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A multimeter is also called a multimeter, a three-meter meter, and a multiplex meter. It refers to a meter that can be used to measure AC and DC voltage, resistance, DC current, and audio level. Advanced multimeters can also be used to measure AC current, capacitance, inductance, and some semiconductor parameters (eg, β). All in all, it is an essential tool for electricians and radio makers. Xiao Bian through the collection of information, the following specific introduction to the use of multimeter and use precautions (digital multimeter use).
In general, we should understand the following aspects before using a multimeter (used in AC millivoltmeters):
(1) Be familiar 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 quantity of electricity, the pointer of the multimeter is pointed to zero voltage or zero current.
(3) According to the type and size of the measurement, select the gear and range of the transfer switch to find the corresponding scale line.
The measurement of the voltage aligns the tip of the range selection switch within the five range marked V. If measuring AC voltage should point to V. And so on, if you want to change the resistance, the switch should point to the Ω range. The current should be measured to mA or UA.
(4) Select the location of the test leads.
(5) Know how to read the multimeter Select a suitable range position based on the approximate value of the circuit under test. Note that the index value of the range switch tip is the corresponding value of the full-scale reading of the gauge on the head. When reading the table, the actual value can be read out as long as it is converted accordingly.
For example, the maximum value of dry batteries is 1.5V per section, so it can be placed in the 5V range. At this time, 500 readings of the full-scale reading on the panel should be made. That is, 100 times smaller. If the hands are pointing at 300 marks, read as 3V. Except for the resistance file, all files of the range switch read the measurement results according to this method.
How to use the multimeter 1. Measuring voltage: When measuring the voltage (or current), select a good range. If you use a small range to measure a large voltage, there is a danger of burning the meter. If you use a large range to measure a small voltage, the pointer is deflected. Too small to read. The range should be chosen so that the pointer is deflected to about 2/3 of full scale. In actual measurement, when it is not possible to determine the approximate value of the measured voltage, the switch can be set to the maximum range first, and then the range can be reduced step by step to the appropriate position. When measuring the voltage generally, connect the meter pen to the circuit under test.
a. Measurement of AC voltage: Place one switch of the multimeter in AC and DC voltage range, and another switch in the appropriate range of AC voltage. The two pens of the multimeter can be connected in parallel with the circuit under test or load.
b Measurement of DC voltage: Place one switch of the multimeter in AC and DC voltage range, and another switch in the appropriate range of DC voltage, and the “+†meter (red pen) receives high potential, “- "The test leads (black pens) receive a low potential, that is, let the current flow from the "+" meter pen and from the "-" meter pen. If the test leads are reversed, the head pointer will be deflected in the opposite direction and it is easy to knock the pointer.
2. Measuring current: When measuring the DC voltage, place one of the multimeter's switches in the DC current range and the other switch in the appropriate range of 50uA to 500mA. The current range selection and reading methods are the same as the voltage. At this time, attention should be paid to positive and negative polarity. If the test leads are reversed, the hands will counterattack. If you do not know the positive and negative polarity of the circuit, you can put Wan Tian meter on the largest scale, quickly test the circuit under test, see how the stylus deflection, you can determine the positive and negative polarity, when measuring AC voltage, the table pen There is no difference between positive and negative. During the measurement, the circuit must be disconnected first. Then follow the direction of the current from “+†to “-†to connect the multimeter in series to the circuit under test. That is, the current flows in from the red meter and flows out from the black meter.
When measuring the DC current, if the multimeter and the load are connected in parallel, the internal resistance of the meter will be very small, which will cause the short circuit to burn the meter. The reading method is as follows: Actual value = indication value × span / full deviation 3. Resistance measurement: When using a multimeter to measure resistance, the following method should be used:
a Mechanical zero adjustment. Before use, you should first adjust the pointer positioning screw to zero the current display to avoid unnecessary errors.
b Select the appropriate override file. The scale of the multimeter's ohm file is uneven, so the selection of the override file should make it suitable for the pointer to stay in the dilute part of the scale line, and the closer the pointer is to the middle of the scale, the more accurate the reading. In general, the pointer should be between 1/3 and 2/3 of the scale.
c ohm zero. Before measuring the resistance, the two test leads should be short-circuited and the “ohm (electrical) zero adjustment knob†should be adjusted at the same time so that the pointer just points to the zero position to the right of the ohmic graticule line. If the pointer cannot be set to zero, the battery voltage is insufficient or there is a problem inside the instrument. And every time you change the override file, you must perform ohmic zero again to ensure accurate measurements.
d Reading: The reading of the meter multiplied by the magnification 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 the meter head), a dial, a range selection switch, a meter pen, and the like. When using the range selection switch to direct current range, the ammeter M is connected with some shunt resistors to achieve the purpose of expanding the range, so that it becomes an ammeter having several sizes and different ranges. The measurement result depends on the reading of the DC current scale on the dial. The second line on the dial is usually the current scale. Similarly, if the range selection switch points to the DC voltage range, the header is connected in series with additional resistors (the principle of dividing the voltage with a series resistor makes it a multi-volt meter). The reading depends on the DC voltage scale on the dial. Most multimeters use a single scale for voltage and current. 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 a set of batteries must be added during the test. When the selection switch points to the resistance range, the first row of resistance-specific scale readings can be found on the dial.
Note on the use of the multimeter There are many types of multimeters, but their basic usage is the same. Take the MF30 multimeter as an example to introduce how to use it.
Preparation before use First, before using the multimeter, you must be familiar with the function of the range selection switch. What do you want to measure? How to measure? Then set the range selection switch to the desired test position. Must not misplace gears. For example, when the voltage is measured and the selector switch is set to the current or resistance level by mistake, it is easy to burn the meter head.
Second, observe whether the hands are in the zero position before use. If you do not refer to the zero position, use a screwdriver to adjust the mechanical zero adjustment screw on the meter head to return the hands to zero (usually without having to adjust each time). The red pen should be inserted into the positive socket, and the black pen should be inserted into the negative socket.
Multimeter Usage Precautions (1) When using the multimeter, do not touch the metal part of the pen with your hands. This can ensure the accuracy of measurement and ensure personal safety on the other hand.
(2) When using the multimeter, it must be placed horizontally so as not to cause errors. At the same time, it is also necessary to take care to avoid the influence of external magnetic fields on the multimeter.
(3) When measuring a certain amount of power, it is not possible to shift gears while measuring, especially when measuring high voltage or high current. Otherwise, it will destroy the multimeter. If you need to shift gears, you should disconnect the test leads before changing gears.
(4) After the multimeter is used up, the switch should be placed in the maximum block of AC voltage. If you do not use it for a long period of time, you should take out the battery inside the multimeter to prevent the battery from corroding other devices in the watch.
At present, they have their own conveniences. It is difficult to say who is good or bad. It is best to have a pointer and a digital one. Amateur electronic production has a pointer type MF30 multimeter, which is a classic model. There are also veteran MF500 multimeters, cheap MF50 multimeters, generally available at the telecommunications store.
Today's multimeter adds a lot of new features, especially digital multimeters, such as measuring capacitance, transistor amplification, diode drop, etc., and even a talking digital multimeter that can broadcast measurement results in a language. Digital multimeter also has many classic models, such as DT830C, DT890D, etc., behind the suffix represents the functional difference, which DT830C has bought more than 30 yuan a, cheap enough.
Basically, A- is used to represent the measured DC current. The general milliampere and Ampere stalls are divided into several segments. V- indicates DC voltage measurement. The advanced multimeter has a millivolt file and the voltage file is divided into several files. V~ is used to measure AC voltage. A ~ test AC current. Ω ohms measured resistance, for the pointer multimeter, once again change the resistance file to do a zero. Zero adjustment is to put the multimeter's red and black table pens together, and then turn the zero button so that the pointer points to the zero position. hFE is to measure the current amplification factor of the triode, as long as the three pins of the triode are inserted into corresponding holes in 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 and the right end is zero. The scale is uneven. There are R×1, R×10, R×100, R×1K, and R×10K files in the resistance range, indicating that the indication of the scale must be multiplied by the multiple, to obtain the actual resistance value (in ohms).
The biggest feature of summing up the multimeter is that there is a range change switch, and each function is * this switch to switch. At present, the common multimeters in the market have two types, analog and digital, and they have their own advantages. This article mainly introduces the use of the multimeter, that is, how to use a multimeter to measure AC and DC voltage, resistance, and DC current. It also gives a brief introduction to the preparation and precautions that need to be taken before using the multimeter.
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