Method of thermal condensate reduction for optical devices

Abstract

The present invention provides a method and system to overcome and eliminate the effects of condensation contamination of optical surfaces that are induced by radiative cooling. The invention counteracts the effects of radiative cooling on optical surfaces and maintains an optical system within a very tight limit to the ambient temperature by utilizing a resistive heater element that is in contact with the optical components subject to condensation. In thermal contact with this optical component is a solid-state precision temperature sensor. In addition, there is a matching solid-state precision temperature in thermal contact with the ambient air but thermally isolated from the optical element. Signals from these two sensors are applied to a comparator that functions to generate a data signal when the optical surface temperature is less than the ambient or reference temperature. This data signal is used to activate a solid-state power switch that applies a voltage to a resistive heating element. An offset may also be applied to the reference temperature sensor allowing compensation for the thermal resistance of the system comprised of the optical component, optical component attachment heater and temperature sensor.

1 . A method of reducing water vapor condensation on an optical surface that is subject to condensation comprising; 
 measuring the ambient temperature of the air surrounding said optical surface;    measuring the surface temperature of said optical surface;    comparing said ambient temperature of the air surrounding said optical surface to said surface temperature of said optical surface to establish a temperature differential;    increasing said surface temperature of said optical surface to reduce said water vapor condensation on said optical surfaces by introducing heat to said optical surface with a heating element;    regulating said amount of heat applied to said optical surface by establishing a temperature setpoint and a thermostatic range for the optical surface based upon said temperature differential.    
   
   
       2 . A method of  claim 1  wherein said measuring of said ambient temperature is performed with a surface mounted thermal sensor that is thermally isolated from said optical surface.  
   
   
       3 . A method of  claim 1  wherein said measuring of the surface temperature of said optical surface is performed with a surface mounted thermal sensor in thermal communication with said optical surface.  
   
   
       4 . A method of  claim 1  wherein said step of regulating said amount of heat applied to said optical surface is performed by controlling the duty cycle of said heating.  
   
   
       5 . A method of reducing water vapor condensation on an optical surface that is subject to condensation comprising; 
 measuring the ambient temperature of the air surrounding said optical surface with a surface mounted thermal sensor that is thermally isolated from said optical surface;    measuring the surface temperature of said optical surface with a surface mounted thermal sensor in thermal communication with said optical surface;    comparing said ambient temperature of the air surrounding said optical surface to said surface temperature of said optical surface to establish a temperature differential;    increasing said surface temperature of said optical surface to reduce said water vapor condensation on said optical surfaces by introducing heat to said optical surface with a heating element;    regulating said amount of heat applied to said optical surface by establishing a temperature setpoint and a thermostatic range for the optical surface based upon said temperature differential.    
   
   
       6 . A method of reducing water vapor condensation on an optical surface of a telescope that is subject to condensation comprising; 
 measuring the ambient temperature of the air surrounding an optical surface of said telescope;    establishing a current ambient temperature from said measurement of said ambient temperature;    measuring the surface temperature of said optical surface;    establishing a current optical surface temperature from said measurement of said surface temperature;    comparing said current ambient temperature to said current surface temperature of said optical surface to establish a temperature differential;    generating a data signal when said temperature differential reaches a selected threshold;    reducing said temperature differential sufficiently to reduce said water vapor condensation on said optical surfaces by heating said optical surface in response to said data signal;    maintaining said reduced temperature differential by controlling the amount of said heating of said optical surface based upon updated temperature measurements    
   
   
       7 . A method of  claim 6  wherein said measuring of said ambient temperature is performed with a surface mounted thermal sensor that is thermally isolated from said optical surface.  
   
   
       8 . A method of  claim 6  wherein said measuring of the surface temperature of said optical surface is performed with a surface mounted thermal sensor in thermal communication with said optical surface.  
   
   
       9 . A method of  claim 6  wherein said step of reducing said temperature differential sufficiently to reduce said water vapor condensation on said optical surfaces by heating said optical surface in response to said data signal further comprises; 
 compensating for the thermal resistance of the system comprising said optical components, said heating and said temperature sensors.    
   
   
       10 . A method of reducing water vapor condensation on an optical surface of a telescope that is subject to condensation comprising; 
 measuring the ambient temperature of the air surrounding an optical surface of said telescope with a surface mounted thermal sensor that is thermally isolated from said optical surface;    establishing a current ambient temperature from said measurement of said ambient temperature;    measuring the surface temperature of said optical surface with a surface mounted thermal sensor in thermal communication with said optical surface;    establishing a current optical surface temperature from said measurement of said surface temperature;    comparing said current ambient temperature to said current surface temperature of said optical surface to establish a temperature differential;    generating a data signal when said temperature differential reaches a selected lower limit threshold, said data signal continues until a selected upper limit threshold above said lower limit threshold is reached;    activating a power switch in response to said data signal that applies a voltage to a resistive heating element mounted on, and in thermal contact with said optical components;    reducing said temperature differential sufficiently to reduce said water vapor condensation on said optical surfaces by controlling the amount of said voltage applied to said resistive heating element;    compensating for the thermal resistance of the system comprising said optical components, said resistive heating element and said temperature sensors;    maintaining said reduced temperature differential by controlling the amount of said voltage applied to said resistive heating element based upon updated temperature measurements.    
   
   
       11 . A method of reducing water vapor condensation on an optical surface that is subject to condensation comprising; 
 measuring the ambient temperature of the air surrounding an optical surface with a thermal sensor that is thermally isolated from said optical surface;    establishing a current ambient temperature from said measurement of said ambient temperature;    measuring the ambient relative humidity of the air surrounding said optical surface with a hygrometric sensor;    establishing a current ambient relative humidity from said measurement of said ambient relative humidity;    measuring the surface temperature of said optical surface with thermal sensor in thermal communication with said optical surface;    establishing a current optical surface temperature from said measurement of said surface temperature;    calculating a dew point for said ambient air by comparing said current ambient relative humidity to said current ambient temperature;    generating a data signal when said surface temperature of said optical surface is lower than a selected threshold above said calculated dew point;    heating said optical components in response to said data signal to increase said surface temperature of said optical surface to a point greater than said selected threshold above said calculated dew point.    
   
   
       12 . A method of  claim 11  wherein said measuring of said ambient temperature is performed with a surface mounted thermal sensor that is thermally isolated from said optical surface.  
   
   
       13 . A method of  claim 11  wherein said measuring of the surface temperature of said optical surface is performed with a surface mounted thermal sensor in thermal communication with said optical surface.  
   
   
       14 . A method of  claim 11  further comprising the step; 
 maintaining said increased surface temperature of said optical surface by controlling the amount of said heating based upon updated temperature and relative humidity measurements.    
   
   
       15 . A method of reducing water vapor condensation on an optical surface of a telescope that is subject to condensation comprising; 
 measuring the ambient temperature of the air surrounding an optical surface of said telescope with a surface mounted thermal sensor that is thermally isolated from said optical surface;    establishing a current ambient temperature from said measurement of said ambient temperature;    measuring the ambient relative humidity of the air surrounding an optical surface of said telescope with a hygrometric sensor;    establishing a current ambient relative humidity from said measurement of said ambient relative humidity;    measuring the surface temperature of said optical surface with a surface mounted thermal sensor in thermal communication with said optical surface;    establishing a current optical surface temperature from said measurement of said surface temperature;    calculating a dew point for said ambient air by comparing said current ambient relative humidity to said current ambient temperature;    generating a data signal when said surface temperature of said optical surface is lower than a selected threshold above said calculated dew point;    activating a power switch in response to said data signal that applies a voltage to a resistive heating element mounted on, and in thermal contact with said optical components    heating said optical components to increase said surface temperature of said optical surface to a point greater than said selected threshold above said calculated dew point;    compensating for the thermal resistance of the system comprising said optical components, said resistive heater and said temperature sensors;    maintaining said increased surface temperature of said optical surface by controlling the amount of said heating based upon updated temperature and relativity measurements.