From this guide, users will learn how to use a digital multimeter, an indispensable tool that can be used to diagnose circuits, study electronic designs, and test batteries. Hence the name multi - meter.
The main parameters to be checked on this device are voltage and current. The multimeter is also great for some basic health checks and troubleshooting. It is often used in the repair of equipment. The notation on the multimeter allows you to understand how much the voltage or current in a particular section of the circuit differs from the original value.
What equipment consists of
Before you start using the technique, you need to find out what parts it consists of. Designations on the multimeter can be obtained by measuring a specific area. Without knowledge of the necessary terminals and contacts, the work cannot be completed.
The multimeter consists of three parts:
- Display.
- Selection knob.
- Ports
The display usually has four digits, as well as the ability to display a negative sign. Some device models have backlit displays for better viewing in low light conditions.
The selection knob allows the user to set the mode and read various indicators, such as milliamps (mA) of current, voltage (V) and resistance (Ohms).
Two sensors are connected to two ports on the front of the device. COM stands for common connection and is almost always connected to ground or the “-” circuit. The COM probe is usually black, but there is no difference between the red and black connections except for color. The designation on the multimeter through each of these conductors will be the same.
10A is a special port used to measure high currents (over 200 mA). mAVΩ is the port to which the red probe is usually connected. It allows you to measure current (up to 200 mA), voltage (V) and resistance (Ω). At the end of the probe there is a connector that connects to the multimeter.
Voltage measurement
Now, having understood the device of the multimeter, we can proceed to the simplest measurements. First you should try to measure the voltage on the AA battery. The designation on the multimeter will indicate the level of the passing current in a particular area.
To do this, the following actions are performed:
- Connect the black probe to COM and the red probe to mAVΩ.
- Set the multimeter to “2 V” in the DC range. Almost all portable electronics use direct current rather than alternating current.
- Connect the black probe to the battery ground or “-”, and the red probe to power or “+”.
- Squeeze the probes by slightly pressing on the positive and negative terminals of the AA-type battery.
If a new battery is used, users should see about 1.5 V on the display. AC voltage (such as wiring from walls) can be dangerous, so you rarely need to use the AC voltage setting (V with a wavy line next to it). It is important to comply with each parameter of the initial value. To answer the question of how to use the multimeter, a detailed instruction for beginners to measure the voltage at different contacts will be presented below.
Measuring the voltage taken from the power supply
To do this, set the knob to “20 V” in the DC range (it is designated as V with a straight line next to it).
Multimeters usually do not have automatic range selection. Therefore, users should set the multimeter to the range that it can measure. For example, 2V measures voltage up to 2 volts, and 20V measures voltage up to 20 volts. If the battery is 12 V, the setting is applied to 20 V. If the parameter is set incorrectly, changing the counter screen will not change at first, and then the indicator will be equal to 1. It should be noted when answering the question: How to use the multimeter ", detailed instructions for beginners may contain different measurement rules. It all depends on the type of digital or analog device. There are advanced models that have additional functions related to tracking current on microcontrollers.
Other measurements
Using this device, you can check various parts of the circuit. This practice is called nodal analysis and is the main method in circuit analysis. Measuring the voltage in the circuit, you need to track what indicator is needed for each section. The whole circuit is checked first. When measuring where the voltage is supplied to the resistor, and then to the ground, on the LED, the user should see the full voltage of the circuit, which should be about 5 V. The AC designation on the multimeter in this case will not work. To do this, you will need to switch to another mode described above.
Measurement overload
The resistance designation may not be displayed on the multimeter. This may be due to problems. What can happen, choose a voltage setting too low, which needs to be measured an interesting question. Nothing bad will happen. The meter simply displays the number 1. So the device indicates that it is overloaded or is out of range. To change the readout, change the multimeter knob to the next maximum setting.
Selection knob
Why the indicator knob shows 20 V, and not 10, is a question that users often ask. If you need to measure a voltage of less than 20 V, you need to switch to a setting of 20 V. This will allow you to read the indicator from 2.00 to 19.99. The first digit on many multimeters can only display “1”, so the ranges are limited to 1.99 instead of 9 9.99. Therefore, the maximum range is 20 V instead of the maximum range of 99 V. The capacitance designation on the multimeter in this case will be inaccurate. However, such errors are negligible.
It is necessary to adhere to direct current circuits (settings on the multimeter with straight lines, not curved lines). Most devices can measure AC systems, but they can be dangerous. If you need to check if the outlet is turned on, use an AC tester.
Resistance measurement
The designation of microamps on the multimeter makes it possible to check the resistance in different electrical areas. This is especially convenient when testing chips.
Normal resistors have color codes located on them. It is impossible to know all the possible combinations and their definitions. There are many online calculators that are easy to use. However, if the user ever finds himself without access to the Internet, a multimeter will help to measure the desired parameter.
To do this, select a random resistor and set the multimeter to 20 kOhm. Then press the probes to the legs of the resistor with the same pressure as when you press a key on the keyboard. The meter will read one of three values - 0.00, 1 or the actual value of the resistor. The symbols on the multimeter panel can be switched in several modes.
In this case, the counter reading is 0.97, which means that the value of this resistor is 970 ohms, or about 1 kΩ. It should be remembered that the meter is in 20 kOhm or 20,000 Ohm mode, so you need to move three decimal places to the right, which will be 970 Ohms.
Measurement Highlights
Many resistors have a tolerance of 5%. This means that color codes can indicate 10 thousand ohms (10 kOhm), but due to differences in the manufacturing process, a 10 kOhm resistor can be as little as 9.5 kOhm or 10.5 kOhm. In the instructions, the description of the multimeter indicates that measurements can only be taken in strictly established ranges.
However, when measuring below the established norm, nothing will change. Since the resistor (1 kΩ) is less than 2 kΩ, it is still shown on the display. Nevertheless, it will be possible to notice that there is another digit after the decimal point, which gives a refinement in calculating the final value.
Typically, a resistor of less than 1 ohm is rare. It should be understood that resistance measurement is not ideal. Temperature can greatly affect reading. In addition, measuring the resistance of a device when it is physically installed in a circuit can be very difficult. The surrounding components on the board can greatly affect the readings. As a result, ohms on the multimeter may not display correctly.
Current measurement
Reading current is one of the most complex measurements in the world of embedded electronics. This is difficult because it is necessary to control the current in several areas at once. Measurement works the same as voltage and resistance - the user must get the correct range. To do this, set the multimeter to 200 mA and work on this value. Current consumption for many circuits is usually less than 200 mA. Make sure that the red probe is connected to the 200 mA fuse port. On a multimeter, a 200 mA hole is the same hole / port as for measuring voltage and resistance (the output is designated as mAVΩ).
This means that you can hold the red probe in the same port to measure current, voltage or resistance. However, if the circuit uses a voltage close to 200 mA or more, it is better to switch the sensor to the 10 A side to be safe. Overcurrent can cause a fuse to blow, and not just show an overload.
What you need to remember when measuring
The multimeter acts like a piece of wire - when the circuit is closed, the circuit turns on. This is important because over time, an LED, microcontroller, sensor or any other measured device can change its energy consumption. For example, turning on the LED may cause a 20 mA increase in one second, and then decrease in a second when it turns “off”.
The multimeter should display the instantaneous current value. All multimeters take readings over time, and then give an average value, so you should expect that the readings will fluctuate. In general, cheaper meters will be averaged more sharply and will respond more slowly.
Continuity check
A continuity test is a test of resistance between two points. If the resistance is very low (less than a few ohms), the two points are connected electrically and a sound signal is emitted. If the resistance exceeds a few ohms, the circuit is open and no sound is produced. This test helps ensure that the connections between the two points are correct. The test also helps determine if two points that should not be connected are connected. In this case, the volts on the multimeter will be displayed in a strictly set value, without errors.
Continuity is perhaps the most important function for craftsmen involved in the repair and testing of electronic equipment. This feature allows you to check the conductivity of materials and track whether electrical connections have been made.
To measure this parameter, you need to perform the following steps:
- Setting the multimeter in the "Continuity" mode. The switch may be different among digital meters. You should look for the symbol of the diode with the propagating waves around it (for example, the sound coming from the speaker).
- Next, you need to touch the probes together. The multimeter should emit a tone (Note: not all multimeters have a continuity setting, but most should). This shows that a very small amount of current can flow without resistance (or at least a very small resistance) between the sensors.
- It is important to shut down the system before checking for continuity.
Continuity is a great way to check if two SMD contacts are in contact. If they are not clearly distinguishable, a multimeter is usually an excellent resource for testing. When the system is down, continuity is another thing that helps troubleshoot power outages.
Here are the steps to take:
- If the system is turned on, carefully check the VCC and GND with voltage settings to make sure that the voltage is at the correct level.
- If the 5 V system is operating at 4.2 V, carefully check the regulator, it may be very hot, indicating that the system is consuming too much current.
- Turn off the system and check for continuity between VCC and GND. If a beep is heard, then somewhere there is a short circuit.
- Turn off the system. Continuously verify that VCC and GND are properly connected to the pins of the microcontroller and other devices. The system may turn on, but individual chips may not be connected correctly.
Capacitors will change indicators until they are filled with energy, and then will act as an open connection. Therefore, a short beep will appear, and then when re-measuring it will not.
Fuse replacement
One of the most common errors of the new multimeter is measuring the current on the breadboard by examining from VCC to GND. This will immediately lead to a short to ground through the multimeter, which will result in loss of power to the power supply. When current flows through the multimeter, the internal fuse heats up and then blows when 200 mA flows through it. This will happen in a split second and without any real sound or physical signs that something is wrong.
If the user tries to measure the current using a blown fuse, he will probably notice that the counter shows “0.00” and that the system does not turn on, as when connecting a multimeter. This is because the internal fuse is broken and acts like a broken wire or an open at the connection.
To replace the fuse, you need to unscrew the bolts with a mini screwdriver. A digital multimeter is pretty easy to make out.
After removing the bolts, the following actions are performed:
- The battery plate is removed.
- Two screws that are hidden behind the battery plate are removed.
- The front panel of the multimeter is slightly lifted.
- Now it is worth paying attention to the hooks on the lower edge of the front of the panel. It will be necessary to slightly move the case to the side to unhook these hooks.
- As soon as the front part is detached, it should be easily removable.
- Further, the fuse is carefully lifted, after which it must independently pop out of the socket.
Be sure to replace the correct fuse with the correct type. If you select a device of a different type of voltage, the multimeter will stop functioning. The components and traces of the printed circuit board inside the device are designed to accept various current values. Therefore, when disassembling and assembling the housing, it is important not to damage the spraying and contacts.
Conclusion
When using a multimeter, it is important to correctly set the desired mode. A common mistake of many users is that they incorrectly set the necessary values and measure high voltage sources. This can lead not only to complete failure of the equipment, but also to injuries of the person measuring it. It is best to use a multimeter to measure the value on microcontrollers and digital boards.