Patent Publication Number: US-2013230813-A1

Title: Sensor and sense line heating device

Description:
BACKGROUND 
     Pressure sensors and associated sensor lines that sense various pressures in engines often experience problems related to moisture. Both water vapor and liquid water can enter the line. Water either enters sensors and sense lines in liquid form, or in gaseous form followed by condensation. The water has been demonstrated in many cases to be a source of malfunctions, leading to costly removals, repairs, problems encountered in flight, redesign and retrofits. 
     Water traps can be used, both flowing and non-flowing, with some effectiveness in removing the water. Heaters can be used with the sensors, but these consume power and add cost. Heaters may be difficult to install to ensure they apply heat to the right locations. Control mechanisms for heaters also add complexity. Flowing water traps can add an error to the sensed signal if the orifice/resulting flow is too large. Small orifices can plug and fail to flow when needed. An alternative way to keep pressure sensors and associated sensor lines free from moisture would be of value. 
     SUMMARY 
     The present invention provides for warming and drying a pressure sensor and sense line by the use of a second tube or line that is heated using engine gasses in a controlled fashion. In one embodiment, a first tube is provided for passage of pressure gas directly from the pressure port to the pressure sensor. A second tube that is larger than the first tube and has the first tube inside it. The second, outer tube is also connected to the pressure port and includes a temperature-sensitive valve, such as a bi-metal valve. When the temperature of the pressure sensor or outer tube drops below a predetermined value, the valve senses the lower temperature and opens, thus allowing hot air to flow from the outer tube connection port at the engine, down the outer tube to the pressure sensor. This warms the first, inner tube until it reaches a predetermined temperature to accomplish keeping the inner tube and sensor dry by evaporation of any water that has developed in the inner tube or sensor. 
     In other embodiments, the valve in the outer tube can be eliminated and warm air would flow continuously to maintain the temperature of the inner tube and sensor above the moisture laden gas&#39;s condensation point temperature. Also, instead of concentric tubes, the two tubes can be parallel to each other, with an overall insulating sheath. 
     A significant advantage of the present invention is that the primary source of gas that goes to the sensor is direct and not affected by any other factor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of the system of this invention. 
         FIG. 2  is a schematic view of an alternative system of this invention. 
     
    
    
     DETAILED DESCRIPTION 
     System  10  provides an effective and simple way to remove moisture from pressure gas as the pressure gas from a combustor  11  exits pressure port  13  and travels to pressure sensor  15  where the pressure is measured. A first tube  17  is used to connect pressure port  13  and pressure sensor  15  directly without any interference from any other equipment. Second tube  19 , shown concentrically enclosing first tube  17  in  FIG. 1 , is also connected to pressure port  13  and receives pressure gas at the same elevated temperature. 
     A temperature sensing device  21  may be provided to determine when the temperature of the first tube  17  and/or sensor  15  drops to a predetermined minimum temperature, at which concern is raised that water vapor in the pressure gas may condense. The temperature sensing device may be a temperature-sensitive valve, such as a bi-metal valve, that opens when the valve senses the temperature has dropped below the predetermined minimum, thus opening and allowing hot air to flow from the pressure port  13  to pressure sensor  15  until sensor  15  warms up to a predetermined temperature value where water will not condense. This temperature is selected to provide the desired drying action to keep first tube  17  and sensor and sensor  15  dry by evaporation of whatever water has developed in tube  17  or sensor  15 . Because the temperature regulation device provided the means to keep sensor  15  at a warmer temperature than would otherwise be seen when the engine is operating in a cold ambient environment, the overall sensor accuracy will be better because the accuracy of pressure sensors is usually affected by ambient temperature. 
     In some systems, it may not be necessary to have temperature activated valve  21  but rather allow warming air to flow in tube  19  continuously. 
       FIG. 2  illustrates an alternative design, placing a first tube  21  to convey pressure gas from pressure port  13  to sensor  15  and the second tube  23  is parallel to tube  21 . Both are surrounded by insulating sheath  25 . It should be noted that it is possible to fan out warm or hot pressure to multiple locations, allowing the system to be used to heat other devices, including ones that do not sense warm pressures or other parameters than pressure, particularly when cold accuracy performance is a concern. 
     Tube  21 , and tube  17 , may have a flowing or non-flowing water trap  27  in  FIG. 2 , depending on the particular engine being fitted with the present invention. Otherwise, tubes  17  and  21  have no other purpose than to transmit pressure gas to sensor  15 . 
     The system and method of this invention provides a simple mechanism to use a small amout of the warm engine pressure to heat sensor  15  and line  17  to drive off moisture. Moisture has also been found to carry other contaminants into the sensed port that interferes with pressure sensing applications, even causing plugging in some instances, added corrosion and otherwise physically interfering with sensing measurement. The system of this invention is simple and easy to install, low cost and can be added to existing engines with little or no modifications. The system and method may also be used on larger components such as “full authority digital electronic control units” (FADECS) when pressure lines are attached thereto, eliminating the need for electrical heaters within the FADECS. 
     The system of this invention may be used with other devices or sensors in addition to pressure sensors, and could be used for sensors that measure other gas properties. The system may also be used with devices such as an actuator that is pressure activated but not a sensor per-se. Also, in some applications a pressure relief valve may be included so that when the engine is not running but turning slowly due to in-flight wind-milling and producing a small pressure, cold air will not pass through the tube and also through the valve. The pressure relief valve would prevent flow from going through the outside tube when the combustor pressure falls below a predetermined value corresponding to an engine off condition. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.