The Ten Digital Multimeter Experiences
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" symbol 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 don't 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 large current (above 0.5 amps, the range should not be charged to change the range, otherwise, it is possible to cause the transfer switch contacts to ignite and burn candles.
4. Pay attention to the measured polarity when measuring DC voltage or DC current. If you don't 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 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 it is not due to the shunt effect of the multimeter, the reading value will be far lower than the actual value. At this time, the multimeter cannot be directly tested. Use other methods. The internal resistance of the voltage block 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 at the DC100 volt block is 5 kΩ, and the internal resistance of the block 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, you may wish to switch to a 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, a large range blocks the internal resistance and a small range blocks the internal resistance.
7. When measuring the resistance, every time you shift gears, you must
zeroing. The value of the geometric center of the multimeter resistance scale multiplied by the magnification of the electric block is the median resistance of the block, which is equal to the internal resistance of the multimeter at the block. Common central scale values are 8. 10. 12. 13. 16. 20. 24. 25. 30. 60. 75 and so on. 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 the Rx10 kohm gear Ro = 130 kohm, this gear is suitable for measuring 13 kohm-1. 3 megohm resistors.
8. When the multimeter measures resistance, the red test lead is connected to the negative pole of the battery in the meter, and the black test lead is connected to the positive pole of the battery in the meter. The purpose of doing this is to make the multimeter no matter when measuring voltage, current or resistance, the current will be uniformly entered by the red pen and exited by the black pen, and the needle can be deflected in the normal direction without reverse strike. Remember that the red test lead is connected to the negative pole of the battery, and the black test lead is connected to the positive pole. It is useful to check polarized components such as transistors, diodes, and electrolytic capacitors.
9. When checking a large-capacity capacitor with an electric barrier, the capacitor should be discharged first to prevent its residual voltage from damaging the multimeter. One end of the resistor should be disconnected when testing the resistance on the line to avoid the influence of other resistances on the line. It is forbidden to measure the resistance on the working circuit with electric barrier.
10. After the measurement is completed, the range switch should be turned to the highest voltage gear to prevent accidental burning of the meter in the next use. For those marked with "black dot" or "OFF", the switch should be turned to this position to short-circuit the measuring mechanism.
