Multimeters, also known as multiplex tables, multimeters, tri-meters, and multi-use meters, are indispensable measuring instruments for power electronics and other departments. Generally, voltage, current and resistance are the main purposes. The multimeter is divided into a pointer multimeter and a digital multimeter according to the display mode. It is a multi-functional, multi-range measuring instrument. The general multimeter can measure DC current, DC voltage, AC current, AC voltage, resistance and audio level, etc. Some can also measure AC current, capacitance, inductance and semiconductor. Some parameters (such as β) and so on.
Multimeter basic function
The multimeter can be used not only to measure the resistance of the object being measured, but also to measure the DC voltage. Even some multimeters can measure the main parameters of the transistor and the capacitance of the capacitor. Fully mastering the use of the multimeter is one of the most basic skills of electronic technology. Common multimeters have pointer multimeters and digital multimeters. The pointer multimeter is a multi-function measuring instrument with a head as the core component, and the measured value is read by the head pointer. The measured value of the digital multimeter is displayed directly by the liquid crystal display in digital form, which is convenient to read, and some also have a voice prompt function. The multimeter is a meter that shares a meter head, a voltmeter, an ammeter, and an ohmmeter.
The DC current file of the multimeter is a multi-range DC voltmeter. The parallel closed-circuit divider resistor of the meter head can expand its voltage range. The DC voltage range of the multimeter is a multi-range DC voltmeter. The meter series resistor divider can expand its voltage range. The voltage divider resistors are different and the corresponding ranges are different. The head of the multimeter is a magnetoelectric measuring mechanism. It can only convert the alternating current into direct current through a direct current, and realize the measurement of the alternating current.
How the multimeter works
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.
Multimeter operating procedures
1. Be familiar with the functions of the multimeter before use. According to the object to be measured, select the gear position, range and pen jack correctly.
2. When the size of the measured data is unknown, the range switch should be set to the maximum value, and then switched from the large range to the small range, so that the meter pointer can be indicated at 1/2 or more of the full scale.
3. When measuring the resistance, after selecting the appropriate magnification file, touch the two test leads to make the pointer point to zero. If the pointer deviates from the zero position, adjust the “zero adjustment†knob to zero the pointer to ensure accurate measurement results. . If you can't zero or the digital display sends a low voltage alarm, you should check it in time.
4. When measuring the resistance of a certain circuit, the power of the circuit under test must be cut off.
5. When using a multimeter for measurement, pay attention to the safety of personal and instrumentation equipment. Do not touch the metal part of the test pen by hand during the test. Do not switch the gear switch with power to ensure accurate measurement and avoid accidents such as electric shock and burning of the instrument. .
Considerations for using the multimeter
1. Before using the multimeter, first perform “mechanical zero adjustmentâ€, that is, when there is no measured power, make the multimeter pointer point at zero voltage or zero current.
2. In the process of using the multimeter, the metal part of the test pen cannot be touched by hand, so that the measurement can be ensured on the one hand, and the personal safety can be ensured on the other hand.
3. When measuring a certain amount of electricity, it is not possible to shift gears while measuring, especially when measuring high voltage or high current. Otherwise, the multimeter will be destroyed. If you need to change gears, you should first disconnect the test leads and then measure them after shifting.
4. When the multimeter is in use, it must be placed horizontally to avoid errors. At the same time, we must also pay attention to avoiding the influence of external magnetic field on the multimeter.
5. After the multimeter is used, the switch should be placed at the maximum of the AC voltage. If it is not used for a long time, the battery inside the multimeter should be taken out to prevent the battery from corroding other devices in the watch.
Can a multimeter measure capacitance? How to use a multimeter to detect capacitance
1, pointer type multimeter detection capacitor
1.1, detection of fixed capacitance
1) Detection of fixed capacitance above 0.01 pF The pointer multimeter is adjusted to R&TImes; 10k ohms, and ohms are zeroed, then the red and black test leads of the multimeter are used to contact the two pins of the capacitor to observe the pointer of the multimeter. Change, as shown in Figure 1. If the test leads are turned on, the pointer of the multimeter swings to the right and then returns to the infinity. After the test pen is changed, the measurement is performed again. The pointer also swings to the right and returns to the infinity. It can be judged that the capacitor is normal. If the pointer of the multimeter swings to near "0", it can be judged that the capacitor is broken down or severely leaked; if the meter is turned on, the pointer will not return to infinity after swinging, then the capacitor can be judged to be leaking; If the pointer does not swing, it can be judged that the capacitor has been opened.
2) Detection of fixed capacitance with a capacity less than 0.01 pF When detecting a small capacitance below 10pF, the capacitance is too small, so use a multimeter to measure whether it has leakage, internal short circuit or breakdown: use a multimeter when measuring R&TImes; 10k block, connect the two test leads to the two pins of the capacitor, and the resistance should be infinite. If the measured resistance is zero, it can be determined that the capacitor is damaged or internally broken.
3) Detect 10pF ~ 0.01; tF fixed capacitor can use the following method. Adjust the multimeter to R&TImes; 10k block, use two triodes 3DC6 (or 9013) with a value greater than 100 to form a composite tube. The circuit schematic is shown in Figure 2. The amplification current of the composite tube is used to amplify the charging current of the measured capacitor to increase the swing amplitude of the multimeter pointer. The capacitor to be tested is connected between the base b and the collector c of the composite tube, and the red and black test leads of the multimeter are respectively connected to the emitter e and the collector c of the composite tube. If the pointer of the multimeter is slightly swung back to infinity, the capacitor is normal; if the pointer does not move or cannot return to infinity, the capacitor is damaged. During the test operation, especially when measuring the smaller capacity capacitor, it is necessary to repeatedly exchange the measured capacitor pins for two points to clearly see the swing of the multimeter pointer.
1.2, detection of electrolytic capacitors
The capacity of electrolytic capacitors is much larger than that of general fixed capacitors. When measuring, select the appropriate range for different capacities. In general, the capacitance between 1 and 47 pF can be measured with R&TImes; 1k block; the capacitance greater than 47 ptF can be measured with R × 100 block. The smaller the capacitance, the larger the electrical blocking ratio should be selected. Before the measurement, the capacitor should be fully discharged, that is, the two pins of the electrolytic capacitor are short-circuited, and the residual charge in the capacitor is discharged. The two pins of the capacitor can be short-circuited by a multimeter, and the schematic diagram of the capacitor discharge method is shown in FIG. The bulk capacitor must be discharged with a metal part of the screwdriver. After the capacitor is fully discharged, connect the red test lead of the pointer multimeter to the negative pole and the black test lead to the positive pole. At the moment of switching on, the multimeter pointer should be deflected to the right by a large angle and then gradually returned to the left until it stops at a certain position. The resistance at this time is the forward insulation resistance of the electrolytic capacitor, which should generally be several hundred kilohms or more. Change the test leads, the pointer repeats the front phenomenon, and the last indicated resistance is the reverse insulation resistance of the capacitor, which should be slightly smaller than the forward insulation resistance. The schematic diagram of the detection of the electrolytic capacitor is shown in Fig. 4.
In the above measurement, if the multimeter pointer does not move during the measurement, the capacitance disappears or the internal circuit is broken; if the positive and negative insulation resistance of the capacitor is small or zero, the capacitor leakage current is large or internal short circuit, and can no longer be used. . For electrolytic capacitors whose positive and negative signs are unknown, the insulation resistance can be determined by measuring the insulation resistance. First, the two pins of the multimeter are used to contact the two pins of the capacitor to measure the insulation resistance of the capacitor. After changing the test leads, measure again. The large value is the forward insulation resistance. At this time, the black meter is connected to the positive pole of the capacitor.
1.3, variable capacitance detection
The variable capacitor capacity is usually small, mainly to detect whether there is a short circuit between the capacitor and the stator.
1 Slowly rotate the shaft by hand, it should feel very smooth, and should not be loose or even stuck. When pushing the front, back, up, down, left and right directions of the rotation axis, the shaft should not be shaken.
2 The variable capacitor with poor contact between the shaft and the rotor cannot be used any more.
3 Place the multimeter in the R×10k block. Connect one of the two test leads to the output of the variable capacitor and the terminal of the fixed piece with one hand. The other hand will rotate the shaft slowly back and forth. The pointer of the multimeter should be at infinity. Do not move. If the pointer sometimes points to zero, it means there is a short circuit between the variable capacitor rotor and the stator; if it is rotated to an angle, the multimeter reading is not infinite but finite resistance, then the variable capacitor rotor and stator There is leakage between them.
2, digital multimeter detection capacitor
The pointer type multimeter can only detect the quality of the capacitor (the disconnection fault of the small capacity capacitor should not be judged) and roughly estimate the size of the capacitor. The capacitance capacity cannot be accurately measured. The capacitance of the capacitor usually requires a capacitance meter, a digital multimeter, and a dedicated The capacitance measuring instrument is used to measure. When measuring the capacitance of a capacitor with a digital multimeter, it is important to note that not all capacitors can be measured, depending on the measurement range of the digital multimeter. Some digital multimeters have multiple capacitance measurement gears, which can measure 2nF~2; tF capacitance, some can measure 20.nF~20.0ctF capacitance, while some digital multimeters only have a 20.0ptF capacitance measurement gear. When using a digital multimeter to measure the capacitance of a capacitor, place the digital multimeter in a capacitive gear and select the appropriate gear according to the size of the capacitor. After the capacitor to be tested is fully discharged, insert the capacitor to be tested directly into the test hole or two test leads. Direct contact is used for measurement. The capacity of the capacitor to be tested is directly displayed on the display of the digital multimeter.
If the displayed value is equal to or very close to the nominal capacity, the capacitor is normal; if the value displayed by the capacitor to be tested is too different from the nominal capacity, check if the nominal capacity is within the test range of the multimeter. The measuring range of the multimeter can be replaced by a multimeter with an appropriate range and then measured. If the measurement is replaced after the multimeter is replaced, the capacitance to be tested has deteriorated and can no longer be used; if the value of the capacitor to be tested is much smaller than the nominal value The capacity indicates that the capacitor to be tested is damaged.
Note: (1) If the capacitance of the capacitor to be tested exceeds the measurement range of the multimeter, it cannot be measured with a digital multimeter.
2) The connection between the test leads of the digital multimeter and the test leads of the pointer multimeter is reversed. The black pen of the pointer multimeter is connected to the positive pole of the power supply in the watch, which is the current outflow end of the watch; the red pen of the digital multimeter is connected to the power supply in the watch. The positive electrode is the current outflow end of the table. After the capacitor is fully discharged, connect the red meter of the multimeter to the positive electrode of the electrolytic capacitor, and the black meter to the negative pole of the electrolytic capacitor to measure the forward insulation resistance. On the contrary, the multimeter red pen is connected to the negative electrode of the electrolytic capacitor, and the black pen is connected to the positive electrode of the electrolytic capacitor to measure the reverse insulation resistance.
3, multimeter voltage method to detect capacitance
Capacitors can also be detected by the AC voltage method. Some multimeters have this function, such as the FM50 multimeter. Take the FM50 multimeter as an example. The detection method is as follows. The dial of the multimeter has a scale corresponding to the AC voltage and the capacity of the capacitor, as shown in Figure 6.
a) Corresponding value of voltage and capacity when the AC voltage is 10V
b) Corresponding value of voltage and capacity when the AC voltage is 50V
c) When the AC voltage is 250\1, the corresponding value of voltage and capacity Figure 6 The scale corresponding to the AC voltage and capacitor capacity on the dial of the multimeter
3.1. Selecting the range According to the withstand voltage value on the capacitor, the AC range is reasonably selected, and the transfer switch is placed in the range.
3.2. Matching AC power supply Prepare a voltage regulator type power transformer, select the voltage output corresponding to the range, and then connect and measure according to the method shown in Figure 7.
3.3. Measurement and reading AC power supply, capacitor and multimeter are connected in series to form a closed loop. After power-on, the measurement is made. After the needle is stable, the number can be counted. Note: Be sure to pay attention to safety when using 250V AC power.
Multimeter basic function
The multimeter can be used not only to measure the resistance of the object being measured, but also to measure the DC voltage. Even some multimeters can measure the main parameters of the transistor and the capacitance of the capacitor. Fully mastering the use of the multimeter is one of the most basic skills of electronic technology. Common multimeters have pointer multimeters and digital multimeters. The pointer multimeter is a multi-function measuring instrument with a head as the core component, and the measured value is read by the head pointer. The measured value of the digital multimeter is displayed directly by the liquid crystal display in digital form, which is convenient to read, and some also have a voice prompt function. The multimeter is a meter that shares a meter head, a voltmeter, an ammeter, and an ohmmeter.
The DC current file of the multimeter is a multi-range DC voltmeter. The parallel closed-circuit divider resistor of the meter head can expand its voltage range. The DC voltage range of the multimeter is a multi-range DC voltmeter. The meter series resistor divider can expand its voltage range. The voltage divider resistors are different and the corresponding ranges are different. The head of the multimeter is a magnetoelectric measuring mechanism. It can only convert the alternating current into direct current through a direct current, and realize the measurement of the alternating current.
How the multimeter works
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.
Multimeter operating procedures
1. Be familiar with the functions of the multimeter before use. According to the object to be measured, select the gear position, range and pen jack correctly.
2. When the size of the measured data is unknown, the range switch should be set to the maximum value, and then switched from the large range to the small range, so that the meter pointer can be indicated at 1/2 or more of the full scale.
3. When measuring the resistance, after selecting the appropriate magnification file, touch the two test leads to make the pointer point to zero. If the pointer deviates from the zero position, adjust the “zero adjustment†knob to zero the pointer to ensure accurate measurement results. . If you can't zero or the digital display sends a low voltage alarm, you should check it in time.
4. When measuring the resistance of a certain circuit, the power of the circuit under test must be cut off.
5. When using a multimeter for measurement, pay attention to the safety of personal and instrumentation equipment. Do not touch the metal part of the test pen by hand during the test. Do not switch the gear switch with power to ensure accurate measurement and avoid accidents such as electric shock and burning of the instrument. .
Considerations for using the multimeter
1. Before using the multimeter, first perform “mechanical zero adjustmentâ€, that is, when there is no measured power, make the multimeter pointer point at zero voltage or zero current.
2. In the process of using the multimeter, the metal part of the test pen cannot be touched by hand, so that the measurement can be ensured on the one hand, and the personal safety can be ensured on the other hand.
3. When measuring a certain amount of electricity, it is not possible to shift gears while measuring, especially when measuring high voltage or high current. Otherwise, the multimeter will be destroyed. If you need to change gears, you should first disconnect the test leads and then measure them after shifting.
4. When the multimeter is in use, it must be placed horizontally to avoid errors. At the same time, we must also pay attention to avoiding the influence of external magnetic field on the multimeter.
5. After the multimeter is used, the switch should be placed at the maximum of the AC voltage. If it is not used for a long time, the battery inside the multimeter should be taken out to prevent the battery from corroding other devices in the watch.
Can a multimeter measure capacitance? How to use a multimeter to detect capacitance
1, pointer type multimeter detection capacitor
1.1, detection of fixed capacitance
1) Detection of fixed capacitance above 0.01 pF The pointer multimeter is adjusted to R&TImes; 10k ohms, and ohms are zeroed, then the red and black test leads of the multimeter are used to contact the two pins of the capacitor to observe the pointer of the multimeter. Change, as shown in Figure 1. If the test leads are turned on, the pointer of the multimeter swings to the right and then returns to the infinity. After the test pen is changed, the measurement is performed again. The pointer also swings to the right and returns to the infinity. It can be judged that the capacitor is normal. If the pointer of the multimeter swings to near "0", it can be judged that the capacitor is broken down or severely leaked; if the meter is turned on, the pointer will not return to infinity after swinging, then the capacitor can be judged to be leaking; If the pointer does not swing, it can be judged that the capacitor has been opened.
2) Detection of fixed capacitance with a capacity less than 0.01 pF When detecting a small capacitance below 10pF, the capacitance is too small, so use a multimeter to measure whether it has leakage, internal short circuit or breakdown: use a multimeter when measuring R&TImes; 10k block, connect the two test leads to the two pins of the capacitor, and the resistance should be infinite. If the measured resistance is zero, it can be determined that the capacitor is damaged or internally broken.
3) Detect 10pF ~ 0.01; tF fixed capacitor can use the following method. Adjust the multimeter to R&TImes; 10k block, use two triodes 3DC6 (or 9013) with a value greater than 100 to form a composite tube. The circuit schematic is shown in Figure 2. The amplification current of the composite tube is used to amplify the charging current of the measured capacitor to increase the swing amplitude of the multimeter pointer. The capacitor to be tested is connected between the base b and the collector c of the composite tube, and the red and black test leads of the multimeter are respectively connected to the emitter e and the collector c of the composite tube. If the pointer of the multimeter is slightly swung back to infinity, the capacitor is normal; if the pointer does not move or cannot return to infinity, the capacitor is damaged. During the test operation, especially when measuring the smaller capacity capacitor, it is necessary to repeatedly exchange the measured capacitor pins for two points to clearly see the swing of the multimeter pointer.
1.2, detection of electrolytic capacitors
The capacity of electrolytic capacitors is much larger than that of general fixed capacitors. When measuring, select the appropriate range for different capacities. In general, the capacitance between 1 and 47 pF can be measured with R&TImes; 1k block; the capacitance greater than 47 ptF can be measured with R × 100 block. The smaller the capacitance, the larger the electrical blocking ratio should be selected. Before the measurement, the capacitor should be fully discharged, that is, the two pins of the electrolytic capacitor are short-circuited, and the residual charge in the capacitor is discharged. The two pins of the capacitor can be short-circuited by a multimeter, and the schematic diagram of the capacitor discharge method is shown in FIG. The bulk capacitor must be discharged with a metal part of the screwdriver. After the capacitor is fully discharged, connect the red test lead of the pointer multimeter to the negative pole and the black test lead to the positive pole. At the moment of switching on, the multimeter pointer should be deflected to the right by a large angle and then gradually returned to the left until it stops at a certain position. The resistance at this time is the forward insulation resistance of the electrolytic capacitor, which should generally be several hundred kilohms or more. Change the test leads, the pointer repeats the front phenomenon, and the last indicated resistance is the reverse insulation resistance of the capacitor, which should be slightly smaller than the forward insulation resistance. The schematic diagram of the detection of the electrolytic capacitor is shown in Fig. 4.
In the above measurement, if the multimeter pointer does not move during the measurement, the capacitance disappears or the internal circuit is broken; if the positive and negative insulation resistance of the capacitor is small or zero, the capacitor leakage current is large or internal short circuit, and can no longer be used. . For electrolytic capacitors whose positive and negative signs are unknown, the insulation resistance can be determined by measuring the insulation resistance. First, the two pins of the multimeter are used to contact the two pins of the capacitor to measure the insulation resistance of the capacitor. After changing the test leads, measure again. The large value is the forward insulation resistance. At this time, the black meter is connected to the positive pole of the capacitor.
1.3, variable capacitance detection
The variable capacitor capacity is usually small, mainly to detect whether there is a short circuit between the capacitor and the stator.
1 Slowly rotate the shaft by hand, it should feel very smooth, and should not be loose or even stuck. When pushing the front, back, up, down, left and right directions of the rotation axis, the shaft should not be shaken.
2 The variable capacitor with poor contact between the shaft and the rotor cannot be used any more.
3 Place the multimeter in the R×10k block. Connect one of the two test leads to the output of the variable capacitor and the terminal of the fixed piece with one hand. The other hand will rotate the shaft slowly back and forth. The pointer of the multimeter should be at infinity. Do not move. If the pointer sometimes points to zero, it means there is a short circuit between the variable capacitor rotor and the stator; if it is rotated to an angle, the multimeter reading is not infinite but finite resistance, then the variable capacitor rotor and stator There is leakage between them.
2, digital multimeter detection capacitor
The pointer type multimeter can only detect the quality of the capacitor (the disconnection fault of the small capacity capacitor should not be judged) and roughly estimate the size of the capacitor. The capacitance capacity cannot be accurately measured. The capacitance of the capacitor usually requires a capacitance meter, a digital multimeter, and a dedicated The capacitance measuring instrument is used to measure. When measuring the capacitance of a capacitor with a digital multimeter, it is important to note that not all capacitors can be measured, depending on the measurement range of the digital multimeter. Some digital multimeters have multiple capacitance measurement gears, which can measure 2nF~2; tF capacitance, some can measure 20.nF~20.0ctF capacitance, while some digital multimeters only have a 20.0ptF capacitance measurement gear. When using a digital multimeter to measure the capacitance of a capacitor, place the digital multimeter in a capacitive gear and select the appropriate gear according to the size of the capacitor. After the capacitor to be tested is fully discharged, insert the capacitor to be tested directly into the test hole or two test leads. Direct contact is used for measurement. The capacity of the capacitor to be tested is directly displayed on the display of the digital multimeter.
If the displayed value is equal to or very close to the nominal capacity, the capacitor is normal; if the value displayed by the capacitor to be tested is too different from the nominal capacity, check if the nominal capacity is within the test range of the multimeter. The measuring range of the multimeter can be replaced by a multimeter with an appropriate range and then measured. If the measurement is replaced after the multimeter is replaced, the capacitance to be tested has deteriorated and can no longer be used; if the value of the capacitor to be tested is much smaller than the nominal value The capacity indicates that the capacitor to be tested is damaged.
Note: (1) If the capacitance of the capacitor to be tested exceeds the measurement range of the multimeter, it cannot be measured with a digital multimeter.
2) The connection between the test leads of the digital multimeter and the test leads of the pointer multimeter is reversed. The black pen of the pointer multimeter is connected to the positive pole of the power supply in the watch, which is the current outflow end of the watch; the red pen of the digital multimeter is connected to the power supply in the watch. The positive electrode is the current outflow end of the table. After the capacitor is fully discharged, connect the red meter of the multimeter to the positive electrode of the electrolytic capacitor, and the black meter to the negative pole of the electrolytic capacitor to measure the forward insulation resistance. On the contrary, the multimeter red pen is connected to the negative electrode of the electrolytic capacitor, and the black pen is connected to the positive electrode of the electrolytic capacitor to measure the reverse insulation resistance.
3, multimeter voltage method to detect capacitance
Capacitors can also be detected by the AC voltage method. Some multimeters have this function, such as the FM50 multimeter. Take the FM50 multimeter as an example. The detection method is as follows. The dial of the multimeter has a scale corresponding to the AC voltage and the capacity of the capacitor, as shown in Figure 6.
a) Corresponding value of voltage and capacity when the AC voltage is 10V
b) Corresponding value of voltage and capacity when the AC voltage is 50V
c) When the AC voltage is 250\1, the corresponding value of voltage and capacity Figure 6 The scale corresponding to the AC voltage and capacitor capacity on the dial of the multimeter
3.1. Selecting the range According to the withstand voltage value on the capacitor, the AC range is reasonably selected, and the transfer switch is placed in the range.
3.2. Matching AC power supply Prepare a voltage regulator type power transformer, select the voltage output corresponding to the range, and then connect and measure according to the method shown in Figure 7.
3.3. Measurement and reading AC power supply, capacitor and multimeter are connected in series to form a closed loop. After power-on, the measurement is made. After the needle is stable, the number can be counted. Note: Be sure to pay attention to safety when using 250V AC power.
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