Fiber optic hygrometer apparatus and method

An apparatus for measuring the dew point of an atmosphere comprising:

• a controller for controlling the operation of said apparatus;
• a first optical fiber having a core and first and second ends, said first end optically connected to a source of light energy coupling said light energy into said core and said second end having an exposed core extending into said atmosphere, said exposed core further including a tip end prepared as a reflecting surface for returning said light energy striking said reflecting surface into said core;
• a second optical fiber having a core and first and second ends, said core of said first end optically connected to said first optical fiber core between said first optical fiber first and second ends arranged to form an optical junction thereat for capturing the light energy reflected from said tip end into said second optical fiber core and arranged to convey said light energy captured to a light detector optically connected to said second optical fiber second end, said light detector arranged to receive and output signals to said controller representative of the magnitude of said light energy captured;
• a cooling device under control of said controller arranged to cool said exposed core to a temperature below the ambient temperature of the atmosphere, to cause water vapor contained in said atmosphere to condense on said exposed core;
• and
• a temperature sensing device for measuring the temperature of said exposed core operatively connected to said controller and responsive to the deposition of condensate on said exposed core an evanescent region is formed in the area of said condensate, decreasing the magnitude of light energy coupled to said second optical fiber, wherein said light detector outputs a signal to said controller representative of said decreased magnitude of light energy, causing said controller to read the temperature of said exposed core measured by said temperature sensor to establish the dew point of said atmosphere.

A method for measuring the dew point of an atmosphere comprising the steps of:

• transmitting light energy from a light energy source to an optical core extending into said atmosphere, said optical core including a reflecting surface reflecting said light energy striking said surface back into said optical core;
• cooling said optical core to a temperature below the ambient temperature of the atmosphere to cause condensation to be deposited on said optical core, forming an evanescent region in the area of said condensate;
• capturing the light energy contained within said optical core and transmitting the captured light energy to a light detector;
• and
• reading the temperature of said optical core responsive to a decreased magnitude of light energy detected by said light detector thereby establishing the dew point of said atmosphere.

An apparatus for measuring the dew point of an atmosphere comprising:

• means for directing light energy to an optical core extending into said atmosphere;
• means for cooling said optical core to a temperature below the ambient temperature of said atmosphere to cause water vapor that may be contained in said atmosphere to condense on said optical core, forming an evanescent region in the area of said condensate;
• means for internally reflecting the light energy contained in said optical core to a light energy detector, said light energy detector arranged to output signals representative of the magnitude of said light energy detected;
• and
• means for measuring the temperature of said optical core arranged to receive said output signals and to read the temperature of said optical core responsive to a decreased magnitude of light energy detected by said light energy detector thereby establishing the dew point of said atmosphere.