Extech Instruments MA640 User manual

User's Guide
600Amp AC/DC True RMS Clamp Meter
Model MA640

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Introduction
Congratulations on your purchase of this Extech MA640 True RMS Clamp Meter. This meter
measures AC/DC Current, AC/DC Voltage, Resistance, Capacitance, Frequency, Diode Test, Duty
Cycle and Continuity. Special features include Thermocouple Temperature and Non-Contact Voltage
detection. The double molded case is designed for heavy duty use. This meter is shipped fully tested
and calibrated and, with proper use, will provide 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.
PER IEC1010 OVERVOLTAGE INSTALLATION CATEGORY
OVERVOLTAGE CATEGORY I
Equipment of OVERVOLTAGE CATEGORY I is equipment for connection to circuits in which
measures are taken to limit the transient overvoltages to an appropriate low level.
Note – Examples include protected electronic circuits.
OVERVOLTAGE CATEGORY II
Equipment of OVERVOLTAGE CATEGORY II is energy-consuming equipment to be supplied from
the fixed installation.
Note – Examples include household, office, and laboratory appliances.
OVERVOLTAGE CATEGORY III
Equipment of OVERVOLTAGE CATEGORY III is equipment in fixed installations.
Note – Examples include switches in the fixed installation and some equipment for industrial use with
permanent connection to the fixed installation.
OVERVOLTAGE CATEGORY IV
Equipment of OVERVOLTAGE CATEGORY IV is for use at the origin of the installation.
Note – Examples include electricity meters and primary over-current protection equipment
WARNING
CAUTION

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SAFETY NOTES
Do not exceed the maximum allowable input range of any function.
Do not apply voltage to meter when resistance function is selected.
Set the function switch OFF when the meter is not in use.
Remove the battery if meter is to be stored for longer than 60 days.
WARNINGS
Set function switch to the appropriate position before measuring.
When measuring volts do not switch to current/resistance modes.
Do not measure current on a circuit whose voltage exceeds 600V.
When changing ranges always disconnect the test leads from the circuit under test.
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.
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.
Function Maximum Input
A AC/DC, 600A DC/AC
V DC, V AC 600V DC/AC
Resistance, Capacitance, Frequency, Diode Test 250V DC/AC
Type K Temperature 30V DC, 24V AC
250V DC/AC

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Description
Meter Description
1. Current clamp
2. Clamp opening trigger
3. Hx % Button
4. MODE Button
5. LCD Display
6. Common Input jack
7. NCV sensor
8. NCV LED indicator
9. HOLD/BACKLIGHT Button and FUNCTION switch
10. RANGE Button
11. MAX-MIN Button
12. RELATIVE Button
13. Battery compartment (rear)
14. Positive Input jack
Display icons Description
HOLD Data Hold
AUTO Autoranging
DC Direct Current
AC Alternating Current
MAX Max reading
MIN Min reading
Low battery
REL Relative
V Volts (Voltage)
Ohms (Resistance)
A Amperes (Current)
F Farad (Capacitance)
Hz Hertz (Frequency)
% Duty Ratio
oF and oC Fahrenheit and Celsius units (Temperature)
n, m, , M, k Unit of measure prefixes: nano, milli, micro, mega, and kilo
))) Continuity test
Diode test

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Operation
NOTES: Read and understand all Warning and Caution statements in this operation manual prior
to using this meter. Set the function select switch to the OFF position when the meter is not in use.
Non-Contact Voltage Detector
WARNING: Risk of Electrocution. Before use, always test the Voltage Detector on a known live
circuit to verify proper operation.
1. Rotate the Function switch to any measurement position.
2. Place the detector probe tip on the conductor to be tested.
3. If AC voltage is present, the NCV detector light will turn on
with a steady red light.
NOTE: The conductors in electrical cord sets are often twisted. For
best results, move the probe tip along a length of the cord
to assure placing the tip in close proximity to the live
conductor.
NOTE: The detector is designed with high sensitivity. Static electricity or other sources of energy
may randomly trip the sensor. This is normal operation.
AC/DC Current Measurements
WARNING: Disconnect the test leads before making clamp measurements.
1. Rotate the Function switch to the 600A AC or
DC position
2. Press the trigger to open jaw. Fully enclose
only one conductor.
3. Read the current value in the display.
4. If the value is less than 60A, rotate the function
switch to the 60A position to improve
resolution.
DCA Zero
The REL feature removes offset values and
improves accuracy for DC current
measurements. To perform a zero, select ADC
and, with no conductor in the jaw, press and the
REL button. The display will zero. The offset value is now stored and removed from all
measurements.

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AC/DC Voltage Measurements
CAUTION: Do not measure voltages if a motor on the circuit is being switched ON or OFF. Large
voltage surges may occur that can damage the meter.
1. Rotate the function switch to the V position.
2. Press the MODE button to select AC or DC Voltage.
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 value in the display.
Resistance Measurements
Note: Remove power from the device under test before making resistance measurements
1. Rotate the function switch to the 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 one side of the device.
Touch the red test probe tip to the other side of the device.
4. Read the resistance value in the display.
Continuity Test
1. Connect as described for resistance measurements.
2. Press the MODE button to select continuity ))).
3. Touch the test probe tips across the circuit or component under test.
4. If the resistance is < 60, a tone will sound.

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Diode Test
1. Connect as described for resistance measurements
2. Press the MODE button to select diode test .
3. Touch the test probe tips to the diode or semiconductor junction under test. Note the meter
reading.
4. Reverse the test lead polarity by reversing the red and black leads. Note this reading.
5. The diode or junction can be evaluated as follows:
If one reading displays a value (typically 0.400V to 01.800V) and the other reading
displays OL, the diode is good.
If both readings display OL the device is open.
If both readings are very small or ‘0’, the device is shorted.
Capacitance Measurements
WARNING: To avoid electric shock, discharge the capacitor before measuring.
1. Rotate the function switch to the CAPcapacitance position.
2. Press the MODE button to select nF capacitance test
3. Insert the black test lead banana plug into the negative COM jack.
Insert the red test lead banana plug into the positive jack.
4. Touch the black test probe tip to one side of the device.
Touch the red test probe tip to the other side of the device.
5. Read the capacitance value in the display.
Note: For very large values of capacitance measurement time can be several
seconds before the final reading stabilizes.

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Frequency and Duty Ratio Measurements
1. Rotate the function switch to the Hz Position.
2. Press the MODE button to select AC Voltage
3. Press the HZ % button to select HZ
4. Insert the black test lead banana plug into the negative COM jack.
Insert the red test lead banana plug into the positive Hz jack.
5. Touch the black test probe tip to one side of the device.
Touch the red test probe tip to the other side of the device.
6. Read the Frequency value on the display.
7. Press the HZ % button to select %
8. Read the Duty Ratio on the display.
Type K Temperature Measurements
1. Rotate the function switch to the Temp position.
2. Press the MODE button to select °F or °C.
3. Insert the Temperature Probe into the input jacks.
4. Place the temperature probe tip where needed.
5. Read the temperature on the display.
Note: In case of an open input or a temperature overrange, the meter will display
“OL”.
Data Hold
To freeze the LCD reading, press the HOLD button. While data hold is active, the HOLD icon
appears on the LCD. Press the HOLD button again to return to normal operation.
MAX/MIN
1. Press the MAX/MIN button to activate the MAX/MIN recording mode. The display icon "MAX"
will appear. The meter will begins recording and displaying the maximum value measured.
2. Press the MAX/MIN button and “MIN” will appear. The meter will display the minimum value
measured during the recording session.
3. To exit MAX/MIN mode press and hold the MAX/MIN button for 2 seconds.

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RANGE
In the Voltage, Resistance, Frequency or Temperature function the meter automatically selects the
best range for the measurements being made. For measurement situations requiring that a range
be manually selected, perform the following:
1. Press the RANGE button. The “AUTO” display icon will turn off.
2. Press the RANGE key to step through the available ranges. Observe the decimal point and
units displayed until the preferred range is located.
3. To exit the Manual Ranging mode and return to Autoranging, press and hold the RANGE key
for 2 seconds.
LCD Backlight
The LCD is equipped with backlighting for easier viewing, especially in dimly lit areas. Press and
hold the HOLD/ button for 2 seconds to turn the backlight on. The backlight will automatically turn
off after 5 seconds.
Automatic Power OFF
In order to conserve battery life, the meter will automatically turn off after approximately 15 minutes
of operation. The meter will beep shortly before the meter shuts off. If a button is pressed, the APO
timer will reset. If the meter is allowed to shut off, turn the function switch to the OFF position and
then to the function again to restart.
Low battery indication
When the icon appears in the display, the battery should be replaced. Refer to the battery
replacement procedure in the maintenance section.

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Maintenance
WARNING: To avoid electrical shock, disconnect the meter from any circuit, remove the test leads
from the input terminals, and turn OFF the meter before opening the case. Do not operate the meter
with an open case.
Cleaning and Storage
Periodically wipe the case with a damp cloth and mild detergent; do not use abrasives or
solvents. If the meter is not to be used for 60 days or more, remove the battery and store it
separately.
Battery Replacement
1. Remove the Phillips head screws that secures the rear battery door
2. Open the battery compartment
3. Replace the 9V battery
4. Secure the battery compartment door
You, as the end user, are legally bound (EU Battery ordinance) to return all used
batteries, disposal in the household garbage is prohibited! You can hand over your
used batteries / accumulators at collection points in your community or wherever batteries /
accumulators are sold!
Disposal: Follow the valid legal stipulations in respect of the disposal of the device at the
end of its lifecycle