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High-speed railway signal technology communication
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Content Guide ID: gaotiexinhao A multimeter is a comprehensive instrument composed of various measurement circuits such as ammeters, voltmeters, and ohmmeters through a switching device. Understanding the principles of each measurement circuit is key to mastering the working principles of the multimeter, with the fundamental principles based on Ohm’s law and the rules of series and parallel resistances.Correct Usage of the Multimeter
1. Measurement Type Selection: Before measuring, first select the type based on the object being measured, and turn the switch to the corresponding position. The range switch must be set to the required measurement range; it must not be set incorrectly. For example, if measuring voltage, setting it to current or resistance mode will damage the meter. 2. Measurement Range Selection: Choose the range based on the approximate value of the measurement. 3. Measurement Connection: When measuring voltage, connect the multimeter in parallel with the circuit being measured; when measuring current, connect the multimeter in series with the circuit. Pay special attention to the polarity when measuring DC. The red probe connects to the positive terminal, and the black probe connects to the negative terminal. 4. Correct Use of the Ohm Mode: (1) Select an appropriate multiplier to keep the pointer close to the center scale of the ohm meter. (2) Always “zero” the meter before measuring. (3) Do not measure resistance while the circuit is energized. (4) The object being measured should not have parallel branches. (5) Adjusting for zero ohms should be done quickly; if not zeroed, be careful not to short the test leads to avoid wasting the battery. 5. Reading Correctly: The dial has multiple scales; read according to the type of measurement. For DC measurements, read from the “DC” or “1” scale; for AC measurements, read from the “AC” or “~” scale; the scale marked with “Ω” is used for resistance measurements. When reading, first identify the type of scale to avoid confusion. 6. Precautions: (1) Before using the multimeter, check if the pointer is at the zero position; if not, use a small screwdriver to adjust the zeroing device on the meter cover to perform “mechanical zeroing” to ensure the pointer is at zero. Do not touch the metal parts of the probes while measuring. (2) When measuring high voltage or large current, be mindful of personal safety. Ensure the test probes are plugged into the appropriate sockets, and set the range switch to the corresponding position. Before measuring, place the multimeter on an insulated stand, disconnect the power from the circuit being measured, and if the circuit contains large capacitors, short-circuit and discharge the capacitor. Then securely connect the probes to the circuit before turning the power back on for measurement. Do not switch the range while the circuit is energized. (3) When measuring DC voltage superimposed with AC signals, consider the maximum voltage rating of the meter’s range switch. (4) After using the multimeter, generally rotate the range switch to the highest AC voltage setting. If the multimeter will not be used for an extended period, remove the battery to prevent leakage and corrosion that could damage the internal components of the multimeter.
