Does the multimeter need to be calibrated to measure the resistance shift?
The ohm range of a multimeter can measure the resistance of a conductor. The ohm file is represented by "Ω", which is divided into four files: R×1, R×10, R×100 and R×1K. Some multimeters also have R×10k files. Use a multimeter to measure the resistance in ohm mode. In addition to the requirements that should be fulfilled before use, the following steps should also be followed.
1. Set the selector switch to R×100 position, short-circuit the two test leads and adjust the zero position adjustment knob of the ohm position, so that the hands point to the zero position at the right end of the resistance scale. If the pointer cannot be adjusted to zero, it means that the voltage of the battery in the watch is insufficient and the battery should be replaced.
2. Use two test leads to touch the two pins of the measured resistance to measure. Correctly read the value of the resistance pointed by the pointer, and then multiply by the magnification (R×100 gear should be multiplied by 100, R×1k gear should be multiplied by 1000...). is the resistance value of the measured resistor.
3. In order to make the measurement more accurate, the pointer should be near the center of the scale line when measuring. If the pointer deflection angle is small, the R×1k gear should be used instead, and if the pointer deflection angle is large, the R×1O gear or R×1 gear should be used instead. After each gear change, the zero adjustment knob of the ohm gear should be adjusted again, and then measured.
4. After the measurement, the test leads should be pulled out, and the selector switch should be placed in the "OFF" position or the maximum position of the AC voltage. Put away the multimeter.
The principle of measuring resistance with a multimeter is the single-coil ohmmeter method. Since the resistance value connected to each resistance gear is different, it increases by 10 times, such as ×1, ×10, ×100, ×1000, ×10k. When the terminals are short-circuited, the internal resistance of the battery is connected in series with the internal resistance of the meter head and the resistance of the ×1 gear. When the battery voltage remains constant, the current flowing through the meter head coil corresponds to the zero ohm, that is, zero The terminal voltage of the meter head coil of the bit is constant. If the resistance value of each gear is changed, the terminal voltage of the meter head will change, so that the current flowing through the meter head will also change accordingly, and the meter needle will no longer point to the ohm zero position. For example, when the resistance gear is changed from R × 1 gear to high gear one by one, the meter voltage and current decrease gradually, and the deflection of the pointer will be less than zero ohm, which will cause a large measurement error. Therefore, the zero adjustment knob must be adjusted to keep the coil current of the meter head unchanged, so that the pointer points to the ohm zero position again, so as to ensure the accuracy of each gear when measuring.
