The correct usage method and measurement requirements of pointer type multimeter
Select the measurement items and range switches on the multimeter based on the measured item. If the order of magnitude being measured is known, select the corresponding range of magnitude. If the order of magnitude of the measured value is unknown, it is necessary to start measuring from selecting the maximum range. When the pointer deviation angle is too small to accurately read, the range should be reduced again.
How to use a pointer multimeter?
(1) Before testing, first place the multimeter in a horizontal state and check if its needle is at zero (referring to the zero point of the current and voltage scales). If it is not, adjust the "mechanical zero adjustment" below the meter head to make the pointer point to zero.
(2) Select the correct measurement items and range switches on the multimeter based on the measured items. If the order of magnitude being measured is known, then select the corresponding range of magnitude. If the order of magnitude of the measured value is unknown, the measurement should start from selecting the maximum range. When the pointer deviation angle is too small to accurately read, the range should be reduced again. The reasonable range is generally based on a pointer deflection angle not less than 30% of the maximum scale.
The multimeter is used as a Ammeter:
① When connecting a multimeter in series in the circuit under test, attention should be paid to the direction of the current. Connect the red lead to the end where the current flows in and the black lead to the end where the current flows out. If you do not know the direction of the current being measured, you can first connect a probe at one end of the circuit, and gently touch the other probe at the other end of the circuit. If the pointer swings to the right, it indicates that the wiring is correct; If the pointer swings to the left (below zero), it indicates incorrect wiring. The positions of the two probes on the multimeter should be changed.
② When the pointer deflection angle is greater than or equal to 30% of the maximum scale, try to choose a large number of range gears. Because the larger the measuring range, the smaller the shunt resistance and the smaller the equivalent internal resistance of the Ammeter, the smaller the error introduced by the circuit under test.
③ When measuring a large current (such as 500mA), do not move the range selection switch during the measurement process to avoid arcing and burning the contacts of the transfer switch.
The multimeter is used as a Voltmeter:
① Connect a multimeter in parallel to the circuit under test. When measuring DC voltage, pay attention to the polarity of the voltage at the measured point, that is, connect the red lead to the high voltage end and the black lead to the low voltage end. If you do not know the polarity of the voltage being measured, you can try the same probing method as before when measuring current. If the pointer is deflected to the right, you can proceed with the measurement; If the pointer is deflected to the left, the red and black pen positions can be adjusted to measure.
② As with the above Ammeter, in order to reduce the error introduced by the internal resistance of the Voltmeter, when the pointer deflection angle is greater than or equal to 30% of the maximum scale, a large number of ranges shall be selected for measurement as far as possible. Because the larger the range, the greater the voltage divider resistance, the greater the equivalent internal resistance of the Voltmeter, and the smaller the error introduced to the circuit under test. If the internal resistance of the circuit to be measured is large, the internal resistance of the Voltmeter is required to be larger, so that the measurement accuracy is high. At this point, it is necessary to use a multimeter with higher voltage sensitivity (greater internal resistance) for measurement.
③ When measuring AC voltage, there is no need to consider polarity issues, as long as the multimeter is connected to both ends of the tested object in parallel. In addition, it is generally not necessary to choose a large range or select a multimeter with high voltage sensitivity. Because in general, the internal resistance of AC power is smaller than that of 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 working frequency of the multimeter, otherwise significant errors will occur.
④ Do not move the range selection switch when measuring a higher voltage (such as 220V) to avoid generating an arc and burning the contact of the transfer switch.
⑤ When measuring the high voltage greater than or equal to 100v, it is necessary to pay attention to safety. It is better to fix one stylus in the common part of the circuit under test first, and then use another stylus to touch the other end of the Test point.
⑥ In circuit systems, the level is commonly used to represent the effective value of the voltage at that point. Therefore, the multimeter has a level scale on the AC voltage range, and zero level refers to the power generated at a 600 ohm impedance of 1mW, which corresponds to a voltage effective value of 0.75V. If the impedance of the broken circuit is not equal to 600 ohms, the calculation should be carried out according to the following formula: actual electronic value=multimeter dB reading+101g (600/z). In the formula, z is the resistance value of the tested circuit. It is worth noting that the measurement should be placed on the 10V level, because the level scale of the multimeter is designed and calculated on that level. If the range is not enough, it needs to be changed to another level for measurement. The multimeter is only suitable for measuring volume and frequency levels, such as DC voltage on the circuit, It is also necessary to connect a 0.1uF/450V capacitor in series to isolate the DC before measuring it
⑦ When measuring the voltage in an inductive circuit, the multimeter must be disconnected before turning off the power after the measurement. Otherwise, when cutting off the power supply, due to the self inductance of the inductive reactance components in the circuit, high voltage may be generated and the multimeter may be burned out.
