Measuring pen is one of the tools often used by electricians to judge whether an object is charged. Its internal structure is a bulb with only two electrodes, which is filled with neon gas, commonly known as neon bubble. One pole of the bulb is connected to the tip of the pen, and the other pole is connected to the other end of the pen after a high resistance is connected in series. When the voltage between the two poles of a neon bubble reaches a certain value, there will be a glow between the two poles, and the intensity of the glow is proportional to the voltage between the two poles. When the voltage of the charged body to the ground is greater than the initial glow voltage of the neon bubble, and the tip of the measuring pen contacts it, the other end is grounded through the human body, so the measuring pen will emit light. The function of resistance in the electric pen is to limit the current flowing through the human body to avoid danger. 

In addition to being able to judge whether an object is charged or not, a measuring pen can also be used for the following purposes:

(1) It can be used for low-voltage phase checking and measuring whether any conductor in the line is in phase or out of phase. The specific method is as follows: stand on an object insulated from the earth, hold a measuring pen in both hands, and then test on the two wires to be tested. If the two measuring pens are very bright, the two wires are out of phase; On the contrary, it is in phase, which is judged by the principle that the voltage difference between the two poles of neon bubble in the measuring pen is proportional to its luminous intensity.

(2) It can be used to distinguish AC and DC. When using the electric pen to test, if both poles of the neon bubble of the electric pen emit light, it is alternating current; If only one of the two poles emits light, it is a direct current.

(3) It can judge the positive and negative of direct current. Connect the measuring pen to the DC circuit to test. The bright pole of neon bubble is the negative pole, and the non bright pole is the positive pole.

(4) It can be used to judge whether DC is grounded or not. In the DC system with insulation to the ground, you can stand on the ground and touch the positive or negative pole of the DC system with a measuring pen. If the neon bubble of the measuring pen is not bright, there is no grounding phenomenon. If the neon bubble is bright, it means that there is grounding phenomenon. If it is bright at the tip of the pen, it means that the positive electrode is grounded. If the light is on the finger end, the negative electrode is grounded. But it must be pointed out that in the DC system with grounding monitoring relay, this method can not be used to judge whether the DC system is grounded.

Editor in charge: LQ