The principle and use of electric test pen
The voltage test pen is one of the tools frequently used by electricians to determine whether an object is charged. Its internal structure is a light bulb with two electrodes. The bulb is filled with neon gas, commonly known as a neon bulb. One pole is connected to the tip of the pen, and the other pole is connected in series with a high resistor and then connected to the other end of the pen. When the voltage between the two poles of the neon bulb reaches a certain value, a glow is produced 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 object to ground is greater than the initial glow voltage of the neon bulb, and the tip of the electric test pen touches it, the other end is grounded through the human body, so the electric test pen will glow. The function of the resistor in the electric test pen is to limit the current flowing through the human body to avoid danger.
In addition to being able to determine whether an object is charged, the voltage test pen also has the following uses:
(1) It can be used to conduct low-voltage phase verification and measure whether any conductors in the line are in phase or out of phase. The specific method is: stand on an object insulated from the earth, hold a test pen in each hand, and then test the two wires to be tested. If the two test pens glow very brightly, the two wires are different. phase; otherwise, it is in the same phase. It is judged by using the principle that the voltage difference between the two poles of the neon bulb in the electric test pen is proportional to the intensity of its luminescence.
(2) Can be used to distinguish alternating current and direct current. When testing with a test pen, if both poles in the neon bulb of the test pen light up, it is alternating current; if only one of the two poles emits light, it is direct current.
(3) The positive and negative poles of DC can be determined. Connect the test pen to the DC circuit to test. The bright pole of the neon bulb is the negative pole, and the non-lit pole is the positive pole.
(4) Can be used to determine whether DC is grounded. In a DC system insulated from the ground, you can stand on the ground and touch the positive or negative pole of the DC system with a test pen. If the neon bulb of the test pen does not light up, there is no grounding phenomenon. If the neon bulb shines, it means there is a grounding phenomenon. If it shines like at the tip of the pen, it means the positive electrode is grounded. If it lights up at the end of your finger, it means the negative pole is grounded. However, it must be pointed out that in a DC system with a ground monitoring relay, this method cannot be used to determine whether the DC system is grounded.
