Multimeter use and use precautions - Solutions - Huaqiang Electronic Network

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In the field of teaching or research, the multimeter is a common measuring instrument. How to use the multimeter? It is necessary for the researcher to master the use of the multimeter and understand the precautions for its use. So what is a multimeter? (Type of spectrum analyzer)

The multimeter is also called a multimeter, a three-meter, and a multiplexer. It refers to a meter that can be used to measure AC/DC voltage, resistance, DC current, and audio level. Advanced multimeters can also be used to measure AC current, capacitance, inductance, and some parameters of the semiconductor (such as β). All in all, it is an essential tool for electrician and radio production. Xiaobian collects and organizes the materials. Here is a detailed introduction to the use of the multimeter and the precautions for use (use of the digital multimeter).

Generally, we should understand the following aspects before using a multimeter (used in AC millivoltmeter):

(1) Familiarize with the meaning of the symbols on the dial and the main functions of each knob and selector switch.

(2) Perform mechanical zero adjustment. That is, when there is no measured power, the multimeter pointer is pointed at the zero voltage or zero current position.

(3) According to the type and size of the measurement, select the gear position and range of the transfer switch to find the corresponding tick mark.

The measurement of the voltage aligns the tip of the range selector switch to the five-range range marked V. If the AC voltage is measured, it should be pointed to V. And so on, if you want to change the resistance, the switch should point to the Ω range. The current should be directed to mA or UA.

(4) Select the position of the test lead jack.

(5) How to understand the reading of the multimeter

Select an appropriate range position based on the approximate value of the circuit under test. Note that the index value of the span of the range switch is the corresponding value of the full scale reading of the meter on the meter head. When reading the table, the real value can be read out according to the calculation.

For example, the dry battery has a maximum value of 1.5V per section, so it can be placed in the 5V range. At this time, 500 of the full scale reading of the needle on the panel should be read as 5. That is to reduce by 100 times. If the hands are at 300 marks, they are read as 3V. In addition to the resistance file, all the range switches are read in this way.

How to use the multimeter

1. Measure voltage: When measuring voltage (or current), select a good range. If you use a small range to measure large voltage, there is a danger of burning the watch. If you use a large amount of process to measure small voltage, the pointer deflection is too small to reading. The range should be chosen to deflect the pointer to about 2/3 of the full scale. In the actual measurement, when the approximate value of the measured voltage cannot be determined, the switch can be first dialed to the maximum range, and then the range can be reduced to the appropriate position. Generally, when measuring voltage, connect the meter to the circuit under test.

a AC voltage measurement: put one switch of the multimeter in the AC and DC voltage files, and the other switch is placed on the appropriate range of the AC voltage. The multimeter's two test leads and the circuit under test or the load can be connected in parallel.

b DC voltage measurement: put one switch of the multimeter in the AC and DC voltage files, another switch on the appropriate range of DC voltage, and the “+” meter (red pen) is connected to the high potential, “- The test pen (black pen) is connected to the low potential, that is, the current flows from the "+" test pen and flows out from the "-" test pen. If the test leads are reversed, the pointer of the watch will deflect in the opposite direction, which is easy to bend the pointer.

2. Measuring current: When measuring DC voltage, put one switch of the multimeter in DC current, and the other switch is placed on the appropriate range of 50uA to 500mA. The range selection and reading method of current is the same as voltage. At this time, you should pay attention to the positive and negative polarity. If the test leads are reversed, the hands will be counter-attacked. If you don't know the positive and negative polarity of the circuit, you can put the metering range on the maximum file, and try it on the circuit under test. If you see how the pen pin is deflected, you can judge the positive and negative polarity. When measuring the AC voltage, the test pen There is no positive or negative. The circuit must be disconnected first, and then the multimeter is connected in series to the circuit under test according to the current from "+" to "-", that is, the current flows from the red meter pen and flows out from the black meter pen.

When measuring DC current, if the multimeter is connected in parallel with the load, the internal resistance of the meter head will be small, which will cause the short circuit to burn the instrument. The reading method is as follows: actual value = indication value × range / full deviation

3. Measuring resistance: When measuring resistance with a multimeter, it should be done as follows:

a mechanical zero adjustment. Before use, the pointer positioning screw should be adjusted so that the current is zero, avoiding unnecessary errors.

bSelect the appropriate magnification file. The multimeter's ohmic scale is not uniform, so the magnification should be chosen so that the pointer stays in the thinner part of the scale, and the closer the pointer is to the middle of the scale, the more accurate the reading. Under normal circumstances, the pointer should be pointed between 1/3~2/3 of the scale.

c ohms zero. Before measuring the resistance, short the two test leads and adjust the “ohmic (electrical) zero adjustment knob” so that the pointer just points to the zero position to the right of the ohmic scale. If the pointer cannot be adjusted to zero, the battery voltage is insufficient or there is a problem inside the meter. And every time you change the magnification file, you must perform ohms zero again to ensure accurate measurement.

d Reading: The reading of the meter is multiplied by the magnification, which is the resistance of the measured resistance.

At first glance, the multimeter is very complicated. In fact, it is composed of an ammeter (commonly known as a meter), a dial, a range selection switch, a test lead, and the like. 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, 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 on the dial is the current scale. Similarly, if the range selector switch points to the DC voltage range, the meter is connected in series with another resistor (using the principle of series resistor divider to make it a multi-channel voltmeter). The reading depends on the DC voltage scale on the dial. Most multimeter voltages and currents use one scale. If a rectifier is connected to the circuit that measures the DC voltage, the AC voltage can be measured. The principle of measuring resistance is similar to that of measuring DC voltage, but only one battery is required for testing. When the selector switch points to the resistance range, the first row of resistance-specific scale readings can be found on the dial.

Considerations for using the multimeter

There are many models of the multimeter, but the basic usage is the same. Now take the MF30 multimeter as an example to introduce its use.

Preparation before use First, before using the multimeter, you must be familiar with the role of the range selector switch. Clearly what to measure? How to measure? Then set the range selector switch to the position where the test file is needed. Do not mistake the gear. For example, when the voltage is measured incorrectly, the selector switch is placed in the current or resistance file, and the meter head is easily burned out.

Second, observe whether the hands indicate the zero position before use. If you do not refer to the zero position, you can use a screwdriver to adjust the mechanical zero adjustment screw on the meter head to return the needle to zero (it is usually not necessary to adjust it every time). The red test pen should be inserted into the positive socket and the black test pen should be inserted into the negative socket.

Multimeter usage precautions

(1) 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.

(2) 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.

(3) When measuring a certain amount of electricity, it is not possible to shift gears while measuring, especially when measuring high voltage or large 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.

(4) 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.

At present, 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 one. 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.

Today's multimeters add a lot of new features, especially digital multimeters, such as measuring capacitance values, triode amplification, diode drop, etc., and a talking digital multimeter that can broadcast the measurement results in language. Digital multimeters also have many classic models, such as DT830C, DT890D, etc. The suffixes on the back indicate functional differences. The DT830C has already bought more than 30 yuan, which is cheap enough.

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 measurement. The multimeter of the advanced point has a millivolt file, and the voltage file is also divided into several files. V~ is used to measure the AC voltage. A~ Measure AC current. Ω ohm test resistance, 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 following uses the MF30 multimeter 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 file has R×1, R×10, R×100, R×1K, and R×10K, which respectively indicate the multiplication of the indication of the scale, and then the actual resistance value (in ohms) is obtained.

The biggest feature of the multimeter is that it has a range switch, and each function is * this switch to switch. At present, the common multimeters on the market have both pointer and digital, each of which has advantages. This article mainly introduces the use of the multimeter, that is, how to apply the multimeter to measure the AC and DC voltage, resistance, DC current, and a brief introduction to the preparations and precautions before using the multimeter.