Handheld models feature a compact design so that they can be held during use. Since they are easy to carry, they can be used in a variety of applications, from laboratories to on-site work. Handheld models are available in a variety of form factors, including compact, card-shaped, and pen-shaped varieties.
By contrast, benchtop models are designed to be placed on a horizontal surface during use. They are often embedded in workbenches, systems, and production lines, and many have a large number of display digits. Many first-time purchasers may feel intimidated by the broad range of functionality offered by digital multimeters. How can one choose the best instrument for a given application?
The first step is to determine whether a candidate model has the necessary functionality and to check specifications like its range and resolution. Multifunctional digital multimeters have the advantage of being usable in an array of situations. Measuring current works the same as voltage and resistance -- you have to get the correct range. Set the multimeter to mA, and work from there. The current consumption for many breadboard projects is usually under mA. Make sure the red probe is plugged into the mA fused port.
This means you can keep the red probe in the same port to measure current, voltage, or resistance. However, if you suspect that your circuit will be using close to or more than mA, switch your probe to the 10A side, just to be safe. Overloading the current can result in a blown fuse rather than just an overload display. More on that in a bit. This circuit was only pulling 1. The average reading was closer to 2. Realize that the multimeter is acting as a piece of wire -- you've now completed the circuit, and the circuit will power on.
This is important because as time goes on the LED, microcontroller, sensor, or whatever device being measured may change its power consumption such as turning on an LED can resulting in a 20mA increase for a second, then decrease for a second when it turns off. On the multimeter display you should see the instantaneous current reading.
All multimeters take readings over time and then give you the average , so expect the reading to fluctuate.
In general, cheaper meters will average more harshly and respond more slowly, so take each reading with a grain of salt. In your head, take an average range such as 7 to 8mA under normal 5V conditions not 7. Similar to the other measurements, when measuring current, the color of the probes does not matter.
What happens if we switch probes? It simply causes the current reading to become negative:. Current is still flowing through the system, you've just changed your perspective and now the meter reads negative. Measuring current can be tricky the first couple of times. Don't worry if you blow the fuse - we've done it dozens of times! We'll show you how to replace the fuse in a later section. Continuity testing is the act of testing the resistance between two points.
This test helps insure that connections are made correctly between two points. This test also helps us detect if two points are connected that should not be. Continuity is quite possibly the single most important function for embedded hardware gurus. This feature allows us to test for conductivity of materials and to trace where electrical connections have been made or not made.
Set the multimeter to 'Continuity' mode. It may vary among DMMs, but look for a diode symbol with propagation waves around it like sound coming from a speaker. Now touch the probes together. The multimeter should emit a tone Note: Not all multimeters have a continuity setting, but most should. This shows that a very small amount of current is allowed to flow without resistance or at least a very very small resistance between probes. On a breadboard that is not powered, use the probes to poke at two separate ground pins.
You should hear a tone indicating that they are connected. It should emit a tone indicating that power is free to flow from the VCC pin to the micro. If it does not emit a tone, then you can begin to follow the route that copper trace takes and tell if there are breaks in the line, wire, breadboard, or PCB. Continuity is a great way to test if two SMD pins are touching.
If your eyes can't see it, the multimeter is usually a great second testing resource. When a system is not working, continuity is one more thing to help troubleshoot the system. Here are the steps to take:.
Continuity and large capacitors: During normal troubleshooting. This is a good sanity check before powering up a prototype to make sure there is not a short on the power system. But don't be surprised if you hear a short 'beep! This is because there is often significant amounts of capacitance on the power system. The multimeter is looking for very low resistance to see if two points are connected. Capacitors will act like a short for a split second until they fill up with energy, and then act like an open connection.
Therefore, you will hear a short beep and then nothing. That's ok, it's just the caps charging up. One of the most common mistakes with a new multimeter is to measure current on a bread board by probing from VCC to GND bad! This will immediately short power to ground through the multimeter causing the bread board power supply to brown out. As the current rushes through the multimeter, the internal fuse will heat up and then burn out as mA flows through it. It will happen in a split second and without any real audible or physical indication that something is wrong.
Wow, that was neat. Now what? Well first, remember that measuring current is done in series interrupt the VCC line to the breadboard or microcontroller to measure current. If you try to measure the current with a blown fuse, you'll probably notice that the meter reads '0. This is because the internal fuse is broken and acts as a broken wire or open.
To change the fuse, find your handy dandy mini screw driver , and start taking out screws. Start by removing the battery plate and the battery. Now notice the hooks on the bottom edge of the face. You will need to slide the face sideways with a little force to disengage these hooks. Make sure to replace the correct fuse with the correct type. In other words, replace the mA fuse with a mA fuse.
The components and PCB traces inside the multimeter are designed to take different amounts of current. You will damage and possibly ruin your multimeter if you accidentally push 5A through the mA port. There are times where you need to measure high current devices like a motor or heating element. Do you see the two places to put the red probe on the front of the multimeter? But if you use the 10A port to measure current, you run a much lower risk of blowing the fuse.
The trade-off is sensitivity. As we talked about above, by using the 10A port and knob setting, you will only be able to read down to 0. Most of my systems use more than 10mA so the 10A setting and port works well enough. Unplug or remove the batteries from the device you want to test. Make sure it is disconnected from all power sources before you proceed. This tests the connection between two points in a circuit. Continuity is the presence of a complete path of electrical flow. For example, a brand new electrical wire should have full continuity.
This is a good way to see if cables are broken internally or not. Plug the probe wires into the multimeter and set the dial to continuity. Turn the dial to the picture that looks like a sound wave. Instead of having a range of numbers in its area, the continuity option only shows 1 sound wave.
Place the black probe on 1 end of the component and the red probe on the other. Make sure that the probes are both touching the ends at the same time so the multimeter works properly. Examples of components you can test the continuity of are wires, switches, fuses, and conductors.
You have to be touching two conductive ends to test for continuity. For example, touch the probes to two bare ends of a wire.
As soon as the two probes are touching the wire's ends, you should hear a beep if the wire is working well. Did you know you can get expert answers for this article? Unlock expert answers by supporting wikiHow. Jesse Kuhlman Master Electrician. Jesse Kuhlman. Support wikiHow by unlocking this expert answer. Not Helpful 0 Helpful 0. Include your email address to get a message when this question is answered.
Helpful 0 Not Helpful 0. Never use a damaged multimeter that has cracked probe handles or frayed wires or you can get shocked. By using this service, some information may be shared with YouTube. Related wikiHows How to. How to. More References 6. About This Article. At first this doesn't seem to make sense you would think the meter would read zero ohms , but the meter is telling you that when no internal contacts are touching inside the switch, the resistance across the open contacts is so large that the meter can't read it.
Now flip the switch On and the meter should read less than one ohm. Another simple test is to rotate the meter dial to the position for continuity. This means a continuous electrical path.
Connect the meter across the switch contacts and flip the switch up and down. The switch is good if the meter beeps with the switch in the On position. The switch is bad if the meter doesn't beep with the switch flipped to On. Then touch the black probe to the round ground prong protruding from the male end. A continuous circuit measured from these two ends will have a resistance of.
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 cord.
Next, insert the red probe into the short hot slot on the female end of the cord. Touch the black probe to the narrow flat prong on the male end.
Electrical continuity through the cord will have a resistance of. Then touch the black probe to the wide flat prong and then the round prong, the meter should show no continuity and an O.
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. Touch the black probe to the narrow prong and then the round prong for an O. Insert the black probe into the round hole in the female end of the cord, and push the red probe into the narrow slot.
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