The measurement process of the digital multimeter is converted into a DC voltage signal by the conversion circuit, and the analog voltage is converted into a digital quantity by an analog/digital (A/D) converter, and then counted by an electronic counter, and finally the measurement result is digital. Displayed directly on the display.
The multimeter measures the voltage, current and resistance functions through the conversion circuit part, while the current and resistance measurements are based on the voltage measurement, which means that the digital multimeter is extended on the basis of the digital DC voltmeter.
The digital DC voltmeter A/D converter converts the analog voltage continuously changing with time into a digital quantity, and then the digital counter counts the digital quantity to obtain a measurement result, and the decoding display circuit displays the measurement result. The logic control circuit controls the coordination of the circuit, and the entire measurement process is completed in sequence under the action of the clock.
How to measure voltage with a multimeter 1. Multimeter is our commonly used test toolIt is mainly used to test voltage, resistance, current and other parameters, and plays a big role in the testing, maintenance and product making of electronic products. The main component of the multimeter is composed of an ammeter, a dial, a range selection switch, and a test lead. There are many models of the multimeter, but basically the method of use is the same. Below we introduce the method of measuring the power supply with a multimeter and the principle of measuring the voltage of the multimeter.
The multimeter voltage measurement method firstly aligns the range switch to the five-speed range marked with V (test the AC voltage to the AC voltage position, and the DC voltage to the DC voltage). When measuring the voltage, connect the meter to the circuit under test. Select an appropriate range position based on the approximate value of the circuit under test. 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. Note that the index value of the span switch tip is the corresponding value of the full scale reading of the gauge on the meter head. When reading the table, the real value can be read out according to this calculation. In addition to the resistance file, all the range switches are read in this way. 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. When measuring the DC voltage, pay attention to the positive and negative polarity. If the test leads are reversed, the hands will be reversed. If you do not know the positive and negative polarity of this circuit, you can put the multimeter's range at the maximum position, try it on the circuit under test quickly, and see how the stylus is deflected, you can judge the positive and negative polarity.
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 leads into the power socket, and the scale indicated by the hands is the measured voltage value. When measuring AC voltage, the test pen has no positive or negative points.
(1) Before using the multimeter, perform “mechanical zeroingâ€, that is, when there is no measured power, the multimeter pointer points to the zero voltage or zero current position.
(2) 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.
(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, 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.
(5) When the multimeter is used, the switch should be placed at the maximum 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.
How to use the multimeter
1. Be familiar with the functions of the multimeter before use. According to the object to be measured, select the gear position, range and pen jack correctly.
2. When the size of the measured data is unknown, the range switch should be set to the maximum value, and then switched from the large range to the small range, so that the meter pointer can be indicated at 1/2 or more of the full scale.
3. When measuring the resistance, after selecting the appropriate magnification file, touch the two test leads to make the pointer point to zero. If the pointer deviates from the zero position, adjust the “zero adjustment†knob to zero the pointer to ensure accurate measurement results. . If you can't zero or the digital display sends a low voltage alarm, you should check it in time.
4. When measuring the resistance of a certain circuit, the power of the circuit under test must be cut off.
5. When using a multimeter for measurement, pay attention to the safety of personal and instrumentation equipment. Do not touch the metal part of the test pen by hand during the test. Do not switch the gear switch with power to ensure accurate measurement and avoid accidents such as electric shock and burning of the instrument. .
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