Working principle of digital multimeter historical digital multimeter
Digital Multimeter Historical Digital Multimeter developed slowly through history. The early multimeter used a dial with a magnet to deflect the pointer, which was the same as the classic galvanometer. Modern digital display is provided by LCD or VFD (Vacuum fluorescent display). Analog multimeter is not difficult to find in the second-hand market, but it is not very accurate, because zero setting and accurate reading from the instrument panel are prone to deviation. Some analog multimeters
History of digital multimeter
Digital multimeter is developed slowly through history. The early multimeter used a dial with a magnet to deflect the pointer, which was the same as the classic galvanometer. Modern digital display is provided by LCD or VFD (Vacuumfluorescentdisplay). Analog multimeter is not difficult to find in the second-hand market, but it is not very accurate, because zero setting and accurate reading from the instrument panel are prone to deviation. Some analog multimeters use vacuum tubes to amplify the input signals. The designed multimeter is also called VacuumTubeVoltMeters (VTVM) or VacuumTubeMultimeters (VTMM). Modern multimeters have all been digitized, and they are called DigitalMultiMeter (DMM). In this device, the measured signal is converted into a digital voltage and amplified by a digital preamplifier, and then the value is directly displayed by a digital display screen; This avoids the deviation caused by parallax when reading. Similarly, better circuit system and electronics also improve the measurement accuracy. The basic accuracy of old analog instruments is between 5[%] and 10[%], while that of modern portable digital multimeter can reach 0.025 [%], and the accuracy of workbench equipment is as high as one millionth.
Working principle of digital multimeter
The basic circuit of digital multimeter is a meter head circuit, and its basic function is to quantize the input DC voltage (analog) and output it; Other functions generally require the addition of external circuits. At present, the chip of multimeter has higher integration and fewer peripheral circuits, which has both advantages and disadvantages. Advantages: high integration, simple external circuit, and fewer quality failures caused by component quality problems; Disadvantages: When a chip breaks down, the replacement cost is high and troublesome. Sometimes, the money for replacing a chip can be used to buy another instrument, so it is generally scrapped when it breaks down.
Dc voltage measurement
1. Insert the black stylus into the COM jack and the red stylus into the V/Ω jack.
2. Place the function switch in the V- range range of DC voltage range, and connect the test probe to the power supply to be tested (measuring the open circuit voltage) or the load (measuring the load voltage drop), and the polarity of the connected end of the red probe will be displayed on the display at the same time.
note:
1. If the measured voltage range is unknown, set the function switch to the maximum range and gradually decrease.
2. If the display only shows "1", which means over range, the function switch should be set to a higher range.
3. ""means not to measure the voltage higher than 1000V V. It is possible to display a higher voltage value, but it is in danger of damaging the internal circuit.
4. When measuring high voltage, pay special attention to avoid electric shock.
Direct current measurement
1. Insert the black stylus into the COM jack. When measuring the maximum current of 200mA, insert the red stylus into the mA jack. When measuring the maximum current of 20A, insert the red stylus into the 20A jack.
2. Place the function switch in the A- range of DC current, and connect the test probe in series to the load to be tested. When the current value is displayed, the polarity of the red probe will be displayed.
note:
1. If the measured current range is unknown before use, set the function switch to the maximum range and gradually decrease.
2. If the display only shows "1", which means over range, the function switch should be set to a higher range.
3. It means that the maximum input current is 200mA, and excessive current will burn the fuse, so it should be replaced. The 20A range is not protected by fuse, and the measurement cannot exceed 15 seconds.
Ac voltage measurement
1. Insert the black stylus into the COM jack and the red stylus into the V/Ω jack.
2. Place the function switch in the range of V~ of AC voltage range, and connect the test pen to the power supply or load to be tested. Test connection diagram as above. When measuring AC voltage, there is no polarity display.
note:
1. See DC voltage note 1.2.4.
2. ""means don't input a voltage higher than 700Vrms. It is possible to display a higher voltage value, but it is in danger of damaging the internal circuit.
Measurement of alternating current
1. Insert the black stylus into the COM jack. When measuring the maximum current of 200mA, insert the red stylus into the mA jack. When measuring the maximum current of 20A, insert the red stylus into the 20A jack.
2. Put the function switch in the range of A~ of AC current, and connect the test probes in series to the circuit to be tested.
