Correct use method and precautions of clamp ammeter
"Clamp meter" is referred to as "clamp meter", which is a portable instrument that can directly measure the AC circuit without disconnecting the line. Some clamp meters use the Hall sensing principle and can even measure DC current.
The clamp meter can be transformed into a digital multimeter by plugging in the test leads. In this way, the clamp meter can not only measure AC and DC current without disconnecting the power supply, but also measure voltage, resistance, capacitance, temperature, etc. Because the clamp meter is more practical than the multimeter and easy to carry, it has been widely used.
working principle
The working part of the clamp meter is actually composed of an open-type current transformer and an ammeter. When the wire under test passes through the current transformer, the magnetic field generated by the current of the wire under test will induce a current on the current transformer, and then display it through the ammeter. The greater the current of the wire under test, the stronger the magnetic field generated, so the greater the current induced on the current transformer, the greater the reading of the ammeter.
Instructions:
1. Check that the appearance of the clamp meter is very damaged, and whether the jaws can be closed tightly. (If the appearance is damaged, it is strictly prohibited to use)
2. Select the appropriate range according to the current of the wire under test (if you don’t know the current, use the largest gear to measure it first, and then switch to the corresponding gear)
3. Open the jaws and put the wire under test into the center of the jaws. (Note that the wire does not need to be stripped) Then release your finger and let the clamp meter close automatically
4. Reading
5. After the reading is completed, open the jaws, take out the wire to be tested, and put the gear in the closed state.
Notice:
1. When measuring current, only measure the current of one wire or the same phase at a time.
If two wires are measured at a time, the measured result is the sum of the currents of the two wires. (Note: The current not only has a magnitude but also a direction; if the current direction is opposite, then the total current is the subtraction of the two current values)
For example: when you measure the neutral and live wires of a light bulb at the same time, since the currents of the zero and live wires are equal in magnitude and opposite in direction, the generated magnetic fields are completely cancelled. So the measured result should be zero.
If the measured result is not zero, it means that the current of the neutral wire and the live wire of the lamp is not equal, and the current of the neutral wire or the live wire of the lamp flows to other places. For example: leakage.
The zero-sequence transformer in the leakage protection device is based on this principle to judge whether the equipment is leakage.
