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How to Use a Multimeter to Test Electrical Resistance

Updated on: December 8, 2018

The Introduction

These recommendations will certainly show you exactly how to use a digital multimeter (DMM), a vital device that you can make use of to detect circuits, discover various other people’s digital designs, and also test electrical resistance. Thus the ‘multi’-‘meter’ or numerous measurement name.

The most basic things we measure are voltage as well as current. A multimeter is likewise wonderful for some fundamental sanity checks and troubleshooting. Is your circuit not working? Does the switch job? Place a meter on it! The multimeter is your first defence when fixing a system. In this tutorial we will certainly cover measuring voltage, current, resistance and continuity.

Every fixer must recognize their way around a multimeter, which has just north of a zillion uses for screening electronic parts and also circuits.

In this tutorial we’re going to show you just how to utilize a multimeter. This tutorial is mostly dealt with for newbies who are starting in electronics and have no suggestion exactly how to utilize a multimeter as well as exactly how it can be beneficial. We’ll check out one of the most common attributes on a multimeter and how to measure current, voltage, resistance and just how to examine continuity.

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

A multimeter is a measurement tool absolutely required in electronic devices. It incorporates three necessary functions: a voltmeter, ohmeter, as well as ammeter, and also in many cases continuity.

The tool permits you to recognize what is taking place in your circuits. Whenever something in your circuit isn’t working, it will assist you fixing. Right here’s some circumstances in electronic devices projects that you’ll discover the multimeter valuable:

  • is the button on?
  • is this wire performing the electrical power or is it broken?
  • just how much current is flowing through this led?
  • just how much power do you have left on your batteries?

What can multimeters measure?

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

Various multimeters have a continuity check, resulting in a loud beep if 2 things are electrically attached. This is useful if, for example, you are developing a circuit and connecting wires or soldering; the beep indicates whatever is linked as well as absolutely nothing has come loose. You can likewise use it to make certain two things are not attached, to assist protect against brief circuits.

A few multimeters likewise have a diode check feature. A diode resembles a one-way shutoff that just lets electrical energy flow in one direction. The exact function of the diode check can vary from one type to another. If you’re working with a diode and can’t inform which way it enters the circuit, or if you’re not certain the diode is working properly, the check function can be fairly useful. If your DMM has a diode check feature, read the handbook to discover precisely how it works.

Advanced models might have other features, such as the capability to measure as well as identify various other electrical elements, like transistors or capacitors. Given that not nearly all multimeters have these attributes, we will not cover them in this tutorial. You can read your multimeter’s guidebook if you need to use these functions.

What Do All Of the Symbols Mean?

There’s a whole lot going on when you consider the selection knob, but if you’re just mosting likely to be doing some fundamental things, you will not also use fifty percent of all the setups. In any situation, right here’s a rundown of what each icon suggests:

Direct Current Voltage (DCV):every now and then it will be denoted with a V– rather. This setting is used to measure direct current (DC) voltage in things like batteries.
Alternating Current Voltage (ACV): Sometimes it will certainly be denoted with a V ~ rather. This setting is made use of to measure the voltage from alternating current sources, which is basically anything that connects into an electrical outlet, in addition to the power coming from the electrical outlet itself.
Resistance (Ω): This gauges how much resistance there remains in the circuit. The reduced the number, the less complicated it is for the current to move through, as well as vice versa.
Continuity: Usually represented by a wave or diode icon. This simply examines whether or not a circuit is complete by sending a very little amount of current through the circuit as well as seeing if it makes it out the other end. Otherwise, then there’s something along the circuit that’s triggering an issue– discover it!
Direct Current Amperage (DCA): Similar to DCV, but as opposed to providing you a voltage reading, it will inform you the amperage.
Direct Current Gain (hFE): This setup is to check transistors and also their DC gain, but it’s mainly useless, given that a lot of electricians and also hobbyists will use the continuity check rather.

Your multimeter might also have a dedicated setup for evaluating the amperage of AA, AAA, and 9V batteries. This setting is typically signified with the battery sign.

Once again, you possibly will not even make use of fifty percent of the setups revealed, so don’t get overwhelmed if you just understand what a few of them do.

Exactly how to Utilize a Multimeter

For starters, let’s go over several of the various parts of a multimeter. At the very fundamental degree you have the tool itself, in addition to two probes, which are the black as well as red cords that have plugs on one end as well as metal suggestions on the other.

The tool itself has a display on top, which provides you your readout, and there’s a large selection knob that you can rotate around to pick a specific setting. Each setting might likewise have different number worths, which exist to measure various strengths of voltages, resistances, and amps. So if you have your multimeter collection to 20 in the DCV area, it will certainly measure voltages approximately 20 volts.

Your DMM will certainly likewise come with two or 3 ports for plugging in the probes:

  • the COM port stands for “Common”, and also the black probe will certainly constantly link into this port.
  • the VΩmA port (sometimes signified as mAVΩ) is simply an acronym for voltage, resistance, and current (in milliamps). This is where the red probe will connect into if you’re measuring voltage, resistance, continuity, as well as current less than 200mA.
  • the 10ADC port (in some cases represented as simply 10A) is utilized whenever you’re measuring current that’s greater than 200mA. If you’re uncertain of the current draw, begin with this port. On the other hand, you would certainly not use this port at all if you’re measuring anything other than current.

Warning: Make sure that if you’re measuring anything with a current greater than 200mA, you plug the red probe right into the 10A port, as opposed to the 200mA port. Or else you might blow the fuse that’s within of the multimeters. Moreover, measuring anything over 10 amps might blow a fuse or damage the multimeter too.

Your measurement tool could have entirely separate ports for measuring amps, while the other port is specifically simply for voltage, resistance, and also continuity, however the majority of less costly multimeters will certainly share ports.

Anyway, allow’s get begun actually making use of a multimeter. We’ll be measuring the voltage of a AA battery, the current draw of a wall clock, and the continuity of an easy cable as some instances to obtain you began and knowledgeable about utilizing a multimeter.

Components of a Multimeter

A multimeter is made up by 4 essential areas:

  • Display: this specific is just where the dimensions are displayed
  • Selection Knob: this chooses what you intend to measure
  • Ports: this is where you connect in the probes
  • Probes: a multimeter includes 2 probes. Usually, one is red as well as the other is black.
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Ports

  • “COM” or “–” port is where the black probe ought to be connected. The COM probe is conventionally black.
  • 10A is utilized when measuring huge currents, greater than 200mA.
  • µAmA is utilized to measure current.
  • allows you to measure voltage and resistance as well as examination continuity.

COM

COM stands for common and also is often linked to Ground or ‘-‘ of a circuit.The COM probe is traditionally black however there is no distinction in between the red probe as well as black probe besides color.

10A

10A is the unique port made use of when measuring large currents (above 200mA).

Selection Knob

The selection knob enables the user to set the tool to read different things such as milliamps (mA) of current, voltage (V) and also resistance (Ω).

Probes

2 probes are connected into 2 of the ports on the front of the system. The probes have a banana type port on the end that links into the multimeter. Any probe with a banana plug will collaborate with this meter. This enables various kinds of probes to be made use of.

Probe Types

There are several sorts of probes readily available. Below are a few of our faves:

  • Banana to Alligator Clips: These are terrific cables for connecting to big cables or pins on a breadboard. Good for executing longer term tests where you don’t have to need to hold the probes in position while you control a circuit.
  • Banana to IC Hook: IC hooks work well on smaller sized ICs and legs of ICs.
  • Banana to Tweezers: Tweezers are helpful if you are needing to check SMD elements.
  • Banana to Test Probes: If you ever before break a probe, they are cheap to replace!

Measuring Voltage

To begin, let’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 (straight current) range. Nearly all mobile electronics make use of direct current), not alternating current. Link the black probe to the battery’s ground or ‘-‘ and also the red probe to power or ‘+’. Squeeze the probes with a little stress versus the favorable as well as negative 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 a little greater than 1.5 V).

You might measure DC voltage or AC voltage. The V with a straight line suggests DC voltage. The V with the curly line means AC voltage.

To measure voltage:

  1. 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.
  2. Ensure the red probe is attached to the port with a V beside it.
  3. Link the red probe to the positive side of your component, which is where the current is coming from.
  4. Attach the COM probe to the opposite side of your component.
  5. Check out the value on the display screen.

Idea: to measure voltage you need to connect your multimeter in parallel with the component you intend 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 going to measure the voltage of a 1.5 V battery. You know that you’ll have approximately 1.5 V. So, you ought to select a variety with the selection knob that can check out the 1.5 V. So you should pick 2V in the case of this multimeter. If you obtain an autorange one, you do not need to fret about the array you need to select.

Begin by switching on it, connecting the probes into their respective ports and after that establishing the selection knob to the greatest number value in the DCV section, which in my instance is 500 volts. If you don’t know at least the voltage variety of the important things you’re measuring, it’s always a great suggestion to begin with the highest value initially and after that work your way down until you obtain an accurate analysis.

In this situation, we understand the AA battery has a really reduced voltage, however we’ll begin at 200 volts just for the sake of instance. Next off, position the black probe on the adverse end of the battery and the red probe on the positive end. Have a look at the analysis on the screen. Given that we have the multimeter set to a high 200 volts, it shows “1.6” on the screen, meaning 1.6 volts.

Nonetheless, I want a more exact analysis, so I’ll relocate the selection knob lower to 20 volts. Here, you can see that we have an even 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 value less than the voltage of the important things you’re checking, the multimeter would certainly simply review “1”, symbolizing that it’s overwhelmed. So if I were to set the knob to 200 millivolts (0.2 volts), the 1.6 volts of the AA battery is as well much for the multimeter to take care of at that setup.

In any kind of situation, you might be asking why you would need to examine the voltage of something to begin with. Well, in this instance with the AA battery, we’re inspecting to see if it has any 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 more useful circumstance, you could do this kind of measuring on an automobile battery to see if it could be dying or if the generator (which is what charges the battery) is going poor. A reading in between 12.4-12.7 volts means that the battery remains in good condition. Anything reduced and that’s evidence of a passing away battery. Additionally, start your car up and rev it up a bit. If the voltage doesn’t enhance to about 14 volts or so, after that it’s likely that the generator is having problems.

Overload

What happens if you choose a voltage setting that is too low for the voltage you’re attempting to measure? Absolutely nothing bad. The meter will merely present a 1. This is the meter trying to tell you that it is overloaded or out-of-range. Whatever you’re attempting to review is too much for that specific setting. Try changing the multimeter handle to a the next highest setup.

Selection Knob

For what reason does the meter knob reviewed 20V and not 10V? If you’re aiming to measure a voltage much less than 20V, you turn to the 20V setting. This will certainly permit you to read from 2.00 to 19.99. The very first digit on lots of multimeters is just able to display a ‘1’ so the varieties are limited to 19.99 rather than 99.99. Therefore the 20V max array rather than 99V max range.

Measuring Resistance

Connect the red probe right into the ideal port and also turn the selection knob to the resistance section. After that, attach the probes to the resistor leads. The method you attach the leads doesn’t matter, the outcome coincides.

Normal resistors have color codes on them. If you do not understand what they suggest, that’s ok! There are a lot of on-line calculators that are very easy to make use of. Nonetheless, if you ever find yourself without internet accessibility, a multimeter is really convenient at measuring resistance.

Select out an arbitrary resistor as well as set the multimeter to the 20kΩ setting. Then hold the probes versus the resistor legs with the same quantity of pressure you when pressing a secret on a keyboard.

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The meter will read among three points, 0.00, 1, or the real resistor worth.

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

If the multimeter checks out 1 or presents OL, it’s overwhelmed. You will need to try a greater mode such as 200kΩ mode or 2MΩ (megaohm) mode. There is no damage if this take place, it just indicates the range handle requires to be readjusted.

In the event that the multimeter reads 0.00 or nearly absolutely no, after that you require to lower the setting to 2kΩ or 200Ω.

Bear in mind that numerous resistors have a 5% resistance. This means that the color codes may indicate 10,000 Ohms (10kΩ), however due to disparities in the manufacturing procedure a 10kΩ resistor could be as low as 9.5 kΩ or as high as 10.5 kΩ. Do not stress, it’ll function just fine as a pull-up or basic resistor.

As a guideline of thumb, it’s unusual to see a resistor much less than 1 Ohm. Keep 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 physically installed in a circuit can be very tricky. The bordering elements on a circuit card can greatly impact the reading.

The mockup usually resembles with a standard clock escaping of a AA battery. On the silver lining, the wire going from the battery to the clock is broken up. We simply position our two probes in between that break to finish the circuit once again (with the red probe linked to the source of power), just this time around our multimeter will certainly review out the amps that the clock is drawing, which in this situation is around 0.08 mA.

While a lot of multimeters can also measure alternating current (AC), it’s not actually a great idea (particularly if its live power), given that AC can be unsafe if you end up slipping up. If you require to see whether or not an outlet is functioning, make use of a non-contact tester instead.

To measure current you need to remember that components in collection share a current. So, you require to attach your multimeter in collection with your circuit.

IDEA: to put the multimeter in collection, you require to put the red probe on the lead of a component as well as the black probe on the next component lead. The multimeter acts as if it was a cable in your circuit. If you separate the multimeter, your circuit won’t function.

Before measuring the current, be certain that you’ve plugged in the red probe in the ideal port, in this instance µAmA. In the instance listed below, the very same circuit of the previous example is utilized. The multimeter becomes part of the circuit.

Test for Continuity

If there is very low resistance in between two factors, which is less than a couple of ohms, the two points are electrically attached and also you’ll hear a constant sound. If the audio isn’t continuous or if you do not listen to any type of sound at all, it implies that what you’re testing has a malfunctioning link or isn’t attached in all.

CAUTION: To test continuity you ought to shut off the system! Shut off the power source!

Touch both probes together and also, as they are connected, you’ll listen to a continuous sound.To test the continuity of a cord, you just require to link each probe to the cord ideas.

Continuity is a terrific method to evaluate if two SMD pins are touching. If your eyes can not see it, the multimeter is typically a wonderful second testing resource. When a system is not functioning, continuity is another thing to help repair the system.

  • Set your multimeter to the continuity setup utilizing the selection knob.
  • The readout on the display will promptly review “1”, which means that there isn’t any kind of continuity. This would certainly be appropriate because we haven’t linked the probes to anything yet.
  • Next off, make certain the circuit is unplugged as well as has no power. Then link one probe to one end of the cable and also the other probe to the various other end– it matters not which probe goes on which end. If there is a full circuit, your multimeter will certainly either beep, show a “0”, or something besides a “1”. If it still reveals a “1”, then there’s a problem and also your circuit isn’t complete.
  • You can likewise check that the continuity attribute deals with your multimeter by touching both probes per various other. This finishes the circuit as well as your multimeter should allow you understand that.

A continuity examination informs us whether 2 points are electrically attached: if something is constant, an electrical current can move freely from one end to the various other.

If there’s no continuity, it means there is a break someplace in the circuit. This could suggest anything from a blown fuse or poor solder joint to an inaccurately wired circuit.

Altering the Fuse

Among one of the most common blunders with a new multimeter is to measure current on a bread board by penetrating from VCC to GND. This will promptly short power to ground via the multimeter causing the bread board power supply to brown out. As the current hurries via the multimeter, the internal fuse will warm up and afterwards wear out as 200mA streams with it. It will happen in a fraction of a second and without any kind of real distinct or physical indication that something is incorrect.

Keep in mind that measuring current is performed 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 most likely see that the meter reads ‘0.00’ as well as that the system doesn’t activate like it should when you affix the multimeter. This is since the internal fuse is damaged and works as a damaged cord or open.

To alter the fuse, locate your handy dandy mini screw driver, and also start taking out screws. The components and also PCB traces inside the multimeter are made to take different amounts of current. You will harm as well as potentially wreck your multimeter if you unintentionally press 5A with the 200mA port.

There are times where you require to measure high current devices like a motor or home heating component. Do you see both places to put the red probe on the front of the multimeter? 10A on the left and also mAVΩ on the right? If you attempt to measure greater than 200mA on the mAVΩ port you risk of blowing the fuse. Yet if you make use of the 10A port to measure current, you run a much reduced threat of blowing the fuse. The compromise is sensitivity. As we discussed above, by making use of the 10A port and also handle setup, you will just be able to review to 0.01 A or 10mA. A lot of systems use greater than 10mA so the 10A setting as well as port functions all right. If you’re attempting to measure very low power (mini or nano amps) the 200mA port with the 2mA, 200uA, or 20uA could be what you need.

Final thought

You’re now prepared to use your digital multimeter to begin measuring the globe around you. Really feel totally free to begin utilizing it to respond to many concerns. A digital multimeter will certainly answer several questions regarding electronic devices.

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 discovered exactly how to measure voltage, current and also resistance, as well as just how to check continuity.