How to Use a Multimeter to Test a Relay Switch



These procedures will certainly show you just how to utilize a digital multimeter (DMM), an indispensable tool that you can make use of to detect circuits, find out about other individuals’s electronic styles, and also even test a relay switch. Therefore the ‘multi’-‘meter’ or several dimension name.

The most fundamental points we measure are voltage as well as current. A multimeter is also terrific for some standard sanity checks and troubleshooting. Is your circuit not functioning? Does the button job? Put a meter on it! The multimeter is your initial protection when fixing a system. In this tutorial we will certainly cover measuring voltage, current, resistance as well as continuity.

Every fixer ought to recognize their means around a multimeter, which has simply north of a zillion makes use of for testing digital parts as well as circuits.

In this tutorial we’re mostly likely to show you how to make use of a multimeter. This tutorial is mainly dealt with for beginners that are starting in electronic devices and also have no concept just how to utilize a multimeter as well as exactly how it can be helpful. We’ll discover one of the most common attributes on a multimeter as well as exactly how to measure current, voltage, resistance and exactly how to examine continuity.

What is a multimeter as well as why do you require one?

A multimeter is a measurement device definitely needed in electronics. It incorporates three important features: a voltmeter, ohmeter, and also ammeter, and in many cases continuity.

The tool allows you to recognize what is taking place in your circuits. Whenever something in your circuit isn’t functioning, it will certainly aid you repairing. Right here’s some circumstances in electronics tasks that you’ll locate the multimeter useful:

  • is the switch on?
  • is this cable carrying out the electrical energy or is it broken?
  • just how much current is flowing through this led?
  • how much power do you have left on your batteries?

What will multimeters measure?

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

A couple of multimeters have a continuity check, leading to a loud beep if two points are electrically attached. This is handy if, as an example, you are constructing a circuit as well as linking wires or soldering; the beep shows everything is linked as well as absolutely nothing has come loose. You can likewise utilize it to ensure two points are not linked, to assist prevent brief circuits.

A couple of multimeters additionally have a diode check function. A diode is like a one-way valve that only allows power circulation in one direction. The precise function of the diode check can vary from one type to another. If you’re collaborating with a diode and also can not tell which means it enters the circuit, or if you’re uncertain the diode is functioning correctly, the check feature can be fairly useful. If your DMM has a diode check function, read the manual to discover specifically just how it works.

Advanced models might have various other functions, such as the capacity to measure as well as identify other electric parts, like transistors or capacitors. Considering that not all multimeters have these attributes, we will not cover them in this tutorial. You can review your multimeter’s manual if you need to use these attributes.

What Do All the Symbols Mean?

There’s a great deal going on when you take a look at the selection knob, but if you’re just mosting likely to be doing some fundamental things, you won’t also utilize half of all the setups. All the same, here’s a run-through of what each sign indicates:

Direct Current Voltage (DCV):once in a while it will certainly be denoted with a V– instead. This setting is used to measure straight current (DC) voltage in points like batteries.
Alternating Current Voltage (ACV): Sometimes it will certainly be signified with a V ~ rather. This setting is made use of to measure the voltage from alternating current resources, which is basically anything that connects into an outlet, as well as the power coming from the outlet itself.
Resistance (Ω): This measures just how much resistance there remains in the circuit. The reduced the number, the much easier it is for the current to stream with, and vice versa.
Continuity: Usually denoted by a wave or diode icon. This simply tests whether a circuit is total by sending out an extremely little quantity of current via the circuit and seeing if it makes it out the various other end. If not, after that there’s something along the circuit that’s creating a trouble– discover it!
Straight Current Amperage (DCA): Similar to DCV, but rather than offering you a voltage analysis, it will certainly tell you the amperage.
Straight Current Gain (hFE): This setting is to check transistors and their DC gain, but it’s mainly pointless, considering that most electrical experts as well as enthusiasts will certainly utilize the continuity check rather.

Your multimeter may additionally have a devoted setting for evaluating the amperage of AA, AAA, and 9V batteries. This setting is generally represented with the battery sign.

Once more, you most likely won’t even use half of the settings revealed, so don’t obtain overwhelmed if you just know what a few of them do.

Just how to Use a Multimeter

For starters, let’s go over a few of the various parts of a multimeter. At the really basic level you have the device itself, together with two probes, which are the black and also red cable televisions that have plugs on one end as well as steel suggestions on the various other.

The tool itself has a display screen at the top, which offers you your readout, as well as there’s a big selection knob that you can rotate around to choose a specific setup. Each setup might additionally have various number worths, which are there to measure various strengths of voltages, resistances, and also amps. So if you have your multimeter set to 20 in the DCV section, it will measure voltages up to 20 volts.

Your DMM will likewise have two or 3 ports for connecting in the probes:

  • COM port mean “Common”, and also the black probe will constantly connect into this port.
  • the VΩmA port (occasionally denoted as mAVΩ) is simply an acronym for voltage, resistance, as well as current (in milliamps). This is where the red probe will connect into if you’re measuring voltage, resistance, continuity, as well as current much less than 200mA.
  • the 10ADC port (occasionally represented as just 10A) is made use of whenever you’re measuring current that’s more than 200mA. If you’re uncertain of the current draw, start with this port. On the other hand, you would not utilize this port at 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. Otherwise you might blow the fuse that’s within of the multimeters. In addition, measuring anything over 10 amps can blow a fuse or destroy the multimeters too.

Your measurement tool could have entirely different ports for measuring amps, while the other port is specifically just for voltage, resistance, as well as continuity, but most less expensive multimeters will certainly share ports.

Anyhow, let’s get going actually utilizing 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 an easy cord as some examples to get you started and accustomed to making use of a multimeter.

Components of a Multimeter

Multimeters are made up by 4 necessary sections:

  • Display: this specific is where the measurements are shown
  • Selection Knob: this chooses what you intend to measure
  • Ports: this is where you plug in the probes
  • Probes: a multimeter features 2 probes. Generally, one is red and the other is black.


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


COM represent common and also is often attached to Ground or ‘-‘ of a circuit.The COM probe is traditionally black yet there is no difference in between the red probe and also black probe aside from color.


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

Selection Knob

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


Two probes are linked into 2 of the ports on the front of the system. The probes have a banana type adapter on completion that connects into the multimeter. Any type of probe with a banana plug will work with this meter. This enables various kinds of probes to be utilized.

Probe Types

There are several various kinds of probes available. Below are a few of our faves:

  • Banana to Alligator Clips: These are terrific cable televisions for connecting to big cords or pins on a breadboard. Excellent for doing longer term examinations where you don’t need to need to hold the probes in position while you manipulate a circuit.
  • Banana to IC Hook: IC hooks work well on smaller sized ICs and also legs of ICs.
  • Banana to Tweezers: Tweezers come in handy if you are requiring to examine SMD components.
  • Banana to Test Probes: If you ever break a probe, they are low-cost to replace!

Measuring Voltage

To begin, let’s measure voltage on a AA battery: Plug the black probe right into COM and also the red probe right into mAVΩ. Establish to “2V” in the DC (straight current) range. Practically all mobile electronics use direct current), not alternating current. Link 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 also unfavorable terminals of the AA battery. If you’ve obtained a fresh battery, you need to see around 1.5 V on the display screen (this battery is new, so its voltage is slightly greater than 1.5 V).

You can easily measure DC voltage or AC voltage. The V with a straight line suggests DC voltage. The V with the wavy line suggests AC voltage.

To be able to measure voltage understand all these steps:

  1. Set the mode 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. See to it the red probe is connected to the port with a V following to it.
  3. Attach the red probe to the positive side of your component, which is where the current is originating from.
  4. Link the COM probe to the various other side of your component.
  5. Check out the value on the display.

Tip: to measure voltage you have to connect your multimeter in parallel with the component you wish to measure the voltage. Positioning the multimeter in parallel is placing each probe along the leads of the component you want to measure the voltage.

Measuring a battery’s voltage

In this instance we’re mosting likely to measure the voltage of a 1.5 V battery. You recognize that you’ll have around 1.5 V. So, you must select an array with the selection knob that can check out the 1.5 V. So you must pick 2V in the instance of this multimeter. If you get an autorange one, you do not have to bother with the variety you require to pick.

Begin by activating it, plugging the probes right into their particular ports and after that establishing the selection knob to the highest number worth in the DCV area, which in my situation is 500 volts. If you do not know a minimum of the voltage variety of the important things you’re measuring, it’s constantly a good concept to begin with the highest worth initially and afterwards function your way down till you obtain an exact analysis.

In this case, we recognize the AA battery has a very reduced voltage, yet we’ll start at 200 volts simply for the purpose of example. Next, place the black probe on the unfavorable end of the battery and also the red probe on the favorable end. Take an appearance at the analysis on the display. Considering that we have the multimeter collection to a high 200 volts, it shows “1.6” on the screen, suggesting 1.6 volts.

Nevertheless, I want an even more accurate reading, so I’ll move the selection knob reduced down to 20 volts. Right here, you can see that we have an even more exact analysis that hovers between 1.60 and 1.61 volts. If you were to ever set the selection knob to a number value less than the voltage of the important things you’re testing, the multimeter would simply review “1”, indicating that it’s strained. So if I were to set the knob to 200 millivolts (0.2 volts), the 1.6 volts of the AA battery is way too much for the multimeter to manage at that setup.

Regardless, you may be asking why you would certainly require to check the voltage of something in the very first area. Well, in this case 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. Nonetheless, if it were to read 1.2 volts, it’s close to being unusable.
In an extra useful situation, you could do this sort of measuring on a cars and truck battery to see if it may be dying or if the generator (which is what charges the battery) is spoiling. An analysis in between 12.4-12.7 volts suggests that the battery remains in great form. Anything reduced and that’s proof of a passing away battery. Additionally, begin your automobile up and rev it up a little bit. If the voltage doesn’t raise to about 14 volts or so, then it’s most likely that the alternator is having concerns.


What takes place if you select a voltage setup that is also low for the voltage you’re attempting to measure? Nothing bad. The meter will simply show a 1. This is the meter trying to inform you that it is overloaded or out-of-range. Whatever you’re attempting to read is way too much for that particular setting. Attempt changing the multimeter knob to a the following highest possible setup.

Selection Knob

Exactly why does the meter knob checked out 20V as well as not 10V? If you’re wanting to measure a voltage less than 20V, you count on the 20V setting. This will permit you to review from 2.00 to 19.99. The very first figure on lots of multimeters is just able to present a ‘1’ so the varieties are restricted to 19.99 rather than 99.99. Hence the 20V max variety as opposed to 99V max variety.

Measuring Resistance

Plug the red probe right into the right port and also turn the selection knob to the resistance section. After that, attach the probes to the resistor leads. The way you attach the leads does not matter, the outcome is the same.

Normal resistors have shade codes on them. If you do not recognize what they mean, that’s ok! There are lots of on the internet calculators that are very easy to use. Nevertheless, if you ever before locate on your own without internet accessibility, a multimeter is extremely helpful at measuring resistance.

Select an arbitrary resistor and also set the multimeter to the 20kΩ setting. After that hold the probes against the resistor legs with the same amount of stress you when pressing a trick on a key-board.

The meter will certainly review among 3 things, 0.00, 1, or the real resistor value.

In this case, the meter checks out 0.97, meaning this resistor has a value of 970Ω, or concerning 1kΩ (remember you are in the 20kΩ or 20,000 Ohm setting so you need to relocate the decimal three places to the right or 970 Ohms).

If the multimeter reviews 1 or shows OL, it’s overwhelmed. You will need to try a higher mode such as 200kΩ mode or 2MΩ (megaohm) setting. There is no harm if this happen, it merely implies the variety handle requires to be adjusted.

If the multimeter reads 0.00 or almost no, then you need to decrease the setting to 2kΩ or 200Ω.

Keep in mind that many resistors have a 5% tolerance. This means that the shade codes might suggest 10,000 Ohms (10kΩ), yet due to inconsistencies in the manufacturing process a 10kΩ resistor might be as reduced as 9.5 kΩ or as high as 10.5 kΩ. Do not fret, it’ll function just fine as a pull-up or basic resistor.

Generally of thumb, it’s uncommon to see a resistor much less than 1 Ohm. Keep in mind that measuring resistance is not excellent. Temperature can affect the checking out a great deal. Likewise, measuring resistance of a gadget while it is literally installed in a circuit can be very difficult. The bordering elements on a circuit card can considerably affect the reading.

The mockup usually resembles with a fundamental clock running of a AA battery. On the silver lining, the wire going from the battery to the clock is separated. We simply put our two probes in between that break to finish the circuit again (with the red probe linked to the source of power), just this time around our multimeter will review out the amps that the clock is pulling, which in this instance is around 0.08 mA.

While most multimeters can additionally measure rotating current (AC), it’s not truly an excellent idea (specifically if its real-time power), since AC can be dangerous if you wind up making a blunder. If you require to see whether or not an outlet is working, use a non-contact tester rather.

To measure current you need to remember that elements in collection share a current. So, you need to link your multimeter in collection with your circuit.

POINTER: to place the multimeter in collection, you need to position 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 cord in your circuit. If you separate the multimeter, your circuit won’t work.

Prior to measuring the current, make sure that you’ve plugged at a loss probe in the right port, in this case µAmA. In the example listed below, the same circuit of the previous example is made use of. The multimeter becomes part of the circuit.

Check for Continuity

If there is very reduced resistance between 2 factors, which is much less than a couple of ohms, both points are electrically connected and also you’ll listen to a constant noise. If the noise isn’t continuous or if you do not hear any audio in any way, it suggests that what you’re testing has a malfunctioning link or isn’t attached in all.

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

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

Continuity is a wonderful method to evaluate if two SMD pins are touching. If your eyes can not see it, the multimeter is normally a great 2nd testing source. When a system is not functioning, continuity is one even more thing to assist fix the system.

  • Establish your multimeter to the continuity setting using the selection knob.
  • The readout on the screen will quickly read “1”, which indicates that there isn’t any continuity. This would be appropriate because we haven’t attached the probes to anything yet.
  • Next off, make sure the circuit is unplugged as well as has no power. Then connect one probe to one end of the cable and the other probe to the various other end– no matter which probe takes place which end. If there is a full circuit, your multimeter will certainly either beep, reveal a “0”, or something aside from a “1”. If it still shows a “1”, after that there’s an issue and your circuit isn’t complete.
  • You can also evaluate that the continuity feature functions on your multimeter by touching both probes to each other. This finishes the circuit and your multimeter ought to let you know that.

A continuity examination informs us whether 2 points are electrically connected: if something is continuous, an electric current can stream easily from one end to the other.

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

Altering the Fuse

One of the most typical errors with a new multimeter is to measure current on a bread board by penetrating from VCC to GND. This will quickly short power to ground with the multimeter causing the bread board power supply to brown out. As the current hurries through the multimeter, the inner fuse will certainly warm up and afterwards wear out as 200mA moves through it. It will certainly take place in a flash as well as without any type of genuine distinct or physical indication that something is incorrect.

Keep in mind that measuring current is performed in collection (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 reviews ‘0.00’ which the system doesn’t switch on like it must when you attach the multimeter. This is because the inner fuse is damaged and also serves as a damaged cable or open.

To alter the fuse, discover your convenient dandy mini screw motorist, as well as start taking out screws. The elements and PCB traces inside the multimeter are made to take different quantities of current. You will damage and perhaps destroy your multimeter if you mistakenly push 5A through the 200mA port.

There are times where you need to measure high current devices like a motor or burner. Do you see the two areas to put the red probe on the front of the multimeter? 10A on the left as well as 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 use the 10A port to measure current, you run a much reduced danger of blowing the fuse. The compromise is sensitivity. As we spoke about above, by using the 10A port and also handle setting, you will just be able to check out down to 0.01 A or 10mA. A lot of systems use greater than 10mA so the 10A setting and also port functions all right. If you’re attempting to measure extremely low power (micro or nano amps) the 200mA port with the 2mA, 200uA, or 20uA could be what you require.


You’re now prepared to use your digital multimeter to begin measuring the globe around you. Do not hesitate to begin using it to answer several questions. A digital multimeter will address lots of concerns about electronic devices.

A multimeter is a crucial device in any type of electronic devices lab. In this guide, we’ve revealed you How To Use a Multimeter. You’ve discovered how to measure voltage, current and also resistance, and also just how to examine continuity.