1. Selection of pointer tables and digital tables:
1. The reading accuracy of pointer meter is poor, but the process of pointer swing is more intuitive, and the swing speed amplitude sometimes objectively reflects the measured size (e.g. the slight jitter of SDL when transmitting data); the reading of digital meter is intuitive, but the process of digital change seems very messy. It's not easy to watch.
2. There are generally two batteries in the pointer meter, one is 1.5V of low voltage, the other is 9V or 15V of high voltage. The black pen is the front end of the red pen. Digital tables often use a 6V or 9V battery. In the resistor gear, the pen output current of the pointer meter is much larger than that of the digital meter. The loudspeaker can emit a loud "beep" sound with R *1 gear, and even light up the light emitting diode (LED) with R *10k gear.
3. In the voltage range, the internal resistance of the pointer meter is smaller than that of the digital meter, and the measurement accuracy is worse. In some cases of high voltage and micro-current, it is even impossible to measure, because the internal resistance will affect the circuit under test (for example, the measured value will be much lower than the actual value when measuring the acceleration stage voltage of the TV kinescope). The internal resistance of the voltage band of the digital meter is very large, at least at mega-ohm level, which has little influence on the circuit under test. However, the extremely high output impedance makes it vulnerable to the influence of induced voltage, and the measured data may be false in some cases of strong electromagnetic interference.
4. In a word, pointer meters, such as TV sets and audio power amplifiers, are suitable for the measurement of analog circuits with relatively high current and high voltage. Digital meters, such as BP machines and mobile phones, are suitable for the measurement of low voltage and low current digital circuits. It is not absolute. Pointer tables and digital tables can be selected according to the situation.
2. Measurement techniques (pointer tables, if not specified):
1. Measuring loudspeaker, earphone and moving coil microphone: With R *1 file, one end of a watch pen is connected to the other end, and the other pen touches the other end, when normal, it will emit a crisp "beep" sound of loudness. If not, the coil is broken. If the noise is low and sharp, there is a scraping ring problem, and it can not be used.
2. Capacitance measurement: Select the appropriate range according to the capacitance of the resistor, and pay attention to the positive capacitance of the electrolytic capacitor black meter pen when measuring.
(1) Estimating the capacitance of microwave normal level capacitors: It can be determined by experience or by referring to the standard capacitance of the same capacity, according to the maximum swing of the pointer. The reference capacitors need not have the same withstand voltage value, as long as the capacity is the same. For example, estimating a capacitor of 100 muF/250V can be referred to by a capacitor of 100 muF/25V. As long as the maximum swing of their pointers is the same, the capacitance can be determined to be the same.
(2) Estimating the capacitance of skin-level capacitors: R *10k is used, but only capacitance above 1000pF can be measured. For a 1000pF or a slightly larger capacitor, as long as the needle oscillates slightly, the capacity can be considered adequate.
(3) Measuring whether the capacitor is leaking: For capacitors above 1000 micrometers, the capacitor can be charged quickly with R *10OH gear, and the capacitor capacity can be estimated initially. Then the capacitor capacity can be changed to R *1kOH gear to continue measuring for a while. At this time, the pointer should not return, but should stop at or very close to or there will be leakage. For some timing or oscillating capacitors (such as the oscillating capacitors of color TV switching power supply) under tens of micrometers, the requirement of leakage characteristics is very high. As long as there is a slight leakage, it can not be used. At this time, the R * 1kOmega gear can be changed to R * 10kOmega gear to continue measuring after charging. Similarly, the needle should stop at instead of returning.
3. Measuring diodes, transistors and regulators on the road: Because in the actual circuit, the bias resistance of transistors or the peripheral resistance of diodes and regulators are generally larger, mostly in hundreds of thousands of ohms. Thus, we can use R * 10Omega or R * 1Omega of multimeter to measure the quality of PN junctions on the road. When measuring the PN junction with R *10Omega, it should have obvious positive and negative characteristics (if the difference between the positive and negative resistances is not obvious, it can be measured with R *1Omega). Generally, the positive resistance should be indicated at about 200 Omega in R *10Omega and 30 Omega in R *1Omega (according to different phenotypes, it may be slightly different). Enter. If the measured positive resistance is too large or the reverse resistance is too small, it indicates that the PN junction has a problem and the tube has a problem. This method is especially effective for maintenance, it can find out the broken pipe very quickly, and it can even detect the pipe which has not completely broken but has deteriorated characteristics. For example, when you measure the forward resistance of a PN junction with a small resistance range, if you weld it down and re-test it with the commonly used R * 1K range, it may still be normal. In fact, the characteristics of the tube have deteriorated, and it can not work normally or be unstable.