How can you measure resistance? Rules for using a tester (multimeter)

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Humanity began to live in the sphere of digital technologies. In everyday life, computers, vacuum cleaners, electric kettles, and telephones are everywhere. Therefore, everyone has had to deal with unexpected breakdowns at least once in their life. You don’t have to be an electrician to identify broken wires, a broken heating element or an iron. Often you just need to ring the wires or an incandescent light bulb, that is, check the resistance value.

To perform these tasks you can do without complex equipment. Quite suitable multimeter. A multimeter is a multifunctional measuring device that allows you to measure current, voltage and resistance.

The measurement of conductor resistance is based on Ohm's law. It says that the resistance of a conductor is equal to the ratio of the voltage to the current flowing in a section of the circuit. The formula is as follows: Resistance = Voltage / Current.

The unit of resistance is Ohm. One Ohm of resistance means that a current of one Ampere flows through a section of the circuit at a voltage of one Volt.

Therefore, if you pass a current, previously measured, at a given voltage through a conductor, you can calculate the resistance of the conductor.

Thus, a multimeter is nothing more than a voltage source and an ammeter for measuring current. The ammeter scale is marked in Ohms.

Description of the multimeter

To date, a large number of multimeters have been developed. Basically they are divided into:

Analog.
Digital.

Analog testers display measured values on the screen with an arrow. Some professionals still prefer them, although these devices have been almost driven out of the market by digital tes. With these devices it is more convenient and clearer to observe changes in the measured parameters.

Digital multimeters display data on a display with numbers. These devices are very popular.

An analog device works well in the range of radio waves and electromagnetic fields. They do not need, unlike digital multimeters, autonomous power supply.

There is a switch on the body of the analog tester. Use it to select the measurement mode. Switching ranges is obtained by multiplying the value on the scale by the scale factor that the switch specified.

The uniform scale is afraid of overloads. If it has values from zero to a certain number, then the device may fail. This is likely if the measurements significantly exceed the permissible limits. Therefore, many analog multimeters are equipped with a logarithmic scale, where the range of possible measured values is from zero to infinity.

Two probes are connected to the device. The ends of the probes look like needles. Sometimes, for convenience, metal clips called “crocodiles” are put on them.

In budget models, the probes are not of very high quality, although they may look impressive in appearance.

When purchasing a device, you should pay attention to the fact that the wire is flexible and elastic. It should be held tightly near the entry point.

The analog multimeter does not require a power supply. It operates on the same principle as an ammeter.

When the probes are connected to a circuit or radio element, current begins to flow in the internal induction coils. Under the influence of the created magnetic fields, the pointer on the device deviates by a certain angle and indicates the value on the screen.

The digital tester is designed a little differently. Inside its case there is a microcircuit located on a printed circuit board. It is entirely responsible for processing input data.

Digital multimeters are more accurate and produce less error than their analog counterparts.

Control and monitoring elements are located on the front panel:

mode and range switch;
LCD display;
connectors for probes.

Checking the indicator with a tester

To switch the multimeter to resistance measurement mode, use the rotary knob to select the “Omega” sector. This sector contains permissible measurement ranges. They are marked with marks 200, 2k, 20k, 200k, 2 M, 20 M, 200 M. These marks indicate the maximum measured resistance that is allowed in this range.

The value of the element being tested must be less than the rightmost value of the range, but greater than the left one. For example, if the value of the resistor being tested is tens of megaohms, then you need to select a range in the “Omega” sector from 20 mOhm to 200 mOhm.

If the resistance range of the resistor is unknown in advance, then you need to start measuring from the largest range. Then reduce the ranges, achieving the required accuracy.

If you set the range to be less than the resistance of the element, the data will not be displayed.

The probes are inserted into the corresponding sockets. The black probe of the device goes into the socket on the tester with the inscription “COM” (short for common), the red one goes into the socket next to which there is the designation “Omega”.

Wire testing process

Before starting any ringing, it is necessary to check the functionality of the device itself. It is possible that there are problems or breaks in the measuring system itself. The same insufficient contact of the probes. To check, the ends of the probes are connected to each other. If there are no breaks in the circuit and the device is operational, the display will show a zero value. Sometimes the values deviate slightly from zero. This is due to the resistance of the probes themselves and their terminals.

There are two ways. Their use depends on whether the device has a sound signal or not. If there is a sound function, then the corresponding icon will be drawn on the body.

Dialing is simple and intuitive. You need to set the switch to buzzer mode and bring the probes to the ends of the conductor being tested. The following tester behavior options are possible:

If the wire is not damaged, a beep will sound.
The wire may be intact, but it is too long. Then its resistance will be greater than that at which the buzzer sounds. Then the display will highlight a number with the resistance value.
If the resistance is much greater than the set range, then one will appear on the display. You should select another mode and take the measurement again.
If there is a break in the conductor, then there will be no indication.

In the case of testing radio components with an analog multimeter, it is set to the minimum possible measurement range. If, when the wire and probes come into contact, the arrow of the device is near zero, then there is no break.

Before measuring the resistance, in addition to the standard multimeter test, you need to conduct one more test. It is necessary to check the reaction of the tester's behavior on the human body. Some people have low resistance. If you hold the probes with your hands in places where there is no insulation, the tester may decide that the area being measured is not broken. Although in reality this will not be the case.

Measuring resistance with a multimeter is very similar to testing wires, but has its own characteristics.

First of all, the radio component being tested must be removed from the electrical board. Or at least one leg. Otherwise, the device can measure the overall resistance of the network, and not a specific part. If the part being tested has several pins, then it is completely desoldered from the board.

Before unsoldering an element from the board, you need to completely de-energize it, remove the galvanic batteries, turn off the switches and discharge the capacitors.

Visually inspect, checking the surface of the body. A burnt part (especially resistors) often has burnt rings on the body, significant darkened areas, and signs of melting.

It is necessary to set the optimal measurement range. Some tester models can detect it automatically.

If measurement accuracy is critical, measurement errors must be taken into account. For example, if the resistance on the resistor is 1kOhm (1000 Ohm), the tolerance percentage should be taken into account. This tolerance for resistors is 10%. As a result, actual resistance values will range from 900 to 1100 Ohms.

The same resistor, tested in the range up to 2000 kOhm, will show a resistance equal to one. But if you set the range to 2 kOhm, a more accurate number will appear on the tester display. For example, 0.97 or 1.02.

In some cases, it is possible to take measurements without desoldering the part from the board. This is only used in special cases. It is necessary to check whether there are shunt circuits in the electrical circuit. Semiconductors affect multimeter readings.

In this case, you need to study the circuit diagram. To make it easier to find problem areas and parts, electrical diagrams always show test points with the corresponding correct parameters.

It is unacceptable to touch the terminals of the element being tested with your hands when measuring resistance. The result will be predictably wrong.

Sometimes you have to take into account the so-called contact resistance. The tails of radio components and pure solder can become covered with an oxide film over time. It is recommended to clean the contact area a little or scratch it with a needle probe.

When measuring resistance, it is important to interpret the data correctly. For example, it is possible that the measurement value is equal to the maximum set as a limiting limit. This may indicate that the multimeter is broken. However, this is a rare scenario. Most likely, the limit is set incorrectly, and you need to increase it using the switch on the case.

If you have doubts about the correctness of the obtained values, it is advisable to measure the resistance value of a known-good and signed suitable element.

It is necessary to regularly check the condition of the galvanic battery inside the tester. Over time and with active use, the battery discharges. In practice, this leads to inaccurate results. In addition, the error increases in proportion to battery discharge.

Features of actions during isolation

Finding out the resistance of ordinary conductors and radio components is relatively simple. In the case of insulation there are special features. Illiterate actions by an electrician can lead to very bad consequences. An important rule: these measurements should be carried out in heated and warm rooms.

If such measurements are taken outdoors at low air temperatures, there is a high probability of microscopic ice formations inside the cable braid. Since water is a dielectric, its conductivity is minimal. Multimeters will not be able to recognize these inclusions. If a cable is moved from a cold street to a warm room, moisture may appear inside the wiring.

Actually, cable insulation resistance measurement happens as follows: needed, located in the distribution panel. The first probe is installed at the end of the neutral wire. The second probe is connected to the phase cable. When taking measurements, it is advisable to disconnect the ends from the terminals. All that remains is to select the correct limit and see the resistance value on the screen.

After which the resistance value is compared with the reference parameters. They are located in the Electrical Installation Rules. The tables below indicate values depending on the cable cross-section, its brand and many other parameters. If the measured data is within the acceptable range according to the tables, then the wiring is not broken. And there are no problems.

When you need to find out the presence of a ground loop in the wiring, then there are several recommendations:

In new houses, the voltage value in the phase-grounding chain is higher than in the phase-neutral one.
A small voltage is possible between the neutral cable and the grounded cable. Due to low potential on the neutral wire.

In general, measuring resistance using modern testers is not difficult. Especially if it's a new digital multimeter. Its operation is very convenient and does not require deep professional skills.

The examiner only needs a small set of knowledge of the basics of constructing electrical circuits from school physics lessons. And of course, in any case, basic safety requirements must be observed.

Multimeters are widely used not only by professional electricians, but also by home craftsmen. Using them, it is possible to measure all known electrical quantities used in practice in various electrical networks. In this article we will look at how to measure resistance with a multimeter. For such purposes, there is a built-in ohmmeter, which makes it possible to check this parameter and obtain a certain value for transformers, coils, capacitors, various electronic elements, as well as cables and wires.

Analog and digital multimeters

The operation of measuring instruments is based on Ohm's law. It defines the concept of resistance, represented as the ratio of the voltage in a conductor to the current flowing in the same conductor (R = U/I). Thus, a resistance of 1 Ohm corresponds to a current of 1 A with a voltage of 1 V. Therefore, if the voltage and current are known in advance, then calculating and measuring the resistance is not at all difficult. The simplest one is essentially both a current source and a scale marked in Ohms.

Initially, instruments for measuring resistance could perform only one function. The measurement was carried out in the shortest possible time and gave accurate results. Subsequently, universal measuring devices appeared - multimeters, where the ohmmeter is only one of the components, included in the desired mode. You also need to be able to use analog devices correctly, from connecting to processing the received data.

The appearance of digital and analog devices is noticeably different. In the first case, the measurement results are displayed on the display in the form of specific digital indicators. In analog instruments, instead of a display, a graduated dial is used, where the needle stops near the desired value. Thus, digital multimeters immediately allow you to determine and provide ready-made data, while analog multimeters require additional processing of the results obtained.

Digital multimeters are equipped with a sensor that indicates the degree of discharge of the power source. If the current is insufficient, the device simply will not work. In such situations, analog devices do not signal in any way, but begin to provide incorrect information. As a rule, any multimeters with sufficient values of the limits of measured resistance can be used in everyday life. They allow you to perform any task, including measuring the resistance of a resistor.

However, these devices are not suitable for measuring large quantities due to low power and weak power supplies. For these purposes, they are used, powered by a powerful battery with a step-up transformer or a current generator.

Preparing for measurements

The accuracy of the results largely depends on the correct settings of the measuring device. The multimeter is controlled by a rotary-type round knob. A scale is marked around it, consisting of several sectors separated by lines or different colors.

The device is switched to resistance measurement mode by turning the knob and moving it to the position opposite the “Ω” icon. Specific operating modes in different devices are set differently:

Icons Ω, kΩ - x1, x10, x100, MΩ. They are located on the scale of any analog tester. The readings marked with an arrow are converted to a more modern format. When applying, for example, 1-10 on a graduation scale, for each mode you will need to multiply the result obtained by this coefficient.
Symbols 200, 2000, 20k, 200k, 2000k. They are marked on the scale of an electronic device (multimeter) and indicate a certain range in which it is possible to measure resistance. The letter k indicates the prefix “kilo”, equivalent to 1000, determined for calculations by a unified measuring system. For example, if the multimeter is set to the “200k” position, and the number 178 is displayed on the display, then the resistance will be 178 x 1000 = 178,000 Ohms, and the maximum permissible for measurements is 200,000 Ohms.
The “Ω” icon on the body indicates the possibility of automatic range detection. On the dials of such devices there are not only digital, but also letter designations - 15 kOhm, 2 Mohm, etc.

The first two versions of the scale assume a direct relationship between the degree of reliability of the displayed results and the measurement error. When you first turn on the device in the maximum range, small resistances of 100-200 Ohms are displayed incorrectly in most cases. Therefore, before carrying out measurements, inexperienced electricians are advised to once again read the instructions defining the procedure.

How to use a multimeter when measuring resistance

After studying the instructions and preparing the multimeter for use, you can begin to take direct measurements. All actions are generally performed in the same way, regardless of the object being measured.

The black test lead must be inserted into the COM socket, and the red end of the conductor must be inserted into the VΩmA socket. Next, by turning the range switch, the multimeter must be turned on.

Before measuring small resistance parameters, the switch must be set in the “Ω” sector. Its final position is fixed opposite the number “200”. Thus, the measurement capability will be in the range from 0.1 to 200 ohms. Next, the measuring circuit must be checked for short circuits. To do this, the probes touch each other, and numbers from 0.3 to 0.7 appear on the screen, showing the resistance value in the test leads. This value should be checked every time you turn on the multimeter. If the wires are open, the number 1 will appear on the left edge of the display.

When taking measurements, you must simultaneously touch the contacts on the area. If the consumer or the circuit itself is in good condition, the readings of the device will differ, since all elements have different resistance. If the integrity of a fuse, cord or wire is checked, the resistance is in the low range, approximately 0.7-1.5 ohms. Connecting to current consumers gives results within 150-200 Ohms. The dependence of power on resistance becomes noticeable: the higher the power of the consumer, the lower its resistance.

When the multimeter readings remain unchanged, the measurement range must be switched to 2000, which makes it possible to take measurements in the range from 0 to 2000 Ohms. If there is no result, you need to switch to the next value and take the measurement again. You should remember the high sensitivity of the multimeter in the “2000k” position. If you simultaneously touch the probes with your hands, the device will show the resistance of the human body and the data obtained will be distorted.

Insulation and continuity resistance of wires

The usual measurement procedure is not suitable for determining the insulation resistance of cables and wires. When solving the problem of how to correctly measure insulation resistance, you should take into account the rules and features of this process, non-compliance with which can cause serious negative consequences.

The main mandatory requirement is to carry out such measurements only in warm rooms with a stable positive temperature. If such work is carried out outdoors in low temperature conditions, then small pieces of ice are likely to form inside the wire braid. In this case, water acts as a dielectric with minimal conductivity. The multimeter is unable to detect these water particles. Subsequently, as the air temperature rises, moisture may form inside the cable.

Measuring resistance with a multimeter is performed in a certain order. Both probes are installed at the ends of the phase and neutral wires, previously disconnected from the terminals. Next, using the switch, the desired measurement range is set and the resistance value is determined. The obtained data is compared with the reference values found in the PUE. The tables below take into account the brand, cable cross-section and other factors. If the measurement result generally coincides with the data in the tables, then the wiring is not broken and is in good condition.

Wire testing can be performed in audible and silent versions. Many multimeters have an audible signal, indicated by an icon in the form of three semicircles. Depending on the model, it may be located in different places. When the device is switched on to dialing mode, a sound signal is generated when the wire resistance is below 50 Ohms. In some devices this figure is 100 Ohms, so before work you need to look at the technical data sheet again.

The continuity test itself does not present any difficulty: the switch is placed near the sound icon, and the probes touch the conductor being measured. The integrity of the wire will be confirmed by an audible signal. If the resistance is higher than normal due to the long length of the solid wire, a number with its real value will be displayed on the screen.

When 1 appears on the display, it means the resistance is too high and you need to switch to another mode in the direction of increasing. If the integrity of the wire is broken, any indication will be absent.

The article talks about how to check resistance with a multimeter. In addition, it is used to measure current strength, voltage between two points, and also connect electrical circuits. Depending on the type of device, it can be used to test diodes, transistors and many other radio components.

What types of multimeters are there?

Previously, a dial (analog) multimeter was used, but now many have switched to digital, as it is more convenient.

The pointer device is still used by professionals. It works better in the range of radio waves and electromagnetic fields, and does not require autonomous power supply, without which it cannot work. At the same time, the accuracy of their readings is significantly affected by the wear of the batteries. They can fail from electrostatic discharge, which does not threaten the analog tester.

A pointer multimeter operates as a microammeter equipped with switches, shunts and voltage dividers that allow it to be switched to the operating modes of various devices. In contrast, a digital device displays the results of comparison and calculation of the difference between the measured parameters and the standards.

Basics of instrument operation

Each multimeter, whose characteristics differ from others, has its own measurement specifics, but there are mandatory rules for all types of devices.

To switch to a specific built-in device, as well as to the required range of measuring its parameters, one switch is used.

Measurements are made by touching metal probes with insulated handles to the conductors.

The measured parameter value must be within the range set by the switch. Measurements are made first at higher ranges, and then the required accuracy is adjusted with a switch.

The voltmeter is connected to two points with different potentials.

To measure the current, create a break in the electrical circuit and connect an ammeter to it.

Resistance is measured on an element disconnected from the circuit by passing an electric current through it from a battery built into the device.

The probe with the black wire is connected to the COM socket with the “-” pole, and the one with the red wire is connected to the VΩmA socket with the positive pole.

There are different models of multimeters available, differing in their operating features. Each of them comes with manufacturer's instructions: how to take measurements and switch operating modes.

Digital multimeter device

The basic functionality of most models is the same. Icons, measurement limits, and additional features may vary slightly. All control and monitoring elements are located on the front panel: mode and range switch, LCD display, connectors for probes.

The most advanced devices automatically select measurement limits.

Probes are designed to transmit a signal from elements of electrical circuits to the device. The device has three adjacent sockets for them. When measuring, you should always hold only the insulated handles.

Principle of operation

The electric multimeter in most budget models operates on a 1CL7106 microcircuit.

When the voltage is measured, the signal is supplied from the switch to input 31 through resistor R17.

To measure the amount of direct current, a multimeter is connected to the open circuit. The current strength is perceived by resistors depending on the set range, after which it is supplied from them to input 32.

The diagram shows only the main functions. Many models have additional ones. Which multimeter is better, each user decides depending on the specifics of the measurements.

Resistance measurement circuit

Whatever the type of multimeter, there are applications for an ohmmeter in almost everyone. Most often, it is used to check transformers, inductors and the serviceability of fuses. Below is a simplified resistance measurement diagram.

Here, reference resistors R1...R6 and current-setting resistors R101 and R103 are used. In the measurement mode, the reference and input voltages are compared, equal to the ratio of the measured and reference resistances.

The device is used to detect open circuits, breakdown of capacitor plates, and check the integrity of printed conductors on electronic boards.

How is resistance measured?

How to check the resistance with a multimeter can be found in the instructions, but the method is common to many models. On the tester there is a section with the "Omega" icon. Common models such as M832, M83x, MAS83x have 5 measurement limits: 200 Ohm, 2 K, 20 K, 200 K, 2 M. In addition, the 6th position is used for testing circuits. The buzzer is triggered when the resistance between the probes is less than 50 ohms. When they are connected to each other, the device shows a resistance value slightly above zero. When a small resistance value is measured, this value is subtracted from the reading.

For example, if you have a resistor whose resistance is approximately 1.5-7 K, you should select a range with a limit of 20 K to measure with the M832 multimeter.

Unlike other devices, an ohmmeter can measure unknown resistance at any range, this will not lead to its failure. If the setting does not meet the required limits, a one or zero will be recorded on the screen. In the first case, it is necessary to increase the upper limit of the measurement range, and in the second, to decrease it.

Note! Before checking resistance with a multimeter, beginners usually touch the current-carrying leads of parts and probes with both hands. As a result, the resistance of the resistor and the body is measured, which introduces an error in the readings of the device. It is especially large when the nominal value is measured in megaohms. The part output and the probe can be held with only one hand. This requirement must be observed when checking any radio components.

When repairing electronic equipment, it is often necessary to measure the resistance of a resistor soldered into the circuit. To get accurate readings, you need to unsolder one of the pins. The measuring circuit should consist only of an ohmmeter and a resistor. If it is soldered into the circuit, the resistance between the terminals and other radio components will add up. If the part has many pins, it must first be completely desoldered to perform measurements.

Resistance measurement example

It is required to measure the resistance of a coil whose rating is unknown. Usually the upper limit is chosen as the maximum. When you set the switch to the “2M” position and connect test leads to the coil terminals, only zeros will appear on the screen. This means that there is electrical resistance of the turns, but the measurement limits are chosen incorrectly.

Then you need to set the switch to the “200 K” position, which corresponds to the range of 0-200 K and reconnect the multimeter probes. A resistance value of 00.5 kOhm will appear on the screen. If there are zeros ahead of the decimal point in the readings, it means that the measurement limits need to be reduced further. At the next position of the switch, the device will show 0.73 kOhm. This value is already more true.

If there is a need to obtain a more accurate result, you need to reduce the range to 0-2 kOhm and repeat the measurement. The screen will show 0.751 kOhm.

If you switch to the measurement limits of 0-200 ohms, the device will display “1”, which means that the measured value is beyond the upper limit.

Before testing the coil with a multimeter to see if there is a break in it, you need to set the switch to this mode and then connect the probes to its terminals. The presence indicates that the circuit is working properly. If the buzzer is silent, it means there is a break in the coil.

Multimeter probes

The probes in budget testers are not of high quality, despite the fact that some of them look impressive. When purchasing, you should choose ones so that the wire is elastic and holds tightly at the entry point.

The conductive ends are made in the form of needles so that you can pierce the insulation of a wire or find pins in microcircuits with a small pitch. The material used is bronze, which does not hold an edge well. In addition, the needles break off at the insertion points.

In the cold, the insulation of the wires becomes hard and the device is inconvenient to use.

Another drawback is unreliable contact in the device socket. When calling circuits, he often gets lost.

Multimeter probes often have to be brought to condition with your own hands. To do this, the wires are soldered to the lugs, and the connectors in the sockets are selected differently. The tip should be tinned so that when pressing on the point being tested, the amount of resistance does not depend on the pressing force.

It is advisable to replace the wires with a larger cross-section to reduce their resistance. The wires included have a resistance of 0.2-0.5 ohms, and sometimes even higher.

Checking the ohmmeter before work

During the operation of the multimeter, the current-carrying conductors of the measuring probes wear out, which negatively affects the measurement results (the readings “jump”). They should be checked before use. To do this, set the device switch to the lowest range and short-circuit the probes with each other. Then its insulated conductors are probed. If there is poor contact inside, the display will begin to lose readings. You can also check the probe in the continuity mode. If the buzzer sound disappears and appears again, this indicates unreliable contacts.

Device power

A 9 V Krona battery is inserted into the device. If a battery icon appears on the multimeter screen, this indicates that it is low and requires replacement. Otherwise, the device readings will be incorrect.

Some multitesters have a HOLD button. When pressed, the instrument readings are recorded for ease of reading. To return to operating mode again, you need to release the button.

Conclusion

Each multimeter model is sold with instructions, which should be carefully studied, since each type of device has its own characteristics.

Before that, you should determine its approximate value. If the value is several ohms, the part does not need to be desoldered from the board. When measured in megaohms, the resistor should be unsoldered and measured without touching the terminals with your hands.

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.

To measure resistance we need.

In order to measure resistance, we need to turn the knob to “measure resistance”. This is our entire top row in green. The letter “K” tells us that we are going to measure kilo-ohms, and the letter “M” means that we are going to measure mega-ohms. The measurement limit is shown before the letter. If a 1 lights up on the multimeter display when measuring resistance, then we switch the knob to a higher limit.

How to measure resistance with a multimeter

Let's take this constant

We see the inscription “82R” on it. It means that its resistance should be 82 Ohms. You can read more about resistor markings. To do this, apply one probe to one end of the resistor, and the other probe to the other end.

As you can see, the multimeter almost accurately showed the resistance value of this resistor.

How to test a variable resistor

Let's measure the resistance of the variable resistor. As you know, with a variable resistor we can change the resistance manually. The same applies to tuning resistors - this is one of the types of variable resistors.

This is his view from below. Here we see the inscription 47 KM. This means its resistance should be 47 KiloOhms between the two extreme contacts.

Using a stick, we can twist it clockwise or counterclockwise, thereby changing the resistance between the middle contact and the two outer contacts

And here is its circuit designation:

We place the probes at the extreme contacts. We measure the total resistance of the variable resistor.

Hmmm... A little different resistance. Our variable resistor is too old, which may be why its resistance does not match what is written. In order to check whether it is working, turn the variable resistor knob all the way counterclockwise and measure the resistance between the left and middle contacts. It should be close to zero.

Turn the handle clockwise, but not all the way. We measure the resistance between the middle and left contacts again.

We measure the resistance between the middle and right contacts.

The total should be the result of the resistance of the two extreme contacts. 12.2+27.6=39.8 Almost everything is correct. Therefore, our variable resistor is working properly. Some variable resistors have a range not from zero, but from some other value, for example from 10 to 100 KOhm. Be careful when checking.

Rules for measuring resistance

Press the probes with some force onto the resistor terminals. In this way, you will eliminate the appearance of contact resistance, which, when pressed lightly, will add up to the measured resistance.
Do not measure resistance under voltage! This could damage the multimeter or cause you an electric shock!
When measuring the resistance of a resistor on a printed circuit board, double-check that the board is de-energized. Then unsolder one end of the resistor and then measure its resistance.
Do not touch the resistor leads when measuring its resistance! The average human body has a resistance of about 1 KiloOhm and depends on many factors. Therefore, by touching the resistor terminals when measuring resistance, you introduce an error into the measurements.
If you want to measure the resistor's resistance as accurately as possible, clean its terminals either with a knife or with the mildest sandpaper. In this case, you will remove the oxide layer, which in some cases introduces a noticeable error in the resistance measurement.