How to check the resistance of a multimeter: a measurement instruction

The article describes how to test the resistance of a multimeter. In addition, it measures the strength of the current, the voltage between two points, and also calls up electrical circuits. Depending on the type of device, it can be used to check diodes, transistors and many other radio components.

What are the multimeters?

Earlier, a multimeter was used (analog), but now many have switched to digital, as more convenient.

The switchgear is still used by professionals. It works better in the area of radio waves and electromagnetic fields, does not need autonomous power, without which digital multimeters can not work. In this case, the accuracy of their indications is largely affected by the deterioration of the batteries. They can break down from electrostatic discharge, which does not threaten the analog tester.

The meter of the switch works like a microammeter equipped with switches, shunts and voltage dividers, which allow switching it to the operating modes of various devices. In contrast, the digital device displays the results of comparison and calculation of the difference between the measured parameters and standards.

Fundamentals of Instrument Operation

For each multimeter, the characteristics of which differ from others, there is a specificity of measurements, but there are mandatory rules for all types of devices.

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

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

The measured value of the parameter must be within the range set by the switch. Measurements are first made at higher ranges, and then the switch adjusts the necessary accuracy.

The voltmeter is connected to two points with different potentials.

To measure the current, a break in the electrical circuit is created and an ammeter is connected to it.

The resistance is measured on an element disconnected from the circuit by passing an electric current through it from the built-in battery.

A probe with a black wire is connected to the COM socket with a "-" pole, with a red lead to the VΩmA socket with a positive pole.

Different models of multimeters, differing in features of work, are produced. Each of them is accompanied by the manufacturer's instructions: how to make measurements and switch modes of operation.

Digital Multimeter Device

The basis of functioning in most models is the same. Here icons, measurement limits and additional functions may differ slightly. All controls and controls are located on the front panel: a switch of modes and ranges, LCD display, connectors for probes.

The most advanced devices automatically select the measurement limits.

Styli are intended for signal transmission from elements of electric circuits to the device. For them in the device three adjacent nests are intended. Always measure with insulated handles when measuring.

Principle of operation

The multimeter electric in most budget models operates on the chip 1CL7106.

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

To measure the DC current, a multimeter is connected to the circuit break. The current is sensed by the resistors depending on the set range, after which the voltage drop from them goes to the input 32.

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

Resistance measurement circuit

Whatever type of multimeter, the use of an ohmmeter is practically in everyone. Most often, it checks the resistance of resistors, transformers, inductors and the serviceability of fuses. Below is a simplified diagram of resistance measurement.

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

The device is used to detect breaks in the circuit, the breakdown of capacitor plates, the integrity of printed conductors on electronic boards.

How is the resistance measured?

How to check the multimeter resistance, you can read the instructions, but the way is common for many models. On the tester, the resistance section is indicated by the "Omega" icon. The common models of type M832, M83x, MAS83x have 5 measurement limits: 200 Ohm, 2 K, 20 K, 200 K, 2 M. In addition, the 6th position serves for the continuity of the circuits. The buzzer is triggered when the resistance between the probes is less than 50 ohms. When they are interconnected, the instrument shows a resistance value slightly above zero. When the value of a small resistance is measured, this value is subtracted from the readings.

For example, in the presence of a resistor, whose resistance is approximately 1.5-7 K, for measurement with the M832 multimeter, a range of 20 K should be chosen.

Unlike other devices, an ohmmeter can measure unknown resistance on any range, this will not lead to its failure. If the installation does not meet the required limits, a unit or zero will be fixed on the screen. In the first case, it is necessary to increase the upper limit of the measuring range, and in the second - to reduce.

Note! Before testing the resistance with a multimeter, beginners usually touch the live 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 instrument. Especially it is great, when the value is measured in megaohms. The workpiece and probe can only be held with one hand. This requirement should be observed when checking any radio components.

When electronic equipment is repaired, it is often necessary to measure the resistance of the resistor soldered into the circuit. In order to obtain an accurate indication, one of the conclusions must be dropped. The measuring circuit must consist of only an ohmmeter and a resistor. If it is soldered into the circuit, the resistance between the terminals and other radio components will be summed up. If the part has many leads, it must first be completely evaporated to perform the measurements.

Resistance measurement example

It is required to measure the resistance of a coil, the nominal value of which is unknown. Usually the upper limit is chosen to be the maximum. When the switch is set to "2M" and connected to the terminals of the probe coil, only zeros appear on the screen. This means that the electrical resistance of the turns is, but the measurement limits are not selected correctly.

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 kΩ appears on the screen. If there are zeros in the indications ahead of the comma, then it is required to reduce the measurement limits still. At the next switch position, the meter will show 0.73 kΩ. This value is more appropriate.

If there is a need to get a more accurate result, you must lower the range to 0-2 kΩ and repeat the measurement. The display will show 0.751 kOhm.

If you switch to the measurement range of 0-200 Ohms, the instrument will show "1", which means that the measured value is out of the upper limit.

Before you call the coil with a multimeter for the presence of a break in it, you must set the switch to this mode, and then connect the test leads to its terminals. The presence of a beep indicates that the circuit is OK. If the buzzer "is silent", it means that there is a break in the coil.

Probes for multimeter

Probes in budget testers are not of high quality, despite the fact that some of them look spectacular. When buying, you should choose such that the wire is flexible and tightly held at the entrance.

The conductive ends are made in the form of needles, so that it is possible to pierce the insulation of the wire or to find the leads in microcircuits with a small pitch. As a material, bronze is used, which does not hold the sharpener badly. In addition, the needles break off at the places of embedding.

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

Another drawback is the unreliable contact in the socket of the device. When dialing schemes it is often lost.

Probes for a multimeter often have to be brought to the standard by their own hands. For this, the wires are soldered to the terminals, and the connectors are selected in the sockets by others. The tip should be tinned, so that when the test point is pressed, the resistance value 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 in the kit have a resistance of 0.2-0.5 Ohm, and sometimes even higher.

Checking the ohmmeter before work

During the operation of the multimeter, the current-carrying veins of the measuring probes wear out, which adversely affects the measurement results (the readings "jump"). Before work, they should be checked. To do this, the instrument switch is set to the lowest range and closes the probes with each other. After it is probed his insulated conductors. With a poor contact inside, the display will begin to falter. You can also check the probe in the continuity mode. If the buzzer beep sounds and reappears, it indicates unreliable contacts.

Power supply

The device inserts the "Crohn" battery to 9 V. If a battery icon appears on the multimeter screen, it indicates that it is dead and you need a replacement. Otherwise, the instrument reading will be incorrect.

On some multiverster there is a HOLD button. When it is pressed, the instrument reading is fixed for easy reading. To return to the operating mode, it is necessary to press the button.

Conclusion

Each model of the multimeter is sold with an instruction that should be carefully studied, as each type of device has its own characteristics.

Before testing the resistance with a multimeter, determine its approximate value. If the value is a few ohms, the part can not be evaporated from the board. With a dimension in megaohms, the resistor should be evaporated and measured without touching the terminals with hands.