The commonly used test pen is shown in Figure 7-33. When in use, hold the cap of the pen and let your fingers touch the metal pen, and let the tip of the pen contact the charged body. At this time, if the voltage on the charged body is above 90V, the neon bulb will emit orange-red light, which proves that there is electricity.
As we all know, the test pen is a common tool for testing mains (220V, 380V AC power). In fact, it can also measure DC voltage, and can determine the positive and negative levels.
Judging AC and DC: When measuring the power supply is AC, the neon light is very bright, but when measuring the DC power supply, the neon light is dim, and only one end is bright.
If the positive and negative poles of the DC power supply are to be distinguished, the front and rear ends of the neon bulb must be carefully observed. The bright front of the neon bulb is negative, and the bright rear of the neon bulb is positive.
