When an electrician uses a digital grounding resistance tester to measure the grounding resistance, measurement errors may be caused due to unfavorable environments and improper operation. It is difficult to confirm the exact value of the grounding resistance to be measured. What causes the inaccuracy of the digital ground resistance tester's inaccurate readings? How can we avoid it?
Digital Ground Resistance Tester Measurement Inaccurate Reading Cause Analysis:
1. There is a large potential table at the surface, and there are multiple independent groundings. For example, the transformer, such as factories and comprehensive buildings, are grounded. Due to various reasons, the grounding resistance becomes large, the insulation of the transformer itself deteriorates, and leakage occurs. Potential differences occur around the pole and if the detection rod is placed around it will affect the accuracy of the measurement.
2. The measured grounding pole itself has alternating current (insulation of the power equipment is not good, and the leakage phenomenon is caused by partial short circuit, and there is a high-voltage power supply connected near the bottom of the lead line); the structure of the previous early buildings was confusing and the wiring was Disorderly, sometimes even zero line potential difference
Above 100V, it directly affects the measurement error of the grounding resistance.
3, poor contact (including the instrument itself): grounding resistance tester wiring connection, due to the use of often bent, easy to break, and because of the existence of protective cover, it is difficult to find, causing the phenomenon of broken time; In addition, due to detection Sticks and crocodile are used for a long time, and there are oxidation and corrosion phenomena, which can also cause poor contact. If the measured grounding pole is seriously oxidized and badly embroidered, it will also affect the measurement reading.
4. Strong electromagnetic fields emitted by nearby transmitters, antennas, etc.: In the vicinity of high-power transmitting bases, such as mobile, microwave, and BP machines, high-voltage equipment and high-voltage lines near the high-voltage lines, frequent start-up place.
5. Grounding devices and metal pipes buried in a relatively complex way can also cause poor or unstable ground resistance measurement, such as gas stations, chemical plants, etc. Due to the complex layout of underground metal pipelines, underground metal roads are plausible when connected according to normal inspection. Existence actually changes the direction of the current at each end of the meter, often resulting in a zero or negative measurement. If there is a different soil resistivity at the same site, this can also be caused.
6, when testing high-rise buildings, too long detection line induced voltage and cause detection error, while the long-term cable itself also exists.
7. When the soil with high resistivity and poor water absorption is used as the foundation cushion for the whole building, the measured grounding resistance is often too large.
8. The operation is not carried out according to the method specified in the instruction manual, the instrument itself is improperly maintained, and the instrument is used to bring sickness or overdetection.
Digital Earth Resistance Tester Measurement Inaccurate Reading Avoid Method:
1. When testing gas stations and liquefied gas stations and high-rise buildings grounding resistance and electrostatic grounding resistance, the layout of metal (oil, gas) pipes and grounding devices and metal devices buried underground is not correctly displayed on the map. Therefore, the detection direction and distance of the test stick when detecting the grounding resistance have a great influence on the measured value. Usually, the value varies with the direction and distance, and sometimes the measured value may even appear negative. In particular, the detection of buried pipeline facilities such as gas stations will often occur. The solution is: to understand the layout of the underground metal pipeline before the test, not only to view the grounding device map, but also to view the layout of other underground metal pipelines, choose to place the P, C grounding pole as small as possible.
2. Where there is a disconnected card at the ground down conductor, disconnect the test as much as possible to avoid the impact of other devices on the test.
3. When an anomaly occurs during the test, the cause should be identified, or detected and compared at different times and in different directions and locations to obtain the correct test value.
4, in order to avoid electromagnetic interference under high electromagnetic field leads, should be relatively shorter detection lead, the diameter of the lead using a qualified multi-strand metal wire.
5. When the grounding resistance is detected at the place where the high-resistivity sandstone cushion is located, the P and C ground electrodes should be placed in a place where the moisture and the ground conduct well, so that the measured grounding resistance is relatively correct.
6, the detection should be carried out according to the operating procedures, testing equipment should be regularly maintained, regular verification, do not use the super-inspection equipment.
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