METREL MicroOhm 2A MI 3242 User manual

MicroOhm 2A
MI 3242
Instruction manual
Version 1.0, Code no 20 752 011

2
Distributor:
Manufacturer:
METREL d.d.
Ljubljanska cesta 77
1354 Horjul
Slovenia
web site: http://www.metrel.si
e-mail: [email protected]
Mark on your equipment certifies that this equipment meets the requirements of the EU
(European Union) concerning safety and electromagnetic compatibility regulations
© 2012 METREL
No part of this publication may be reproduced or utilized in any form or by any means
without permission in writing from METREL.

MI 3242 MicroOhm 2A Table of contents
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Table of contents
1General description................................................................................................5
1.1 Features ............................................................................................................5
2Safety and operational considerations.................................................................6
2.1 Warnings and notes ..........................................................................................6
2.2 Battery and charging .........................................................................................8
2.2.1 New battery cells or cells unused for a longer period ........................................... 9
2.3 Standards applied ...........................................................................................10
3Instrument description.........................................................................................11
3.1 Front panel ......................................................................................................11
3.2 Connector panel ..............................................................................................12
3.3 Back side.........................................................................................................13
3.4 Accessories .....................................................................................................14
3.5 Display organization ........................................................................................15
3.5.1 Battery and time indication.................................................................................. 15
3.5.2 Message field ...................................................................................................... 15
3.5.3 Help screens ....................................................................................................... 16
3.5.4 Backlight and contrast adjustments .................................................................... 17
4Instrument operation............................................................................................18
4.1 Function selection ...........................................................................................18
5Settings menu.......................................................................................................19
5.1 Selection language..........................................................................................19
5.2 Initial settings...................................................................................................20
5.3 Limits settings..................................................................................................20
5.4 Memory ...........................................................................................................21
5.5 Setting date and time ......................................................................................21
5.6 Instrument info.................................................................................................22
6Measurements ......................................................................................................23
6.1 Four wire Kelvin method..................................................................................23
6.2 Resistance measurement................................................................................24
6.2.1 Single Mode ........................................................................................................ 25
6.2.2 Continuous Mode ................................................................................................ 26
6.2.3 Auto Mode........................................................................................................... 27
6.2.4 Inductive Mode.................................................................................................... 28
6.3 Voltage TRMS .................................................................................................29
7Data handling........................................................................................................30
7.1 Memory organization.......................................................................................30
7.2 Data structure..................................................................................................30
7.3 Storing test results...........................................................................................31
7.4 Recalling test results .......................................................................................32
7.5 Clearing stored data ........................................................................................33
7.5.1 Clearing complete memory content .................................................................... 33
7.5.2 Clearing measurement(s) in selected location .................................................... 34

MI 3242 MicroOhm 2A Table of contents
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7.5.3 Clearing individual measurements ...................................................................... 34
9Maintenance..........................................................................................................37
9.1 Cleaning ..........................................................................................................37
9.2 Periodic calibration ..........................................................................................37
9.3 Service ............................................................................................................37
10 Technical specifications...................................................................................38
10.1 Resistance measurement................................................................................38
10.2 Measurement parameters ...............................................................................39
10.3 Voltage and frequency.....................................................................................39
10.3.1 Voltage ................................................................................................................ 39
10.3.2 Frequency ........................................................................................................... 39
10.4 General data....................................................................................................40

MI 3242 MicroOhm 2A General description
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1 General description
1.1 Features
MI 3242 MicroOhm 2A is a portable, lightweight (< 1.5 kg) bidirectional low resistance
ohmmeter using four wire Kelvin method to measure low resistances of:
Switches
Relays
Connectors
Bus bars
Power distribution cable joints
Motor & generator winding
Power transformers
Power inductors
Rail track joints
Wire and cable resistance
Welding joints
The instrument is designed and produced with the extensive knowledge and experience
acquired through many years of of working in this sector.
Available functions offered by the MicroOhm 2A meter:
Resistance measurement (Four wire Kelvin method);
High Resolution 24-Bit Σ-ΔADC
Wide measuring range (1 μΩ ... 199.9 Ω);
Adjustable test current (10 mA ... 2 A);
Hi/Lo limits;
Automatic thermal EMF elimination;
Noise rejection (50/60 Hz);
Four different measuring modes (single, continuous, inductive, automatic);
USB and RS232 communication;
TRMS voltage meter;
High over-voltage category CAT III 600V.
A 128x64 dot matrix LCD offers easy-to-read results and all associated parameters.
The operation is straightforward and clear to enable the user to operate the instrument
without the need for special training (except reading and understanding this Instruction
Manual).
Test results can be stored on the instrument. PC software HVLink PRO that is supplied
as a part of standard set enables transfer of measured results to PC where can be
analysed or printed.

MI 3242 MicroOhm 2A Safety and operational considerations
6
2 Safety and operational considerations
2.1 Warnings and notes
In order to maintain the highest level of operator safety while carrying out various tests
and measurements Metrel recommends keeping your MicroOhm 2A instruments in
good condition and undamaged. When using the instrument, consider the following
general warnings:
The symbol on the instrument means »Read the Instruction manual
with special care for safe operation«. The symbol requires an action!
If the test equipment is used in a manner not specified in this user manual,
the protection provided by the equipment could be impaired!
Read this user manual carefully, otherwise the use of the instrument may
be dangerous for the operator, the instrument or for the equipment under
test!
Do not use the instrument or any of the accessories if any damage is
noticed!
Consider all generally known precautions in order to avoid risk of electric
shock while dealing with hazardous voltages!
Do not use the instrument in supply systems with voltages higher than
600 V!
Service intervention or adjustment is only allowed to be carried out by
competent authorized personnel!
Use only standard or optional test accessories supplied by your
distributor!
The instrument comes supplied with rechargeable Ni-MH battery cells. The
cells should only be replaced with the same type as defined on the battery
compartment label or as described in this manual. Do not use standard
alkaline battery cells while the power supply adapter is connected,
otherwise they may explode!
Hazardous voltages exist inside the instrument. Disconnect all test leads
and switch off the instrument before opening the battery compartment.

MI 3242 MicroOhm 2A Safety and operational considerations
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Warnings related to measurement functions:
Resistance, voltage and frequency measurements
Resistance measurement should only be performed on de-energized objects!
Do not touch the test object during the measurement or before it is fully
discharged! Risk of electric shock!
When a resistance measurement has been performed on an inductive object,
automatic discharge may not be done immediately!
Do not connect test terminals to external voltage higher than 600 V (AC or DC) in
order not to damage the test instrument!
Notes related to measurement functions:
General
Warning will appear on screen and the resistance test will not be performed if
voltages higher than 8 V (AC or DC) are detected between test terminals. There
will be no warning if all terminals are at the same potential.
PASS / FAIL indication is enabled when limit is set. Apply appropriate limit value
for evaluation of measurement results.
The internal memory is full!

MI 3242 MicroOhm 2A Safety and operational considerations
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2.2 Battery and charging
The instrument uses six AA size alkaline or rechargeable Ni-MH battery cells. Nominal
operating time is declared for cells with nominal capacity of 2100 mAh.
Battery condition is always displayed in the lower right display part.
In case the battery is too weak the instrument indicates this as shown in figure 2.1. This
indication appears for a few seconds and then the instrument turns itself off.
Figure 2.1: Discharged battery indication
The battery is charged whenever the power supply adapter is connected to the
instrument. The power supply socket polarity is shown in figure 2.2. Internal circuit
controls charging and assures maximum battery lifetime.
+
-
Figure 2.2: Power supply socket polarity
The instrument automatically recognizes the connected power supply adapter and
begins charging.
Symbols:
Indication of battery charging
Figure 2.3: Charging indication
When connected to an installation, the instruments battery compartment can
contain hazardous voltage inside! When replacing battery cells or before
opening the battery compartment cover, disconnect any measuring accessory
connected to the instrument and turn off the instrument,
Ensure that the battery cells are inserted correctly otherwise the instrument will
not operate and the batteries could be discharged.
If the instrument is not to be used for a long period of time, remove all batteries
from the battery compartment.
Alkaline or rechargeable Ni-MH batteries (size AA) can be used. Metrel
recommends only using rechargeable batteries with a capacity of 2100mAh or
above.
Do not recharge alkaline battery cells!

MI 3242 MicroOhm 2A Safety and operational considerations
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Use only power supply adapter delivered from the manufacturer or distributor of
the test equipment to avoid possible fire or electric shock!
2.2.1 New battery cells or cells unused for a longer period
Unpredictable chemical processes can occur during the charging of new battery cells or
cells that have been left unused for a longer period (more than 3 months). Ni-MH and
Ni-Cd cells can be subjected to these chemical effects (sometimes called the memory
effect). As a result the instrument operation time can be significantly reduced during the
initial charging/discharging cycles of the batteries.
In this situation, Metrel recommend the following procedure to improve the battery
lifetime:
Procedure Notes
Completely charge the battery. At least 14h with in-built charger.
Completely discharge the battery.
This can be performed by using the
instrument normally until the instrument is
fully discharged.
Repeat the charge / discharge cycle
at least 2-4 times.
Four cycles are recommended in order to
restore the batteries to their normal
capacity.
Notes:
The charger in the instrument is a pack cell charger. This means that the battery
cells are connected in series during the charging. The battery cells have to be
equivalent (same charge condition, same type and age).
One different battery cell can cause an improper charging and incorrect
discharging during normal usage of the entire battery pack (it results in heating of
the battery pack, significantly decreased operation time, reversed polarity of
defective cell,…).
If no improvement is achieved after several charge / discharge cycles, then each
battery cell should be checked (by comparing battery voltages, testing them in a
cell charger, etc). It is very likely that only some of the battery cells are
deteriorated.
The effects described above should not be confused with the normal decrease of
battery capacity over time. Battery also loses some capacity when it is repeatedly
charged / discharged. Actual decreasing of capacity, versus number of charging
cycles, depends on battery type. This information is provided in the technical
specification from battery manufacturer.

MI 3242 MicroOhm 2A Safety and operational considerations
10
2.3 Standards applied
The MicroOhm 2A instruments are manufactured and tested in accordance with the
following regulations:
Electromagnetic compatibility (EMC)
EN 61326 Electrical equipment for measurement, control and laboratory
use – EMC requirements
Class A
Safety (LVD)
EN 61010-1 Safety requirements for electrical equipment for measurement,
control and laboratory use – Part 1: General requirements
EN 61010-2-030 Safety requirements for electrical equipment for measurement,
control and laboratory use – Part 2-030: Particular requirements for
testing and measuring circuits
EN 61010-031 Safety requirements for electrical equipment for measurement,
control and laboratory use – Part 031: Safety requirements for hand-
held probe assemblies for electrical measurement and test
Note about EN and IEC standards:
Text of this manual contains references to European standards. All standards of
EN 6XXXX (e.g. EN 61010) series are equivalent to IEC standards with the same
number (e.g. IEC 61010) and differ only in amended parts required by European
harmonization procedure.

MI 3242 MicroOhm 2A Instrument description
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3 Instrument description
3.1 Front panel
The operator’s panel is shown in Figure 3.1 below.
Figure 3.1: Front panel
Legend:
1 LCD 128 x 64 dots matrix display with backlight.
4 TEST Starts testing / confirms selected option
5 UP
6 DOWN Modifies selected parameter.
7 MEM Store / recall tests in memory of instrument.
8
11 Function selector Selects test function.
9 Backlight,
Contrast Changes backlight level and contrast.
Switches the instrument power on or off.
10 ON / OFF The instrument automatically turns off 15 minutes after the
last key was pressed.
12 HELP Accesses help menus.
13 TAB Selects the parameters in selected function.
2 FAIL Red indicator
3 PASS Green indicator Indicates PASS/ FAIL of result.

MI 3242 MicroOhm 2A Instrument description
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3.2 Connector panel
Figure 3.2: Connector panel
Legend:
1 Test connector Measuring inputs / outputs
2 Protection cover
3 Charger socket For connection of external charger
4 USB connector Communication with PC USB (1.1) port
5 PS/2 connector Communication with printer
Communication with PC RS-232 port
Warnings!
Maximum allowed voltage between any test terminal and ground is 600 V!
Maximum allowed voltage between test terminals is 600 V!
Maximum short-term voltage of external power supply adapter is 14 V!
Use original test accessories only!

MI 3242 MicroOhm 2A Instrument description
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3.3 Back side
Figure 3.3: Back side
Legend:
1 Inserts for side belt
2 Battery compartment cover
3 Fixing screw for battery compartment cover
4 Back side information label
5 Holder for inclined position of the instrument
Figure 3.4: Battery compartment
Legend:
1 Battery cells Size AA, alkaline or rechargeable NiMH
2 Serial number label

MI 3242 MicroOhm 2A Instrument description
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3.4 Accessories
The accessories consist of standard and optional accessories. Optional accessories can
be delivered upon request. See attached list for standard configuration and options or
contact your distributor or see the METREL home page: http://www.metrel.si.
Figure 3.5: Standard set of the instrument
Instrument MI 3242 MicroOhm 2A
Test lead, 2,5 m, 1 pcs (black, red)
Crocodile clip, 4 pcs (black, red)
Test probe, 2 pcs (black)
Small soft carrying bag
Set of NiMH battery cells 6pcs
Power supply adapter
RS232 – PS2 serial cable
USB cable
PC SW HVLink PRO
Instruction manual (on CD)
Calibration certificate

MI 3242 MicroOhm 2A Instrument description
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3.5 Display organization
Figure 3.6: Typical function
display
Function name
Result field
Test parameter field
Message field
Battery and time
indication
3.5.1 Battery and time indication
The indication indicates the charge condition of battery and connection of external
charger.
Battery capacity indication.
Low battery.
Battery is too weak to guarantee correct result. Replace or
recharge the battery cells.
Recharging in progress (if power supply adapter is connected).
Time indication (hh:mm).
Warning:
If the batteries are removed for more than 1 minute, set time and date will be lost
and Initial settings will be restored.
Note:
Date and time is attached to each stored result.
3.5.2 Message field
In the message field warnings and messages are displayed.
Test result can be saved.
High voltage is present on terminals.
Measurement in progress.

MI 3242 MicroOhm 2A Instrument description
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P1, P2, C1 or C2 terminal is not connected to the instrument or
too high resistance is detected.
Low test current (test current is out of defined limits Iset -10%).
Measurement result is within defined limits.
Measurement result is out of defined limits.
Measurement result is out of defined high limit.
Measurement result is out of defined low limit.
3.5.3 Help screens
HELP Opens help screen.
Help menus are available in all functions. The Help menu contains schematic diagrams
for illustrating how to properly connect the instrument to the test object.
Press the HELP key in order to view the associated Help menu.
Keys in help menu:
UP / DOWN Selects next / previous help screen.
Function selector / HELP Exits help menu.
Figure 3.7: Examples of help screens

MI 3242 MicroOhm 2A Instrument description
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3.5.4 Backlight and contrast adjustments
With the BACKLIGHT (☼) key backlight and contrast can be adjusted.
Click Toggles backlight intensity level.
Keep pressed for 1 s Locks high intensity backlight level until power is turned off or
the key is pressed again.
Keep pressed for 2 s Bargraph for LCD contrast adjustment is displayed.
Figure 3.8: Contrast adjustment menu
Keys for contrast adjustment:
DOWN Reduces contrast.
UP Increases contrast.
TEST Accepts new contrast.
BACKLIGHT (☼) Exits without changes.

MI 3242 MicroOhm 2A Instrument operation
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4 Instrument operation
4.1 Function selection
For selecting test function the FUNCTION SELECTOR shall be used.
Keys:
FUNCTION
SELECTOR
Select test / measurement function:
<RESISTANCE> Resistance measurement.
<VOLTAGE TRMS> Voltage and frequency measurement.
<SETTINGS> General instrument settings.
UP/DOWN Selects sub-function in selected measurement function.
TAB Selects the test parameter to be set or modified.
TEST Runs selected test / measurement function.
Keys in test parameter field:
UP/DOWN Changes the selected parameter.
TAB Selects the next measuring parameter.
FUNCTION SELECTOR Exits test parameter field selection.

MI 3242 MicroOhm 2A Settings menu
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5 Settings menu
In the Settings menu different parameters of the instrument can be viewed or set.
Figure 5.1: Settings menu
Keys:
UP/DOWN Select the setting to adjust or view:
<SELECT LANGUAGE> instrument language;
<INITIAL SETTINGS> factory settings.
<LIMITS SETTINGS> limit values selection;
<MEMORY> to recall or clear stored results;
<SET DATE/TIME> date and time;
<INSTRUMENT INFO> basic instrument information.
TEST Confirms selection.
FUNCTION
SELECTOR
Returns to the Main menu.
5.1 Selection language
The instrument language can be set in this menu.
Figure 5.2: Language menu
Keys:
UP/DOWN Selects the language.
TEST Confirms selection and returns to Settings menu.
FUNCTION
SELECTOR Returns to Main menu without changes.

MI 3242 MicroOhm 2A Settings menu
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5.2 Initial settings
In this menu the following instrument parameters can be set to their initial values:
all measurement parameters;
LCD settings;
language;
Figure 5.3: Initial settings menu
Keys:
TAB Selects YES or NO
TEST
Confirms selection.
The instrument will restart with the default settings (if YES is selected).
Returns to the Settings menu without changes (if NO is selected).
FUNCTION
SELECTOR Returns to Main menu without changes.
5.3 Limits settings
With High and Low limit the user is allowed to set limit resistance values. Measured
resistance is compared against those limits. Result is validated only if it is within the
given limits.
Figure 5.4: Limits settings menu
Parameters for Limits settings:
Limit Hi
Limit Lo
Resistance limit value [OFF, 1.00 μΩ - 10.00 μΩ, 20.0 μΩ - 100.0 μΩ,
0.200 mΩ- 1.000 mΩ, 2.00 mΩ- 10.00 mΩ, 20.0 mΩ- 100.0 mΩ,
0.200 Ω- 1.000 Ω, 2.00 Ω- 10.00 Ω, 20.0 Ω- 200.0 Ω]
Keys:
UP/DOWN Selects the High or Low limit to be modified.
TEST Enters Limits modification screen.
FUNCTION
SELECTOR Returns to Main menu without changes.
Figure 5.5: Limits modifications