How to check for leakage with a digital multimeter
Set the digital meter at AC-750V. As shown in the attached figure. A pen contact power socket on the metal plating, hand touching the other pen metal part, the meter is very clear display voltage value of 119V! After investigation, is the socket fixing screw top broken the plastic sheath of the firewire, contact with the californian heart, the screw pressed on the metal plating, so that the socket is electrified. Digital meter voltage block internal resistance of more than lOMΩ. Human body and the earth can be equated with a resistance (shoes, wooden floor series resistance l and a capacitance (distributed capacitance between the human body and the earth) in parallel, see the attached figure. The voltage on the firewire through the pen l, meter, pen 2, the human body, the DC resistance of the board and the human body in parallel with the distributed capacitance to the earth, the meter shows the internal resistance of the meter at both ends of the formula UDY for the firewire to the ground voltage, RB for the internal resistance of the voltmeter, Z for the total impedance between the human body to the earth. Obviously, the greater the internal resistance of the meter, the higher the sensitivity of the power test. It must be pointed out that the above method of power test, the human body must have a current through. Meter only have instructions. Undoubtedly, it should be small enough, so small that the human body can not feel the existence of the current. Digital multimeter has lOMΩ, the internal resistance, even if the bare feet standing in the wet ground, the current flowing through the human body when the firewire voltage of 220V, the effective value of the current flowing through the human body is only 22 μA. Pointer multimeter can not be used to check the electricity, because the voltage of such a meter is much smaller than the internal resistance of the block lOMΩ. Therefore, check the power of the sensitivity is very low. Attempts to use the small voltage block to improve the sensitivity of the power test is wrong, because the small voltage block is usually small internal resistance (pointer multimeter voltage block internal resistance per volt ohm value multiplied by the voltage range). Indication of the sensitivity of almost no improvement, but easy to electrocution accidents.
