Do you really know how to use a multimeter? Illustrations of how to use various functions of multimeter

Before introducing it in detail, let’s first talk about the common sense and reading conventions of general measurement.

Instruments are divided into pointer type (analog type), digital display type (digital), and wave type (graphic) to display measurement results.

Measure different categories of power parameters, use corresponding instruments, and select corresponding function gears. For example, if you use a ruler to measure length, you may need rulers of different types and accuracy for different things. The same goes for the measurement of electricity and parameters.

Some instruments may need to be preheated, debugged, zeroed, etc. before official use to bring them into normal working condition. Then estimate the size of the measured component parameters and electrical parameter values, and select the appropriate range to improve measurement accuracy. If you are not sure, generally use a large range test first to ensure the safety of the instrument.

The selection of the measuring range is generally more accurate when the pointer is at 1/3-2/3 of the full scale or the number is close to the gear value, and the graphics are fully displayed with graphic outlines and are as large and clear as possible.

During the measurement process, it is sometimes necessary to adjust knobs or switches such as the mode or level of display results, magnification and other functions to facilitate observation and result display. At this time, the hold key can lock the measurement results or store the data.

For readings of pointer instruments, refer to the selected function gear, range, and dial position indicated by the pointer.

The function block is used to determine the measurement category and unit, and the measuring range is used to determine the unit and reading. For the dial, you need to know which one to look at. Generally, look at the corresponding function or the most accurate one, and at the same time look at the pointer deflection position reading.

There are four reading relationships, namely addition, subtraction, multiplication and division.

Addition and subtraction are the most representative in level meters. If you select the +3db and +10db blocks or buttons, and the pointer points at +6db, the measurement result is +19db. If the pointer points at -5db, the measurement result is +8db.

The multiplication relationship is like the ohm block resistance reading. If the rx100 block is selected and the pointer points to the 20 position, multiply 20 by 100 to get 2kω. This resistance is 2kω. There is also the measurement of signal amplitude. For example, if the amplitude level is selected to be 1mv, the total number of grids from the peak to the valley point of the waveform is 5. Use 1x 5 to equal 5mv. The amplitude of this signal is 5mv.

In addition to the relationship between the voltage and current test gears of an analog multimeter, which range you choose represents the value of the full-scale range, and the deflection position of the pointer represents how many parts it occupies. For example, if the DC voltage range is 50v, and the pointer points at the 26 scale, it means that 50v is divided into 5 large parts, and each part is divided into 10 small parts, that is, the total is divided into 50 parts, accounting for 26 parts, and the measurement result is 26v.

For logarithmic display instruments, you can read directly, and the unit is determined by the selected range. Some automatic ranges will also display the unit.

Multimeter related knowledge

Multimeters can be divided into two categories: pointer type and digital type based on the measurement principle and result display method. The main differences between the two are as follows.

Digital multimeters have higher measurement, reading accuracy and sensitivity than analog multimeters, and have larger internal resistance. When measuring voltage, digital multimeters are closer to ideal measurement conditions. At the same time, digital multimeters have more measurement functions, such as measuring capacity, temperature, frequency, etc.

When a digital multimeter measures a dynamic process, the numbers jump and cannot reflect the dynamic change process well. The pointer multimeter can well reflect the continuous change process and change trend of the quantity, and observe the dynamic process more intuitively.

When measuring DC voltage or current, if the polarity of the test leads of the analog multimeter is reversed, the pointer will deflect in the opposite direction, while the digital multimeter can automatically identify and display the polarity. If it is a negative number, there will be "—" before the negative number. number is displayed.

When the analog multimeter is used to measure voltage and current beyond the range, the pointer will deflect to the right to the extreme position, which can easily damage the meter head or reduce the accuracy. The digital multimeter displays 1, indicating that it is out of range, and the same is true when measuring resistance.

Analog multimeters are prone to human errors based on the pointer and dial readings, while digital ones eliminate human errors. However, digital multimeters are susceptible to interference, and digital jumps cause trouble in determining digital values. Generally, the middle value is used , in some cases the minimum or maximum value should be taken.

Next is the difference shown in Table 1. This is especially important for beginners and must be paid attention to.

Table 1 The relationship between the positive and negative poles of the test leads and the battery in the connected meter

In view of the advantages of analogue multimeters and digital multimeters, it is recommended to use both types of meters together. Generally speaking, digital multimeters are much easier to use and have more complete functions, so they should be the first choice.

Tips for selecting an analog multimeter:

When the multimeter is placed horizontally, vertically or flatly, the closer the pointer is to the zero position, the higher the accuracy of the multimeter. Then conduct some resistance and voltage measurements to see if the function settings are good and how accurate they are. If necessary, you should also take a look at the usage. manual.

When measuring various parameters, the black test pen is connected to the com public socket, and the red test pen is plugged into the corresponding jack according to the measurement of different items, as shown in Figure 1. Different models of multimeters have different socket layouts and insertion methods.

Figure 1 Multimeter function socket

The multimeter function labels are identified as follows.

v and acv represent the AC voltage block; a and dca represent the DC current block; hz frequency block; ω and ohm represent the electrical barrier; hfe represents the block; f is the capacitance measurement block.

Precautions for using multimeter

(1) First of all, pay attention to personal safety. Do not expose metal wires when connecting test leads. When measuring voltage and current online, you must develop the habit of one-handed operation. Hold the test lead with one hand like a chopstick. In order to facilitate the measurement of DC voltage, you can also fix the black test lead at the ground wire position (such as inserting it into the ground wire spring at the graphite layer of the TV picture tube, or into some heat sink holes connected to the ground wire, and clamp it on the ground wire with an alligator clip) also).

During the voltage measurement process, do not let your hands touch the metal parts of the test leads, circuit solder joints, and metal parts of components to prevent electric shock.

(2) The analog multimeter must be zeroed before use, that is, let the pointer point at the zero scale.

Use the potentiometer to zero the ohmic block: short-circuit the two test leads and adjust the zero-setting potentiometer so that the pointer is at zero on the right. Note that every time you change the electrical blocking range, you need to perform a zero adjustment.

Zero adjustment of the voltage and current gear: adjust the spring on the meter head, which is the central "1" screwdriver adjustment point, so that the pointer is at the zero mark on the left.

(3) During the process of measuring voltage or current, if the two test leads are still on the road, the gear and range cannot be changed, especially in the case of high voltage and large current. Otherwise, the multimeter will be damaged, and in some cases, circuit components will be damaged.

(4) Do not use electricity to block measurements when the circuit board is powered on (or when the large capacitor is still powered), otherwise the multimeter may be easily damaged.

(5) The current block of the pointer multimeter cannot measure voltage and resistance when power is on, otherwise the high current will damage the meter head. Do not turn the wrong gear when measuring current and voltage. If you mistakenly block electricity or current to measure voltage, it is easy to burn out the multimeter.

(6) If it is found that the digital multimeter has a battery symbol display, the pointer multimeter is difficult to zero when measuring resistance, and the measurement accuracy decreases, etc., it indicates that the built-in battery of the multimeter is insufficient and needs to be replaced. If it is not used for a long time, take out the battery. At the same time, for the analog multimeter, the gear should be set to the off position or the maximum AC voltage range to prevent damage to the multimeter due to misoperation the next time it is used.

(7) When measuring electrical resistance, do not touch the component pins and the metal parts of the test leads with your hands. Especially when the component resistance is large, the parallel connection of the human body resistance will reduce the resistance value, thus affecting the measurement accuracy. .

(8) Another point is to make a habit of regularly checking whether your instruments and tools are safe and reliable, and whether the measurement function and accuracy are normal. Otherwise, it will cause trouble and misjudgment the next time you use it. This leads to the generation of undesirable results, thus putting maintenance and inspection into trouble.