ELECTRICAL MEASUREMENTS AND MEASURING INSTRUMENTS
CONTENTS 1 MEASURING INSTRUMENTS INTRODUCTION CLASSI?CATIONS OF MEASURING INSTRUMENTS ANALOG AND DIGITAL INSTRUMENTS ABSOLUTE AND SECONDARY INSTRUMENTS ABSOLUTE INSTRUMENTS SECONDARY INSTRUMENTS INDICATING, RECORDING AND INTEGRATED INSTRUMENTS INDICATING INSTRUMENTS RECORDING INSTRUMENTS INTEGRATED INSTRUMENTS E?ECTS USED IN MEASURING INSTRUMENTS INDICATING INSTRUMENTS DE?ECTING DEVICE CONTROL DEVICE SPRING CONTROL GRAVITY CONTROL DAMPING DEVICES AIR FRICTION DAMPING FLUID FRICTION DAMPING EDDY-CURRENT DAMPING CONSTRUCTIONAL DETAILS OF INDICATING INSTRUMENTS BALANCING TORQUE AND WEIGHT RATIO METHODS OF SUPPORTING MOVING SYSTEM PERMANENT MAGNETS USED IN INDICATING INSTRUMENT POINTERS AND SCALES CASTING FOR METERS CLASSI?CATION OF INDICATING INSTRUMENTS ACCORDING TO LIMITING ERROR SOLVED EXAMPLES REVIEW QUESTIONS 2 INDICATING INSTRUMENTS TYPES OF AMMETERS AND VOLTMETERS AMMETERS AND VOLTMETERS MOVING IRON INSTRUMENTS TYPES OF MOVING IRON INSTRUMENTS ATTRACTION TYPE REPULSION TYPE RELATION BETWEEN TORQUE AND INDUCTANCE RELATION BETWEEN TORQUE AND INDUCTANCE: (MORE FUNDAMENTAL METHOD) ERRORS IN THE MOVING INSTRUMENT MOVING COIL PERMANENT MAGNET TYPE (PMT) TORQUE EXPRESSION REQUIREMENTS FOR SHUNTS AND MULTIPLIERS CIRSCALE TYPE OF MOVING COIL PERMANENT MAGNET TYPE DYNAMOMETER TYPE (ELECTRO DYNAMIC) MOVING COIL DISADVANTAGES THERMOCOUPLE INSTRUMENTS THERMOCOUPLE AMMETER COMPENSATED TYPE BRIDGE TYPE THERMOCOUPLES INDUCTION TYPE INSTRUMENTS FERRARIS TYPE TORQUE FREQUENCY COMPENSATION TEMPERATURE ERRORS SHADED POLE TYPE CONSTRUCTION HOT WIRE INSTRUMENTS MAGNI?CATION OF THE EXPANSION CONSTRUCTIONAL DETAILS OF HOT WIRE INSTRUMENT (DOUBLE SAY TYPE) ADVANTAGES ELECTROSTATIC TYPE TYPES OF INSTRUMENTS BRAM TYPE ELECTROSCOPE SYMMETRICAL TYPE STRING ELECTROMETER QUADRANT ELECTROMETER THEORY KELVIN ABSOLUTE ELECTROMETER KELVIN MULTICELLULAR VOLTMETER EXTENSION OF RANGE OF ELECTROSTATIC VOLTMETERS RESISTANCE POTENTIAL DIVIDER CAPACITOR MULTIPLIERS 2 10 POWER FACTOR METERS 2 10 1 INTRODUCTION 2 10 2 PRINCIPLE OF POWER FACTOR METER 2 10 2 1 FORCE BETWEEN TWO MAGNETS 2 10 2 2 FORCE BETWEEN TWO COILS CARRYING CURRENTS 2 10 3 SINGLE PHASE DYNAMOMETER TYPE POWER FACTOR METER 2 10 3 1 DISADVANTAGES 2 10 4 THREE-PHASE P F METERS: DYNAMOMETER TYPE FOR BALANCED LOADS 2 10 4 1 MATHEMATICAL TREATMENT 2 10 5 THREE-PHASE DYNAMOMETER P F METER 2 10 6 MOVING IRON TYPE 2 10 6 1 WESTING HOUSE TYPE P F METER 2 10 6 2 MATHEMATICAL PROOF 2 10 6 3 NALDER AND LIPMAN P F METER (FOR BALANCED LOADS) 2 11 SYNCHROSCOPES 2 11 1 TYPE OF SYNCHROSCOPES 2 11 2 LINWIN TYPE SYNCHROSCOPE (DYNAMOMETER TYPE) 2 11 3 WESTING HOUSE TYPE 2 11 4 WESTON TYPE 2 12 MEASUREMENT OF FREQUENCY 2 12 1 CAMPBELL’S FREQUENCY BRIDGE 2 12 2 FREQUENCY METERS 2 12 2 1 VIBRATING REED FREQUENCY METER 2 12 3 B T H RESONANCE FREQUENCY METER 2 12 4 WESTON FREQUENCY METER EXERCISE PROBLEMS 3 INSTRUMENT TRANSFORMERS ADVANTAGES OF INSTRUMENT TRANSFORMERS AS COMPARED WITH SHUNTS AND MULTI- PLIERS CURRENT TRANSFORMER CALCULATION OF RATIO AND PHASE ANGLE ERRORS IN CURRENT TRANSFORMER PHASE ANGLE DESIGN CONSIDERATIONS CHARACTERISTICS OF CURRENT TRANSFORMERS E?ECT OF FREQUENCY E?ECT OF OPEN CIRCUITING THE SECONDARY SIDE OF C T METHODS OF DEMAGNETISATION AFTER OPEN CIRCUIT BRITISH STANDARD SPECI?CATIONS METHOD OF COMPENSATION FOR PHASE ANGLE 3 10 POTENTIAL TRANSFORMER 3 10 1 CALCULATION OF RATIO OF P T 3 10 2 PHASE ANGLE ERROR 3 10 3 CHARACTERISTICS OF P T 3 10 4 B S S SPECI?CATIONS 3 11 TESTING OF INSTRUMENT TRANSFORMERS 3 11 1 METHODS OF TESTING 3 11 2 ABSOLUTE METHOD OF TESTING C T 3 11 3 ABSOLUTE METHOD OF TESTING P T 3 11 4 SECONDARY METHOD OF TESTING C T (ARNOLD METHOD) 3 11 5 COMPARISON METHOD OR SECONDARY METHOD OF TESTING P T 4 MEASUREMENT OF POWER TYPES OF WATTMETERS DYNAMOMETER TYPE DYNAMOMETER TYPE (PIVOTED COIL TYPE) DYNAMOMETER TYPE (SUSPENDED COIL OR TORSION TYPE) INDUCTION WATTMETER PHASE COMPENSATION EXPRESSION FOR TORQUE IN TERMS OF MUTUAL INDUCTANCE COMPENSATION FOR INDUCTANCE OF THE PRESSURE COIL ERRORS IN WATTMETER READING ERRORS DUE TO CAPACITANCE OF P C RESISTANCE ERRORS DUE TO EDDY CURRENTS ERRORS DUE TO TEMPERATURE E?ECT OF STRAY MAGNETIC FIELDS ERRORS DUE TO METHOD OF CONNECTION COMPENSATION FOR LOSS IN PRESSURE COIL USE OF INSTRUMENT TRANSFORMERS WITH WATTMETERS AND ERRORS FERRODYNAMIC OR IRON CORE OR IRON CLAD WATTMETERS 4 10 ELECTROSTATIC TYPE OF WATTMETERS 4 11 MEASUREMENT OF POWER 4 11 1 THREE VOLTMETER METHOD 4 11 2 THREE AMMETER METHOD 4 11 3 MEASUREMENT OF POWER IN THREE PHASE CIRCUITS (BLONDELS THEOREM) 4 11 4 TWO WATTMETER METHOD 4 11 5 MEASUREMENT OF POWER BY WATTMETER METHOD IN CASE OF BALANCED LOADS 4 11 6 MEASUREMENT OF POWER WITH 1 : 1 P T AND USING SINGLE WATTMETER FOR BALANCED LOADS 4 11 7 MEASUREMENT OF POWER IN A BALANCED LOAD USING ONLY ONE WATTMETER AND IN CONJUNCTION WITH 1 : 1 C T’S 4 12 MEASUREMENT OF REACTIVE POWER IN A BALANCED LOAD BY 1-WATTMETER METHOD 5 SUPPLY METERS TYPES OF ENERGY OR SUPPLY METERS D C SUPPLY METERS (A H METERS) MERCURY MOTOR METER TYPE A H METER COMMUTATOR MOTOR TYPE A H METER FERRANTI AMPERE HOUR METER (D C ) MAGNETIC SHUNT SELF-HEATING ERRORS CHAMBERLAIN AND HOOKHAM DIRECT CURRENT A H METER E?ECTS OF VARIATION OF TEMPERATURE 5 10 WATT-HOUR METERS 5 10 1 CHAMBERLAIN AND HOOKHAM DIRECT CURRENT WATTMETER 5 10 1 1 ERRORS AND THEIR COMPENSATION 5 10 2 COMMUTATOR TYPE OF D C WATT-HOUR METER 5 10 2 1 ERRORS IN THE INSTRUMENT 5 11 TESTING OF D C SUPPLY METERS 5 11 1 PHYSICAL INSPECTION 5 11 2 INSULATION TEST 5 11 3 STARTING CURRENT TEST 5 11 4 METHODS OF TESTING 5 11 5 TESTING OF THE METER 5 12 1-? A C ENERGY METER 5 12 1 THEORY OF INDUCTION METER 5 12 2 PHASOR DIAGRAM 5 12 3 INDUCTIVE LOAD ADJUSTMENT 5 12 4 LOW LOAD ADJUSTMENT 5 12 5 ANTI-CREEPING DEVICES 5 12 6 FULL LOAD ADJUSTMENT 5 12 7 DUAL MAGNET SYSTEM 5 12 8 COMPARISON OF MAGNETIC SYSTEMS 5 12 9 PREPARATION OF BRAKE MAGNETS 5 12 10FACTORS WHICH IN?UENCE THE SHAPE OF CHARACTERISTICS CURVE 5 12 11IN?UENCE OF VOLTAGE ELECTROMAGNET ON PERFORMANCE 5 13 ERRORS DUE TO CHANGE OF FREQUENCY 5 13 1 PERMISSIBLE ERRORS DUE TO CHANGE IN FREQUENCY 5 14 ERRORS DUE TO CHANGE IN TEMPERATURE 5 14 1 PERMISSIBLE ERRORS DUE TO CHANGE OF TEMPERATURE: (SELF HEATING) 5 14 2 TEMPERATURE COMPENSATION 5 15 COMPARISON OF 1-? ENERGY METERS 5 16 CLASSI?CATION OF 1-? ENERGY METERS 5 17 TESTING OF A C SUPPLY METERS 5 17 1 METHODS OF TESTING (CALIBRATION) 5 18 REGISTERING MECHANISM 5 19 3-? ENERGY METERS (INDUCTION TYPE) 5 19 1 MEASUREMENT OF ENERGY IN THREE-PHASE 3 WIRE SYSTEM 5 19 2 MEASUREMENT OF ENERGY IN 3-PHASE 4-WIRE SYSTEM 5 19 3 MEASUREMENT OF ENERGY BY USING TWO SINGLE PHASE METERS 5 19 4 THREE-PHASE THREE WIRE BALANCED LOAD METER 5 20 SINE OR REACTIVE METER 5 20 1 REACTIVE METER 5 20 2 SINGLE PHASE REACTIVE METERS 5 20 3 POLYPHASE REACTIVE METERS 5 20 4 TWO-PHASE REACTIVE METERS 5 20 5 REACTIVE METERS FOR THREE-PHASE CIRCUITS 5 21 IN?UENCE OF P F ON THE COST OF ENERGY 5 22 KVAH METER FOR RESTRICTED RANGE OF POWER FACTOR 5 23 KVAH METERS FOR P F RANGE BETWEEN U P F TO ZERO 5 24 LANDIS AND GYR TRIVECTOR METER 5 25 WESTING HOUSE TYPE 5 26 MAXIMUM DEMAND INDICATORS 5 26 1 TYPES OF DEMAND METERS 5 26 2 MERZ PRICE DEMAND INDICATOR 5 26 3 THERMAL TYPE MAXIMUM WRIGHT DEMAND METER 5 26 4 CHARACTERISTICS OF MAXIMUM DEMAND INDICATORS 5 26 5 COMPARISON OF THERMAL AND MERZ DEMAND INDICATORS 5 27 TESTING PROCEDURES FOR 1-? ENERGY METER 6 POTENTIOMETERS D C POTENTIOMETER COMPARISON OF E M F’S STANDARDS OF E M F WESTON STANDARD CELL PRECAUTIONS TO BE OBSERVED IN USING STANDARD CELL AYRTON UNIVERSAL SHUNT VOLT RATIO BOX ACCURATE FORMS OF D C POTENTIOMETERS (CROMPTON POTENTIOMETER) STANDARDISATION OF POTENTIOMETER MEASUREMENT OF EMF CONSTRUCTIONAL DETAILS LEAKAGE STANDARDISING DEVICE TINSLEY VERNIER POTENTIOMETER BROOK’S DE?ECTION POTENTIOMETER 6 10 GALVANOMETER 6 11 APPLICATIONS OF POTENTIOMETERS 6 11 1 ANY UNKNOWN RESISTANCE CAN BE DETERMINED 6 11 2 MEASUREMENT OF UNKNOWN CURRENT 6 11 3 MEASUREMENT OF UNKNOWN VOLTAGE AND CALIBRATION OF VOLTMETER 6 11 4 MEASUREMENT OF POWER 6 12 POTENTIOMETER ANALYSIS 6 13 ANALYSIS OF POTENTIOMETER ERRORS 6 14 GALVANOMETER SENSITIVITY LIMITATIONS 6 15 A C POTENTIOMETER 6 16 DRYSDALE POLAR POTENTIOMETER 6 17 HOW TO USE POTENTIOMETER 6 17 1 STANDARDISATION (WITH D C) 6 17 2 STANDARDISATION (WITH A C ) 6 17 3 MEASUREMENT OF UNKNOWN A C VOLTAGE 6 18 GALL-TINSLEY COORDINATE POTENTIOMETER 6 18 1 STANDARDISATION OF IN-PHASE POTENTIOMETER 6 18 2 STANDARDISATION OF IN-PHASE POTENTIOMETER WITH A C 6 18 3 STANDARDISATION OF QUADRATURE POTENTIOMETER 6 19 MEASUREMENT OF UNKNOWN A C VOLTAGE 6 20 APPLICATIONS OF A C POTENTIOMETERS 6 20 1 DETERMINATION OF UNKNOWN RESISTANCE 6 20 2 MEASUREMENT OF UNKNOWN CURRENT: (CALIBRATION OF A C AMMETER) 6 20 3 DETERMINATION OF UNKNOWN VOLTAGE AND CALIBRATION OF A C VOLTMETER 6 20 4 CALIBRATION OF WATTMETER AND TESTING OF ENERGY METER 7 MEASUREMENT OF RESISTANCE MEASUREMENT OF LOW RESISTANCE POTENTIOMETER METHOD MEASUREMENT OF MEDIUM RESISTANCE AMMETER AND VOLT METER METHOD SUBSTITUTION METHOD DI?ERENTIAL GALVANOMETER METHOD WHEATSTONE BRIDGE TO ?ND BEST GALVANOMETER RESISTANCE FOR MAXIMUM SENSITIVITY MEASUREMENT OF HIGH RESISTANCE MEASUREMENT OF INSULATION RESISTANCE OF A CABLE DIRECT DE?ECTION METHOD PRICE’S GUARD WIRE METHOD LOSS OF CHARGE METHOD SURFACE AND VOLUME RESISTIVITY OF A MATERIAL OHMMETER SIMPLE METHODS OF MEASUREMENT OF INDUCTANCE AND CAPACITANCE MEASUREMENT OF SELF-INDUCTANCE AMMETER AND VOLTMETER METHOD A C POTENTIOMETER METHOD THREE VOLTMETER METHOD THREE AMMETER METHOD TURNER’S METHOD MEASUREMENT OF MUTUAL INDUCTANCE SECONDARY INDUCED E M F METHOD MEASUREMENT AS A SELF-INDUCTANCE DIRECT OPPOSITION METHOD BALLISTIC GALVANOMETER METHOD MEASUREMENT OF CAPACITANCE AMMETER AND VOLTMETER METHOD A C POTENTIOMETER METHOD BALLISTIC GALVANOMETER METHOD BRIDGES BRIDGE ACCESSORIES SOURCE TYPES OF DETECTORS 7 10 D C BRIDGES 7 10 1 WHEATSTONE BRIDGE 7 10 1 1 SOLUTION FOR DETECTOR CURRENT 7 10 1 2 CONCLUSIONS 7 10 1 3 CURRENT AND VOLTAGE SENSITIVITY OF THE BRIDGE 7 10 1 4 INTERCHANGE OF BATTERY AND GALVANOMETER 7 10 1 5 COMPARISON OF CURRENT SENSITIVITY BASED ON EQUAL VOLTAGE 7 10 1 6 BRIDGE SENSITIVITY BASED ON CONSTANT CURRENT 7 10 2 KELVIN DOUBLE BRIDGE 7 10 3 CAREY-FOSTER SLIDE WIRE BRIDGE 7 10 3 1 CONDITION FOR BALANCE 8 A C BRIDGES RATIO ARM BRIDGE PRODUCT ARM BRIDGE MAXWELL’S INDUCTANCE BRIDGE HAY’S BRIDGE FOR MEASUREMENT OF INDUCTANCE ANDERSON BRIDGE OWEN’S BRIDGE HEAVISIDE BRIDGE CAMPBELL’S MODI?CATION OF THE HEAVISIDE BRIDGE 8 10 HEAVISIDE CAMPBELL-EQUAL RATIO BRIDGE 8 11 MEASUREMENT OF CAPACITANCE BY DE SAUTY BRIDGE 8 12 WIEN’S BRIDGE 8 13 SCHERING BRIDGE 8 14 WAGNER’S EARTH CONNECTION 9 MAGNETIC MEASUREMENTS D C TESTS BALLISTIC GALVANOMETER ANALYTICAL PROOF DETERMINATION OF G AND C DETERMINATION OF B G CONSTANT K MEASUREMENT OF FLUX BY BALLISTIC GALVANOMETER USE OF SHUNT WITH BALLISTIC GALVANOMETER FLUX METER ANALYTICAL APPROACH USE OF SHUNT WITH FLUX METER MAGNETIC COMPENSATION OF SUSPENSION TORQUE IN A FLUX METER DETERMINATION OF A B H CURVE OF A SPECIMEN CALCULATION OF B HYSTERESIS LOOP (B H LOOP) METHOD OF REVERSALS BALLISTIC TESTS USING FLUX METER B H CURVE FOR BAR SPECIMEN 9 10 FAHY SIMPLEX PERMEAMETER 9 11 OTHER METHODS OF MEASURING MAGNETIC FIELD INTENSITY 9 11 1 USE OF SEARCH COIL 9 11 2 BISMUTH SPIRAL 9 11 3 MAGNETIC BALANCE 9 11 4 MAGNETOMETER (GAUSS METER) 9 11 5 DE?ECTING COIL 9 11 6 HALL E?ECT 9 12 MAGNETIC TESTING WITH A C 9 12 1 SEPARATION OF IRON LOSSES 9 12 2 DETERMINATION OF LOSS BY WATTMETER 9 13 MEASUREMENT OF IRON LOSS BY A C POTENTIOMETER MULTIPLE CHOICE QUESTIONS