The measurement process of the digital multimeter is converted into a DC voltage signal by the conversion circuit, and then the analog/digital (A/D) converter converts the voltage analog into a digital quantity, and then counts through an electronic counter, and finally uses the digital measurement result. displayed directly on the display.
The function of measuring voltage, current and resistance of the multimeter is realized by the conversion circuit part, and the measurement of current and resistance is based on the measurement of voltage, that is to say, the digital multimeter is extended on the basis of the digital DC voltmeter.
The digital DC voltmeter A/D converter converts the analog voltage that changes continuously with time into a digital quantity, and then counts the digital quantity by an electronic counter to obtain the measurement result, and then the decoding display circuit displays the measurement result. The logic control circuit controls the coordinated work of the circuit, and completes the entire measurement process in sequence under the action of the clock.
How to measure voltage with a multimeter
1. The multimeter is our commonly used test tool
It is mainly used to test parameters such as voltage, resistance, current, etc. It plays a great role in the testing, maintenance and production of electronic products. The main components of a multimeter are an ammeter, a dial, a range selection switch, and test pens. There are many models of multimeters, but basically the method of use is the same. Below we introduce the method of measuring power with a multimeter and the principle of measuring voltage with a multimeter.
2. How to measure voltage with a multimeter
The voltage measurement method of the multimeter is to first align the range switch within the five-speed range marked with V (the AC voltage should be aligned with the AC voltage gear, and the DC voltage should be aligned with the DC voltage gear). When measuring the voltage, connect the meter leads to the circuit under test in parallel. According to the approximate value of the circuit under test, select a suitable range position. The maximum value of each dry cell is 1.5V, so it can be placed in the 5V range. At this time, the 500 of the full scale reading of the needle on the panel should be read as 5. That is 100 times smaller. If the needle points at the 300 mark, it reads 3V. Note that the index value indicated by the tip of the range switch is the corresponding value of the full-scale reading of the needle on the meter head. When reading the meter, you can read the real value as long as it is converted accordingly. Except for the resistance gear, all gears of the range switch read the measurement results in this way. In the actual measurement, when the approximate value of the measured voltage cannot be determined, the switch can be turned to the maximum range first, and then the range can be reduced to the appropriate position. When measuring DC voltage, you should pay attention to the positive and negative polarities. If you don't know the positive and negative polarity of the circuit, you can set the range of the multimeter to the maximum range, try it on the circuit under test quickly, and see how the pen needle is deflected, you can judge the positive and negative polarity.
3. Measure 220V AC
Turn the range switch to AC 500V. At this time, the full scale is 500V, and the reading is read according to the scale of 1:1. Insert the two test pens into the power supply socket, and the measured voltage value is at the scale pointed by the pointer. When measuring AC voltage, there is no positive or negative test lead.
4. The principle of measuring voltage with a multimeter
(1) DC voltage conversion circuit
(2) AC voltage conversion circuit
5. Precautions for the use of the multimeter
(1) Before using the multimeter, "mechanical zero adjustment" should be performed first, that is, when there is no electricity to be measured, make the pointer of the multimeter point to the position of zero voltage or zero current.
(2) In the process of using the multimeter, do not touch the metal part of the test pen with your hands, so on the one hand, it can ensure the accuracy of the measurement, and on the other hand, it can also ensure personal safety.
(3) When measuring a certain amount of electricity, it is not possible to change gears while measuring, especially when measuring high voltage or large current, more attention should be paid. Otherwise, the multimeter will be destroyed. If you need to change gears, you should disconnect the test leads first, and then go to measure after changing gears.
(4) When the multimeter is in use, it must be placed horizontally to avoid errors. At the same time, pay attention to avoid the influence of external magnetic fields on the multimeter.
(5) After the multimeter is used, the transfer switch should be placed in the maximum block of AC voltage. If it is not used for a long time, the battery inside the multimeter should also be taken out to prevent the battery from corroding other components in the meter.
How to use the multimeter
1. Before use, you should be familiar with the functions of the multimeter, and select the correct gear, range and test lead jack according to the object to be measured.
2. When the size of the measured data is unknown, the range switch should be set to the maximum value first, and then switched from the large range to the small range, so that the pointer of the meter indicates more than 1/2 of the full scale.
3. When measuring the resistance, after selecting the appropriate magnification gear, touch the two test pens to make the pointer point at the zero position. If the pointer deviates from the zero position, adjust the "zero" knob to make the pointer return to zero to ensure accurate measurement results. . If it cannot be adjusted to zero or the digital display emits a low voltage alarm, it should be checked in time.
4. When measuring the resistance of a circuit, the power supply of the circuit under test must be cut off, and no live measurement is allowed.
5. When using the multimeter to measure, pay attention to the safety of the person and the instrument and equipment. During the test, do not touch the metal part of the test pen with your hands, and it is not allowed to switch the gear switch with electricity to ensure accurate measurement and avoid accidents such as electric shock and burning of the instrument.
