Extech Instruments MN25 User manual

User's Guide
MiniTecTM Series
Model MN25 MultiMeter

MN25 Version 2.2 Aug 2003
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Warranty
EXTECH INSTRUMENTS CORPORATION warrants this instrument to be
free of defects in parts and workmanship for one year from date of shipment
(a six month limited warranty applies on sensors and cables). If it should
become necessary to return the instrument for service during or beyond the
warranty period, contact the Customer Service Department at (781) 890-
7440 ext. 210 for authorization or visit our website at www.extech.com (click
on ‘Contact Extech’ and go to ‘Service Department’ to request an RA
number). A Return Authorization (RA) number must be issued before any
product is returned to Extech. The sender is responsible for shipping
charges, freight, insurance and proper packaging to prevent damage in
transit. This warranty does not apply to defects resulting from action of the
user such as misuse, improper wiring, operation outside of specification,
improper maintenance or repair, or unauthorized modification. Extech
specifically disclaims any implied warranties or merchantability or fitness for
a specific purpose and will not be liable for any direct, indirect, incidental or
consequential damages. Extech's total liability is limited to repair or
replacement of the product. The warranty set forth above is inclusive and no
other warranty, whether written or oral, is expressed or implied.
Introduction
Congratulations on your purchase of Extech’s MN25Multimeter.
This meter measures AC/DC Voltage, AC/DC Current,
Resistance, Capacitance, Frequency, Duty Cycle, Temperature,
Diode Test and Continuity. Proper use and care of this meter will
provide many years of reliable service.

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Safety
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 or current to the meter that exceeds
the specified maximum:
Input Limits
Function Maximum Input
V DC, V AC 600V DC/AC, 200Vrms on 200mV range
mA DC 200mA 250V fast acting fuse
A DC, A AC 10A 250V fast acting fuse(30 seconds
max every 15 minutes)
Resistance,
Continuity
250Vrms for 15sec max
2. USE EXTREME CAUTION when working with high
voltages.
3. DO NOT measure voltage if the voltage on the "COM"
input jack exceeds 500V above earth ground.
4. NEVER connect the meter leads across a voltage source
while the function switch is in the current, resistance, or
diode mode. Doing so can damage the meter.
5. ALWAYS discharge filter capacitors in power supplies and
disconnect the power when making resistance or diode
tests.
6. ALWAYS turn off the power and disconnect the test leads
before opening the doors to replace the fuse or batteries.

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Safety Symbols
NEVER operate the meter unless the back
cover and the battery and fuse doors are in
place and fastened securely. This symbol
adjacent to another symbol, terminal or
operating device indicates that the operator
must refer to an explanation in the Operating
Instructions to avoid personal injury or
damage to the meter.
This WARNING symbol indicates a potentially
hazardous situation, which if not avoided,
could result in death or serious injury.
This CAUTION symbol indicates a potentially
hazardous situation, which if not avoided, may
result damage to the product.
This symbol advises the user that the
terminal(s) so marked must not be connected
to a circuit point at which the voltage with
respect to earth ground exceeds (in this case)
500 VAC or VDC.
This symbol adjacent to one or more terminals
identifies them as being associated with
ranges that may, in normal use, be subjected
to particularly hazardous voltages. For
maximum safety, the meter and its test leads
should not be handled when these terminals
are energized.
This symbol indicates that a device is
protected throughout by double insulation or
reinforced insulation.
WARNING
CAUTION
MAX
500V

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Specifications
Function Range Resolution Accuracy
200mV 0.1mV
2000mV 1mV
20V 0.01V
200V 0.1V
DC Voltage
(V DC)
600V 1V
±(0.5% reading + 2
digits)
200V 0.1VAC Voltage
(V AC) 600V 1V
±(1.5% reading + 5 digits
(Frequency 50/60Hz)
200mA 100µA ±(1.2% reading + 2
digits)
DC Current
(A DC)
10A 10mA
±(2.0% reading + 2
digits)
200mA 100µA ±(1.8% reading + 5
digits)
AC Current
(A AC)
10A 10mA
±(3.0% reading + 5
digits)
200Ω0.1Ω
2000Ω1Ω
20kΩ0.01kΩ
200kΩ0.1kΩ
±(0.8% reading + 2
digits)
Resistance
2000kΩ1kΩ±(1.0% reading + 2
digits)
9V 10mVBattery Test
1.5V 10mV
±(1.0% reading + 2
digits)
NOTE: Accuracy specifications consist of two elements:
•(% reading) – This is the accuracy of the measurement circuit.
•(+ digits) – This is the accuracy of the analog to digital
converter.
NOTE: Accuracy is stated at 65oF to 83oF (18oC to 28oC) and less
than 75% RH.

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Display 3 ½ digit, 2000 count LCD, 0.5” digits
Overrange indication “1” is displayed
Diode Test Test current of 1mA maximum, open
circuit voltage 2.8V DC typical
Continuity Check Audible signal will sound if the
resistance is less than approximately
30Ω
Battery Test current 9V (6mA); 1.5V (100mA)
Input Impedance >1MΩ
ACV Bandwidth 45Hz to 450Hz
DCA voltage drop 200mV
Polarity Automatic (no indication for positive
polarity); Minus (-) sign for negative
polarity.
Measurement Rate 2 times per second, nominal
Low Battery Indication ‘BAT’ is displayed if battery voltage
drops below operating voltage
Battery 9 Volt Battery
Fuses mA, µA ranges; 0.2A/250V fast blow
A range; 10A/250V fast blow
Operating Temperature 41ºF to 104ºF (5ºC to 40ºC)
Storage Temperature -4oF to 140oF (-20oC to 60oC)
Operating Humidity Max 80% up to 87ºF (31ºC) decreasing
linearly to 50% at 104ºF (40ºC)
Storage Humidity < 80%
Operating Altitude 7000ft. (2000) meters maximum.
Weight 9.17 oz. (260g).
Size 4.78 x 2.38 x 1.57” (121.5 x 60.6 x
40mm)
Safety For indoor use and in accordance with
Overvoltage Category II, Pollution
Degree 2. Category II includes local
level, appliance, portable equipment,
etc., with transient overvoltages less
than Overvoltage Category III.

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Meter Description
1. LCD Display
2. Function switch
3. 10A jack
4. COM jack
5. Positive jack
Note: Tilt stand, fuse and battery
compartment are on rear of unit.
LCD Display Indicators
•))) Continuity
Diode test
m milli ( volts, amps)
k kilo (ohms)
Ω ohms
V DC volts direct current
V AC volts alternating current
A DC amps direct current
A AC amps alternating current
BAT Low battery and battery test
1
2
5
3 4 5

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Operation
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 “OL” appears in the display during a measurement, the
value exceeds the range you have selected. Change to a
higher range.
NOTE: On some low AC and DC voltage ranges, with the test
leads not connected to a device, the display may show a
random, changing reading. This is normal and is caused by the
high-input sensitivity. The reading will stabilize and give a proper
measurement when connected to a circuit.
DC Voltage Measurements
CAUTION: 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 highest VDC
position.
2. Insert the black test lead banana plug into
the negative (COM) jack.
Insert the red test lead banana plug into
the positive (V) jack.
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 display. Reset the function switch to
successively lower VDC positions to obtain a higher
resolution reading. The display will indicate the proper
decimal point and value. If the polarity is reversed, the
display will show (-) minus before the value.

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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.
1. Set the function switch to the highest VAC
position.
2. Insert the black test lead banana plug into
the negative (COM) jack.
Insert red test lead banana plug into the
positive (V) jack.
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 display. Reset the function switch to
successively lower VAC positions to obtain a higher
resolution reading. The display will indicate the proper
decimal point and value.

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DC Current Measurements
CAUTION: Do not make current measurements on the 10A
scale for longer than 30 seconds. Exceeding 30 seconds may
cause damage to the meter and/or the test leads.
1. Insert the black test lead banana
plug into the negative (COM) jack.
2. For current measurements up to
200mA DC, set the function switch to
the 200m ADC position and insert the
red test lead banana plug into the
(mA) jack.
3. For current measurements up to 10A
DC, set the function switch to the
10A range and insert the red test
lead banana plug into the (10A) jack.
4. Remove power from the circuit under
test, then open up the circuit at the point where you wish to
measure current.
5. 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.
6. Apply power to the circuit.
7. Read the current in the display. The display will indicate the
proper decimal point and value.

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AC Current Measurements
CAUTION: Do not make current measurements on the 10A
scale for longer than 30 seconds. Exceeding 30 seconds may
cause damage to the meter and/or the test leads.
1. Insert the black test lead banana plug
into the negative (COM) jack.
2. For current measurements up to 200m
A AC, set the function switch to the
200m AAC position and insert the red
test lead banana plug into the (mA)
jack.
3. For current measurements up to 10A
AC, set the function switch to the 10A
range and insert the red test lead
banana plug into the (10A) jack.
4. Remove power from the circuit under
test, then open up the circuit at the point where you wish to
measure current.
5. Touch the black probe tip to the negative side of the circuit.
Touch the red test probe tip to the positive side of the circuit.
6. Apply power to the circuit.
7. Read the current in the display. The display will indicate the
proper decimal and value.

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Resistance Measurements
WARNING: To avoid electric shock, disconnect power to the
unit under test and discharge all capacitors before taking any
resistance measurements. Remove the batteries and unplug
the line cords.
1. Set the function switch to the highest Ω
position.
2. Insert the black test lead banana plug into
the negative (COM) jack
Insert the red test lead banana plug into
the positive Ω jack.
3. Touch the test probe tips across the circuit
or part under test. It is best to disconnect
one side of the part under test so the rest
of the circuit will not interfere with the resistance reading.
4. Read the resistance in the display and then set the function
switch to the lowest Ωposition that is greater than the actual
or any anticipated resistance. The display will indicate the
proper decimal point and value.
Battery Test
1. Insert the black test lead banana plug into the negative COM
jack and the red test lead banana plug into the positive V
jack.
2. Select the 1.5V or 9V BAT position using the function select
switch.
3. Connect the red test lead to the positive side of the 1.5V or
9V battery and the black test lead to the negative side of the
1.5V or 9V battery.
4. Read the voltage in the display.
Good Weak Bad
9V battery: >8.2V 7.2 to 8.2V <7.2V
1.5V battery: >1.35V 1.22 to 1.35V <1.22V

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Diode Test
1. Insert the black test lead banana plug into the negative COM
jack and the red test lead banana plug into the positive
diode jack.
2. Turn the rotary switch to the position.
3. Touch the test probes to the diode under test. Forward
voltage will indicate 400 to 700mV. Reverse voltage will
indicate “I”. Shorted devices will indicate near 0mV. Shorted
devices will indicate near 0mV and an open device will
indicate “I” in both polarities.
Continuity Check
WARNING: To avoid electric shock, never measure continuity
on circuits or wires that have voltage on them.
1. Set the function switch to the position.
2. Insert the black lead banana plug into the negative (COM)
jack
Insert the red test lead banana plug into the positive (Ω)
jack.
3. Touch the test probe tips to the circuit or wire you wish to
check.
4. If the resistance is less than approximately 30Ω, the audible
signal will sound. If the circuit is open, the display will
indicate “1”.

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Maintenance
Battery Replacement
WARNING: To avoid electric shock, disconnect the test leads
from any source of voltage before removing the battery door.
When the batteries drop below the operating voltage, ‘BAT’ will
appear in the right-hand side of the LCD display. The batteries
should be replaced as follows.
1. Disconnect the test leads from the meter.
2. Remove the protective rubber holster (if
installed).
3. Open the battery door by loosening the
screw using a Phillips head screwdriver.
4. Insert the battery into battery holder,
observing polarity.
5. Put the battery door back in place.
Secure with the screw.
Fuse Replacement
WARNING: To avoid electric shock, disconnect the test leads
from any source of voltage before removing the fuse door.
1. Disconnect the test leads from the meter and any item under
test.
2. Remove the protective rubber holster.
3. Open the fuse door by loosening the screw on the door
using a Phillips screwdriver.
4. Remove the old fuse from its holder by gently pulling it out.
5. Install the new fuse into the holder.
6. Always use a fuse of the proper size and value (0.2A/250V
fast blow for the 200mA range, 10A/250V fast blow for the
10A range).
7. Put the fuse door back in place. Insert the screw and tighten
it securely.

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
Support Hotline [phone]
Tech support: Ext. 200; Email: [e-mail]
Repair/Returns: Ext. 210; Email: r[email protected]
Website: www.extech.com
Calibration and Repair Services
Extech offers repair and calibration services for the products we
sell. Extech also provides NIST certification for most products.
Call the Customer Service Department for information on
calibration services available for this product. Extech
recommends that annual calibrations be performed to verify
meter performance and accuracy.
Copyright ©2003 Extech Instruments Corporation
All rights reserved including the right of reproduction in whole or in part in
any form.