Capacitive coupled clamp-on voltage probe

• US 4,090,130 A
• Filed: 12/06/1976
• Issued: 05/16/1978
• Est. Priority Date: 12/06/1976
• Status: Expired due to Term

• Current Assignee: Clean Air Technologies Inc.
• Original Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Willenbecher, James F. Jr.
• Primary Examiner(s): Rolinec, Rudolph V.
• Assistant Examiner(s): Karlsen, Ernest F.
• Application Number:
  US05/747,756
• Time in Patent Office: 526 Days
• Field of Search: 324/126, 324/127, 324/15, 324/129, 361/302
• US Class Current: 324/126
• CPC Class Codes: F02P 17/12 Testing characteristics of the spark, ignition voltage or current testing of sparking plugs H01T13/60
• CPC Class Codes: F02P 2017/006 using a capacitive sensor
• CPC Class Codes: G01R 15/16 using capacitive devices
• CPC Class Codes: H01T 13/60 of electrical properties

Abstract

A capacitive coupled clamp-on voltage probe having three concentric cylindrical capacitive plates each separated by a thin dielectric is adapted to be clamped onto an insulated wire such as the ignition wire in an automobile to measure the potential of the wire. In one embodiment the probe contains a solid dielectric center with a slot along its longitudinal axis which extends radially from the outside to the center of the probe thereby allowing the probe to be easily positioned over and released from an automobile ignition wire by slipping the probe over any insulated portion of the wire. The slot is dimensioned to hold the wire securely at the center of the probe. The probe also includes a releasable clamp having a thumb actuated lever to assist in maintaining the wire securely at the probe center and to permit easy positioning and release of the wire. In a second embodiment the probe is separated into two symmetrical semicylindrical halves which open and close by a spring loaded lever to admit the wire whose potential is to be measured.

Claims

1. 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.

2. A probe according to claim 1 in which said second conducting plate extends beyond the ends of said first conducting plate along the longitudinal axis defined by said insulated wire.