What is the working principle of the electric tester
The principle of detecting light emission with an electric pen is that there is a certain potential difference between the charged body and the ground. When the potential difference exceeds a certain value, the neon bubble will emit light, and below a certain value, it will not emit light. The voltage measurement range of ordinary low-voltage voltage tester is generally between 60-500V, and neon bubbles may not emit light below 60V. When the voltage is higher than 500V, it cannot be tested with a low-voltage tester, otherwise insulation breakdown may occur, posing a risk of electric shock to the human body.
When standing on a stool or other insulation to test the live wire with a handheld electric pen, a large current will pass through the high resistance voltage reducing resistor inside the pen and become a weak small current. Then, it will pass through neon bubbles and the human body, discharging into the surrounding environment. At this time, the neon bubbles will emit light. However, there is no risk of electric shock to the human body at this time.
Because the neutral wire is short circuited but the live wire is connected, a circuit is formed between the charged body, the test pen, the human body, and the ground during electrical testing, so the neon bubbles in the test pen will emit light. When measuring the live wire, there is a voltage U=220V between the live wire and the ground, and the human body resistance is generally very small.
Usually only a few hundred to a few thousand ohms, and the resistance inside the measuring pen is usually a few megaohms. The current passing through the measuring pen is very small, usually less than 1 milliampere. When such a small current passes through the human body, it is not harmful, but when such a small current passes through the neon bubble of the measuring pen, the neon bubble will emit light.
Why can electric current make a measuring pen emit light without causing electric shock? Physical answer
1. The working principle of a measuring pen: The measuring pen consists of a metal conductor (in contact with the live wire), a resistor (with a high resistance value), a light-emitting diode, and a metal cap (in contact with the human body). The current flows from the live wire to the resistor, then to the light-emitting diode, the metal cap, and finally to the human body and ground, forming a circuit, which causes the light-emitting diode to emit light.
2. The average current that the human body can withstand is below 0.1A.
3. By measuring the current of the electric pen, it can be calculated. Assuming the resistance R in the measuring pen is 50000 ohms (or greater), the current passing through is I=U/R=220V/50000 ohms=0.0044A, which is much lower than the current that the human body can withstand, so there will be no electric shock!
