Mastech MS8251B User manual

REL MAX MIN %
AUTO kHz
nmF
Hz
kM
C F
mVA
0 10 20 30 40 50 60 66
MS8251B
DIGITAL MULTIMETER
OPERATION MANUAL
MS8251B

01 02
1. Safety Information 1.2 Use
To reduce the risk of electrical shock, product damage
or personal injury, please follow the safety instructions
described in the user manual. read the user manual
before using the meter.
This instrument meets GB/T 13978-92 and
GB4793.1-2007 (IEC-61010-1,IEC-61010-2-032)
standards for safety requirements for electronic testing
instruments,pollution degree 2,And over voltage
rating of CAT III 1000V and CAT IV 600V.
Follow all safety instructions to ensure safe use of the
instrument.Proper use and protection of the meter will
ensure long life of the meter.
1.1 Preparation
1.1.1
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-
1.1.2
When using the meter, follow the following
safety rules:
Always take precaution to prevent electrical shock
Never misuse the instrument
Check to see if the meter or any components were
damaged during shipment.
Check the meter and accessories thoroughly
before using.
Inspect test leads and probes for cracks, breaks or
crazes on the insulation before using the meter.
Use test leads provided with the unit.If necessary,
replace test leads with identical specifications.
1.1.3
1.1.4
1.1.5
1.2.1
1.2.2
1.2.3
1.2.4
Turn the rotary switch to the required function and
range to be measured.
When using the CAT Ⅳ environment, if the
measuring voltage between terminals and earth
ground exceeds 600V, CAT III environments or
voltage measurement between the terminal and
the earth more than 1000V, do not measure voltage.
Always be careful when working with voltages above
60V DC or 30V AC RMS. Keep fingers behind the
probe barriers while measuring.Never touch probes
during measurement.
Choose the highest range when the value to be
measured is unknown.
1.2.5 Remove test leads before switching functions on
the rotary switch.
1.2.6 Do not perform resistance, capacitance, diode and
continuity measurements on powered circuits.
1.2.7 Never connect the test leads across a voltage
source while the rotary switch is in the resistance,
diode or continuity mode. Doing so can damage
the meter.
1.2.8 Power off the circuit and discharge capacitors
before testing capacitance.
1.2.9 Do not place the meter in any environment with
high pressure, high temperature, dust, explosive
gas or vapor.
1.2.10 Stop using the meter if any failure or abnormal
function is observed.
1.2.11 Do not use meter unless battery cover is in place
a secured.
1.2.12 Avoid direct sunlight, exposing batteries to
humidity, any strong magnetic field, or high
temperatures to ensure the extended life of the
meter.
Warning

03 04
1.3 Mark
Note (Important safety information. Refer to
the operation manual)
CAT IV
Refers to the impulse withstand voltage protection
level in accordance with IEC-61010-1 standard
overvoltage(installation)category IV,pollution
degree 2
Dangerous Voltage
Compliance with requirements for double insulation
(Category II)
1.4 Maintenance
remove any oil, grease or grime. Do not use liquid
solvent or detergent.
1.4.5 When the instrument is not in use, turn rotary switch
to “OFF”
1.4.6 If the instrument is not to be used for an extended
period of time, remove the batteries to prevent
damage to the instrument.
2. Features and Components
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The MS8251B is a portable, hand-held yet professional
meter that features an LCD with backlight, overload
protection and low battery indicator. These meters are
easy to use with one hand, suitable for professional
users or amateurs, and ideal for school or home use.
Functions include: AC/DC voltage, AC/DC current,
resistance, capacitance, continuity, diode test,
frequency and duty cycle.
Auto and manual range.
Auto power off.
Max measurement.
Min measurement.
Relative measurement
Reading Hold function.
True RMS
Simultaneously display frequency during AC voltage/
current measurements.
Non-contact voltage test
Meter complies with European Community (EU)
standards
Earth Ground
2.1 Components
(1)
(2)
(3)
(4)
Non-contact voltage detection indicator
LCD screen
Function buttons
Rotary switch
(5) Input sockets
(6) Non-contact voltage sensor
CAT III Refers to the impulse withstand voltage protection
level in accordance with IEC-61010-1 standard
overvoltage (installation)category III,pollution
degree 2.
1.4.1 To avoid electric shock or personal injury, repairs
or servicing not covered in this manual should be
performed only by qualified personnel.
1.4.2 Remove test leads before opening battery cover
1.4.3 To avoid incorrect readings causing electric shock
or personal injury,when low battery symbol,“ ”
appears, replace batteries immediately.
1.4.4 The meter can be cleaned with a soft cloth to
Complies with U.S. and Canadian safety standards.

05 06
2.2 Buttons and Symbols
HOLDbutton: hold current reading on screen.
FUNC button: switch between functions.
RANGE button: switch between auto/manual ranges.
REL button: relative reading
MAX/MIN button: switch between maximum/ minimum
readings.
b
OFF position:
COM
utton: turn on/off backlight.
EMP position: thermocouple temperature measurement.
LO-Z position: identify ghost voltages.
turn off meter.
Temp V Hz% jack:voltage, current, resistance,
capacitance, diode, continuity, frequency, duty cycle,
temperature input terminal.
jack: common input terminal.
µAmA jack: current measurements <600mA.
10A jack: current measurements >600mA to 10A.
2.3 LCD display
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AUTO kHz
nmF
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kM
C F
mVA
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3
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REL MAX MIN %
AUTO kHz
nmF
Hz
kM
C F
mVA
0 10 20 30 40 50 60 66
MS8251B

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3.1 General Specifications
3.1.1 Manual and auto range
3.1.2 Full range overload protection
3.1.3The maximum voltage allowed between the measuring
end and the earth:CAT IV measurement environment
for 600V DC or AC(RMS),CAT III measurement
environment for 1000VDC or AC(RMS).
3.1.4 Maximum working height: 2000m
3.1.5 Display:LCD
3.1.6 Maximum display value:6599
3.1.7 Polarity indication:“-” indicates negativepolarity
3.1.8 Overload indication:“0L” or “-0L”
3.1.9 Sampling frequency: 0.4s (digital display)/ 0.04s
(bar graph).For current readings, 1s (digital display)
/ 0.1s (bar graph)
3.1.10 Units display: functions and units
3.1.11 Auto power off: 15 minutes
3.1.12 Power supply: 9V 6F22 battery
3.1.13 Low battery indication: LCD displays“ ”
Temperature coefficient: less than 0.1x specified
accuracy/°C
Operating temperature:0°C ~40°C
3.1.16 Storage temperature:-10°C ~50°C
3.1.17 Dimensions:175×85×52mm
3.1.18 Weight:approx.420g(including battery)
3. Specifications
The Meter should be calibrated annually between
18°C~28°C and a relative humidity less than 75%.
Alternating current
Direct current
Diode
Continuity
Autoranging mode
Maximum value
Minimum value
Low battery
Percentage (duty cycle)
Hertz, Kilohertz (frequency)
Millivolt, Volt (voltage)
Micro amp, Milliamp, Amp (current)
Nanofarad, Microfarad, Millifarad
(capacitance)
Ohm, Kilohm, Megaohm (resistance)
Relative value
AUTO
MAX
MIN
%
Hz, kHz
mV, V
REL
Ω, kΩ, MΩ
nF, μF, mF
μA, mA, A
Auto power off
NCV Non-contact voltage detection
Data hold

09 10
3.2.3 DC Voltage
3.2 Technical Specifications
3.2.1 True RMS Characteristics
• For non-sinusoidal signal measurement, the Meter
provides more accurate measurement than the
traditional averaging method.
• If in AC current mode, the Meter may display a random
reading between 1 and 50 when the input is not active.
This will not affect the accuracy of measurement.
• True RMS requires a minimum input level, AC current
or voltage should be 2%~100% of the maximum level.
3.2.2 Dual Impedance Characteristics
• Normal impedance(10M) with normal testing capabilities.
• Low impedance Lo-Z (400kΩ) for testing where “ghost
voltage” may be present.Ghost voltage can occur when
power supply conductors and adjacent unused
conductors create a capacitive coupling between
conductors.If this possibility exists, or when testing for
the presence of voltage, use the Lo-Z mode to switch to
the low impedance setting to remove the ghost voltages
during measurement.
- Input impedance: 10MΩ
- Overload protection: 660mV range: 250V DC or AC
(RMS),6.6V-1000V range: 1000V DC/AC (RMS)
- Maximum input voltage: 1000V DC
0.1mV ±(0.8% of reading + 3 digits) 660mV
0.001V
0.01V
0.1V
1V
6.6V
66V
660V
1000V
±(0.5% reading + 5 digits)of
Resolution Accuracy
range
±(0.8% reading + 3 digits)of
3.2.4 AC Voltage
Frequency Range
40 ~ 60Hz
40 ~400Hz
40 ~ 400Hz
- Input impedance: 10MΩ
- Overload protection: 660mV range: 250V DC or AC
(RMS),6.6V-1000V range: 1000V DC/AC (RMS)
- Maximum input voltage: 1000V AC (RMS)
- :Response True RMS
0.1mV ±(1.5% reading
+ 5 digits)
of
660mV
0.001V
0.01V
0.1V
6.6V
66V
660V
±(1.2% reading
+ 5 digits)
of
Resolution Accuracy
range
±(1.0% reading
+ 3 digits)
of
3.2.4.1AC Voltage (A position)
1V
1000V

3.2.6 Capacitance
- Overload protection: 250V DC or AC (RMS)
0.001nF6.6nF
0.01nF
0.001µF
0.01µF
66nF
6.6µF
66µF
660µF
±(3.0% reading + 3 digits)
0.1µF
Resolution Accuracy
range
0.1nF660nF
0.001mF6.6mF
66mF 0.01mF
±(4.0% reading + 5 digits)
±(4.0% reading + 5 digits)
3.2.5 Resistance
- Open circuit voltage: 1.0V
- Overload protection: 250V DC /AC (RMS)
approx.
0.1Ω660Ω
0.001kΩ
0.01kΩ
0.1kΩ
6.6kΩ
66kΩ
660kΩ
6.6MΩ
±(0.8% of reading + 5 digits)
±(1.5% reading + 5 digits)of
66MΩ0.1MΩ
0.001MΩ
Resolution Accuracy
range
Frequency Range
40 ~ 60Hz
40 ~400Hz
40 ~ 400Hz
- Input impedance: 400kΩ
- Overload protection: 660mV range: 250V DC or AC
(RMS),6.6V-1000V range: 1000V DC/AC (RMS)
- Maximum input voltage: 1000V AC (RMS)
- :Response True RMS
0.1mV ±(1.5% reading
+ 5 digits)
of
660mV
0.001V
0.01V
0.1V
6.6V
66V
660V
±(1.2% reading
+ 5 digits)
of
Resolution Accuracy
range
±(1.0% reading
+ 3 digits)
of
3.2.4.2 AC Voltage Low Impedance(lo-Z)
±(1.2% reading
+ 5 digits)
of
11 12
3.2.7 Diode Test
- Forward DC current : 1mA
-
approx.
Revers DC voltage: approx. 3.2V
- Overload protection:250V DC/AC(rms)
Shows approximate forward
voltage of diode
0.001V
Resolution Function
range
3.2.8 Continuity
- Open circuit voltage: approx. 1.0V
- Overload protection:250V DC/AC(rms)
If measured resistance is
less than 50Ω, a buzzer will
sound
0.1Ω
Resolution Function
range
1V
1000V

13 14
660µA
±(1.5% reading + 5 digits)
66mA
10A
0.1µA
1µA
10µA
10mA ±(3.0% reading + 5 digits)
6600µA
660mA 100µA
Resolution Accuracy
range
3.2.11 AC Current
Overload protection:
µA and mA grade: Fuse FF600mA/1000V,
A : Fuse FF10A/1000V.
- Frequency range: 40 ~ 400Hz
position
- Response: True RMS
When the target current is larger than 5A, do not continue
measurement for more than 10 sec. Pause for 1 minute
after the measuring.
3.2.10 DC Current
Overload protection:
µA and mA : Fuse FF600mA/1000V,
: Fuse FF10A/1000V.
position
A position
When the target current is larger than 5A, do not continue
measurement for more than 10 sec. Pause for 1 minute
after the measuring.
660 Aµ
±(1.0% reading + 5 digits)
66mA
10A
0.1µA
1µA
10µA
10mA ±(2.0% reading + 5 digits)
6600 Aµ
660mA 100µA
Resolution Accuracy
range
- :
- : >
Range 10Hz~10kHz
Input Voltage 0.2V AC (Input voltage should increase
along with the frequency)
3.2.9 Frequency
3.2.9.1 Frequency (V position):
66Hz
±(1.5% reading + 5 digits)
660Hz
6.6kHz
10kHz
0.01Hz
0.1Hz
0.001kHz
0.01kHz
Resolution Accuracy
range
66Hz ±(1.5% reading + 5 digits)
660Hz
660kHz
6.6MHz
0.01Hz
0.1Hz
0.1kHz
1kHz
Resolution Accuracy
range
3.2.9.2 Frequency (Hz position):
66MHz 10kHz
6.6kHz
66kHz
0.001kHz
0.01kHz
±(1.5% reading + 5 digits)
- Overload protection:250V DC/AC(rms)
- Input Voltage:3V peak to peak AC
1 - 99% ±2.0%
0.1%
Resolution Accuracy
range
3.2.9.3 Duty Cycle

15 16
3.2.12 Temperature
Range Input Test Range Accuracy
Ambient Temp ±2 digits
±4 digits
±5 digits
±4 digits
±20 digits
0~1000°C 400°C
1000°C
800°F
1800°F
32~1832°F
±(1.0% of reading
+3 digits)
4. Using the Meter
4.1 Data Hold
4.2.1
Note:
In voltage, current, resistance and capacitance
modes, the default range is “AUTO”
4.2.2 Press “RANGE” to enter manual ranging.Each
press switches to a higher range.Pressing the
button at the highest range will return to the lowest
range.
4.2.3 Hold “RANGE” to return to “AUTO”
4.2.4 Pressing “RANGE” in Max/Min mode will return the
meter to normal reading.
Manual range is disabled in frequency mode.
4.2 Manual Range
4.1.1 During a measurement, press the “HOLD” button
once to hold the reading.
4.1.2 Press “HOLD” again to release the hold.
4.3 Relative Measurement Mode Switch
4.3.1
will store the reading when pressed and display the
difference between current reading and the stored
reading.
Press “REL to enter relative measurement. This
4.4.1 Press “MAX/MIN” to display the maximum value
recorded
4.4.2 Press “MAX/MIN” again to display the minimum
value recorded.
4.4.3 Hold “MAX/MIN” to return to normal readings.
4.4 Maximum/Minimum Reading
4.5 Function Switching
4.6 Backlight
4.7 Automatic Power-off
4.8 Non-Contact Voltage Detection (NCV)
4.7.1 If there is no operation for 15 minutes after turning
the machine on, the meter will automatically power
off to save the battery.
4.7.2 After automatic power-off, press any key to turn the
meter on again.
4.7.3 Holding the "FUNC" key when powering on will
cancel automatic power-off function.
4.8.1 With the rotary switch in any position except OFF,
hold down the “NCV” button.
4.8.2 Move the tip of the meter near the voltage source
or conductor.If the voltage detected is greater than
110VAC, the buzzer will beep and the NCV indicator
near the tip of the meter will flash.
4.5.1 In voltage or current modes, press “FUNC” to
switch between AC and DC.
4.5.2 In resistance, diode or continuity modes, press
“FUNC” to switch between measurements.
4.5.3 In temperature mode, press “FUNC” to switch
between °C and °F.
4.6.1 Press “ ”to turn on backlight.Press again to turn off.
4.3.2 Press “REL ” again to return to normal.
Ambient Temp ±2 digits

17 18
Note：
1.Even though there is no indication,voltage may still
exist.Do not rely solely on NCV detector to determine
the presence of voltage in a wire.The measurement
may be affected by the design of the outlet,type of
insulation and other external factors.
2.The voltage sensing indicator may turn on when a
voltage is fed to the meter.
3.Other external interference(ex.Flashlight,motor)may
trigger the NCV sensor.
4.9 AC/DC Voltage
Voltage is the electrical potential difference between two
points in a circuit. AC polarity changes over time, where
DC polarity stays constant.
Measuring AC or DC voltage:
4.9.1 Move the rotary switch to the “V” position.
4.9.2 Connect the red test lead to the “V” jack and the
black test lead to the “COM” jack.
4.9.3 Connect the test leads to the voltage source or load.
4.9.4 The measured voltage will be displayed.For DC
voltage, polarity of the red test lead will be
indicated.
4.9.5 Press “FUNC” to switch between AC/DC voltage.
4.11 Continuity
4.11.1 In resistance mode, press “FUNC” to switch to
continuity mode.
4.11.2 Connect the red test lead to the input jack and the
black test lead to the “COM” jack.
4.11.3 Connect the test leads to the circuit.
4.11.4 If the resistance of the circuit is less than 50Ω, a
buzzer will sound.
4.12 Diode
4.12.1 In continuity mode, press “FUNC” to switch to
diode mode.
4.12.2 Connect the red test lead to the input jack and the
black test lead to the “COM” jack.
4.12.3 Connect the red test lead to the anode (+) and the
black lead to the cathode (-) of the diode.
4.12.4 The meter will display the forward biased voltage
drop across the diode.
4.10 Resistance
Ω
4.10.1 Move the rotary switch to the position.
4.10.2 Connect the red test lead to the “Ω” jack and the
black test lead to the “COM” jack.
4.10.3 Connect the test leads to the circuit.
4.10.4 Resistance value will be displayed.
”
4.13 Capacitance
4.13.1 Move the rotary switch to the “
4.13.2 Connect the red test lead to the input jack and the
black test lead to the “COM” jack.
4.13.3 Connect the test leads to the circuit/capacitor.
4.13.4 Capacitance value will be displayed.
”position.
4.14 Frequency and Duty Cycle
4.14.1 Move the rotary switch to the “Hz%” position.
4.14.2 Connect the red test lead to the input jack and the
black test lead to the “COM” jack.
4.14.3 Connect the test leads to the circuit.
4.14.4 The measured frequency and duty cycle will be
displayed simultaneously.

19 20
4.15 Current
4.15.1 Remove power to the circuit and discharge all
capacitance.
4.15.2 Move the rotary switch to the appropriate position
(µA, mA or A).
4.15.3 Connect the black test lead to the “COM” jack.
If the current to be measured is <600mA, connect
the red test lead to the “µAmA” jack.If the current
to be measured is >600mA, connect the red test
lead to the “10A” jack.
4.15.4 Break the circuit.Connect the test leads across
the break, with the red lead to the higher voltage
side, and the black lead to the lower voltage side.
4.15.5 Power on the circuit and the current value will be
displayed.If “OL” appears on the display, it means
the current exceeds the selected mode.Move the
rotary switch to the next higher position.
5. Maintenance
5.1 Replace Battery
To avoid electrical shock, damage or personal injury,
remove test leads before openning battery cover.
5.1.1 “ ”
. .
Note:
If the low battery symbol appears, the battery
needs to be changed.
5 1 2 Unscrew the battery cover from the back of the
meter and remove the old battery.
5.1.3 Insert a new battery and replace the cover and
tighten it to the meter.
Be sure to note the battery polarity when replacing.
Warning
NCV
5.2 Test Lead Replacement
Replace the test leads with identical or compatible
leads.lead spec:1000V 10A.
Replace test leads if leads become worn.
6. Accessories
Warning
1.Test Leads 1 pair
2.Manual 1 pc
3.Battery 9V 6F22
4.multifunctional test socket 1 pc
5.electromagnetic pendant 1 pc
6.K-type temperature probe 1 pc
1 pc

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