Does a multimeter need to be calibrated when measuring resistance shifting?
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: R × 1, R × 10, R × 100, and R × 1K. Some multimeters also have an R × 10k range. To measure resistance using a multimeter in the ohm range, in addition to the requirements that should be met 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 knob of the ohm range, so that the pointer points to the zero position on 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 respectively touch the two pins of the measured resistor for measurement. Correctly read the value of the resistance pointed by the pointer, and then multiply it by the multiplication factor (R × 100 should be multiplied by 100, R × 1k should be multiplied by 1000...). It is the resistance value of the measured resistor.
To ensure accurate measurement, the pointer should be placed near the center of the scale line during measurement. If the pointer angle is small, switch to R × 1k gear. If the pointer angle is large, switch to R × 10 gear or R × 1 gear. After each gear shift, adjust the Ohm gear zero adjustment knob again before measuring.
After the measurement is completed, the probe should be pulled out 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 resistance level, they increase tenfold, such as x 1, x 10, x 100, x 1000, x 10k. 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 point to the zero ohm position. For example, when the resistance level is gradually changed from R × 1 to high, the voltage of the meter head also decreases gradually, the current decreases gradually, and the pointer deflection will not reach the zero ohm position, which will cause significant measurement errors. So it is necessary to adjust the zero knob to maintain the current of the meter coil constant, so that the pointer can point back to the zero position in ohms, to ensure the accuracy of measurement for each gear.
