Extech Instruments EX420A User manual

USER MANUAL

Digital Multimeter

Extech EX420A

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Introduction

Congratulations on your purchase of the Extech EX420A 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. For copies of this user manual in other languages please visit the

www.extech.com website.

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

1. Improper use of this meter can cause damage, shock, injury or death. Read and understand

this user manual before operating the meter.

2. Always remove the test leads before replacing the battery or fuses.

3. 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.

4. Use great care when making measurements if the voltages are greater than 25VAC rms or

35VDC. These voltages are considered a shock hazard.

5. Warning! This is a class A equipment. This equipment can cause interference to devices in

the home; in this case the operator can be required to carry out adequate measures to

prevent interference.

6. Always discharge capacitors and remove power from the device under test before

performing Diode, Resistance or Continuity tests.

7. 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".

8. If the equipment is used in a manner not specified by the manufacturer, the protection

provided by the equipment may be impaired.

9. This device is not a toy and must not reach children’s hands. It contains hazardous objects

as well as small parts that children could swallow. In case a child swallows any of the parts,

please contact a physician immediately

10. Do not leave batteries and packing material unattended; they can be dangerous for children.

11. In case the device is going to be unused for an extended period of time, remove the

batteries to prevent them from draining.

12. Expired or damaged batteries can cause cauterization on contact with skin. Always use

suitable hand protection.

13. See that the batteries are not short-circuited. Do not put batteries into fire.

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OVERVOLTAGE CATEGORY III

This meter meets the IEC 61010-1 (EN61010-1), 2010, 3rd edition 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 600V, 200Vrms on 400mV range

mA AC/DC 500mA 600V fast acting fuse

A AC/DC 10A 600V 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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Description

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

567

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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 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 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 10A DC, set the function switch to the

yellow 10A range and insert the red test lead banana plug into the 10A

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 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 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 10A AC, set the function switch to the

yellow 10A range and insert the red test lead banana plug into the 10A

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.

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CAPACITANCE MEASUREMENTS

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

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.

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.

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