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S9086-Q5-STM-010/CH-491R1REVISION 1NAVAL SHIPS’ TECHNICAL MANUALCHAPTER 491ELECTRICAL MEASURINGANDTEST INSTRUMENTSTHIS CHAPTER SUPERSEDES CHAPTER 491, DATED 1 AUGUST 1976DISTRIBUTION STATEMENT B: DISTRIBUTION AUTHORIZED TO U.S. GOVERNMENTAGENCIES ONLY; ADMINISTRATIVE AND OPERATIONAL USE (1 AUGUST).OTHER REQUESTS FOR THIS DOCUMENT MUST BE REFERRED TO THE NAVAL SEASYSTEMS COMMAND (SEA-03Z71).WARNING: THIS DOCUMENT CONTAINS TECHINCAL DATA WHOSE EXPORT ISRESTRICTED BY THE ARMS EXPORT CONTROL ACT (TITLE 22, U.S.C.,SEC. 2751, ETSEQ.) OR EXECUTIVE ORDER 12470. VIOLATIONS OF THESE EXPORT LAWS ARESUBJECT TO SEVERE CRIMINAL PENALTIES. DISSEMINATE IN ACCORDANCE WITHPROVISIONS OF OPNAVINST 5510.161, REFERENCE (JJ).DESTRUCTION NOTICE: DESTROY BY ANY METHOD THAT WILL PREVENT DISCLOSURE OF CONTENTS OR RECONSTRUCTION OF THE DOCUMENT.PUBLISHED BY DIRECTION OF COMMANDER, NAVAL SEA SYSTEMS COMMAND1 SEP @@@@

S9086-Q5-STM-010/CH-491R1Certification SheetTITLE-2

S9086-Q5-STM-010/CH-491R1TABLE OF CONTENTSChapter/Paragraph491SECTION 1.PageELECTRICAL MEASURING AND TEST INSTRUMENTS . . . . . . . . . . . .491-1INTRODUCTION491-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-1.1SCOPE OF CHAPTER. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-1491-1.2CLASSIFICATION OF INSTRUMENTS . . . . . . . . . . . . . . . . . . . . . . . .491-1491-1.3 PORTABLE INSTRUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-1.3.1 ALLOCATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-1.3.2 INTERCHANGE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-2491-2491-3491-1.4SHOCK RESISTANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-3SECTION 2.DESCRIPTION AND SPECIAL OPERATING PRECAUTIONS . . . . . . . . .491-3491-2.1 CURRENT MEASURING INSTRUMENTS . . . . . . . . . . . . . . . . . . . .491-2.1.1 GALVANOMETERS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-2.1.2 AMMETERS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-2.1.3 CONSTRUCTION OF DIRECT-CURRENT INSTRUMENTS. . . . . . .491-2.1.4 CONSTRUCTION OF ALTERNATING-CURRENT INSTRUMENTS. .491-2.1.5 SPLIT CORE AMMETERS. . . . . . . . . . . . . . . . . . . . . . . . . .491-2.1.6 SHUNTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-2.1.7 CURRENT TRANSFORMERS. . . . . . . . . . . . . . . . . . . . . . . .491-2.1.8 SPECIAL PRECAUTIONS IN THE USE OF CURRENT MEASURINGINSTRUMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-2.2 VOLTAGE MEASURING INSTRUMENTS . .491-2.2.1 VOLTAGE TESTER. . . . . . . . . . .491-2.2.2 VOLTMETERS. . . . . . . . . . . . . .491-2.2.3 MULTIPLIERS. . . . . . . . . . . . . .491-2.2.4 POTENTIAL TRANSFORMERS. . . .491-2.2.5 SPECIAL PRECAUTIONS IN USE OFINSTRUMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .VOLTAGE MEASURING. . . . . . . . . . . . . . . .491-2.3 POWER MEASURING INSTRUMENTS . . . . . . . .491-2.3.1 POWER MEASUREMENTS. . . . . . . . . . .491-2.3.2 WATTMETERS. . . . . . . . . . . . . . . . . . .491-2.3.3 MEASUREMENT OF THREE-PHASE POWERWATTMETERS. . . . . . . . . . . . . . . . .491-2.3.4 THREE-PHASE WATTMETERS. . . . . . . . .491-2.3.5 VARMETERS. . . . . . . . . . . . . . . . . . .491-2.3.6 PRECAUTIONS IN USE OF WATTMETERS. . . . . . . . . .WITH. . . . . . . . . . . . .491-3491-3491-4491-4491-4491-4491-5491-5. .491-6.491-6491-6491-6491-7491-7. . . . .491-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .SINGLE-PHASE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-8491-8491-8.491-8491-9491-9491-9491-2.4 ENERGY AND AMPERE-HOUR MEASURING INSTRUMENTS . . . . . . . . . . 491-10491-2.4.1 WATT-HOUR METERS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-10i

S9086-Q5-STM-010/CH-491R1TABLE OF CONTENTS - RECT-CURRENT WATT-HOUR METERS AND AMPERE-HOURMETERS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-10ALTERNATING-CURRENT WATT-HOUR METERS. . . . . . . . . . . . . 491-10491-2.5ALTERNATING-CURRENT CIRCUIT CHARACTERISTIC-MEASURINGINSTRUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-2.5.1 GENERAL FEATURES. . . . . . . . . . . . . . . . . . . . . . . . .491-2.5.2 FREQUENCY METERS. . . . . . . . . . . . . . . . . . . . . . . . .491-2.5.3 POWER FACTOR METERS. . . . . . . . . . . . . . . . . . . . . .491-2.5.4 SYNCHROSCOPES. . . . . . . . . . . . . . . . . . . . . . . . . . .491-2.5.5 PHASE ROTATION OR PHASE SEQUENCE INDICATORS. . . .491-2.5.6 EXCITATION INDICATOR OR STABILITY METER. . . . . . . .491-2.5.7 OSCILLOSCOPES. . . . . . . . . . . . . . . . . . . . . . . . . . . 91-2.6 RESISTANCE MEASURING INSTRUMENTS . . . . . . . . . . . . .491-2.6.1 TESTING GENERATORS OR MAGNETOS. . . . . . . . . .491-2.6.2 VOLTMETERS AND AMMETERS. . . . . . . . . . . . . . .491-2.6.3 RESISTANCE BOX. . . . . . . . . . . . . . . . . . . . . . . .491-2.6.4 DECADE TESTING SETS. . . . . . . . . . . . . . . . . . . .491-2.6.5 INSULATION RESISTANCE INDICATING INSTRUMENTS.491-2.6.6 GROWLERS. . . . . . . . . . . . . . . . . . . . . . . . . . . .491-2.6.7 CURRENT TEST SET. . . . . . . . . . . . . . . . . . . . . . .491-2.6.8 ELECTRIC TOOL TESTER. . . . . . . . . . . . . . . . . . . . . . 91-17491-2.7 SPECIAL INSTRUMENT ASSEMBLIES . . . . . . . . . . . .491-2.7.1 PORTABLE INSTRUMENT ASSEMBLIES. . . . . . .491-2.7.1.1 Alternating-Current Power-Circuit Analyzer.491-2.7.1.2 Volt-Ohm-Milliammeters. . . . . . . . . . .491-2.7.1.3 Stroboscopic Tachometer. . . . . . . . . . .491-17491-17491-17491-17491-17. . . . . . . . . .SECTION 3.MAINTAINING ACCURACY OF ELECTRICAL INSTRUMENTATION . . . . 491-19491-3.1BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-19491-3.2 POLICY . . . . . . . . . . . . . . . . . . . . . . . . .491-3.2.1 GENERAL. . . . . . . . . . . . . . . . . . .491-3.2.2 DEFINITIONS. . . . . . . . . . . . . . . . .491-3.2.3 FACTORS WHICH AFFECT ACCURACY.491-3.2.4 FIELD CALIBRATION ACTIVITIES. . . .491-3.2.5 INITIAL ACCURACY. . . . . . . . . . . . DICITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-23491-3.4 CHECKS AND ADJUSTMENTS . .491-3.4.1 ZERO ADJUSTMENT. . . .491-3.4.2 PIVOT FRICTION. . . . . .491-3.4.3 MECHANICAL BALANCE.ii.491-24491-24491-24491-24

S9086-Q5-STM-010/CH-491R1TABLE OF CONTENTS - 4.11491-3.4.12491-3.4.13SECTION 4.VOLTMETERS AND AMMETERS. . . . . . . . . . . . . . . .WATTMETERS. . . . . . . . . . . . . . . . . . . . . . . . . . . .WATT-HOUR METERS. . . . . . . . . . . . . . . . . . . . . . .FREQUENCY METERS. . . . . . . . . . . . . . . . . . . . . . .POWER FACTOR METERS. . . . . . . . . . . . . . . . . . . .INSTRUMENT TRANSFORMERS. . . . . . . . . . . . . . . .RESISTANCE STANDARDS AND DECADE TESTING SETS.OHMMETERS AND MEGGERS. . . . . . . . . . . . . . . . . .VACUUM TUBE AND CAPACITOR ANALYZERS. . . . . . .STROBOSCOPIC TACHOMETERS. . . . . . . . . . . . . . . 91-26491-26491-26491-26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-27491-4.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-4.1.1 OVERVIEW. . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-4.1.2 USE OF INSTRUCTION BOOKS. . . . . . . . . . . . . . . .491-4.1.3 NEED FOR PRECAUTIONS. . . . . . . . . . . . . . . . . . .491-4.1.4 AVOIDING MECHANICAL SHOCK. . . . . . . . . . . . . .491-4.1.5 AVOIDING EXPOSURE TO STRONG MAGNETIC FIELDS.491-27491-27491-27491-27491-27491-27491-4.2 CONNECTING AND USING INSTRUMENTS . . . . . . . . . . . . . . . . . . . . 491-28491-4.2.1 GENERAL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-28491-4.3 OBTAINING ACCURATE RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . 491-29491-4.3.1 GENERAL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-29491-4.4 USING PORTABLE INSTRUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . 491-30491-4.4.1 GENERAL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-30491-4.5INSTALLATION OF SWITCHBOARD INSTRUMENTS . . . . . . . . . . . . . . . 491-30491-4.6ELECTRONIC TYPE INSTRUMENTS USING HIGH VOLTAGES . . . . . . . . . 491-30SECTION 5.MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-31491-5.1 ESSENTIALS OF CARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-31491-5.1.1 GENERAL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-31491-5.2LUBRICATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-31491-5.3SWITCHBOARD INSTRUMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . 491-32491-5.4 REPAIRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-5.4.1 GENERAL. . . . . . . . . . . . . . . . . . . . . . . .491-5.4.2 REPLACEMENT OF CATHODE RAY TUBES. . . .491-5.4.3 REQUISITIONING OF REPLACEMENT METERS.491-32491-32491-32491-32iii

S9086-Q5-STM-010/CH-491R1LIST OF TABLESTableTitle491-1-1ivPageELECTRICAL MEASURING AND TEST INSTRUMENTS AND ACCESSORIESON NAVAL SHIPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-3-1FLUKE 760A SPECIFICATIONS491-3-2INITIAL ACCURACY REQUIREMENTS491-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-20. . . . . . . . . . . . . . . . . . . . . . . 491-22

S9086-Q5-STM-010/CH-491R1LIST OF ILLUSTRATIONSFigureTitleCertification Sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491-2-1Page0-2Tag for Stroboscopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491-19v

S9086-Q5-STM-010/CH-491R1NOTETHIS CHAPTER HAS BEEN REFORMATTED FROM DOUBLE COLUMNTO SINGLE COLUMN TO SUPPORT THE NSTM DATABASE. THE CONTENT OF THIS CHAPTER HAS NOT BEEN CHANGED.vi

S9086-Q5-STM-010/CH-491R1CHAPTER 491ELECTRICAL MEASURING AND TEST INSTRUMENTSSECTION 1.INTRODUCTION491-1.1SCOPE OF CHAPTER491-1.1.1 This chapter contains engineering information on electrical measuring and test instruments used onboard ship.a. These instruments are used principally for measuring basic parameters such as current, voltage, resistance, andspeed of rotation, or for general purpose testing of elements that are common to most electrical systems suchas fuses, vacuum tubes, and condensers. For convenience the chapter includes a brief description of eachinstrument. The descriptive data are based upon current specification requirements and the actual instrumentsonboard ship may differ in minor respects. Detailed information and operating instructions contained in themanufacturer’s instruction book should be consulted.b. Measuring and test instruments of a highly specialized nature are covered in the chapters of the manual dealing with the associated circuits and equipment.c. Instruments operating on the same general principles as those discussed herein are also utilized on shipboardas components of equipments which provide indications of some nonelectrical quantity; for example, a voltmeter may be used as part of a propeller-revolution indicating equipment. In the case of instruments utilizedfor this purpose, the instructions contained herein are applicable for use as a general guide.491-1.2CLASSIFICATION OF INSTRUMENTS491-1.2.1 Electrical measuring and test instruments are classified with respect to the following characteristics(Table 491-1-1 is a tabulation of measuring and test instruments furnished to naval ships):a. The electrical quantity or characteristic measured, or the type of test function for which designed; and, ifapplicable, whether used on alternating or on direct current circuits; for example, direct current ammeters,alternating current voltmeters.b. The type of mounting: switchboard or portable (abbreviated as S and P in Table 491-1-1). In some casesinstruments are mounted on a switchboard but provision is made for removing the instrument from the boardand using as a portable meter. This is the case, for example, with volt-ohm-milliam meters mounted on newdesign interior-communication switchboards.c. Other features such as degree of enclosure, nature of mounting arrangements, sizes, ranges, grades, shockresistance and type of external power supply.491-1

S9086-Q5-STM-010/CH-491R1491-1.3PORTABLE INSTRUMENTS491-1.3.1 ALLOCATION. Portable instruments are furnished to each vessel in accordance with the allowanceestablished in the Ship Portable Electrical and Electronic Test Equipment Requirements List (SPETERL). Theseinstruments are normally assigned to the custody of specific working groups on board ship as follows:a. User code 1. For maintenance of prime electronic systems by Data Processing Technicians, Data SystemsTechnicians, Electronic Technicians, Fire Control Technicians, Operational Specialists, Radiome