User`s Manual
Contents
1. 6 4 3 To find out approximate value of Rx 7 4 4 Interpolation 8 4 5 Murray Loop 8 4 6 Varley Loop 9 5 PRINCIPLES OF OPERATION 10 6 MAINTENANCE 11 COMPONENT LOCATION DIAGRAM 11 PART 12 CIRCUIT DIAGRAM 13 IM 2755 97E 1 GENERAL The 2755 Portable Wheatstone Bridge is quite conve nient with general resistance measurement and fault point detection of lines by Murray and Varley loop testing meth ods 2 SPECIFICATIONS Measuring Range Measuring arm Ratio arm Accuracy Overall 1000 to 100 100 to 1 10 to 10MQ IM 2755 97E 10 to 10MQ 4 digits 10 10 100 10 100010 10000x10 4 dials X0 001 0 01 x0 1 x1 10 100 x1000 and for Murray loop test M10 M100 M1000 0 1 of reading 0 396 of reading 0 6 of reading Measuring arm 1000 0 06 x 100 0 1 x10 0 5 x1 3 Including residual resistance Multiply dial Ratio 0 1 X1 X10 0 07 x100 x0 01 0 2 x 1000 0 001 0 596 M10 M100 M1000 0 1 Temperature Coefficient of Resistance Elements 5 10 5 to 35 C 2 107 20 to 35 C Gal2. AEW 502 Z 51 GALVANOMETER X TERMINALS Fig 6 1 Component Location Diagram H1 H2 H3 H4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 R16 R17 R18 R19 R20 R21 R22 PART LIST Resistor Manganin wire wounded 10 20 50 100 200 500 1000 2000 5000 10000 20000 50000 0 9990 8 9020 81 0090 409 090 409 090 81 0090 412 R23 R24 R25 R26 R27 R28 R29 R30 D1 D2 GA K1 K2 S1 S2 S3 S4 S5 S6 S7 BA Diode Silicon Galvanometer Moving coil type Switch Push button n Switch Rotary Switch Toggle Switch Toggle Dry cell three Circuit Board 8 9020 0 9990 11110 10 10 RD1 4PY 3300 RD2PY 100 RD2PY 5100 RD2PY 5100 1004 equivalent n B9350DM A9150YB n B9350BP n B9350BP A9285SR 904255 SUM 1 B9350DQ IM 2755 97E MULTIPLY 0 0010 ad af 000 9 A60 81 00 AT O IM 2755 97 A gt m 2090 0 0 0Q 9990 RB 99020 RIF To K l 090290 22 9 0091 3 49020 Pot e 9941 RY Rio Ril n 201 2000 qn EZE EXTBA 25 Fig 6 2 Circuit Diagram 19 YOKOGAWA 9 Yokogawa Meters amp Instruments Corporation Yokogawa Meters amp Instruments Corporation International Sales Dept Tachihi Bld No 2 6 1 3 Sakaecho Tachikawa shi Tokyo 190 8586 Japan Phone 81 42
3. B and B terminals and turn the power supply selector switch to EXT BA Minimum circuit resistance between B and B terminals is approximate 1010 ohms Maximum external power supply voltage is 70V DC and maximum current is 60mA DC Continuous 1 2W type protective resistance is inserted between the external power supply and bridges so when the 1000 dial is set to 0 the circuit is pro tected from overcurrent IM 2755 97E 3 4 Cell Replacement Remove the cell cover on the bottom of the case by pulling leg of the cover while pushing the clamp ing plate towards the arrowed direction to the end To restore the cell cover push the clamping plate to wards the arrowed direction insert the hollowed part of the cover under the clamping plate and press the cover down Fig 3 5 Bottom View IM 2755 97E 4 OPERATION 4 1 Preparation 1 Confirm that EXT GA terminals are perfectly short circuited with short circuiting bar 2 Confirm that the galvanometer indicates O by opening Rx terminals without pushing GA and BA button switch If the galvanometer does not indicate 0 adjust the zero point by turning the zero adjustor De press BA push button switch 3 GA button switch should be at OFF position 4 2 Resistance Measurement 1 Apply unknown resistor to Rx terminals 2 Turn the selector switch to R 3 Set the MULTIPLY dial to proper range according to Table 4 1 4 Set the Measuring di
4. 534 1413 Facsimile 81 42 534 1426 YOKOGAWA CORPORATION OF AMERICA U S A Phone 1 770 253 7000 Facsimile 1 770 251 2088 YOKOGAWA EUROPE B V THE NETHERLANDS Phone 31 334 64 1611 Facsimile 31 334 64 1610 YOKOGAWA ENGINEERING ASIA PTE LTD SINGAPORE Phone 65 6241 9933 Facsimile 65 6241 2606 YOKOGAWA AMERICA DO SUL S A BRAZIL Phone 55 11 5681 2400 Facsimile 55 11 5681 1274 YOKOGAWA MEASURING INSTRUMENTS KOREA CORPORATION KOREA Phone 82 2 551 0660 to 0664 Facsimile 82 2 551 0665 YOKOGAWA AUSTRALIA PTY LTD AUSTRALIA Phone 61 2 9805 0699 Facsimile 61 2 9888 1844 YOKOGAWA INDIA LTD INDIA Phone 91 80 4158 6000 Facsimile 91 80 2852 1441 YOKOGAWA SHANGHAI TRADING CO LTD CHINA Phone 86 21 6880 8107 Facsimile 86 21 6880 4987 YOKOGAWA MIDDLE EAST E C BAHRAIN Phone 973 358100 Facsimile 973 336100 LTD YOKOGAWA ELECTRIC RUSSIAN FEDERATION
5. EASURING DIALS ohms fetu s Rx1 Resistance between 1 terminal Table 4 3 Varley Loop Test and the fault point 2L Total resistance of looped line 1 Connect the looped line under test to Rx termi under test nals Connect the G terminal to the earth 2 Turn the selector switch to MV 3 Set the MULTIPLY dial to proper range of 0 001 to 1000 IM 2755 97E 4 Press the BA button switch and button switch Adjust measuring arm dials until the gal vanometer indicates O 5 Obtain the value refering to the following equa tion 2L MULTIPLY factor x Total Rx2 1 MULTIPLY factor value of MEASURING DIALS ohms Rx2 Resistance between X terminal and the fault point 2L Total resistance of looped line under test 5 PRINCIPLES OF OPERATION Fig 5 1 is the theoretical diagram of Wheatstone bridge When the current at the galvanometer is set to zero by adjusting Rs the following equation will be established Ix Is Is Rs Is Rx Ra Ix Rs Re Ra Rx Ra Hs As this 2755 Portable Wheatstone Bridge is so designed that Ra Re can be set within the range of 0 001 to 1000 by MULTIPLY dial the unknown resis tance value Rx can be obtained by multiplying the Rs value by the multiplying factor IM 2755 97E Fig 5 1 Theoretical Circuit Diagram IM 2755 97E Bn 6 MAINTENANCE S to DRY CELL X41000 to DRY CELL N 7 8 S3 X100 Se
6. Hmm User s 2755 Manual Portable Wheatstone Bridge With Murray and Varley Loop Tester YOKOGAWA Yokogawa Meters amp Instruments Corporation 5th Edition June 2007 Cautionary Notes for Safe Use of the Product The following symbol is indicated on the instrument to ensure safe use Handle with care This symbol is indicated where the operator must refer to instructions in the manual or attached material in order to protect personnel and the instrument Since mishandling the instrument can result in an accident that may lead to injury or death of the operator such as an electric shock be sure to observe the following instructions A ma Protective Measures If a crack appears in the instrument after it has been accidentally dropped or bumped the safety purpose insulation may be damaged By all means do not use the instrument but ask the manufacturer for repair Connection To avoid electric shock be sure to apply protective grounding to the grounding terminal Measurement Always maintain the instrument within the limits for allowable current voltage and power during operation If there is more than one limit for any of these parameters the lowest limit takes precedence External Power Supply Only operate the instrument a supply voltage no greater than 70 V DC Operating Environment Do not operate the instrument in a flammable or explosive gas atmosphere Do not operate t
7. al at 1999 and push BA push button switch Then push GA push button switch for a moment to check to which direction or the galvanometer deflects IM 2755 97E 5 When the pointer deflects side increase mea IM 2755 97E suring dials and when the pointer deflects mi nus side decrease measuring dials Adjust measuring dials until the galvanometer indicates O Then the unknown resistance value is measured by the following equation MULTIPLY less than 100 100 to 1000 1000 to 1 1kQ to 10kQ 10kQ to 100kQ 100kQ to 1 MQ 1MQ to 10MQ Table 4 1 MULTIPLY Dial Setting Rx MULTIPLY factor Total value of MEASURING DIALS ohms MULTIPLY Fig 4 1 Resistance Measurement 4 3 To find out approximate value of Rx When the resistance value to be measured is en tirely unknown and if there is no suitable circuit tester ohm meter available the following procedure shall be effected to find out approximate value of the un known resistance Set MULTIPLY dial to 1 and measuring arm dials to 1000 Pressing the BA button switch then lightly pressing GA button switch to check to which direc tion the galvanometer deflects When the pointer de flects to side Rx is higher than 1000 ohms Then increase MULTIPLY dial to 10 and press BA and GA button switches again If the galvanometer still deflects to side turn MULTIPLY dial to 100 Suppose that the pointer deflects to minus side by t
8. en to avoid excess current flow since all wire wound bridge elements used in this instrument can endure up to 1 watt max Before higher voltage is applied take rough balance of bridge with low voltage Caution must be taken not to set 1000 dial to 0 and not to short circuit Rx terminals IM 2755 97E A BT Operation of Button Switch BA and GA button switches should be at OFF position after measurement During measurement BA button switch must be pressed prior to GA button switch If this order is inverted the movement of the galvanometer will be kicked when BA button switch is pushed due to inverse emf of inductance of the object under test and the direction of measuring dial adjustment shall be thereby misled Lead Resistance In measurement of resistances below 10 ohms the lead wire resistance should not be neglected The lead resistance compensation must be made by measuring the lead resistance separately CONTENTS Page GENERAL a UM 1 2 SPECIFICATIONS 1 CONSTRUCTION 3 1 Front 44 3 3 2 External Galvanometer 4 3 3 External Power Supply 4 3 4 Cell 5 4 OPERATION M 6 4 1 Preparation 6 4 2 Resistance Measurement
9. he instrument if there is any condensation on it Disassembly Nobody except members of the manufacturer s service staff is allowed to disassemble the instrument Since mishandling the instrument can result in an accident such as an electric shock that may injure the operator or damage the instrument be sure to observe the following instructions A Batteries e Do not use a mixture of different types of batteries or a mixture of old and new batteries If the instrument will not be used for a prolonged period remove the batteries before storage The battery fluid will leak more readily during long term storage resulting in an instrument malfunction Plastic Case The panel and case of this instrument are made of ABS resin Special caution must be taken to protect them from heat and organic solvent such as lacquer thinner Notice regarding This User s Manual 1 The information covered in this user s manual is subject to change without prior notice 2 Every effort has been made to ensure accuracy in the preparation of this manual Should any errors or omissions come to your attention however please inform Yokogawa Corporation accordingly 3 Yokogawa Corporation is by no means liable for any damage resulting from the user s mishandling of the product IM 2755 97E Precautions for Use A ma External Power Supply When external power supply is employed to increase sensitivity full caution must be tak
10. his adjustment Rx is in the range between 10 kilo ohms and 100 kilo ohms On the other hand when the galvanometer deflects to side by the first settings Rx is lower than 1000 ohms In this case decrease MULTIPLY dial to 0 1 or 0 01 so as to make the pointer deflect to side Approximate value of Rx can be obtained by the above process 4 4 Interpolation There might exist a case where perfect balance of galvanometer can not be taken even by adjustment to minimum figure X1 dial Read in such a case the amount of unbalance from the scale of the galva nometer and estimate fractional parts of the lowest dial by proportional galvanometer deflections 4 5 Murray Loop Test Simplified circuit diagram of Murray loop test is illustrated in Fig 4 2 Table 4 2 Murray Loop Test IM 2755 97E 1 Connect the looped line under test to Rx termi 4 6 Varley Loop Test nals Connect G terminal to the earth Simplified circuit diagram of Varley loop test is il 2 Turn the selector switch to MV lustrated in Fig 4 3 3 Set MULTIPLY dial between M10 M100 and M1000 line 4 Press the BA button switch and GA button 20 7 eee PG switch Adjust measuring arm dials until the gal vanometer indicates 0 5 Obtain the value refering to the following equa tion gt ne o MULTIPLY factor MULTIPLY factor Total value Rx1 2L Wh oe of M
11. vanometer less than Sensitivity 0 9uA div 20 Internal resistance 1500 20 Period Within 2 6 seconds Operating Temperature 5 to 35 C Operating Humidity 8596 R H or less Power Source Three 1 5V batteries built in type SUM 1 Dimentions Approx 182226 128mm Weight Approx 2kg 4 4165 Accessory User s manual 1 copy Carrying case B9350AW 1pc Optional Accessory Carrying case B9350AW 275600 Note For the measurement of more than 100 it is recom mended to use external galvanometer which has high sen sitivity For example the 2707 Electronic Galvanometer Portable type 10uV div sensitivity is suitable for above requirement It is possible to measure 0 1 variation of Rx value of 2MQ 4 5V power supply IM 2755 97E 3 CONSTRUCTION 3 1 Front Panel POWER SUPPLY EXTERNAL SELECTOR SWITCH BATTERY TERMINALS MEASURING ARM DIALS MV R SELECTOR MULTIPLY EXTERNAL GALVA TERMINALS PUSH BUTTON UNKNOWN SWITCH RESISTANCE Fig 3 1 Panel IM 2755 97E Fig 3 2 Connection of External Galvanometer BATTERY Fig 3 3 Connection of External Battery 3 2 3 3 External Galvanometer When a high sensitive galvanometer is required move short circuitting bar and short INT GA termi nals After that connect the galvanometer to EXT GA terminals are shown in Fig 3 2 External Power Supply When external power supply is necessary con nect the power supply to
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