Multimeter check short circuit, broken circuit, leakage techniques
Checking a short circuit with a multimeter
A "short circuit" is when the two ends of a power supply are directly connected by wires. Checking a short circuit with a multimeter is actually measuring the resistance to determine whether the line is open or closed. As the multimeter resistance file can not be charged measurement, so the resistance measurement must be carried out in the case of power failure.
Judgement method:
First disconnect the power supply to ensure that there is no power, and then use the multimeter resistance file to measure the ends of the object being measured. Under normal circumstances there is a certain resistance value, if the measured resistance is zero indicates that the object being measured short-circuit.
Can also be in the case of power failure, with the multimeter's beeping file or diode file to measure the ends of the object under test. If a sharp beeping sound is emitted, it indicates that a short circuit has occurred in the object under test.
Note: If the measured resistance has a certain value but is very small, it is also likely that a short circuit has occurred, which is caused by contact resistance.
We sometimes encounter this situation when measuring, for example, you press the multimeter pen a little tighter, the measured result will become smaller; relax the pen a little, the measured result will become larger. This is because the meter pen and the measured wire is not connected well, the contact resistance of the connection point is also measured.
In order to minimise the measurement error and restore the authenticity of the results. So in the measurement of the meter pen and the measured object wire must be connected tightly; if the measured wire corrosion or oxidation is serious, to scrape off the conductor surface of the oxide layer. (Under normal circumstances, copper is a bright golden yellow, after being oxidised to show a dull black; aluminium wire is also the same)
Multimeter check broken circuit
Know how to use a multimeter to measure a short circuit, then the measurement of broken circuit is also very simple.
Judgement method:
First of all, disconnect the power supply to ensure that there is no power, and then use the multimeter resistance file to measure the two ends of the line. Under normal circumstances, the resistance is zero or a certain resistance value, if the measured resistance is infinitely large that is the line ends do not pass, that is, a circuit break.
Can also be in the case of power failure, using the multimeter beeping file or diode file measured by the line ends. If the beeping sound, the line is through; on the contrary, if there is no sound indicates that the line may be short-circuited.
Note: under normal circumstances, the resistance of the two ends of the wire is zero (or close to zero); electrical equipment under normal circumstances have a certain resistance, but the specific resistance and how much their own. So determine whether the line or electrical equipment is disconnected, it is best to use a large range of resistance gear. Because the resistance value of some electrical equipment is very large, such as energy-saving lamps with a small range is not measured.
Multimeter to measure leakage
First of all, we have to think about a problem, equipment leakage and normal when what is different?
Under normal circumstances, the zero fire line of the electrical equipment is insulated, it is not with the equipment shell. Once the insulation of the electrical equipment damage, such as zero or fire wire on the shell, then there will be current flow to the shell, so that the shell charged. So determine whether the electrical equipment leakage can be measured by measuring the zero line or fire line and the shell pass through to determine whether the leakage.
Judgement method:
First disconnect the power supply to ensure that there is no electricity, the gear position in the maximum range of resistance gear, and then use a multimeter to measure the zero line (or fire) and the shell (or connected to the shell of the ground) between the resistance. Under normal circumstances, the resistance value should be infinite, if measured with a certain resistance value, it means that there is a leakage.
Note: multimeter leakage only applies to very serious leakage, such as zero or fire wire to the metal casing and so on. For insufficient insulation strength caused by leakage can not be detected, such as wire skin aging but still have a certain insulation capacity. Because the wire skin has a certain insulation strength, so in the low voltage is not conductive, but the voltage will be high leakage.
If you want to accurately measure whether the line or equipment leakage, you need to use more professional equipment - megohmmeter (shaking table).
