Multimeter measures AC voltage and DC and AC and DC current

When measuring AC and DC, a multimeter should measure both the effective value, that is, the root mean square value.

How to use a multimeter to measure alternating current and direct current. Use
a digital multimeter to measure AC voltage: Connect the black test lead to - or ground (marked in the test lead jack), and connect the red pen to the AC (or add a ~ under the V letter) hole; the gear position points to AC~ The 750 (some are 1000) range in the column (if measuring 220V mains power). Then touch the two pens to the two holes of the power socket respectively, and the reading is the AC voltage value.

Use the pointer meter to measure the AC voltage: connect the black test lead to negative or ground, the red lead to +, set the gear to AC~500V, insert the two leads of the same digital multimeter to measure, the number pointed by the pointer should be read corresponding to the maximum range on the right: that is, the selected one It is the 500V level. When reading, look at the row with the largest number marked 50 on the right side of the reading plate. If the pointer points to 20, then the reading is 200V.

Measuring DC voltage with a digital multimeter: Same as measuring AC, except that the red pen is connected to the + hole and the red pen is also in contact with the + pole of the power supply. The gear is DC (or the one with a short horizontal line under the V letter). The measuring range depends on the specific situation, from Big to small. For example, if you are measuring an AA battery, choose the 2V range. If the polarity is reversed, there will be a negative polarity display before the reading.

Measuring DC voltage with an analog multimeter: The measurement method is the same as that of a digital multimeter. The reading is the same as for measuring AC voltage. When the positive and negative poles of the DC voltage cannot be determined, you can first measure it as AC, but you don’t care about the reading. Just reverse the polarity of the test leads. Conduct a sex test to see which pointer deflects in the two measurements, then the positive and negative polarities that the test leads are touching this time are correct. Then set the gear to the appropriate range of DC voltage and take the reading again.

Digital multimeters are very popular among radio enthusiasts because of their advantages such as accurate measurement, convenient value acquisition, and complete functions. The most common digital multimeter generally has resistance measurement, on-off sound detection, and diode forward voltage measurement. AC and DC voltage and current measurement, triode amplification and performance measurement, etc. Some digital multimeters have added functions such as capacitance measurement, frequency measurement, temperature measurement, data memory and voice reporting, which bring great convenience to actual detection work. However, due to improper use of digital square meters, components within the meter may be damaged and malfunction may occur during actual testing. Based on the actual situation that caused damage to the digital multimeter, I have summarized the precautions in the use of the digital square meter for the reference of beginners, so as to prevent the damage of the digital multimeter as much as possible.

In most cases, the damage to the digital multimeter is caused by the wrong measurement gear. For example, when measuring AC mains power, the measurement gear is placed in the electrical barrier. In this case, once the test leads contact the mains power, the internal components of the multimeter can be damaged in an instant. damage. Therefore, before using a multimeter to measure, be sure to check whether the measurement gear is correct. After use, set the measurement selection to AC 750V or DC 1000V, so that no matter what parameters are mismeasured during the next measurement, the digital multimeter will not be damaged.

Some digital multimeters are damaged because the measured voltage and current exceed the range. For example, when measuring mains power at the AC 20V range, it is easy to cause damage to the AC amplifier circuit of the digital multimeter, causing the multimeter to lose its AC measurement function. When measuring DC voltage, if the measured voltage exceeds the measurement range, it is also easy to cause circuit failure in the meter. When measuring current, if the actual current value exceeds the range, it will generally only cause the fuse in the multimeter to blow out and will not cause other damage. Therefore, when measuring voltage parameters, if you do not know the approximate range of the measured voltage, you should first set the measurement gear to the highest gear, measure the value and then change gears to obtain a more accurate value. If the voltage value to be measured is far beyond the maximum range that the multimeter can measure, an additional high-resistance measuring pen should be used. Such as detecting the second anode high voltage and focusing high voltage of black and white color TV sets.

The upper limit of the DC voltage range of most digital multimeters is 1000V. Therefore, when measuring DC voltage, the maximum voltage value is below 1000V, which generally does not damage the multimeter. If it exceeds 1000V, the multimeter is likely to be damaged. However, different digital multimeters may have different upper limits of measurable voltage. If the measured voltage exceeds the range, a resistance step-down method can be used to measure it. In addition, when measuring a DC high voltage of 40O to 1000V, the test leads must be in good contact with the measuring point without any jitter. Otherwise, in addition to causing damage to the multimeter and making the measurement inaccurate, in serious cases the multimeter may not have any show.

When measuring resistance, be careful not to measure while it is live.
Multimeter measures AC and DC current
1. Before measuring current, first determine the nature of the current (AC and DC) and the current size range.
2. Choose appropriate measurement tools (such as safety, accuracy and ease of use during on-site measurements) and measurement gears. After choosing the appropriate measuring tool, if you are not a professional technician but just a hobbyist, it is recommended to read the instructions for use.

3. General operating steps:
1) If it is a small electrical device (such as electronic equipment, etc.), you can read the description of the product's electrical power in the product manual. This part explains the current range that sometimes passes when the electrical device is working. Marked in the instructions. If the instruction manual only indicates the electrical power and voltage, the current can be calculated by the formula "A=W/V". When it is necessary to test the total current when multiple devices are working, add the currents of the individual devices to calculate the total current on the main line.

If actual measurement is required:
  (1) Select the appropriate gear (measure current, current value range)
  (2) Disconnect the line under test (but the electrical equipment and load cannot be disconnected, otherwise the line will be short-circuited!), and insert the multimeter into the lines (note that they are connected in series), at this time the resistance of the multimeter is almost zero, and the current flowing through the multimeter is equal to the current flowing through the electrical equipment and load.
    2) If it is a larger electrical equipment (working voltage is generally 220V to 380V), it is recommended to use a clamp ammeter (multimeter). The principle is that a closed electromagnetic field is formed on the energized line, and changes in the electromagnetic field cause the multimeter to generate current. This current has a proportional relationship with the measured line current, so the line current can be read directly in the ammeter.