Extech Instruments MG325 User manual

USER MANUAL
Insulation Tester + DMM
Model MG325

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TableofContents
1.INTRODUCTION3
2.SAFETY3
3.METERDESCRIPTION5
4.CONTROLBUTTONS6
5.SYMBOLSANDANNUNCIATORS6
6.OPERATINGINSTRUCTIONS7
6.1DisplayBacklight7
6.2DataHold7
6.3LowBatteryIndication7
6.4DCVOLTAGEMEASUREMENTS7
6.5ACVOLTAGEMEASUREMENTS8
6.6RESISTANCEMEASUREMENTS9
6.7CONTINUITYMEASUREMENTS10
6.8CAPACITANCEMEASUREMENTS11
6.9INSULATIONRESISTANCEMEASUREMENTS12
6.9.1DisableLockModeforInsulationandContinuityTests13
6.9.2InsulationResistanceTestTimer13
6.9.3DielectricAbsorptionRatio[DAR]InsulationTesting13
6.9.4PolarizationIndex[PI]InsulationTesting14
6.9.5ComparatorUtility14
7.DATARECORDING15
8.SETUPMODE15
9.MAINTENANCE16
9.1BATTERYINSTALLATION16
9.2REPLACINGTHEFUSE16
10.SPECIFICATIONS17

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1. Introduction
Congratulations on your purchase of the MG325 True RMS Insulation Resistance CAT IV 600V DMM.
The MG325 features a rugged design for heavy duty use. The MG325 measures Insulation
Resistance, AC/DC Voltage, Frequency, Leakage Current, Low Resistance, Continuity, and
Capacitance. Insulation Resistance tests are automatic ranging with 5 test voltages from 50V to
1000V. The MG325 can store and recall up to 99 measurements.
The MG325 is suitable for measuring the insulation resistance on elecrical equipment such as
transformers, motors, cables, switches, and appliances.
Proper use and care of this meter will provide years of reliable service.
Features
DC and True RMS AC Voltage Measurments to 600V
Insulation Resistance Measurements up to 200G
Frequency of the AC Voltage
Leakage Current Insulation test mode
Capacitance Measurements
Low Resistance and Continuity Measurements with ZERO function
Auto Ranging measurments
Polarization Index (PI) and Dielectric Aborption Ratio (DAR) tests
Five (5) Insulation Resistance test voltages (50, 100, 250, 500, and 1000V)
Insulation Resistance tests in 10% voltage steps (from 50% to 120% of range)
Eight (8) Insulation Resistance measurement ranges (automatic ranging)
Pass/Fail Comparator function for Insulation Resistance and Continuity
Auto-discharge at end of test
Output voltage alert light and display symbols
Hand’s free test lock feature
Manually store and recall up to 99 readings
Overload indication
Remote test probe for controlling the TEST button remotely
Test leads, alligator clips, batteries, user manual, and case included
2. Safety
Warning and Caution safety label
Double Insulation
DC Direct Current
AC Alternating Current
Low Battery
Fuse symbol
High Voltage Alert
Audible beeper
Earth ground
Complies with EC standard

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PER IEC1010 OVERVOLTAGE INSTALLATION CATEGORY
OVERVOLTAGE CATEGORY I
Equipment of OVERVOLTAGE CATEGORY I is equipment for connection to circuits in which measures are taken
to limit the transient over-voltages to an appropriate low level.
Note – Examples include protected electronic circuits.
OVERVOLTAGE CATEGORY II
Equipment of OVERVOLTAGE CATEGORY II is energy-consuming equipment to be supplied from the fixed
installation.
Note – Examples include household, office, and laboratory appliances.
OVERVOLTAGE CATEGORY III
Equipment of OVERVOLTAGE CATEGORY III is equipment in fixed installations.
Note – Examples include switches in the fixed installation and some equipment for industrial use with permanent
connection to the fixed installation.
OVERVOLTAGE CATEGORY IV
Equipment of OVERVOLTAGE CATEGORY IV is for use at the origin of the installation.
Note – Examples include electricity meters and primary over-current protection equipment
SAFETY INSTRUCTIONS
This meter has been designed for safe use, but must be operated with caution. The rules listed below
must be carefully followed for safe operation.
1. NEVER apply voltage to the meter that exceeds the specified maximum:
Input Protection Limits
Function Maximum Input
V DC or V AC 600VDC/AC rms
Low Resistance 250VDC/AC rms
Capacitance 250VDC/AC rms
Insulation Resistance and Continuity 250VDC/AC rms
Surge Protection: 8kV peak per IEC 61010
2. USE EXTREME CAUTION when working with high voltages.
3. DO NOT measure voltage if the voltage on the "COM" input jack exceeds 600V above earth
ground.
4. NEVER connect the meter leads across a voltage source while the function switch is in the
resistance mode. Doing so can damage the meter.
5. ALWAYS discharge filter capacitors in power supplies and disconnect the power when making
resistance, continuity, and capacitance tests.
6. ALWAYS turn off the power and disconnect the test leads before opening the covers to replace
the fuse or batteries.
7. NEVER operate the meter unless the battery/fuse cover is in place and fastened securely.
8. If the equipment is used in a manner not specified by the manufacturer, the protection provided
by the equipment may be impaired.

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SAFETY STANDARDS
This instrument is designed and produced strictly in accordance with the safety requirements for GB4793 electronic
measuring instruments and IEC61010-1 safety standards. This instrument meets the double insulation over-voltage
standard CAT IV 600V and pollution degree II. Failure to use the instrument as described in this user manual can
weaken or negate the protections provided.
Check the instrument, test leads, and test pen before use. Check for any abnormal conditions such as
exposed test lead wire, damaged meter housing, no display or random display errors.
Do not use this instrument with an open battery compartment.
Damaged test leads must be replaced with those of the same type or specifications.
Do not touch bare wires or conductors, unused input terminals, or the circuit being measured when the
instrument is in operation.
Use caution when measuring voltages greater than 42V DC or 30V AC. Keep fingers behind the finger guard
on the test leads to avoid electrical shocks when measuring.
Do not apply signals greater than those specified between any two terminals or any terminal and ground.
Set the function switch the correct position before beginning a test. Never move the function switch during a
test. Please stop testing and remove connections to the circuit under test before moving the function switch to
a new position.
Do not store or use the instrument in an explosive or flammable environment or an environment characterized
by high temperature, high humidity, or strong electromagnetic fields.
There are no user-serviceable parts in this instrument. Please refer all service and repairs to Extech
Instruments.
Replace the batteries as soon as the low battery icon appears in order to ensure the highest measurement
accuracy.
3. MeterDescription
1. 5999 count backlit LCD display with bargraph
2. Control buttons; detailed in next section
3. Rotary function switch
4. Continuity (+) positive input jack
5. Continuity (-) COM input jack
6. Insulation, Voltage, Capacitance, Resistance (-) input jack
7. Insulation, Voltage, Capacitance, Resistance (+) input jack
8. Test Voltage alert LED indicator
Note: Tilt stand and battery compartment on back
1
2
3
4
56
7
8

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4. Controlbuttons
1. Data Hold on/off (short press) for AC/DC Voltage,
Resistance and Capacitance modes only. Also for
display Backlight on/off (long press)
2. Short press to Recall stored readings. Another
short press to exit this mode. Also used as an
ENTER confirmation button in SETUP mode.
3. Save reading (short press) and Clear all stored
readings (long press)
4. Comparator (short press) and Zero (long press)
5. PI and DAR test mode selection (short presses). Also used to access the SETUP mode (long
press) where Insulation Resistance and Continuity tests can be customized.
6. Insulation Test Lock button (long press to activate/deactivate lock mode)
7. Up arrow for menu navigation and for scrolling recalled readings
8. Down arrow for menu navigation and scrolling recalled readings. Also used to select
capacitance or resistance modes when the function switch is set to the capacitance and
resistance position.
9. Press to start Insulation or Low Resistance tests. Insulation tests output high voltages and
measure insulation resistance.
5. SymbolsandAnnunciators
1. Test voltage output alert
2. ZERO function
3. Battery status
4. Audible beeper
5. TEST in progress
6. Test lock ON
7. PI/DAR test modes
8. Elapsed Timer ON
9. Auxiliary display
10. Main display
11. PI/DAR test time area
12. Bargraph measurement representation
13. Comparator area: Test [PASS, FAIL], units [K, M], and reference value.
14. Over-range alert symbol
15. Save/Recall readings memory (01-99); Data Hold [H] icon is also shown in this area
1
2
3
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6
7
8
9
1234 56 7
15
8
9
10
11
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6. OperatingInstructions
WARNING: Risk of electrocution. High-voltage circuits, both AC and DC, are very dangerous and should be
measured with great care.
1. ALWAYS turn the function switch to the OFF position when the meter is not in use.
2. If “>” appears in the display during a measurement, the value exceeds the maximum range of
the meter.
6.1 Display Backlight
Press and hold the button to switch the backlight on or off. Excessive use of the backlight will
cause the batteries to drain quicker.
6.2 Data Hold
The Data Hold function freezes the reading in the display. To freeze or unfreeze the reading, press
H (Data Hold) key. The Hicon is shown when data hold is active. This mode is only available for the
AC/DC Voltage, Resistance, and Capacitance modes.
6.3 Low Battery Indication
When the icon appears in the display, the battery must be replaced. See the Maintenance
section for details on battery and fuse replacement.
6.4 DC VOLTAGE MEASUREMENTS
CAUTION:
When the measured voltage is > 42VDC or 600VAC the meter flashes the warning icon on the upper left.
Do not measure DC voltages if a motor on the circuit is being switched ON or OFF. Large voltage surges may
occur that can damage the meter.
1. Set the function switch to the position.
2. Insert the black test lead banana plug into the negative EARTH jack
(6).
Insert the red test lead banana plug into the positive Vjack (7).
3. Touch the black test probe tip to the negative side of the circuit.
Touch the red test probe tip to the positive side of the circuit.
4. Read the Voltage in the main display and in the lower bargraph.
5. Press the button to store the reading.
6. Short press the H (Hold) button to freeze (Hicon displayed) or
unfreeze (no Hicon displayed) the displayed reading.
7. Note that the Auto Power OFF function activates after 10 minutes of
inactivity. The meter will audibly beep just prior to shutting off.
V DC
100 200 300 4000 500 600 700

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6.5 AC VOLTAGE MEASUREMENTS
WARNING: Risk of Electrocution. The probe tips may not be long enough to contact the live parts inside
some 240V outlets for appliances because the contacts are recessed deep in the outlets. As a result, the reading
may show 0 volts when the outlet actually has voltage on it. Make sure the probe tips are touching the metal
contacts inside the outlet before assuming that no voltage is present.
CAUTION
Do not measure AC voltages if a motor on the circuit is being switched ON or OFF. Large voltage surges may
occur that can damage the meter.
Do not measure voltages higher than 600V
When the measured voltage is > 60VDC or 600VAC the meter flashes the warning icon on the upper left.
Do not measure AC voltages if a motor on the circuit is being switched ON or OFF. Large voltage surges may
occur that can damage the meter.
1. Set the function switch to the position.
2. Insert the black test lead banana plug into the negative EARTH
jack (6).
Insert red test lead banana plug into the positive Vjack (7).
3. Touch the black test probe tip to the neutral side of the circuit.
Touch the red test probe tip to the “hot” side of the circuit.
4. Read the voltage in the main display and in the lower bargraph.
5. Read the Frequency in the auxiliary display (upper right)
6. Short press the H (Hold) button to freeze (Hicon displayed) or
unfreeze (no Hicon displayed) the displayed reading.
7. Press to store the reading
8. Note that the Auto Power OFF function activates after 10
minutes of inactivity. The meter will audibly beep just prior to
shutting off.
Hz
V AC
100 200 300 4000 500 600 700

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6.6 RESISTANCE MEASUREMENTS
WARNING: To avoid electric shock, disconnect power to the unit under test and discharge all capacitors
before taking resistance measurements. Remove the batteries and unplug the line cords.
WARNING: To avoid electric shock, never measure resistance on circuits or wires that have a voltage.
1. Set the function switch to the k Ωposition.
2. Insert the black test lead banana plug into the negative
EARTH jack (6).
Insert the red test lead banana plug into the positive jack
(7).
3. Use the button to choose the Resistance mode (the
button toggles Capacitance and Resistance modes).
4. Reset the display to zero before testing: Short the test
probes and note the value. Short the test probes again and
press and hold ZERO until ZERO is displayed (0.00Ω
reading when successful). Press and hold ZERO again to
exit.
5. Before testing, it is best to disconnect one side of the part
under test so that other circuits do not interfere with the
resistance reading.
6. Touch the test probe tips across the circuit or part under test.
7. Read the resistance in the main display and with the lower
bargraph.
8. If the circuit is open, the display will indicate “>”. If 2V or
more are sensed on the device under test, the meter will
stop the test.
9. Short press the H (Hold) button to freeze (Hicon displayed)
or unfreeze (no Hicon displayed) the displayed reading.
10. Press to store the reading
11. Note that the Auto Power OFF function activates after 10 minutes of inactivity. The meter will
audibly beep just prior to shutting off.
k

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6.7 CONTINUITY MEASUREMENTS
WARNING: To avoid electric shock, disconnect power to the unit under test and discharge all capacitors
before taking continuity measurements. Remove the batteries and unplug the line cords.
WARNING: To avoid electric shock, never measure continuity on circuits or wires that have a voltage.
1. Set the function switch to the position.
2. Insert the black test lead banana plug into the negative
COM jack (5).
Insert the red test lead banana plug into the positive
jack (4).
3. Press the TEST button on the meter (or on the test leads, if
using the test lead with the TEST button) to put the meter
in test mode. The display will show TEST and the alert
LED will light.
4. The meter defaults to test lock mode (lock icon displayed)
so the test will run without having to hold TEST. Press and
hold the lock button to change to manual test mode (TEST
button must be held throughout the test).
5. Reset the display to zero before testing: Short the test
probes and note the value. Short the test probes again and
press and hold ZERO until ZERO is displayed (0.00Ω
reading when successful). Press and hold ZERO again to
exit.
6. Touch the test probe tips across the circuit or part under
test.
7. If the continuity buzzer is turned on in the SETUP mode,
the buzzer will sound if the resistance <30. Read the
resistance in the main display and with the lower bargraph.
8. If the circuit is open, the display will indicate “>”. If 2V or more are sensed on the device under
test, the meter will stop the test and ‘UE HI TEST’ will display.
9. If the ‘FU FAIL’ prompt appears, the fuse must be replaced before use (see the Maintenance
section for fuse and battery replacement information).
10. Short press the H (Hold) button to freeze (Hicon displayed) or unfreeze (no Hicon displayed)
the displayed reading.
11. Press to store the reading
12. Note that the Auto Power OFF function activates after 10 minutes of inactivity. The meter will
audibly beep just prior to shutting off.
mA
TEST
>