Performance and application of electric test pencil

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Performance and application of electric test pencil [Copy link]

In daily maintenance work, whether it is to inspect electrical circuits or various household electrical appliances, a small tester is indeed an indispensable tool. It can help analyze many faults of various electrical appliances and equipment conveniently and quickly. Testers can be divided into three types, namely the most common low-voltage tester, the medium-voltage tester for mines, and the high-voltage tester for distribution stations. Although the three types of testers are suitable for measuring different voltage ranges, their working principles are basically the same.

The structure of the test pen is composed of metal pen tip, voltage limiting resistor, neon tube, spring, metal body at the end of the pen, etc. Its working principle is quite simple. When the metal pen tip of the test pen contacts the live wire of the power supply and the metal body at the end of the pen contacts the human hand, the current will return to the power ground wire through the pen tip, resistor, neon tube, metal body at the end of the pen, human body and ground, forming a complete current path. Then the weak current limited by the resistor will make the neon tube glow. Since the current flowing through the human body is extremely weak, there will be no numbness when measuring charged conductors.

Although the electric tester has a simple structure and is easy to use, it can often lead to misjudgment if it is used incorrectly. Therefore, it is very necessary for novice maintenance personnel to understand how to use the electric tester correctly.

(1) If the neon tube lights up after the handheld tester touches a charged object, it means that the object being tested is charged. If the neon tube does not light up after touching the conductor, it cannot be immediately determined that the conductor being tested is not charged, because if the surface of the conductor is unclean and has oil stains, etc., it will cause poor contact between the tester and the conductor. It is best to use the tip of the tester to repeatedly scratch the surface of the object being tested several times. At this time, if the neon tube still does not light up, it can be determined that the object being tested is not charged. (2) When using a tester to determine whether the transmission line is in phase or out of phase, you can connect insulated wires at both ends of the tester and touch the two line wires respectively. As long as the tester does not touch other objects (including insulated objects), it will be suspended in the air. When the tester lights up, the two lines are out of phase, and when it does not light up, they are in phase.

(3) When using an electric tester to determine whether there is AC or DC in a circuit, if only one end of the neon tube lights up, it means that there is DC in the circuit being tested. Conversely, if both ends of the neon tube light up at the same time, there is AC in the circuit.

(4) When it is necessary to determine the positive and negative poles of a DC circuit, you can use a tester to touch the wires of the circuit being tested. The electrode where the neon tube lights up is connected to the negative pole of the DC, and the electrode where the neon tube does not light up is connected to the positive pole of the DC.

(5) When you need to determine which electrode is grounded between the negative and positive electrodes of direct current, you can touch the point to be tested with a test pencil. If the neon tube lights up, it means that one end of the direct current is grounded. If the front end of the neon tube lights up, it means that the positive electrode of the circuit is grounded; if the back end of the neon tube lights up, it means that the negative electrode is grounded.

(6) When there is a tingling sensation on the outer casing of an electrical device and it is necessary to distinguish whether it is induced current or circuit leakage, you can touch the outer casing of the electrical device with a tester. If one or both ends of the neon tube emit a faint flashing red light, it indicates that the outer casing of the electrical device carries induced current. At this time, if you touch the outer casing with your hand, the neon tube will go out. If the neon tube glows very brightly, it means that there is leakage inside the appliance.