How to use a multimeter to measure AC and DC power?
1. Measuring AC voltage with a digital multimeter: Connect the black lead to - or ground (indicated in the probe socket), and connect the red lead to AC (or add a~below the letter V); The gear refers to the range of 750 (some are 1000) in the AC~column (if it is 220V for measuring mains power). Then the two pens touch the two holes of the power socket respectively, and the reading is the AC voltage value.
2. Measuring AC voltage with a pointer meter: connect the black lead to negative or ground, connect the red lead to+, set the gear to AC~500V, insert two probes into the same digital multimeter for measurement, and the number indicated by the pointer should correspond to the maximum range on the right. When selecting the 500V gear, the reading should be based on the row marked with the maximum number of 50 on the right side of the reading plate. If the pointer points to 20, the reading should be 200V.
3. Measuring DC voltage with a digital multimeter: Measure AC simultaneously, with the red pen connected to the+hole and the red pen also in contact with the power supply+pole. The range is in the DC (or V letter with a short horizontal line) range, depending on the specific situation, from large to small. For example, if measuring a No. 5 battery, choose a 2V range. If the polarity is reversed, there will be a negative display before the reading.
4. Measuring DC voltage with a pointer multimeter: the same as measuring AC voltage with a digital multimeter; When the positive and negative poles of the DC voltage cannot be determined, it can be measured as AC power first, but it does not care about the reading. Instead, the polarity of the probe should be adjusted to see which of the two measurements the pointer needs to deflect. This time, the probe contacts the correct positive and negative polarity. Then set the gear to the appropriate range of DC voltage before measuring the reading.
Digital multimeter is highly popular among radio enthusiasts due to its advantages such as accurate measurement, convenient value taking, and complete functions. The most common digital multimeter generally includes resistance measurement, on/off sound detection, and diode forward conduction voltage measurement. AC and DC voltage and current measurement, transistor amplification factor and performance measurement, etc.
Some digital multimeters have added functions such as capacitance measurement, frequency measurement, temperature measurement, data memory, and voice counting, bringing great convenience to actual testing work.
However, due to improper use, digital multimeter can easily cause damage to the components inside the meter and cause malfunctions during actual testing.
Based on the actual situation that caused damage to the digital multimeter, summarize the precautions for using the digital multimeter to prevent damage as much as possible.
In most cases, damage to a digital multimeter is caused by incorrect measurement gear. For example, when measuring AC mains power, the measurement gear is set to the resistance gear. In this case, once the probe contacts the mains power, it can instantly cause damage to the internal components of the multimeter.
Therefore, before using a multimeter for measurement, it is necessary to check whether the measurement gear is correct.
After use, place the measurement selection at AC 750V or DC 1000V, so that no matter what parameter is mistakenly measured in the next measurement, it will not cause damage to the digital multimeter
Some digital multimeters are damaged due to the measured voltage and current exceeding the range. For example, measuring the mains power in the AC 20V gear can easily cause damage to the AC amplification 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 can also cause circuit faults in the meter. When measuring current, if the actual current value exceeds the range, it usually only causes the fuse in the multimeter to burn out and will not cause any other damage.
Therefore, when measuring voltage parameters, if the approximate range of the measured voltage is not known, the measurement gear should be set to the highest gear first, and the value should be measured before shifting to obtain a more accurate value.
If the voltage value to be measured far exceeds the maximum amount that a multimeter can measure
Cheng, a high resistance measuring probe should be provided separately. For example, detecting the second anode high voltage and focusing high voltage of black and white color televisions.
Most digital multimeters have a maximum DC voltage range of 1000V, so when measuring DC voltage, the highest voltage value is below 1000V, which generally does not damage the multimeter. If it exceeds 1000V, it is highly likely to cause damage to the multimeter.
However, the upper measurable voltage limit values of different digital multimeters may vary. If the measured voltage exceeds the range, resistance voltage reduction can be used for measurement.
In addition, when measuring high DC voltage between 40O and 1000V, the probe must be in good contact with the measuring point and there must be no shaking. Otherwise, in addition to causing damage to the multimeter and inaccurate measurement, it can also cause the multimeter to show no display in severe cases
When measuring resistance, be careful not to measure with electricity.
