Shape memory alloy thermal exposure monitor

• US 6,425,343 B1
• Filed: 04/28/1999
• Issued: 07/30/2002
• Est. Priority Date: 04/28/1998
• Status: Expired due to Fees

• Current Assignee: Akers, Jeffrey W., Zerkus, James Michael
• Original Assignee: Akers, Jeffrey W., Zerkus, James Michael
• Inventors: Zerkus, James Michael, Akers, Jeffrey W.
• Primary Examiner(s): Gutierrez, Diego
• Assistant Examiner(s): Guadalupe, Yaritza
• Application Number:
  US09/301,418
• Time in Patent Office: 1,189 Days
• Field of Search: 116/216, 116/221, 116/207, 426/88, 374/102, 374/104, 374/106, 374/187, 374/205, 374/206, 374/207
• US Class Current: 116/216
• CPC Class Codes: G01K 5/483 using materials with a configuration memory, e.g. Ni-Ti alloys

Abstract

A thermal exposure monitor has a thermally-conductive housing adapted to be placed in close proximity to a product to be monitored and at least one thermally-responsive shape memory alloy member in the housing that has a first shape at temperatures below a critical temperature and a second shape at temperatures above the critical temperature and a transformation temperature range encompassing a prescribed detrimental temperature related to the product being monitored. An indicator associated with the thermally-responsive member is moved from an initial position as the thermally-responsive member changes from the first shape to the second shape so as to be visually observed through a window on the housing to visually indicate whether the product being monitored has been exposed to temperatures above the prescribed detrimental temperature for a period of time that would be detrimental to the product.

Claims

1. A cumulative thermal exposure monitor for indicating absorption of heat outside of a prescribed temperature range for a prescribed period of time, comprising:

a thermally-conductive housing having a transparent window portion, said housing formed of a material having prescribed thermal properties;

a thermally-responsive member in said housing formed of a shape memory alloy having a first shape at temperatures below a critical temperature and changing to a second shape at temperatures above the critical temperature and having a transformation temperature range encompassing said prescribed temperature range;

indicator means associated with said thermally-responsive member to be moved from an initial position thereby as said thermally-responsive member moves between said first shape and said second shape so as to be visually observed through said window;

a photochromic film material disposed in said housing closely adjacent to said indicator means and said thermally-responsive member;

either of said indicator means or said thermally-responsive member containing a radiation emitting substance to effect said film material;

said prescribed thermal properties of said housing and said transformation temperature range of said shape memory alloy correlated such that said thermally-responsive member moves between said first shape and said second shape upon absorption of heat above said critical temperature for said prescribed period of time;

said indicator means remaining in a position at which it was moved by said thermally-responsive member to indicate the absorption of heat above said critical temperature for said prescribed period of time; and

said film is altered by exposure to the radiation emitting substance with respect to time and location of said indicator means and said thermally-responsive member as said thermally-responsive member changes from said first shape to said second shape to provide a time and temperature log of environmental thermal events indicating absorption of heat above said critical temperature for said prescribed period of time.

2. A cumulative thermal exposure monitor for indicating absorption of heat outside of a prescribed temperature range for a prescribed period of time, comprising:

a thermally-conductive housing having a transparent window portion, said housing formed of a material having prescribed thermal properties;

a thermally-responsive member in said housing formed of a shape memory alloy having a first shape at temperatures below a critical temperature and changing to a second shape at temperatures above the critical temperature and having a transformation temperature range encompassing said prescribed temperature range;

indicator means associated with said thermally-responsive member to be moved from an initial position thereby as said thermally-responsive member moves between said first shape and said second shape so as to be visually observed through said window;

a latch member having one end disposed in said housing formed of a thin strip or wire of shape memory alloy material having an initial remembered configuration and changing to a second configuration at or below a prescribed austenitic start temperature;

said latch member in said initial remembered configuration is engaged with said indicator means to hold said thermally-responsive member in its said first shape and upon said latch member reaching its said prescribed austenitic start temperature changing to its said second configuration and becoming disengaged therefrom to allow said thermally-responsive member to change to its said second shape;

said prescribed thermal properties of said housing and said transformation temperature range of said thermally-responsive member shape memory alloy correlated such that said thermally-responsive member moves between said first shape and said second shape upon absorption of heat above said critical temperature for said prescribed period of time; and

said indicator means remaining in a position at which it was moved by said thermally-responsive member to indicate the absorption of heat above said critical temperature for said prescribed period of time.