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How to Use a Multimeter to Test Resistance

Updated on: December 9, 2018

Intro

These procedures will reveal you exactly how to make use of a digital multimeter (DMM), an important device that you can make use of to detect circuits, discover other individuals’s electronic styles, and also test resistance. For this reason the ‘multi’-‘meter’ or multiple dimension name.

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

Every fixer should know their means around a multimeter, which has simply north of a zillion utilizes for testing digital components as well as circuits.

In this tutorial we’re mostly likely to show you exactly how to make use of a multimeter. This tutorial is primarily resolved for novices that are beginning in electronics and also have no suggestion just how to use a multimeter and also just how it can be beneficial. We’ll check out the most usual attributes on a multimeter as well as exactly how to measure current, voltage, resistance as well as exactly how to check continuity.

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

A multimeter is a measurement tool absolutely essential in electronic devices. It integrates three important features: a voltmeter, ohmeter, and ammeter, and in many cases continuity.

The tool allows you to comprehend what is taking place in your circuits. Whenever something in your circuit isn’t working, it will certainly assist you fixing. Below’s some scenarios in electronic devices jobs that you’ll locate the multimeter beneficial:

  • is the button activate?
  • is this cord conducting the electrical power or is it damaged?
  • just how much current is flowing via this led?
  • exactly how much power do you have left on your batteries?

What would multimeters measure?

Nearly all multimeters can measure voltage, current, and also resistance.

Quite a few multimeters have a continuity check, causing a loud beep if two things are electrically linked. This is practical if, as an example, you are building a circuit and also connecting cables or soldering; the beep shows every little thing is linked as well as nothing has come loose. You can likewise use it to make certain 2 points are not linked, to help prevent brief circuits.

A number of multimeters also have a diode check feature. A diode resembles a one-way shutoff that just lets power flow in one instructions. The exact feature of the diode check can differ from one type to another. If you’re working with a diode as well as can’t tell which means it goes in the circuit, or if you’re not sure the diode is working effectively, the check attribute can be rather handy. If your DMM has a diode check feature, read the guidebook to locate out precisely just how it works.

Advanced models could have other functions, such as the capability to measure and also recognize various other electrical elements, like transistors or capacitors. Given that not all of the multimeters have these functions, we will certainly not cover them in this tutorial. You can read your multimeter’s guidebook if you need to use these functions.

What Do All the Symbols Mean?

There’s a whole lot taking place when you check out the selection knob, yet if you’re just mosting likely to be doing some fundamental things, you won’t even use fifty percent of all the settings. All the same, below’s a review of what each icon indicates:

Direct Current Voltage (DCV):from time to time it will certainly be denoted with a V– rather. This setup is utilized to measure direct current (DC) voltage crazes like batteries.
Alternating Current Voltage (ACV): Sometimes it will certainly be signified with a V ~ instead. This setup is made use of to measure the voltage from alternating current resources, which is quite much anything that links into an electrical outlet, along with the power originating from the outlet itself.
Resistance (Ω): This determines just how much resistance there remains in the circuit. The lower the number, the much easier it is for the current to stream via, as well as the other way around.
Continuity: Usually denoted by a wave or diode icon. This just checks whether or not a circuit is full by sending a really small amount of current via the circuit and also seeing if it makes it out the other end. Otherwise, after that there’s something along the circuit that’s triggering a trouble– find it!
Straight Current Amperage (DCA): Similar to DCV, yet rather of giving you a voltage reading, it will certainly inform you the amperage.
Direct Current Gain (hFE): This setting is to examine transistors and their DC gain, however it’s primarily useless, considering that the majority of electrical experts as well as enthusiasts will utilize the continuity check instead.

Your multimeter may likewise have a dedicated setup for examining the amperage of AA, AAA, as well as 9V batteries. This setting is typically denoted with the battery icon.

Once again, you most likely will not even utilize fifty percent of the settings revealed, so don’t get overwhelmed if you only recognize what a few of them do.

Exactly how to Utilize a Multimeter

For beginners, allow’s look at several of the different parts of a multimeter. At the really fundamental degree you have the gadget itself, together with 2 probes, which are the black as well as red wires that have plugs on one end as well as metal tips on the various other.

The tool itself has a screen at the top, which provides you your readout, as well as there’s a big selection knob that you can spin around to select a specific setting. Each setting may likewise have different number worths, which exist to measure different strengths of voltages, resistances, as well as 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 2 or three ports for connecting in the probes:

  • COM port represent “Common”, as well as the black probe will certainly always connect into this port.
  • the VΩmA port (sometimes represented as mAVΩ) is just a phrase for voltage, resistance, and also current (in milliamps). This is where the red probe will plug into if you’re measuring voltage, resistance, continuity, and current much less than 200mA.
  • the 10ADC port (in some cases signified as simply 10A) is made use of whenever you’re measuring current that’s even more than 200mA. If you’re unsure of the current draw, start with this port. On the other hand, you would not use this port at all if you’re measuring anything besides 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, as opposed to the 200mA port. Or else you can blow the fuse that’s within the multimeter. In addition, measuring anything over 10 amps could blow a fuse or damage the multimeters too.

Your measurement tool might have completely separate ports for measuring amps, while the other port is especially just for voltage, resistance, and also continuity, however a lot of cheaper multimeters will certainly share ports.

Anyhow, let’s start in fact making use of a multimeter. We’ll be measuring the voltage of a AA battery, the current draw of a wall surface clock, and the continuity of a simple cable as some examples to obtain you began and also acquainted with making use of a multimeter.

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Components of Multimeters

Multimeters have four components:

  • Display: this particular is just where the measurements are presented
  • Selection Knob: this selects what you want to measure
  • Ports: this is where you connect in the probes
  • Probes: a multimeter comes with two probes. Normally, one is red and also the various other is black.

Ports

  • “COM” or “–” port is where the black probe must be linked. The COM probe is conventionally black.
  • 10A is utilized when measuring big currents, greater than 200mA.
  • µAmA is utilized to measure current.
  • permits you to measure voltage and also resistance and test continuity.

COM

COM stands for common as well as is usually attached to Ground or ‘-‘ of a circuit.The COM probe is conventionally black yet there is no distinction in between the red probe and also black probe aside from color.

10A

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

Selection Knob

The selection knob permits the user to establish the tool to read different points such as milliamps (mA) of current, voltage (V) as well as resistance (Ω).

Probes

2 probes are linked into 2 of the ports on the front of the unit. The probes have a banana kind connector on the end that links into the multimeter. Any probe with a banana plug will certainly collaborate with this meter. This permits different sorts of probes to be utilized.

Probe Types

There are numerous various sorts of probes offered. Here are a few of our favorites:

  • Banana to Alligator Clips: These are fantastic cable televisions for attaching to large wires or pins on a breadboard. Good for executing longer term examinations where you do not have to have to hold the probes in position while you manipulate a circuit.
  • Banana to IC Hook: IC hooks function well on smaller sized ICs and also legs of ICs.
  • Banana to Tweezers: Tweezers are handy if you are requiring to evaluate SMD parts.
  • Banana to Test Probes: If you ever before damage a probe, they are cheap to change!

Measuring Voltage

To begin, let’s measure voltage on a AA battery: Plug the black probe into COM and the red probe into mAVΩ. Set to “2V” in the DC (straight current) array. Almost all portable electronics utilize direct 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 versus the positive and also negative terminals of the AA battery. If you’ve got a fresh battery, you need to see around 1.5 V on the screen (this battery is all new, so its voltage is somewhat more than 1.5 V).

You can measure DC voltage or AC voltage. The V with a straight line means DC voltage. The V with the bumpy line means AC voltage.

Measuring voltage

  1. Set the setting to V with a bumpy line if you’re measuring AC voltage or to the V with a straight line if you’re measuring DC voltage.
  2. Ensure the red probe is attached to the port with a V beside it.
  3. Attach the red probe to the favorable side of your component, which is where the current is originating from.
  4. Connect the COM probe to the various other side of your component.
  5. Check out the worth on the display.

Idea: to measure voltage you need to link your multimeter in parallel with the component you desire to measure the voltage. Positioning the multimeter in parallel is positioning each probe along the leads of the component you want to measure the voltage.

Measuring a battery’s voltage

In this example we’re going to measure the voltage of a 1.5 V battery. You know that you’ll have approximately 1.5 V. So, you should select a range with the selection knob that can review the 1.5 V. So you need to select 2V in the case of this multimeter. If you obtain an autorange one, you don’t need to worry concerning the variety you need to select.

Begin by switching on it, plugging the probes right into their corresponding ports and after that setting the selection knob to the greatest number value in the DCV area, which in my situation 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 suggestion to start with the highest worth initially and afterwards function your means down up until you obtain an exact reading.

In this case, we understand the AA battery has an extremely reduced voltage, however we’ll start at 200 volts simply for the sake of example. Next, position the black probe on the unfavorable end of the battery and also the red probe on the positive end. Have a look at the analysis on the screen. Considering that we have the multimeter set to a high 200 volts, it reveals “1.6” on the display, indicating 1.6 volts.

Nevertheless, I want an even more accurate analysis, so I’ll relocate the selection knob reduced to 20 volts. Right here, you can see that we have a more accurate analysis that floats in between 1.60 and also 1.61 volts. If you were to ever establish the selection knob to a number worth reduced than the voltage of things you’re testing, the multimeter would certainly simply review “1”, signifying that it’s strained. So if I were to establish the knob to 200 millivolts (0.2 volts), the 1.6 volts of the AA battery is excessive for the multimeter to take care of at that setup.

All the same, you could be asking why you would certainly need to evaluate the voltage of something to begin with. Well, in this instance with the AA battery, we’re checking to see if it has any kind of juice left. At 1.6 volts, that’s a fully-loaded battery. However, if it were to read 1.2 volts, it’s close to being pointless.
In a much more practical circumstance, you can do this kind of measuring on a vehicle battery to see if it could be dying or if the generator (which is what charges the battery) is going poor. An analysis in between 12.4-12.7 volts suggests that the battery remains in good condition. Anything lower which’s proof of a dying battery. In addition, begin your cars and truck up and also rev it up a bit. If the voltage does not enhance to around 14 volts or two, then it’s most likely that the alternator 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 bad. The meter will simply present a 1. This is the meter trying to tell you that it is overloaded or out-of-range. Whatever you’re trying to check out is excessive for that particular setup. Attempt changing the multimeter knob to a the next greatest setup.

Selection Knob

Just why does the meter knob read 20V and not 10V? If you’re aiming to measure a voltage less than 20V, you look to the 20V setup. This will certainly enable you to read from 2.00 to 19.99. The very first digit on many multimeters is only able to display a ‘1’ so the arrays are limited to 19.99 as opposed to 99.99. Thus the 20V max array rather of 99V max range.

Measuring Resistance

Connect the red probe into the ideal port and also turn the selection knob to the resistance area. Then, connect the probes to the resistor leads. The means you link the leads doesn’t matter, the outcome is the exact same.

Normal resistors have shade codes on them. If you do not understand what they imply, that’s ok! There are a lot of online calculators that are very easy to utilize. However, if you ever before discover on your own without net gain access to, a multimeter is extremely useful at measuring resistance.

Pick out a random resistor and also set the multimeter to the 20kΩ setting. After that hold the probes versus the resistor legs with the very same amount of pressure you when pushing a secret on a keyboard.

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The meter will review among 3 points, 0.00, 1, or the actual resistor worth.

In this situation, the meter reads 0.97, suggesting this resistor has a value of 970Ω, or regarding 1kΩ (remember you are in the 20kΩ or 20,000 Ohm setting so you need to move the decimal three locations to the right or 970 Ohms).

If the multimeter reads 1 or displays OL, it’s strained. You will certainly need to try a greater setting such as 200kΩ setting or 2MΩ (megaohm) setting. There is no damage if this occur, it simply implies the array knob needs to be readjusted.

In the instance the multimeter reads 0.00 or virtually zero, then you require to lower the mode to 2kΩ or 200Ω.

Bear in mind that several resistors have a 5% resistance. This implies that the color codes may show 10,000 Ohms (10kΩ), however because of disparities in the manufacturing process a 10kΩ resistor can be as reduced as 9.5 kΩ or as high as 10.5 kΩ. Do not fret, it’ll function simply great as a pull-up or basic resistor.

As a guideline of thumb, it’s uncommon to see a resistor much less than 1 Ohm. Keep in mind that measuring resistance is not best. Temperature can influence the reading a great deal. Also, measuring resistance of a gadget while it is literally mounted in a circuit can be extremely tricky. The surrounding elements on a circuit board can substantially influence the reading.

The mockup normally appears like with a fundamental clock running off of a AA battery. On the favorable side, the wire going from the battery to the clock is separated. We simply position our two probes in between that break to finish the circuit again (with the red probe attached 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 the majority of multimeters can also measure rotating current (AC), it’s not really a good suggestion (especially if its online power), given that AC can be hazardous if you finish up making a mistake. If you require to see whether an electrical outlet is functioning, utilize a non-contact tester rather.

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

TIP: to position the multimeter in collection, you need to place the red probe on the lead of a component and the black probe on the following component lead. The multimeter acts as if it was a wire in your circuit. If you separate the multimeter, your circuit won’t function.

Prior to measuring the current, make certain that you’ve connected at a loss probe in the ideal port, in this case µAmA. In the instance listed below, the exact same circuit of the previous example is used. The multimeter is part of the circuit.

Testing Continuity

If there is very reduced resistance in between 2 points, which is much less than a couple of ohms, the two factors are electrically linked and also you’ll hear a continual noise. If the audio isn’t constant or if you don’t listen to any sound in all, it implies that what you’re testing has a malfunctioning connection or isn’t linked in any way.

WARNING: In order to evaluate continuity you ought to shut off the system. Shut off the power supply!

Touch both probes with each other and, as they are connected, you’ll hear a constant sound.To examination the continuity of a wire, you just require to attach each probe to the cord ideas.

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

  • Set your multimeter to the continuity setup utilizing the selection knob.
  • The readout on the screen will quickly review “1”, which means that there isn’t any type of continuity. This would certainly be appropriate given that we haven’t connected the probes to anything yet.
  • Next, see to it the circuit is unplugged and also has no power. Then attach one probe to one end of the cable and the other probe to the various other end– it doesn’t matter which probe goes on which end. If there is a full circuit, your multimeter will certainly either beep, show a “0”, or something aside from a “1”. If it still shows a “1”, after that there’s a problem and also your circuit isn’t complete.
  • You can also check that the continuity feature services your multimeter by touching both probes per various other. This finishes the circuit as well as your multimeter must let you recognize that.

A continuity examination informs us whether two things are electrically attached: if something is constant, an electrical current can flow freely from one end to the other.

If there’s no continuity, it means there is a break somewhere in the circuit. This can indicate anything from a blown fuse or poor solder joint to an incorrectly wired circuit.

Altering the Fuse

Among one of the most common errors with a brand-new multimeter is to measure current on a bread board by penetrating from VCC to GND. This will instantly short power to ground via the multimeter creating the bread board power supply to brown out. As the current rushes via the multimeter, the interior fuse will heat up and then stress out as 200mA flows via it. It will certainly happen in a flash and with no real audible or physical indication that something is incorrect.

Keep in mind that measuring current is performed in series (disturb the VCC line to the breadboard or microcontroller to measure current). If you attempt to measure the current with a blown fuse, you’ll possibly see that the meter checks out ‘0.00’ which the system doesn’t activate like it should when you connect the multimeter. This is due to the fact that the internal fuse is damaged and acts as a busted wire or open.

To alter the fuse, discover your handy dandy mini screw vehicle driver, and begin getting screws. The components and also PCB traces inside the multimeter are made to take various quantities of current. You will certainly harm and potentially destroy your multimeter if you inadvertently push 5A via the 200mA port.

There are times where you need to measure high current devices like an electric motor or burner. Do you see both places to place the red probe on the front of the multimeter? 10A left wing and also mAVΩ on the right? If you try to measure greater than 200mA on the mAVΩ port you risk of blowing the fuse. Yet if you utilize the 10A port to measure current, you run a much lower threat of blowing the fuse. The trade-off is level of sensitivity. As we spoke about above, by utilizing the 10A port as well as handle setting, you will just have the ability to review to 0.01 A or 10mA. A lot of systems utilize more than 10mA so the 10A setting and also port works all right. If you’re attempting to measure extremely reduced power (mini or nano amps) the 200mA port with the 2mA, 200uA, or 20uA can be what you require.

Conclusions

You’re now all set to use your digital multimeter to start measuring the world around you. Do not hesitate to begin using it to respond to many questions. A digital multimeter will answer many concerns concerning electronics.

A multimeter is a crucial tool in any electronics lab. In this guide, we’ve shown you How To Use a Multimeter. You’ve learned exactly how to measure voltage, current as well as resistance, and also just how to examine continuity.