To measure resistance displacement, does a multimeter need to be calibrated?
The ohm range of a multimeter can measure the resistance of a conductor. The ohmic gear is represented by "Ω" and is divided into four gears: R×1, R×10, R×100 and R×1K. Some multimeters also have R×10k scale. Use the ohm setting of a multimeter to measure resistance. In addition to the requirements that should be met before use, you should also follow the following steps.
1. Set the selector switch to the R×100 position, short-circuit the two test leads and adjust the ohm position zero adjustment knob so that the meter needle points to the zero position at the right end of the resistance scale line. If the pointer cannot be adjusted to zero, it means that the battery voltage in the meter is insufficient and the battery should be replaced.
2. Use two test leads to touch the two pins of the resistor under test to measure. Correctly read the value of the resistor pointed by the pointer, and then multiply it by the magnification (R×100 gear should be multiplied by 100, R×1k gear should be multiplied by 1000...). It is the resistance of the resistor being measured.
3． In order to make the measurement more accurate, the pointer should be pointed near the center of the scale line when measuring. If the pointer declination angle is small, the R×1k gear should be used. If the pointer declination angle is large, the R×1O gear or R×1 gear should be used. After each gear change, the ohm gear zero adjustment knob should be adjusted again and then measured again.
4． After the measurement is completed, the test leads should be pulled out and the selector 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. Since the resistance values connected to each resistance range are different, they increase by 10 times, such as ×1, × 10, × 100, × 1000, × 10k. When the terminals are short-circuited, the internal resistance in the battery is connected in series with the internal resistance of the meter and the resistance of ×1. When the battery voltage remains unchanged, the current flowing through the coil of the meter exactly corresponds to the ohmic zero position, that is, it corresponds to zero. The terminal voltage of the meter coil is constant. If the resistance value of each gear is changed, the terminal voltage of the meter will change, so that the current flowing through the meter will also change accordingly, and the needle of the meter will no longer point to the ohm zero position. For example, when the resistance level is gradually changed from the R × 1 level to the high level, the voltage of the meter head is also gradually reduced, the current is gradually reduced, and the pointer deflection will be less than the ohm zero position, which will cause a large measurement error. Therefore, the zero-adjustment knob must be adjusted to maintain the meter coil current unchanged and make the pointer point at the ohm zero position again to ensure the accuracy of each gear during measurement.
