Abstract:
An immersion thermowell with an electrically isolated sensor tube allows for ready conduction of heat energy to a temperature sensor probe. An electrical signal originating on the fluid container chassis can be conducted into the water, which can then be conducted to the electrically isolated thermowell tip and the signal can be made available to control apparatus.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates in general to simultaneous measurement of liquid temperature and liquid level in boilers for hot water and steam heating. 
     Immersion thermowells are commonly used to provide a ready means to place temperature sensors in thermally conductive relationship with the liquid in boilers and other liquid vessels. Immersion thermowells are typically supplied with most residential heating boilers and are designed to mount temperature regulating and indication controls to the boilers, as well as offering temperature sensing orifices in the boiler. It is well know by those skilled in the art that immersion thermowells provide a simple means to place sensors in thermal relationship with the fluid in the boiler but also allows easy removal for service without the need to drain the boiler which can be a time consuming and cumbersome task. 
     Liquid level sensors are not commonly provided by boiler manufacturers due to the significant added cost but are becoming more popular as various US states legislate their use. Specifically, liquid level sensors are used in conjunction with low water cut off limit controls to prevent the boiler from firing when the water level falls below a safe level. 
     Boiler manufacturers normally do not provide level sensing devices since some states do not require their use. Therefore the installation of low water cut-off controls is typically left to the installer where they are required or desired. The installer may be required to bore holes in the wall of the boiler to provide access to the water, or more commonly will complete the labour-intensive task of routing external piping in the heating system specifically to allow a low water cut-off control to be installed. Homeowners in states not legislating their use are more inclined not to have one installed due to the high cost of installation, despite the obvious added safety that is offered. 
     In the North America boiler temperature limit controls are subject to the same UL and CSA safety standard as boiler level controls. Since they are subject to the same standard and essentially provide the same function to enable or disable the burner it would be efficient to offer a single control to boiler manufacturers that incorporated both functions in one device. Since virtually all boiler temperature controls mount to immersion thermowells that are designed to only allow thermal conduction of water temperature but preventing the sensors from coming in direct contact with the water it is not practical to provide level sensing means through the immersion thermowells currently available. 
     The Arekapudi U.S. Pat. No. 5,178,009 discloses an integral temperature and liquid level sensor and control that effectively provide such a solution, but Arekapudi teaches a combination sensor that is permanently fixed to the vessel wall. 
     John, in U.S. Pat. No. 5,111,691 also provides a single sensor control apparatus that combines liquid level and temperature measurement but also requires the sensor to be mounted directly in the sidewall of the boiler in direct contact with the fluid. 
     Perry in US patent application publication # 2007/0253463 discloses a means to detect fluid conductivity but requires a plurality of sensors spaced some distance apart. 
     In U.S. Pat. No. 4,859,076 Twerdochlib discloses a split thermowell for water and steam detection that uses dual temperature sensors and a heating element to detect the presence of water in vessel. 
     SUMMARY OF THE INVENTION 
     Accordingly it is therefore an object of the present invention to provide an immersion thermowell to allow for simultaneous measurement of liquid temperature and liquid level in vessels without direct contact between the sensors and the liquid. 
     It is a further object of the present invention to provide an immersion thermowell to allow for either measurement of liquid temperature or liquid level in vessels without direct contact between the sensors and the liquid. 
     It is yet another object of the present invention to provide a means to allow for easy insertion and removal of sensors in communicating relationship with the liquids in boilers. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Other objects and advantages will become apparent to those skilled in the art as this specification of the invention is disclosed in detail with reference to the drawings in which like numerals have been used to designate like elements throughout and wherein. 
         FIG. 1  is a three-dimensional diagrammatic representation of the preferred embodiment of the present invention. 
         FIG. 2  is a side view, diagrammatic representation of the preferred embodiment of the present invention. 
         FIG. 3  is a cross sectional view diagrammatic representation of the preferred embodiment of the present invention. 
         FIG. 4  is a cross sectional view diagrammatic representation of another preferred embodiment of the present invention. 
         FIG. 5  is a cross sectional view diagrammatic representation of yet another preferred embodiment of the present invention. 
         FIG. 6  is a cross sectional view diagrammatic representation of the preferred embodiment of the present invention in a typical boiler application. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, with reference to  FIG. 1  there is disclosed the preferred embodiment of the present invention. Electrically conductive housing shell  1  is coaxially joined to electrically insulating collar  2 , which is in turn coaxially joined to electrically and thermally conductive sensor tube  3 . In the preferred embodiment housing shell  1  is constructed by lathe-turned brass or similar metal known to those skilled in the art, while collar  2  is formed from a suitable plastic or ceramic material. Sensor tube  3  is formed from copper, brass or some other suitable material that exhibits thermal and electrically conductive characteristics. 
     Turning to  FIG. 2 , a side view of a preferred embodiment, discloses housing shell  1  with annular pipe thread  4  in a position intermediate to first end  5  and second end  6 . Collar  2  is coaxially joined to housing shell  1  so that collar  2  extends beyond housing shell  1  to a point intermediate housing shell  1  and second end  6 . 
     Now turning to  FIG. 3  there is disclosed a cross sectional view of the preferred embodiment of the present invention. Collar  2  is coaxially joined to housing  1  with the mating surfaces only maintaining contact to a point intermediate the axial length of housing  1 . Sensor tube  3  is likewise coaxially joined to collar  2  with the mating surfaces only maintaining contact to a point intermediate the axial length of collar  2 . Bonding of mating surfaces may be with cement, friction or another method well known to those skilled in the art. 
       FIG. 4  discloses a cross sectional view of another preferred embodiment of the present invention. Collar  2  is formed from mildly flexible material such as nylon or some other suitable plastic known to those skilled in the art. Collar  2  is coaxially joined to housing  1  with the mating surfaces only maintaining contact to a point intermediate the axial length of housing shell  1 . Sensor tube  3  is coaxially joined to collar  2  and extends to first end  5 . A second collar  9  electrically isolates sensor tube  3  from housing shell  1  and further electrically isolates retaining nut  7  from housing shell  1 . Retaining nut  7  is threaded onto sensor tube  3  to cause flange  9  to compress collar  2  forming a watertight seal. 
     Now turning to  FIG. 5  there is disclosed a cross sectional view another preferred embodiment of the present invention. Collar  2  is coaxially joined to housing shell  1  with the mating surfaces maintaining contact the entire axial length of housing shell  1  to first end  5 . Sensor tube  3  is likewise coaxially joined to collar  2  with the mating surfaces maintaining contact the entire axial length of collar  2  to first end  5 . Bonding of mating surfaces may be with cement, friction or another method well known to those skilled in the art. 
     Lastly, turning to  FIG. 6  there is disclosed a cross sectional view of the preferred embodiment of the present invention in a typical boiler application showing apparatus external to the present invention. Housing shell  1  is threaded into boiler wall  16  by way of annular pipe threads  4 . Collar  2  and sensor tube  3  are shown immersed in boiler fluid  14 . Control apparatus  13  injects a fluid conductivity signal into control enclosure  15 , which conducts said fluid conductivity signal into housing shell  1 . Housing shell  1  conducts said fluid conductivity signal into boiler wall  16 , which further conducts fluid conductivity signal into boiler fluid  14 . When boiler fluid  14  is at a level that immerses sensor tube  3  said fluid conductivity signal is conducted through boiler fluid  14  into sensor tube  3  to integrated temperature and level sensor  12 . Said fluid conductivity signal is conducted through level signal carrying means  10  to control apparatus  13 . The temperature of boiler fluid  14  is conducted through sensor tube  3  to sensor  12 . An electrical signal indicative of temperature of boiler fluid  14  is conducted from sensor  12  through temperature signal conduction means  11  to control apparatus  13 . 
     While the preferred embodiments of the present invention have been disclosed and illustrated, the invention should no be limited thereto, but may be otherwise embodied within the scope of the above claims.