Extech Instruments 380940 User manual

User's Guide
True RMS AC / DC Power Clamp Meter
Model 380940

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Introduction
Congratulations on your purchase of the Extech 380940 True RMS Watt Clamp DMM. This meter
combines multimeter and clamp meter functionality in one convenient meter. Careful use of this
meter will provide years of reliable service.
Safety
1. NEVER exceed the specified voltage/current maximum
2. USE EXTREME CAUTION when working with high voltages.
3. DO NOT measure voltage if the voltage on the "COM" input jack exceeds 500V above earth
ground.
4. NEVER connect the meter leads across a voltage source while the function switch is in the
current mode. Doing so can damage the meter.
5. ALWAYS discharge filter capacitors in power supplies and disconnect the power when
measuring.
6. ALWAYS turn off the power and disconnect the test leads before opening the back to replace
the fuse or batteries.
7. NEVER operate the meter unless the back cover and the battery/fuse door are in place and
fastened securely.
International Safety Symbols

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Meter Description
1. Conductor under test
2. Clamp Jaws
3. Jaw trigger – Opens the meter jaws
4. ZERO button – Zeroes the DCA reading
5. Positive input jack (for red test lead)
6. Function select dial
7. HOD button freezes the displayed reading
8. MAX/MIN button – Press to track and view highest and lowest readings
9. LCD Display with function indicators and bargraph
10. COM input jack (for black test lead)
Function Select Switch

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Display icons
Low battery
DC Direct current
AC Alternating current
Minus sign
AUTO Automatic range (frequency only)
MAN Manual range
ZERO Zero / Relative function
HOLD HOLD function
MAX Highest reading
MIN Lowest reading
Audible continuity
VVoltage unit of measure
ACurrent unit of measure
MPrefix MEGA (millions of units)
kPrefix KILO (thousands of units)
Ohm (unit of measure for resistance and continuity
Hz Hertz (unit of measure for frequency)
Bargraph display
The 40 segment bargraph display shown below is a graphical interpretation of the measurement. It
is displayed under the display digits on the LCD.
The bars in the bargraph indicate a presence of an electronic signal. The more bars showing, the
higher the signal. The digits below the graph help the user see how many bars are showing. If 40
segments are showing, the bars will reach the ‘40’ mark, if 20 bars are showing the bars will reach
the ‘20’ mark.
The bargraph is to be interpreted based on the range the meter is in while the measurement is
being made. If the bargraph shows 40 segments lit, then the signal is at the highest end of the
meter’s present range.

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Operation
AC + DC Power Watt Measurements
1. Connect the test leads to the voltage source in parallel with the load (refer to diagram).
2. Clamp onto one of the wires connected to the load.
3. Select the AC or DC voltage range using the function select switch and check the voltage
reading.
4. Select the AC or DC current range using the function select switch and check the current
reading.
5. Select the appropriate Watt range using the function select switch.
6. Read the KW value on the LCD.
AC Current Measurements
WARNING: To avoid electric shock, disconnect the test leads from the meter before making current
measurements.
1. Set the Function switch to the AC Current position.
2. Press the jaw trigger and clamp around a single conductor fully enclosing it. Do not allow a gap
between the two halves of the jaw.
3. Read the ACA value on the LCD.
DC Current Measurements
WARNING: To avoid electric shock, disconnect the test leads from the meter before making current
measurements.
1. Set the Function switch to the DC Current position.
2. Press the DCA zero key to null the meter display.
3. Press the jaw trigger and clamp around a single conductor fully enclosing it. Do not allow a gap
between the two halves of the jaw.
4. Read the DCA value on the LCD.

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AC Voltage Measurements
WARNING: To avoid electric shock or damage to the meter, do not make any voltage
measurements that exceed the maximum specified.
1. Set the Function switch to the AC Voltage position.
2. Insert the test leads to the meter as follows: Red lead to “V,,Hz” terminal; Black lead to the
COM input.
3. Measure voltage with the pointed end of the test leads. Remember that voltage measurements
are made in parallel with the device/circuit under test.
4. Read the ACV value on the LCD.
DC Voltage Measurements
WARNING: To avoid electric shock or damage to the meter, do not make any voltage
measurements that exceed the maximum specified.
1. Set the Function switch to the DC Voltage position.
2. Insert the test leads to the meter as follows: Red lead to “V,,Hz,” terminal; Black lead to the
COM input.
3. With the pointed end of the test leads measure voltage. Remember that voltage measurements
are made in parallel with the device or circuit under test.
4. Read the DCV value on the LCD.
Frequency Measurements
1. Set the Function switch to the Hz position.
2. Insert the test leads into the meter’s input terminals.
3. Connect the other ends of the test leads in parallel with the device/circuit under test.
4. Read the Frequency measurement on the LCD in Hz.
MIN, MAX Function
Pressing the MIN/MAX key allows the meter to display ONLY the highest and the lowest readings
encountered. Press the MIN/MAX key once to view the minimum reading, press it again to view the
maximum reading. Note that the meter will only change its displayed reading when a measurement
is taken higher than the previous MAX or lower than the previous MIN readings. The HOLD display
icon (along with the MIN or MAX icon) will appear on the LCD in MIN/MAX mode. Pressing the
MIN/MAX key a 3rd time returns the meter to normal operation.
Data Hold
To freeze the current reading on the LCD, press the Data Hold key. To release the Data Hold
function and return the meter to normal operation, press the Data Hold key again.
Relative Mode
1. Press the Zero key and the present measurement will Zero.
2. All subsequent measurements are displayed with respect to the zeroed reading. For example, if
a 20A reading is zeroed and a 30A reading is subsequently measured, the LCD will display 10A.
3. To return to normal operation, press and hold the zero key for 2 seconds.
4. Note that Relative mode is not available if MIN/MAX mode is enabled.

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Auto Power OFF
To extend battery life, the meter will auto power off after 30 minutes of operation. To resume
operation either turn the meter OFF and then ON again or press the HOLD button.
Battery Replacement
1. When the low battery symbol appears on the LCD, the batteries must be replaced.
2. Turn the meter off and remove the rear battery compartment screw.
3. Lift off the battery compartment cover and replace the two 1.5V AA cells.
4. Replace the compartment cover and secure the screw.
You, as the end user, are legally bound (Battery ordinance) to return all used batteries
and accumulators; 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
Cleaning
Use only a dry cloth to clean the plastic case.
Specifications
General Specifications
Display 3-3/4 digit (4000 count) LCD with 40 segment bargraph
Functions Watts, ACA, DCA, ACV, DCV, Frequency
Polarity “-“ indicates negative polarity; positive assumed
Current sensor Hall effect sensor type
Overload indication Left blinking digit
DCA zero adjust One touch zero key
Display rate 2 readings/second (20 readings/second for bargraph)
Auto Power Off Meter turns off automatically after 30 minutes
Battery Two 1.5V AA batteries
Operating temp. -100C to 500C (40F to 1220F)
Operating Humidity < 85% RH
Power consumption Approximately 10mA DC
Weight 190g (6.7 oz) including battery
Dimensions 183 x 63.6 x 35.6mm (7.2 x 2.5 x 1.4”) (HWD)
Jaw opening 23mm (0.9”) maximum conductor size
Standards IEC 1010 Category III 300V, Category II 600V

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Range Specifications
Function Range Resolution Accuracy Overload protect
40kW 10W ±(1.5% + 3dgts) 250V, 400A
Note: 50/60Hz, PF 0.6 to 1, Vpeak < 360V
240kW 100W ±(1.5% + 3dgts) 600V, 400A
Note: 50/60Hz, PF 0.6 to 1, Vpeak < 850V
40kW 10W ±(2.5% + 3dgts) 250V, 400A
Note: 40Hz to 100Hz, PF 0.6 to 1, Vpeak < 360V
240kW 100W ±(2.5% + 3dgts) 600V, 400A
AC Power
Note: 40Hz to 100Hz, PF 0.6 to 1, Vpeak < 850V
40kW 10W ±(1.5% + 3dgts) 250V, 400ADC Power
240kW 100W ±(1.5% + 3dgts) 250V, 400A
DC Current 400A 100mA ±(1.5% + 3dgts) 600A DC
50/60Hz 40 to 100HzAC Current
True RMS, Crest factor
< 4 400A 100mA ±1.5% ±3dgts ±2.5% ±4dgts 600A AC
DC Voltage 400V 0.1V ±(1.0% + 2dgts) 800V DC
50/60Hz 40 to 1kHzAC Voltage
True RMS, Crest factor
< 4, Input impedance
10M
600V 1V ±(1.5% + 2dgts) ±(2.0% + 4d) 800V AC
Frequency 10Hz - 10kHz 0.01- 10Hz ±(0.8% + 2dgts) Sensitivity 10V 600V AC
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