MEASURING SYSTEM FOR NON-DESTRUCTIVE THICKNESS MEASUREMENT OF ELECTRICALLY NON-CONDUCTIVE COATINGS ON ELECTRICALLY CONDUCTIVE BODIES

• US 3,801,900 A
• Filed: 11/28/1972
• Issued: 04/02/1974
• Est. Priority Date: 12/08/1971
• Status: Expired due to Term

• Current Assignee: Imre Szasz
• Original Assignee: Imre Szasz
• Inventors: Szasz, Imre
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US05/310,106
• Time in Patent Office: 490 Days
• Field of Search: 324/61R 317/246 323/93 340/200
• US Class Current: 324/671
• CPC Class Codes: G01B 7/085 for measuring thickness of coating
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24

Abstract

A measuring device for non-destructive thickness measurement of a dielectric coating on an electrically conductive body comprises a conductive probe plate adapted to be applied to the surface of the dielectric coating; a high frequency voltage generator connected to either the probe plate or the conductive body for supplying a high frequency signal thereto; a reference capacitor having known capacitance connected to the probe plate or the conductive body, whichever is not connected to the high frequency voltage generator; a measuring device connected across the reference capacitor for measuring the voltage drop across the reference capacitor; and a display device connected to the measuring device for displaying the measured voltage drop, which directly indicates the layer thickness of the dielectric coating.

Claims

1. A measuring device for non-destructive thickness measurement of a dielectric coating on an electrically conductive body comprising a conductive probe plate adapted to be applied to the surface of the dielectric coating, whereby said probe plate acts as a first capacitor plate, the conductive body acts as a second capacitor plate, and the dielectric coating acts as an insulating capacitive layer when said probe plate is applied to the surface of the dielectric coating;

high frequency voltage generating means connected in series to one of said capacitor plates for supplying a high frequency signal thereto;

a reference capacitor having known capacitance connected in series to the other of said capacitor plates;

measuring means connected across said reference capacitor for measuring the voltage drop across said reference capacitor; and

display means connected to said measuring means for displaying the measured voltage drop, said voltage drop directly indicating the layer thickness of the dielectric coating.

2. The measuring device of claim 1, wherein the capacitance of said reference capacitor approximately corresponds to the capacitance of the smallest layer thickness which is to be measured.

3. The measuring device of claim 1 comprising several reference capacitors, said reference capacitors being selectively series connected to said probe plate.

4. The measuring device of claim 1 comprising at least two reference capacitors selectively series connected to said probe plate, wherein the capacitance of one of said reference capacitors approximately corresponds to the capacitance of the smallest layer thickness which is to be measured and the capacitance of the other reference capacitors vary decadicly therefrom.

5. The measuring device of claim 1 comprising means for varying the voltage of said high frequency voltage generating means and means for adjusting the capacitance of the reference capacitor.

6. The measuring device of claim 1 coMprising an integrated amplifier having an input and an output connected to said high frequency voltage generating means, said output of said amplifier being connected back by a Zener diode to said input of said amplifier.

7. The measuring device of claim 1 comprising an impedance converter connected between said reference capacitor and said display means.

8. The measuring device of claim 1 comprising amplifying means connected to said reference capacitor and rectifying means connected between said amplifying means and said display means.

9. The measuring device according to claim 1, wherein said probe plate is circular shaped, having a diameter of approximately 10 mm.

10. The measuring device of claim 1 comprising a probe casing, said probe casing accommodating said reference capacitor and said probe plate in immediate proximity therewith.

11. The measuring device of claim 7 comprising a probe casing, said probe casing accommodating said reference capacitor and said probe plate in immediate proximity therewith.

12. The measuring device of claim 11 wherein said impedance converter is accommodated within said probe casing.

13. The measuring device of claim 4 comprising a probe casing, said probe casing accommodating said reference capacitor and said probe plate in immediate proximity therewith.

14. The measuring device of claim 13 wherein said probe casing includes a switching means connected to said reference capacitors for selectively connecting said reference capacitors to said measuring means.

15. The measuring device of claim 14 comprising rubber fastening means resiliently connecting said probe plate to said insulating case for permitting all-around tilting of the device.

16. The measuring device of claim 10 comprising an insulating case within said probe casing enveloping said probe plate.

17. The measuring device of claim 16 wherein said probe plate comprises elastic electrically conductive material.