Extech Instruments EX320 User manual

User's Guide
Mini Multimeter
with Non-Contact Voltage Detector (NCV)
Model EX320

Model EX320 - Version 4.0 –05/20062
Introduction
Congratulations on your purchase of the Extech 320 MultiMeter. The EX320 offers AC/DC
Voltage, AC/DC Current, Resistance, Diode, and Continuity testing plus a built-in non-contact
Voltage Detector. Proper use and care of this meter will provide many years of reliable
service.
Safety
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 600V.
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.
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 AC and DC
mA AC/DC 200mA DC/AC
A AC/DC 10A DC/AC (for 30 seconds max. every 15 minutes
Resistance, Diode Test, Continuity 250V DC/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 power and disconnect 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.
8. If the equipment is used in a manner not specified by the manufacturer, the protection provided by the
equipment may be impaired.
WARNING
CAUTION
MAX
600V

Model EX320 - Version 4.0 –05/20063
Controls and Jacks
1. AC Voltage Detector Sensor
2. AC Voltage Detector indicator light
3. LCD display
4. MAX push-button
5. MODE button
6. Non-contact AC Voltage Detector test
button
7. Rotary function dial
8. 10 ampere test lead jack
9. COM test lead jack
10. Test lead jack for voltage, milli-amp, micro-
amp, & resistance functions
11. RANGE button
12. HOLD button
13. Protective rubber holster (must be
removed to access the rear battery
compartment)
Display Symbols and Annunciators
•))) Continuity
Diode test
Battery status
µ micro (10-6) (amps)
m milli (10-3) (volts, amps)
k kilo (103) (ohms)
M mega (106) (ohms)
V Volts
A Amps
Ω Ohms
AC Alternating current
DC Direct current
HOLD Display hold
AUTO Autoranging
MAX Highest reading
C, F Temperature units
1
2
3
4
5
6
7
8
12
13
11
10
9
10A
for
30 sec.
MAX
every
15 min.
FUSED

Model EX320 - Version 4.0 –05/20064
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. Press the HOLD button to freeze a displayed reading
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.
NON-CONTACT AC VOLTAGE DETECTOR
The EX320 can detect the presence of AC voltage (from 100 to 600VAC) simply by being
held very near to a voltage source.
WARNING: Test the AC voltage detector on a known live circuit before each use.
WARNING: Before using the meter in the AC Voltage Detector mode, verify that the battery
is fresh by confirming characters appear on the LCD when the function dial is turned to any
position. Do not attempt to use the meter as an AC Voltage Detector if the battery is weak
or bad.
NON-CONTACT VOLTAGE (NCV)
The NCV function works on any rotary switch position.
1. Test the detector on a known live circuit before use.
2. Press and hold the NCV button for the duration of the test.
The meter will beep once when the button is pushed.
3. Hold the top of the meter very close to the voltage source
as shown.
4. If voltage is present, the rim of the LCD display will flash a
bright orange and an audible warning will sound.

Model EX320 - Version 4.0 –05/20065
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 VAC position.
2. Insert the black test lead banana plug into the
negative COM jack. Insert the red test lead
banana plug into the positive Vjack.
3. Touch the black test probe tip to the neutral
side of the circuit.
4. Touch the red test probe tip to the “hot” side of
circuit.
5. Read the voltage in the display.
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 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 Vjack.
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.

Model EX320 - Version 4.0 –05/20066
AC / DC CURRENT MEASUREMENTS
CAUTION: Do not make current measurements at 10 Amps 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 2000µA, set the function switch to the µA position
and insert the red test lead banana plug into the mA/µA jack
3. For current measurements up to 200mA, set the function switch to the mA position
and insert the red test lead banana plug into the mA/µA jack.
4. For current measurements up to 10A, set the function switch to the 10A range and
insert the red test lead banana plug into the 10A jack.
5. Use the MODE button to select AC or DC current.
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.

Model EX320 - Version 4.0 –05/20067
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 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 Ωjack.
3. Touch the test probe tips across the circuit or
component under test. It is best to disconnect
one side of the circuit under test so the rest of
the circuit will not interfere with the resistance
reading.
4. Read the resistance in the display.
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.
3. Insert the red test lead banana plug into
the positive jack.
4. Use the MODE button to view the icon
on the display.
5. Touch the test probe tips to the circuit or
wire under test.
6. If the resistance is less than
approximately 100Ω, the audible signal
will sound. If the circuit is ‘open’ (bad), the
display will indicate “OL”.

Model EX320 - Version 4.0 –05/20068
DIODE TEST
1. Set the function switch to the position.
2. Insert the black test lead banana plug into the
negative COM jack and the red test lead
banana plug into the positive jack.
3. Use the MODE button to view the icon 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.
AUTO-MANUAL RANGE SELECTION
When the meter is first turned on, it automatically goes into the Auto Range mode. This
automatically selects the best range for the measurements being made and is generally
the best mode for most measurements. For measurement situations requiring that a range
be manually selected, perform the following:
1. Press the RANGE key. The AUTO display indicator will turn off.
2. Press RANGE to step through the available ranges until the desired range is
selected.
3. To exit the Manual Ranging mode and return to Auto Range mode, press and hold
the RANGE key for 2 seconds.
MAX MODE
Press the MAX button (the MAX icon will appear on the LCD). The meter will now only
display the highest reading during a test. Each time a higher reading is encountered, the
display will update. Press the MAX button again to exit this mode.

Model EX320 - Version 4.0 –05/20069
Maintenance
WARNING: To avoid electric shock, disconnect the test leads from any source of voltage
before removing the back cover or the battery or fuse covers.
WARNING: To avoid electric shock, do not operate your meter until the battery and fuse
covers are in place and fastened securely.
This MultiMeter is designed to provide years of dependable service, if the following care
instructions are performed:
1. KEEP THE METER DRY. If it gets wet, dry it immediately.
2. USE AND STORE THE METER IN NORMAL TEMPERATURES. Temperature
extremes can shorten the life of the electronic parts and distort or melt plastic parts.
3. HANDLE THE METER GENTLY AND CAREFULLY. Dropping it can damage the
electronic parts or the case.
4. KEEP THE METER CLEAN. Wipe the case occasionally with a damp cloth. DO
NOT use chemicals, cleaning solvents, or detergents.
5. USE ONLY FRESH BATTERIES OF THE RECOMMENDED SIZE AND TYPE.
Remove old or weak batteries so they do not leak and damage the unit.
6. IF THE METER IS TO BE STORED FOR A LONG PERIOD OF TIME, the battery
should be removed to prevent damage to the unit.
UL LISTED
The UL mark does not indicate that this product has been evaluated for its accuracy.
AUTO POWER OFF
The meter will automatically turn off after 15 minutes of inactivity. This will conserve battery
energy. To turn the meter on after an Auto Power OFF, simply turn the rotary switch to OFF
and then back to the desired setting.

Model EX320 - Version 4.0 –05/200610
BATTERY INSTALLATION and LOW BATTERY INDICATION
WARNING: To avoid electric shock, disconnect the test leads from any source of voltage
before removing the battery cover.
LOW BATTERY INDICATION
The icon will appear in the lower left-hand corner of the display when the battery
voltage becomes low. Replace the batteries when this appears.
BATTERY REPLACEMENT
1. Disconnect the test leads from the meter.
2. Remove the protective rubber holster. See diagram.
3. Remove the Phillips head screw located on the lower back of the instrument.
4. Flip up the fuse/battery compartment cover to access the batteries. See diagram.
5. Gently remove batteries and install two new 1.5V ‘AAA’ batteries observing polarity.
6. Secure the fuse/battery compartment cover.
7. Place the protective rubber holster on the meter.
1. Removable Rubber Holster
2. Meter
3. Battery
4. Fuses
5. Compartment Cover
6. Rubber Holster
WARNING: To avoid electric shock, do not operate the meter until the battery is in place
and fastened securely.
REPLACING THE FUSES
WARNING: To avoid electric shock, disconnect the test leads from any source of voltage
before removing the fuse cover.
1. Disconnect the test leads from the meter.
2. Remove the protective rubber holster.
3. Remove the Phillips head screw located on the lower back of the instrument.
4. Flip up the fuse/battery compartment cover to access the fuses.
5. Gently remove the fuse(s) and install new fuse(s) into the holder(s).
6. Always use fuses of the proper size and value (200mA/250V fast blow for the mA /
µA ranges, 10A/250V fast blow for the A range).
7. Secure the fuse/battery compartment cover.
8. Place the protective rubber holster on the meter.
WARNING: To avoid electric shock, do not operate your meter until the fuse cover is in
place and fastened securely.