Sensing device and method

A sensing device for indicating changes in a certain predetermined condition such as temperature and humidity in a fluid medium comprising:

• a fixed support post having a first central axis;
• a sensing coil including a spiral wound sensing element having an inner end, an outer end, and a second central axis, said sensing element having a substantially constant width along its length, said sensing element defining an outside surface thereon of said substantially constant width along its length generally parallel to said central axis and said sensing element expanding and contracting in response to changes in the certain condition in the fluid medium to open and close said coil said inner end of said sensing element of said coil affixed to said post to support said coil so that said second central axis of said coil coincides with said first central axis of said support post so that said inner end of said sensing element is relatively fixed while the remainder of said sensing element moves as said sensing element expands and contracts;
• an indicator affixed to said outside surface of said sensing element, said indicator having a width substantially equal to the width of said sensing element, said indicator lying within the confines of said outside surface of said sensing element at a prescribed position along the length of said outside surface so that said indicator moves with said sensing element as said sensing coil opens and closes;
• an annular optically reflective member fixably carried by said support post concentrically about said first and second central axes outboard of said sensing coil, said optically reflective member defining an annular optically reflective surface thereon concentric about said first and second central axes, said reflective surface laterally aligned with said outside surface of said sensing element and with said indicator, said optically reflective surface defining a prescribed including angle with respect to said first and second central axes so that an optical image of said indicator is generated in a reading plane normal to said central axis;
• and,
• indicia means operatively associated with said optical image of said indicator in said reading plane to quantify the movement of said indicator on said sensing element of said coil.