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How to Calculate the Capacitance Per Meter for a Cable

Electronic transmission lines find applications in many industries. There are important characteristics of the cabling that need consideration when deciding whether a given cable will satisfy the requirements of a particular application. For coaxial cables, the capacitance of the cable is an important value. The capacitance of the cable defines the charging current required to send signals back and forth along the transmission line.

Instructions

- 1
  Find the physical dimensions and characteristics of the coaxial cable in question. The capacitance per meter of cable is dependent on the diameter of the core conductor, the insulator material and the radius of the cable sheath.
- 2
  Calculate the capacitance of the cable in the absence of a dielectric between the capacitive layers of the core and sheath. The total capacitance is equal to the capacitance without dielectric times the dielectric constant for the dielectric material. The equation for calculating the capacitance without a dielectric is 2 * pi * eo * L /ln(b/a). The total capacitance of the cable is therefore k * pi * eo *L/ln(b/a). The variable used in the equation are: L is the length of cable, b is the outer radius of the sheath, a is the inner radius of the core, k is the dielectric constant and eo is the electric constant, which equals 8.854 X 10^-12 F m-1.
- 3
  Rearrange the equation given to k * pi * eo/ln(b/a). The units of total capacitance result as capacitance per meter. Substitute the actual values for your cable into the equation and solve. This will tell you the capacitance of your cable per meter of cable.

Insects & Science