1. Selection of pointer table and digital table:
1. The reading precision of the pointer table is poor, but the process of the pointer swing is more intuitive, and the amplitude of the swing speed can sometimes more objectively reflect the measured size (such as the slightness of the TV data bus (SDL) when transmitting data (Jitter); the digital meter reading is intuitive, but the process of digital change looks messy and not easy to watch.
2. There are generally two batteries in the pointer table, one low-voltage 1.5V and one high-voltage 9V or 15V. The black test pen is positive for the red test pen. Digital watches usually use a 6V or 9V battery. In the resistance range, the output current of the pointer of the pointer table is much larger than that of the digital table. The R × 1Ω range can make the speaker emit a loud “click†sound, and the R × 10kΩ range can even light the light-emitting diode (LED).
3. In the voltage range, the internal resistance of the pointer meter is relatively small compared to the digital meter, and the measurement accuracy is relatively poor. Some high-voltage micro-current occasions cannot even be calibrated because the internal resistance will affect the circuit under test (for example, when measuring the acceleration voltage of the TV picture tube, the measured value will be much lower than the actual value). The internal resistance of the digital meter voltage file is very large, at least in the megohm level, and has little effect on the circuit under test. However, the extremely high output impedance makes it susceptible to the influence of induced voltage, and the data measured in some occasions with strong electromagnetic interference may be false.
4. In short, the pointer table is suitable for relatively large current and high voltage analog circuit measurement, such as TV sets and audio amplifiers. It is suitable for the measurement of low voltage and small current digital circuits, such as BP machine and mobile phone. Not absolute, you can choose pointer table and digital table according to the situation.
Second, the measurement skills (if not specified, the pointer table is used):
1. Loudspeaker, earphone, dynamic microphone: use R × 1Ω file, any test lead is connected to one end, and the other test lead touches the other end, it will emit a clear click sound when normal. If it does not sound, the coil is broken. If the sound is small and sharp, there is a problem of rubbing and it can not be used.
2. Capacitance measurement: Use a resistance file, select the appropriate range according to the capacitance, and pay attention to the positive electrode of the electrolytic capacitor black test pen when measuring. ①Estimate the size of the capacitance of the microwave method: it can be judged according to the maximum amplitude of the pointer swing based on experience or with reference to the standard capacitance of the same capacity. The referenced capacitors do not need to have the same withstand voltage, as long as they have the same capacity. For example, an estimated 100μF / 250V capacitor can be referenced with a 100μF / 25V capacitor. As long as the maximum amplitude of the pointer swing is the same, the same capacity can be determined. ② Estimate the capacity of picofarad capacitors: use R × 10kΩ file, but only measure capacitors above 1000pF. For a capacitor of 1000pF or a little larger, as long as the hands of the watch slightly swing, it can be considered that the capacity is enough. ③ Check whether the capacitor is leaking: For capacitors over a thousand microfarads, you can quickly charge them with R × 10Ω file, and preliminary estimate the capacitance, and then change to R × 1kΩ file and continue to measure for a while, then the pointer is not Should return, but should stop at or very close to ∞, otherwise there is leakage. For some timing or oscillating capacitors below tens of microfarads (such as the oscillating capacitors of color TV switching power supplies), the leakage characteristics are very high, as long as there is a slight leakage, it can not be used. In this case, the R × 1kΩ file can be charged Then use the R × 10kΩ file to continue the measurement. Similarly, the hand should stop at ∞ instead of returning.
3. The diodes, transistors and voltage regulators in the road test are good or bad: because in the actual circuit, the bias resistance of the transistors or the peripheral resistance of the diodes and voltage regulators are generally relatively large, most of them are in the hundreds or thousands of ohms. , We can use the R × 10Ω or R × 1Ω file of the multimeter to measure the quality of the PN junction on the road. During road measurement, the PN junction measured with the R × 10Ω file should have more obvious forward and reverse characteristics (if the difference between the forward and reverse resistance is not obvious, you can use the R × 1Ω file to measure), generally the forward resistance is at R The needle should indicate around 200Ω when measuring in × 10Ω range, and about 30Ω when measuring in R × 1Ω range (may vary slightly according to different types). If the measurement result is too large in the forward resistance or too small in the reverse resistance, it means that there is a problem with this PN junction, and this tube also has a problem. This method is particularly effective for repairs. It can find out bad pipes very quickly, and can even measure pipes that have not been completely broken but have deteriorated characteristics. For example, when you use a small resistance file to measure the forward resistance of a PN junction is too large, if you solder it down and then use the commonly used R × 1kΩ file to retest, it may still be normal. In fact, the characteristics of this tube have deteriorated. Not working properly or unstable anymore.
4. Measuring resistance: It is important to select a good range. When the pointer indicates 1/3 to 2/3 full scale, the measurement accuracy is the highest and the reading is the most accurate. It should be noted that when measuring a large resistance of megohm level with R × 10k resistance file, do not pinch your fingers at both ends of the resistance, as the human body resistance will make the measurement result smaller.
5. Measuring voltage-stabilizing diode: The voltage-stabilizing value of the voltage-stabilizing tube we usually use is generally greater than 1.5V, and the resistance file below R × 1k of the pointer meter is powered by the 1.5V battery in the meter. The resistance regulator measuring below R × 1k is just like measuring a diode, with complete unidirectional conductivity. However, the R × 10k file of the pointer meter is powered by a 9V or 15V battery. When using R × 10k to measure a voltage regulator with a regulated value less than 9V or 15V, the reverse resistance value will not be ∞, but a certain Resistance, but this resistance is still much higher than the forward resistance of the regulator. In this way, we can initially estimate the quality of the regulator. However, a good voltage regulator tube must have an accurate voltage regulation value. How to estimate this voltage regulation value in amateur conditions? It's not difficult, just find another pointer table. The method is: first place a meter in the R × 10k file, and connect the black and red test pens to the cathode and anode of the voltage regulator tube respectively. At this time, the actual working state of the voltage regulator tube is simulated, and then another table is placed On the voltage range V × 10V or V × 50V (according to the stabilized voltage value), connect the red and black test leads to the black and red test leads of the meter just now. The measured voltage value at this time is basically this The voltage regulation value of the regulator tube. "Basically" is because the bias current of the first table to the regulator is slightly smaller than the bias current during normal use, so the measured voltage value will be slightly larger, but the difference is basically the same. . This method can only estimate the regulator tube whose voltage regulation value is less than the high voltage battery voltage of the pointer meter. If the voltage regulation value of the voltage regulator tube is too high, it can only be measured by the method of external power supply (so it seems that when we use the pointer meter, the high-voltage battery voltage of 15V is more suitable than 9V).
6. Transistor measurement: Usually we need to use R × 1kΩ file, whether it is NPN tube or PNP tube, whether it is low power, medium power, high power tube, the be junction cb junction should show the same single guide as the diode Electrical, the reverse resistance is infinite, and the forward resistance is about 10K. In order to further evaluate the quality of the tube, if necessary, the resistance range should be changed for multiple measurements. The method is: set R × 10Ω to measure the PN junction forward resistance is about 200Ω; set R × 1Ω to measure The forward conduction resistance of the PN junction is about 30 Ω (the above is the data measured by the 47-type meter, the other models are roughly different, you can try to test a few good tubes to summarize, to be aware) If the reading is too large Too much, it can be concluded that the characteristics of the pipe are not good. You can also place the meter in R × 10kΩ and measure again, the tube with the lowest withstand voltage (basically the withstand voltage of the triode is above 30V), the reverse resistance of its cb junction should also be in ∞, but the reverse resistance of its be junction There may be some, the needle will deflect slightly (generally will not exceed 1/3 of the full range, depending on the pressure resistance of the tube). Similarly, when measuring the resistance between ec (for NPN tube) or ce (for PNP tube) with R × 10kΩ, the hands may deflect slightly, but this does not mean that the tube is bad. But when measuring the resistance between ce or ec with R × 1kΩ or less, the indicator on the meter should be infinity, otherwise the pipe is a problem. It should be noted that the above measurements are for silicon tubes, but not for germanium tubes. However, germanium tubes are now rare. In addition, the "reverse direction" refers to the PN junction, and the directions of the NPN tube and the PNP tube are actually different.
Most of the common transistors are now plastic-encapsulated. How to accurately determine which of the three pins of the transistor are b, c, and e? The b pole of the triode is easy to measure, but how to determine which is c and which is e? Three methods are recommended here: the first method: for a pointer table with a triode hFE jack, first measure the pole b, then insert the transistor into the jack at will (of course, the pole b can be inserted accurately), measure Check the hFE value, and then turn the tube upside down and test again. Once the measured hFE value is relatively large, the position of each pin is correct. The second method: for the meter without hFE measurement jack, or the tube is too large to insert into the jack, you can use this method: for the NPN tube, first measure the b pole (the tube is NPN or PNP and its b pin It ’s easy to measure, right?), Put the meter in the R × 1kΩ file, connect the red lead to the hypothetical e pole (note that the hand holding the red lead should not touch the tip or pin of the lead), and the black lead to the hypothetical one C pole, at the same time hold the tip of the test pen and this pin with your finger, pick up the tube, and lick the b pole with the tip of your tongue to see that the pointer of the meter should have a certain deflection. If you connect each test pen correctly, the pointer deflection will If the connection is incorrect, the pointer deflection will be smaller. The difference is obvious. From this, the c and e poles of the tube can be determined. For the PNP tube, connect the black test lead to the hypothetical e-pole (do not touch the pen tip or pin), and the red test lead to the hypothetical c-pole, while holding the tip of the meter and the pin with your finger, then lick the b with the tip of the tongue Extremely, if the test leads are connected correctly, the head pointer will deflect relatively large. Of course, the test leads should be exchanged twice during the measurement, and the final judgment can only be made after comparing the readings. This method is suitable for all triodes, which is convenient and practical. According to the deflection amplitude of the hands, the amplification capacity of the tube can also be estimated, of course, this is based on experience. The third method: first determine the NPN or PNP type of the tube and its b-pole, then place the meter in the R × 10kΩ file. For the NPN tube, the black pen connects to the e-pole and the red pen connects to the c-pole. For deflection, for the PNP tube, the black test lead is connected to the c-pole, and the red test lead is connected to the e-pole, the needle may have a certain deflection, and in turn, there will be no deflection. From this, the c and e poles of the triode can also be determined. However, for high pressure pipes, this method is not applicable.
For common imported models of high-power plastic tubes, the C pole is basically in the middle (I have not seen b in the middle). Some b in medium and small power tubes are most likely in the middle. For example, commonly used 9014 transistors and other series of transistors, 2SC1815, 2N5401, 2N5551 and other transistors, some of them are in the middle. Of course, they also have c poles in the middle. Therefore, when repairing and replacing the triode, especially these low-power triodes, they should not be installed directly as they are, and they must be tested first.
1. The reading precision of the pointer table is poor, but the process of the pointer swing is more intuitive, and the amplitude of the swing speed can sometimes more objectively reflect the measured size (such as the slightness of the TV data bus (SDL) when transmitting data (Jitter); the digital meter reading is intuitive, but the process of digital change looks messy and not easy to watch.
2. There are generally two batteries in the pointer table, one low-voltage 1.5V and one high-voltage 9V or 15V. The black test pen is positive for the red test pen. Digital watches usually use a 6V or 9V battery. In the resistance range, the output current of the pointer of the pointer table is much larger than that of the digital table. The R × 1Ω range can make the speaker emit a loud “click†sound, and the R × 10kΩ range can even light the light-emitting diode (LED).
3. In the voltage range, the internal resistance of the pointer meter is relatively small compared to the digital meter, and the measurement accuracy is relatively poor. Some high-voltage micro-current occasions cannot even be calibrated because the internal resistance will affect the circuit under test (for example, when measuring the acceleration voltage of the TV picture tube, the measured value will be much lower than the actual value). The internal resistance of the digital meter voltage file is very large, at least in the megohm level, and has little effect on the circuit under test. However, the extremely high output impedance makes it susceptible to the influence of induced voltage, and the data measured in some occasions with strong electromagnetic interference may be false.
4. In short, the pointer table is suitable for relatively large current and high voltage analog circuit measurement, such as TV sets and audio amplifiers. It is suitable for the measurement of low voltage and small current digital circuits, such as BP machine and mobile phone. Not absolute, you can choose pointer table and digital table according to the situation.
Second, the measurement skills (if not specified, the pointer table is used):
1. Loudspeaker, earphone, dynamic microphone: use R × 1Ω file, any test lead is connected to one end, and the other test lead touches the other end, it will emit a clear click sound when normal. If it does not sound, the coil is broken. If the sound is small and sharp, there is a problem of rubbing and it can not be used.
2. Capacitance measurement: Use a resistance file, select the appropriate range according to the capacitance, and pay attention to the positive electrode of the electrolytic capacitor black test pen when measuring. ①Estimate the size of the capacitance of the microwave method: it can be judged according to the maximum amplitude of the pointer swing based on experience or with reference to the standard capacitance of the same capacity. The referenced capacitors do not need to have the same withstand voltage, as long as they have the same capacity. For example, an estimated 100μF / 250V capacitor can be referenced with a 100μF / 25V capacitor. As long as the maximum amplitude of the pointer swing is the same, the same capacity can be determined. ② Estimate the capacity of picofarad capacitors: use R × 10kΩ file, but only measure capacitors above 1000pF. For a capacitor of 1000pF or a little larger, as long as the hands of the watch slightly swing, it can be considered that the capacity is enough. ③ Check whether the capacitor is leaking: For capacitors over a thousand microfarads, you can quickly charge them with R × 10Ω file, and preliminary estimate the capacitance, and then change to R × 1kΩ file and continue to measure for a while, then the pointer is not Should return, but should stop at or very close to ∞, otherwise there is leakage. For some timing or oscillating capacitors below tens of microfarads (such as the oscillating capacitors of color TV switching power supplies), the leakage characteristics are very high, as long as there is a slight leakage, it can not be used. In this case, the R × 1kΩ file can be charged Then use the R × 10kΩ file to continue the measurement. Similarly, the hand should stop at ∞ instead of returning.
3. The diodes, transistors and voltage regulators in the road test are good or bad: because in the actual circuit, the bias resistance of the transistors or the peripheral resistance of the diodes and voltage regulators are generally relatively large, most of them are in the hundreds or thousands of ohms. , We can use the R × 10Ω or R × 1Ω file of the multimeter to measure the quality of the PN junction on the road. During road measurement, the PN junction measured with the R × 10Ω file should have more obvious forward and reverse characteristics (if the difference between the forward and reverse resistance is not obvious, you can use the R × 1Ω file to measure), generally the forward resistance is at R The needle should indicate around 200Ω when measuring in × 10Ω range, and about 30Ω when measuring in R × 1Ω range (may vary slightly according to different types). If the measurement result is too large in the forward resistance or too small in the reverse resistance, it means that there is a problem with this PN junction, and this tube also has a problem. This method is particularly effective for repairs. It can find out bad pipes very quickly, and can even measure pipes that have not been completely broken but have deteriorated characteristics. For example, when you use a small resistance file to measure the forward resistance of a PN junction is too large, if you solder it down and then use the commonly used R × 1kΩ file to retest, it may still be normal. In fact, the characteristics of this tube have deteriorated. Not working properly or unstable anymore.
4. Measuring resistance: It is important to select a good range. When the pointer indicates 1/3 to 2/3 full scale, the measurement accuracy is the highest and the reading is the most accurate. It should be noted that when measuring a large resistance of megohm level with R × 10k resistance file, do not pinch your fingers at both ends of the resistance, as the human body resistance will make the measurement result smaller.
5. Measuring voltage-stabilizing diode: The voltage-stabilizing value of the voltage-stabilizing tube we usually use is generally greater than 1.5V, and the resistance file below R × 1k of the pointer meter is powered by the 1.5V battery in the meter. The resistance regulator measuring below R × 1k is just like measuring a diode, with complete unidirectional conductivity. However, the R × 10k file of the pointer meter is powered by a 9V or 15V battery. When using R × 10k to measure a voltage regulator with a regulated value less than 9V or 15V, the reverse resistance value will not be ∞, but a certain Resistance, but this resistance is still much higher than the forward resistance of the regulator. In this way, we can initially estimate the quality of the regulator. However, a good voltage regulator tube must have an accurate voltage regulation value. How to estimate this voltage regulation value in amateur conditions? It's not difficult, just find another pointer table. The method is: first place a meter in the R × 10k file, and connect the black and red test pens to the cathode and anode of the voltage regulator tube respectively. At this time, the actual working state of the voltage regulator tube is simulated, and then another table is placed On the voltage range V × 10V or V × 50V (according to the stabilized voltage value), connect the red and black test leads to the black and red test leads of the meter just now. The measured voltage value at this time is basically this The voltage regulation value of the regulator tube. "Basically" is because the bias current of the first table to the regulator is slightly smaller than the bias current during normal use, so the measured voltage value will be slightly larger, but the difference is basically the same. . This method can only estimate the regulator tube whose voltage regulation value is less than the high voltage battery voltage of the pointer meter. If the voltage regulation value of the voltage regulator tube is too high, it can only be measured by the method of external power supply (so it seems that when we use the pointer meter, the high-voltage battery voltage of 15V is more suitable than 9V).
6. Transistor measurement: Usually we need to use R × 1kΩ file, whether it is NPN tube or PNP tube, whether it is low power, medium power, high power tube, the be junction cb junction should show the same single guide as the diode Electrical, the reverse resistance is infinite, and the forward resistance is about 10K. In order to further evaluate the quality of the tube, if necessary, the resistance range should be changed for multiple measurements. The method is: set R × 10Ω to measure the PN junction forward resistance is about 200Ω; set R × 1Ω to measure The forward conduction resistance of the PN junction is about 30 Ω (the above is the data measured by the 47-type meter, the other models are roughly different, you can try to test a few good tubes to summarize, to be aware) If the reading is too large Too much, it can be concluded that the characteristics of the pipe are not good. You can also place the meter in R × 10kΩ and measure again, the tube with the lowest withstand voltage (basically the withstand voltage of the triode is above 30V), the reverse resistance of its cb junction should also be in ∞, but the reverse resistance of its be junction There may be some, the needle will deflect slightly (generally will not exceed 1/3 of the full range, depending on the pressure resistance of the tube). Similarly, when measuring the resistance between ec (for NPN tube) or ce (for PNP tube) with R × 10kΩ, the hands may deflect slightly, but this does not mean that the tube is bad. But when measuring the resistance between ce or ec with R × 1kΩ or less, the indicator on the meter should be infinity, otherwise the pipe is a problem. It should be noted that the above measurements are for silicon tubes, but not for germanium tubes. However, germanium tubes are now rare. In addition, the "reverse direction" refers to the PN junction, and the directions of the NPN tube and the PNP tube are actually different.
Most of the common transistors are now plastic-encapsulated. How to accurately determine which of the three pins of the transistor are b, c, and e? The b pole of the triode is easy to measure, but how to determine which is c and which is e? Three methods are recommended here: the first method: for a pointer table with a triode hFE jack, first measure the pole b, then insert the transistor into the jack at will (of course, the pole b can be inserted accurately), measure Check the hFE value, and then turn the tube upside down and test again. Once the measured hFE value is relatively large, the position of each pin is correct. The second method: for the meter without hFE measurement jack, or the tube is too large to insert into the jack, you can use this method: for the NPN tube, first measure the b pole (the tube is NPN or PNP and its b pin It ’s easy to measure, right?), Put the meter in the R × 1kΩ file, connect the red lead to the hypothetical e pole (note that the hand holding the red lead should not touch the tip or pin of the lead), and the black lead to the hypothetical one C pole, at the same time hold the tip of the test pen and this pin with your finger, pick up the tube, and lick the b pole with the tip of your tongue to see that the pointer of the meter should have a certain deflection. If you connect each test pen correctly, the pointer deflection will If the connection is incorrect, the pointer deflection will be smaller. The difference is obvious. From this, the c and e poles of the tube can be determined. For the PNP tube, connect the black test lead to the hypothetical e-pole (do not touch the pen tip or pin), and the red test lead to the hypothetical c-pole, while holding the tip of the meter and the pin with your finger, then lick the b with the tip of the tongue Extremely, if the test leads are connected correctly, the head pointer will deflect relatively large. Of course, the test leads should be exchanged twice during the measurement, and the final judgment can only be made after comparing the readings. This method is suitable for all triodes, which is convenient and practical. According to the deflection amplitude of the hands, the amplification capacity of the tube can also be estimated, of course, this is based on experience. The third method: first determine the NPN or PNP type of the tube and its b-pole, then place the meter in the R × 10kΩ file. For the NPN tube, the black pen connects to the e-pole and the red pen connects to the c-pole. For deflection, for the PNP tube, the black test lead is connected to the c-pole, and the red test lead is connected to the e-pole, the needle may have a certain deflection, and in turn, there will be no deflection. From this, the c and e poles of the triode can also be determined. However, for high pressure pipes, this method is not applicable.
For common imported models of high-power plastic tubes, the C pole is basically in the middle (I have not seen b in the middle). Some b in medium and small power tubes are most likely in the middle. For example, commonly used 9014 transistors and other series of transistors, 2SC1815, 2N5401, 2N5551 and other transistors, some of them are in the middle. Of course, they also have c poles in the middle. Therefore, when repairing and replacing the triode, especially these low-power triodes, they should not be installed directly as they are, and they must be tested first.
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