Having learnt the basics of analog and digital multimeters, you are now ready to make measurements. Resistance, voltage and current are the common measurements taken with the multimeter. Let us take a look at these common measurements using a digital multimeter.
If you are new to this page then please read the introductory post: Basics of a Multimeter: A Guide For Technical and Non-Technical People
How to Measure Resistance With a Multimeter:To carry out resistance measurements, power to the component under test must be switched off. A resistor will scarcely short, but typically will open. If a resistor does open, the digital meter display will flash on and off or display OL (open line) because the resistor has an infinite resistance. To measure resistance with a digital multimeter, connect the multimter leads as shown below:
Follow the steps outlined below:
1) Turn off power to the circuit or component under test
2) Select resistance Ω function using the rotary selector switch
3) Plug the black test lead into the COM jack and the red test lead into the Ω jack (here you will see the letter V for voltage, Ω sign and diode sign)
4) Connect the test leads tips across the component or part of the circuit for which you intend to determine the resistance.
5) View the reading and be sure to note the unit of measurement: Ω or KΩ or MΩ depending on what you are measuring.
How to Measure Voltage With a Multimeter:
Before making voltage measurements, take all necessary precautions as any carelessness on your part could lead to injury or fatality depending on the value of the voltage you are measuring. Note for voltage measurements, there must be power in the circuit or component whose voltage is to be determined.
To start, connect the test leads as shown in the diagram below:
Follow the steps outlined below:
1) Connect power to the circuit or component under test
2) Select volts AC (V~), volts DC (V---), mvolts (V---) as desired
3) Plug the black test lead into the COM jack and the red test lead into the V jack
4) Touch the test leads tips to the circuit across across a load or power source as shown in the diagram above(parallel to the circuit to be tested)
5) View the reading and be sure to note the unit of measurement.
When taking DC voltage readings of the correct polarity (+ or -), touch the red test lead to the positive side of the circuit, and the black test lead to the negative side of the circuit ground. If you reverse the connections, a DMM with auto-polarity will merely display a minus sign indicating negative polarity. With an analog meter, you need to ensure the right polarity. Any mistake could lead to the damage of the meter.
How to Measure Current With a Multimeter
Most times during a troubleshooting process, hardly do we make current measurements. However if there is need for current measurements, connect the meter test leads in series as shown below:
Follow the steps outlined below to take the measurement:
1) Turn off power to the circuit under test.
2) Disconnect, cut or unsolder the circuit and connect the meter in the circuit as shown above.
3) Select Amps AC(A~) or Amps DC(A---) as desired
4) Plug the black test lead into the COM jack and the red test lead into the 10 Amps or 300mA jack depending on the value of the reading you are expecting
5) Connect the test leads tips to the circuit in series so that all current flows through the meter.
6) Turn the circuit power back on
7) View the reading and be sure to note the unit of measurement. Note if test leads are reversed, a negative sign will be displayed on the meter LCD.
I hope you have found these posts on multimeters useful.