Extech Instruments 420 User manual

User's Guide

Digital Multimeter

Extech 420

EX420-EU_ENG V3.1 6/09

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

EX420-EU_ENG V3.1 6/09

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.

EX420-EU_ENG V3.1 6/09

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

00V DC

750V

200Vrms on 4

00mV range

AC/

250V fast acting fuse

AAC/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.

EX420-EU_ENG V3.1 6/09

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

EX420-EU_ENG V3.1 6/09

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.

EX420-EU_ENG V3.1 6/09

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.

EX420-EU_ENG V3.1 6/09

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.

EX420-EU_ENG V3.1 6/09

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.

EX420-EU_ENG V3.1 6/09

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

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.

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