Does a multimeter need to be calibrated for measuring resistance and shifting gears
The ohm range of a multimeter can measure the resistance of a conductor. The ohm range is represented by "Ω" and is divided into four levels: Rx1, Rx10, Rx100, and Rx1K. Some multimeters also have an R × 10k range. Using a multimeter ohmmeter to measure resistance, in addition to the requirements that should be followed before use, the following steps should also be followed.
1. Place the selector switch in the R × 100 position, short circuit the two probes to adjust the zero position of the ohm range adjustment knob, so that the probe points to the zero position at the right end of the resistance scale line. If the pointer cannot be adjusted to zero, it indicates that the battery voltage in the meter is insufficient and the battery should be replaced.
2. Use two probes to contact the two pins of the measured resistance for measurement. Correctly read the value of the resistance indicated by the pointer and multiply it by the multiplier (R × 100 should be multiplied by 100, R × 1k should be multiplied by 1000...). It is the resistance value of the measured resistance.
To make the measurement more accurate, the pointer should be placed near the center of the scale line during measurement. If the pointer has a small deviation angle, the R × 1k gear should be used. If the pointer has a large deviation angle, the R × 1O gear or R × 1 gear should be used. After each gear shift, adjust the ohm gear zero adjustment knob again and then measure again.
After the measurement is completed, the probe should be removed and the selection switch should be placed in the "OFF" position or the maximum AC voltage position. Put away the multimeter.
The principle of measuring resistance with a multimeter is the single coil ohmmeter method. Due to the different resistance values connected to each level of the resistance range, there is a tenfold increase, such as x1, x10, x100, x1000, x10k. When the terminal is short circuited, the internal resistance inside the battery is connected in series with the internal resistance of the meter head and the resistance of level 1. When the battery voltage remains constant, the current flowing through the meter head coil corresponds exactly to the ohmic zero position, that is, the terminal voltage of the meter head coil corresponding to the zero position is constant. If the resistance values of each gear are changed, the terminal voltage of the meter will change, causing the current flowing through the meter to also change accordingly, and the meter needle will no longer refer to the ohmic zero position. For example, when the resistance range is gradually changed from R × 1 to high gear, the voltage on the meter head also decreases step by step, and the current decreases step by step. The pointer will not deviate to the zero position of the ohm, which will cause significant measurement errors. So it is necessary to adjust the zero adjustment knob to maintain the current of the meter coil unchanged, so that the pointer points back to the ohmic zero position to ensure the accuracy of each measurement level.
