LOM-4000/4001 Manual
Contents
1. 3 1 Initial Inspection After unpacking inspect unit for shipping damage and report any problem immediately to the carrier retain ing packaging materials for inspection 3 2 Safety This unit has been designed and tested in accordance with IEC Standard EN61010 1 entitled Safety Re quirements for Electronic Measuring Apparatus and has been supplied in a safe condition This instruc tion manual contains information and warnings which should be followed by the user to ensure safe opera tion and to keep the unit in safe condition 3 3 Features 3 3 1 Measurement Polarity The user can reverse the measuring current polarity by reversing the test leads This is particularly useful when evaluating circuits with thermal emf or circuits where diode effects can influence the measurement For measurements where thermal emf can cause a large zero error there is an automatic average AVE button When it is pressed the measuring current will automatically be reversed and the average value displayed thus eliminating the need for external com putations This averaging feature also doubles the measurement time from 20 ms to 40 ms The AVE lamp will light to indicate that the current polarity is changing 3 3 2 Range Selection Any of the six measuring ranges can be selected manually by simply pressing the desired RANGE UP or DOWN buttons Over range is indicated by the display reading An auto range capabili2. PRECISION INSTRUMENTS FOR TEST AND MEASUREMENT 4 LOM 4000 SERIES Digital Ohmmeter User and Service Manual Copyright O 2005 IET Labs Inc LOM 4000 im February 2005 IET LABS INC Standards Decades Strobes Sound Level Meters Bridges 534 Main Street Westbury NY 11590 www ietlabs com TEL 516 334 5959 800 899 8438 FAX 516 334 5988 WARRANTY We warrant that this product is free from defects in material and workmanship and when properly used will perform in accordance with applicable IET specifications If within one year after original shipment it is found not to meet this standard it will be repaired or at the option of IET replaced at no charge when returned to IET Changes in this product not approved by IET or application of voltages or currents greater than those allowed by the specifications shall void this warranty IET shall not be liable for any indirect special or consequential damages even if notice has been given to the possibility of such damages THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES EXPRESSED OR IMPLIED INCLUD ING BUT NOT LIMITED TO ANY IMPLIED WARRANTY OF MERCHANTIBILITY OR FITNESS FOR ANY PARTICULAR PURPOSE N WARNING AN OBSERVE ALL SAFETY RULES WHEN WORKING WITH HIGH VOLTAGES OR LINE VOLTAGES Dangerous voltages may be present inside this instrument Do not open the case Refer servicing to qulified personnel HIGH VOLTAGES MAY BE PRESENT AT THE TERMINALS OF THI
3. ZERO AVE MEAS e e e Operation LOM 4000 Series CAL 9 S m Tr g 4 z AUTO EDIT ZERO 1063 AVE o d o v MEAS OK Enables the Calibration mode Selects and enters temperature compensation coefficients ModelLOM 4001 only Toggles display between temperature and resistance measurement ModelLOM 4001 Only Switches unit ON and OFF Up key selects next highest measuring range It also increases the selected digit used for setting coefficients and for entering calibration code Down Key selects next lowest measuring range It also decreases selected digit used for setting coefficients and for enterina calibration code Selects autorange mode EDIT Selects edit mode when changing coefficients etc Internally shorts the current leads and nulls the reading eliminating errors due to emf in the measuring circuit Also acts as Left Key selects the next digit to the left flashing digit indicates the active one Selects average measurement mode the measuring current is automatically reversed and the average of the forward and reverse measurements is displayed Also acts as Right Key selects the next digit to the left flashing digit indicates the active one Starts and Stops the measurement a single press triggers a single measurement Press and hold down until a long bleep is heard and the unit is in continuous measurement mode Also used for verifying input values OK Operation
4. of the same current rating 1 A and at least a 40 000 A interrupting capacity 3 6 Temperature Compensation Model LOM 4001 Only Automatic temperature compensation is available on the model LOM 4001 A Pt100 temperature sen sor should be connected to the DIN socket next to the measuring terminals To activate this function press the DISP key the Rc LED will light to show that the displayed value is the compensated resistance The Pt100 sensor will mea sure the ambient temperature and compensate the reading for the temperature coefficient ofthe mea sured Rx Different temperature coefficients may be selected by pressing the COMP key Copper and aluminium coefficients are preset a user coefficient may also be entered Repeated pressing of the COMP key cycles through these options To set the user coeffi cients the arrow keys are used select and increment or decrement the digits 3 7 Temperature Measurement Model LOM 4001 Only The model LOM 4001 can also be used as thermom eter using a Pt100 temperature probe inserted into the socket next to the measuring terminals Press the DISP key until the C LED lights The LOM 4001 will now display the temperature measured by the Pt100 sensor I U U GROUND Fig 3 4 Connection Diagram for Pt100 plug viewed from the rear Operation LOM 4000 Series Chapter 4 CALIBRATION 4 1 Calibration Process This procedure describes the standard calibration method for the
5. 2 Combined current and potential probes Kelvin clips Operation LOM 4000 Series Connections to Stud Terminals Connections to Cable Joint Connections to Current Shunt Fig 3 3 Connections for resistance measurements with various DUT configurations Measurements will continue until the MEAS key is pressed again To preserve battery life the unit will automatically turn offafter several minutes of inac tivity 3 4 4 Current Mode The current mode can be set to AVE The AVE mode may be selected for measurements that are not in ductive in order to eliminate errors caused by ther mal emf in the measurement circuit or test leads In the AVE mode the LOM D4000 1 takes readings Operation with the current flowing in both directions and dis plays the average of the two readings The AVE mode should not be used for measurement of in ductive circuits 3 4 5 Over Range Ifthe measured value exceeds the upper limit of the range selected the display will indicate Select a higher range In AUTO mode this display indicates a value above the range of the instrument LOM 4000 Series 3 4 6 Open Circuit Lead If one of the test leads is open circuited or exceeds a preset resistance the display will indicate OC The I terminals are checked for compliance volt age Measurements cannot be made if this warning message is displayed This warning will also be dis played if the current lead resi
6. 4 5 4 Use the procedure of 4 4 1 above to perform the calibration using discrete standards Replace the zero setting and resistance values of the MTS2 with the shorting procedure above and the discrete resistance standards to be used Calibration LOM 4000 Series Chapter 5 MAINTENANCE 5 1 General Normally no maintenance is required other than clean ing with a moist cloth Avoid strong detergents or solvents Ifa failure occurs or if the unit cannot be calibrated it should be returned to IET or to an IET representa tive Contact IET for an RMA number before return ing the unit directly to IET CAUTION Replace only with the correct fuse type shown below The input circuits are protected by a 1 A fuse located in a holder on the printed circuit board Open the case by removing the six screws holding the two sections together Examine the fuse and replace if necessary Maintenance CAUTION Replace only with the correct fuse type shown be low or an equivalent part with the same or higher interrupting capacity NFC 63210 Altech 1C10x38G1 or Cooper Bussman KTK 1 11
7. LOM 4000 1 Micro ohmmeter using the IET MTS2 Calibration Standard or a method us ing discrete resistance standards of the required val ues CAUTION The LOM 4000 1 comes factory calibrated to its full accuracy and any recalibration by the user will invali date this initial calibration The user should therefore be certain that only authorized and competent per sonnel are permitted access to the calibration process which is password protected 4 2 Equipment Required IET Calibration Standard MTS2 or equivalent 4 ter minal standard s 4 3 Preparation 4 3 1 Place the instrument in a temperature con trolled environment 20 C 5 C for a minimum of 2 hours Ensure that the batteries are fresh or fully charged 4 4 Calibration Using MTS2 Standard 4 4 1 Connect each of the four LOM 4000 1 termi nals to the equivalent terminals on the calibration stan dard Calibration 4 4 2 Entering a password and Calibration 1 Turn the LOM 4000 1 on while holding down the CAL key The display will show CODE for a few seconds and the 0000 with a flashing cursor under the first zero Enter the calibration code 9252 using the UP and DOWN keys to select the digits and the ZERO and AVE keys with the left and right arrows to select the position When done press the MEAS OK key When the entry has been validated the instrument enters the calibration mode and the CAL LED illuminates 2 The display will now show 0 0 with the
8. first digit flashing Set the MTS2 to zero and press OK This calibrates the zero on the first range The display will then show the full scale reading on that range 4 000 with the first digit flashing Set the MTS2 to the same value and if desired for better accuracy enter the exact calibrated value for that MTS2 setting using the arrow keys as above The press OK 3 The calibration process then switches automati cally to the next range Proceed as above until all ranges are calibrated Then press the CAL button to exit the calibration mode 4 5 Calibration Using Discrete Resistance Standards 4 5 1 Discrete 4 terminal resistance standards may be used in place of the MTS2 Calibration Standard The standards must have an uncertainty better than 0 01 if full calibration accuracy is to be achieved The following nominal standards are recommended 4 kQ 400 Q 40 Q 4 Q 400 mQ 40 mQ and 4 mQ 10 LOM 4000 Series 4 5 2 In all measurements the U and and the I and terminals are connected to the equivalent terminals usually marked Sense and Current on the four terminal standards used 4 5 3 For the ZERO measurement short the Sense ter minals of the standard connected to the instrument using the shorting clip supplied with the standard or a heavy wire All four leads between the instrument and the standard should remain connected Remove the short after the ZERO calibration is completed
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10. S INSTRUMENT WHENEVER HAZARDOUS VOLTAGES gt 45 V ARE USED TAKE ALL MEASURES TO AVOID ACCIDENTAL CONTACT WITH ANY LIVE COMPONENTS USE MAXIMUM INSULATION AND MINIMIZE THE USE OF BARE CONDUCTORS WHEN USING THIS INSTRUMENT Use extreme caution when working with bare conductors or bus bars WHEN WORKING WITH HIGH VOLTAGES POST WARNING SIGNS AND KEEP UNREQUIRED PERSONNEL SAFELY AWAY N CAUTION N DO NOT APPLY ANY VOLTAGES OR CURRENTS TO THE TERMINALS OF THIS INSTRUMENT IN EXCESS OF THE MAXIMUM LIMITS INDICATED ON THE FRONT PANEL OR THE OPERATING GUIDE LABEL vii Contents Chapter 1 INTRODUCTION sivccccnaseascastsctensanstaseasscnecvesnssdneanscnveiasdeseosedestacsdedaseuseonebasenseateckedanedeensesestssusecasaseenssuadsatie 1 General Description ti edere e eei taedet ans ite ie ep edenda 1 1 2 Theory of Operations ere cR epe Og ete pe eti vet ita dtes 1 13 Case RE NA 1 1 4 Available ACCESSOCIES reor rd e rd rias 1 Chapter2 10 elio Ce Nuove 2 2 Getieral iss scabs Sete eR A es aeg Cop ese Fi a eth e ee aT aeg et 2 2 2 Measurement crise ortis edere Etc e tddi 2 Chapter 3 OPERATION pee 3 A A IEEE 5 DAN AS te E EEEE E hib lt E EE eae 5 3 3 Features x Listen ia edie qu eet 5 3 3 1 Measurement Polarity it cde boire bee 5 3 32 Range SelectIon2 n ctore te deed ANN 5 3 39 Error de Stats Lambps o ee eret e eet e ahd vane dece eere dete eda 5 3 4 Making Measurements sse enr enn entente nennen innert
11. cation d Fig 3 3 illustrates connections to various types of test resistors e When measuring 4 terminal resistance standards or using them for calibration the Kelvin clips may not be usable because of terminal geometry Make four separate connections to the current and potential ter minals 3 4 2 Start up When the LOM DO7e is first switched on an inter nal self test is automatically performed The display indicates 8888 followed by PASS then performs an automatic zero sequence and finally sets to the 4kQ range The unit is now ready to make mea surements The unit will shut off automatically after several minutes of inactivity If the internal checks indicate an error the display will read FAIL Contact our Service Department or your IET Representative for assistance 3 4 3 Measurement Connect the resistance to be measured Rx to the measuring terminals in accordance with the diagram on the instrument panel and using the most appropri ate connection technique for the unknown See Figs 3 2 and 3 3 Select the range required or AUTO and the AVE measurement mode if desired The AVE button LED will light to indicate that the AVE func tions is active To initialize the measurement press the MEAS button A single measurement will be taken and the value held on the display To take continuous readings press and hold the MEAS button until a long beep is heard this will activate a continuous reading mode Fig 3
12. d current and potential probes Kelvin clips essen Figure 3 3 Connections for resistance measurements with various DUT configurations sess Figure 3 4 Connection Diagram for Pt100 plug viewed from the rear ssssssseeeeeeeee LOM 4000 Series Chapter 1 INTRODUCTION 1 1 General Description The LOM 4000 and LOM 4001 are accurate bench portable handheld Digital Milli ohmmeters for the mea surement of resistance in the range 10 uQ to 4000 Q They utilize the four terminal Kelvin resistance mea surement method to eliminate the effects of lead re sistance The measured values are displayed on a 4 digit 4000 count LED display there is also an over flow indicator The LOM 4001 allows temperature compensation of readings and temperature measure ment if the user connects a 100 ohm platinum resis tance thermometer PRT Simple push button or auto range selection of the range required makes the LOM 4000 Series easy to use Error and status warnings are illuminated when appropriate The unit will withstand accidental appli cation of line voltage to the measuring terminals 1 2 Theory of Operation The measurement is true 4 terminal using the Kelvin principle A stable current 1s produced across the resistance to be measured via the current I termi nals and the voltage drop across the unknown resis tance Rx is measured at the voltage U terminals This potential drop is t
13. hen compared against the volt age drop across internal standards The ratio ofthese is then converted to the resistance value of Rx and displayed in ohms on the digital display Use of spe cially selected components assures high accuracy and long term stability Introduction 1 3 Case Design The case 1s ruggedly constructed from ABS plastic The front panel is a reverse printed polycarbonate overlay with clear and unambiguous text The batter ies are housed in a removable cassette for quick and easy replacement 1 4 Available Accessories Supplied 1 Set of test leads 1 Set of alkaline batteries 1 Operation Manual Optional Lead Sets HSO1 P Duplex Handspikes with 2 5 meter leads for Kelvin measurements of plates or buss bars HSO2 P Similar to HSO1 P but with 2 5 meter and 15 meter leads LSO3 P Large Kelvin clips with 3 meter leads accept cables and bars up to 38 mm in diameter LSO4 P Similar to LSO3 but with 3 meter and 15 meter leads Other Optional Accessories CO1 1 Meter Cable Test Fixture Wood Base CO2 1 Meter Cable Test Fixture Metal Base MTS2 Calibration Standard For most efficient operation a spare battery cassette BP 02 is recommended LOM 4000 Series Chapter 2 SPECIFICATIONS 2 1 General Digital Display 4 digit 0 6 high LCD 4000 count with automatic decimal point and polarity indication additional annunciator lamps Operating temperature range 0 to 40 C with maxi
14. mum relative humidity of 80 Storage temperature 20 C to 50 C Power Five AA alkaline batteries supplied Rechargeable batteries optional Battery Life 12 hours Dimensions 250 x 130 x 55 mm 9 9 x 5 1 x 2 2 Weight 0 8 kg 1 5 Ib RESISTANCE 2 2 Measurement Resistance True four terminal measurement with fixed dc measuring currents Measuring time Approximately 20 ms for normal measurement 40 ms for average AVE mode Polarity Selectable positive or negative current flow by manually reversing test leads plus an average mode which automatically displays the average value of the positive and negative polarity measurements Temperature Measurement 200 C to 800 C with user supplied Pt100 sensor Range Resolution Current Accuracy Temperature Coefficient 10 100 uA 0 05 Rdg 0 02 FS 30 ppm Rdg 1 ppm FS 0 05 Rdg 0 02 FS 30 ppm Rdg 1 ppm FS 0 05 Rdg 0 02 FS 30 ppm Rdg 1 ppm FS 0 05 Rdg 0 03 FS 30 ppm Rdg 4 ppm FS 0 05 Rdg 0 05 FS 40m0 1010 100 mA 0 05 Rdg 0 1 FS 30 ppm Rdg 25 ppm FS 30 ppm Rdg 25 ppm FS TEMPERATURE Rage Resolution Accurac 50 800 C 0 1 C 0 2 C Specification LOM 4000 Series Chapter 3 OPERATION Display Mode LED s 4001 only Calibration ow Battery LED Units Indication og COEFF DISP RANGE o Boliuo Function Keys t 4 er o e
15. stance is high 3 4 7 Low Battery The LOBAT LED will light when the battery has 10 charge remaining When this occurs a spare battery cassette should be installed or the existing cassette should be resupplied with fresh or recharged batteries Full measurement accuracy is maintained even when the LOBAT LED is ht 3 4 8 Connections To make the most accurate possible measurements ensure that all test leads are in good condition and have less than 0 2 Q resistance Some spade lugs and alligator clips especially nickel plated brass types can produce high thermal emf s when heated This can sometimes cause problems for example when connecting to hot motor windings Avoid such prob lems by using plain copper or brass connections and keeping them clean and oxide free 3 5 Protection This instrument is protected against voltages being applied inadvertently to the terminals A high inter rupting capacity fuse 1s installed internally in the cur rent circuit The voltage terminals are not fused and will withstand up to 460 Volts without damage to the instrument To replace the protection fuse the unit should be opened by removing the six screws on the bottom of the case but only after ac power and all input con nections are removed The protection fuse is located on the printed circuit board This fuse has a 40 000 to 200 000 A interrupting capacity depending on the exact type used Always replace this fuse with one
16. ty is also provided pressing Operation LOM 4000 Series the AUTO key puts the instrument into the auto range mode 3 3 3 Error Status Lamps The following LEDs will light to indicate the instru ment status CAL Instrument is in the calibration mode LOBAT Battery capacity is nearly depleted The following LED s are for LOM 4001 only Rx The display shows a resistance reading Re The display shows a compensated resistance reading C The display shows a temperature reading 3 4 Making Measurements 3 4 1 Ohmmeter Connections The LOM D4000 1 employ a four wire method of measurement i e four connections to the resistor under test are required The unit is supplied with four leads two voltage leads to be placed across the ex act measurement points and two current leads to be placed outside the measurement points The Kelvin clips shown in Figure 3 2 place voltage and current connections at the same point a Connect the red leads to the I and U terminals and the black leads to the I and U terminals b Clip the test leads onto the resistor under test Cleanliness is important ifthe DUT is not clean clean it with fine emery cloth or steel wool to remove ox ides LOM 4000 Series c It is not always possible to use the combined current and potential Kelvin clips in which case test leads with spade lugs or a special test fixture may have to be made for a particular appli
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