The multimeter measures the relationship between the deflection angle of the resistance pointer and the resistance
When measuring resistance, pay attention to:
1. The measured resistance should be removed from the circuit before measurement.
2. Do not touch the two test leads together for a long time.
3. Two hands cannot touch the metal rods of the two test leads or the two pins of the measured resistance at the same time. It is better to hold the two test leads at the same time with the right hand
4. If the ohm range is not used for a long time, the battery in the meter should be taken out.
When the multimeter measures resistance, the measured value reflected on the meter head is actually the corresponding current passing through the measured resistance. The larger the measured resistance is, the smaller the current is, that is, the smaller the deflection angle. The relationship between the pointer deflection angle and the measured resistance is:
α=(RZθ)/(RX+RZ)
In the formula: α - pointer deflection angle;
RZ - the center resistance of the multimeter;
RX - the measured resistance;
θ———The angle when the pointer is fully deflected, this angle is mostly 90°
It can be seen from the ohm scale of the multimeter that the scale is an uneven reverse scale, and the smaller the deflection angle is, the greater the resistance value indicated. The resistance value between each scale line at the high-resistance end is very different. If you look at the pointer at an angle on this section of the scale line during measurement, it will cause a large error. Especially when measuring small resistance, the error is more obvious. Therefore, in order to ensure the accuracy of the measurement, when measuring a small resistance, the method of shifting gears should be used to keep the pointer near the center position as much as possible.
How to check short circuit with multimeter
A short circuit means that two lines that should not be connected are connected. A short circuit is between phases and phases, and between phases and ground. One is a phase-to-phase short circuit and the other is a ground short circuit. Grounding is relative grounding, and grounding is divided into dead grounding. The larger the resistance between the phase and the ground, the better, and the small resistance is called leakage.
When measuring with a multimeter, the larger the phase-to-phase resistance, the better. The small resistance between phases is called phase-to-phase leakage, and the resistance to zero is called phase-to-phase short circuit.
Use a multimeter to measure both ends of a line. If the resistance is zero, the line is connected. If the resistance is infinite, it is an open circuit. Sometimes the resistance is zero and sometimes it is not, indicating that the line is virtual.
Put a wire on the ground, with both ends guided without touching the ground, connect one end of the test lead to the wire, and the other test lead to the ground. The larger the resistance, the better, which means that the connection value is high, and the small resistance value means leakage, and the insulation performance is not good. Generally not less than 0.5 megohm, the state stipulates 1V1 ohm, low resistance wires should be scrapped.
