Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2000-04-04
2001-05-29
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S649000, C324S662000, C324S667000, C073S30400R, C073S170260, C702S057000
Reexamination Certificate
active
06239601
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to measurement devices and more specifically to a device and method for determining the thickness of a layer of ice, or a layer containing a mixture of ice and water or other liquid.
2. Description of the Related Art
This applicant in U.S. Pat. No. 4,766,369, which is hereby incorporated by reference, disclosed a dual-geometry, capacitance-type ice thickness-measuring gauge. The gauge disclosed therein uses two capacitance sensors having greatly different electrode configurations and spacing to measure the thickness of surface ice independently of the temperature and impurities in the ice. That device works well if the ice is homogeneously solid, with no water or other liquid mixed in the ice, and when the temperature is not close to the melting point.
Ice formation often occurs with some liquid water present. In certain applications, e.g., aircraft icing, conditions, runway or roadway icing conditions, etc., it is critical to know that ice is forming and to determine its thickness even if it is not completely frozen. For such cases when liquid water is present, or when ice is not far from the freezing temperature, the electrical conductivity of the ice can be a significant or even dominant part of the total impedance across the ice. This conductivity, which is not accounted for in the dual geometry gage of U.S. Pat. No. 4,766,369, could result in indicated thickness measurements which are highly inaccurate if this term is not properly accounted for.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a thickness measurement device and method that determines the thickness of a layer of ice, or a layer of ice having, some water or other liquid mixed with the ice, over a surface.
The foregoing and additional objects of the present invention, which will become more obvious are attained by providing a device and method for determining the thickness of an ice layer, which may have liquid water or other liquid content, accumulated over the surface of the device.
A temperature sensor is first used to determine if freezing conditions, i.e., temperatures below 0° C., are even possible. If freezing, conditions are possible, and ice accumulation is suspected, the system measures the suspected ice thickness. Thickness measurements would be obtained for the layer whether it is ice or a mixture of ice and water or other liquid. The measurement would be obtained by using two different geometry gages at two predetermined frequencies. The predetermined frequencies would be selected in a range where the dielectric constant and the relative conductivity of both ice and water are relatively frequency independent.
A first total impedance sensor with its measurement circuit measures the near wall effect of the accumulations of coating material at the two selected frequencies. A second total impedance sensor along with its measurement circuit measures the bulk average effect of the accumulation of the coating material all the way from the wall to the outer surface of the layer at the same two frequencies. An analog circuit (or computer program) processes the outputs from the first and second measuring circuits to separate, for both gages, the value of capacitance from the total impedance. This capacitance is a far better indicator of thickness than total impedance due to the far lower variation in the dielectric constant value for ice, or ice with a small amount of water, compared to the variation in conductivity. The ratio of capacitance can then be used in a similar fashion to the method of U.S. Pat. No. 4,766,369 to obtain thickness. One of the novel features of the present invention is to identify and remove the conductivity effects from the impedance data to properly obtain a more accurate capacitance response.
REFERENCES:
patent: 3882381 (1975-05-01), Gregory
patent: 3986110 (1976-10-01), Overall et al.
patent: 4766369 (1988-08-01), Weinstein
patent: 5191791 (1993-03-01), Gerardi et al.
patent: 5394340 (1995-02-01), Inkpen
patent: 5793640 (1998-08-01), Wu et al.
patent: 5955887 (1999-09-01), Codner et al.
Deb Anjan K.
Hammerle Kurt G.
Metjahic Safet
The United States of America as represented by the Administrator
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