How to measure resistance without a device. How to check a resistor with a multimeter for serviceability? How to test a variable resistor with a multimeter? Digital and analog multimeters

Someone has such a device at home, inherited it and lies in the closet... We will try to partially reveal its potential, and first we will look at how to check the resistance with a tester!

How to measure resistance with a tester and where are such operations necessary?

The point of carrying out work related to grounding not only closed, but also open conductive parts of electrical loads is to calculate the possible electrical potentials that may arise on electrical loads when there is a fault, to the ground potential.

How to check resistance with a tester - research methods

There are many different methods for measuring the grounding system that are found among users. Many of them have their advantages and limitations. The most common methods are:

• using an internal generator and 2 electrodes;
• using external measuring voltage without connecting auxiliary measuring electrodes;
• using external voltage and auxiliary electrodes;
• using an internal generator and 2 measuring electrodes, or using one measuring clamp;
• a rodless method that uses two measuring clamps.

If the work is carried out using the internal generator method and using two measuring electrodes, a sinusoidal measuring signal will be used in this case. This signal is an ideal option, unlike the rectangular one. More often, a sine wave signal is used if the grounding system measurement has inductive components in addition to active resistances. This method is applicable where grounding is done using metal strips that go around the work objects. Also, this approach is most preferable when all conditions, including physical ones, allow its implementation.

The method, which uses an external measuring voltage without turning on auxiliary measuring electrodes, is examined if it is necessary to measure grounding in TT systems. The main advantage of this method is that there is no need to use auxiliary measuring electrodes. This is a very valuable condition for cities, since there is little free space on the ground to place test electrodes. The method, which uses not only external measuring voltage, but also auxiliary electrodes, is actively being examined in remote settlements and rural areas. To work with this method you need a lot of free space.

The method using an internal generator and 2 measuring electrodes, or using just a measuring clamp, works when it is not necessary to disconnect the ground electrodes. Often these electrodes can be connected in parallel to the test electrodes. The rodless method works when it is necessary to carry out measurements in complex grounding systems (especially if these are multiple parallel grounding electrodes). This method is also used in the presence of a secondary system with low grounding resistance. Thanks to this method, measurements can be performed without auxiliary electrodes. An important advantage is that there is no need to break the grounding buses.

Measuring resistance with a tester - features of the process

Now let's discuss the most interesting thing - how to measure grounding resistance with a tester. Any such work should begin with an external inspection of all elements of the grounding loops. It is imperative to check not only the quality of welding work, but also the quality of bolted connections. If there were no serious comments during the examination, then you can safely begin taking measurements. Usually, in addition to the main device, the work requires the presence of special electrical measuring units.

In order to fully and correctly measure grounding resistance, you need to know and follow all the general operating rules. It is important to first pay attention to the fact that the device is in a horizontal position and all batteries are installed. It is necessary to monitor the arrow of the device: if the position of the range switch is in the required state, then it should be at zero. All wires must be connected only according to special diagrams.

If direct resistance measurements are carried out and, in addition to the probe, additional electrodes in the form of metal rods are used, then they should be buried in the ground at a distance of about 0.5 m. All resistance tests of any grounding devices must be carried out according to a schedule approved by the enterprise. They are usually held once every six months. If it is impossible to carry out the analysis yourself, then you need to seek help from specialized organizations. When performing measurements, it is important to ensure maximum safety when using electricity.

Most often, resistor malfunctions are associated with burnout of the conductive layer or poor contact between it and the clamp. For all cases of defects there is a simple test. Let's figure out how to test a resistor with a multimeter.

Types of Multimeters

The device can be pointer or digital. The first one does not require a power source. It works as a microammeter with switching of shunts and voltage dividers into specified measurement modes.

The digital multimeter shows on the screen the results of a comparison of the difference between the reference and measured parameters. It requires something that affects the accuracy of measurements as it discharges. It is used to test radio components.

Types of faults

A resistor is an electronic component with a specific or variable value of electrical resistance. Before checking the resistor with a multimeter, it is inspected, visually checking its serviceability. First of all, the integrity of the body is determined by the absence of cracks and chips on the surface. The terminals must be securely fastened.

A faulty resistor often has a completely burnt surface or partially in the form of rings. If the coating has darkened a little, this does not yet indicate the presence of a malfunction, but only indicates its heating, when the power released on the element at some point exceeded the permissible value.

The part may look like new even if the contact inside breaks. Many people have problems here. How to check the resistor with a multimeter in this case? It is necessary to have a circuit diagram according to which voltage measurements are made at certain points. To facilitate troubleshooting in the electrical circuits of household appliances, control points are identified with the value of this parameter indicated on them.

Checking resistors is done as a last resort, when there is no doubt about the following:

• semiconductor parts and capacitors are in good condition;
• there are no burnt tracks on the printed circuit boards;
• there are no breaks in the connecting wires;
• The connector connections are secure.

All of the above defects appear with a much higher probability than resistor failure.

Resistor characteristics

Resistance values ​​are standardized in series and cannot take any value. For them, permissible deviations from the nominal value are specified, depending on the manufacturing accuracy, ambient temperature and other factors. The cheaper the resistor, the greater the tolerance. If, during measurement, the resistance value goes beyond its limits, the element is considered faulty.

Another important parameter is the power of the resistor. One of the reasons for premature failure of a part is its incorrect selection according to this parameter. Power is measured in watts. It is chosen the one for which it is designed. In the symbol diagram, the power of the resistor is determined by the signs:

• 0.125 W - double slash;
• 0.5 W - straight longitudinal line;
• Roman numeral - power value, W.

The replacement resistor is selected according to the same parameters as the faulty one.

Checking resistors for compliance with ratings

To check, you need to find the resistance values. They can be seen by the serial number of the element on the diagram or in the specification.

Measuring resistance is the most common way to test a resistor. In this case, compliance with the rating and tolerance is determined.

The resistance value must be within the range that is set by the switch on the multimeter. The probes are connected to the COM and VΩmA sockets. Before checking a resistor with a tester, the serviceability of its wires is first determined. They are connected to each other, and the device should show a resistance value equal to zero or slightly more. When measuring small resistances, this value is subtracted from the instrument readings.

If the energy of the batteries is insufficient, a resistance other than zero is usually obtained. In this case, the batteries should be replaced as the measurement accuracy will be low.

Beginners, not knowing how to test a resistor for functionality with a multimeter, often touch the probes of the device with their hands. When quantities are measured in kilo-ohms, this is unacceptable, since distorted results are obtained. Here you should know that the body also has a certain resistance.

When the device registers a resistance value equal to infinity, this indicates the presence of a break ("1" lights up on the screen). It is rare to see a breakdown of a resistor when its resistance is zero.

After measurement, the resulting value is compared with the nominal value. In this case, tolerance is taken into account. If the data matches, the resistor is OK.

When doubts arise about the correctness of the instrument readings, you should measure the resistance value of a working resistor with the same rating and compare the readings.

How to measure resistance when the value is unknown?

Setting the maximum threshold when measuring resistance is not necessary. In ohmmeter mode, you can set any range. The multimeter will not fail because of this. If the device shows "1", which means infinity, the threshold should be increased until the result appears on the screen.

Dialing function

How can you check the resistor with a multimeter for serviceability? A common method is dialing. The switch position for this mode is indicated by a diode icon with a signal. The sign of the signal can be different, the upper limit of its response does not exceed 50-70 Ohms. Therefore, it makes no sense to ring resistors whose values ​​exceed the threshold. The signal will be weak and may not be heard.

When the circuit resistance values ​​are below the limit value, the device emits a squeak through the built-in speaker. Continuity testing is done by creating a voltage between the points of the circuit selected using probes. For this mode to work, you need suitable power sources.

Checking the serviceability of the resistor on the board

Resistance is measured when the element is not connected to the others in the circuit. To do this, you need to release one of the legs. How to check a resistor with a multimeter without desoldering it from the circuit? This is done only in special cases. Here it is necessary to analyze the connection diagram for the presence of shunt circuits. Semiconductor parts especially affect the readings of the device.

Conclusion

When deciding how to test a resistor with a multimeter, you need to understand how electrical resistance is measured and what limits are set. The device is intended for manual use and you should remember all the techniques for using the probes and switch.

We noticed that when measuring resistance, at the initial moment, numbers begin to flash on the multimeter display and stop at a certain value. Digital algorithms are used inside, which do not allow you to instantly get the desired answer. It is especially difficult for those measuring small resistances with a multimeter. Its accuracy is low; fractional parts cannot be found. How to check resistance with a multimeter is the topic of today's review.

Measuring resistance with a multimeter

Unlike capacitances, every tester can measure resistance. This is a simple operation. The trick is that mechanical models work with voltage without a battery, and to evaluate the parameters of resistors, a certain charge is needed to form an auxiliary voltage. Of course, the limitations can be circumvented by creating a resistive divider using an external source - for example, an outlet. The difference between digital multimeters is that the devices do not work without power supply.

The disadvantage of modern models is the limited scale. You want to measure the resistance of a resistor with a multimeter, but you come across continuous difficulties. The maximum limit does not exceed 2000 kOhm. This is only 2 MOhm; radio amateurs know that this is far from the upper limit for a decent resistor. The insulation resistance of electrical appliances must be 20 megohms. It will not be possible to check its quality using an ordinary multimeter. The first rule of measuring resistance with a multimeter is: “The size of the scale corresponds to the value being measured.”

Compliance is not easy to understand. In the old days, the value was stamped on the resistor body. For models that are too small, it is difficult to see the numbers. The rating does not depend on the dimensions. We have to guess: the baby is a couple of ohms or megohms. The difference is a million times, I don’t want to make a mistake. Most resistors today are marked with colored stripes. There is no need to learn the table by heart. We recommend using a simple technique: find an online calculator on the Internet to solve your own problems. A similar one is located at http://www.chipdip.ru/info/rescalc/.

Everything is presented in the form of a table, and it is shown that the resistors are marked with four or five stripes. Acceptable colors are shown in the rows of the table created by the authors of the site. The lane numbers are in columns. Selecting the desired gamma occurs by clicking on the radio boxes. There is only one color possible for each stripe. At the top, the current changes are displayed on a schematically drawn resistor, which adds convenience. Usually the outermost strip is thicker than the rest, but in practice this is impossible to notice.

Then they try to get a diagram of the device to get their bearings. If the approximate denomination is known, it is difficult to make a mistake. Secondly, they look at the stripes. For example, gold and silver colors are found exclusively on the extreme thin strip. In practice, very few people will be able to tell the difference between yellow and gray. It's too difficult without experience. You will need to enter both options on the calculator (from left to right and from right to left), then start measuring with a multimeter from the maximum value obtained.

So, to get the value in the online calculator you will need to enter all the bands. You won't be able to work in real time on Chip&Dip - a small drawback. As a result of your efforts, the following appears in the text field:

1. Resistor value, resistance in standard units. For example, Omaha.
2. Separated by a comma is a tolerance for accuracy. The worst resistors show a deviation of 10% (in both directions separately). As a result, the spread of resistance values ​​is large. Therefore, checking the resistance with a multimeter is required.

The form of the calculator is not the best, but it is located on the website of the famous Chip&Dip store, where you can order the necessary parts. In accordance with the found value, the multimeter scale is set with a margin. Let's say for a 10k resistor the limit is 20k. We remind you that on the front panel a group of scales measuring resistance is marked with the Greek letter omega Ω.

How to test a resistor with a multimeter

Typically the test begins with a nominal measurement as shown above. The corresponding number will appear on the display. Please note that the denomination parameter can vary greatly while maintaining tolerance for accuracy. The accuracy of the digital multimeter is 0.5 ohms, the device shows only integer values. Taking into account that the internal resistance of the multimeter is also present, it is impossible to evaluate the parameters of a resistor with a small value.

Important Notes:

• When measuring resistance, sometimes the readings are close to zero, or vice versa - a break is detected. This means the resistor has failed. In the first case, the nearest turns were shorted, in the second, the thread burned out. Most resistors consist of a ceramic base and a high-resistance core wound around it. Each element is characterized by a maximum dissipation power indicated in the technical data. If the parameter is exceeded, the effects described above occur. Often the resistor body darkens. Not every blackness means failure - in most cases, the paint is less resistant to heat than the core and darkens.
• A lot depends on the tolerance. Cheap resistors, even in one set, differ by 15 percent or more. It doesn’t mean that the multimeter is lying, you just need to take this fact into account when assembling the circuit. Approach wisely. If it is written that you need to get a resistive divider with equal arms of 100 Ohms, nothing terrible will happen if you take ratings of 90 Ohms. The main thing is to maintain equality.

The parameters of small resistances need to be assessed by indirect methods. Let's say we assemble a resistive divider as shown in the figure. Let's give a brief explanation. Firstly, we see two resistors, one of which is a reference resistor. This is a small nominal resistance with a minimum tolerance of 0.05% (gray bar, not silver). This will ensure maximum accuracy when working. The supply voltage +12 V was not taken by chance. This is the maximum denomination, easily obtained, for example, using a power supply from a personal computer. The higher the voltage, the more accurate the measurements. We got to the main subtlety: voltage can be measured with amazing accuracy - down to tenths of mV.

This will help determine the potential difference across the resistor under study. Then the nominal value is calculated from the proportion: (12 - U) / U = Ret / R. Where Ret is the resistance of the reference resistor, and U is the measured value (see figure). The picture shows where to connect the multimeter probes; the ground is taken from the power source (often the black wire). Let's see the benefits of using the scheme. Let's say there is a 1.5 ohm resistor with a tolerance of 10%. Obviously, a direct resistance measurement will give a reading of 1 or 2 on the display. This is clearly not enough. Now we take a reference resistor with a nominal value of 2.7 Ohms, assemble the circuit and see the voltage value of 4.4 V. Let's calculate the proportion:

(12 - 4.4) / 4.4 = 2.7 / R;

from where we find that R = 1.56 Ohm. We would not be able to measure the resistance with a multimeter at such low nominal values. In addition, the accuracy is great - down to hundredths! The main thing is that it becomes clear that the resistor complies with the technical documentation and is suitable for its intended use. Using the described method, it is permissible to try to measure the resistance of the wire over a long length. For example, a kilometer of copper core with a cross-section of 6 square meters. mm is a few ohms. The cable resistance is lower, we are talking about a whole bay.

Remember, to measure ground loop resistance you will need to find a reference point. This is a circuit that is guaranteed to be grounded. Or the potential can be removed from Uet, and the formula can be altered accordingly to suit the required case. By the way, there is no need to use exactly 220 V AC voltage. +12 V is much safer, it is not a fact that the accuracy will become lower, given the presence of a limit of 200 mV among the digital multimeter scales. This will allow, if you have a good reference resistor, to measure the ground resistance with a multimeter extremely accurately.

Measuring the resistance of nonlinear elements with a multimeter

In the lessons on elemental base, they said that in the open state the voltage drop across a silicon diode is twice that of germanium. Semiconductor elements are also made from gallium arsenide. Before assessing the resistance of the diode in the forward direction, you need to understand that this is a nonlinear element. Its characteristics depend on the applied voltage. The resistance measured by different multimeters will not be the same: each tester generates an auxiliary voltage on the probes, which is not the same for different devices.

To navigate the current-voltage characteristic of the diode (a graph that shows the dependence of the output current on the voltage applied to the contacts), you will need to know the characteristics of the multimeter. Often auxiliary quantities are not indicated in the passport; a test will be required. Take a medium capacitor. Let's charge with auxiliary voltage. We set the range to measure resistance and, not forgetting about the polarity (red probe is plus), apply it to the capacitor. When the resistance on the display completes its run from zero to infinity, we move on to measuring DC voltage (not forgetting about polarity).

As a result, the auxiliary voltage value is available. Now, using it, it is possible to find the current: I = U / R, where R is read from the display in the resistance measurement mode (a similar thing happens with the diode testing mode, marked with a characteristic bold arrow with a crossbar at the end). Now we look at the current-voltage characteristic and see whether the resulting point coincides with the position of the intersection of U and I. If the deviation is within the normal range, the diode is clearly suitable. Otherwise, if the diode opens and closes, the part can be used in circuits that are not critical to accuracy.

Measuring device resistances with a multimeter

If you take a 60 W bulb, it is easy to quickly verify that the resistance of the spiral is only 68 ohms. With an applied voltage of 220 V, a current of more than 3 A would flow through the device, which corresponds to a power of 700 W. The reason is the nature of the 50 Hz alternating voltage. Checking the resistance of an electric stove is carried out taking into account this simple fact. When talking about acoustics, we mean a certain average frequency for the sound spectrum, which is, for example, 2.5 kHz. Therefore, the resistance of the spark plug and the resistance of the speaker are intended to be measured by indirect methods under conditions close to real ones. The divider is assembled and a test circuit is created.

And the resistance of the ignition coil can be measured with a tester. To do this, you will have to find complete technical data on the number of turns and wire cross-section.

When repairing radio and electrical products, repairing wiring, there is a need to search for contact of current conductors in a place where a short circuit may occur (in this case, resistance = 0), to search for a place of poor contact between conductors (resistance tends to infinity). In this case, you should use a device called an Ohmmeter. Resistance is designated by the letter R and measured in Ohms.

An ohmmeter is a device (battery) with a digital or dial indicator connected in series. Also, an ohmmeter is used to check measuring instruments and measure insulation resistance at elevated voltages. All multimeters and testers have a resistance measurement function.

Note! Measure the resistance with the devices completely de-energized so that the ohmmeter does not fail. To do this, remove the plug from the socket or the battery. If the circuit includes capacitors with a large capacity, they should be discharged. Short-circuit the leads of the capacitors through a resistor whose rated current is 100 kOhm for a couple of seconds.

In order to use the Ohm measurement, set the slider on the device to the position that corresponds to the minimum resistance value measurement.

Before taking measurements, check the device for functionality. To do this, connect the ends of the probes to each other.

If this is a tester, you need to set the arrow to the “0” mark. If that doesn't work, replace the batteries. When checking an incandescent lamp, you can use a device whose batteries are discharged and the needle does not set to zero, but when connecting the probes it deviates from “0”.

If there is a deviation from zero, it means the circuit is intact. Digital instruments have the ability to display readings in tenths of Ohms. If the circuit is open, digital instruments flash overload; on pointer instruments, the arrow tends to “0”.

If the device has a function for testing circuits (diode symbol), it is better to test low-impedance circuits and wires in this way. If the result is positive, a beep will be heard.

The lamp in the lamp does not light? What is the reason? The failure may be in the socket, switch or electrical wiring. An incandescent, energy-saving, fluorescent lamp is checked by a tester. And this is quite easy to do. To do this, set the slider on the tester to the minimum resistance measurement position and touch the base with the ends of the probes.

The screen shows that the filament resistance is 51 ohms. This means that the lamp is working properly. If the thread were broken, infinite resistance would appear on the screen. A 12V, 100W car lamp shows a resistance of 1.44 ohms. A 220 V and 50 W halogen produces 968 Ohms.

The filament will show less resistance when cooled, when the paw is heated, this figure can increase several times. Therefore, lamps often burn out when turned on. This is because when turned on, the current flowing through the thread exceeds the permissible value several times.

Checking the headphones of the headset

There are problems with headphones associated with loss or distortion of sound, or its complete absence. The reason for this may be a failure of the headphones or the device from which the signal is received.

Using an ohmmeter you can determine the cause of the malfunction. To check the headphones, you need to attach the ends of the probes to the connector through which the headphones are connected to the equipment. Usually this is a 3.5 jack connector. The contact located in the connector closer to the holder is common, figured for the left channel, ring, located between them, for the right.

We bring one end of the probe to the common terminal, and touch the other end alternately to the right and left. The resistance at both ends should be 40 ohms. Often, all the parameters are indicated in the earphone passport.

If the difference in readings is large, there is a short circuit. This is easy to check. It is enough to touch the probes to the left and right channels at the same time. The resistance should increase by 2 times, that is, show 80 Ohms.

It turns out that we are measuring two series-connected circuits. If the resistance changes when you move the wire, the wire is frayed in some place. This usually occurs where the emitters or jack exit. To accurately determine the location of the breakdown, fix the wire, bend it locally, and connect an ohmmeter. If there is a gap where the Jack is installed, you need to buy a collapsible Jack.

You will have to bite off the old one along with part of the frayed wire, solder the contacts to the new connector according to the same principle as they are soldered to the Jack. If a break was found in the headphones, cut off the old piece of wire, solder a new one to the spot where the old solder was.

Resistor value measurement

Resistances (called resistors in a circuit) are widely used in electrical circuits. Often come to check the resistor for serviceability in order to determine the breakdown of the electrical circuit.

In the diagram, the resistor is shown as a rectangle; sometimes there is an inscription inside that may indicate its power. For example, I – 1 W and so on.

To determine the nominal value with an ohmmeter, turn it on in resistance measurement mode. The resistance testing sector is divided into parts. This is done to improve measurement efficiency. For example, the “200” slider indicates that we can measure resistance up to 200 Ohms. “2k” - 2000 Ohms and so on. “k” indicates that you need to add 1000 to the number, since it is a kilo prefix; “M” is mega, therefore the number is multiplied by 1,000,000.

If you set the slider to “2k” measurements and at the same time measure a 300 kOhm resistor, an overload icon will appear on the display. This means you need to set the slider to position 2M. It doesn’t matter in what position it is installed, you can change it during the measurement process.

During resistance measurements, the tester may show other readings than those indicated on the resistor. Such a resistor is not suitable for further use.

Modern resistors are color coded.

Checking diodes with a multimeter or tester

If it is necessary to convert alternating current to direct current, semiconductor diodes are used. When checking the board, the first attention should be paid to them. They are made from silicon, germanium and other materials that serve as semiconductors.

The diodes differ in appearance. The body can be made of plastic, glass, metal. They can be either colored or transparent. Despite this, they all have 2 outputs. In circuits, as a rule, LEDs, zener diodes, and rectifier diodes are used.

Conventionally, they are shown as an arrow that rests on a line segment. The diode is designated by the letters VD and only the LEDs are designated HL. The purpose of the diodes directly depends on the designations that are shown in the drawing. Due to the fact that the circuit may include a huge number of diodes connected in parallel, they are numbered.

The diode is easy to check if you know its operating principle. And it’s simple, it’s like a nipple. When air enters, the wheel is inflated, but it will not come back out. The same operating principle applies to diodes. Only he passes current through himself. To check its performance, you need a constant power source, which can be an ohmmeter or a tester, since they use batteries.

The photo shows a diagram of how the tester works when checking resistance. The terminals receive voltage of a certain type of polarity. “+” is supplied to the red terminal, “-” to the black terminal. When we touch, it turns out that there will be a positive probe at the anode terminal, and a negative one at the cathode terminal. Current will begin to flow through the diode.

If you mix up the probes, the current will not flow. The diode can be broken, serviceable, or broken. When a breakdown occurs, no matter which direction we connect the probes, current will flow through the diode. This is all because the diode in this case will be a piece of wire.

If a break occurs, no current will flow. It rarely happens that the junction resistance changes. Such a breakdown can be easily identified by looking at the display. Using this principle, you can check the rectifier diode, LED, zener diode, Schottky diode. Diodes can be either with leads or have an SMD design. Let's practice.

First, insert the probes into the device, observing the color markings. COM – black cable, R/V/f – red, plus. Next, set the slider to “dialing”. The photo shows the 2kOm position. We turn on the device, close the probes, and make sure that it works.

First of all, let's check the germanium diode D7. He is already 53 years old. Such diodes are not currently produced, since the price of raw materials is high, and the operating temperature is low (max 80-100). However, they are good because they have low noise and low voltage drop. They are appreciated by people who collect tube audio amplifiers.

When connected directly, the voltage drop is 0.129 mV. The dial gauge will show somewhere around 130 Ohms. If you change the polarity, the multimeter reading will be equal to 1, and the pointer, in turn, will show infinity. This means that the resistance is too great. The diode is OK.

A silicon based diode is tested in the same way. The case has 2 cathode terminals, which are marked with a dot, line or circle. With a direct connection, the drop is about 0.5 V. More powerful diodes will show approximately 0.4 V. Schottky diodes, whose drop is 0.2 V, are tested in this way.

Powerful LEDs have a drop of more than 2 V, the device can show 1. In this case, the LED is an indicator. If it glows, even faintly, then everything is fine.

Some types of higher-power LEDs are made according to the chain principle. That is, they have several LEDs connected in series. This is not visible from the outside. The drop across them can be up to 30 V; they should be checked with a power supply that has the appropriate voltage and resistors included in the circuit.

Checking electrolytic capacitors

Capacitors are divided into 2 types: electrolytic and simple. Simple ones are connected to the circuit in any way. But this method will not work with electrolytic ones. It is important to observe the polarity so as not to damage it.

Capacitors are shown on the diagram using two parallel lines. If the capacitor is electrolytic, you must indicate the polarity by placing a “+” sign next to it. Such capacitors are not reliable and most often they are the cause of failure of the power supply. A swollen capacitor in a device can often be noticed.

You can check such a capacitor with a multimeter or tester; in common parlance they say “ring.” Before starting the test, you need to unsolder the capacitors and discharge it. To do this, simply short-circuit its leads with tweezers or a similar object whose body is made of metal. The device should be set to test resistance in the range from hundreds of kilos to megaohms.

Use the probes to touch the terminals of the capacitor. At the same time, the arrow on the device will smoothly quickly deviate and smoothly fall. This depends on the size of the capacitor being tested. The larger the capacity, the slower the return of the arrow to its original position. The tester will show low resistance, but after a while it can reach hundreds of megohms.

Every person at least once in his life has had the need to carry out certain measurements of electrical quantities. Whether it's the voltage in the outlet or just checking the battery charge in the car, we all resort to using measuring instruments. During the Soviet era, measuring instruments were very scarce, it was very difficult to get them, and not everyone understood how to use them.

Today there are no problems with purchasing this or that instrument, you can buy whatever your heart desires, even a laboratory for measurements, as they say - “any whim for your money.”

But today’s article will not be about a laboratory for measurements (this is already at a professional level), but about ordinary multimeters that electricians, including me, so often use.

I welcome all friends to the “Electrician in the House” website. Previously, I have already published articles on how to use a multimeter when taking measurements, but due to the fact that I receive a lot of questions and comments asking me to tell How can you check if a light bulb is working properly? or measure the resistance of the resistor, I decided to publish detailed material on how to measure resistance with a multimeter.

Method for measuring electrical resistance - how the device works

The principle by which it is carried out measuring electrical resistance with a multimeter, is based on the most important law of electrical engineering - Ohm's law. The formula we know from a school physics course says the following: the current flowing through a section of a circuit is directly proportional to the voltage (EMF) and inversely proportional to the resistance in this section I (current) = U (voltage) / R (resistance).

It is through this connection that the device operates. Knowing two of the quantities, you can easily calculate the third. The built-in power source (DC) of the device, which is a standard 9 V battery, is used as a voltage source.

Essentially, measurements are performed using an indirect method. If you apply a measured resistance, for example Rx, to the probes of the device, the current flowing in the circuit will depend only on it. Knowing the current and voltage, you can easily calculate the resistance.

Device settings before measurements

So, friends, let's take a closer look at the device itself. In my case this is . The standard kit includes one pair of probes for force measurements and a thermocouple for measuring temperature, which I have never used before.

There is a rotary switch on the front panel. It is with this switch that the operating mode and measurement range are selected. The switch works like a “ratchet” and is fixed in each new position.

The entire circular panel is divided into sectors and has multi-colored markings (this is in my case). Sometimes sectors are outlined with separate lines, as if separating the required parameter.

Sector resistance measurements located at the top and divided into seven ranges: 200, 2k, 20k, 200k, 2M, 20M, 200M. The prefixes "k" and "M" stand for kilo (10 to the 3rd power) and mega (10 to the 6th power), respectively.

To operate, the switch must be set to the desired sector position. We are interested in resistance; therefore, before measuring resistance with a multimeter, we need to set the switch to the sector indicated by the “Ω” icon.

For ease of use with the device, the probes have different colors. It makes no difference where to insert which probe, but the generally accepted rule is that the black probe is inserted into the terminal marked “com” (short for common), and the red probe is inserted into the terminal marked “VΩCX+”.

Before performing any measurements, it is necessary to check the functionality of the device itself, since there may be a break in the measuring circuit (for example, poor contact of the probes). To do this, the ends of the probes are short-circuited with each other. If the device is working properly and there is no break in the circuit, then zero readings will appear on the display. Perhaps the readings will not be zero, but thousandths of an ohm. This is due to the resistance of the test leads and the transition resistance between the probes and their terminals.

When the probes are open, the display will show “1” (one) with a measurement range mark.

These simple steps prepare a multimeter for measuring resistance.

Some multimeters are equipped with a useful option called “diagnosis”. If you set the operating mode switch to the diode icon, a signal (buzzer) sounds when the probes are shorted. This allows you to check the health of circuits and direct junctions of semiconductors with a resistance of up to 50 Ohms by ear, without being distracted by the display.

How to measure the resistance of a resistor with a multimeter

We got acquainted with the theory and at first glance everything seems to be clear, but as practice shows, it is during practical work that people often have questions. So let's try to measure some element, for example a resistor.

Let's take this one constant resistor. This is one of the common types of fixed resistors. Its resistance should be 50 kOhm, I know this for sure, since I bought it in a store. Let's check if this is true? To do this, apply one probe to one end, the other to the other end.

Before that, you need to set the operating switch to the desired range. At what point should the slider be set if the resistor value is not known?

It is necessary that the switch is always in the nearest larger measuring position. Since I know that the resistor value is 50 kOhm, I set the switch to nearest greater position, in this case it is 200k. If you set the switch to a position lower than the corresponding resistance (at the 20k mark), the display WILL NOT show data. The internal lock will be activated.

This applies not only resistance measurements, but also when measuring quantities such as voltage and current. For example, if you want to measure the voltage in a socket, and on a scale from the operating ranges of 200 and 750 V, the switch must be set to the 750 V position. If you set the switch to the 200 V position and insert the probes into the socket, this will not damage the device since there is there is a security block in this regard, but still you will not receive any data.

Another resistor that I happened to have on hand is 10 ohms, let’s measure its resistance.

We set the multimeter switch to 200 (this is the nearest higher position for a given rating) and measure.

Friends, I want to note that the switch must be set to the nearest higher position; this will depend on accuracy of measurements. The higher the measurement limit from the nominal value of the resistance being measured, the greater the error the device will produce.

We measure the resistance of a variable resistor

Friends, we measured the resistance of a constant resistor, the electrical resistance of which will not change and cannot be adjusted. Let's now try to take measurements for variable resistor.

The difference between them is that the resistance of the latter can be changed manually by switching the slider to the desired position.

I have a 10 kOhm variable resistor, as evidenced by the inscription on it.

How to measure resistance with a multimeter in this case? Everything is very simple: the value of 10 kOhm corresponds between the two extreme contacts. The contact located in the middle is “floating”. If you apply probes between the outer and middle contacts and adjust the slider (turn clockwise or counterclockwise), you can see how the resistance changes depending on the positions of the slider.

The resistance should increase or decrease evenly and continuously from zero to the nominal value. The most common malfunction is the disappearance of the current collector contact when scrolling, which will be indicated by an “infinity” reading on the device.

Checking incandescent light bulbs with a multimeter

Now let's look at the practical use of a multimeter at home. Often unpleasant situations such as lighting failures arise at home.

Moreover, the reason can be the most extraordinary, from the burnout of the light bulb itself to a malfunction of the lamp or light switch, or much worse, damage to the junction box.

The most common malfunction, of course, is a burnt-out light bulb, so before you pick the electrical box, you need to check the integrity of the light bulb. Visually inspecting the integrity of the thread is not always possible to identify a malfunction. Moreover, the thread may not necessarily burn out. Less commonly, a short circuit occurs in the base and current inputs (electrodes).

Therefore, using a conventional tester you can easily check not only home incandescent lamp, but also a car or motorcycle headlight.

How to measure filament resistance with a multimeter? The minimum measurement limit “Ω” must be set. One probe should be touched to the base body, the other tip should be pressed against the upper contact of the base.

As you can see, the resistance of a 100 W incandescent working lamp is 36.7 Ohms.

If, during measurements, “1” is displayed on the multimeter display, and for analog (arrow) devices the reading is “infinity,” this will indicate an internal breakage/burnout of the filament in the lamp.

That’s all, dear friends, I hope this article has fully covered the question of how to measure resistance with a multimeter. If you have any questions, ask them in the comments. If the article was interesting for you, I would be grateful for a repost on social networks.