How to Use a Multimeter
How to use a multimeter. This paper describes the basics of using a multimeter. The multimeter depicted here is a basic low cost meter. A basic multimeter will measure: DC voltage, AC voltage, Resistance, Continuity and Amps.
The main sources for Direct Current, DC voltage, in devices we use each day are batteries. Devices that are powered by a battery are on DC voltage. Any device on your car that runs off the car battery your cordless drill camera drones and toys that runs on batteries uses DC voltage. To test voltage you need to set it here where you see V for voltage with these straight and dotted lines. Next you need to make sure your test leads are in the right location. Your black ground or common test lead will always need to be where it says COM. The red test lead is the one that you will need to switch around based on what you are measuring. To measure voltage you need to place your red test lead on the multimeter where you see the sign for voltage. Then place the red test lead on the positive or powered side of the device or circuit you are measuring. The black test lead connects on the ground side.
Set the dial on your multimeter to the number just above the maximum amount of voltage you are measuring.
For example when measuring a 1.5v AA battery set the dial to 2 volts and the read out shows we have 1.6 volts which mean this is a fully charged battery. However if you are unsure of how much voltage you are supposed to measure you can always start higher and come lower to get a more precise measurement.
Measuring the voltage on a 12 volt car battery you can see there are 12 volts but we are also seeing a negative sign. A negative sign means the test leads on the circuit backwards. This does not damage the multimeter; it is a good way to find out your positive and groundside when you are unsure which one is which.
AC voltage devices are ones that plug into the wall socket they run on AC voltage. When measuring AC voltage the black and red test lead stays in the same place.
You need to set your dial where you have the voltage sign and also has the wave sign.
When you want to see if we have current at a wall receptacle we set the multimeter to 200 in the AC voltage area that is because in the US we get about 110 volts at the socket. The 120 volt label is just a nominal figure; the actual voltage could be anywhere in the range of 110-125 volts. Modern electrical device designs tolerate the fluctuations.
A word about safety when you are measuring high voltage. You need to be sure of the integrity of your multimeter and the test leads and when you take your measurement make sure you keep your fingers far from the tip of the test leads and that the leads don’t come close to each other when you are taking the measurements. For added safety you should wear safety gloves. Next we put in our test leads first the ground which goes here in the bigger hole and then our red test lead goes into the smaller hole. As you can see we have 119 volts which is good.
This lower bottom one is the wall unit ground point and a good way to see if it is grounded is to put your ground test lead on here and measure voltage as well.
Resistance is the opposition that any material has to the flow of electric current. Ohms is the unit of measurement for resistance. For example a piece of wood is extremely resistant to the flow of electric current where as a pair of wires have next to no resistance to the flow of electric current.
Different components of an electronic circuit or system have a certain amount of resistance so that the whole circuit works properly. So knowing how to measure resistance correctly is crucial. When measuring resistance set your dial to this setting where you can see this Ω sign which is for resistance.
The red test lead stays in the same location because as you can see we have the sign for resistance here as well.
We will use a spark plug wire to test its resistance. A spark plug wire has a resistance of approximately 10,000 Ohms is the unit of measurement for resistance. We set the multimeter to the next number up which is 20K or 20,000 ohms. The K represents a thousand.
Our test of the spark plug wire shows we have 9.87K ohms which means this spark plug wire is within specification.
Continuity is checking an electric circuit to verify that current can flow through it. This is done by sending a very small amount of voltage through it on a multimeter continuity is usually verified by a beep sound. In order to test for continuity we set are multimeter here where we see the sound wave sign which also is part of the resistance settings so our test leads stay in the same location.
For this example, if you have a set of wires attached to a connector and you wish to verify that the wiring is not faulty. Attach a test lead to one end and the corresponding test lead to the connector end.
A beep from the multimeter means the circuit has continuity. If there is no beep the wire has a short. Always unplug the device or remove the batteries before testing. Never check an active or hot circuit for resistance or continuity. This test is especially useful to check large circuits or the continuity on small circuit boards like.
An ampere (Amp) is the unit used to measure electric current. To measure amps on this multimeter your need to switch your red test leads to one of two slots.
The slot on the right is fused and can only measure up to 200 mA or in other words .200 Amps or the slot on the left is unfused and measures up to 20 A. The one that is fused means if you are in this setting and end up measuring more than 200 mA a fuse inside will blow saving your multimeter but the other one that is unfused means your multimeter will blow if you measure more than 20 amps. You need to be alert when measuring a circuit with higher amps or purchase a multimeter that is fused on this side as well. First since we are going to measure the amperes of a battery powered light bulb set the dial on 20 amps on the DC voltage setting.
When measuring amps you need to place your multimeter inside of the circuit on the power side. For example in this basic circuit you make a break on the power side grab the red test lead and place it close to the power source. Place the black test lead on the other side completing the circuit and then let your multimeter measure the current flowing through it.
This small light bulb uses 1.95 amps of current.
These are the basics steps for measuring: DC voltage, AC voltage, Resistance, Continuity and Amps.
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