The most basic things we measure are voltage and current. A multimeter is also great for some necessary sanity checks and troubleshooting. Is your circuit not working? Does the switch work? Put a meter on it!
The multimeter is your first defense when troubleshooting a system. In this tutorial, we will cover measuring voltage, current, resistance, and continuity.
In this post, we’re going to show you how to use a multimeter. This post is mostly addressed for beginners who are starting in electronics and have no idea how to use a multimeter and how it can be useful.
We’ll explore the most common features of a multimeter and measure current, voltage, resistance, and how to check continuity.
What is a Multimeter, and What Does it Measure?
A multimeter is a combination of a voltmeter, ammeter, and ohmmeter and works as a piece of standalone test equipment. It’s not limited to only these three measurements — it can also measure capacitance, frequency, and transistors’ gain.
These meters were invented back in the 1920s and are still used as they provide high accuracy and have the capability to measure quantities in micro and nano ranges. These electronic meters are of two types: analog and digital. Digital meters are used widely because of their capability to display data in decimals.
Types of Digital Multimeters
There are two types of digital multimeters (DMM): auto-range and manual range. As per the name, in manual range DMMs, you have to select your measuring entities’ scope. This type of DMM is very cheap compared to auto range multimeters, Auto-range DMMs don’t have any protection circuits, and if they’re misused, they could blow up.
Besides all of its excellent electrical-testing capabilities, most modern multimeters can also take temperature readings. Rotate the meter’s dial to the temperature mode, then press the select button to toggle between Fahrenheit and Celsius.
Plug the thermocouple into the meter to read air temperature, or insert the temperature probe to take temperature readings of liquids, gels or to track the surface temperature of a gas dryer. You can observe the appliance’s temperature cycle without touching it with your hand.
Testing Extension Cords
It’s smart to use your meter to occasionally test old extension cords because damaged cords can shock you or start a fire. Begin by unplugging the extension cord from the wall and turning the meter’s dial to the Ohm setting.
To test the cord’s ground, push the red probe into the small hole on the cable’s female end. Then touch the black probe to the ground (soil) prong protruding from the male end. A continuous circuit measured from these two ends will have a resistance of .8 ohms or even less. Now, touch the red probe to each of the flat prongs on the male end to ensure an O.L reading.
There should be an open circuit when the cord is analyzed in this fashion; there should be no contact between the wire that connects the ground pin and either of the other two wires inside the cable.
Next, insert the red probe into the short (hot) slot on the cord’s female end. Touch the black probe to the narrow flat prong on the male end. Electrical continuity through the cable will have a resistance of .8 ohms or less.
Then touch the black probe to the broad flat prong and then the round prong. The meter should show no continuity and an O.L. for reading in these two positions.
Finally, take the red probe and push it into the longer (neutral) slot on the female end of the cord. Take the black probe and touch the wide flat prong. The continuity will have a resistance of .8 ohms or less. Touch the black probe to the narrow prong and then the round prong for an O.L. reading.
After confirming that the cord doesn’t have any shorts, run a voltage test. Plug the cable into an electrical outlet and rotate the meter’s dial to Volts AC. Insert the black probe into the round hole in the female end of the cord, and push the red probe into the narrow slot.
You should get a reading close to 120 volts. Now move the red probe into the longer (neutral) slot to confirm a reading of about .1 millivolts (there is a negligible voltage between the outlet’s ground and neutral and the cord’s ground and neutral).
Leave the red probe in the more extended slot and move the black probe to the shorter slot to get a voltage reading of about 120 volts, confirming that the extension cord is in good condition.
Testing Electrical Outlets
Here’s how to determine if the wall outlets in your home deliver the correct voltage, which in most modern homes is 120 volts. Plug the black probe into the meter’s black COM jack and the red probe into the red Volts jack. Then turn the rotary switch to Volts AC (Vac), which is also indicated by a wavy line on the dial.
Push the red probe’s tip into the shorter (hot) of the two vertical slots on the outlet. Insert the black probe into the more extended slot (neutral). Check the readout on the meter’s screen. A properly functioning outlet should produce 110 to 120 volts.
Next, remove the black probe from the outlet—leave the red probe in place—and insert the black probe into the small, rounded hole (ground) below the two slots. The reading should remain the same. If it doesn’t, the outlet is improperly wired, or perhaps the ground is missing; call an electrician.
Selecting a multimeter
You can find a wide variety of multimeters with different functionalities and accuracy. A basic multimeter costs about $5 and measures the three most straightforward but most essential values in your circuit: voltage, current, and resistance.
However, you can guess that this multimeter won’t last long and isn’t very accurate. The best multimeter for you will depend on what you intend to do if you’re a beginner or a professional electrician and on your budget.