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ELECTRICAL DEPARTAMENT
ELECTRICAL MEASUREMENT AND MEASURING
INSTRUMENT(2130903)
•DIGITAL MULTIMETER
•MALAVIYA GRUHEN
•(130350109040)
What is a Digital Multimeter?
It is a common & important laboratory instrument. It
is used to measure AC/DC voltage, AC/DC current and
resistance with digital display. It gives digital output,
which is very accurate. As the name suggests, multimeter
are those measuring instruments which can be used to
calculate multiple circuit characteristics.
A multimeter has three parts:
•
•
•
Display
Selection Knob
Ports
• Two probes are plugged into two of the
ports on the front of the unit.
• COM stands for common and is
almost always connected to Ground
or ‘-’ of a circuit.
• 10A is the special port used when
measuring large currents (greater
than 200mA).
•
mAVΩ is the port that the red probe is
conventionally plugged in to. This port
allows the measurement of current (up to
200mA), voltage (V), and resistance (Ω).
Rear of the multimeter encases a 9V battery and a fuse.
Placed between the battery and the input ports, the
fuse acts as circuit protector cutting the measuring
process off when inputs higher than bearable range are
applied on the multimeter.
The PCB contains an assortment of various
components including various types of resistors,
capacitors, diodes and integrated circuits. Also, it
hosts the battery, crystal oscillator, PTC, LCD and
the buzzer which tests the continuity of device
under test .
The PCB is bound to the top casing of
the multimeter with the help of
screws. A LCD and a rotary knob
switch are sandwiched between the
top casing and the other side of the
PCB. Also, the contacts for switching
the multimeter on and off can be
seen.
• Some multimeter employ the rotary switch to handle the
switching ON and OFF options while some require a slider
switch.
• The selection knob allows the user to set the multimeter to
read different things such as milliamps (mA) of current,
voltage (V) and resistance (Ω).
• The LCD is embedded
on the PCB and is
interfaced through pinouts on the PCB itself
• A transparent plastic
casing is over the LCD
protecting it from the
scratches. Also, shock
absorption is provided
by the rubber pads
closely attached at the
top and bottom of the
LCD.
• The display usually has four digits and the
ability to display a negative sign. A few
multimeter have illuminated displays for better
viewing in low light situations.
Measuring Voltage
To start, let’s measure voltage on
a AA battery: Plug the black
probe into COM and the red
probe into mAVΩ. Set the
multimeter to “2V” in the DC
(direct current) range. Almost all
portable electronics use direct
current), not alternating current.
Connect the black probe to the
battery’s ground or ‘-’ and the
red probe to power or ‘+’.