The “multimeter†is the abbreviation of the universal meter, which is an indispensable tool in our electronic production. The multimeter can measure current, voltage, resistance, and some can also measure the amplification of the triode, frequency, capacitance value, logic potential, decibel value and so on. There are many types of multimeters, and the most popular ones are mechanical pointers and digital multimeters (see figure). They all have their own advantages. For electronic beginners, it is recommended to use a pointer multimeter because it is very helpful for us to familiarize ourselves with some principles of electronic knowledge. Below we introduce the principle and use of some mechanical pointer multimeters.
The basic principle of the multimeter
The basic principle of the multimeter is to use a sensitive magneto-electric DC ammeter (micro-ampere meter) as the head. When a small current passes through the meter, there is a current indication. However, the meter head cannot pass a large current, so it is necessary to shunt or step down some resistors in series with the series head to measure the current, voltage and resistance in the circuit. Introduced separately below.
·Measure DC current principle
As shown in Figure 1a, the current range can be extended by shunting an appropriate resistor (called a shunt resistor) on the meter head for shunting. Changing the resistance of the shunt resistor changes the current measurement range.
·Measure DC voltage principle
The voltage range can be extended by stepping down a suitable resistor (called a multiplier) in the header to step down. Changing the resistance of the multiplying resistor changes the measurement range of the voltage. ·Measure the principle of AC voltage
Because the meter head is a DC meter, when measuring AC, a parallel and half-wave rectifier circuit is required to rectify the AC into DC and then pass through the meter head, so that the AC voltage can be measured according to the magnitude of the DC power. The method of expanding the AC voltage range is similar to the DC voltage range.
·Measure the resistance principle
As shown in Figure 1d, a suitable resistor is connected in parallel and in series on the meter head, and a battery is connected in series to pass current through the resistor under test. The resistance value can be measured according to the magnitude of the current. Changing the resistance of the shunt resistor changes the range of the resistor.
Use of the multimeter
The dial of the multimeter (for example, the 105 type). The measurement items and measurement ranges are changed by the knob of the changeover switch. The mechanical zero knob is used to keep the pointer at the left zero position at rest. The “Ω†zero adjustment knob is used to measure the resistance so that the pointer is aligned to the right zero position to ensure accurate measurement values.
The measuring range of the multimeter is as follows:
· DC voltage: 5 files - 0-6V; 0-30V; 0-150V; 0-300V; 0-600V.
·AC voltage: 5 files - 0-6V; 0-30V; 0-150V; 0-300V; 0-600V
· DC current: divided into 3 files - 0-3mA; 0-30mA; 0-300mA.
·Resistance: 5 files - R * 1; R * 10; R * 100; R * 1K; R * 10K Measuring resistance: - first short the table rod together, so that the pointer is turned to the right, then adjust “Ω†zero knob, so that the pointer just points to 0. Then, the two rods are respectively contacted with the two ends of the measured resistance (or circuit), and the reading of the pointer on the ohmic scale line (the first line) is read, and then the number of the index is multiplied, which is the resistance value of the measured resistance. . For example, the resistance is measured by R*100, and the pointer is at 80, and the measured resistance is 80*100=8K. Since the left side of the “Ω†tick is densely read and difficult to see, the appropriate ohms should be selected for the measurement. Make the pointer in the middle or right of the tick mark so that the readings are clear and accurate. Each time you change gears, you should short-circuit the two bars and re-adjust the pointer to zero to measure. Measure DC voltage:--First estimate the magnitude of the voltage to be measured, then turn the transfer switch to the appropriate V range, connect the positive bar to the "+" terminal of the measured voltage, and the negative bar to the measured voltage "-" terminal. . Then, according to the number of the range and the number indicated by the pointer on the standard DC symbol "DC-" scale line (second line), the magnitude of the measured voltage is read. If you measure with V300 volts, you can directly read the indication value of 0-300. If you use V30 volts measurement, you only need to remove a "0" from the digit on the scale line 300, which is regarded as 30, and then treat the numbers such as 200 and 100 as 20, 10 and directly read the pointer indication value. For example, the V6 voltage is used to measure the DC voltage, and the pointer is at 15, the measured voltage is 1.5 volts. Measure DC current: -- Estimate the current to be measured first, then turn the transfer switch to the appropriate mA range, and then connect the multimeter in series. At the same time, observe the tick mark marked with the DC symbol "DC". If the current range is selected in the 3 mA range, then the number on the surface tick mark 300 should be removed from the two "0"s, which is regarded as 3, and then 200. 100 is regarded as 2, 1, so that the measured current value can be read. For example, the DC current is measured with a DC 3 mA range, and the pointer is at 100, and the current is 1 mA. Measuring AC voltage: The method of measuring AC voltage is similar to measuring DC voltage. The difference is that there is no positive or negative difference in AC power. Therefore, when measuring AC, the meter bar does not need to be positive or negative. The reading method is the same as the above-mentioned reading of the measured DC voltage, except that the number should be the position of the pointer on the scale line marked with the AC symbol "AC".
Considerations for using a multimeter
The multimeter is a relatively sophisticated instrument. If it is used improperly, it will not only cause inaccurate measurement but also be easily damaged. However, as long as we master the use of the multimeter and precautions, and be cautious, the multimeter can be durable. The following should be noted when using a multimeter:
· Measurement of current and voltage cannot be misaligned. If the resistance or current is mistakenly measured, the meter will be easily burned out. When the multimeter is not in use, it is best to rotate the gear to the highest level of the AC voltage to avoid damage due to improper use.
· When measuring DC voltage and DC current, pay attention to the "+" and "-" polarity. Do not connect the wrong ones. If you find that the pointer is open and reversed, you should immediately change the watch bar to avoid damaging the pointer and the meter.
· If you do not know the magnitude of the voltage or current to be measured, you should first use the highest grade, and then select the appropriate gear to test, so as to avoid excessive deflection of the hands and damage the meter. The closer the selected gear is to the measured value, the more accurate the measured value will be.
• When measuring resistance, do not touch the bare ends of the components (or the metal parts of the two bars) with your hands to prevent the human body resistance from being connected in parallel with the measured resistance, making the measurement results inaccurate.
· When measuring resistance, if the two sticks are shorted, adjust the “zero ohm†knob to the maximum, the pointer still can't reach 0. This phenomenon is usually caused by insufficient battery voltage in the watch. It should be replaced with new battery. Only accurate measurement can be made.
·When the multimeter is not in use, do not screw it in the resistance file, because there is a battery inside. If you accidentally make the two watch rods touch and short circuit, it will not only consume the battery, but even damage the meter when it is serious.
The basic principle of the multimeter
The basic principle of the multimeter is to use a sensitive magneto-electric DC ammeter (micro-ampere meter) as the head. When a small current passes through the meter, there is a current indication. However, the meter head cannot pass a large current, so it is necessary to shunt or step down some resistors in series with the series head to measure the current, voltage and resistance in the circuit. Introduced separately below.
·Measure DC current principle
As shown in Figure 1a, the current range can be extended by shunting an appropriate resistor (called a shunt resistor) on the meter head for shunting. Changing the resistance of the shunt resistor changes the current measurement range.
·Measure DC voltage principle
The voltage range can be extended by stepping down a suitable resistor (called a multiplier) in the header to step down. Changing the resistance of the multiplying resistor changes the measurement range of the voltage. ·Measure the principle of AC voltage
Because the meter head is a DC meter, when measuring AC, a parallel and half-wave rectifier circuit is required to rectify the AC into DC and then pass through the meter head, so that the AC voltage can be measured according to the magnitude of the DC power. The method of expanding the AC voltage range is similar to the DC voltage range.
·Measure the resistance principle
As shown in Figure 1d, a suitable resistor is connected in parallel and in series on the meter head, and a battery is connected in series to pass current through the resistor under test. The resistance value can be measured according to the magnitude of the current. Changing the resistance of the shunt resistor changes the range of the resistor.
Use of the multimeter
The dial of the multimeter (for example, the 105 type). The measurement items and measurement ranges are changed by the knob of the changeover switch. The mechanical zero knob is used to keep the pointer at the left zero position at rest. The “Ω†zero adjustment knob is used to measure the resistance so that the pointer is aligned to the right zero position to ensure accurate measurement values.
The measuring range of the multimeter is as follows:
· DC voltage: 5 files - 0-6V; 0-30V; 0-150V; 0-300V; 0-600V.
·AC voltage: 5 files - 0-6V; 0-30V; 0-150V; 0-300V; 0-600V
· DC current: divided into 3 files - 0-3mA; 0-30mA; 0-300mA.
·Resistance: 5 files - R * 1; R * 10; R * 100; R * 1K; R * 10K Measuring resistance: - first short the table rod together, so that the pointer is turned to the right, then adjust “Ω†zero knob, so that the pointer just points to 0. Then, the two rods are respectively contacted with the two ends of the measured resistance (or circuit), and the reading of the pointer on the ohmic scale line (the first line) is read, and then the number of the index is multiplied, which is the resistance value of the measured resistance. . For example, the resistance is measured by R*100, and the pointer is at 80, and the measured resistance is 80*100=8K. Since the left side of the “Ω†tick is densely read and difficult to see, the appropriate ohms should be selected for the measurement. Make the pointer in the middle or right of the tick mark so that the readings are clear and accurate. Each time you change gears, you should short-circuit the two bars and re-adjust the pointer to zero to measure. Measure DC voltage:--First estimate the magnitude of the voltage to be measured, then turn the transfer switch to the appropriate V range, connect the positive bar to the "+" terminal of the measured voltage, and the negative bar to the measured voltage "-" terminal. . Then, according to the number of the range and the number indicated by the pointer on the standard DC symbol "DC-" scale line (second line), the magnitude of the measured voltage is read. If you measure with V300 volts, you can directly read the indication value of 0-300. If you use V30 volts measurement, you only need to remove a "0" from the digit on the scale line 300, which is regarded as 30, and then treat the numbers such as 200 and 100 as 20, 10 and directly read the pointer indication value. For example, the V6 voltage is used to measure the DC voltage, and the pointer is at 15, the measured voltage is 1.5 volts. Measure DC current: -- Estimate the current to be measured first, then turn the transfer switch to the appropriate mA range, and then connect the multimeter in series. At the same time, observe the tick mark marked with the DC symbol "DC". If the current range is selected in the 3 mA range, then the number on the surface tick mark 300 should be removed from the two "0"s, which is regarded as 3, and then 200. 100 is regarded as 2, 1, so that the measured current value can be read. For example, the DC current is measured with a DC 3 mA range, and the pointer is at 100, and the current is 1 mA. Measuring AC voltage: The method of measuring AC voltage is similar to measuring DC voltage. The difference is that there is no positive or negative difference in AC power. Therefore, when measuring AC, the meter bar does not need to be positive or negative. The reading method is the same as the above-mentioned reading of the measured DC voltage, except that the number should be the position of the pointer on the scale line marked with the AC symbol "AC".
Considerations for using a multimeter
The multimeter is a relatively sophisticated instrument. If it is used improperly, it will not only cause inaccurate measurement but also be easily damaged. However, as long as we master the use of the multimeter and precautions, and be cautious, the multimeter can be durable. The following should be noted when using a multimeter:
· Measurement of current and voltage cannot be misaligned. If the resistance or current is mistakenly measured, the meter will be easily burned out. When the multimeter is not in use, it is best to rotate the gear to the highest level of the AC voltage to avoid damage due to improper use.
· When measuring DC voltage and DC current, pay attention to the "+" and "-" polarity. Do not connect the wrong ones. If you find that the pointer is open and reversed, you should immediately change the watch bar to avoid damaging the pointer and the meter.
· If you do not know the magnitude of the voltage or current to be measured, you should first use the highest grade, and then select the appropriate gear to test, so as to avoid excessive deflection of the hands and damage the meter. The closer the selected gear is to the measured value, the more accurate the measured value will be.
• When measuring resistance, do not touch the bare ends of the components (or the metal parts of the two bars) with your hands to prevent the human body resistance from being connected in parallel with the measured resistance, making the measurement results inaccurate.
· When measuring resistance, if the two sticks are shorted, adjust the “zero ohm†knob to the maximum, the pointer still can't reach 0. This phenomenon is usually caused by insufficient battery voltage in the watch. It should be replaced with new battery. Only accurate measurement can be made.
·When the multimeter is not in use, do not screw it in the resistance file, because there is a battery inside. If you accidentally make the two watch rods touch and short circuit, it will not only consume the battery, but even damage the meter when it is serious.
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