What Is an Electric Pen?

Test pencil is also called test pencil, referred to as "electric pencil". It is an electrician's tool used to test whether live wires are live. There is a neon bulb in the pen body. If the neon bulb glows during the test, it means that the wire has electricity or is a live line of the path. The pen tip and pen end of the test pencil are made of metal materials, and the pen holder is made of insulating materials. When using a test pencil, be sure to touch the metal part of the end of the test pencil with your hands. Otherwise, because the charged body, the test pencil, the human body and the ground do not form a loop, the neon bulb in the test pencil will not emit light, causing a misjudgment. Not charged.

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According to the measurement of high and low voltage:

High-voltage electric pen: used for 10kv and above projects, as a daily testing tool for electricians;

Low voltage test pen: for line voltage 500V and below

In addition to determining whether the object is charged, the stylus has the following uses:

(1) It can be used to carry out low-voltage nuclear phase and measure whether any conductor in the line is in phase or out of phase. The specific method is: stand on an object that is insulated from the earth, hold a test pen in each hand, and then test on the two wires to be tested. If the two test pens are very bright, the two wires are different Phase; otherwise, it is the same phase.

(1) Judgment of AC and DC power: The electric pen determines AC and DC, AC is bright and DC is dark, AC neon tube is bright, DC neon tube is bright.

Note: First of all, tell readers that before using a low-voltage electric pen, you must test it on a confirmed charged body; you must not use it before confirming that the electric pen is normal. When distinguishing between AC and DC power, it is best to make a comparison between the "two power sources". This is very obvious. When measuring AC power, both ends of the neon tube light up at the same time. When measuring DC power, only one end of the neon tube lights up.

(2) Judging the positive and negative poles of the direct current: The electric pen determines the positive and negative poles. Observe the neon tube carefully, the bright front end is the negative electrode, and the rear bright end is the positive electrode.

Note: The front end of the neon tube refers to the tip of the pen, and the back end of the neon tube refers to the end of the hand. The bright front end is the negative electrode, otherwise it is the positive electrode. When testing, pay attention to: the power supply voltage is 110V and above; if the person is insulated from the ground, one hand touches either pole of the power supply, and the other holds the test pen. The metal tip of the pen touches the other pole of the power supply under test, and the front end of the neon tube emits On, the power source of the touch is the negative pole; if the back end of the neon tube is bright, the power source of the touch is the positive pole, which is based on the principle of DC unidirectional flow and electrons flowing from the negative pole to the positive pole.

(3) The difference between judging whether the DC power supply is grounded and positive and negative grounding: the DC coefficient of the substation, the touch of the pen is not illuminated; if the light is near the tip of the pen, the positive pole has a ground fault; if the light is near the finger, the ground fault is at the negative pole.

Note: The DC coefficients of power plants and substations are insulated from the ground. When people stand on the ground and touch the positive or negative pole with an electric pen, the neon tube should not be illuminated. If it is illuminated, it indicates that the DC system has Grounding phenomenon; if the light is on the end near the pen tip, it is the positive ground; if the light is on the end near the finger, it is the negative ground.

(4) Judgment of in-phase and out-of-phase: determine that the two wires are the same and different, hold a pen in each hand, and keep the two feet insulated from the ground. Touch the two pens to make a line. Look at the pen with your eyes. different.

Note: In this test, remember that both feet and ground must be insulated. Because most of our country is powered by 380 / 220V, and the neutral point of the transformer is generally directly grounded, when testing, the human body and the ground must be insulated to avoid forming a loop, so as to avoid misjudgment; The display is the same, so just look at one.

(5) Judging the ground fault of the 380 / 220V three-phase three-wire power supply line: the star-connected three-phase line, the electric pen touches two lights, the remaining one is weak, and the phase wire is grounded; if it is hardly seen, Faulty metal ground.

Note: The secondary side of the power transformer is generally connected in a Y-shape. In a three-phase three-wire system where the neutral point is not grounded, when the three phase wires are touched with the test pen, two are slightly brighter than usual, and the other is If the brightness is weaker, it indicates that the weak phase wire has a grounding phenomenon, but it is not too serious; if the two are very bright, and the remaining one is almost invisible, the phase wire has a metal ground fault. .

(1) Before using the test pencil, first check whether there is a safety resistance in the test pencil, and then visually check whether the test pencil is damaged, wet, or water-drenched, and use it only after passing the inspection.

(Principle: There is a resistor in the test pen, and a luminous body-a neon tube. The key is the neon tube. After the resistance is reduced, a voltage reaches the end of the neon tube to form a high potential. Your hand needs to touch the metal at the end of the pen. End, now you are the ground wire. There are two thin metal wires in the neon tube, which are close to each other, but they are not connected. The neon tube is naturally filled with neon gas, and a proper potential difference can produce glow. Light discharge. If the voltage is too large, it will instantly break through the neon tube. At this time, the neon tube acts as a safety feature and will not cause much damage to you. The low voltage will be more dangerous because the traditional electric pen is the neon tube electric pen at 100V. Only the left and right lights will turn on, and you can't be careless. In addition, don't put water into the electric pen, otherwise you will know the feeling of electric shock.)

(2) When using a test pencil, do not touch the metal probe on the front of the test pencil with your hands. Doing so will cause an electric shock.

(3) When using the test pencil, be sure to touch the metal part of the end of the test pencil with your hand, otherwise, because the charged body, test pencil, human body and the earth do not form a loop, the neon bulb in the test pencil will not emit light, causing misjudgment. It is considered dangerous that the charged body is not charged.

(The luminous voltage of the neon tube is more than 70V, and the string resistance is 500K. When testing the 220V voltage, the maximum current flowing through the human body is: I = (220-70) ÷ 500 = 0.3mA and the human body passes a current of 1mA. Will produce a tingling sensation.)

(4) Before measuring whether the electrical equipment is electrified, first find a known power source and test whether the neon bulb of the electric pen can glow normally, and it can glow normally before it can be used.

(5) When testing a charged body under bright light, special attention should be paid to whether the neon bulb really glows (or does not glow). If necessary, the other hand can be used to block the light and judge carefully. Do not cause misjudgment, judge the neon bulb to emit no light, and judge the electricity to no electricity.

The test pencil is basically the same in construction principle regardless of its appearance, and its shell is mostly a plastic insulator, which is composed of a metal conductor, a small bulb and a resistance wire. The small bulb is filled with a colorless inert gas (neon gas) that can produce red light with strong transmission force under the excitation of an electric field. When the object is charged, use an electric pen to test that the neon bubble is red, otherwise the neon bubble will not be bright.