Use multimeter to measure short circuit and open circuit with on-off gear or resistance gear.
On-off gear is also called buzzer gear. In this gear, if the actual resistance value of the tested line is lower than a certain value (I forget how much it is, and there is a detailed explanation in the manual), the buzzer will sound.
Take the digital multimeter as an example. It seems that the buzzer can measure the resistance of 2 kiloohms at most.
For example, when measuring a pure line (like a 100-meter coil of wire), the wire will buzz without breaking.
Another example is a section of line, in which some resistive elements (such as coils and motor windings) may be connected in series, or the line is very long and has many connection interfaces. When this gear is measured, it may not beep, but it will show a value, which is the resistance of this line, but it cannot fully explain that this line is open.
For example, if you choose a good AC contactor coil at random and measure both ends of the coil with a buzzer, it won't chirp, but it will display a value (assuming it is 758); If you measure it again with a resistance of 2 kiloohms, the measured value is still 758, that is, the resistance of this coil is 758 ohms. At this time, you can't say that the coil is open. If the coil is open, the indicator will be zero and there will be no chirping.
If you don't call and show the number, strictly speaking, it still can't be said that this line is open. Because as mentioned above, the maximum resistance of this gear can only be measured at 2 kiloohms. So it is possible that the resistance of this line is higher than 2 kiloohms, so you can change to a higher resistance gear and test it again.
In practice, there is generally no need to delve into this. For example, a 100-meter coil of wire mentioned above, if it doesn't buzz when measured with a buzzer, it can basically be judged that the coil is not in line.
Another example is to know that the winding of the motor is to be measured. Before the measurement, there are so many in my heart that I don't call when I measure it with the buzzer. In order to ensure the accuracy, I should change to a larger gear and measure it again.
Anyway, what I personally think should be paid attention to is: 1. The buzzer can only measure the resistance below 2 thousand ohms; Only when the actual resistance value is lower than the set value will it sing. Remember this, and then predict the accuracy of the measured results according to the actual situation. Or predict what gear measurement is most suitable according to the actual situation.
