LOMVUM T28B User manual

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T28B User Manual
Auto-ranging Digital Multimeter with TRUE RMS
Thank you for your purchase of this precision instrument, the T28B multi-meter. We
hope that this precision instrument will be one of the supporting tools contributing
to your work efficiency.
Before using the device, please read the manual carefully and if you have any
questions, kindly contact our customer service via email.
[email protected]
Thank you for your support.

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Contents
Safety Information........................................................................................03
Safety instructions.........................................................................................03
Safety symbols...............................................................................................04
Overview.......................................................................................................05
Product Functions Overview..........................................................................05
Backlight / Flashlight.....................................................................................06
Auto Power Off..............................................................................................06
Display Hold.................................................................................................. 06
Manual and Auto-Ranging.............................................................................06
Measurement...............................................................................................06
DC/AC Voltage Measurement.......................................................................07
Resistance Measurement..............................................................................07
Diode Measurement....................................................................................08
Continuity Measurement............................................................................08
Capacitance Measurement..........................................................................09
Frequency/Duty Measurement...................................................................09
DC/AC Current Measurement.......................................................................09-10
NCV Test......................................................................................................10
Temperature Measurement........................................................................11
Specifications..............................................................................................11
Frequency....................................................................................................11
Temperature...............................................................................................12
AC Voltage..................................................................................................12
DC Voltage..................................................................................................12
Diode / Continuity......................................................................................12
AC Current..................................................................................................13
DC Current..................................................................................................13
Resistance..................................................................................................14
Capacitance...............................................................................................14
Maintenance.............................................................................................14
Cleaning.....................................................................................................15
Install Batteries & Replace Fuses...............................................................15

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Safety Information
The Meter conforms to IEC61010-1 CAT III 600V, 1000V CAT II IEC61010 and pollution
level 2.
Safety instructions
*When using this meter, the user must comply with all the standard safety
regulations as follows:
1) Protection against electric shocks.
2) Preventing the misuse of the multimeter safety procedures.
*To ensure your personal safety, please use the test leads provided with the meter,
please check before use, and make sure they are intact.
To prevent possible electrical shock, fire, or personal injury, please observed the
following safety measure:
1) Do not alter, modify or tamper with the multimeter. Use only as specified,
otherwise, user safety can be compromised.
2)Do not use the multimeter near explosive gas, vapor, or in damp, wet or dusty
environments.
3)Do not operate the multimeter with the covers removed or the case open.
Hazardous voltage exposure is possible.
4)Do not apply more than the rated voltage, between the terminals or between each
terminal and earth ground.
5)Do not use test leads if they are damaged. Examine the test leads for damaged
insulation, exposed metal, or the wear is shown on the indicator. Always check the
test leads before use.
6)Use the correct terminals, function, and range for measurements.
7)The range switch should be placed in the correct range position.
8)The input value must not exceed the limit of the value specified for each range to
prevent electric shock and damage to the multimeter.

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9)When measuring televisions or switching power supplies, be aware that there may
be pulses in the circuit that can damage the circuit.
10)Remove the batteries if the multimeter is not used for an extended period, or if
stored in temperatures above 50°C.
Safety symbols

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Overview
Product Functions Overview

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Backlight IFlashlight
Push button to toggle the backlight on and off.
Push this button for 2 seconds to toggle the flashlight on and off.
The backlight/flashlight automatically turns off after 30 seconds.
Auto Power Off
The multimeter will automatically turn off if it is left idle for about 15 minutes.
You can press any button to restart the device in the automatic shutdown mode.
Display Hold
In the display hold mode, the multimeter freezes the display. Push button for 2
seconds to activate/deactivate the display hold ('H ' shows on the display.)
Manual and Auto-ranging
The multimeter is defaults to the Auto-range.
Push the' RANGE' button for 2 seconds to enter the Auto-range mode.
In the Auto-range mode, the multimeter selects the range with the best resolution.
(‘ AUTO' shows on the display.)
Push the' RANGE ' button to enter the Manual range.
In the Manual Range mode, you override Auto-range and select the range yourself.
Push the' RANGE ' button to increase the range. After the highest range, the
multimeter wraps to the lowest range.
Measurement
•Check the battery first, if' ’ is displayed, the battery needs to be changed.
' 'signal beside the sockets warns of the maximum input of voltage and current.
•Switch to the right range before measurement.
•The red lead mentioned in this manual is positive in polarity, and the black lead is
negative.

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DC/AC Voltage Measurement
1. Put the black lead into the' COM ' port and the red lead into the port.
2. Switch to the' ' or ranges and put the test leads to the loaded circuit.
3. DC signal will be displayed, indicating DC voltage test. Press button to ACV
test. ('AC ' is shown on the screen.)
Note：
1. The voltage above DC1000V or AC750V can't be measured, otherwise the
multimeter may be damaged.
2. In the AC/DC 600mV and AC 6V ranges, the multimeter will display some numbers
even with no input or test leads connected. In this case, short-circuit the'
' port and COM port. If the multimeter display returns to zero, it indicates that the
multimeter is normal.
Resistance Measurement
1. Put the black lead into the' COM ' port and the red lead into the port.
2. Switch to the ('Ω' shows on the display.)
3. Connect the test leads to the resistor to be tested.
Note:
•' OL' means overload, please switch to a higher range.
•' OL' will also be displayed if it is open-circuited.
•If the tested resistor > 60M Ω, it may take a few seconds to read.
•Before testing a resistor in the circuit, please make sure the circuit is powered off
and the high-voltage capacitor is completely discharged.
•To measure low resistance accurately, please short-circuit the two test leads and
read the resistance value of the short circuit of the test leads. After measuring the
measured resistance, the resistance value needs to be subtracted.

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Diode Measurement
1. Put the black lead into the' COM ' port and the red lead into the port.
2. Switch to the and press button 2 times.
( shows on the display.)
3. Touch the diode anode with the red probe, the black probe contacts the diode
cathode.
Note:
1. ' OL' will be displayed if open-circuited.
2. If the test leads are connected reversely with the diode polarity, ' OL' will also be
displayed.
Continuity Measurement
1. Put the black lead into the ’COM ’port and the red lead into the ' 'port.
2. Switch to the ' 'and press' ' button.
(‘ ’ is shown on the display.)
3. Contact the probe to the measured circuit or resistance.
4. The multimeter will buzz and the indicator light is yellow if the resistance between
the two points is less than 40Ω. When the resistance is >40Ω and <60Ω , the buzzer
does not buzz and the indicator light is red.
Note:
•'OL' will be displayed if it is open-circuited.
•Before ‘Continuity’ testing, please make sure the circuit is powered off and the
high-voltage capacitor is completely discharged.

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Capacitance Measurement
1. Put the black lead into the ’COM ‘ port and the red lead into the ' ' port .
2. Switch to the ranges and put the test leads to the circuit to be tested.
Note:
•Before testing a capacitor in the circuit, please make sure the circuit is powered off
and the high-voltage capacitor is completely discharged.
•For larger capacitance, it may take a bit longer time for the reading to stabilize.
Frequency/Duty Measurement
1. Put the black lead into the ‘COM ' port and the red lead into the ' port.
2. Switch to the Hz% and switch the Frequency or Duty Ratio by the ‘ '
button.
3. Put the test leads to the circuit to be tested.
Note:
•Do not test any voltage higher than 250V to prevent electric shock or damage to
the multimeter.
DC/AC Current Measurement
1. Put the black lead into the' COM ' port and red lead into the ' mA' port if the
current is under 600mA and put the red lead into the' 20A' port if the current is
between 600mA - 20A.
2. Switch to the， ， ，or ranges.
3. ' DC' signal will be displayed, indicating DC current test. Press button to AC

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current test. (' AC ' shows on the display.)
4. Connect the test leads to the loaded circuit.
Note:
1.' OL' means overload, please switch to a higher range.
2. The voltage above 250V can't be measured, otherwise, the multimeter may be
damaged.
3. Pay special attention to safety when measuring high voltage to avoid electric shock
or personal injury.
4. Test the known current with the multimeter before use.
NCV Test
1. Turn the knob to the NCV
2. Then NCV probe gradually approaches the detected point.
3. When the multimeter senses weak AC signals, the yellow indicator lights up with a
slow beeping sound. When the multimeter senses strong AC signals, the red
indicator lights up with fast beeping sound.
Note:
•Even if there is no indication that the voltage may exist, do not rely on non-contact
voltage detectors to determine if there is a voltage present, which may be caused
by socket depth, insulation thickness, type, etc.
•When the voltage is input to the multimeter the indicator may light up due to the
presence of induced voltage.
•External interference such as flashlights, motors, etc., may trigger non-contact
voltage detection.