Ten Key Operational Experiences for Professional Multimeter Application
1. Before use, it is necessary to check whether the function conversion switch is in the corresponding position of the measured power and whether the probe is in the corresponding socket
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, adjust the mechanical zero position first
3. Choose the appropriate range based on the size of the measured electricity When measuring voltage and current, try to deflect the pointer to more than 1/2 of full scale, which can reduce testing errors If you don't know the size being measured, you can first measure with the maximum range and gradually reduce the range until the pointer has a significant deviation But when testing high voltage (above 100 volts) or high current (above 0.5 amps), the range should not be changed with electricity, otherwise it may cause the switch contacts to ignite and burn
4. When measuring DC voltage or DC current, pay attention to the polarity of the measured object If you don't know the voltage level of the two points being measured, you can briefly touch these two points with the two probes, determine the potential level based on the direction of the pointer impact, and then measure again
5. When measuring AC voltage, it is necessary to understand whether the frequency of the AC voltage is within the working frequency range of the multimeter. Generally, the working frequency range of the multimeter is 45-1500Hz. If it exceeds 1500Hz, the measured reading will sharply decrease The AC voltage scale is based on the effective value of sine waves, so a multimeter cannot be used to measure non sine wave voltages such as triangular waves, square waves, sawtooth waves, etc When there is a DC voltage superimposed on the AC voltage, a DC isolation with sufficient withstand voltage should be connected in series before 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, due to the shunt effect of the multimeter, the reading value will be much lower than the actual value. In this case, the multimeter cannot be directly used for testing, and other methods should be used instead The internal resistance in the voltage range of a multimeter is equal to the voltage sensitivity multiplied by the full voltage value. The MF-30 multimeter has a voltage sensitivity of 5 kiloohms in the DC100V range, and the internal resistance in this range is 500 kiloohms Generally speaking, the internal resistance is small in the low range range range and large in the high range range range. When testing a certain voltage in the low range range, if the internal resistance is small and the shunt effect is large, it is advisable to switch to the high range test. This way, although the pointer deflection angle is small, the accuracy may be higher due to the small shunt effect There is a similar situation when measuring current. When a multimeter is used as an ammeter, the internal resistance of the large range is smaller than that of the small range
7. When measuring resistance, it is necessary to zero every gear shift The value of the geometric center of the resistance scale of a multimeter multiplied by the ratio of the resistance range is the median resistance of that range, which is equal to the internal resistance of the multimeter in that range Common center scale values include 8, 10, 12, 13, 16, 20, 24, 25, 30, 60, 75, and more The resistance scale is non-linear, so when using it, choose the appropriate gear to make the pointer point as close to the center as possible. Usually, the reading is accurate within the range of 0.1Ro-10Ro (Ro median resistance), and there is a large error outside of this range For example, the center scale value of the MF10 multimeter is 13. When Ro=130 kiloohms in the Rx 10 kiloohm range, this range is suitable for measuring resistance between 13 kiloohms and 1.3 megaohms
8. When measuring resistance with a multimeter, the red probe is connected to the negative terminal of the battery inside the meter, and the black probe is connected to the positive terminal of the battery inside the meter The purpose of doing this is to ensure that the multimeter can measure voltage, current, or resistance uniformly with the red probe in and the black probe out, and the probe can deflect in the normal direction without reversing Remember to connect the red probe to the negative terminal of the battery and the black probe to the positive terminal For checking polarized components such as crystals, electrolysis is useful
9. When checking large capacity capacitors with resistance settings, the capacitors should be discharged first to prevent residual voltage from damaging the multimeter One end of the resistor on the test circuit should be disconnected to avoid the influence of other resistors on the circuit It is prohibited to measure the resistance of a working circuit using resistance settings
10. After the measurement is completed, the range switch should be turned to the high voltage level to prevent accidental burning of the meter during the next use If there is a "black dot" or "OFF" mark, the switch should be turned to this position to short-circuit the measuring mechanism
