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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
First Claim
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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.

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