Multimeter Basics Multimeter Basics
Don't let all the dials and knobs fool you -- even a novice can learn to use a multimeter. It may look a little scary, but once you've used it a few times, you will get the drift. The one thing you do want to remember is that you will be working with electrical items and you should always use caution. A basic definition for a multimeter is simple: it's an electronic measuring instrument that combines multiple functions such as a voltmeter, ammeter and ohmmeter.
The Terminology: AC and DC
AC is alternating current, where an electrical charge periodically reverses direction, about 60 times per second. It is the current that runs through your house making lights and outlets work.
DC is direct current, where electricity runs in only one direction. It's used for anything that is run on batteries. (Your car is DC voltage because it starts with a battery.) A multimeter can measure both AC and DC current.
Symbols and Parts on a Multimeter
There are many multimeters out there. They can range from $10 to hundreds. To keep things simple, all the information in this article was done using a digital, easy-to-use and read multimeter. An inexpensive digital multimeter is all you need to diagnose most problems around the house.
On the meter I am using there are three basic sections: 1.Voltage (V) with one row of dashed lines under a solid line (this is the DC side of the meter. Most meters will start at 200 millivolts and go up to 600 volts. 2. Ohms (looks like an upside down horseshoe). Ohms measures resistance, or how hard it is for electricity to flow. The higher the reading, the harder it is for electricity to flow through a cord. 3. There is also a wave looking symbol in one section. This is the symbol for alternating current or AC. This section goes from 200 milliamps to 600 volts. Symbols can vary on different meters, but the sections are the same.
There are two cords that come with the meter. One red and one black. On most meters the black wire goes into the black port and the red into the red port. On the other end of the wire there are metal protrusions called probes.
Things You Can Do With a Multimeter
Test Your Batteries to Save Some Cash
The easiest, and probably best place to start is a lesson on testing batteries. It’s a great thing to know how to test a battery simply because it can save you money. There have been many times I tossed batteries because I thought they were bad and it turned out that the flashlight was bad…not the batteries.
To test a battery, put the selector to DC volts. Most batteries, including AA and AAA batteries, are 1.5 volts. All batteries have their voltage written somewhere on the outside of the battery. On the meter dial select a 4 or more volt range. It doesn’t hurt the meter to go to a higher setting, but the closer you can get to the volts listed on the battery the better the reading will be. Place the red probe on the positive end of the battery and the black probe on the negative. If the reading is one volt or less, you might as well recycle the battery. If it is 1.45 volts, it won’t be long before you will need to replace it.
To test a 9 volt battery, all you need to do is change the DC scale to a 40 volt range. A 9 volt is dead if the reading is below 7.5 volts.
Test Fuses to Save on Appliance Repair
Many household appliances have fuses in them. Microwaves, air conditioners and other small appliances all have fuses. This is another area where you can save big. If you knew that a fuse was bad and not the whole appliance, the repair cost would be nominal compared to replacing the appliance. However, most of the time you will not be able to tell a fuse is bade unless you test it. First, disconnect the appliance from the electrical socket. Carefully pull the fuse out of your appliance without touching any other parts inside the fuse box. Change your meter to the Ohm section. Touch one end of the probe to one end of the fuse and the other probe to the other end of the fuse. It doesn’t matter which probe goes to which end because you are just measuring the continuity of the circuit inside the fuse. The probes serve to complete the circuit. If your meter comes with a speaker, you will hear a high-pitched sound if the fuse is good. If there is no noise, the fuse is bad. If your meter doesn’t come with a speaker, then the Ohm reading should be zero if the fuse is good. If you get a high reading, the fuse is bad.
Test Cords With an Alligator Clip
You can test electrical cords in the Ohm setting too, but you will need an alligator clip accessory for your probes. To test a cord, just clip one alligator clip to each end of the plug, and bend the cord gently near the plug end while you are watching the meter. If the reading swings up to a normal setting and then down to no reading, then there is an issue with the cord. If the cord is good, there will be little or no variability in the reading.
Test Electrical Sockets
If you want to test something in the AC section of the meter, no need to look any further than an electrical socket. Set the dial to 400 V on the AC side of the meter. Put one probe in the hot slot and one probe in the neutral. The meter should read 120 to 125 volts. This is a normal reading for most U.S. households.
These are just a few things you can do with your multimeter. Most meters come with an instruction booklet that will give you other ideas on its uses. Just remember to use extreme caution if testing anything with live electrical power.