A Multimeter is a versatile equipment for measurement of
different electrical quantities in a circuit. In the course of lab work it
is often required to measure voltage, current and resistance. Instead of
using three different meters it is better to use a Multimeter. The
Multimeter is equipped with circuitry that allows it to be used as a
voltmeter, an ohmmeter or as an ammeter. That is the reason why a Multimeter
is also known as Volt-Ohm-Milliammeter (VOM).
Constituents of a Multimeter
Probes
: Probes is used for connecting the Multimeter into the circuit.
With Probes, connections are simply touched for measurement and the
Multimeter gives the readings.
Depending on the voltage or current to be measured, a variety of Probes
are used. As a rule higher the current higher would be the number of
probes between the probes and thicker the cables.
Ports
: One of the question which puzzles the users of Multimeter is that
there are only two probes whereas there is number of sockets. A diagram
of the ports is shown here. The diagram shown here is of a Multimeter
with four probes. This is not a standard design, a Multimeter can have
more or less ports. Let's understand the function of each of the ports.
» Number 1 is the common port.Normally, the black probe is plugged
here (negative). Truly according to the name it is a common element to
all of the testing circuits.
» Number 2 is the voltage, resistance and continuity port. The red
probe(positive) is connected to this port for voltage and resistance
readings or for checking of wire continuity.
» Number 3 is for current up to 300mA and is used for counting
electrons in a circuit.
» Number 4 port does the same work as above but can take more
current up to 10A
- Symbols :Some of the common symbols found in the knob of a
Multimeter is discussed here.
»
Alternate Current : The symbol depicted here is of AC current.
This is turned for testing that has an AC current running through.
»
DC :This is the symbol for direct current.
»
Continuity : This great for checking continuity and checking for
shorts. When current is put through two terminals, and if the resulting
value is within the contact range it will beep or give light indication.
»
Resistance : This is the symbol for resistance, and its unit is
in Ohms. Using this setting the resistance between two points can be
measured.
»
Voltage : This is for measuring the potential difference between
two probes. For measuring voltage the positive probe is connected to a
port marked as V or Voltage.
» Current : This has the symbol of A called
Amps. This measures the current flow in the part of circuit between two
probes.
Types of Multimeter
Analog Multimeter

Analogue
multimeters utilizes very little power from the circuit to be tested for
operating of the pointer . Analogue Multimeter should have a high
sensitivity that is minimum 20kO/V. Anything below this can upset the
circuit to be tested and give rise to an incorrect reading. For obtaining a
valid reading the meter resistance must be at the minimum 10 times the
circuit resistance. While looking for Analog Multimeter a crucial
environmental parameter to consider is the operating temperature. Some of
the features to look for in Analog Multimeter includes the following:
- Battery power
- Overload protection
- Temperature compensation
- Mirrored scale
- Range switch
- Provision for Diode and battery test
Digital Multimeter

A
Digital Multimeter display a constant resistance that is at least 1MO (often
10MO) applicable on all their DC voltage ranges. This is often more than
sufficient for almost all the circuits.
A Digital Multimeter is a versatile instrument that contains three meters
namely ammeter, voltmeter and ohmmeter. Digital multimeters are now coming
in different types of models such as bench top or handheld. If used with
handles and wheels bench top models can also be portable. Handheld
multimeters can be operated with a single hand. Some of the features to look
for in Digital multimeter include the following:
- Battery power
- Analog bar graph
- Data acquisition and storage
- Data logging
- Auto-ranging
- Adjustable sampling rate
- DB readings
- Removable data storage
Layout of a Digital Multimeter
A Digital Multimeter is designed to contain the Digital display panel on
the top which can display any number between 0 to 1999 or even higher. Below
the digital readout area is a knob called the function switch. With this
switch the Digital Ammeter can perform different functions. After the knob
is the ports where the probes are connected for taking readings.