Membrane type non-intrusive ice detector

• US 4,611,492 A
• Filed: 05/03/1984
• Issued: 09/16/1986
• Est. Priority Date: 05/03/1984
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Koosmann, Mark R.
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US06/606,663
• Time in Patent Office: 866 Days
• Field of Search: 73/590, 73/579, 73/576, 73/583, 73/702, 73/170 R, 340/582
• US Class Current: 73/579
• CPC Class Codes: B64D 15/20 Means for detecting icing or initiating de-icing
• CPC Class Codes: G01N 2291/0251 Solidification, icing, curing composites, polymerisation
• CPC Class Codes: G01N 29/12 by measuring frequency or resonance of acoustic waves measuring frequency or resonant frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04, G01H13/00; acoustic resonators G10K11/04; vibration or shock testing of structures G01M7/00
• CPC Class Codes: G01W 1/00 Meteorology

Abstract

An ice detector of the vibrating element type comprises a tube that vibrates along its longitudinal axis, and is driven by an excitation coil at the natural frequency of the tube is sealed by a diaphragm which has a surface exposed to an air stream in which icing is to be sensed. The exposed diaphragm surface is deflectable during vibration of the tube at a flexible support portion of the diaphragm. As ice accumulates on the exposed surface of the flexible support the spring rate or flexibility of the flexible support changes, thereby changing the natural frequency of the vibration of the tube section. The changes in the natural frequency are sensed to determine that ice is accumulating. The diaphragm is of low mass, and small so that stiffness of small amounts of ice significantly changes the spring constant of the flexible support and the diaphragm is shaped to conform to adjacent aerodynamic surfaces.

Claims

1. An ice detector adapted for mounting on a wall having a curved outer surface, said ice detector comprising a disphragm member adapted to be exposed with such wall to an air stream in which ice is to be detected, said diaphragm member having a center portion, an outer edge support portion, and a flexible wall portion extending between the outer edge support portion and the center portion, said flexible wall portion permitting deflecting movement of the center portion in direction generally normal to the diaphragm member;

the diaphragm member being curved to form a smooth continuation of the curved outer surface of a wall on which the diaphragm member is mounted, means connected to the center portion of the diaphragm member to vibrate the center portion and having a mass that is selected to cause the natural frequency of vibration of the means to vibrate and the connected center portion of the diaphragm member to be dependent upon the flexibility of said flexible wall portion between the center portion and the outer edge support portion of said diaphragm member; and

means to sense changes in natural frequency of said means to vibrate upon change in flexibility of the flexible wall portion due to stiffness of ice accumulating on said diaphragm member.

2. The ice detector according to claim 1 wherein said flexible wall portion comprises a reduced thickness section between the outer edge support portion and the center portion.

3. The apparatus as specified in claim 2 wherein said flexible wall portion is an annular wall section surrounding the center portion.

4. An ice detector comprising a small diaphragm member exposed to an air stream in which ice is to be detected, said diaphragm member having a center portion, an outer edge support portion, and a flexible wall portion extending between the outer edge support portion and the center portion, said flexible wall portion permitting deflecting movement of the center portion in direction generally normal to the diaphragm member;

means connected to the center portion for vibrating the center portion of the diaphragm member and having a mass that is selected to cause the natural frequency of vibration of the connected center portion and the means for vibrating to be dependent upon the flexibility of said flexible wall portion between the center portion and the outer support edge portion of said diaphragm member wherein said means for vibrating said center portion comprising a tube member positioned on a side of said diaphragm member opposite from the airstream, a nodal support for supporting said tube member and dividing the tube member into first and second tube sections, the first tube section extending toward the diaphragm member and having its outer end connected to the center portion of said diaphragm member, and the second tube section extending in direction from said nodal support away from said diaphragm member, said first and second tube sections having substantially the same natural frequency of vibration in direction along the longitudinal axis, means for exciting the first and second tube sections into vibration at a natural frequency and for detecting such frequency of vibration, whereby changes in the natural frequency of one of the first and second tube sections results in an indication of change of frequency in the other tube section; and

means to sense changes in natural frequency of said means to vibrate upon change in flexibility of the flexible wall portion due to stiffness of ice accumulating on said diaphragm member.

5. The apparatus as specified in claim 4 wherein said outer edge support portion comprises a peripheral member surrounding the center portion, and heater means mounted in said peripheral member.

6. The apparatus as specified in claim 4 wherein the mass of the first tube section and the connected center portion are selected in relation to the spring constant of the flexible wall portion so that the natural frequency of the first tube section and the connected center portion of the diaphragm member is affected by the stiffness of the ice forming on the diaphragm member a significantly greater proportional amount than the mass of such ice which forms on the diaphragm.

7. The apparatus of claim 6 wherein the natural frequency of the tube sections are substantially governed by the following equations:

##EQU3## wherein f_n1 is the natural frequency of the first tube section

K₁ is the spring constant of the first tube section

K₂ is the spring constant of the flexible wall portion.

M₁ is the mass of the center portion.

M₂ is the mass of the first tube section.

f_n2 is the natural frequency of the second tube section

K₃ is the spring constant of the second tube section

M₃ is the mass of the second tube section.

8. An ice detector for mounting with respect to a wall having an outer surface exposed to an airstream in which formation of ice is to be detected comprising a diaphragm member adapted to be mounted on the wall and having an outer surface in the airstream, said diaphragm member having a center portion, an outer edge support portion, and a spring wall portion extending between the outer edge support portion and the center portion, said spring wall portion permitting deflecting movement of the center portion under spring load in a first direction axis;

a housing adapted to be mounted with respect to the wall and positioned on a side of said diaphragm member opposite from the airstream;

a tube member;

a support mounting said tube member to the housing to form a nodal support for the tube member and dividing the tube member into two vibrating tube sections, one of said tube sections extending from the nodal support toward the diaphragm member and having the outer end connected to the center portion of said diaphragm member for causing deflecting movement of the center portion along the first direction axis, said first direction axis being generally parallel to the orientation of the longitudinal axis of the tube member, and the other of said tube sections extending in direction from said nodal support away from said diaphragm member, said two tube sections having substantially the same natural frequency of vibration in direction along the longitudinal axis;

means for exciting the tube sections into vibration along the longitudinal axis at a natural frequency, and for detecting such frequency of vibration, whereby changes in the natural frequency of one of the tube sections results in an indication of change of frequency in the other tube section;

the center portion of said diaphragm vibrating with the first tube section, said first tube section and center portion being of a combined mass that is selected to cause the natural frequency of vibration of the first tube section to be dependent upon the spring constant of said spring wall portion between the center portion and the outer support portions of said diaphragm member; and

means to sense changes in natural frequency of said tube sections upon change in spring constant of the spring wall portion due to stiffness of ice accumulating on the outer surface of said diaphragm member.