Apparatus and method for determining the existence of ice or water on a surface from the capacitance between electrodes on said surface

• US 5,874,672 A
• Filed: 09/03/1996
• Issued: 02/23/1999
• Est. Priority Date: 03/09/1993
• Status: Expired due to Fees

• Current Assignee: Innovative Dynamics, Inc.
• Original Assignee: Innovative Dynamics, Inc.
• Inventors: Hickman, Gail A., Khatkhate, Ateen A., Pruzan, Dan A., Gerardi, Joseph J.
• Primary Examiner(s): FELBER, JOSEPH LEON
• Application Number:
  US08/707,778
• Time in Patent Office: 903 Days
• Field of Search: 73/170.26, 340/580, 340/962, 324/688, 324/671
• US Class Current: 73/170.26
• CPC Class Codes: B64D 15/20 Means for detecting icing or initiating de-icing
• CPC Class Codes: G01M 5/0016 of aircraft wings or blades
• CPC Class Codes: G01M 5/0083 by measuring variation of impedance, e.g. resistance, capacitance, induction
• CPC Class Codes: G08B 19/02 Alarm responsive to formation or anticipated formation of ice

Abstract

The present invention is an improved ice sensor which is particularly effective in measuring and quantifying non-uniform, heterogeneous ice typically found on aircraft leading edges and top wing surfaces. In one embodiment, the ice sensor comprises a plurality of surface mounted capacitive sensors, each having a different electrode spacing. These sensors measure ice thickness by measuring the changes in capacitance of the flush electrode elements due to the presence of ice or water. Electronic guarding techniques are employed to minimize baseline and parasitic capacitances so as to decrease the noise level and thus increase the signal to noise ratio. Importantly, the use of guard electrodes for selective capacitive sensors also enables distributed capacitive measurements to be made over large or complex areas, independent of temperature or location, due to the capability of manipulating the electric field lines associated with the capacitive sensors.

Claims

1. A device for determining the existence of ice or water associated with a surface comprising:

a first insulating layer disposed on said surface;

alternating pairs of positive and ground electrodes disposed on said first insulating layer for establishing electrical fields therebetween, each of said positive and ground electrodes having a capacitance associated therewith responsive to ice or water accretion therebetween; and

guard electrodes disposed on insulator sheets placed above each of said positive electrodes for substantially confining the electrical fields between said positive and ground electrodes substantially along a horizontal plane to said insulating layer such that said capacitance is substantially responsive only to water or ice accretion near said insulating layer.

2. The device of claim 1 further comprising

a second insulating layer, and

guarding means disposed between said first and second insulating layers for substantially eliminating electrical fields between said positive electrode and said surface.

3. The device of claim 2 further comprising

means for measuring at least at two frequencies the capacitances between said positive and ground electrodes so as to determine whether the accretion therebetween is ice, water or some other contaminant.

4. The device of claim 1 wherein said positive electrodes are electrically connected in parallel, and said ground electrodes are electrically connected in parallel.

5. The device of claim 4 wherein said guard electrodes are electrically connected in parallel.

6. A method for determining the existence of ice or water associated with a surface comprising the steps of:

a) establishing an electric field between a plurality of positive and ground electrodes positioned on an insulating layer placed on the surface, each of said positive and ground electrodes protruding from the insulating layer and having a capacitance associated therewith;

b) confining the established electric field as to provide electric field lines substantially parallel to the insulating layer such that the capacitance associated with said electrodes is substantially responsive only to water or ice accretion near the insulating layer;

c) measuring the capacitance associated with said electrodes; and

d) processing the measured capacitance to determine the existence of ice or water associated with the surface.

7. The method of claim 6 further comprising the step of measuring at least at two frequencies the capacitance between said positive and ground electrodes so as to determine whether the accretion therebetween is ice, water or some other contaminant.

8. The method of claim 6 wherein the step of confining is performed by establishing electric potentials at guard electrodes disposed on insulator sheets placed above each of said positive electrodes.

9. The method of claim 8 wherein the electric potentials established at said guard electrodes are substantially equal to electric potentials established at the positive electrodes.