AC voltage detector tester pen to measure the positive and negative poles of direct current
When measuring direct current, only one end of the neon tube lights up. At this time, the positive and negative poles of the power supply can be judged by the position where the neon tube emits light. When measuring the positive pole of the power supply, the end of the neon tube close to the pen tip will light up; when measuring the negative pole of the power supply, the end of the neon tube farther away from the pen tip will light up.
