قياس مقاومة مكهر التاريض هُبوطِ الجُهْدِ - ثَلاثَةُ أَقْطاب
تَتَطَلَّبُ كُودَةُ التَّمْديداتِ الكَهْرَبائيَّةِ، فَحْصَ المَكاهِرِ الأَرْضيَّةِ، لِتَأَكُدّ اَنْ مُقاوَمَتِها مُطابِقَةً لِاشْتِراطاتِ الكّوْدَة ، مَعَ العِلْمِ أَنَّ القيمَةَ المَقْبولَةَ لِمُقَاوَمَةِ مُكَهَّرِ التَّأْرِيض، فِي َمُعْظَمِ دوَلِ العالَمِ هِيَ أقل مِنْ خمسة إومّ،
هُنَاكَ عِدَّةُ طُرُقٍ مُتَداوَلَةٌ، لِقِيَاسِ مُقاوَمَةِ مُكَهَّرِ التَّأْرِيض وَلَكِنْ أَكْثَرَها اسْتِخْدامًا وَ دِقَّة هِيَ طَريقَةُ الأَقْطَابِ الثَّلاثَةِ، والْمَعْروفَةُ أَيْضًا بِاسْمِ فَحْصِ هُبوطِ الجُهْدِ - ثَلاثَةُ أَقْطابٍ،
وَيُسْتَخْدَمُ فِي هَذِهِ الطَّريقَةِ، جِهازُ قِيَاسِ مُقاوَمَةِ الأَرْضي وَمِسْمَارَين مُسَاعِدَين،
ويوضح هذا الفيديو طريقة تنفيذها
Fall-of-Potential Measurement
The Fall-of-Potential test method is used to measure the ability of an earth ground system or an individual electrode to dissipate energy from a site.
How Does the Fall-of-Potential Test Work?
First, the earth electrode of interest must be disconnected from its connection to the site. Second, the tester is connected to the earth electrode. Then, for the 3-pole Fall-of-Potential test, two earth stakes are placed in the soil in a direct line-away from the earth electrode.
A known current is generated by the earth tester between the outer current stake and the earth electrode, while the drop in voltage potential is measured between the inner potential earth stake and the earth electrode. Using Ohm's Law (V = IR), the tester automatically calculates the resistance of the earth electrode.
How Do You Place the Stakes?
To achieve the highest degree of accuracy when performing a 3-pole ground resistance test, it is essential that the probe is placed outside the sphere of influence of the ground electrode under test and the auxiliary earth.
For testing a single earth electrode, the outer current stake can usually be placed 50 ft from the electrode under test, with P placed about 31 ft away. With a small grid of two earth electrodes, the outer current stake can usually be placed about 100 to 125 ft from the electrode under test; P correspondingly can be placed about 62 to 78 ft away. If the earth electrode system is large, consisting of several rods or plates in parallel, for example, the distance for the outer current stake must be increased to possibly 200 ft, and for P to some 125 ft. You’ll need even greater
Simplified Fall-of-Potential Test
start with the inner potential earth stake midway between the earth electrode and outer current stake. This reading with P at 50 percent of the distance from the earth electrode to outer current stake is noted as R1. Reference probe P is then moved to a location 40 percent of the distance to outer current stake. The reading at this point is noted as R2. A third reading, R3, is made with outer current stake at a 60 percent distance. The average of R1, R2 and R3 is calculated as RA. You determine the maximum deviation from the average by finding the greatest difference between individual readings and the average. If 1.2 times this percentage is less than your desired test accuracy, RA can be used as the test result.
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