How to Use a Multimeter to Measure Resistance

Updated on: December 9, 2018

Contents

The Intro

This guide will certainly reveal you exactly how to use a digital multimeter (DMM), a vital device that you can make use of to detect circuits, discover about various other people’s digital styles, and even measure resistance. Hence the ‘multi’-‘meter’ or numerous measurement name.

One of the most fundamental things we measure are voltage as well as current. A multimeter is additionally great for some standard peace of mind checks and troubleshooting. Is your circuit not functioning? Does the button job? Put a meter on it! The multimeter is your first support when troubleshooting a system. In this tutorial we will cover measuring voltage, current, resistance as well as continuity.

Every fixer needs to understand their way around a multimeter, which has just north of a zillion utilizes for testing digital parts and also circuits.

In this tutorial we’re going to show you just how to make use of a multimeter. This tutorial is mainly addressed for newbies that are starting in electronics and also have no suggestion just how to utilize a multimeter and how it can be beneficial. We’ll check out the most typical attributes on a multimeter and just how to measure current, voltage, resistance as well as how to check continuity.

What is a multimeter and also why do you need one?

A multimeter is a measurement device definitely needed in electronic devices. It integrates 3 crucial functions: a voltmeter, ohmeter, and ammeter, and in some instances continuity.

The tool allows you to recognize what is going on in your circuits. Whenever something in your circuit isn’t working, it will certainly help you fixing. Below’s some circumstances in electronics jobs that you’ll discover the multimeter valuable:

is the switch on?
is this cord performing the electrical power or is it damaged?
just how much current is streaming through this led?
just how much power do you have left on your batteries?

What would multimeters measure?

Practically all multimeters can measure voltage, current, as well as resistance.

Quite a few multimeters have a continuity check, resulting in a loud beep if two points are electrically attached. This is useful if, as an example, you are constructing a circuit and also attaching cables or soldering; the beep indicates every little thing is linked as well as nothing has actually come loose. You can also use it to ensure 2 points are not connected, to assist stop brief circuits.

A number of multimeters additionally have a diode check feature. A diode resembles a one-way valve that only allows electrical power flow in one instructions. The exact feature of the diode check can vary from one type to another. If you’re working with a diode and also can not tell which means it enters the circuit, or if you’re uncertain the diode is functioning effectively, the check feature can be fairly helpful. If your DMM has a diode check function, read the handbook to discover precisely just how it works.

Advanced models could have various other features, such as the ability to measure and identify other electrical parts, like transistors or capacitors. Given that not most multimeters have these functions, we will certainly not cover them in this tutorial. You can read your multimeter’s manual if you need to use these functions.

What Do Every One Of the Symbols Mean?

There’s a whole lot taking place when you check out the selection knob, however if you’re only going to be doing some fundamental things, you will not even utilize fifty percent of all the settings. Regardless, below’s a review of what each sign means:

Direct Current Voltage (DCV):Occasionally it will be denoted with a V– instead. This setup is used to measure direct current (DC) voltage crazes like batteries.
Alternating Current Voltage (ACV): Sometimes it will certainly be signified with a V ~ rather. This setting is used to measure the voltage from alternating current sources, which is virtually anything that connects right into an electrical outlet, along with the power originating from the electrical outlet itself.
Resistance (Ω): This gauges just how much resistance there is in the circuit. The lower the number, the simpler it is for the current to stream with, as well as the other way around.
Continuity: Usually signified by a wave or diode icon. This just tests whether or not a circuit is total by sending out a very percentage of current via the circuit as well as seeing if it makes it out the other end. Otherwise, after that there’s something along the circuit that’s creating a problem– discover it!
Direct Current Amperage (DCA): Similar to DCV, however instead of giving you a voltage analysis, it will tell you the amperage.
Straight Current Gain (hFE): This setting is to evaluate transistors and their DC gain, but it’s mainly ineffective, because many electrical contractors and also hobbyists will use the continuity check rather.

Your multimeter could additionally have a committed setup for evaluating the amperage of AA, AAA, as well as 9V batteries. This setup is generally denoted with the battery sign.

Once more, you possibly won’t even utilize half of the settings shown, so don’t obtain bewildered if you just recognize what a few of them do.

Just how to Use a Multimeter

For beginners, allow’s review several of the different components of a multimeter. At the very basic degree you have the gadget itself, along with two probes, which are the black and also red cords that have plugs on one end as well as metal suggestions on the other.

The tool itself has a screen at the top, which provides you your readout, and there’s a large selection knob that you can spin around to choose a particular setup. Each setting might additionally have various number values, which are there to measure different staminas of voltages, resistances, and also amps. So if you have your multimeter set to 20 in the DCV area, it will measure voltages approximately 20 volts.

Your DMM will certainly additionally feature two or three ports for connecting in the probes:

COM port represent “Common”, as well as the black probe will always connect into this port.
the VΩmA port (often represented as mAVΩ) is simply a phrase for voltage, resistance, and also current (in milliamps). This is where the red probe will certainly link into if you’re measuring voltage, resistance, continuity, as well as current less than 200mA.
the 10ADC port (sometimes denoted as just 10A) is made use of whenever you’re measuring current that’s more than 200mA. If you’re not exactly sure of the current draw, start with this port. On the various other hand, you would not utilize this port in all if you’re measuring anything aside from current.

Warning: Make certain that if you’re measuring anything with a current higher than 200mA, you plug the red probe into the 10A port, instead of the 200mA port. Or else you could blow the fuse that’s within of the multimeter. In addition, measuring anything over 10 amps could blow a fuse or destroy the multimeters too.

Your measurement tool could have entirely different ports for measuring amps, while the various other port is especially just for voltage, resistance, and continuity, yet most cheaper multimeters will share ports.

Anyway, allow’s start in fact using a multimeter. We’ll be measuring the voltage of a AA battery, the current draw of a wall clock, as well as the continuity of a simple cord as some examples to obtain you started as well as familiar with making use of a multimeter.

Components of a Multimeter

Multimeters have four components:

Display: this is just where the dimensions are displayed
Selection Knob: this chooses what you wish to measure
Ports: this is where you plug in the probes
Probes: a multimeter features two probes. Usually, one is red and also the other is black.

Ports

“COM” or “–” port is where the black probe must be connected. The COM probe is traditionally black.
10A is made use of when measuring big currents, more than 200mA.
µAmA is made use of to measure current.
VΩ allows you to measure voltage as well as resistance and also examination continuity.

COM

COM mean usual as well as is usually connected to Ground or ‘-‘ of a circuit.The COM probe is conventionally black but there is no distinction in between the red probe as well as black probe aside from color.

10A

10A is the unique port used when measuring large currents (higher than 200mA).

Selection Knob

The selection knob permits the individual to establish the tool to review various things such as milliamps (mA) of current, voltage (V) as well as resistance (Ω).

Probes

Two probes are plugged into 2 of the ports on the front of the device. The probes have a banana type connector on the end that plugs into the multimeter. Any type of probe with a banana plug will certainly work with this meter. This enables for different types of probes to be used.

Probe Types

There are several kinds of probes readily available. Here are a few of our favorites:

Banana to Alligator Clips: These are excellent cables for connecting to large cords or pins on a breadboard. Helpful for doing longer term tests where you do not have to need to hold the probes in position while you adjust a circuit.
Banana to IC Hook: IC hooks function well on smaller ICs as well as legs of ICs.
Banana to Tweezers: Tweezers are helpful if you are requiring to check SMD elements.
Banana to Test Probes: If you ever before damage a probe, they are inexpensive to replace!

Measuring Voltage

To start, allow’s measure voltage on a AA battery: Plug the black probe right into COM as well as the red probe right into mAVΩ. Set to “2V” in the DC (direct current) range. Nearly all mobile electronics use straight current), not alternating current. Attach the black probe to the battery’s ground or ‘-‘ as well as the red probe to power or ‘+’. Squeeze the probes with a little pressure against the positive and adverse terminals of the AA battery. If you’ve got a fresh battery, you must see around 1.5 V on the screen (this battery is all new, so its voltage is somewhat more than 1.5 V).

You may measure DC voltage or AC voltage. The V with a straight line means DC voltage. The V with the wavy line implies AC voltage.

So as to measure voltage follow all these steps:

Set the setting to V with a wavy line if you’re measuring AC voltage or to the V with a straight line if you’re measuring DC voltage.
Make certain the red probe is attached to the port with a V alongside it.
Link the red probe to the positive side of your component, which is where the current is coming from.
Connect the COM probe to the various other side of your component.
Read the worth on the screen.

Suggestion: to measure voltage you need to attach your multimeter in parallel with the component you want to measure the voltage. Positioning the multimeter in parallel is putting each probe along the leads of the component you intend to measure the voltage.

Measuring a battery’s voltage

In this example we’re mosting likely to measure the voltage of a 1.5 V battery. You know that you’ll have around 1.5 V. So, you should choose an array with the selection knob that can review the 1.5 V. So you ought to select 2V in the situation of this multimeter. If you get an autorange one, you do not need to bother with the variety you require to choose.

Start by switching on it, plugging the probes right into their corresponding ports and after that establishing the selection knob to the highest possible number worth in the DCV area, which in my case is 500 volts. If you don’t understand a minimum of the voltage series of the important things you’re measuring, it’s constantly a great idea to start with the highest possible value first as well as after that work your method down till you obtain an exact analysis.

In this situation, we understand the AA battery has a very low voltage, however we’ll begin at 200 volts just for the sake of instance. Next off, position the black probe on the unfavorable end of the battery and also the red probe on the favorable end. Have a look at the analysis on the display. Because we have the multimeter collection to a high 200 volts, it shows “1.6” on the screen, suggesting 1.6 volts.

However, I want an even more exact analysis, so I’ll relocate the selection knob lower to 20 volts. Here, you can see that we have an even more precise analysis that hovers between 1.60 and 1.61 volts. If you were to ever establish the selection knob to a number worth lower than the voltage of the important things you’re testing, the multimeter would certainly just check out “1”, symbolizing that it’s overloaded. So if I were to establish the knob to 200 millivolts (0.2 volts), the 1.6 volts of the AA battery is too much for the multimeter to manage at that setup.

All the same, you could be asking why you would need to check the voltage of something to begin with. Well, in this instance with the AA battery, we’re inspecting to see if it has any type of juice left. At 1.6 volts, that’s a fully-loaded battery. Nevertheless, if it were to check out 1.2 volts, it’s close to being pointless.
In an extra practical situation, you could do this kind of measuring on a car battery to see if it could be dying or if the alternator (which is what charges the battery) is spoiling. A reading between 12.4-12.7 volts implies that the battery remains in good condition. Anything reduced and that’s evidence of a passing away battery. Moreover, start your automobile up and rev it up a bit. If the voltage doesn’t increase to around 14 volts or two, then it’s most likely that the generator is having issues.

Overload

What happens if you select a voltage setting that is also low for the voltage you’re attempting to measure? Absolutely nothing negative. The meter will merely display a 1. This is the meter attempting to inform you that it is overloaded or out-of-range. Whatever you’re attempting to check out is also much for that certain setup. Try transforming the multimeter handle to a the next highest setup.

Selection Knob

For what reason does the meter knob read 20V and also not 10V? If you’re looking to measure a voltage less than 20V, you rely on the 20V setting. This will certainly allow you to read from 2.00 to 19.99. The very first number on several multimeters is only able to display a ‘1’ so the varieties are restricted to 19.99 as opposed to 99.99. For this reason the 20V max range as opposed to 99V max range.

Measuring Resistance

Plug the red probe right into the right port as well as turn the selection knob to the resistance area. Then, link the probes to the resistor leads. The way you link the leads doesn’t matter, the outcome is the same.

Normal resistors have color codes on them. If you don’t know what they imply, that’s ok! There are lots of on the internet calculators that are simple to utilize. Nonetheless, if you ever before locate yourself without net gain access to, a multimeter is very useful at measuring resistance.

Choose out an arbitrary resistor and also set the multimeter to the 20kΩ setup. Then hold the probes versus the resistor legs with the same quantity of pressure you when pressing a key on a key-board.

The meter will read one of 3 points, 0.00, 1, or the real resistor value.

In this case, the meter checks out 0.97, implying this resistor has a worth of 970Ω, or concerning 1kΩ (remember you remain in the 20kΩ or 20,000 Ohm mode so you require to move the decimal 3 places to the right or 970 Ohms).

If the multimeter reads 1 or displays OL, it’s overwhelmed. You will certainly need to attempt a higher setting such as 200kΩ setting or 2MΩ (megaohm) mode. There is no harm if this occur, it simply implies the variety handle requires to be changed.

Whenever the multimeter reads 0.00 or virtually zero, then you require to reduce the setting to 2kΩ or 200Ω.

Keep in mind that many resistors have a 5% tolerance. This means that the shade codes may suggest 10,000 Ohms (10kΩ), but due to inconsistencies in the manufacturing procedure a 10kΩ resistor could be as low as 9.5 kΩ or as high as 10.5 kΩ. Do not fret, it’ll function simply fine as a pull-up or general resistor.

Generally of thumb, it’s rare to see a resistor less than 1 Ohm. Bear in mind that measuring resistance is not perfect. Temperature level can influence the reviewing a lot. Likewise, measuring resistance of a device while it is literally set up in a circuit can be really challenging. The surrounding components on a motherboard can significantly affect the analysis.

The mockup typically appears like with a standard clock running off of a AA battery. On the favorable side, the cable going from the battery to the clock is separated. We just position our 2 probes in between that break to complete the circuit once more (with the red probe connected to the power resource), only this time our multimeter will review out the amps that the clock is pulling, which in this situation is around 0.08 mA.

While many multimeters can likewise measure rotating current (AC), it’s not really a great concept (particularly if its online power), since AC can be harmful if you wind up making an error. If you need to see whether or not an outlet is working, use a non-contact tester rather.

To measure current you require to bear in mind that components in series share a current. So, you need to link your multimeter in series with your circuit.

SUGGESTION: to position the multimeter in collection, you need to place the red probe on the lead of a component and also the black probe on the following component lead. The multimeter acts as if it was a cord in your circuit. If you disconnect the multimeter, your circuit won’t work.

Before measuring the current, be sure that you’ve connected at a loss probe in the appropriate port, in this instance µAmA. In the example listed below, the same circuit of the previous instance is made use of. The multimeter is part of the circuit.

How To Test For Continuity

If there is really low resistance between two points, which is less than a couple of ohms, the 2 points are electrically connected and also you’ll listen to a constant noise. If the sound isn’t continuous or if you do not hear any type of noise whatsoever, it implies that what you’re testing has a defective connection or isn’t attached whatsoever.

WARNING: In order to test continuity you must switch off the system! Turn off the power source!

Touch the 2 probes together and also, as they are linked, you’ll hear a continual sound.To test the continuity of a cord, you just require to link each probe to the cable ideas.

Continuity is an excellent way to test if two SMD pins are touching. If your eyes can’t see it, the multimeter is typically a wonderful second testing source. When a system is not working, continuity is one even more thing to aid repair the system.

Set your multimeter to the continuity setting utilizing the selection knob.
The readout on the display will instantly check out “1”, which means that there isn’t any kind of continuity. This would be proper since we have not linked the probes to anything yet.
Next off, see to it the circuit is unplugged and also has no power. Then connect one probe to one end of the cable as well as the various other probe to the other end– it does not matter which probe takes place which end. If there is a total circuit, your multimeter will either beep, reveal a “0”, or something other than a “1”. If it still shows a “1”, after that there’s a problem and your circuit isn’t full.
You can likewise examine that the continuity function deals with your multimeter by touching both probes to each various other. This completes the circuit and also your multimeter must allow you understand that.

A continuity examination informs us whether 2 things are electrically connected: if something is constant, an electric current can move freely from one end to the other.

If there’s no continuity, it indicates there is a break someplace in the circuit. This could show anything from a blown fuse or bad solder joint to an incorrectly wired circuit.

Altering the Fuse

One of one of the most common mistakes with a new multimeter is to measure current on a bread board by probing from VCC to GND. This will immediately brief power to ground through the multimeter causing the bread board power supply to brown out. As the current hurries via the multimeter, the internal fuse will heat up as well as then burn out as 200mA flows via it. It will take place in a split second and with no actual distinct or physical sign that something is incorrect.

Keep in mind that measuring current is done in collection (interrupt the VCC line to the breadboard or microcontroller to measure current). If you attempt to measure the current with a blown fuse, you’ll probably notice that the meter checks out ‘0.00’ and that the system doesn’t turn on like it must when you affix the multimeter. This is since the internal fuse is broken as well as acts as a damaged wire or open.

To change the fuse, discover your useful dandy mini screw vehicle driver, and also start securing screws. The components and PCB traces inside the multimeter are made to take different quantities of current. You will certainly harm and also perhaps spoil your multimeter if you mistakenly press 5A via the 200mA port.

There are times where you require to measure high current devices like a motor or burner. Do you see the 2 areas to place the red probe on the front of the multimeter? 10A on the left and also mAVΩ on the right? If you try to measure more than 200mA on the mAVΩ port you risk of blowing the fuse. Yet if you use the 10A port to measure current, you run a much reduced threat of blowing the fuse. The trade-off is sensitivity. As we discussed above, by making use of the 10A port as well as handle setup, you will just be able to review to 0.01 A or 10mA. Many of systems make use of even more than 10mA so the 10A setting as well as port functions all right. If you’re trying to measure extremely reduced power (mini or nano amps) the 200mA port with the 2mA, 200uA, or 20uA can be what you require.

Final thought

You’re now ready to utilize your digital multimeter to begin measuring the world around you. Do not hesitate to begin using it to answer many concerns. A digital multimeter will certainly respond to numerous questions about electronics.

A multimeter is a crucial tool in any type of electronics laboratory. In this overview, we’ve revealed you How To Use a Multimeter. You’ve learned just how to measure voltage, current and resistance, as well as just how to inspect continuity.