Tips for using a multimeter_Using skills of a multimeter
1. Before use, you must see clearly whether the function switch is in the position corresponding to the measured power, and whether the test leads are in the corresponding sockets.
2. According to the requirements of the "ground" or ""arrow"" symbols on the meter head, place the multimeter vertically or horizontally. If the pointer does not point to the starting point of the scale, the mechanical zero position should be adjusted first.
3. Select the appropriate range according to the measured electric quantity. When measuring voltage and current, try to make the pointer deflect to more than 1/2 of the full scale, which can reduce the test error. If you do not know the size to be measured, you can first measure with the maximum range and then gradually reduce the range until the pointer has a large deflection. However, when testing high voltage (above 100 volts) or high current (above 0.5 amps), the range should not be changed with electricity, otherwise, the transfer switch contacts may be ignited and ablated.
4. Pay attention to the measured polarity when measuring DC voltage or DC current. If you do not know the voltage level of the two points to be measured, you can test the two test leads for a short time, judge the potential level according to the direction of the pointer impact, and then measure.
5. When measuring AC voltage, it is necessary to know whether the AC voltage frequency is within the working frequency range of the multimeter. Generally, the working frequency range of the multimeter is 45-1500Hz. Exceeding 1500Hz, the measurement reading will be sharply lower. The AC voltage scale is calibrated against the effective value of the sine wave, so the multimeter cannot be used to measure non-sine wave voltages such as triangle waves, square wave sawtooth waves, etc. When the DC voltage is superimposed on the AC voltage, a DC blocking capacitor with sufficient withstand voltage should be connected in series for measurement.
6. When measuring the voltage on a certain load, it is necessary to consider whether the internal resistance of the multimeter is much greater than the load resistance. If not, the reading value will be far lower than the actual value due to the shunt effect of the multimeter. At this time, the multimeter cannot be used to test directly. Use another method instead. The internal resistance of the voltage range of the multimeter is equal to the voltage sensitivity multiplied by the full-scale voltage value. For example, the voltage sensitivity of the MF-30 multimeter in the DC100 volt range is 5 kΩ, and the internal resistance of this range is 500 kΩ. Generally speaking, the internal resistance of the low-range range is small, and the internal resistance of the high-range range is large. When using a low-voltage range to test a certain voltage due to the small internal resistance and the shunt effect is large, it is advisable to switch to the high-range test. In this way, although the pointer deflects The angle is smaller, but due to the small shunt effect, it may be more accurate. There is a similar situation in measuring current. When the multimeter is used as an ammeter, the internal resistance of the large range is smaller than the internal resistance of the small range.
7. When measuring resistance, it must be zeroed every time when shifting gears. The value of the geometric center of the resistance scale of the multimeter multiplied by the multiplier of the resistance file is the median resistance of the file, which is equal to the internal resistance of the multimeter in the file. Common center scale values are 8. 10. 12. 13. 16. 20. 24. 25. 30. 60. 75 etc. The resistance scale is non-linear. When using it, select the appropriate gear so that the pointer points as close to the center as possible. Usually, the reading is accurate within the range of 0.1Ro-10Ro (Ro-----median resistance), and outside this range The error is large. For example, the center scale value of MF10 multimeter is 13, when Rx10 kohm gear Ro=130 kohm, this gear is suitable for measuring the resistance of 13 kohm-1.3 megohm.
