Extech Instruments EX420-NIST User manual

User's Guide
Digital Multimeter
Extech 420
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Extech EX420-NIST 11 Function Professional MultiMeter
Extech EX420 Professional Multimeter

EX420-EU-EN v3.3 08/13
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Introduction
Congratulations on your purchase of the Extech 420 (part number EX420) Autoranging Multimeter.
This meter measures AC/DC Voltage, AC/DC Current, Resistance, Capacitance, Frequency, Duty
Cycle, Diode Test, and Continuity plus Thermocouple Temperature. Proper use and care of this meter
will provide many years of reliable service.
Safety
International Safety Symbols
This symbol, adjacent to another symbol or terminal, indicates the user must refer to the
manual for further information.
This symbol, adjacent to a terminal, indicates that, under normal use, hazardous voltages
may be present
Double insulation
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) 600 VAC or VDC.
WARNING
CAUTION
MAX
600V
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CAUTIONS
Improper use of this meter can cause damage, shock, injury or death. Read and understand
this user manual before operating the meter.
Always remove the test leads before replacing the battery or fuses.
Inspect the condition of the test leads and the meter itself for any damage before operating the
meter. Repair or replace any damage before use.
Use great care when making measurements if the voltages are greater than 25VAC rms or
35VDC. These voltages are considered a shock hazard.
Warning! This is a class A equipment. This equipment can cause interferences in the living
quarters; in this case the operator can be required to carry out adequate measures.
Always discharge capacitors and remove power from the device under test before performing
Diode, Resistance or Continuity tests.
Voltage checks on electrical outlets can be difficult and misleading because of the uncertainty
of connection to the recessed electrical contacts. Other means should be used to ensure that
the terminals are not "live".
If the equipment is used in a manner not specified by the manufacturer, the protection provided
by the equipment may be impaired.
This device is not a toy and must not reach children’s hands. It contains hazardous objects as
well as small parts that the children could swallow. In case a child swallows any of them,
please contact a physician immediately
Do not leave batteries and packing material lying around unattended; they can be dangerous
for children if they use them as toys
In case the device is going to be unused for an extended period of time, remove the batteries
to prevent them from training
Expired or damaged batteries can cause cauterization on contact with the skin. Always,
therefore, use suitable hand gloves in such cases
See that the batteries are not short-circuited. Do not throw batteries into the fire.
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OVERVOLTAGE CATEGORY III
This meter meets the IEC 610-1-2001 standard for OVERVOLTAGE CATEGORY III. Cat III meters
are protected against overvoltage transients in fixed installation at the distribution level. Examples
include switches in the fixed installation and some equipment for industrial use with permanent
connection to the fixed installation.
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 or current to the meter that exceeds the specified maximum:
Input Protection Limits
Function Maximum Input
V DC or V AC 1000V DC/750V AC, 200Vrms on 400mV range
mA AC/DC 500mA 250V fast acting fuse
A AC/DC 20A 250V fast acting fuse(30 seconds max every 15
minutes)
Frequency, Resistance, Capacitance,
Duty Cycle, Diode Test, Continuity
250Vrms for 15sec max
Temperature 60V DC/24V AC
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
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 covers to replace
the fuse or battery.
7. NEVER operate the meter unless the back cover and the battery and fuse covers are in place
and fastened securely.
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Controls and Jacks
1. 4000 count LCD display
2. HOLD
3. SELECT button
4. Function switch
5. mA, uA and A input jacks
6. COM input jack
7. Positive
input jack
8. RANGE hold button
9. RELATIVE
button
10. Backlight button
11. Protective holster
Note: Tilt stand and battery compartment are on rear of unit.
Symbols and Annunciators
•))) Continuity
Diode test
Battery status
Test lead connection
error
n nano (10-9) (capacitance)
µ micro (10-6) (amps, cap)
m milli (10-3) (volts, amps) A Amps
k kilo (103) (ohms) F Farads (capacitance)
M mega (106) (ohms)  Ohms
Hz Hertz (frequency) V Volts
% Percent (duty ratio) REL Relative
AC Alternating current AUTO Autoranging
DC Direct current HOLD Display hold
ºF Degrees Fahrenheit ºC Degrees Centigrade
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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 “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 green V position.
2. Press the SELECT button to indicate “DC” on the display.
3. Insert the black test lead banana plug into the negative COM jack.
Insert the red test lead banana plug into the positive Vjack.
4. 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.
5. Read the voltage in the display.
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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 green V position.
2. Press the SELECT button to indicate “AC” on the display.
3. Insert the black test lead banana plug into the negative COM jack.
Insert red test lead banana plug into the positive Vjack.
4. 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.
5. Read the voltage in the display.
DC CURRENT MEASUREMENTS
CAUTION: Do not make current measurements on the 20A 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 4000µA DC, set the function
switch to the yellow µA position and insert the red test lead
banana plug into the µA/mA jack
3. For current measurements up to 400mA DC, set the function
switch to the yellow mA position and insert the red test lead
banana plug into the µA/mA jack.
4. For current measurements up to 20A DC, set the function switch
to the yellow 20A range and insert the red test lead banana plug
into the 20A jack.
5. Press the SELECT button to indicate “DC” on the display.
6. Remove power from the circuit under test, then open up the circuit
at the point where you wish to measure current.
7. 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.
8. Apply power to the circuit.
9. Read the current in the display.
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AC CURRENT MEASUREMENTS
CAUTION: Do not make current measurements on the 20A 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 4000µA AC, set the function
switch to the yellow µA position and insert the red test lead
banana plug into the µA/mA jack
3. For current measurements up to 400mA AC, set the function
switch to the yellow mA position and insert the red test lead
banana plug into the µA/mA jack.
4. For current measurements up to 20A AC, set the function switch
to the yellow 20A range and insert the red test lead banana plug
into the 20A jack.
5. Press the SELECT button to indicate “AC” on the display.
6. Remove power from the circuit under test, then open up the
circuit at the point where you wish to measure current.
7. 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.
8. Apply power to the circuit.
9. Read the current in the display.
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 green  position.
2. Insert the black test lead banana plug into the negative COM jack.
Insert the red test lead banana plug into the positive jack.
3. Press the SELECT button to indicate on the display.
4. 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.
5. Read the resistance in the display.
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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 green position.
2. Insert the black lead banana plug into the negative COM jack.
Insert the red test lead banana plug into the positive jack.
3. Press the SELECT button to indicate on the display.
4. Touch the test probe tips to the circuit or wire you wish to check.
5. If the resistance is less than approximately 150, the audible signal will
sound. If the circuit is open, the display will indicate “OL”.
DIODE TEST
1. Set the function switch to the green position.
2. Insert the black test lead banana plug into the negative COM
jack and the red test lead banana plug into the positive
diode jack.
3. Press the SELECT button to indicate on the display.
4. Touch the test probes to the diode under test. Forward
voltage will typically indicate 0.400 to 0.700V. Reverse
voltage will indicate “OL”.. Shorted devices will indicate near 0V
and an open device will indicate “OL” in both polarities.
CAPACITANCE MEASUREMENTS
WARNING: To avoid electric shock, disconnect power to the unit
under test and discharge all capacitors before taking any capacitance measurements. Remove the
batteries and unplug the line cords.
1. Set the rotary function switch to the green position.
2. Insert the black test lead banana plug into the negative COM jack.
Insert the red test lead banana plug into the positive jack.
3. Touch the test leads to the capacitor to be tested.
4. Read the capacitance value in the display
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FREQUENCY MEASUREMENTS
1. Set the rotary function switch to the green “Hz” position.
2. Insert the black lead banana plug into the negative COM jack and
the red test lead banana plug into the positive Hz jack.
3. Touch the test probe tips to the circuit under test.
4. Read the frequency on the display.
% DUTY CYCLE
1. Set the rotary function switch to the “Hz” position.
2. Insert the black lead banana plug into the negative COM jack and
the red test lead banana plug into the positive Hz jack.
3. Press the SELECT key momentarily to select % in the display.
4. Touch the test probe tips to the circuit under test.
5. Read the % duty cycle on the display.
CONTACT TEMPERATURE MEASUREMENTS
1. Set the function switch to the black Type K ºC or ºF position.
2. Insert the Temperature Probe into the input jacks, making sure to observe the correct polarity.
3. Touch the Temperature Probe head to the part whose temperature you wish to measure. Keep the
probe touching the part under test until the reading stabilizes (about 30 seconds).
4. Read the temperature in the display.
Note: The temperature probe is fitted with a type K mini connector. A mini connector to
banana connector adaptor is supplied for connection to the input banana jacks.
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