UNI-T UT276A, Operating Manual

Page 1: ...P N 110401103514 ...

Page 2: ... 2 Range and Accuracy 3 Technical Specification V Clamp Meter Structure VI Liquid Crystal Display 1 Liquid Crystal Display 2 Instruction for Special Symbol 3 Display Demonstration VII Operation Methods 1 Power on 2 Power off 3 Resistance Measurement 4 Current measurement 5 Data hold unlock store 1 3 4 5 5 6 7 9 10 10 11 12 16 16 18 18 21 22 ...

Page 3: ... jaw of clamp can close or open freely When starting it don t pull the trigger and clamp any wires Clamp the objects being tested only after displaying the sign OL after started the instrument UT276A 278A OPERATING MANUAL UT276A 278A OPERATING MANUAL 7 Alarm Function Setting 8 Alarm Critical Value Inquiry 9 Data Wipe 10 Data Uploading to Computer VIII Measurement Principles 1 Resistance Measuremen...

Page 4: ... the meter stop using it immediately and pack it to the authorized qualified institution to address the problem The contents labeled with in the user manual shall be only applicable to UT278A II Product Overview The series of clamp on ground resistance tester represents a significant breakthrough of the traditional ground resistance measurement techniques and apply widely to grounding resistance m...

Page 5: ...beep Measurement scope has increased to 0 01 1200 With 99 group storage data lower energy consumption and with working current less 50mA in maximum start up III Unpack and Check Unpack and take out the instrument please check carefully if the following attachment are complete or intact if any lack or damage were found please contact with your supplier Meter Test ring Data up loading software disk ...

Page 6: ...light alarm Scope of alarm critical value setting Power Working temperature and humidity LCD 99groups To upload stored data into the computer for data analysis RS232communication wire with 1 8m long beep beep beep alarm press AL key to control the on off status Resistance 1 199 current 1 499mA 6VDC 4 AA dry alkaline batteries 20 55 10 RH 90 RH 4bit LCD digit display dimension 47mm 28 5mm UT276A 27...

Page 7: ...etch size Clamp jaw dimension 8 9 65mm 32mm 28mm Shift 40A m 1V m 0 5s 1KHz Frequency of the current being measured V Clamp Meter Structure 1 Long clamp head 65 32mm 2 Trigger control the closure and open of clamp jaw 3 Function keys ke key described as key POWER power on and off exit SAVE key data inquiry wipe data AL alarm function key alarm function on off Left right arrow key resistance curren...

Page 8: ...amp meter 5 L0 01 symbol it means the resistance being measured exceeds the lower limit of the clamp meter 6 OL A symbol it means the current being measured exceeds the upper limit of the clamp meter indicates that it might be artificial pull off the trigger or the clamp jaw has been too dirty to measure requiring clamp jaw cleaning 1 clamp jaw open symbol It shall display when the clamp jaw is op...

Page 9: ... accuracy of the time can t be guaranteed 10 NOISE Symbol when there are quite big interference current to the earth 3 Display Demonstration 1 as clamp jaw is open it can t measure It might be caused by the dirtiness of the clamp jaw please clean the clamp jaw surface power on error indication Er Error It might be caused by the dirtiness of the clamp jaw please clean the clamp jaw surface resistan...

Page 10: ...on and the current being measured exceed the set alarm critical value battery low voltage display and the measurement accuracy can t be guaranteed current being measured is 8 40A hold the present display value store the present hold value as the No 37 group data 8 inquiry No 08 group stored data resistance being measure is 30 0 the data is measured under strong interference signal UT276A 278A OPER...

Page 11: ...play OL and enter automatically into the resistance measurement mode as shown in picture2 If automatic calibration under improper power on the meter will display the symbol Er indicating error occurs in power on as shown in picture3 Picture 1 Picture2 Picture 3 The power on error might be resulted by the bad closure of clamp jaw or by the dirt on the clamp jaw surface please clean it Picture 4 If ...

Page 12: ...s and press key POWER to power off 3 Resistance Measurement If display OL after power on self check you can measure the resistance Pull the trigger and open clamp jaw clamp the loop being measured to read the resistance value Users are required to test by random test ring as shown in picture 5 The displayed value should be the same with standard value on the test ring 10 0 which is the value under...

Page 13: ...es the meter is mainly used for ground resistance test and the current measurement shall be only applicable to the current test on the ground wire but the power line or affect the magnetic property of the clamp head and finally affect the ground resistance test accuracy After power on self check clamp meter shall enter into the resistance measurement mode After display the OL press key A clamp met...

Page 14: ...old the present value and when displaying the symbol HOLD the hold value could be set as a group of data and numbered automatically orderly and be stored Press key HOLD to cancel hold the symbol HOLD would disappear and continue to measure Operate as the above steps you can store 99 groups of data If the memory is full the symbol MEM will flicker As shown in picture 9 hold the measured resistance ...

Page 15: ...e test mode press key AL to open or close the alarm function Under the test mode press key AL 3 seconds to enter into the alarm critical value setting function and the highest digit number shall flicker set the highest digit as shown in picture 13 and 14 Press key AL to convert the number on high digit and low digit When the present digit number is flickering press right and left arrow key to chan...

Page 16: ...previous set resistance alarm critical value is 20 Flicker Picture 15 9 Data Wipe Under the data inquiry mode press key SA VE POWER automatically wipe all stored data after it meter shall display as shown in the picture 12 and all wiped data shall not able to recover 10 Data Uploading to Computer Connect the meter host with computer with the RS233 communication wire deployed with the meter and the...

Page 17: ... know the measured resistance R by the following formula R E I 2 Current Measurement Principle The basic principle of UT278A clamp on ground resistance meter is the same with that of current transformer measurement The AC current I of the measured wire passing through the current magnetic ring and current coil on the clamp jaw produce the induction current I1 which could be measured by the clamp m...

Page 18: ...rical engineering meaning is not the parallel value slightly bigger than that of general electrical engineering meaning but ground hemisphere of each tower is much smaller than the distance between towers and the great number of ground points R0 is much smaller than R1 Thus it is reasonable to speculate R0 0 from the engineering aspect and the resistance we measured should be R1 After many compari...

Page 19: ...culating program software from our company user shall be able to solve it by using an of fice computer or laptop Principally except for the neglect of mutual resistance the method would not result in any measurement error brought by neglecting R0 Users need to pay attention that the number of connected ground bodies in your ground system shall be exactly equal to that of measurement value for prog...

Page 20: ... test line Resistance RL could be measured by clamp meter by connecting the test line end to end If measurement value of clamp meter is smaller than the allowable value of ground resistance ground resistance of the two ground bodies shall be qualified 2 Three point method As shown in the following picture find two independent ground bodies RB and RC near the ground body RA being measured If no exi...

Page 21: ...eps reading of each step is the parallel value of two ground resistance so each ground resistance value can be easily calculated As R1 RA RB R2 RB RC R3 RC RA So RA R1 R3 R2 2 This is the ground resistance value of ground body RA To memorize the above formula easily the 3 ground bodies could be regarded as a triangle and the resistance being measured equals to the sum of adjacent lines resistance ...

Page 22: ...t is possible that more than 2 ground down leads of the same tower or transformer are connected underground It is need to maintain only one ground down lead and unfasten others 3 Application of power plant and substation UNIT series clamp meter can test the loop contact and connect condition and can measure the connection between equipment in the station with the ground net by a test line The grou...

Page 23: ...n of the building lightning protection ground system If ground polarities of building are independent the ground resistance measurement of each ground polarity shall be referred to the following picture If measurement value of clamp meter is lower than the allowable value of ground resistance ground resistance of computer room and launching tower shall be qualified If measurement value of clamp me...

Page 24: ...istance Oil filling machine ground resistance Ground resistance of the oil filling machine oil hose B clamp meter have gained the explosion prevention accreditation with the explosion proof mark being Exia BT3 The clamp can apply to the flammable and explosive atmosphere 1 Oil tank and loading point ground resistance measurement Auxiliary polarityB Test line Oil tank polarity A Loading point polar...

Page 25: ...nstance loading point polarity Connect them with test line and read RT with the clamp meter We can calculate that Oil filling machine ground resistance R RT RC Of which RT is the resistance value measured by clamp meter and RC is the loading point ground resistance 3 Measurement of the oil filling machine oil hose connection resistance Hose Test line Oil filling machine Oil stopper UT276A 278A OPE...

Page 26: ...For instance the ground resistance allowable value stipulated in the GB50061 97 Code for Design of 66kV or Under Overhead Electrical Power T ransmission Line is designed for Each Tower It is clearly stated in the standard that ground resistance of each tower refers to the resistance value measured after disconnecting the electric connection of ground wire from ground body If the ground body have n...

Page 27: ...esistance is called the ground resistance of ground equipment The stipulation is equally stated clearly as in term of lightning prevention the wire resistance and ground body ground resistance is equivalent 2 Selection of the Measurement Point In some ground systems as shown in the following picture you should select a correct measurement point of measure or get dif ferent measurement results In m...

Page 28: ...B R over head wire R ground down lead 5 0 as over head wires and ground down lead are metal conduct with low resistance which can be neglected the real ground resistance value of the ground net A B in parallel to ground shall definitely 2 5 then we can judge if the real ground resistance value of the ground net A B in parallel is qualified If real ground resistance value of the ground net A B in s...

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