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The ground resistance clamp meter is also called a clamp-type ground resistance measuring instrument. Its advantage is that it can measure the current in the line without disconnecting the line being measured. No matter what form of ground resistance clamp meter it is, Generally, only the AC current of the workpiece is measured. There are also some ground resistance clamp meters specially used to measure the DC current. Let me introduce to you the difference between a clamp-type ground resistance tester and a multimeter:
In order to ensure the accuracy and safety of measurement, the following inspections should be performed on the ground resistance clamp meter before use.
1. Appearance inspection: There should be no defects such as damage. Pay special attention to the fact that the jaws should be closed tightly. The iron core part should be free of rust and dirt.
2. If it is a mechanical pointer type ground resistance clamp meter, the pointer should point to "0" at this time. Otherwise it should be adjusted to the "0" position.
3. Estimate the size of the current being measured and select the appropriate gear. The principle of gear selection is: adjust it to be greater than the measured value. And the one that is close to it.
Open the jaws when measuring. Clamp the wire to be measured into the jaws, close the jaws, and deflect the meter needle. The measured current value can be read out. Before reading, the surface of the ground resistance clamp meter should be kept as flat as possible (mechanical pointer type ground resistance clamp meter). A digital ground resistance clamp meter doesn't matter.
Things to note when measuring
1. Gloves should be worn during testing (insulating gloves to clean and dry wire gloves). A guardian should be appointed when necessary.
2. When it is necessary to change gears for measurement, the wire should be withdrawn from the jaws first. After shifting gears, clamp the wire in for measurement.
3. The voltage of the conductor under test. Do not exceed the voltage rating of the ground resistance clamp meter.
4. It is forbidden to use grounding resistance clamp meter to measure poor insulation and wires.
5. When measuring, be sure to keep a safe distance from nearby charged objects. And care should be taken not to cause phase-to-phase short circuit and phase-to-ground short circuit.
6. It is not suitable to measure line current in high temperature environment. It is not suitable to measure near strong magnetic fields. The external magnetic field has a great influence on the measured values. The ground resistance clamp meter is not suitable for measurements near busbars and high-load current equipment such as large-capacity motors and transformers. The measurement should be done in another place to reduce the error caused by the magnetic field.
7. It is not suitable to measure in humid places and thunderstorm weather, because the ground resistance clamp meter must be held in hand to directly measure the operating electrical equipment. During measurement, the jaws and handle of the ground resistance clamp meter and the hands of the measuring personnel must be kept clean and dry.
8. The ground resistance clamp meter has a large error in measuring non-work-rated current. The working principle of the ground resistance clamp meter determines that the ground resistance clamp meter must be used under the specified rate. In addition to measuring sine wave current, the measurement of other waveform currents will produce errors. Generally, odd harmonics are better than even harmonics. The waveform error is large. Especially the third harmonic error becomes larger, and the error is also larger when measuring the half-wave rectified current with a grounding resistance clamp meter.
9. After use, the gear should be set to the high current level, and if there is a watch cover, put it into the watch cover. Store in a dry, dust-free, corrosive gas-free and vibration-free place.
10. High-voltage current cannot be measured, and the voltage of the circuit under test cannot exceed the rated voltage of the ground resistance clamp meter. Ground resistance clamp meters cannot measure high-voltage electrical equipment.
