When the multimeter is measuring the short circuit, why is it a short circuit when the power is on, and it is an open circuit when it is not energized?
The principle of multimeter measuring resistance
The principle of measuring resistance with a multimeter is actually based on Ohm's law. In the multimeter, its voltage is the voltage of the battery; it has several resistance values, including the resistance we want to test, its adjustable resistance (the internal resistance of the multimeter is different for different gears), and its fixed resistance. And the current is calculated when our test resistance is equal to zero. In this way, we can get a formula: I=U/(Rg+Rset+Radjustment+Rmeasurement) U is the voltage of its internal battery, Rg is the resistance of the meter head, R is fixed, a fixed value connected in series with the meter head Resistance, R adjustment, variable resistance for zero adjustment, R measurement, the resistance to be measured. Due to the different ranges of resistance to be measured, the fixed value resistors used are also different, which makes the multimeter divided into several grades.
When measuring with a multimeter, the resistance reading is actually the current reading, but the current when R measurement = 0: I = U/(Rg+R setting + R adjustment) is marked as R = 0, when there is no current, the resistance is marked as no resistance Large, I and is a functional relationship, they are not a simple proportional relationship. Choose different resistance files, R is set differently, when R=0, I is different, so it must be zeroed before each measurement
So when there is voltage, there will be current, and the multimeter will act as a short circuit.
How to use this multimeter to test whether a section of line is open or broken
Point blocking one end of the line under test is directly connected to the ground terminal, the end under test is connected to a test lead, and the other test lead is directly pressed to a nearby reliable ground terminal, the pointer points to zero or close to zero, and the line is basically connected. If the pointer does not change, the circuit breaks. If the digital display meter is zero, it means pass.
If you know that the other line is connected, you can directly short-circuit one end of the line under test with this line, connect the other end of the line under test to the test lead, and connect the other test lead to one end of the line. That's it.
