Mastech M839b Instruction Manual

POCKET-SIZED

DIGITAL MULTIMETER

OPERATOR’S
INSTRUCTION MANUAL

F250mA250V

SAFETY INFORMATION

The meter has been designed according to IEC1010 concerning
electronic measuring instruments with an overvoltage category (CATII)
and pollution 2.
Follow all safety and operating instructions to ensure the meter is used
safely and is kept in good condition.
Full compliance with safety standards can be guaranteed only with test
leads supplied. If necessary, they must be replaced with the type specified
in this manual.

DURING USE

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Never exceed the protection limit indicated in the specifications for
each range of measurement.
When the meter is linked to measurement circuit, be careful not to
touch unused terminals.
Never use the meter to measure voltages that might exceed 600V
above earth groud in category II installations.
Always be careful when working with voltages above 60V dc or
30V ac rms. Keep fingers behind the probe barriers while
measuring.
Before attempting to insert transistors for testing, always be sure
that test leads have been disconnected from any measurement
circuits.
Components should not be connected to the hFE socket when
making voltage measurements with test leads.
Do not perform resistance measurements on live circuits.

SAFETY SYMBOLS

Important safety information, refer to the instruction manual.

Dangerous voltage may be present.
Earth ground.
Indicates compliance with requirements for double insulation
Fuse must be replaced with ratings specified in the

manual.

MAINTENANCE

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Before opening the case, always disconnect test leads from all
energized circuits.
For continuous protection against fire, replace fuse only with
ratings: F 250mA/250V (Quick Acting).

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Never use the meter unless the back cover is in place and
fastened completely.
Do not use abrasives or solvents on the meter. To clean
it using only a damp cloth and mild detergent.

FRONT PANEL DESCRIPTION

1 Rotary Switch

This switch is used to select the function and desired ranges as
well as to turn on/off the meter.

2 Display

3 1/2 digit, 7 segment, 0.5″ high LCD.

3 “COM” Jack

Plug in connection for black (negative) test lead.

4 “VΩmA” Jack

Plug in connection for red (positive) test lead for voltage, resistance
and current (except 10A) measurements.

5 “10A” Jack

Plug in connection for red (positive) test lead for 10A

measurement.

SPECIFICATIONS

Accuracy is guaranteed for 1 year, 23℃± 5℃, less than 75% relative
humidity.

AC VOLTAGE

Range Resolution Accuracy
200V 100mV ±1.2 % of rdg ± 10 digits

600V 1V ±1.2 % of rdg ± 10 digits
Overload protection: 600V dc or rms ac for all ranges.
Frequency range: 45Hz to 450Hz
Response: Average responding, calibrated in rms of a sine wave.

DC VOLTAGE

Range Resolution Accuracy

200mV 0.1mV ±0.5% of rdg ± 2 digits

2000mV 1mV ±0.5% of rdg ± 2 digits

20V 10mV ±0.5% of rdg ± 2 digits

200V 100mV ±0.5% of rdg ± 2 digits

600V 1V ±0.8% of rdg ± 2 digits
Overload protection: 250V rms. ac for 200mV range and 600V dc or rms
ac for other ranges.

DC CURRENT

Range Resolution Accuracy

200μA 0.1μA ±1.0% of rdg ± 2 digits

2000μA 1μA ±1.0% of rdg ± 2 digits

20mA 0.01mA ±1.0% of rdg ± 2 digits

200mA 0.1mA ±1.5% of rdg ± 2 digits

10A 10mA ±3.0% of rdg ± 2 digits
Overload protection: F250mA 250V fuse (10A range unfused).

RESISTANCE

Range Resolution Accuracy

200Ω 0.1Ω ±0.8% of rdg ± 3 digits

2000Ω 1Ω ±0.8% of rdg ± 2 digits

20kΩ 10Ω ±0.8% of rdg ± 2 digits

200kΩ 100Ω ±0.8% of rdg ± 2 digits

2000kΩ 1kΩ ±1.0% of rdg ± 2 digits
Maximum open circuit voltage: 3.2V
Overload protection: 250V rms. ac on all ranges.

DIODE TEST

Range Description

Show the approx. forward voltage drop of the diode.

Overload protection: 250V rms. ac.

GENERAL

Maximum voltage between

terminals and earth ground

: CAT II 600V

Fuse protection : F 250mA/250V, 10A range

unfuse.

Power supply : 1 × 9V

, 6F22 or NEDA 1604

Display : LCD, 1999 counts,

updates 2-3/ sec.

Measuring method : Dual-slope integration A / D

converter
Overrange Indication : Only figure “1” on the display
Polarity indication : “-”displayed for negative polarity
Operating Environment : 0 to 40℃ (32°F to 104°F)
Storage temperature : −10℃ to 50℃ (10°F to 122°F).
Low battery indication : “BAT” appear on the display
Size : 126×70×25mm
Weight : Approx. 170g

OPERATING INSTRUCTIONS
AC VOLTAGE MEASUREMENT

1. Connect the red test lead to “VΩmA” jack and the black lead to the
“COM” jack.

2. Set the rotary switch at desired V~ position.

3. Connect test leads across the source or load being measured and read
voltage value on the LCD display.

DC VOLTAGE MEASUREMENT

1. Connect red test lead to “VΩmA” jack and the black test lead to the
“COM” jack.

2. Set rotary switch at desired V

position. If the voltage to
be measured is not known beforehand, set range switch at the highest
range position and then reduce it until satisfactory
resolution is obtained.

3. Connect test lead across the source or load being measured. Read
voltage value on the LCD display along with the polarity of the red lead
connection.

DC CURRENT MEASUREMENT

1. Connect the red test lead to the “VΩmA” jack and the black lead to
“COM” jack. (For measuring current between 200mA and 10A, remove
red lead to “10A” jack.)

2. Set the rotary switch at desired A position.

3. Open the circuit in which the current is to be measured, and

connect

test leads in series with the circuit.

4. Read current value on the LCD display along with the polarity of red
lead connection.

RESISTANCE MEASUREMENT

1. Connect the red test lead to “VΩmA” jack and the black lead to “COM”
jack. (The polarity of red lead is positive “+”)

2. Set the rotary switch at desired Ω range position.

3. Connect test leads across the resistance to be measured and read
LCD display.

4. If the resistor being measured is connected to a circuit, turn off power
and discharge all capacitors before applying test leads.

TRANSISTOR TEST

1. Set the rotary switch at “hFE” position.

2. Determine whether the transistor under testing is NPN or PNP type and
locate the emitter, base and collector leads. Insert the leads into proper
holes of the hFE socket on the front panel.

3. The meter will show the approximate hFE value at the condition of base
current 10μA and Vce 3V.
NOTE:
Before attempting to insert transistors for testing, always be sure that test
leads have been disconnected from any measurement circuits.
Components should not be connected to the hFE socket when making
voltage measurements with test leads.

DIODE TEST

1. Connect the red test lead to “VΩmA” jack and the black lead to “COM”
jack. (The polarity of red lead is positive “+”).

2. Set the rotary switch at

position.

3. Connect the red lead to the anode of the diode to be tested and the
black lead to the cathode of the diode.

4. The approx. forward voltage drop of the diode will be display in mV. If
the connection is reversed, only figure “1” will be shown.

BATTERY & FUSE REPLACEMENT

If the sign “BAT” appears on the LCD display, it indicates that the battery
should be replaced. Loosen screws on the back cover and open the case.
Replace the exhausted with a new one of the same type.
Fuse really need replacement and blow almost always as a result of
operator’s error. Open the case and replace the blown fuse with the
ratings specified: F250mA/250V.

WARNING

Before attempting to open the case, always be sure that test leads have
been disconnected from measurement circuits. Close case and tighten
screws completely before using the meter to avoid electrical shock
hazard.

ACCESSORIES

• Operator’s instruction manual

• Set of test leads

• Battery: 1 × 9V

6F22 or NEDA 1604 type

CAUTION:

Using this appliance in an environment with a strong radiated
radio-frequency electromagnetic field (approximately 3V/m), may
influence its measuring accuracy. The measuring result can be strongly
deviating from the actual value.

HYS004369