⒈The instrument is equipped with an automatic power cut-off circuit. When the working time of the instrument is about 30 minutes to 1 hour, the power supply is automatically cut off and the instrument enters the sleep state. At this time, the instrument consumes about 7μA of current.
⒉When the power of the instrument is cut off, if you want to turn on the power again, please press the power switch twice.
pointer multimeter
⒈ The reading accuracy of the pointer table is poor, but the process of the pointer swing is relatively intuitive, and its swing speed can sometimes reflect the measured size objectively (for example, the slight jitter of the TV data bus (SDL) when transmitting data) ); the reading of the digital meter is intuitive, but the process of digital change looks messy and not easy to watch.
⒉ There are generally two batteries in the pointer watch, one is low voltage 1.5V, and the other is high voltage 9V or 15V. The black test pen is the positive end of the red test pen. Digital meters usually use a 6V or 9V battery. In the case of electrical blockage, the output current of the test pen of the analog watch is much larger than that of the digital meter. Using the R×1Ω file can make the speaker emit a loud “click” sound, and the R×10kΩ file can even light up the light-emitting diode (LED).
⒊In the voltage block, 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 and micro-current situations cannot even be measured accurately, because the internal resistance will affect the circuit under test (for example, when measuring the acceleration stage voltage of a TV picture tube, the measured value will be much lower than the actual value). The internal resistance of the digital meter voltage block is very large, at least in the megohm level, and has little impact on the circuit under test. However, the extremely high output impedance makes it susceptible to induced voltage, and the measured data may be false in some occasions with strong electromagnetic interference.
Measurement Skills
1. Measuring speakers, earphones, and dynamic microphones:
Use the R×1Ω gear, connect any test pen to one end, and the other test pen to touch the other end, and it will make a clear and loud "click" sound under normal conditions. If there is no sound, the coil is broken. If the sound is small and sharp, there is a problem of rubbing the coil and it cannot be used.
2 measuring capacitance:
Use electricity to block, select the appropriate range according to the capacitance capacity, and pay attention to the positive electrode of the capacitor for the black test lead of the electrolytic capacitor during measurement.
①. Estimate the size of the microwave-class capacitor capacity: it can be determined by experience or by referring to the standard capacitor of the same capacity, according to the maximum amplitude of the pointer swing. The reference capacitors do not have to have the same withstand voltage value, as long as the capacity is the same. For example, estimating a 100μF/250V capacitor can be referenced by a 100μF/25V capacitor. As long as the maximum amplitude of their pointer swings is the same, it can be concluded that the capacity is the same.
②. Estimate the capacitance of the pico-farad level capacitor: use R×10kΩ block, but only the capacitance above 1000pF can be measured. For 1000pF or slightly larger capacitors, as long as the needle swings slightly, it can be considered that the capacity is sufficient.
3. Measure whether the capacitor is leaking: For capacitors above 1,000 microfarads, you can use the R×10Ω block to quickly charge it, and initially estimate the capacitance capacity, and then change to the R×1kΩ block to continue measuring for a while, when the pointer does not Should return, but should stop at or very close to ∞, otherwise there will be leakage. For some timing or oscillating capacitors below tens of microfarads (such as the oscillating capacitors of color TV switching power supplies), their leakage characteristics are very demanding, as long as there is a slight leakage, they cannot be used. Then use the R×10kΩ block to continue the measurement, and the needle should stop at ∞ instead of returning.
3. Test the quality of diodes, triodes, and voltage regulators on the road:
Because in the actual circuit, the bias resistance of the triode or the diode, and the peripheral resistance of the Zener tube are generally relatively large, most of which are more than hundreds of thousands of ohms. In this way, we can use the R×10Ω or R×1Ω block of the multimeter. Come and measure the quality of the PN junction. When measuring on the road, use the R×10Ω gear to measure the PN junction should have obvious forward and reverse characteristics (if the difference between the forward and reverse resistance is not obvious, you can use the R×1Ω gear to measure). Generally, the forward resistance is at R The needle should indicate about 200Ω when measuring in ×10Ω, and around 30Ω when measuring in R×1Ω (there may be slight differences according to different phenotypes). If the forward resistance value of the measurement result is too large or the reverse resistance value is too small, it means that there is a problem with the PN junction, and there is a problem with the tube. This method is particularly effective for repairs, where bad tubes can be found very quickly, and even tubes that are not completely broken but have deteriorated characteristics can be detected. For example, when you measure the forward resistance of a PN junction with a small resistance value, if you solder it down and use the commonly used R×1kΩ block to test again, it may be normal. In fact, the characteristics of this tube have deteriorated. Not working properly or unstable anymore.
4. Resistance measurement:
It is important to choose the range for the most accurate readings. It should be noted that when using the R×10k resistance gear to measure the large resistance value of the megohm level, do not pinch your fingers at both ends of the resistance, so that the resistance of the human body will make the measurement result small.
5. Measure the Zener diode:
The voltage regulator value of the voltage regulator tube we usually use is generally greater than 1.5V, and the electric barrier below R×1k of the pointer meter is powered by the 1.5V battery in the meter, so the electric barrier below R×1k is used. Just like measuring diodes, measuring zener tubes have complete unidirectional conductivity. However, the R×10k block of the pointer meter is powered by a 9V or 15V battery. When using the R×10k block to measure the voltage regulator tube with a voltage regulation value of less than 9V or 15V, the reverse resistance value will not be ∞, but has A certain resistance value, but this resistance value is still much higher than the forward resistance value of the Zener tube. In this way, we can preliminarily estimate the quality of the Zener tube. However, a good voltage regulator must have an accurate voltage regulation value. How to estimate this voltage regulation value under amateur conditions? It's not difficult, just find another pointer watch. The method is: first place a watch in the R×10k gear, and the black and red test pens are connected 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 watch is placed on the On the voltage range V×10V or V×50V (according to the voltage regulation value), connect the red and black test leads to the black and red test leads of the watch just now, the voltage value measured at this time is basically this The voltage regulator value of the Zener tube. Saying "basically" is because the bias current of the first watch to the voltage regulator tube is slightly smaller than the bias current in normal use, so the measured voltage regulator value will be slightly larger, but the difference is basically the same . This method can only estimate the zener tube whose voltage regulation value is less than the voltage of the pointer meter's high-voltage battery. If the voltage regulator value of the Zener tube is too high, it can only be measured by means of an external power supply (in this way, when we choose a pointer meter, it is more suitable to use a high-voltage battery with a voltage of 15V than 9V).
6. Measure the triode:
Usually we use R×1kΩ block, 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 exactly the same unidirectional conductivity as the diode, reverse The resistance is infinite, and its forward resistance is about 10K. In order to further estimate the quality of the tube characteristics, if necessary, the resistance gear should be changed for multiple measurements. The method is: set the R×10Ω block to measure the forward on-resistance of the PN junction at about 200Ω; set the R×1Ω block to measure The forward conduction resistance of the PN junction is about 30Ω. (The above is the data measured by the 47-type meter, and other models are slightly different. You can test a few more good tubes to sum up, so that you know what you have in mind.) If the reading is too large Too many and it can be concluded that the characteristics of the tube are not good. You can also place the meter in R×10kΩ and test again. The tube with low withstand voltage (basically the withstand voltage of triodes is above 30V), the reverse resistance of its cb junction should also be ∞, but the reverse resistance of its be junction There may be some, and the needle will deflect slightly (generally not more than 1/3 of the full scale, depending on the pressure resistance of the tube). However, when measuring the resistance between ce or ec with the gear below R×1kΩ, the indication of the meter should be infinite, otherwise there is a problem with the tube. It should be noted that the above measurements are for silicon tubes and not applicable to germanium tubes. In addition, the "reverse" refers to the PN junction, and the direction of the NPN tube and the PNP tube is actually different.
