How to measure current with a multimeter: setting up a measuring device, connection rules when measuring amperage

A multimeter is a device for measuring various electrical parameters. It allows you to measure AC and DC voltage, current, resistance, as well as many specific parameters, such as the performance of diodes, transistors, signal frequency. In order to know how to measure the current strength with a multimeter, you need to understand the basic principles of this device.

Checking readings with a multimeter

It is important to measure the current when checking the correct operation of the devices. Often you need to check the charging current level of the battery for the car, laptop, tablet, power-bank.

Measurement of current of various nature produced in different ways inside the measuring device. Therefore, the multimeter always has an element whose task is to select a parameter, measurement mode and signal level. Sometimes, in more advanced equipment, the signal level is determined automatically.

Usually the parameter and measurement mode are selected by turning the knob on the multimeter body. The selectable characteristics are grouped according to their types. They are usually designated as follows:

• Direct current: A -, DCA, I -;
• Alternating current: A ~, ACA, I ~;
• Constant voltage: V-, DCV, U -;
• Variable voltage: V ~, ACV, U ~;
• Resistance: Ω, R, Ohm;
• The definition of the capacitance of capacitors is often indicated by a capacitor icon, or the letter C;
• Diode ringing is usually indicated by a diode icon.

DC current measurement

To measure the required indicators, first you need to determine what type of current flows in the tested circuit. It depends on the power source of the circuit. For example, rechargeable batteries and batteries are permanent power supplies. To measure DC current, you need to set the rotary knob of the multimeter to the A -, DCA or I - icon, or press the button on the front panel corresponding to the desired mode. Both AC and DC currents are measured in amperes. Therefore, the value on the display of the measuring device will be displayed in this value.

To understand how to measure amperes with a multimeter, you need to know that the current in the circuit section is always the same. When the ammeter is connected to the circuit in series (that is, the probes of the device are connected to different points of the circuit break), it will not create a tangible change in the parameters of the circuit. In this case, it will be able to display the correct value of the flowing current. It is important to connect the meter in the correct polarity, that is, the red probe to the branch that goes to the plus of the power supply, and the black one to the minus. Otherwise, the device will show negative values.

When preparing for a measurement, it is very important to know what signal level you need to check. If milliamperes are leaking in the circuit, then the red probe must be connected to the socket of the meter, which says V Ω mA, or there is a specific measurement limit (usually 300 - 400 mA). If a power circuit is being checked, the values ​​in which are measured in units of amperes, then the probe must be connected to the socket marked, A or NA (usually from 5 to 10 amperes flows here). Failure to follow this rule can damage the measuring device. There are also more powerful ammeters, but they are used for special purposes.

Having connected the device correctly, you can start working. The procedure for measuring the amperage with a multimeter is as follows:

1. Install the test leads into the appropriate sockets of the meter corresponding to the signal level.
2. Select constant current mode with the regulator or by pressing the corresponding button on the front panel.
3. If necessary, select the level of the measured signal with a regulator or button. The level should be chosen just above the expected value.
4. Connect the multimeter to the open circuit of the circuit branch, observing the polarity of the connection.
5. Switch on the power supply.

Battery check

In order to assess the performance of the simplest portable battery - a battery with a multimeter, just check its voltage and amperage, it is not necessary to use a load. To check, you need to install the red wire in the hole with the inscription, A (NA), select the constant current mode and the measurement limit on the front panel of the multimeter, and apply the probes in accordance with the polarity to the battery terminals - red to positive, black to minus. After a few seconds, the meter will display the DC generated by the element on the screen.

If the values ​​are in the range of 4 - 6 amperes, then the battery is "fresh" and ready for use. With readings below 4 amperes, it can only be used in low wattage appliances. At values ​​below 2.5 A, it is better to refuse to use such an element.

The correct voltage values ​​must correspond to those indicated on the battery.

Battery test with a measuring device

Among the parameters of the batteries the output current is important. You can check it with a multimeter, but at the same time a load must be connected in series with the meter. The load can be a conventional incandescent lamp. Its resistance does not exceed several hundred ohms, and it can also be measured with a multimeter in resistance measurement mode. To do this, you need to attach the meter probes to the thread of the lamp base and the center terminal. The display will show the resistance value.

If we consider the resistance of the multimeter not making large changes in the current values, then its value should be equal to:

I = U / R, where I is the current in the circuit, amperes, U is the voltage supplied by the battery, and R is the load resistance (lamp).

The readings of the measuring device must be compared with this calculated value. If the readings differ, the battery may be undercharged.

You can also check the battery leakage current. If you disconnect the positive terminal, and install a multimeter between it and the positive terminal of the battery, it will show a leak into the vehicle's on-board network. Pulling out the fuses in a car, you can even find out what the leakage is in different parts of the on-board network. With some experience, it is realistic not only to learn how to measure amperes with a multimeter, but also to determine the causes of some auto electrical faults.

Measuring the current when charging the battery

Most car battery chargers have indicators that display charging parameters. But if they are faulty or missing, the charge current can be shown by a multimeter. When recharging the battery, you can include a measuring device in the charging circuit. To display correct readings, you need:

1. Install the red probe into the hole of the device marked with the inscription, A (NA), the black probe is usually connected to the input marked COM;
2. Select DC current measurement mode and signal level;
3. Connect in series the positive terminal of the charger with the black probe of the multimeter, the red probe of the meter connect to the positive terminal of the battery, and connect the negative terminal of the battery to the negative terminal of the charger devices;
4. Next, you need to turn on the charger to the network. The multimeter will display the current, which should not exceed 10% of the value of the battery capacity.

AC current measurement

Situations often arise when it is necessary to check the electrical network of a building. The same is the usual electrical network in apartment buildings. Knowing how to measure the current strength with a multimeter in a variable network, you can make minor repairs to the wiring at home.

The electrical outlet also cannot be tested without load.. The best load for a variable network would be an incandescent lamp. For measurements, you need to do the following:

1. Install the red probe into the socket of the device, marked with the inscription, A (NA), leave the black one in its proper place;
2. Select AC current measurement mode and signal level;
3. Connect the load in series with the measuring device to the socket;
4. The device displays the current value of the current, and the lamp starts to glow.

Since the voltage in the network has a variable sinusoidal form, the measuring device shows the effective value, which is 1.41 times less than the amplitude value.

According to the proposed technique, it is possible to check any variable of a circuit, including transformers, inductors, asynchronous and synchronous motors.

Determination of voltage magnitude

AC and DC voltage values can also be found with a multimeter. For this you need:

1. Connect the red wire with the measuring probe to the instrument input marked with the inscription V Ω mA, the black wire must be left in the socket marked COM;
2. Using the regulator of the measuring device, select the DC or AC voltage test mode (depending on the characteristics of the circuit);
3. If required, select the level of the signal to be checked;
4. Connect the probes to the circuit, parallel to the section where you want to measure the voltage;
5. The required value will be displayed on the multimeter screen.

The multimeter is an indispensable device for efficient work with electrical circuits and signals. With the help of such a device, you can quickly identify a malfunction, determine the required signal parameters, so it is important to always have it at hand.