In this post we’re going to show you how to use a multimeter. This post is mostly addressed for beginners who are starting out in electronics and have no idea how to use a multimeter and how it can be useful. We’ll explore the most common features on a multimeter and how to measure current, voltage, resistance and how to check continuity.
What is a multimeter and why do you need one?
A multimeter is a measurement tool absolutely necessary in electronics. It combines three essential features: a voltmeter, ohmeter, and ammeter, and in some cases continuity.
A multimeter allows you to understand what is going on in your circuits. Whenever something in your circuit isn’t working, the multimeter will help you troubleshooting. Here’s some situations in electronics projects that you’ll find the multimeter useful:
- is the switch on?
- is this wire conducting the electricity or is it broken?
- how much current is flowing through this led?
- how much power do you have left on your batteries?
These and other questions can be answered with the help of a multimeter.
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 simplest but most important values in your circuit: voltage, current, and resistance.
However you can guess that this multimeter won’t last longer 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.
Getting familiar with a multimeter
A multimeter is composed by four essential sections:
- Display: this is where the measurements are displayed
- Selection knob: this selects what you want to measure
- Ports: this is where you plug in the probes
- Probes: a multimeter comes with two probes. Generally one is red and the other is black.
Note: There isn’t any difference between the red and the black probes, just the color.
So, assuming the convention:
- the black probe is always connected to the COM port.
- the red probe is connected to one of the other ports depending on what you want to measure.
The “COM” or “–“ port is where the black probe should be connected. The COM probe is conventionally black.
- 10A is used when measuring large currents, greater than 200mA
- µAmA is used to measure current
- VΩ allows you to measure voltage and resistance and test continuity
This ports can vary depending on the multimeter you’re using.
You can measure DC voltage or AC voltage. The V with a straight line means DC voltage.
The V with the wavy line means AC voltage.
To measure voltage:
- Set the mode to V with a wavy line if you’re measuring AC voltage or to the V with a straight line if you’re measuring DC voltage.
- Make sure the red probe is connected to the port with a V next to it.
- Connect the red probe to the positive side of your component, which is where the current is coming from.
- Connect the COM probe to the other side of your component.
- Read the value on the display.
Tip: to measure voltage you have to connect your multimeter in parallel with the component you want to measure the voltage. Placing the multimeter in parallel is placing each probe along the leads of the component you want to measure the voltage.
Example: measuring a battery’s voltage
In this example we’re going to measure the voltage of a 1.5V battery. You know that you’ll have approximately 1.5V. So, you should select a range with the selection knob that can read the 1.5V. So you should select 2V in the case of this multimeter. If you have an autorange multimeter, you don’t have to worry about the range you need to select.
What if you didn’t know what was the value of the voltage? If you need to measure the voltage of something, and you don’t know the range in which the value will fall under, you need to try several ranges.
If the range you’ve selected is lower than the real value, on the display you’ll read 1 as shown in the picture below. The 1 means that the voltage is higher than the range you’ve selected.
If you select a higher range, most part of the times you’ll be able to read the value of the voltage, but with less accuracy.
What happens if you switch the red and the black probe?
Nothing dangerous will happen. The reading on the multimeter has the same value, but it’s negative.
Example: measuring voltage in a circuit
In this example we’ll show you how to measure the voltage drop across a resistor in a simple circuit. This example circuit lights up an LED.
TIP: two components in parallel share voltage, so you should connect the multimeter probes in parallel with the component you want to measure the voltage.
To wire the circuit you need to connect an LED to 9V battery through a 470 Ohm resistor.
To measure the voltage drop across the resistor:
- You just have to place the red probe in one lead of the resistor and the black probe on the other lead of the resistor.
- The red probe should be connected to the part that the current is coming from.
- Also, don’t forget to make sure the probes are plugged in the right ports.
To measure current you need to bear in mind that components in series share a current. So, you need to connect your multimeter in series with your circuit.
TIP: to place the multimeter in series, you need to place the red probe on the lead of a component and the black probe on the next component lead. The multimeter acts as if it was a wire in your circuit. If you disconnect the multimeter, your circuit won’t work.
Before measuring the current, be sure that you’ve plugged in the red probe in the right port, in this case µAmA. In the example below, the same circuit of the previous example is used. The multimeter is part of the circuit.
Plug the red probe into the right port and turn the selection knob to the resistance section. Then, connect the probes to the resistor leads. The way you connect the leads doesn’t matter, the result is the same.
As you can see, the 470Ω resistor, only has 461Ω.
Most multimeters provide a feature that allows you to test the continuity of your circuit. This allows you to easily detect bugs such as faulty wires. It also helps you check if two points of the circuit are connected.
To use this functionality select the mode that look like a speaker.
How does continuity work?
If there is very low resistance between two points, which is less than a few ohms, the two points are electrically connected and you’ll hear a continuous sound.
If the sound isn’t continuous or if you don’t hear any sound at all, it means that what you’re testing has a faulty connection or isn’t connected at all.
WARNING: To test continuity you should turn off the system! Turn off the power supply!
Touch the two probes together and, as they are connected, you’ll hear a continuous sound.
To test the continuity of a wire, you just need to connect each probe to the wire tips.
A multimeter is an essential tool in any electronics lab. In this Beginner’s Guide, we’ve shown you How To Use a Multimeter. You’ve learned how to measure voltage, current and resistance, and how to check continuity.
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