Capacitive coupled clamp-on voltage probe

A probe adapted to be clamped about an insulated conducting wire for measuring the potential of said wire comprising:

• a first thin cylindrical plate of conductive material adapted to substantially surround said insulated wire, said first plate being separated from said insulated wire by a medium having a low dielectric constant, said first plate having a radius which is at least four times the radius of said insulated wire and an axial length much smaller than that of the portion of said insulated wire positioned within said probe so that the capacitance between said first plate and said wire is no more than one third the characteristic capacitance of said wire to minimize the effects of variations in the characteristics of said insulated wire;
• a second thin cylindrical plate of conductive material concentrically surrounding said first plate and insulated therefrom, said second plate being spaced a very short distance from said first plate relative to the distance between said insulated wire and said first plate and shielding said first plate from external fields;
• clamping means including a longitudinally extending discontinuity in the circumference of said first and second conducting plates for admitting and securely positioning said wire substantially coaxially within said first and second plates without disconnecting said wire, said clamping means restricting motion of said wire within said probe;
• and
• a transmission cable including a pair of electrical conductors respectively connected to said first plate and to said second plate.