Learn the basics of Electrical Engineering.

Basics of Digital Multimeter

The digital multimeter is used to measure voltage, current, and resistance. Modern multimeters can also be used to measure the frequency, capacitance. Today you'll learn:
  1. Parts of digital multimeters
  2. How to use it
  3. Symbols you should know while using multimeter
  4. How to measure resistance
  5. How to measure voltage
  6. How to measure current
  7. How to measure the voltage at your wall outlet

Parts of Digital Multimeter

A digital multimeter has four parts:
  1. The input jack
  2. Two Probes (Red and black)
  3. Display screen
  4. Rotary knob
The figure below presents a visual representation of these parts:
Let's understand how it works.

Probes [Black and Red] and input jack

One end of both probes connect to the input jack, whereas the other end (tip) of both probes are connected to the circuit under test.
The black probe always connects to the blackjack. The red probe can be inserted in either of the two red jacks.
  1. The current is measured by inserting the red probe into the amps jack. Usually, the amps jack is labeled with the current, amps, A or mA.
  2. The voltage is measured by inserting the red probe into the volts jack. The volt jack is also used for measuring the frequency, capacitance, and other measurements. In short, the volts jack is used for all measurements other than current.
You should be extra careful while inserting probes in jack. A wrong probe-jack insertion results in severe damage to your digital multimeter. In certain cases, it leads to fatal injuries.

Display screen

The display screen is the main output screen which displays the measured quantity.

The rotary knob

The rotary knob of the multimeter is used to switch between different quantities. It contains various symbols that are arranged in a circular configuration. Before doing measurements you are required to set the knob on a proper scale. If you are measuring the resistance you should set the knob to Ω scale. The figure below displays various symbols you'll encounter:
A DC quantity is always labeled with --- or ‗‗ symbols. An AC quantity can be identified by observing the ~ symbol.

The above information is quite enough to start. Let's roll in the field.

How to measure resistance [Digital Multimeter as Ohmmeter]

  1. Set the multimeter to resistance (Ω) scale.
  2. Remove the resistor from the circuit.
  3. Connect probes to a multimeter.
Resistors don't have any polarity so can connect the meter in any way. The figure below illustrates the use of multimeter as an ohmmeter.

How to measure voltage [Digital multimeter as Voltmeter]

  1. Set the multimeter to voltage scale. In case of DC, you should select the DC scale (---) and in case of ac choose AC scale (~).
  2. Connect the meter in parallel to the circuit. Since voltage always remains same in parallel, a voltmeter is connected in parallel.
Precaution: Never connect the voltmeter in series with the circuit. Doing so will yield fault readings.

How to measure current [Digital Multimeter as Ammeter]

  1. Set the multimeter to the current/ampere scale. In case of AC use AC ~ and in case of DC choose ---.
  2. Break the circuit and connect the ammeter in series. {The figure below illustrates this]

How to measure the voltage at your wall outlet

A digital multimeter can also be used to monitor the voltage at the outlet of your home.
  1. Set the multimeter to AC voltage scale. [Since the outlet voltage is ac]
  2. Connect the multimeter the wall outlet.
  3. 120/230 or a closer value will appear.

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