 1 15114 xw ca 5 8 5 75 A2C2 s xg Xov 5 9 5 77 A2R14 T 5 9 5 80 A2R16 4 8 va 10 9 5 82 Etched Circuit Board Repair 5 9 Section Page VI CIRCUIT
22. Probes 22524 04 asa a Jal Section Page INSTALLATION 25 1 2 1 Introduction 2 1 2 3 Initial Inspection 557221 2 9 Power Requirements 2 1 2 7 Grounding Requirements 2 1 2 10 Installation 2 1 2 12 Bench Mounting 2 1 2 14 Rack Mounting 2 1 2 16 Combination Mounting 2 1 2 18 Repackaging for Shipment 2 1 Section Page OPERATING INSTRUCTIONS 3 1 3 1 Introduction 3 1 3 3 Front and Rear Panel Description Operating Instructions Mechanical Zero Adjustment Turn On Procedure 1 DC Measurements 2 Resistance Measurements 3 AC Measurements 6 Section IV THEORY OF 4 1 General 4 5 DC Ohms Operation AC Operation 2 Circuit Descriptions 3 DC Amplifier A1 6 DC Offset 2 9 AC Metering Circuit A2 3 Battery Regulator Al Section MAINTENANCE 5 1 Introduction 9 3 Required Equipment 5 5 Performance Checks DB Measurements Q3 C2 Q3 023 2 C3 CO 09 se D po Eo eR PPP PP SP hh 1 3 P J 93 I 1 w tO DD to D Section MAINTENANCE 4 9 7 Accuracy and Frequency
23. and the Model 421A as shown in Figure 5 2 and set the decade for 10 0 c 427A meter should read within 5 of the known resistance one small scale divi sion one half small division d Repeat steps a through c using the RANGE and decade resistor settings listed in Table 5 2 DECADE RESISTOR GENERAL RADIO 14322 990090090869 Model 427 The DC ZERO adjustment need only be made on the X10 and X1K ranges Table 5 2 Resistance Accuracy Check RANGE 5 16 DC ACCURACY 5 11 The DC Accuracy Check requires voltage standard that is accurate to within 0 2 of its indi cated output from 0 1 volt to 300 V The hp Model 738BR Voltmeter Calibrator is accurate to within 0 1 of the indicated output Figure 5 3 shows the test setup for the DC Accuracy Check Set the Model 427A FUNCTION to and the RANGE to 0 1 hp 427A VOLTMETER 427 4 8 0533 Figure 5 2 Resistance Accuracy Check VOLTMETER CALIBRATOR hp 7388R hp 427A VOLTMETER 427A B 0330 Figure 5 3 DC Accuracy and Linearity Check 01791 3 p o Model 427A b Adjust the DC ZERO Q for zero This ad justment need only be made on the 0 1 volt range c Connect the voltmeter calibrator and the Model 427A as shown in Figure 5 3 Set voltmeter calibrator output to 0 1 volts dc The Model 427A should read 0 1 volt
24. circuit adjusts the meter current for an indication of with the input open When R is equal tothe parallel combination of and Rp the total re Bistance from the OHMS terminal to ground will be half the parallel combination of R4 and the voltage into the amplifier will be halved and the meter indi cation will be half scale The Model 427A is designed that thefull RANGE setting will be displayed in the center of the scale For example 10 the X10 range is a center scale reading 4 9 AC OPERATION 4 10 Figure 4 4 shows a block diagram of the 427A in the AC Mode of Operation The input signal goes to the AC Range Attenuator On the 1 volt range and be low the signal is not affected by the AC Range Attenuator but on all the higher ranges the signal is attenuated by 504 Capacitor C3adjusts the frequency response of the attenuator with 3 volt 100 input signal from the AC Range Attenuator goes through the DC Amplifier to the AC Post Attenuator where it is attenuated by 10 dB for each step of the RANGE selector The DC Amplifier matches the low impe dance of the Post Attenuator to the high impedance of the Range Attenuator acting preamplifier FILTER AMPLIFIER FEEDBACK DC Operation Section IV OHMS ATTENUATOR 427 ty Model 427A DC AMPLIFIER FEEDBACK Figure 4 3 Ohms Operation AC RANGE AT TENUATOR DC AMPLIFIER FEEDBAC
25. effect transistor my millivolt 9 10 volte pree precision lemperature w watt s fixed miero 10 6 6 coefficient long term w with GaAs gallium ars enide uM microvolt s 107 volts and or tot ve inverse voltage GHz gigahertz 10 pi giga s 107 hertz Mylar E AW cowitevound guard e nanoampere s 10 resistor germanium amperes Rh rhodium 5 u rn gr ground ed NC normally closed rms root mean square al neon rot rotary ne m y H henry ies NO normally open omitted Hg mercury NPG negative positive zero Se selenium no standard type num Hz hertz cycle s per zero temperature co sect section ber assigned selected second efficient Si silicon or special type REV Dupont de Nemours 01791 2 4 1 Section 427 hp DESIGNA TOR PART NO AL 00427 66501 Table 7 1 Replaceable Parts Cont d DESCRIPTION MFR PART NO 1 Assembly board DC Amplifier includes C1 thru C6 Q1 thru Q9 CR1 thru CR5 R1 thru R21 1 1 0160 0170 C fxd 0 22 uF 80 20 25 56289 5C9A A1C2 A1C3 0160 0168 C fxd 0 1 10 200 vdew 56289 192P10492 1 4 0150 0093 C fxd 0 01 uF 80 20 100 vdew 91418 obd A1C5 0180 0224 C fxd Al el
26. scale Set test oscillator to expand and adjust the set level control REF SET for convenient meter indication d Record set level indication for use as a re ference in steps e and f e Change the oscillator frequency to 10 Hz and reset the oscillator am plitude to the set level indication establishedinstepc DO NOT re adjust the set level control on the oscillator The 427A indication should not vary by more than 2 minor scale divisions x 296 f Repeat step e for 100 Hz 1 kHz 10 kHz 100 kHz 500 kHz and 1 MHz in each case the 427A indication should not vary by more than 2 minor scale divisions 29 5 13 Paragraph 5 11 with the 427 RANGE set to 3 volts and test oscillator output set to give 3 V reading 427A step b 427A reading should not vary by more than 2 1 1 2 small scale divisions 5 1 Section 5 14 RESISTANCE ACCURACY CHECK 5 15 To check the resistance accuracy precision resistances are needed Figure 5 2 shows the resis tance accuracy check using General Radio Model 14322 Decade Resistor The resistance used should be accurate to within 0 5 and should have range of 10 ohms to 10 ohms a With the input open set the Model 427A FUNCTION to OHMS and the RANGE to X10 Adjust the DC ZERO Sx adjustment for an indication of on the meter face The needle should rest on the mark just to the left of b Connect the decade resistor
27. tively 00000 Figure 3 1 Location of Front Panel Controls and Indicators 3 0 01791 2 Model 427A SECTION INSTRUCTIONS OPERATING 3 1 INTRODUCTION 3 2 The Model 427 may be operated volt meter ac voltmeter ohmmeter or dB meter This section contains operating instructions for each mode of operation 3 3 FRONT AND REAR PANEL DESCRIPTION 3 4 Figure 3 1 shows the location of all the Model 427A controls and indicators and explainsthe function of each Option 01 rear panel is shown standard rear panel is blank 3 5 OPERATING INSTRUCTIONS NOTE To obtain maximum battery life set the FUNCTION switch of OFF when the instrument is not in use 3 6 MECHANICAL ZERO ADJUSTMENT 3 7 Before any measurements are made complete the Mechanical Zero Adjustment inthe following steps Be sure instrument has been off for at least one minute b Rotate Mechanical Zero Adjustment screw CLOCKWISE until meter pointer istothe left of zero and moving upscale toward zero c Continue to rotate adjustment screw clockwise STOP when needle is exactly on zero If needle overshoots repeat step b When pointer is exactly over zero rotate adjustment screw slightly COUNTERCLOCK WISE to relieve tension on suspension the pointer to the left repeat whole procedure but make the counterclockwise rotation less 3 8 TURN ON PROCEDURE
28. 19 AC METERING CIRCUIT A2 4 20 Figure 6 3 contains the schematic of the AC Metering Circuit The ac input from the ac post at tenuator is applied through A2C1 tothe base of A2Q1 A2Q2 is an emitter follower that provides impedance matching to common emitter output stage A2Q3 Capacitor A2C4 provides an ac feedback path for gain stabilization 4 21 The output from the collector of A2Q3 is recti fied by A2CR3 and A2CR4 and applied to the meter movement 4 22 Resistor A2R17 is used to calibrate the ampli at low frequency is adjusted for full scale meter deflection witha 10 400 Hz input Capacitor 2 3 is used to calibrate the amplifier at high fre quency With 10 mV 1 MHz input A2C3 is adjusted for full scale 4 23 BATTERY REGULATOR Ai See Figure 6 3 4 24 The Battery Regulator regulates the dc voltage fromthe 22 5 volt battery or from the optional power supply The voltage drop across A1CR2 and the emitter base junction of A1Q3 provides the 6 7 volt referencefor the power supply andthe 6 7 volt output A1Q5 senses changes in the 6 7 volt output and trols A1Q2 the positive series regulator 101 isa current source for A1Q5 and diodes A1CR3 CR4 and CR5 provide temperature stabilization sistor A1Q4 provides a current shunt for A1CR2 to keep its voltage constant under heavy current loads Section Model 427A Table 5 1 Required Test Equipment INSTRUMENT RE
29. 275 e Repeat steps a through e for each RANGE selection to 300 V by setting the voltmeter calibrator output to the full scale value for each range The Model 427A indication should not vary from the known input by more than 2 on any range 2 corresponds to 2 min or divisions on the 0 1 scale and 1 1 2 minor division on the 0 3 scale 1 Set the dc RANGE to 1000 V and the voltmeter calibrator to 300 V The Model 427A should read 300 V 2 of full scale on the 1000 volt range Set the Model 427A to the 1 volt range and apply 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 and 0 1 volt dc signals from the voltmeter calibrator 1n each case the reading should be within two minor divisions of the known input voltage Set the Model 427A to the 3 volt range and apply 2 5 2 1 5 1 and 0 5 volt dc signals In each case the reading should be within 1 2 minor division on the 0 3 scale i Repeat setps a through f with the FUNCTION set to DCV and the voltmeter calibrator set for a negative output test results should be the same 5 18 AC REJECTION CHECK 3 19 A peak ac superimposed noise signal 100 times the full scale input should affect the Model 427A read ing less than 1 Figure 5 4 shows the test setup using a variable line transformer as a noise generator 7 07 volt rms output from the variable line trans former corresponds to a 10 volt peak noise signal The 10 volt noise signal will be applied to the 0 1 vol
30. 4 0180 0033 fxd elect 50 uF 100 10 6 vdew 30D506G006CB4M1 0180 0039 fxd elect 100 uF 12 vdew 30D 107G012DC4M1 7 2 01791 3 gt Model 427A Section VII MPR MFR PART NO 30D 356G006BB4 30D 107G012DC4M1 Table 7 1 Replaceable Parts Cont d REFERENCE hp DESIGNATOR PART NO DESCRIPTION 2 7 2 8 0180 0064 fxd elect 35 uF 100 10 6 vdcw A2C9 0180 0039 fad elect 100 12 vdcw A2CR1 1902 0571 Diode zener 14 V 5210939 224 A2CR2 Not assigned A2CR3 1910 0022 Diode Ge HD1872 obd A2CR4 2N3855A obd A2Q1 A2Q2 A2Q3 1854 0057 1853 0023 TSTR Si 2N3855A TSTR Si NPN 2N3703 0757 0283 fxd prec met 2000 ohms 1 1 8 W CEA T O A2RI A2R2 0698 4202 fxd prec met flm 8870 ohma 1 1 8 W A2R3 2100 0328 var ww 500 ohms 10 1 1 2 W 110 obd A2R4 2100 0291 var ww 1500 ohma 20 1 1 2 W 110 obd A2R5 2100 0205 var prec ww 5000 ohms 10 1 1 2 W A2R6 0757 0449 fxd prec met flm 20K 1 1 8 W CEA obd A2R7 2100 0094 var pot comp lin 50K 30 1 10 W UPE 70RE hp obd A2R8 0757 0465 fxd prec met 100K 1 1 8 W obd A2R9 0698 4207 fxd prec met fim 44 2K 1 1 8 W obd A2R10 0757 0481 fxd prec met 68 1K 1 1 8 W CEA T 0 obd
31. 5 ADJ V IV ADJ DC CAL 0000000000 OOCOCGOGGOO SgTA C OTM LEFT SIDE A2R3 lV CAL Figure 5 6 NOTE Before beginning the calibration be sure to adjust the mechanical meter zero according to the steps in Para graph 3 6 AMPLIFIER BALANCE AND ZERO OFFSET JUSIMENT Short VOLTSand COM terminals set FUNC TION to either DCV or DCV Set DC ZERO Q for zero deflection Remove shorting connection from VOLTS and COM terminals If meter deflects adjust A2R7 OFF ADJ for zero deflection Short VOLTS and COM terminals and recheck zero adjustment Repeat steps b and c if Set the FUNCTIONto DCV and turnDC ZERO 2 fully to the right Set Range to 0 1 Re cord position of indicator Turn FUNCTION to DCV and rotate DC fully to the left Note meter indication Repeat steps d and e and adjust A1R15 BAL until the meter indication in both steps is the same NOTE H the range of adjustment A1R15 is insufficient refer to Paragraph 5 74 REGULATOR ADJUST Complete Amplifier Balance and Offset adjust ment Paragraph 5 30 01791 2 A2R4 5 CAL Section AIRIS XIO OHMS CAL AIR2O XIK OHMS CAL AIR 5 AIRS AMP BAL REG ADJ mem RIGHT SIDE 3V ADJ Location of Internal Adjustments b Short VOLT
32. 8 6 min Emitter A1Q3 0 5 Collector A1Q3 0 2V Collector 194 6 7V 56 4V min Base A1Q5 0 5 Across A1CR2 6 2 5 63 DC AMPLIFIER 5 64 make operational check oftheDC Ampli fier set the RANGE switch to 1 and the FUNCTION switchto DCV Connecta 1 volt sourcetothe VOLTS and COM terminals and monitor the voltage at A1 pin 8 Since the DC Amplifier is a unity gain amplifier the voltage should be 1 07 0 07 volts dc If this reading is correct the DC Amplifier is operating properly If it is incorrect proceed with the follow ing troubleshooting procedures 5 65 Check at the collector of A1Q9 for 3 5 Vdc and check for 3 0 Vdc at AITP1 If the voltage at the collector of A1Q9 is quite high 6 or 7 volts and the voltage at AITP1 is 3 0 Vdc 109 is probably open If the collector voltage is low and the test point voltage is correct 108 is probably shorted If both voltages are incorrect A1Q7 or A1Q8 is probably bad 5 66 If the collector voltage on A1Q is correct and the voltage at AITP1 is slightly higher than normal A1Q6 is probably bad NOTE 196 is replaced and the meter remains pegged or indicates upscale and cannot be adjusted check the value of factory selected component 18197 See Paragraph 5 71 and 5 73 Model 427A 5 67 AC METERING CIRCUIT 5 68 To check the AC Metering Circuit set the RANGE to 0 01 and the FUNCTION to ACV Connect 10 mV rms source to t
33. K 427A ROA AC POST ATTENUATOR AC METERING CIRCUIT AC FEEDBACK Figure 4 4 AC Operation 4 11 The AC Metering Circuit contains both a feedback Stabilized ac amplifier andan averaging meter circuit The meter circuit converts the ac signal to a dc volt age proportional to the average of the ac amplifier output A2R17 adjusts the current through the meter so that the scale reading is in rms volts 4 12 CIRCUIT DESCRIPTIONS 4 13 DC AMPLIFIER 1 4 14 Figure 6 3 is the schematic diagram of the Model 427A The input to the DC Amplifier 1 is applied through Pin 2 to the impedance converter A1Q6 A field effect transistor is used as the impe dance converter because of its characteristicaily high input impedance Transistors 107 and A1Q9 make two stage amplifier with 4109 as emitter follower output stage The signal from the emitter of 109 is fed back to the base of 107 for gain sta bilization 4 15 A1Q8actsasa constant current source for A1Q6 The constant current from A1Q8 assures linearity in A1Q6 and helps minimize drift 4 2 4 16 DC OFFSET A2 4 17 The gate leakage from 196 Iggg amounts to fraction of a nanoamp This current is insignificant with the input shorted but with the input open it flows through the DC Range Attenuator resistance of 10 M2 resulting in a few millivolts deflection on the lower ranges Consequently the meter indications with the input open and wit
34. NOTES SCREWDRIVER ADJUST AVERAGE VALUE SHOWN OPTIMUM VALUE SELECTED AT FACTORY DENOTES COMPONENTS NOT MOUNTED ON ASSEMBLY 824 DENOTES WIRE COLOR COLOR CODE SAME AS RESISTOR COLOR CODE FIRST NUMBER IDENTIFIES BASE COLOR SECOND NUMBER IDENTIFIES WIDER STRIP THIRD NUMBER IDENTIFIES NARROWER STRIP 924 WHITE RED YELLOW OHMS RANGE Kf ATTENUATOR A 926 FUNCTION P O S2A R SIE F R i 226 yy OHMS gt RIS 17 5 ACV 9 2 14 lt 8 16 c5 1 295 B 20 9 gt I D DC RANGE x S2ALF f ATTENUATOR VOLTS gt RI IOK SIE F R 9 SIDIR D R2 9 R3 R4 25 R7 RANGE f ATTENUATOR i SIAR 95 7 3PF ADJ 2 5 RANGE ATTENUATOR R25 7 5 R24 682k O 823 67 6 R22 6750 6750 675 ud NO 59 SIF F R RI9 67 5M 945 REI SIE F R He74M eoo 19 15 101 5 Ri5 1174 NO RIS 5 RI7 18 8K Ris 1 295 gt V 9 9 DC RANGE ATTENUATOR RI 10K SIB F R 9 SID R RE ng 20 9 R2 6 837 R3 2463
35. QUIRED RECOMMENDED TYPE CHARACTERISTICS USE MODEL DC Voltage Range 0 300 V Performance Checks hp Model 738BR Standard Accuracy 0 2 meter Calibrator Test Oscillator Frequency Range 10 Hz to 1 MHz Performance Checks hp Model 652A Oscil Output 0 to 3 Vac lator Variable Line Frequency Range 50 to 60 Hz Performance Checks Powerstat Type 116B Transformer Voltage Range 0 to 120 V Decade Resistor Range 102 to 10 MQ Performance Checks General Radio Model Accuracy 0 5 1432Z Decade Resistor DC Voltmeter Range 0 50 Vdc Troubleshooting hp Model 427A Volt Accuracy 2 meter AC Voltmeter Range 0 50 Vac Troubleshooting hp Model 427A Volt Accuracy 2 meter Resistors 100 1 Performance Checks hp Part 0811 0460 1 1 hp Part No 0811 0473 Contained hp E02 738BR VTVM Calibration System VOLTMETER CALIBRATION SYSTEM hpE02 7386R hp 427A VOLTMETER VOLTMETER CALIBRATOR TEST OSCILLATOR Apes2a 4274 B 1180 Figure 5 1 AC Accuracy and Frequency Response Check 5 0 01791 2 A o Model 427A EE Section V SECTION V MAINTENANCE 5 1 INTRODUCTION 5 2 This section contains information necessary to maintain the Model 427A The following paragraphs describe the Performance Checks the Calibration Procedures and the Troubleshooting Procedures 5 3 REQUIRED EQUIPMENT 5 4 Table 5 1 15 list of the equipment ne
36. S to and OHMS to COM Set FUNCTION to DCV Meter should be zero ed within 2 minor divisions upscale Switch FUNCTIONtoOHMS If meter deflects adjust AIRS REG ADJ for zero deflection This may affect zero setting so rotate FUNCTION back and forth between OHMS and DCV and adjust 1 5 until meter reading is the same in both positions 5 32 AC CALIBRATION 5 33 Three adjustments must be made to calibrate the ac circuits in the Model 427A First A2R17 ad justs the absolute amplitude calibration with a 10 400 Hz input Then A2C3 is adjusted with a 10 mV 1 MHz input to calibrate the high frequency response Finally the frequency response of the AC Range At tenuator is set by adjusting C3 with a 3 100 kHz signal applied to the input 5 34 LOW FREQUENCY CALIBRATION Connect the Model 427A as shown in Figure 5 1 and set 51 to position A b Set the voltmeter calibrator output to 400 Hz at 0 01 volt rms and set the 427A RANGE to 0 01 and FUNCTION to Adjust A2R17 400 CPS ADJ for exactly 0 01 volt indication on the 427A If the range of adjustment A2R17 is insufficient refer to Paragraph 5 81 HIGH FREQUENCY CALIBRATION Connect the Model 427A shown in Figure 5 1 5 5 EEE EEE EE ee EE gt Section Set 51 to position Set 427A RANGE to 0 01 and FUNCTION to b Set the oscillator to 400 Hz and adjust the output for exactly 0 01 volt indication on the 427A
37. an indi cation indicator should rest on the mark just to the left of o c Change RANGE to X1K short OHMSto COM and adjust DC 2 for zero indication Open the input and adjust AIR20 X1K OHMS CAL for an indication 5 38 DC CALIBRATION 5 39 Adc voltage standard is neededto calibrate the dc ranges A2R3 A2R4 and A2R5 are adjusted for 5 6 Model 427A full scale inputs the 0 1 0 3 and 1 volt ranges respectively The 3 volt through 1000 volt ranges are calibrated by A2R5 and require no special cali bration Use the test setup in Figure 5 3 Set FUNCTION to DCV and RANGE to 0 1 Set the voltmeter calibrator output to 0 1 volt b Adjust A2R3 0 1 V DC CAL for full scale on the 0 1 scale c Rotate RANGE to 0 3 and change the cali brator output to 0 3 volt d Adjust A2R4 0 3 V DC CAL for on the 0 3 Scale e Rotate RANGE to 1 and changethe calibrator output to 1 volt f Adjust A2R5 1 V DC CAL for full scaleonthe 0 1 scale 5 40 ALTERNATE PERFORMANCE CHECKS AND CALIBRATION PROCEDURES 5 41 The following alternate procedures should be used only if the equipment in Table 5 1 is not avail able In each alternate procedure use an instrument of the specified accuracy If a less accurate instru ment is used the calibration ortest may not be within the Model 427A specifications To guarantee a specific accuracy use a standard at least four times more accurate
38. e top cover on 427A before inserting it into the Com bining Case The Combining Case is a full module unit which accepts various combinations of submodular units Being a full module unit itself itcan be bench or rack mounted and is analogous to any full module instrument 2 18 REPACKAGING FOR SHIPMENT 2 19 The following paragraphs contain general guide for repackaging ofthe instrumentfor shipment Refer to Paragraph 2 20 if the original container is to be used 2 21 if it is not NOTE If the instrument is to be shipped to Hewlett Packard for service or repair attach a tag to the instrument identifying the owner and indicating the service or repair to be accomplished include the model number and full serial number of the instrument In any correspondence identify the instrument by model number serial number and serial number prefix 2 20 If original container is to be used proceed as follows a Place instrument in original container If original container is not available a suitable container can be purchased from your near est hp Sales and Service Office b Ensure that container is well sealed with strong tape or metal bands 2 21 original container is notto used proceed as follows a Wrap instrument in heavy paper or plastic before placing in an inner container b Place packing material around all sides of in strument and protect panel face with cardboard strips c Place instrumen
39. ect 10 75 10 15 vdew 56289 300106 015 4 A1C6 0180 1800 C fxd Al elect 100 uF 1100 10 6 vdew 56289 Non polar 30D type obd A1CR1 1901 0025 Diode Si 100 mA at 1V 100 piv 12 pF hp A1CR2 1902 0568 Diode breakdown 6 2 V 5 12954 27508019 1 thru 1910 0022 Diode HD1872 03877 obd A1CR5 A1Q1 1850 0111 TSTR Ge PNP 2N404A 01295 2N404A A1Q2 1854 0087 TSTR Si NPN 2N3417 24446 1 2N3417 A1Q3 1854 0033 TSTR Si NPN 2N3391 24446 2N3391 A1Q4 1850 0111 TSTR Ge PNP 2N404A 01295 2N404A 24446 2N3391 A1Q5 1854 0033 TSTR Si NPN 2N3391 A1Q6 1855 0023 TSTR FET 50527 17856 50527 A1Q7 1854 0057 TSTR Si 2N3855A 24446 2N3855A A1Q8 1853 0036 TSTR Si PNP 253906 07263 A1Q9 1854 0057 TSTR Si 2N3855A 24446 2N3855A AIRI 0757 0198 R fxd prec met flm 100 ohms 1 1 2 W 75042 CEC T O A1R2 0684 5611 xd comp 560 ohms 10 1 4 W 01121 CB5611 A1R3 0684 1541 R fxd comp 150K 10 1 4 W 01121 CB1541 0757 0444 fxd prec met fim 12 1K 1 1 8 W 75042 CEA T O obd A1R5 2100 1735 var ww 5 ohms 10 1 1 2 W 11236 110 A1R6 A1R7 0699 4972 R fxd prec met flm 499K 1 1 2 W 75042
40. eded to properly maintain the Model 427A If the recommended model is not available use any substitute that meets the required characteristics 5 5 PERFORMANCE CHECKS 5 6 The Performance Checks are in cabinet tests that compare the Model 427A with its specifications These procedures can be used both for incoming in spection and periodic inspection A Performance Check Test Cardis providedat the endof this section for recording the performance of the Model 427A during the performance checks The card canbe removed from the manual and used as a permanent record of the incoming inspection or of a routine performance check if the Model 427A does not meet its specifi cations refer tothe Adjustment and Calibration Pro cedures Paragraph 5 25 5 7 AC ACCURACY AND FREQUENCY RESPONSE CHECK 5 8 The AC Accuracy and Frequency Response Check requires a test oscillator that is flat within 0 5 from 10 Hz to 1 MHz The absolute value of the ap plied voltage must be accurate within 0 2 The hp Model 738BR Voltmeter Calibrator produces a 400 Hz signal that is within less than 0 2 of the in dicated output The hp Model 652A Test Oscillator can be adjusted to within less than0 25 of a desired reference from 10 Hz to 10 MHz NOTE Before beginning the Performance Checks be sure to adjust the me chanical meter zero according to the steps in Paragraph 3 6 5 9 AC ACCURACY CHECK 5 10 Connect the test oscillator and t
41. en dB reading is equal to the algebraic sum of the range andthe meter reading For example if the meter reading were 6 and the instrument were on the 10 volt 20 dB range the final reading would be 20 dB 6 dB 14 dB The 427A meter is calibrated in dBm 0dBm is equivalent to 0 775 volt dropped acrossa 6002 load Consequently any dBm measure ments must be made acrossatotal impedance of 6002 Measurements across other imped ances will be in dB not dBm To convert a dB reading to dBm usethe Im pedance Correction Graph Figure 3 2 For example to convert a 30 dB reading made across 502 load to dBm locate the 500 load impedance on the bottom of the graph Follow the impedance line to the heavy black line and read the meter correction at that point correction for 500 is 10 5 dBm and the corrected reading is 40 5 dBm 01791 2 eee ee JE 7 4 Model 4274 pm L 1 1 I Esi L 0 HHHH H LHP SO 1915 k 4011 __ _ 111 TT I EN e ee a 7 __ __ _ pref ft j 1 ERE ESE Fi S I Ll on L1
42. flm 21 63K 0 5 1 4 W CEB T O obd R8 0698 4203 fxd prec met flm 10K 0 5 1 4 W CEB T O obd R9 0884 1051 fxd comp 1 meg 10 1 4 W CB1051 0698 4128 fxd prec met flm 10 meg 0 25 1 2 W 70 0698 4129 fxd prec met flm 31 723 0 1 1 4 W 3 0698 4219 fxd prec carbon 11 74 meg 1 1 W DC1 obd 0698 4189 fxd prec met flm 10 15 ohms 1 1 4W MF6C T obd 0698 4191 fxd prec met fim 101 5 ohms 1 1 4W obd 0698 4198 fxd prec met fim 1174 1 1 4 W 0698 4204 0698 4210 0698 4215 MF6C T obd MF6C T obd CEC obd fxd prec met flm 11 75K 1 1 4 W fxd prec met flm 118 8K 1 1 4 W fxd prec met fim 1 295 meg 1 1 2W MF6C obd PAY PIPED Daman 01791 3 7 3 Section VII Model 427A Table 7 1 Replaceable Parts Cont d REFERENCE DESIGNA TOR PART NO LM DESCRIPTION 0698 4220 fxd prec carbon flm 67 5 meg 1 2 W 0698 4194 fxd prec met flm 675 ohms 0 5 1 4 W 0698 4201 fxd prec met flm 6750 ohms 0 5 1 4W 0698 4208 fxd prec met fim 67 6K x0 5 1 4 W 0698 4213 fxd prec met fim 682K 40 5 1 4 W 0730 0131 fxd prec carbon flm 7 5 meg 1 1 W 0698 4200 fxd prec met flm 3419 ohms 0 25 1 8 W 0698 4197 fxd prec met flm 1081 ohms 0 25 1 8 W 0698 4193 fxd prec met 341 9 ohms 0 25 1 8W 0698 4192 fxd prec met 108 1 ohms 0 25
43. ged Use the pro cedure outlined in the following paragraph to select A2R14 5 79 If a zero offset greater than 2 two minor divisions on the 0 1 scale exists in ACV FUNCTION replace A2R14 with a smaller value of resistance The correct value for A2R14 is the largest value of resistance that adjusts the zero offsetto less than 2 Tracking error could result if the zero offset indica tion is reduced below 1 nominal value for A2R14 is 91 ohms hp Part No 0683 9105 recommended replacement value for A2R14 is either 47 ohm hp Part No 0683 4705 or 68 ohm hp Part No 0683 6805 1 4 W 5 resistor 9 80 A2R16 5 81 A2R16 adjusts the range of the low frequency Calibration Resistor A2R17 400 CPS ADJ If the AC Metering Circuit is functioning properly and the 400 CPS ADJ cannot be adjusted for the proper indication during low frequency calibration Paragraph 5 34 A2R16 may need to be changed If the reading is consistently low change A2R16 to 56 2 ohms hp Part 0757 0395 01791 2 ee 2 Section V 5 82 ETCHED CIRCUIT BOARD REPAIR 5 83 The Model 427A uses plated through double sided etched circuit boards To prevent damage to the circuit board and components observe the follow ing rules when soldering Wear clean lint free cotton or rubber gloves when handling the circuit boards Avoid touching the board or components with bare fingers as skin oils can cau
44. gure 4 3 open Check R19 through R25 on 51 Range resistors Figure 4 3 shorted Check R12 throughR18 81 Check Power Suppl Either one of R19 through R25 Rg shorted or one of R12 through R18 OHMS range always Teads near zero DCV and ACV ok OHMS always reads DCV and ACV ok open Intermittent operation Power supply check 1 Q4 See Paragraph 5 60 Zero offset in ACV AC Metering Circuit as greater than 2 Meter pegs full scale on any AC range See Paragraph 5 67 AC Metering Circuit check 2 and A2CR4 See Paragraph 5 67 5 7 C J U A SG 5 60 POWER SUPPLY 5 61 Check at 1 pin 7 for 6 4 to 7 volts and 1 pin 9 for 6 4 to 7 volts If there is no output check 104 first power supply has been overloaded A1Q4 may be bad Minimum battery voltage is 15 5 volts 5 62 Measure the dc voltages at the check points given in Table 5 5 All measurements are made with reference to circuit ground Table 5 5 Power Supply Voltages NOTE The voltages listed in this table are nominal tolerance of 10 should be allowed except for minimum voltages listed CHECK POINT VOLTAGE Emitter A1Q1 15V 8V min Collector 101 7 3V Base 101 14 7 8V min Emitter 10 2 6 6 4V min Collector A1Q2 15V
45. h the input shorted can be different When measuring across a low impedance Iggg flows mostly through the low impedance and this difference does not effect the measurement Unless 1065 is compensated for it will effect measurements made across high impedances gt 1 9 4 18 The DC Offset Circuit A2 see Figure 4 5 compensates for the leakage from A1Q6 A positive voltage tapped from A2R7 reverse biases A2CR1 The reverse leakage current from A2CR1 Ir meets extremely high resistance at the gate of A1Q6 and passes through the much lower resistance of the at tenuator a direction opposite to that of Iqgg adjusting A2R7 Ip can be set so that it and cancel eachother The net voltage dropacross the attenuator 01791 2 4 Model 427A 2 RG OF 4127 lt RESISTANCE lt OF ATTENUATOR lt IO MEGOHMS Y 4274 8 0560 Figure 4 5 DC Offset Circuit would then be zero alternative method of mini mizing the effects of would beto zero the instru ment with the impedance of the measurement source connected to input terminals rather than with the input shorted A2CR1 has temperature charac teristic quite similar to that of A1Q6 Therefore 01791 2 Iu Section IV both and Ig change by approximately the same amount with temperature and the amount of additional error at higher temperatures is lessened 4
46. he 1 volt 0 3 volt and 0 1 volt ranges only three different voltages are needed 5 49 Amercury battery has good short term stability Connect a series voltage divider with a variable output across the battery and monitor the output with a recently calibrated dc voltmeter knownto be four times as accur ate as the Model 427A Use this output to calibrate the 0 1 0 3 and 1 volt ranges 5 50 AC REJECTION 5 51 To check AC Rejection on 0 1 volt range an oscillator with output of 10 volt peak to peak into 10 M ohms may be used I the hp Model 738BR Volt meter Calibrator is available a 400 Hz 10 volt peak output may also be used to check the AC Re jection of Model 427A 5 52 INPUT IMPEDANCE CHECK 5 53 Measure the resistance betweenthe VOLTS COM terminals directly with the Model 427A Function Switchat DCV or DCV using an accurate ohmmeter Another Model 427A could be used for this purpose If an L C meter or capacitance bridge is available measure the input capacitance between the VOLTS and COM terminalsdirectly Be sure the Model 427A FUNCTION switch is in the ACV position 5 54 BATTERY REPLACEMENT 5 55 Figure 5 7 shows the battery holder and the bat tery connectlons Turnthe twist lock fastener 1 4 turn counterclockwise tiltthe battery and holder toward the rear of the instrument and lift out Replace the battery with an Eveready 763 or RCA VS102 22 1 2 volt dry cell E
47. he VOLTS and COM terminals and monitor the signal at 2 0 The signal at 2 0 should be 10 7 mV rms 0 7 mV If the mea sured signal is incorrect the trouble is in either the DC Amplifier or the AC Post Attenuator 5 69 Monitor the signal at the collector of A2Q3 The signal should be 0 28 V rms 0 04 V the measured signal is correct the AC Metering Circuit is functioning properly If not proceed with the following troubleshooting procedures 5 70 Check for dc voltage levels listed in Table 5 6 given reading is wrong the trouble is probably in that component or its associated circuit If A2CR3 or A2CR4 are replaced and the zero offset in FUNCTION is 2 check the value of factory selected component A2R14 See Paragraph 5 72 and 5 77 Table 5 6 AC Metering Circuit Voltages NOTE The voltages listed in this table are nominal A tolerance of 10 Should be allowed CHECK POINT VOLTAGE 2 1 201 Collector A2Q2 Emitter A2Q3 Collector 5 71 ADJUSTMENT OF FACTORY SELECTED COMPONENTS 5 72 Certain components within the Model 427A individually selected in order to compensate for slightly varying circuit parameters These compo nents are denoted by an asterisk on the schematic and the optimum or average value is shown The following paragraphs describe the function of each factory selected component and give instructions for their selection No
48. he voltmeter calibrator as shown in Figure 5 1 a Set the voltmeter calibrator for an output of 0 01 volts at 400 Hz b Set 51 in Figure 5 1 to position A c Set the Model 427A FUNCTION to ACV and the range to 0 01 d The 427A should read 0 01 volts rms 2 2 minor scale division 01791 3 Repeat steps through d for each RANGE selection through 300 V by setting the volt meter calibrator output tothe full scale value for each range Model 427A indication should not vary from the known input by more than 2 any range 2 corresponds to 2 minor divisions on the 0 1 scale and 1 1 2 minor divisions on the 0 3 scale f Set the Model 427A to the 1 volt range and apply 0 9 0 8 0 7 0 6 0 5 0 3 0 2 and 0 1 volt signals In each case the reading should be within two minor divisions of the known input signal Set the Model 427A to the 3 volt range and apply 2 5 2 1 5 1 and 0 5 volt signals In each case the reading should be within 1 1 2 minor divisions of the knowninput sig nal 9 11 FREQUENCY RESPONSE CHECK 9 12 The frequency range of the hp Model 652A 10 Hz to 10 MHz The set level indication men tioned in the following steps is used to re establish the proper amplitude each time the frequency is changed a Set S1 in Figure 5 1 to position B Set the Model 427A RANGE to 0 01 b Setthe test oscillator to 400 Hz and adjust the output for a 0 95 indication on the 427A 0 1
49. nce unity gainamplifier used toamplify de and resistance inputs It also serves as preamplifier for ac signals The AC Metering Circuit amplifies ac signals from the preamplifier converts them to dc signals proportional to the average ac and connects them to the meter The meter is calibrated to display the rms value of the ac input 4 4 The DC Offset Adjust A2 compensates for leakage current from the de amplifier and DC CAL and OHMS CALareresistive circuits used for calibration 4 5 DC OPERATION 4 6 Figure 4 2 shows Model 427A in the DC Mode of Operation The input is first applied to the DC Range Attenuator where it is attenuated by 10dB for each stepoftheattenuator Thedc signal from the at tenuator goes to the DC Filter and the filter rejects any ac superimposed noise that may be present on the input The dc output of the filter goes to the DC Am 1 and then to the meter The DC Amplifier matches the high impedance of the attenuator to the low impedance of the meter The DC CAL circuits ATTENUATOR Figure 4 2 01791 2 OPERATION are resistive circuits in series with the meter used to adjust the meter current to calibrate the lower ranges 4 7 OHMS OPERATION 4 8 Figure 4 3 15 a block diagram of the Model 427A in the OHMS Mode of Operation With the input open Ra and Rp forma voltage divider The voltage across R causes full scale current toflow through the meter The OHMS CAL
50. nufacturers Association NEMA recom mends that the instrument panel and cabinet be ground ed The Option 01 427A is equipped with a three conductor power cable which when plugged into an appropriate receptacle grounds the instrument The offset pin on the power cable three prong connector is the ground wire 2 9 To preserve protectionfeature when operating the instrument from atwo contact outlet use three prong to two prong adapter and connect the pigtail on the adapter to ground 2 10 INSTALLATION 2 11 The Model 427A is fully transistorized there fore no special cooling is required However the instrument should not be operated where the ambient temperature exceeds 559 1310F For additional information address inquiries to your local hp Sales and Service Office See Appendix B for office locations 2 12 BENCH MOUNTING 2 13 Model 427A is shipped with plastic feet and tilt stand in place ready for use as bench instrument 01791 3 2 14 RACK MOUNTING 2 15 Model 427A may be rack mounted by using an Adapter Frame hp Part No 5060 0797 The adapt er frame is a rack frame that accepts any combination of submodular units It can be rack mounted only 2 16 COMBINATION MOUNTING 2 17 The Model 427A may be mounted incombination with other submodular units by using a Combining Case Model 1051A If the 427A is equipped witha carrying handle it will be necessary to remove th
51. r reference design tors and indi cates the description hp part number of each part together with any applicable notes and provides the following Total quantity used in the instrument column b Description of the part See list of abbrevia tions below Typical manufacturer of the part five digit code See Appendix A for list of manu facturers d Manufacturer s part number 4 3 Miscellaneous parts are listed at the end of Table 7 1 Each factory selected component is keyed to paragraph describing the selection of the component value 7 4 ORDERING INFORMATION 7 5 To obtain replacement parts address order or inquiry to your local Hewlett Packard Field Office See Appendix for list of office locations Identify parts by their Hewlett Packard part numbers 7 6 NON LISTED PARTS 7 7 To obtain a part that is not listed include Instrument model number b Instrument serial number Description of the part 9 Function and location of the part DESIGNATORS A assembly fuse mechanical part TC thermocouple B motor FL filler P plug vacuum tube neon BT batlery HR heater Q Lranaistor bulb photocell etc capacitor Ic integrated circuit QcR transisior diode w cable diode I jack R resistor x socket DL delay line K relay RT thermistor lampholder DS lamp L inductor 5 Switch fuseholder
52. rmally these components do not need to be changed unless another associated compo nent is changed For example replacement of a transistor may require the changing of an associated factory selected component 5 13 1 19 5 74 A1R19 adjusts the range of the BAL re sistor A1R15 the AMP BAL A1R15 cannot be ad justed properly after replacing transistor A1Q6 1 R19 may need to be changed Use the following steps to select A1R19 Set RANGE to 0 3 b Set DC 7 adjustment to center and A1R15 to its center 01791 3 RR a a mm Py Ve Model 427A Select the FUNCTION DCV or DCV which will produce an upscale deflection d If the FUNCTION selected is DCV increase the value of AIR19 if DCV is selected de crease AIR19 The value range of AIR19 is 0 to 18509 5 75 A2C2 5 76 A2C2 adjusts the range of the high frequency calibration capacitor A2C3 1 MC ADJ during the high frequency calibration Paragraph 5 35 A2C3 can not be adjusted for the proper reading the value of A2C2 should be changed ifthe reading is consistently high change the value of A2C2 to 47 pF If the read ing is consistently low remove 2 2 5 77 A2R14 5 78 A2R14 is factory selected to improve upscale meter tracking and correct any non linearity of diodes A2CR3 and A2CR4 If diode A2CR3 A2CR4 re placed A2R14 may need to be chan
53. se leakage paths b Use low heat 25 to 50 watts small tip soldering iron and small diameter rosin core solder To remove component clip heat sink long nose pliers commercial heat sink tweezers etc onthe component lead close to the component as possible Place the soldering iron directly on the component lead and pull up on the lead H a component is obviously damaged or faulty clip leads close to the components and then remove the leads from the board EXCESSIVE OR PROLONGED HEAT CAN LIFT THE CIRCUIT FOIL FROM THE BOARD OR CAUSE DAMAGE TO COMPONENTS d Cleanthe component lead holes by heatingthe solder in the hole quickly removing the sol dering iron and inserting pointed non metallic object such toothpick To mount new component shape the leads and insert them in the holes Clip heat sink on the component heat with the soldering iron and add solder as necessary to obtain a good electrical connection f Clipexcess leads off after soldering and clean excess flux from the connection and adjoining area using type TF Freon hp Part No 8500 0232 5 9 Model 427A Section VI ur 2 C 2 PLI 1 munie E YIIIMG Jo UOINEBIUT 71 9 91950 5 59339 J3HlO 844410 SHIBWNN Nid VIS ININNSLSNI 30 1 084 2401108 387 HOLIMS
54. switch DO NOT APPLY MORE THAN 1200 VDC TO ANY DC RANGE Connect input across VOLTS and COM ter minals and read magnitude of input on meter RESISTANCE MEASUREMENTS DAMAGE 427A INPUT CIR CUIT RESULT IF DC OR AC VOLTAGE IS APPLIED TO OHMS TERMINAL Rotate the FUNCTION switch to OHMS Selectthe approximate range withthe RANGE switch and withthe input terminals open just the DC ZERO Qe thumbwheel for an indication onthe ohms scale Pointer should rest on the mark just to the left of 3 1 Section Connect the unknown resistance across the OHMS and COM terminals Read the resis tance value on the ohms scale NOTE For best accuracy select an ohms range that will place the meter pointer near the center of the scale 3 13 AC MEASUREMENTS 3 14 The Model 427 responds to the average value the ac input and is calibrated in rms volts for a sine wave input value of non sinusoidal signal are different any distortion on the input will affect the accuracy of the reading Table3 1 shows the effect of harmonic dis tortion on reading NOTE The following table is uni versal in application since these errors are inherent in all average responding volt meters The error shown above may vary with the phase relation ship between the harmonic and fundamental Table 3 1 Effects of Harmonic Distortion INPUT VOLTAGE TRUE RMS METER CHARACTERISTICS VALUE INDICATION
55. t dc range VARIABLE LINE TRANSFORMER 42TA B O53t Section V Set the 427A FUNCTION to DCV and short the input Set the RANGE to 0 1 and adjust the DC for 0 meter indication b Switch the FUNCTION to ACV and the RANGE to 10 Connect the variable line transform er and the Model 427A as shown in Figure 5 4 c Adjust the transformer output for a reading of 7 07 volts rms on the 427A d Switch the 427A FUNCTION to DCV andthe RANGE to 0 1 e meter reading shouldbe 0 1 1 minor scale division NOTE The meter may move upscale momentarily and then return to zero This indicatesthe charging of the DC Filter capacitors and is normal 1 Repeat steps a through e using the 1 volt dc range and 70 7 volt rms signal from thetrans foriner 5 20 INPUT IMPEDANCE CHECK 5 21 INPUT RESISTANCE CHECK 5 22 Figure 5 5 shows the setup for the input resis tance check 1 resistor is connected in series with the input and the voltage drop across the input resistance will be Rin Fapplied Reeries Rin With 1 volt applied will be 0 91 volt if the input resistance is 10 varies directly with changes in Rin Connect the Model 427A and the voltmeter calibrator to position illustrated in Figure 5 5 Set the Model 427A FUNCTION to DCV and RANGE to 1 V b Set the voltmeter calibrator for 1 V output Connect the voltmeter calibrator to position
56. t and inner container inaheavy cartonor wooden box and seal with strong tape or metal bands d Mark shipping container with DELICATE INSTRUMENT FRAGILE etc 2 1 TET tn oe wama Section Model 427A a MODEL 427A FRONT PANEL MODEL 427 REAR PANEL OPTION Ol HEWLE1 PACKARD 7 427 VOLTMETER 4 FUNCTION RANGE IO XIOOK 5 30 IOO N 300 gt 1000 ZERO I 00 427 8 0529 BATT LINE option 01 only slide switch Se COM terminal Connects to instrument com lects either battery or line operation mon Common input for ACV OHMS and DCV 115 230 slide switch option 01 only Selects either 115 Vac or 230 Vac for line operation VOLTS terminal Applies unknown ac or dc voltage to instrument Line input option 01 only Connects ac erati er to instrument op ing pow 2 FUNCTION switch Selects mode of operation Selections are OFF BATT DC DC OHMS and AC RANGE switch Selects appropriate range of unknown input e DC ZERO 2 thumbwheel Usedto electrical Mechanical zero Mechanically zeroes the ly zerothe instrument in DC mode and to infinity meter set the instrument in OHMS mode Meter face Displays the magnitude of unknown OHMS terminal Connects unknown resistance resistance or voltage in ohms or volts respec to instrument
57. t the oscillator frequency to 60 Hz and ad just the amplitude for a full scale display on the Model 427A Connect the oscillator to position and in crease the frequency until the meter display drops to 0 707 The frequency at this point should be about 40 kHz The input capacitance is nominally specified at 40 pF and may vary from instrument to instrument A frequency variation of 10 is acceptable d Repeat stepsathroughc using the 3 volt range of the 427A Increase the frequency in step until the reading drops to 2 1 volts This should occur at about 80 kHz This verifies input capacitance of 20 pF on 3 volt range and above ADJUSTMENT AND CALIBRATION PROCEDURES 5 25 5 26 The following adjustment and calibration pro cedures should be used only if it has been determined through the performance checks in Paragraphs 5 5 through 5 24 that the Model 427A is not performing within its specifications The location of the internal adjustments is shown in Figures 5 6 and 6 2 5 27 COVER REMOVAL 5 28 To remove the top or bottom covers remove the Phillips screws securing the cover slide the cover about 1 inch to the rear and lift it off place the cover reverse the removal procedure 5 29 remove side cover remove the four Phillips screws and lift it off 01791 3 a 44 5 31 A2C3 IOM IMC L Model 427A A2Ri7 A2R5 JOMV 4
58. than the Model 427A 5 43 Any test oscillator with low distortion lt 2 may be used as an ac voltage standard If the distor tion level is too high the calibration may be wrong as the 427A is an average responding rms calibrated meter The effects of harmonic distortion are dis cussed in more detail in Section III Paragraphs 3 14 and 3 15 5 44 Monitor the oscillator output with a recently calibrated rms voltmeter known to be four times as accurate as the Model 427A over the same band of frequencies rms voltmeter serves as a refer ence Each time the oscillator frequency is changed readjust the output for the reference The Model427A ac calibration is based on a 400 Hz absolute refer ence so always start the ac calibration or perform ance checks at 400 Hz 5 45 RESISTANCE CIRCUITS 5 46 decade resistor is not available a selec tion of precisionresistors may be used The resistors Should be at least 1 resistors andthe values selected should correspond to the RANGE settings hp part numbers for 1 resistors for each range are given in Table 5 3 01791 3 Model 427A Table 5 3 1 Resistors RESISTOR 2195 hp PART NO 0757 0984 0757 0198 0757 0159 0757 0839 0757 0367 0698 3583 0698 3592 5 47 DC CIRCUITS 5 48 precision dc voltage source is required for de calibration and performance checks Since the 427A is only calibrated on t
59. umaman 10 _ Fundamental 10 second harmonic Fundamental 20 102 second harmonic Fundamental 50 112 100 110 second harmonic Fundamental 10 third Fundamental 20 third harmonic 3 15 Use the following stepsto make measure Fundamental 50 ment third harmonic Rotate FUNCTION switch to NOTE With the input shorted there may be zero offset of about two minor divisions This is caused by the bias current through the meter bridge and does not affect the accuracy of ac measurements as the meter moves upscale Since the average value and the rms b Model 427 a Rotate RANGE switch to approximate range of input voltage DO NOT APPLY MORE THAN 425V RMS WHEN THE INSTRUMENT IS ON RANGES ABOVE 3 OR MORE THAN 300V RMS ON RANGES BE LOW 3 Connectthe signal to be measured to the VOLTS and COM terminals and read the magnitude on the voltage scale 3 16 DB MEASUREMENTS Making dB dBm measurement is essen tially the same as making an ac voltage mea surement Follow steps Paragraph 3 13 but read the magnitude on the dB scale The 1 volt position of the RANGE switch is the 0 dBm range Each position above 1 volt is 10 dB increase and each position below 1 volt is 10 decrease Table 3 2 lists the dB value of each range Table 3 2 DB Range Identification giv
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