Multimeter used as a voltmeter
①Connect the multimeter to the circuit under test. When measuring the DC voltage, pay attention to the polarity of the voltage at the point under test, that is, connect the red test lead to the high voltage end and the black test lead to the low voltage end. If you don’t know the polarity of the voltage to be measured, you can try it according to the above-mentioned tentative method when measuring the current. If the pointer deflects to the right, you can measure it; if the pointer deflects to the left, exchange the positions of the red and black test leads. Measurement.
②Same as the above-mentioned ammeter, in order to reduce the error introduced by the internal resistance of the voltmeter, when the deflection angle of the pointer is greater than or equal to 30% of the maximum scale, try to select a large range for measurement. Because the larger the measuring range, the larger the voltage dividing resistance, and the larger the equivalent internal resistance of the voltmeter, the smaller the error introduced to the circuit under test. If the internal resistance of the circuit under test is large, the internal resistance of the voltmeter is required to be larger to make the measurement accuracy high. At this time, it is necessary to use a multimeter with higher voltage sensitivity (larger internal resistance) for measurement. For example, the maximum DC voltage sensitivity (100 kΩ/V) of the MFl0 multimeter is higher than that of the ME30 type multimeter (20 kΩ/V).
③ When measuring the AC voltage, it is not necessary to consider the polarity problem, as long as the multimeter is connected to both ends of the test. In addition, it is generally not necessary to choose a multimeter with a large range or a high voltage sensitivity. Because under normal circumstances, the internal resistance of the AC power supply is smaller than that of the glue. It is worth noting that the measured AC voltage can only be a sine wave, and its frequency should be less than or equal to the allowable operating frequency of the multimeter, otherwise a large error will occur.
④ Do not toggle the range selection switch when measuring a higher voltage (such as 220v), so as not to generate arcs and burn out the contacts of the transfer switch.
⑤ Pay attention to safety when measuring high voltage greater than or equal to 100v. It is best to fix one test lead on the common ground of the circuit under test, and then use another test lead to touch the other test point.
⑥The level is commonly used in the circuit system to represent the effective value of the voltage at this point. Therefore, the multimeter has a level scale on the AC voltage range. Zero level refers to the power of 1mW generated on the 600 ohm impedance, that is, the corresponding effective voltage value is 0.75V. If the impedance of the circuit under test is not equal to 600 ohms, calculate according to the following formula: actual electronic value = multimeter dB reading + 101g (600/z) where z is the resistance value of the circuit under test. It is worth pointing out that when measuring the level, it should be placed on the 10v file, because the level scale of the multimeter is designed and calculated on this file. If the range is not enough, you need to change to another file to measure. In addition, the multimeter is only suitable for measuring the volume and frequency levels, such as circuit There is a DC voltage on it, and a 0.1uF/450V capacitor must be connected in series to cut off the DC before measuring
⑦ When measuring the voltage in a circuit with inductive reactance, the multimeter must be disconnected and then turned off after the measurement. Otherwise, when the power is cut off, due to the self-inductance of the inductive components in the circuit, high voltage will be generated and the multimeter may be burned out.
