One of the most useful tools in electronics is a multimeter, which is also sometimes called a multitester or VOM (volt-ohm-milliammeter). You’ve probably seen one at home in your dad’s toolbox, or perhaps when an electrician comes by to repair a broken circuit. A multimeter can be used to diagnose a circuit, study an electronic design, and test a battery’s remaining capacity, among other practical uses.
Most multimeters are designed to measure voltage, current, and resistance and are used in most homes, offices, and engineering fieldworks for which you can train using these engineering cpd courses. Depending on the model of your multimeter, you may also have a continuity check function, which is extremely useful when building a circuit to ensure that everything is connected properly. A diode check function is also a handy feature especially if you’re working with a diode and can’t tell which way it should go in the circuit or you aren’t sure if the diode is functioning properly.
There are two basic types of multimeters: analog and digital. The main difference between the two is the display. Whereas an analog multimeter uses a needle to show the measured value, a digital multimeter flashes numbers on the screen. While some prefer the easy readability of a digital multimeter, some might like the precision of an analog multimeter. Whichever you prefer, RS Components has a wide selection of multimeters to suit your needs.
But no matter what type of multimeter you have, the operations boils down to the same procedures. Here are the basics of using a multimeter.
Plugging the Probes
Multimeters usually have black and red probes, and there is usually no difference between the two other than the color. However, the black probe is the one that is usually plugged into the “COM” port, and the red one into the mAVΩ port. If you are measuring currents greater than 200mA, then you can plug the red probe into the 10A port.
After ensuring that no current is running through the circuit that you are going to test (turn it off, unplug it from the wall socket, and remove any batteries), switch on your multimeter and set the dial to continuity mode. The icon usually looks like a sound wave. If your multimeter doesn’t have one, select the lowest setting in the resistance mode, indicated by the Ω symbol.
Place one probe at each end of the circuit you want to test. If there’s continuity, meaning an electric current can flow freely from one end of the circuit to the other, the multimeter should indicate a value of zero or near zero (say, 0.5). A digital multimeter will also indicate this status by a beeping sound. If there is no continuity, the multimeter will indicate a value of 1 or, in the case of digital multimeters, the letters OL meaning “open loop.” This means that there’s a break somewhere in the circuit, likely caused by things like broken conductors, blown fuses, and other loose or damaged components.
You can also test the continuity of your own multimeter by touching the probes together. Again, the result should be zero or near zero, to ensure that the current can flow from one end of your multimeter’s probe to the other.
To test for voltage, connect the probes accordingly, turn on the multimeter, and then set it to the DC voltage mode. The icon is usually a V with the ⎓ symbol. If your multimeter is autoranging, then you’re in luck. If not, you have to choose the correct setting, which should be slightly higher than the value you are expecting to measure.
For example, you are measuring the voltage output of an old battery and you expect the output to be in the range of 9 volts. If your multimeter has settings for 200mV, 2V, 20V, and 200V, the first two options are too small. It would be like using a 12-inch ruler to measure something that is more than 12 inches. Therefore, you need to choose the 20V setting.
If you’re unsure, you can start the highest setting although keep in mind that this will result in less accurate measurements. You can turn down the setting until you get it right. You will know that you have a too-low setting if the multimeter reads 1 or OL.
Place the red probe on the positive terminal and the black probe on the negative terminal to get the voltage output reading. Reversing the probes won’t damage your multimeter, however. It will just show a negative reading.
Similar to performing a continuity test, you have to ensure that no current is running through the circuit or component that you are going to test. If you want to test the resistance of an individual component, test it by itself while still unattached to the circuit. The resistance mode is indicated by the Ω symbol.
Just like how you test for voltage, choose the setting that is a little bit above your expected measurement (again, this is unless your multimeter is autoranging). Place one probe at each end of the circuit or component that you are testing—it doesn’t matter which probe goes where, since resistance is non-directional. If the multimeter reads close to zero, the range you selected is probably too high; if the range is too low, the multimeter will read either 1 or OL. Adjust your range accordingly so you get the most accurate measurement.
It’s a bit tricky to measure current since your multimeter technically has to be part of the circuit (in series) so that it can measure the current as it flows through the board. It doesn’t matter where you connect the multimeter, however, as long as the loop is closed.
Once you have the multimeter connected to the circuit, you simply have to follow the same steps when measuring voltage and resistance — get the correct range and place the probes accordingly. If you get a negative reading, simply switch the placement of the probes. Usually, the 200mA setting works fine for most projects. However, if you suspect that you will be using more than close to or more than 200mA, plug the red probe to the 10A just to be safe, as too much current will likely result into a blown fuse.
And there you have it. You are now ready to use your multimeter for your next project. Can your lemon battery power up a lightbulb? Can you use aluminum foil to replace a wire in a simple circuit? There are a lot of interesting questions about science and electronics that you can answer with the help of a multimeter!
Photo Credit: https://learn.sparkfun.com/tutorials/how-to-use-a-multimeter
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