Instructions for use of digital multimeter
⒈The instrument is equipped with an automatic power-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. The instrument consumes about 7 μA of current at this point.
⒉After the instrument is powered off, if you need to restart, please press the power switch twice to turn on the power.
1. Pointer meter
⒈ The reading accuracy of the pointer meter is poor, but the process of the pointer swing is more intuitive, and its swing speed can sometimes objectively reflect the size of the measured value (such as the slight jitter when the TV data bus (SDL) transmits data); digital meter reading is intuitive, but The process of digital change looks disorganized and difficult to watch.
⒉ Pointer watches generally have two batteries, one is 1.5V low voltage, and the other is 9V or 15V high voltage. The black test lead is the positive side of the red test lead. Digital meters typically use 6V or 9V batteries. In the resistance mode, the output current of the pointer meter is much larger than that of the digital meter. Use the R×1Ω range to make the loudspeaker “click”, and the R×10kΩ range to even light up the light-emitting diodes (LEDs).
⒊In 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 and micro-current situations cannot even be measured accurately because the internal resistance can 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 voltage range of the digital meter has a large resistance, at least in the megohm level, and has little effect on the circuit under test. However, the high output impedance makes it vulnerable to induced voltage, and in some occasions with strong electromagnetic interference, the measurement data may be wrong.
2. Measurement technology
1. Measure speakers, headphones and dynamic microphones:
Using R×1Ω, connect either test lead to one end and the other end to the other test lead. "Dah" sound. If there is no sound, the coil is broken. If the sound is small and sharp, there is a problem with the friction coil and it cannot be used.
2. Capacitance measurement:
Use the resistance gear, select the appropriate range according to the capacitance capacity, and pay attention to the positive electrode of the capacitor of the black test lead of the electrolytic capacitor when measuring.
① Estimation of microwave power level capacity: It can be determined by experience or with reference 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, a 100μF/250V capacitor can be estimated by using a 100μF/25V capacitor as a reference. As long as the maximum amplitudes of their pointer swings are the same, it can be concluded that the capacities are the same.
② Estimating the capacitance of pico-farad capacitors: Use the R×10kΩ range, but only the capacitance above 1000pF can be measured. For 1000pF or slightly larger capacitors, as long as the needle wiggles a little, the capacity is considered sufficient.
③Measure whether the capacitor is leaking: For capacitors above 1000 microfarads, you can first use R×10Ω to quickly charge, initially estimate the capacitance, and then change to R×1kΩ to continue measuring for a while, and then the pointer should not return, but should stop at or very close to ∞, otherwise leaks will occur. For some timing or oscillating capacitors below tens of microfarads (such as oscillating capacitors of color TV switching power supplies), their leakage characteristics are very demanding, and they cannot be used as long as there is slight leakage. Then continue the measurement with the R×10kΩ gear, the pointer should stop at ∞ instead of going back.
3. The quality of road test diodes, triodes and voltage regulators:
Because in the actual circuit, the bias resistance of the transistor or the peripheral resistance of the diode and the Zener tube is generally relatively large, mostly in the hundreds of thousands. Ohm or more, so that we can use the R×10Ω or R×1Ω gear of the multimeter to measure the quality of the PN junction on the road. 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, when the forward resistance is at R, the pointer should indicate about 200Ω when measuring in the ×10Ω gear, and about 30Ω when measuring in the R×1Ω gear (there may be slight differences according to the phenotype). 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 the tube. This method is particularly effective for repairs, where bad pipes can be quickly found, and even pipes that have not yet been fully ruptured but whose properties have deteriorated can be detected. For example, if you measure the forward resistance of a PN junction with a small resistance value, if you solder it down and test it with the commonly used R×1kΩ file, it may be normal. In fact, the properties of such tubes have deteriorated. No longer working or unstable.
4. Resistance measurement:
The important thing is to choose the range, the reading is the most accurate. It should be noted that when using the R×10k resistance gear to measure the large resistance value of the megohm level, do not clamp the fingers at both ends of the resistance, so that the resistance of the human body will make the measurement result smaller.
5. Measure the Zener diode:
The voltage regulator value of the Zener diode we usually use is generally greater than 1.5V, and the resistance gear below R×1k of the pointer meter is powered by the 1.5V battery in the table, so the resistance gear lower than R×1k for measuring the Zener tube is like Measure a diode with full unidirectional conductivity. However, the R×10k range of the analog meter is powered by a 9V or 15V battery. When using R×10k to measure the voltage regulator tube whose voltage voltage is less than 9V or 15V, the reverse resistance value will not be ∞, but a certain value. resistance, but this resistance is still much higher than the forward resistance of the zener. In this way, we can initially estimate the quality of the Zener tube. However, a good regulator must have accurate regulation values. How to estimate this voltage regulation value under amateur conditions? It's not difficult, just find another pointer table. The method is: first put the watch in the R×10k gear, and connect the black and red test pens to the cathode and anode of the voltage regulator tube respectively. At this time, simulate the actual working state of the voltage regulator tube, and then put another watch on the voltage range V×10V or V×50V (according to the voltage regulation value), and then connect the red and black test to lead out the black and red test pens of the watch just now. The voltage value measured at the time is basically the voltage regulation value of this Zener tube. "Basic" is said because the bias current of the first watch to the voltage regulator tube is slightly smaller than that in normal use, so the measured voltage regulation value will be slightly larger, but the difference is basically the same. This method can only estimate the voltage regulator whose voltage regulation value is less than the voltage of the pointer meter's high-voltage battery. If the voltage regulation value of the voltage regulator is too high, it can only be measured by using an external power supply (so that when we choose a pointer meter, it is more suitable to choose a 15V high-voltage battery than 9V).
6. Measure the triode:
Usually we use R×1kΩ file, no matter it is NPN tube or PNP tube, no matter it is low power, medium power or high power tube, the be junction cb junction should be measured with a diode. The same unidirectional conductivity, the reverse resistance is infinite , the forward resistance is around 10K. To further estimate the quality of the tube characteristics, if necessary, the resistance gear should be replaced for multiple measurements. The method is: set the R×10Ω gear to measure the forward conduction resistance of the PN junction at about 200Ω; set the R×1Ω gear to measure the forward conduction resistance of the PN junction to be about 30Ω. (The above is the measured data of the 47-type meter. Other models are slightly different. You can test a few better tubes to summarize, so that you know what you have in mind.) If the reading is too large, it can be concluded that the characteristics of the tube are not good. it is good. You can also put the meter in R×10kΩ and test again. For tubes 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 may have 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). But when measuring the resistance between ce or ec with a 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 do not apply to germanium tubes. In addition, the so-called "reverse" refers to the PN junction, and the direction of the NPN tube and the PNP tube is actually different.
