User's Guide
Contents
1. MH 10 Digital micro ohmmeter User s Guide GU 1081 03031601 Vv Safety Precautions This equipment should be operated only by qualified and duly trained people closely observing the corresponding safety regulations and instructions contained in the present User Guide It should be checked that the item to be measured is voltage free Before starting with the measurements be sure that the battery is well charged and that the line voltage is between specified limits Do not connect or disconnect the test leads during the measurement There are no adjustable parts or parts that can be replaced by the user within the equipment Taking out the Control Panel in order to have an access to the internal parts may be dangerous as there are high voltages inside capable of causing fatal accidents Cleaning of this instrument should be carried out using a soft cleaning anti static liquid after verifying that it doesn t attack the plastic parts used in the case and in the Control Panel of this equipment This equipment should be used only by a trained and competent person strictly applying suitable safety rules Used symbols Y Caution refer to User Guide Equipment complies with current EU Directives Index Safety Precautions Used symbols Description Operating principle Operating instructions Control panel Mains supply Measurement Messages Some notes about accuracy Battery condition Battery and charger2. RS 232 output Cleaning Technical specifications Accessories 4 4 6 6 7 7 8 8 A a e Og BwWwWONN O Description The MH 10 micro ohmmeter is a portable microprocessor controlled instrument used to accurately measure very low contact resistances of breakers and switches busbars transformers and engines windings etc with test currents from 1 mA to 10 A both in the laboratory and out in the field e Kelvin architecture four terminal method Digital reading alphanumeric display e Up to 4 digits readings e Powered by rechargeable battery or mains supply e 1 uQ Resolution e 200 Q Maximum reading Operating principle This device uses the Kelvin Bridge architecture with four terminals avoiding testing leads resistance to cause error during measurement The operator may choose test current and the reading is obtained by comparison through internal high stability standards The result appears in the alphanumeric display that is very easy to read Operating instructions Control panel ha l FUSE v POWER CORD connector ON OFF switch 3 Battery charge LED Current terminal C am
3. equipment is connected to the mains supply even if the ON OFF switch is turned off Charging procedure e Check that the ON OFF key is OFF e Connect the equipment to the mains supply e The indicator 3 will keep on lightning with a red light up to completing the charge At that point it will change to a green light being like this up to the equipment disconnection from the mains supply RS 232 output 5 32 Al LT D The equipment has an RS 232 output in the control panel that can be used to register measurements in a serial printer or data collector The outputs are the following ones Pin 2 Rx Pin 3 Tx Pin 5 Gnd Rate 4800 bps 8 bits no parity 1 stop bit 8 n 1 Note In order to assure the compatibility with most printers available in the market the resistance units are shown with the following symbols uR micro ohm mR milli ohm R ohm n Cleaning Cleaning of this instrument should be carried out using a soft cleaning anti static liquid after verifying that it doesn t affect the plastic parts used in the case and in the Control Panel of this equipment v Replacement fuse To check the instrument FUSE remove it with a screw driver If the fuse is ruptured replace it by another with the follow ing specifications Fuse Schurter model SPT 5x20 Time lag 5A 250V High breaking capacity H Technical specifications Test currents 1 mA 10 mA 100 mA 1A 10A Eac
4. ents by reversing the polarity in order to compute the average value Nevertheless if the operator suspect that there is a difference of temperature between the contact points that would can generate thermoelectric voltages it is necessary to carry out two measurements by reversing the current cables and so the circu lation sense of the current through the resistance under measurement The resistance value to be measured will be the average between the values in one sense and in the contrary direct and inverse current Battery condition The charge condition of the battery can be verified before or during the resistance measurement In order to achieve that the operator has to press the BATTERY key while the equipment is turned on The bar graph shows remaining charge as a percentile value If during measurement the charge of the battery achieves a critical level the display will show the BAT message notifying that the charge level is low After a few minutes the measurement will be automatically inter rupted in order to preserve the battery from a deep discharge that is prejudicial for its expected useful life Battery and charger Battery description The CIRCUTOR MH 10 micro ohmmeter uses a sealed rechargeable lead acid 12V 7Ah battery At the end of the useful life that battery has to be recycled or disposed of properly in order to take care of the environment Battery charger The built in battery charger is always active when the
5. er to optimize the readings PRESS START The equipment is ready to start a measurement thus the operator has to press the START button LOW CURRENT It shows that the test current is not enough to carry out the reading It appears at the beginning of each test and it keeps on being there up to the operator rotates the TEST CURRENT control clockwise as necessary for the test current to be higher than 10 of the nominal current in the scale The inappropriate connection of the cables may cause a difficult circulation of test current If this message keeps on being displayed please check that the current cables are connected appropriately OVERRANGE It indicates that the measured resistance is higher than the maximum value readable in the selected scale H Indicates that the value is the one retained in the memory when pressing the HOLD button BAT lt shows that the battery is quite discharged The available energy is enough to work during a few minutes only lt is necessary the battery to be recharged ee j Some notes about accuracy In order to obtain the specified accuracy the operator has to adjust the test current to a value higher than the 80 of the nominal value If it were necessary it is possible to use a lower current but by doing this the accuracy will be affected MH 10 has an auto compensation system that automatically eliminates the error produced by internal offset Thus it is not necessary to carry out measurem
6. h current may be continuously adjustable from 0 to 100 Resistance ranges 0 2000 19 10 A 0 20 MQ 10 A 0 200 M 1A 0 2000 MQ 100 mA 0 20 0 10 mA 0 200 Q 1 mA Resolution gt 1nQ 10A Output voltage Up to 10 Vc c 1 A open circuit Measurement principle Four terminal Kelvin type Basic accuracy 0 2 of reading 2 digits Advanced features Digital direct reading of very low resistances in the alphanumerical display with up to 4 digits Very fast and accurate measurements Serial data output RS 232 4800 bps Suitable for data collection in an external serial printer computer or data logger Environmental protection IP54 with closed lid Safety class E M C Electrostatic immunity Power supply Built in battery charger Operating temperature range Storage temperature range Humidity range Maximum altitude Weight Dimensions Accessories Meets the requirements of IEC61010 1 1990 IEC 61010 1 1992 amendment 2 In accordance with IEC 61326 1 In accordance with IEC 1000 4 2 Internal battery powered Rechargeable battery sealed lead 12V 7Ah or mains MH 10 is manufactured in different versions to be compliant with the mains supply specifications in the destination country Please check the value indicated in the Control Panel in order to be sure that it is appro priate for the local A C supply 1 5 C to 50 C 1 25 C to 65 C 95 RH non condens
7. ing 3000m Approx 8 8 kg including battery and accessories 378 x 308 x 175mm e Combined current and potential leads with alligator clips 1 8m 2 Charger Power cord e RS 232 cable e Operating instructions Protective bag for instrument and cable ee
8. p Potential terminal P gt Potential terminal P Current terminal C RS 232 output ALPHANUMERIC DISPLAY that shows both the measured resistance value and user s messages START switch STOP switch HOLD switch It retains the last measurement in the display BATTERY Switch to measure the battery charge condition TEST CURRENT control 0 Scale and test CURRENT SELECTOR 1 ON led Mains supply MH 10 is manufactured in different versions to be compliant with the mains supply specifications in the destination coun try Please check the value indicated in the Control Panel in order to be sure that it is appropriate for the local A C sup ply Measurement 1 Before turning the equipment on connect the test leads to the item to be measured and to the front panel terminals ELEMENT TO BE MEASURED The alligator clamps in the drawings are only S for illustration The E i E supplied clamps could 1 shown in the drawing be different than what s 2 Using the CURRENT SELECTORO choose the range and the current to be used 3 Choose the power supply to use If you are going to use the battery advance to the following point If you are going to use the mains supply plug the power cord into the connectorv 4 Switch the equipment on using the ON OFF ee 5 The PRESS START message will appear showing tha
9. t measurement can be started Press the START switch Depending on the position of the TEST CURRENT control the LOW CURRENT message will turn up 6 Turning the TEST CURRENT control clockwise increases the current Adjust this control until obtaining the desired value or until the current indicator bar graph indicates 100 The bar graph will show the test current value as a percentage of the nominal value selected by using the CURRENT SELECTORO 7 The lowest current for measuring is 10 of the scale nominal value It is important to consider that the measure ment errors increase while test current decreases The error is specified for test currents higher than 80 8 The DISPLAY will show the resistance value measured and the corresponding unit QA ohms mA milli ohms or uQ micro ohms 9 That value can be retained in the display by pressing the HOLD key Pressing this key again the value will be erased 10 Press the STOP switch in order to finish the measurement 11 Finally when finishing measurements turn the equipment off using the ON OFF switch Precaution Do not connect or disconnect the test leads during the measurement Messages CIRCUTOR MH 10 When turning the equipment on using the ON OFF switch this introductory message appears for a while During that time the equipment carries out some functional checking WAIT This message appears each time the equipment needs to adjust any parameter in ord
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