मृदा प्रतिरोधकता

नये स्थानों पर ग्राउण्डिंग प्रणाली (grounding system ) की समुचित डिजाइन करने के लिये वहाँ की मृदा प्रतिरोधकता (Soil Resistivity) का ज्ञान अति आवश्यक है।

विभिन्न स्थानों पर मृदा की प्रतिरोधकता में बहुत अन्तर पाया जाता है, जिसके लिये नमी, ताप, तथा मृदा का रसायनिक संरचना का लग-अलग होना मुख्य कारण हैं। मृदा प्रतिरोधकता के सामान्य मान ये हैं-

• सामान्य मान : 10 से 1000 (Ω-m)
• असामान्य मान : 1 up to 10000 (Ω-m)

मृदा प्रतिरोधकता का मापन

विनर विधि (Wenner method)

The Wenner four-pin method, as shown in figure above, is the most commonly used technique for soil resistivity measurements. Using the Wenner method, the apparent soil resistivity value is:

$\rho _{E}={\frac {4\cdot {\pi }\cdot a\cdot R_{W}}{1+{\frac {2\cdot a}{\sqrt {a^{2}+4\cdot b^{2}}}}-{\frac {a}{\sqrt {a^{2}+b^{2}}}}}}\,$

where

ρ_E = measured apparent soil resistivity (Ωm)

a = electrode spacing (m)

b = depth of the electrodes (m)

R_W = Wenner resistance measured as "V/I" in Figure (Ω) If b is small compared to a, as is the case of probes penetrating the ground only for a short distance (as normally happens), the previous equation can be reduced to:

$\rho _{E}=2\cdot \pi \cdot a\cdot R_{W}\,$

स्लम्बर्गर विधि (Schlumberger method)

In the Schlumberger method the distance between the voltages probe is a and the distances from voltages probe and currents probe are c (see figure above)।

Using the Schlumberger method, if b is small compared to a and c, and c>2a, the apparent soil resistivity value is:

$\rho _{E}={\pi }{\frac {c\cdot (c+a)}{a}}R_{S}\,$

where

ρ_E = measured apparent soil resistivity (Ωm)

a = electrode spacing (m)

b = depth of the electrodes (m)

c = electrode spacing (m)

R_S = Schlumberger resistance measured as "V/I" in Figure (Ω)

इन्हें भी देखें

• भू-संपर्कन (grounding)