How to Use a Multimeter

Herbalist Dr MziziMkavu · 2014-10-17T02:39:18+00:00

Introduction So how do I use a multimeter? This tutorial will show you how to use a digital multimeter (DMM), an indispensable tool that you can use to diagnose circuits, learn about other peoples electronic designs, and even test a battery. Hence the multi-meter (multiple measurement) name. We will be using the SparkFun VC830L throughout the tutorial but these methods should apply to most multimeters. Would you rather watch a video of this tutorial? Weve got you covered over here. The most basic things we measure are voltage and current. A multimeter is also great for some basic sanity checks and troubleshooting. Is your circuit not working? Does the switch work? Put a meter on it! The multimeter is your first defense when troubleshooting a system. In this tutorial we will cover measuring voltage, current, resistance and continuity. Parts of a Multimeter A multimeter is has three parts: Display Selection Knob Ports The display usually has four digits and the ability to display a negative sign. A few multimeters have illuminated displays for better viewing in low light situations. The selection knob allows the user to set the multimeter to read different things such as milliamps (mA) of current, voltage (V) and resistance (Ω). Two probes are plugged into two of the ports on the front of the unit. COM stands for common and is almost always connected to Ground or - of a circuit. The COM probe is conventionally black but there is no difference between the red probe and black probe other than color. 10A is the special port used when measuring large currents (greater than 200mA). mAVΩ is the port that the red probe is conventionally plugged in to. This port allows the measurement of current (up to 200mA), voltage (V), and resistance (Ω). The probes have a banana type connector on the end that plugs into the multimeter. Any probe with a banana plug will work with this meter. This allows for different types of probes to be used. Measuring Voltage To start, lets measure voltage on a AA battery: Plug the black probe into COM and the red probe into mAVΩ. Set the multimeter to 2V in the DC (direct current) range. Almost all portable electronics use direct current), not alternating current. Connect the black probe to the batterys ground or - and the red probe to power or +. Squeeze the probes with a little pressure against the positive and negative terminals of the AA battery. If youve got a fresh battery, you should see around 1.5V on the display! Use the V with a straight line to measure DC VoltageUse the V with a wavy line to measure AC Voltage If youre measuring DC voltage (such as a battery or a sensor hooked up to an Arduino) you want to set the knob where the V has a straight line. AC voltage (like what comes out of the wall) can be dangerous so we rarely need to use the AC voltage setting (V with a wavy line next to it). If youre messing with AC, we recommend you get a non-contact tester rather than use a digital multimeter. What happens if you switch the red and black probes? The reading on the multimeter is simply negative. Nothing bad happens! The multimeter measures voltage in relation to the common probe. How much voltage is there on the + of the battery compared to common or the negative pin? 1.5V. If we switch the probes, we define + as the common or zero point. How much voltage is there on the - of the battery compared to our new zero? -1.5V! Now lets measure voltage on a breadboard or on a device: This is a very useful step to make sure the circuit you are working on is powered up correctly. If your project should be at 5V but is less than 4.5V or greater than 5.5V, this would quickly give you an indication that something is wrong and you may need to check your power connections or the wiring of your circuit. Set the knob to 20V in the DC range (the DC Voltage range has a V with a straight line next to it). Multimeters are generally not autoranging. You have to set the multimeter to a range that it can measure. For example, 2V measures voltages up to 2 volts. 20V measures voltages up to 20 volts. So if youve measuring a 12V battery, use the 20V setting. 5V system? Use the 20V setting. If you set it incorrectly, you will probably see the meter screen change and then read 1. With some force (imagine poking a fork into a piece of cooked meat), push the probes onto two exposed pieces of metal. One probe should contact a GND connection. One probe to the VCC or 5V connection. This is the meter trying to tell you that it is overloaded or out-of-range. Whatever youre trying to read is too much for that particular setting. Try changing the multimeter knob to a different range. Selection Knob Why does the meter knob read 20V and not 10V? If youre looking to measure a voltage less than 20V, you turn to the 20V setting. This will allow you to read from 2.00 to 19.99. The first digit on many multimeters is only able to display a 1 so the ranges are limited to 19.99 instead of 99.99. Hence the 20V max range instead of 99V max range. Warning: In general, stick to DC circuits (the settings on the multimeter with straight lines, not curvy lines). Most multimeters can measure AC (alternating current) systems, but AC circuits can be dangerous. A wall outlet with AC or main voltage is the stuff that can zap you pretty good. VERY carefully respect AC. If you need to check to see if an outlet is on then use a AC tester. Really the only times weve needed to measure AC are when weve got an outlet that is acting funny (is it really at 110V?), or if were trying to control a heater (such as a hot plate). Go slow and double check everything before you test an AC circuit.

Thread starter Herbalist Dr MziziMkavu
Start date Oct 17, 2014

Herbalist Dr MziziMkavu

JF-Expert Member

Oct 17, 2014

Herbalist Dr MziziMkavu

JF-Expert Member

Oct 17, 2014

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