Thermal condensate reducer for optical devices

• US 6,866,391 B2
• Filed: 10/22/2002
• Issued: 03/15/2005
• Est. Priority Date: 11/14/2001
• Status: Expired due to Fees

• Current Assignee: Remotelight, Inc.
• Original Assignee: Remotelight, Inc.
• Inventors: Krausse, George J.
• Primary Examiner(s): SIKDER, MOHAMMAD YUNUS
• Application Number:
  US10/279,140
• Publication Number:
  US 20030091089A1
• Time in Patent Office: 875 Days
• Field of Search: 359512-513, 374/16, 374/28, 219202-205, 219495-508
• US Class Current: 359/512
• CPC Class Codes: G02B 27/0006 with means to keep optical surfaces clean, e.g. by preventing or removing dirt, stains, contamination, condensation G02B1/18 takes precedence; cleaning in general B08B
• CPC Class Codes: G02B 7/008 with means for compensating for changes in temperature or for controlling the temperature; thermal stabilisation
• CPC Class Codes: G02B 7/1815 with cooling or heating systems cooling arrangements for laser mirrors H01S3/0401

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.

Claims

1. A system for reducing water vapor condensation on an optical surface that is subject to condensation comprising;

a first temperature sensor for measuring the surface temperature of said optical surface;

a second temperature sensor for measuring the ambient temperature of the air surrounding said optical surface;

a comparator for comparing said first temperature sensor to said second temperature sensor and establish a temperature differential from said comparison;

a heating element to transfer heat to said optical surface;

a controller to regulate said heating element by establishing a temperature setpoint and a thermostatic range for the optical surface based upon said temperature differential.

2. The system of claim 1 wherein said first temperature sensor is a surface mounted thermal sensor in thermal communication with said optical surface.

3. The system of claim 1 wherein said second temperature sensor is a surface mounted thermal sensor that is thermally isolated from said optical surface.

4. The system of claim 1 wherein said first and second temperature sensors are solid-state precision temperature sensors.

5. The system of claim 1 wherein said controller is used to activate a solid-state power switch that applies voltage to said heating element.

6. The system of claim 1 wherein said heating element is an electric resistive heating element.

7. The system of claim 6 wherein said electric resistive heating element is a thin, flexible printed circuit board populated with surface mount chip resistors bonded to a flexible strip.

8. The system of claim 7 wherein said flexible strip includes said thermal sensors.

9. The system of claim 1 wherein said controller further comprises;

a compensator for incorporating the thermal resistance of the system comprising said optical surface, said heating element and said temperature sensors.

10. A system for reducing water vapor condensation on an optical surface that is subject to condensation comprising;

a surface mounted first temperature sensor for measuring the surface temperature of said optical surface that is in thermal communication with said optical surface, wherein said first temperature sensor is a solid-state precision temperature sensor;

a surface mounted second temperature sensor for measuring the ambient temperature of the air surrounding said optical surface that is thermally isolated from said optical surface, wherein said second temperature sensor is a solid-state precision temperature sensor;

a comparator for comparing said first temperature sensor to said second temperature sensor and establish a temperature differential from said comparison;

an electric resistive heating element to transfer heat to said optical surface;

a controller to activate a solid-state power switch that applies a voltage to regulate said electric resistive heating element by establishing a temperature setpoint and a thermostatic range for the optical surface, based upon said temperature differential, said electric resistive heating element further comprising a thin, flexible printed circuit board populated with surface mount chip resistors bonded to a flexible strip;

a compensator for incorporating the thermal resistance of the system comprising said optical surface, said heating element and said temperature sensors.

11. A system for reducing water vapor condensation on an optical surface of a telescope that is subject to condensation comprising;

a first temperature sensor for measuring the surface temperature of said optical surface that generates a current surface temperature data signal;

a second temperature sensor for measuring the ambient temperature of the air surrounding said optical surface that generates a current ambient temperature data signal;

a comparator that establishes a temperature differential by comparing said current surface temperature data signal to said current ambient temperature data signal;

a signal generator that generates a heater control signal;

a heating element that responds to said heater control signal to transfer heat to said optical surface and reduce said water vapor condensation on said optical surface;

a controller that analyzes said temperature differential and said heater control signal to regulate said heat applied to said heating element and maintain a selected thermostatic temperature range for the optical surface by controlling the amount of said heat applied by said heating element.

12. The system of claim 11 wherein said first temperature sensor is a surface mounted thermal sensor in thermal communication with said optical surface.

13. The system of claim 11 wherein said second temperature sensor is a surface mounted thermal sensor that is thermally isolated from said optical surface.

14. The system of claim 11 wherein said first and second temperature sensors are solid-state precision temperature sensors.

15. The system of claim 11 wherein said heater control signal is used to activate a solid-state power switch that applies voltage to said heating element.

16. The system of claim 11 wherein said signal generator generates said heater control signal when said temperature differential reaches a selected lower limit threshold and continues until a selected upper limit threshold above said selected lower limit threshold is reached.

17. The system of claim 11 wherein said heater control signal varies with the change in said temperature within said temperature differential.

18. The system of claim 11 wherein said heating element is an electric resistive heating element.

19. The system of claim 18 wherein said electric resistive heating element is a thin, flexible printed circuit board populated with surface mount chip resistors bonded to a flexible strip.

20. The system of claim 19 wherein said flexible strip includes said thermal sensors.

21. The system of claim 11 wherein said controller further comprises;

a compensator for incorporating the thermal resistance of the system comprising said optical surface, said heating element and said temperature sensors.

22. A system for reducing water vapor condensation on an optical surface of a telescope that is subject to condensation comprising;

a first surface mounted solid-state precision temperature sensor in thermal communication with said optical surface for measuring the surface temperature of said optical surface;

said first sensor that generates a current surface temperature data signal;

a second surface mounted solid-state precision temperature sensor that is thermally isolated from said optical surface for measuring the ambient temperature of the air surrounding said optical surface;

said second sensor that generates a current ambient temperature data signal;

a comparator that establishes a temperature differential by comparing said current surface temperature data signal to said current ambient temperature data signal;

a signal generator that generates a heater control signal used to activate a solid-state power switch that applies voltage to said heating element;

an electric resistive heating element comprising a thin, flexible printed circuit board populated with surface mount chip resistors and said bonded to a flexible strip, activated by a solid-state power switch that applies voltage to electric resistive heating element in response to said heater control signal to transfer heat to said optical surface and reduce said water vapor condensation on said optical surface;

a controller that analyzes said temperature differential and said heater control signal to regulate said heat applied to said heating element and maintain a selected thermostatic temperature range for the optical surface by controlling the amount of said heat applied by said heating element.

a compensator for incorporating the thermal resistance of the system comprising said optical surface, said heating element and said temperature sensors.

23. A system for reducing water vapor condensation on an optical surface of a telescope that is subject to condensation comprising;

a first temperature sensor that measures the surface temperature of said optical surface to provide a current surface temperature data signal;

a second temperature sensor that measures the ambient temperature of the air surrounding said optical surface to provide a current ambient temperature data signal;

a hygrometric sensor for measuring the ambient relative humidity of the air surrounding said optical surface to provide a current ambient relative humidity data signal;

a controller that calculates a dew point of said ambient air by comparing said current ambient relative humidity to said current ambient temperature;

a comparator that establishes a temperature differential by comparing said current surface temperature data signal to said dew point;

a signal generator that generates a heater control signal;

a heating element that responds to said heater control signal to transfer heat to said optical surface.

24. The system of claim 23 wherein said first temperature sensor is a surface mounted thermal sensor in thermal communication with said optical surface.

25. The system of claim 23 wherein said second temperature sensor is a surface mounted thermal sensor that is thermally isolated from said optical surface.

26. The system of claim 23 wherein said first and second temperature sensors are solid-state precision temperature sensors.

27. The system of claim 23 wherein said signal generator generates said heater control signal when said temperature differential reaches a selected lower limit threshold and continues until a selected upper limit threshold above said dew point is reached.

28. The system of claim 23 wherein said heater control signal varies with the change in said temperature within said temperature differential.

29. The system of claim 23 wherein said heater control signal is used to activate a solid-state power switch that applies voltage to said heating element.

30. The system of claim 23 wherein said heating element is an electric resistive heating element.

31. The system of claim 30 wherein said electric resistive heating element is a thin, flexible printed circuit board populated with surface mount chip resistors bonded to a flexible strip.

32. The system of claim 31 wherein said flexible strip includes said thermal and said hygrometric sensors.

33. The system of claim 23 wherein said controller further comprises;

a compensator for incorporating the thermal resistance of the system comprising said optical surface, said heating element, said temperature sensors and said hygrometric sensors.

34. A system for reducing water vapor condensation on an optical surface of a telescope that is subject to condensation comprising;

a first surface mounted solid-state precision temperature sensors in thermal communication with said optical surface for measuring the surface temperature of said optical surface;

said first sensor that generates a current surface temperature data signal;

a second surface mounted solid-state precision temperature sensors that is thermally isolated from said optical surface for measuring the ambient temperature of the air surrounding said optical surface;

said second sensor that generates a current ambient temperature data signal;

a hygrometric sensor for measuring the ambient relative humidity of the air surrounding said optical surface that generates a current ambient relative humidity data signal;

said hygrometric sensor that generates a current ambient relative humidity data signal;

a controller that calculates a dew point of said ambient air by comparing said current ambient relative humidity to said current ambient temperature;

a comparator that establishes a temperature differential by comparing said current surface temperature data signal to said dew point;

a signal generator that generates a heater control signal;

said signal generator generates said heater control signal when said temperature differential reaches a selected lower limit threshold and continues until a selected upper limit threshold above said dew point is reached

an electric resistive heating element comprising a thin, flexible printed circuit board populated with surface mount chip resistors and said bonded to a flexible strip, activated by a solid-state power switch that applies voltage to electric resistive heating element in response to said heater control signal to transfer heat to said optical surface;

a compensator for incorporating the thermal resistance of the system comprising said optical surface, said heating element and said temperature sensors.

35. A system for reducing water vapor condensation on an optical surface that is subject to condensation comprising;

a first temperature sensing means for measuring the surface temperature of said optical surface;

a second temperature sensing means for measuring the ambient temperature of the air surrounding said optical surface;

a comparing means for comparing said first temperature sensor to said second temperature sensor and establish a temperature differential from said comparison;

a heating means to transfer heat to said optical surface;

a controlling means to regulate said heating means by establishing a temperature setpoint and a thermostatic range for the optical surface based upon said temperature differential.