是万用电表的简称，它是我们电子制作中一个必不可少的工具。 Multimeter simulator is the abbreviation of multimeter , it is an indispensable tool in our electronic production. The multimeter can measure current, voltage, resistance, and some can also measure the magnification of the triode, frequency, capacitance value, logic potential, decibel value, etc. There are many types of multimeters, and the most popular are mechanical pointer and digital multimeters. They each have advantages. For electronic beginners, the analog multimeter is recommended, because it is helpful for us to familiarize ourselves with some electronic knowledge principles. Below we introduce the principles and use of some mechanical pointer multimeters. The basic principle of a multimeter is to use a sensitive magnetoelectric DC ammeter (microampere meter) as the meter head. When a small current passes through the meter head, there will be a current indication. However, the meter head cannot pass large current, so you must shunt or step down some resistors in parallel and in series on the meter head to measure the current, voltage, and resistance in the circuit. Introduced below. An appropriate resistor (called a shunt resistor) is shunted in parallel with the meter head to expand the current range. Changing the resistance of the shunt resistor can change the current measurement range. An appropriate resistor (called a doubling resistor) is connected in series to the meter head to reduce the voltage, and the voltage range can be extended. Changing the resistance of the multiplier can change the measurement range of the voltage. Because the meter head is a DC meter, when measuring AC, you need to install a parallel and serial half-wave rectifier circuit to rectify the AC into DC and then pass the meter head, so you can measure the AC voltage according to the size of the DC power. The method of extending the AC voltage range is similar to the DC voltage range. Appropriate resistance is connected in parallel and in series on the meter head, and a battery is connected in series at the same time, so that the current passes through the measured resistance. According to the magnitude of the current, the resistance value can be measured. Changing the resistance of the shunt resistor can change the range of the resistor.
的使用万用表（以105型为例）的表盘通过转换开关的旋钮来改变测量项目和测量量程。 The dial of the multimeter emulator uses a multimeter (take 105 as an example). The dial of the switch is used to change the measurement item and measurement range. The mechanical zero knob is used to keep the pointer at the left zero position at rest. The "Ω" zero adjustment knob is used to align the pointer to the right zero position when measuring resistance to ensure accurate measurement values.
The measurement range of the multimeter is as follows:
DC voltage: 5 levels—0-6V; 0-30V; 0-150V; 0-300V; 0-600V.
AC voltage: 5 levels—0-6V; 0-30V; 0-150V; 0-300V; 0-600V
DC current: 3 levels—0-3mA; 0-30mA; 0-300mA.
Resistance: divided into 5 levels—R * 1; R * 10; R * 100; R * 1K; R * 10K
Measure the resistance:-first put the meter stick together to short circuit, make the pointer deflect to the right, and then adjust the "Ω" zero adjustment knob to make the pointer just reach 0. Then touch the two meter bars to the two ends of the resistance (or circuit) to be measured, read the pointer's reading on the ohm scale (the first line), and then multiply it by the number on the scale. This is the resistance value of the measured resistance. . For example, if R * 100 is used to measure the resistance and the pointer is at 80, then the measured resistance value is 80 * 100 = 8K. Since the left part of the "Ω" scale is densely read and difficult to see, you should choose an appropriate ohm range when measuring. Keep the pointer in the middle or right of the scale so that the reading is clear and accurate. Each time you change gears, you should short the two gauges again and readjust the hands to the zero position to get the accuracy.
Measure the DC voltage:-first estimate the measured voltage, then set the transfer switch to the appropriate V range, connect the positive meter rod to the "+" terminal of the measured voltage, and the negative meter rod to the "-" terminal of the measured voltage . Then read the magnitude of the measured voltage according to the block range number and the number indicated by the pointer on the DC-marked “DC-” scale line (the second line). If you use V300 to measure, you can directly read the indicated value of 0-300. If you use V30 to measure, you only need to remove the "0" from the number 300 on the scale line, see it as 30, and then take the numbers 200, 100 and so on as 20 and 10, you can directly read the pointer value. For example, the DC voltage is measured with V6 volts, and the pointer is at 15, then the measured voltage is 1.5 volts to measure the DC current:-first estimate the size of the measured current, then set the transfer switch to the appropriate mA range, and then The multimeter is connected in series in the circuit. At the same time, observe the scale line marked with the DC symbol "DC". If the current range is selected in the 3 mA range, the 300 number on the surface scale line should be removed, and the two "0" s should be removed as 3, and then 200, 100 is regarded as 2, 1 so that the measured current value can be read out. For example, if the DC current is measured with the DC 3mA range, and the pointer is at 100, the current is 1mA. Measuring AC voltage: The method of measuring AC voltage is similar to measuring DC voltage. The difference is that there is no difference between positive and negative, so when measuring AC, the meter rod does not need to be divided into positive and negative. The method of reading is the same as the method of measuring the DC voltage, except that the number should be the position of the pointer on the scale marked with the AC symbol "AC".
Notes on using a multimeter
是比较精密的仪器，如果使用不当，不仅造成测量不准确且极易损坏。 The multimeter simulator is a relatively precise instrument. If it is not used properly, it will not only cause inaccurate measurement but also be easily damaged. However, as long as we master the use and precautions of the multimeter and take care, the multimeter will be durable. When using a multimeter, pay attention to the following: Measure the current and voltage. If you measure the voltage by resistance or current, you will easily burn the meter. When the multimeter is not in use, it is best to rotate the gear to the highest level of AC voltage to avoid damage due to improper use. When measuring DC voltage and DC current, pay attention to the polarity of "+" and "-", and don't connect wrongly. If the hands are found to be reversed, the meter bar should be replaced immediately to avoid damaging the hands and the meter head. If you do not know the measured voltage or current, you should use the highest grade first, and then select the appropriate gear to test, so as not to deflect the meter hand and damage the meter head. The closer the selected gear is to the measured value, the more accurate the measured value will be. When measuring the resistance, do not touch the naked ends of the component (or the metal parts of the two watch rods) with your hands, otherwise the human resistance will be connected in parallel with the measured resistance, making the measurement results inaccurate. When measuring the resistance, if you short the two meter bars and turn the "zero ohm" knob to the maximum, the pointer still does not reach 0. This phenomenon is usually caused by insufficient battery voltage in the meter. You should replace it with a new battery. Can measure accurately. When the multimeter is not in use, do not rotate it in the resistance position, because there is a battery inside. If you accidentally make the two meter sticks short, it will not only consume the battery, but even damage the meter head in severe cases.