How to use pointer/clamp/ordinary multimeter

　　Precautions for using a multimeter

　　(1) Before using the multimeter, you should first perform "mechanical zero adjustment", that is, when there is no electricity to be measured, make the multimeter pointer point to the position of zero voltage or zero current.

　　(2) When using the multimeter, do not touch the metal part of the test lead with your hands. This can ensure the accuracy of the measurement on the one hand, and personal safety on the other hand.

　　(3) When measuring a certain amount of electricity, you cannot change gears while measuring, especially when measuring high voltage or large current. Otherwise, the multimeter will be damaged. If you need to change gears, you should disconnect the test leads first, and then measure after changing gears.

　　(4) When using the multimeter, it must be placed horizontally to avoid errors. At the same time, you must also pay attention to avoid the influence of external magnetic fields on the multimeter.

　(5) After using the multimeter, the conversion switch should be set to the maximum AC voltage. If the multimeter is not used for a long time, the battery inside the multimeter should be removed to prevent the battery from corroding other components in the meter.

Use of Ohm Block

　　1. Choose the right magnification. When measuring resistance with an ohmmeter, you should choose the right magnification so that the pointer indicates near the midpoint. It is best not to use the left third of the scale, as the scale density in this part is poor.

　　2. Adjust to zero before use. 3.

　　Do not measure with power on.

　　4. The measured resistor cannot have parallel branches.

　　5. When measuring the equivalent resistance of polar components such as transistors and electrolytic capacitors, you must pay attention to the polarity of the two pens.

　　6. When measuring the equivalent resistance of nonlinear components with different magnifications of the ohmmeter, the measured resistance values ​​are different. This is because the midpoint resistance and full-scale current of each gear are different. In mechanical meters, generally, the smaller the magnification, the smaller the measured resistance value.

　　When the multimeter measures DC

　　1. Perform mechanical zeroing.

　　2. Select the appropriate range.

　　3. When using the current range of a multimeter to measure current, the multimeter should be connected in series in the circuit being measured , because only a series connection can make the current flowing through the ammeter the same as the current of the branch being measured. When measuring, the branch being measured should be disconnected, and the red and black test leads of the multimeter should be connected in series between the two disconnected points. Special attention should be paid to the fact that the ammeter cannot be connected in parallel in the circuit being measured. Doing so is very dangerous and can easily burn the multimeter.

　　4. Pay attention to the polarity of the measured electrical quantity.

　　5. Use the scale and reading correctly.

　　6. When the 2.5a range of DC current is selected, the red test lead of the multimeter should be inserted into the 2.5a measurement jack, and the range switch can be set to any range of the DC current range.

　　7. If the DC current measured by the quilt is greater than 2.5a, the 2.5a range can be expanded to the 5a range. The method is very simple. The user can connect a 0.24 ohm resistor between the "2.5A" jack and the black test lead jack, so that the gear becomes the 5A current gear. The connected 0.24A resistor should be a wire wound resistor of more than 2W. If the power is too small, it will burn out.

Use a digital multimeter to determine the transistor pins (graphic tutorial)

     Nowadays, digital multimeters are very popular electrical and electronic measuring tools. They are easy to use and accurate, and are loved by maintenance personnel and electronic enthusiasts. But some friends say that it is not as good as a pointer multimeter when measuring some parts, such as transistors. I think digital multimeters are more convenient when measuring transistors. The following is my own experience. I usually judge small transistor devices in this way. You may try it to see if it is easy to use or correct. If you have any comments or questions, please send me an email. I
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　  
have some BC337 transistors on hand. Suppose I don’t know whether it is a pnp tube or an npn tube.

Figure 1 Transistor

We know that the inside of a triode is like two diodes combined. Its form is like the figure below. The middle one is the base (pole b).

Figure 2 The internal structure of a transistor

First, we need to find the base and determine whether it is a pnp or npn tube. As can be seen from the above figure, the base of the pnp tube is the common point of the two negative poles, and the base of the npn tube is the common point of the two positive poles. At this time, we can use the diode range of the digital multimeter to measure the base, see Figure 3. For the pnp tube, when the black test lead (connected to the negative pole of the battery in the meter) is on the base, the red test lead is used to measure the other two poles. Generally, the reading is small (generally 0.5-0.8) with little difference. If the test leads are connected in reverse, it will be a larger reading (generally 1). For the npn meter, the red test lead (connected to the positive pole of the battery in the meter) is connected to the base. From Figures 4 and 5, we can know that the BC337 on hand is an npn tube, and the middle pin is the base.

Figure 3 Diode measurement mode of the multimeter

Figure 4 Determining the b-pole and tube type of bc337 (1) Figure 4 Determining the b-pole and tube type of bc337 (2)

     找到基极和知道是什么类型的管子后，就可以来判断发射极和集电极了。如果使用指针式万用表到了这个步可能就要用到两只手了，甚至有朋友会用到嘴舌，可以说是蛮麻烦的。而利用数字表的三伋管hfe档（hfe 测量三极管直流放大倍数）去测就方便多了，当然你也可以省去上面的步骤直接用hfe去测出三极管的管脚极性，我自己则认为还是加上上面的步骤方便准确一些。

     把万用表打到hfe档上，bc337卑下到npn的小孔上，b极对上面的b字母。读数，再把它的另二脚反转，再读数。读数较大的那次极性就对上表上所标的字母，这时就对着字母去认bc337的c，e极。学会了，其它的三极管也就一样这样做了，方便快速。

Figure 5 HFE range on the multimeter

Figure 6 Judging the poles of c and e

Figure 7 Judging the poles c and e

Basic usage of multimeter

1. Basic usage of multimeter

There are many types and structures of multimeters. When using them, only by mastering the correct method can you ensure the accuracy of the test results and guarantee the safety of people and equipment!

(1) Use of sockets and conversion switches

First, you need to select the position of the jack or switch according to the purpose of the test. Since the voltage, current and resistance are measured alternately during use, you must not forget to change gears. Do not use the gear for measuring current or resistance to negotiate voltage. If you use DC current or resistance to measure 220 AC voltage, the multimeter will burn out immediately.

(2) Use of test leads

The multimeter has two pens, red and black. You need to know how to use them properly. If you connect them in the wrong position, it will lead to the possibility of test errors or burn out the meter. Generally, the red pen is "+" and the black pen is "-".

When inserting the probe into the multimeter jack, be sure to strictly follow the color and positive and negative. When measuring DC voltage or DC current, be sure to pay attention to the positive and negative polarity. When there is no current, the probe is connected in series with the circuit. When measuring voltage, the probe is connected in parallel with the circuit. Don't make a mistake.

(3) How to read correctly

Before using the multimeter, check whether the pointer is at zero. If it is not at zero, adjust the mechanical regulator on the cover to zero.

The multimeter has multiple scales. You must recognize the corresponding reading scale. You cannot mix the AC and DC scales for the sake of convenience, and you must not make mistakes.

The multimeter has multiple ranges for the same measurement item. For example, the DC voltage ranges are 1V, 10V, 15V, 25V, 100V, 500V, etc. The range selection should make the pointer close to 2/3 of the full scale. When measuring resistance, the pointer should be pointed to the center value of the range, so that the measurement can be accurate.

2. Measurement of commonly used devices

(1) Measurement of resistance

When measuring resistance with a multimeter, you should first short-circuit the test leads, turn the zeroing potentiometer to zero, and make the pointer at the ohm zero position. And you need to readjust the zeroing potentiometer to zero after each gear change. When selecting the ohm gear, try to choose a position where the resistance value to be measured is close to the resistance reading in the center of the dial to improve the accuracy of the test results; if the resistor is on the circuit board, one of the legs should be unsoldered before testing, otherwise the resistor has other shunt devices and the reading is inaccurate! When measuring resistance, do not touch the test leads and the pins of the resistor with your fingers to prevent the shunt of human body resistance and increase the error~

(2) Measure resistance value to ground

The so-called resistance measurement to ground means to connect the red probe of the multimeter to the ground, and the black probe to one point of the measured component, measure the resistance value of the point to ground in the circuit, and compare it with the normal resistance value to determine the scope of the fault. When measuring, the resistance gear is set to R*1k. When the resistance value of the measured point is significantly different from the normal value, it means that there is a fault in this part of the circuit, such as leakage of filter air, open circuit of resistor or damage of integrated IC, etc.

(3) Transistor measurement

Switch the multimeter to the ohm range R*100 or R*1K to measure the diode. Do not use the R*10 or R*10K range. The former is because one of the two resistors is too small and the other is too large, the current passing through the diode is too large, and the diode is easily damaged. The latter is because the internal voltage is high and it is easy to break through the diode with low withstand voltage. If the measured resistance is only a few hundred ohms to a few thousand ohms (forward resistance), the red and black test leads should be swapped and measured again. If the resistance value that is not measured at this time should be a few hundred kiloohms (reverse resistance), it means that this diode can be used. When measuring the forward resistance value, the end measured by the red test lead is the negative pole of the diode, and the end measured by the black test lead is the positive pole of the diode~ (the unidirectional conductive characteristic of the diode)~