Several Methods for Measuring Resistance with a Multimeter
The principle of measuring resistance with a multimeter is actually based on Ohm's law. The voltage of a multimeter is the voltage of the battery, and it has several resistance values, including the resistance we want to test, its adjustable resistance (the internal resistance of a multimeter varies depending on the gear), and its fixed resistance. And the current is calculated when our test resistance is zero. So we come up with a formula: I=U/(Rg+R constant+R adjustment+R measurement) U is the voltage of its internal battery, Rg is the resistance of the meter head, R constant, a constant value resistor connected in series with the meter head, R adjustment, a variable resistor for zero adjustment, and R measurement, the resistance to be measured. When the measured resistance Rx=0, the current in the circuit is maximum. Adjust R to make the deflection angle of the measuring mechanism pointer the full-scale value. At this time, the current value I0 in the circuit is E/R. As the measured resistance Rx increases, the current I=E/(R+Rx) gradually decreases, and the deflection angle of the pointer also decreases. Therefore, the resistance value scale on the dial of the multimeter is reversed and the scale is uneven. If the measured resistance Rx=R, the current I=I0/2, and the pointer deflection angle is half of the full deflection angle. Therefore, the resistance value marked at the midpoint of the scale (referred to as the median resistance) is the internal resistance value of the multimeter within that range. The effective reading range of a resistance scale is usually 0.1 to 10 times the median resistance value.
The three main steps of measuring resistance with a multimeter
1. The multimeter we use has a common meter head for measuring voltage, current, and resistance. When measuring resistance, we first need to set it to the ohm range. Generally, there are several gears: X1, X10, X100, and X1000.
2. If the pointer of the meter or (when the second arm of the digital multimeter is short circuited, the reading is not zero) before measurement, it will cause zero error in the reading. If we find that it has not been reset to zero before testing, we must first adjust it to zero position. The method is as follows:
3. Select magnification
Using a multimeter to measure resistance with a resistance meter, in order to facilitate accurate readings, it is necessary to place the pointer as close as possible to the middle of the dial, so it is necessary to select the appropriate magnification gear. If the multimeter does not have a 10k multiplier gear, the closest gear can be selected.
