Measuring voltage/current/resistance: Introduction to the use of digital multimeter
A digital multimeter, as the name suggests, operates mainly based on digital circuits to detect and analyze signals, and then provides LCD display through an analog-to-digital converter.
Although a digital multimeter is a complex electronic measuring tool, operating it correctly according to the instructions, paying attention to routine precautions, and maintaining a good operating environment will greatly improve and stabilize the lifespan and accuracy of the instrument. The digital multimeter uses a liquid crystal display as the reading device, which has the characteristics of high measurement accuracy and safe and reliable use. It has a wide variety of models and is very easy to measure.
The digital multimeter mainly has common measurement functions such as DC voltage, DC current, AC voltage, AC current, resistance, circuit on/off test, diode test, etc; With the development of electronic technology, multimeter has many application functions such as data storage, data transmission, oscilloscope, etc. Some of them have developed into professional application fields: power meters for power testing, leakage current testers, insulation resistance testers, infrared thermometers used in industrial and mining industries, noise meters for environmental testing, anemometers, etc. Taking the UT58C handheld ordinary digital multimeter from Unitech as an example, the following will explain the knowledge of using a multimeter. UT58C is a 3l/2-digit digital multimeter, but in addition to voltage, current, and resistance testing functions, it also has capacitance, frequency, diode, on/off beep, transistor hFE, and temperature measurement. Its unique large screen display and input prompt functions also bring a lot of convenience to users.
Measurement of AC and DC voltage:
Place the power switch in the ON position, and adjust the range switch to the appropriate range within the DCV (DC) or ACV (AC) range as needed. Insert the red probe into the V/Ω hole and the black probe into the COM hole. Then connect the two probes to the measured point, and the voltage of the measured point will be directly displayed on the LCD display. When measuring the flow voltage of instruments and meters, a black probe should be used to contact the low potential end of the measured voltage (such as the common ground terminal or casing of the signal generator), in order to reduce measurement errors.
Attention: If the range of the measured voltage is unknown, it is recommended to set the gear to the highest gear (1000V) and then switch to a more suitable range based on the display screen reading to ensure the accuracy of the test results. When the user selects a range for UT58C, the display screen will prompt you with the corresponding input position of the probe to be selected (AC/DC voltage, resistance, and frequency are tested using two input terminals: "COM" and "Hz/V/Ω").
The testing method for AC voltage V and DC voltage V is the same.
Measurement of AC and DC currents:
Turn the range switch to the appropriate range within the DCA (direct current) or ACA (alternating current) range, insert the red probe into the A hole (≤ 200 mA) or 10 A hole (>200 mA), insert the black probe into the COM hole, and connect the multimeter in series with two probes in the circuit under test. When measuring DC current, a digital multimeter can automatically switch or display polarity.
After using the multimeter, the red lead should be removed from the current socket and then inserted into the voltage socket.
Attention: The current range of this meter below 200mA is equipped with a safety device, so if the measured current exceeds the range, it may cause the fuse to blow. You can replace it according to the instructions in the manual. When testing for currents exceeding 200mA, it is necessary to convert the probe to "A".
Resistance and on/off buzzer test
The maximum resistance of a multimeter can be tested to 20M Ω, and the connection method of the probe is the same as that of the voltage test; Ordinary multimeter does not support online testing. If testing a single resistor or conductor, it is necessary to disconnect the tested resistor or conductor from the circuit; In addition, when deleting the test, it is necessary for the tester to cut off the power supply of the tested circuit or conductor, and live testing is not allowed to ensure the accuracy of the deletion results and the safety of the instrument. This is specifically stated in the precautions for instrument use.
