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The multimeter is also called a multimeter, a three-meter, and a multiplexer. It is a multi-function, multi-range measuring instrument. The multimeter has a wide range of uses. This article tells you about the basic use of the multimeter.
What is a Multimeter
The multimeter is also called multi-meter, three-meter, and multiplex meter. It is a multi-function, multi-range measuring instrument. The general multimeter can measure DC current, DC voltage, AC voltage, resistance and audio level, etc. AC current, capacitance, inductance and some parameters of the semiconductor. It is a simple and practical measuring instrument. Today’s most popular common multimeters are digital multimeters, and pointer multimeters are rarely used. Digital multimeters are relatively simple measuring instruments. As a multi-purpose electronic measuring instrument, it generally includes functions such as an ammeter, a voltmeter, an ohmmeter, and the like, and is sometimes referred to as a multimeter, a multimeter, a multimeter, or a three-meter. The multimeter has a wide range of uses. Let’s talk about the basic use of the multimeter.
Considerations for using the multimeter
- Before using the multimeter, perform “mechanical zeroing”, that is, when there is no measured power, make the multimeter pointer point to zero voltage or zero current.
- In the process of using the multimeter, the metal part of the test pen cannot be touched by hand, so that the measurement can be ensured on the one hand, and the personal safety can be ensured on the other hand.
- When measuring a certain amount of electricity, it is not possible to shift gears while measuring, especially when measuring high voltage or high current. Otherwise, the multimeter will be destroyed. If you need to change gears, you should first disconnect the test leads and then change the gears before measuring.
- When the multimeter is used, it must be placed horizontally to avoid errors. At the same time, we must also pay attention to avoiding the influence of external magnetic field on the multimeter.
- When the multimeter is used, the switch should be placed at the maximum limit of the AC voltage. If it is not used for a long time, the battery inside the multimeter should be taken out to prevent the battery from corroding other devices in the watch.
When using the analog multimeter, insert one end of the two measuring pens into the measuring end according to the requirements of red positive (+) and black negative (-), and then confirm whether the pointer is at the “0” position. The pointer should be aligned with the end line on the left side of the dial. If it is not consistent, a zero adjustment is required. Before making current and voltage measurements, first estimate the range of current and voltage to be measured, first set to a larger gear, and then adjust to the appropriate gear to avoid excessive current burning the multimeter.
When making measurements, consider the effects of the internal resistance of the multimeter. For example, in order to measure the voltage, the test leads are connected to the circuit under test. At this time, a current flows through the resistors in the multimeter, which has a certain influence on the measured values. When measuring the voltage at the same point, if different gears are used, the internal resistance of the multimeter is different and the degree of influence is different.
When measuring the transistor electronic circuit, it is better to select the internal resistance of 20kΩ/V with DC block. This value is usually marked on the dial of the multimeter. In addition, transistor circuits often need to measure low-value voltages, such as 0.1V, when the selected multimeter has a measurement range of 1V.
How to use the multimeter
Use of ohms
- First, choose the appropriate magnification. When measuring the resistance in the ohmmeter, select the appropriate magnification so that the pointer is near the median. It is best not to use the left third of the scale, which is very dense.
- Second, you must zero before using.
- Third, can not be powered measurements.
- Fourth, the measured resistance can not have parallel branches.
- Fifth，when measuring the equivalent resistance of polar components such as transistors and electrolytic capacitors, the polarity of the two pens must be noted.
- Sixth, when measuring the equivalent resistance of the nonlinear component with the ohmmeter of different multipliers of the multimeter, the measured resistance values are different. This is caused by the difference in the median resistance and full-scale current of each gear. In mechanical watches, the smaller the general magnification, the smaller the measured resistance.
Use of diode block
First, we will learn the simplest diode file, rotate the multimeter’s knob to the position where the diode identifier is located, then short the two test leads, you will hear the buzzer sound, which means the file can be used normally. In addition, it can be determined that the resistance between the two test leads is zero. In life, it is often used to measure whether the circuit has an open circuit and whether the device is electrically connected. Since the file is a diode file, we can use this file to measure the diode. Pressure drop, the red test pen is placed at the anode of the diode during measurement, and the black test pen is placed at the cathode of the diode. The voltage drop value can be directly displayed on the display screen. In addition, the diode can be used to determine whether the diode is a silicon tube or a fistula. And if the diode is damaged.
Use of resistance files
From the diode position clockwise, you can see the resistance file. There is an Ω symbol to indicate the measurement resistance. When measuring, we should first judge the size of the selected resistor, and then select the knob to select the range. If you don’t know how big the resistor is, you can Select an intermediate gear to try to measure, and then change the gear according to the measured estimated value. We use 1K resistor to test, so change the pointer to 2K, then read the value directly on the display. As for the needle part, due to There is no positive or negative resistance, so the red and black test leads can be connected to both sides of the resistor (do not touch the test leads when measuring large resistance), regardless of positive or negative.
Use of triode files
Rotate the knob clockwise to reach the hFE gear position. This gear position is the measurement parameter of the triode amplification parameter. There are generally two types of jacks, one is NPN and the other is PNP. Before we measure, we must clearly distinguish Is the NPN type transistor or the PNP type transistor? We use the NPN type here. Since the transistor has three pins, the function of each pin is also different. So after we clear the pin, insert it correctly according to the pin name. The measuring jack can directly read the magnification of the triode on the display.
Use of voltage files
Rotate the measuring knob again, the next gear is the voltage gear. In this multimeter, both the AC and DC gears are in this range, so before measuring, we should first judge whether our measuring voltage is AC or DC. If the selection type is not Test type, you can press AC and DC to change the gear position (that is, the multimeter DC/AC conversion gear position, some multimeter DC and AC are separate, this does not change the gear button), and choose the appropriate range, if before the measurement I don’t know what the voltage is to be measured. At this time, I must choose the gear with the largest range. The common communication is the AC used by the family. The voltage is 220v. The typical DC power is the output voltage of our computer USB socket. It is DC. 5v.
Use of frequency meter
Then rotate clockwise, then the measurement frequency. The 10MHz on the dial indicates that the maximum measurement frequency is 10KHz. When measuring, connect the meter to the two ends of the frequency meter. The measured value can be read directly on the display. The test leads should be connected correctly to the positive end of the signal source, and the negative pole should be connected to the negative side of the signal source.
Use of capacitor files
Sometimes we will use a multimeter to measure the capacitance. The first step is to determine the size of the capacitor and select the multimeter range. After the selection, put the test leads on both ends of the capacitor, without dividing the positive and negative poles. If the polar capacitors can also be directly measured, do not distinguish Positive and negative, the size of the capacitor can be read directly on the display. In addition, it is necessary to note that when measuring the capacitance, the red test pen needs to be inserted into the jack marked mA. Only the result can be measured on this jack.
Tips for measuring DC when the multimeter is used
- Perform mechanical zeroing.
- Choose the appropriate range gear.
- When measuring the current using the multimeter current block, the multimeter should be connected in series to the subtest circuit, because only the series connection can make the current flowing through the ammeter the same as the measured branch current. When measuring, disconnect the measured branch and connect the multimeter red and black test leads between the two points that are disconnected. In particular, it should be noted that the ammeter cannot be connected to the sub-test circuit. This is very dangerous, and it is easy to burn the meter.
- Pay attention to the polarity of the measured power.
- Correct use of scales and readings.
- When selecting a 2.5A block with DC current, the multimeter red test pen should be inserted in the 2.5A measurement jack, and the range switch can be placed on any range of the DC current block.
- If the DC current measured by the submeter is greater than 2.5A, the 2.5A gear can be expanded to 5A gear. 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 a 5A current block. The 0.24A resistor connected should be selected with a wirewound resistor of 2W or more. If the power is too small, it will burn out.
The current multimeters are divided into pointers and digits. They have their own conveniences. It is hard to say who is good or who is bad. It is better to have one for each pointer and digital. Amateur electronics can have a pointer-type MF30 multimeter, which is a classic model. There is also a veteran MF500 multimeter, a cheap MF50 multimeter, which can generally be bought at a telecommunications store.
The three basic functions of the multimeter are to measure resistance, voltage, and current, so the older generation called it a three-meter. Today’s multimeters add a lot of new features, especially digital multimeters, such as measuring capacitance values, triode amplification, diode voltage drop, etc., and a talking digital multimeter that can broadcast the measurement results in language. (In fact, it is not very difficult, I once wanted to use MCU and voice circuit to do one)
Digital multimeters also have many classic models, such as DT830C, DT830C, DT890D, etc. The suffixes on the back indicate functional differences. The DT830C has already bought more than 30 yuan, which is cheap enough. Bitbaby has installed a MF50 multimeter in the school. The circuit principle is not complicated. It is just that so many components are not fixed by the printed board, but directly soldered to the wiring board. It is still troublesome for beginners.
The biggest feature of the multimeter is that it has a range switch, and each function is switched by this switch. Basically, A- is used to indicate the DC current. Generally, the milliamp and the amper are divided into several files. V- indicates the DC voltage, the multimeter of the advanced point has a millivolt, and the voltage file is divided into several files. V~ is used to measure the AC voltage. A~ Measure AC current. Ω ohms resistance test, for the pointer multimeter, each time you change the resistance file, you need to do a zero adjustment. Zeroing is to put the multimeter’s red and black pens together, then turn the zero button to point the pointer to zero. hFE is the current amplification factor of the triode. As long as the three pins of the triode are inserted into the corresponding holes on the universal surface plate, the hFE value can be measured. Note that PNP and NPN are different.
The MF30 multimeter is taken as an example to illustrate the reading of the multimeter. The first tick mark is the resistance value indication, the leftmost end is infinity, the right end is zero, and the scale is uneven. The resistance files are R&TImes; 1, R&TImes; 10, R&TImes; 100, R&TImes; 1K, R×10K, respectively, indicating the indication of the scale and multiplying the multiples to obtain the actual resistance value (in ohms).
For example, if a resistance is measured by R×100, the pointer is indicated as “10”, then its resistance value is 10×100=1000, that is, 1K. The second tick mark is shared between the 500V gear and the 500mA gear. It should be noted that the indication principle of the voltage gear and the current gear is different from the resistance gear. For example, the 5V gear indicates that the gear can only measure the voltage below 5V, and the 500mA gear can only measure 500mA. The following currents, if they exceed the range, can damage the multimeter.
Note: The multimeter should be placed horizontally when in use. The red test pen is inserted in the + hole, and the black test pen is inserted into the hole. The test current uses the current file, but the voltage file and the electric block cannot be misused. Others are the same. Otherwise, the fuse in the multimeter is burned, and the meter is damaged. If you don’t know the range beforehand, try to measure with the maximum range, then disconnect the measurement circuit and then shift the gear. If the hands are quickly deflected to the end, the circuit should be disconnected immediately for inspection.
Finally, there is a rule that the multimeter after the appointment is used to set the range switch to the highest level of the AC voltage, in case someone else accidentally measures the 220V mains voltage and is damaged.
A multimeter is a meter used to measure AC and DC voltage, resistance, DC current, and the like. It is an indispensable tool for electrician and radio production. At first glance, the multimeter is very complicated. In fact, it consists of an ammeter (commonly known as a meter), a dial, a range selector switch, a test lead, etc., as shown in Figure 1. When using the range selection switch to direct current range, the current meter M is connected with some shunt resistors to achieve the purpose of expanding the range (Rg is the head resistance), making it an ammeter with several ranges of different sizes. The measurement results are taken by reading the DC current scale on the dial. Usually the second behavior current scale on the dial, as shown in Figure 2. Similarly, if the range selector switch points to the DC voltage range, the meter is connected in series with other resistors (such as R2 and R3, using the principle of series resistor divider to make it a multi-channel voltmeter as shown in Figure 3. The reading depends on The DC voltage scale on the dial. Most multimeter voltages and currents are combined with one scale. If a rectifier is connected to the circuit that measures DC voltage, the AC voltage can be measured. The principle of the resistance is similar to the DC voltage measurement, but only the test. A set of batteries must also be added. When the selector switch points to the resistance range, the first row of resistors can be read on the dial. The multimeter has many models, but the basic method is the same.
This is an example about using multimeter to test resistance — How to Test a Resistance Detection