Inductive pickup sensor with enhanced cross-talk immunity

• US 5,612,620 A
• Filed: 03/27/1996
• Issued: 03/18/1997
• Est. Priority Date: 03/27/1996
• Status: Expired due to Fees

• Current Assignee: Fluke Corporation (Fortive Corp.)
• Original Assignee: Fluke Corporation (Fortive Corp.)
• Inventors: Heuvel, Johannes B. O.
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): DO, DIEP N
• Application Number:
  US08/623,388
• Time in Patent Office: 356 Days
• Field of Search: 324/628, 324/127, 324/128, 324/132, 324/391-393, 324/402
• US Class Current: 324/402
• 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 2017/003 using an inductive sensor, e.g. trigger tongs
• CPC Class Codes: F02P 2017/006 using a capacitive sensor
• CPC Class Codes: G01R 1/07 Non contact-making probes

Abstract

An inductive pickup sensor employing an isolation transformer to achieve substantially improved immunity to capacitively-induced cross-talk signals is provided. A magnetic pickup coil is coupled to a spark plug wire to receive a spark signal. The spark signal developed across the magnetic pickup coil is then coupled to via a sensor cable to the primary winding of an isolation transformer which is configured to provide a relatively low interwinding capacitance level to substantially reduce the cross-talk signal amplitude relative to the spark signal at a detector circuit. The detector turns the spark signal into a trigger signal at a pair of output terminals.

Claims

1. An inductive pickup sensor with enhanced immunity to cross-talk comprising:

(a) an inductive pickup coil for inductively receiving a spark signal from a selected spark plug wire while capacitively receiving a cross-talk signal from a cross-talk source;

(b) an isolation transformer having a primary winding and a secondary winding, said primary winding coupled to said inductive pickup coil wherein said spark signal is inductively coupled to said secondary winding and said cross-talk signal is capacitively coupled to said secondary winding;

(c) a detector coupled to said secondary winding for converting said spark signal into a trigger signal wherein the amplitude of said cross-talk signal at said detector is reduced to obtain a desired amount of cross-talk immunity by setting an appropriate distance between said primary winding and said secondary winding; and

(d) a pair of terminals for coupling said trigger signal to a test instrument.

2. An inductive pickup sensor with enhanced immunity to cross-talk according to claim 1 further comprising an electrostatic shield enclosing said isolation transformer and said detector to reduce the amplitude of said cross-talk signal at said detector.

3. An inductive pickup sensor with enhanced immunity to cross-talk comprising:

(a) an inductive pickup coil for inductively receiving a spark signal from a selected spark plug wire while capacitively receiving a cross-talk signal from a cross-talk source;

(b) an isolation transformer having a primary winding and a secondary winding, said primary winding coupled to said inductive pickup coil wherein said spark signal is inductively coupled to said secondary winding and said cross-talk signal is capacitively coupled to said secondary winding;

(c) a detector coupled to said secondary winding for converting said spark signal into a trigger signal;

(d) an electrostatic shield enclosing said isolation transformer and said detector wherein the amplitude of said cross-talk signal at said detector is reduced to obtain a desired amount of cross-talk immunity by setting an appropriate distance between said primary winding and said secondary winding and by using said electrostatic shield; and

(e) a pair of terminals for coupling said trigger signal to a test instrument.