Abstract:
In one aspect, a pneumatic detector assembly is provided. The assembly includes a housing, a sensor tube, a contact pin, and at least one switch having a bellows operatively associated with the sensor tube and the contact pin. The bellows is configured to move into and out of contact with the contact pin based on a pressure in the sensor tube.

Description:
BACKGROUND OF THE INVENTION 
     Reliable fire detection is critical for many aircraft. Common thermal fire detector types include point thermocouple, point thermistor, continuous thermocouple, continuous thermistor, resistance wire, and pneumatic tube. 
     Some pneumatic tube detector systems include a titanium or vanadium wire inserted into a capillary sensor tube. The wire is exposed to and absorbs high temperature energy and pressurized hydrogen gas and subsequently stores the gas as the wire cools to form a hydrogen saturated wire. This saturated wire is inserted into a sensor tube, which is pressurized with an inert gas, and sealed at both ends to form a pressure vessel, which can be used as a pneumatic detector. One of the ends of the pressure vessel is incorporated into a housing that includes a plenum, where alarm and integrity switches are located. 
     When the sensor tube portion of the pneumatic detector is exposed to high temperature, the pressure is increased inside the tube as the inert gas expands in accordance to physical gas laws. Such pneumatic fire detectors may include diaphragms that are pre-formed prior to assembly. The detectors may also include part of the gas seal for the device. The diaphragms may be pre-formed to operatively position the diaphragm in various positions such as, for example: (a) an open switch (alarm switch) condition requiring the background pressure to increase to create a closed or alarm condition; or (b) a maintained closed switch (integrity switch) condition with the background pressure. 
     For an alarm switch configuration, the diaphragm may be deformed so it is responsive to a predetermined background pressure to further deform sufficiently outward and create a closed switch. The diaphragm may also be deformed such that a portion of the interior side of the disc forms part of the pressure seal for the plenum. With this configuration, in the event of an overheat or fire condition, pressure in the sensor tube and plenum will rise. If a predetermined high temperature condition is reached, the pressure within the plenum will increase to such an extent that the diaphragm will be deformed outward and into electrical contact and create a closed switch. 
     For an integrity switch configuration, the diaphragm may be deformed so that the diaphragm responds to a predetermined drop in background pressure and deforms sufficiently inward to lose electrical contact with a switch. The diaphragm may also be deformed such that a portion of the interior side of the diaphragm forms part of the pressure seal for the plenum. With this configuration, the integrity switch opens if a loss of pressure occurs in the sensor tube or plenum. If a predetermined pressure loss occurs, the pressure within the plenum will decrease to such an extent that the diaphragm will lose electrical contact and create an open switch. 
     However, such pneumatic detectors may have complex designs, numerous parts, and may be hard to manufacture. Accordingly, it is desirable to provide a pneumatic detector assembly having a less complex design, fewer parts, reduced amount of brazing or welding of parts, overall ease of manufacture, and reduced tests to ensure hermeticity of the assembly. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a pneumatic detector assembly is provided. The assembly includes a housing, a sensor tube, a contact pin, and at least one switch having a bellows operatively associated with the sensor tube and the contact pin. The bellows is configured to move into and out of contact with the contact pin based on a pressure in the sensor tube. 
     In another aspect, a method of assembling a pneumatic detector assembly is provided. The method includes providing a sensor tube, providing a contact pin, and providing at least one switch having a bellows. The method further includes operatively coupling the bellows to the sensor tube and the contact pin such that the bellows is configured to move into and out of contact with the contact pin based on a pressure in the sensor tube 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic illustration of an exemplary pneumatic detector assembly in a first position; 
         FIGS. 2A and 2B  are a schematic illustrations of a portion of the assembly shown in  FIG. 1  in a second position; 
         FIG. 3  is a schematic illustration of another exemplary pneumatic detector assembly in a first position; 
         FIG. 4  is a schematic illustration of the assembly shown in  FIG. 3  in a second position; 
         FIG. 5  is a schematic illustration of the assembly shown in  FIG. 3  in a third position; 
         FIG. 6  is a schematic illustration of another exemplary pneumatic detector assembly in a first position; 
         FIG. 7  is a schematic illustration of the assembly shown in  FIG. 6  in a second position; and 
         FIG. 8  is a schematic illustration of the assembly shown in  FIG. 6  in a third position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1, 2A, and 2B  illustrate an exemplary pneumatic detector assembly  10  that generally includes an alarm switch  20 , a fault (integrity) switch  30 , and a sensor tube  40 .  FIG. 1  illustrates switches  20 ,  30  in normal operating positions, and  FIGS. 2A and 2B  illustrate switches  20 ,  30  in alarm/fault positions. 
     Although pneumatic detector assembly  10  is illustrated with one alarm switch  20  and integrity switch  30 , assembly  10  may have any number or combination of switches  20 ,  30 . Alarm switch  20 , fault switch  30 , and at least a portion of sensor tube  40  may be packaged in one or more hermetically sealed housings (not shown). 
     Alarm switch  20  is coupled to sensor tube  40  and includes a bellows  22  and a contact pin  24 . In the exemplary embodiment, the location of contact pin  24  is adjustable. However, contact pin  24  may be fixed in a desired location. Bellows  22  includes a contact face  26  and is connected to a power source  28 . A power return  29  is connected to contact pin  24 , which facilitates establishing an electrical continuity between bellows  22  and contact pin  24  when bellows  22  contacts the contact pin  24  ( FIG. 2A ). This electrical connection or continuity indicates an alarm, which may be communicated to another device or system (e.g., a controller), which may subsequently generate an alarm signal and/or issue an alarm (e.g., a visual or audible warning). 
     Bellows  22  is designed to respond in a predetermined manner in response to pressure outputs generated by sensor tube  40  to ensure contact face  26  will come in contact with contact pin  24  at those pressure outputs. For example, bellows  22  may be designed with a predetermined spring rate, effective area, convolutions, material thickness/type, and/or other properties that may be varied during manufacture of bellows  22 . With a known expansion/contraction of bellows  22  for a given pressure, contact pin  24  and bellows  22  may be located apart from each other at a predetermined distance ‘D 1 ’ to ensure contact therebetween at that given pressure. 
     In addition, an intermediate or pre-alarm switch (e.g., an overheat switch, not shown) may be used as a warning that a component or compartment is hotter than normal operation temperatures, but has not yet reached a fire alarm condition. Such a switch would function in the same manner as alarm switch  20  and bellows  22  described above. For example, the switch may be designed to respond in a predetermined manner in response to pressure outputs generated by sensor tube  40  to ensure that its contact face would come into contact with its contact pin at the desired pressure outputs. For example, the switch may be designed with a predetermined spring rate, effective area, convolutions, material thickness/type, and/or other properties that may be varied during manufacture of the bellows that would differ somewhat from alarm switch  20  and bellows  22 . With a known expansion/contraction of its bellows for a given pressure, which would normally be below the pressure to activate alarm switch  20  and bellows  22 , its contact pin and bellows may be located apart from each other at a predetermined distance different than D 1  to ensure contact therebetween at that given pressure. 
     Integrity switch  30  is coupled to sensor tube  40  and includes a bellows  32  and a contact pin  34 , which may have a fixed or adjustable location. Bellows  32  includes a contact face  36  and is connected to a power source  38 . A power return  39  is connected to contact pin  34 , which facilitates establishing an electrical continuity between bellows  32  and contact pin  34  when bellows  32  contacts the contact pin  34 . As shown in  FIG. 2B , a loss of electrical connection or continuity indicates a fault, which may be communicated to another device or system (e.g., a controller), which may subsequently generate an alarm signal and/or issue an alarm (e.g., a visual or audible warning). 
     Bellows  32  is similarly designed to respond in a predetermined manner in response to pressure outputs generated by sensor tube  40  to ensure contact face  36  will break electrical contact with contact pin  24  at those pressure outputs. For example, bellows  32  may be designed with a predetermined spring rate, effective area, convolutions, material thickness/type, and/or other properties that may be varied during manufacture of bellows  32 . With a known expansion/contraction of bellows  32  for a given pressure, contact pin  34  and bellows  32  may be initially located in contact, but configured to be located apart from each other at a predetermined distance ‘D 2 ’ to ensure no electrical contact therebetween at that given pressure. 
     In the exemplary embodiment, sensor tube  40  includes a core element  42 , which stores hydrogen gas and is spiral wrapped to allow a gas path in the event of sensor damage (e.g., crushing). A pressurized helium gas is disposed between a wall  44  and core  42 . 
     In operation, ambient helium gas pressure in sensor tube  40  is directly related to average temperature in, for example, an airplane engine compartment. Engine compartment overheat or fire conditions (as applicable) causes a proportionate rise in gas pressure in sensor tube  40 , and when the compartment temperature rises to a factory set alarm rating, the rising gas pressure expands bellows  22  and closes alarm switch  20  ( FIG. 2A ). When compartment cooling reduces the gas pressure, alarm switch  20  opens (i.e., bellows  22  contracts) and is ready to respond again. When sensor tube  40  is cut, the helium gas escapes and integrity switch  30  opens (i.e., bellows  32  contracts) (see  FIG. 2B ). 
     As such, alarm switch  20  which is normally opened ( FIG. 1 ) would close in response to an overheat or fire condition ( FIG. 2A ). This would be caused by an increase in gas pressure in sensor tube  40 , which would force bellows contact face  26  against contact pin  24 . Similarly, if sensor tube  40  was cut or lost pressure, which would release its gas pressure, integrity switch  30  which is normally closed ( FIG. 1 ) between bellows contact face  36  and contact pin  34  would open ( FIG. 2B ), indicating a fault condition of assembly  10 . 
     A method of assembling pneumatic detector assembly  10  includes providing alarm switch  20  and/or integrity switch  30  and providing sensor tube  40 . Alarm switch  20  is provided with bellows  22  and contact pin  24 , and integrity switch  30  is provided with bellows  32  and contact pin  34 . Bellows  22  is operably coupled to sensor tube  40 , and bellows  22  and contact pin  24  are located at a predetermined distance from each other that corresponds to a distance of travel of bellows  22  when sensor tube  40  reaches a predetermined pressure. Bellows  32  is operably coupled to sensor tube  40 , and bellows  32  is located in contact with contact pin  34 . Bellows  32  is configured to retract and break electrical contact with contact pin  34  when sensor tube  40  reaches a predetermined pressure. 
       FIGS. 3-5  illustrate an exemplary pneumatic detector assembly  100  that is similar to assembly  10  except it includes a combined alarm and integrity switch  102  having an alarm switch portion  120 , an integrity switch portion  130 , and a sensor tube  140 .  FIG. 3  illustrates combined alarm and integrity switch  102  in a normal operating position,  FIG. 4  illustrates alarm switch portion  120  in an alarm position, and  FIG. 5  illustrates integrity switch portion  130  in a fault position. 
     Alarm switch portion  120  is coupled to sensor tube  140  and includes a bellows  122  and a contact pin  124 , which may have a fixed or adjustable location. Bellows  122  includes a contact face  126  and is connected to a power source  128 . A power return  129  is connected to contact pin  124 , which facilitates establishing an electrical continuity between bellows  122  and contact pin  124  when bellows  122  contacts the contact pin  124  ( FIG. 4 ). This electrical connection or continuity indicates an alarm, which may be communicated to another device or system that may subsequently generate an alarm signal and/or issue an alarm. 
     Integrity switch portion  130  is coupled to alarm switch portion  120  and sensor tube  140  and includes a bellows  132  and a contact pin  134 , which may have a fixed or adjustable location. Bellows  132  includes a contact face  136  and is connected to a power source  138 . A power return  139  is connected to contact pin  134 , which facilitates establishing an electrical continuity between bellows  132  and contact pin  134  when bellows  132  contacts the contact pin  134 . As shown in  FIG. 5 , a loss of electrical connection or continuity indicates a fault, which may be communicated to another device or system to generate an alarm signal and/or issue an alarm (e.g., a visual or audible warning). 
     Bellows  122 ,  132  are designed to respond in a predetermined manner in response to pressure outputs generated by sensor tube  140  to ensure contact faces  126 ,  136  will establish/break contact with contact pins  124 ,  134  at those pressure outputs. With a known expansion/contraction of bellows  122 ,  132  for a given pressure, contact pins  124 ,  134  and bellows  122 ,  132  may be located apart from each other at a predetermined distance ‘D 1 ’, ‘D 2 ’ to ensure contact/no contact therebetween at that given pressure. 
     In the exemplary embodiment, sensor tube  140  includes a core element  142 , which stores hydrogen gas and is spiral wrapped to allow a gas path in the event of sensor damage. A pressurized helium gas is disposed between a wall  144  and core  142 . 
     In operation, alarm switch portion  120  which is normally opened ( FIG. 3 ) closes in response to an overheat or fire condition ( FIG. 4 ). This would be caused by an increase in gas pressure in sensor tube  140 , which would force bellows contact face  126  against contact pin  124 . Similarly, if sensor tube  140  is cut or loses pressure, which would release its gas pressure, integrity switch portion  130  which is normally closed ( FIG. 3 ) between bellows contact face  136  and contact pin  134  would open ( FIG. 5 ), indicating a fault condition of assembly  100 . 
     A method of assembling pneumatic detector assembly  100  includes providing combined alarm and integrity switch  102  having alarm switch portion  120  and integrity switch portion  130 . In the exemplary embodiment, alarm switch portion  120  is coupled to integrity switch portion  130  (e.g., by welding) and switch portions  120 ,  130  are operably coupled to provided sensor tube  140 . Alarm switch portion  120  is provided with bellows  122  and contact pin  124 , and integrity switch portion  130  is provided with bellows  132  and contact pin  134 . Bellows  122  and contact pin  124  are located at a predetermined distance from each other that corresponds to a distance of travel of bellows  122  when sensor tube  140  reaches a predetermined pressure. Bellows  132  is located in contact with contact pin  134  and is configured to retract and break contact with contact pin  134  when sensor tube  140  reaches a predetermined pressure. 
       FIGS. 6-8  illustrate an exemplary pneumatic detector assembly  200  that is similar to assembly  10  except it includes a combined alarm and integrity switch  202  and a sensor tube  240 .  FIG. 6  illustrates combined alarm and integrity switch  202  in a normal operating position,  FIG. 7  illustrates combined switch  202  in an alarm position, and  FIG. 8  illustrates combined switch  202  in a fault position. 
     In the exemplary embodiment, combined alarm and integrity switch  202  is coupled to sensor tube  240  and includes a bellows  250 , an alarm contact point  252 , and an integrity contact point  254 . Contact points  252 ,  254  may have a fixed or adjustable location. In the exemplary embodiment, integrity contact point  254  is annular and has an inner diameter that is larger than an outer diameter of bellows  250  to enable bellows  250  to extend therethrough. 
     Bellows  250  includes a contact face  256  and is connected to a power source  258 . A power return  260  is connected to alarm contact point  252  and a power return  262  is connected to integrity contact point  254 . Power returns  260 ,  262  respectively establish an electrical continuity (e.g., completed electrical circuit) between bellows  250  and contact points  252 ,  254  when bellows  250  expands to contact the contact point  252  ( FIG. 7 ) or retracts to contact the contact point  254  ( FIG. 8 ). This electrical connection or continuity indicates an alarm or fault, which may be communicated to another device or system (e.g., monitoring system) for subsequent generation of an alarm/fault signal and/or issue of an alarm. 
     In the exemplary embodiment, sensor tube  240  includes a core element  242 , which stores hydrogen gas and is spiral wrapped to allow a gas path in the event of sensor damage. A pressurized helium gas is disposed between a wall  244  and core  242 . 
     Bellows  250  is designed to respond in a predetermined manner in response to pressure outputs generated by sensor tube  240  to ensure contact face  256  will come in contact with contact points  252 ,  254  at those pressure outputs. With a known expansion/contraction of bellows  250  for a given pressure, contact points  252 ,  254  and bellows  250  may be located apart from each other at a predetermined distance ‘D 1 ’, ‘D 2 ’ to ensure contact therebetween at that given pressure. 
     As such, combined switch  202  which is normally opened ( FIG. 6 ) would close in response to an overheat or fire condition ( FIG. 7 ). This would be caused by an increase in gas pressure in sensor tube  240 , which would force bellows contact face  256  against alarm contact point  252 . Similarly, if sensor tube  240  was cut or lost pressure, which would release its gas pressure, combined switch  202  which is normally open ( FIG. 1 ), would force bellows contact face  256  against integrity contact point  254 , thereby indicating a fault condition of assembly  200 . 
     A method of assembling pneumatic detector assembly  200  includes providing combined alarm and integrity switch  202  and providing sensor tube  240 . Switch  202  is provided with bellows  250 , alarm contact point  252 , and integrity contact point  254 . Bellows  250  is operably coupled to sensor tube  240 , and bellows contact face  256  and alarm contact point  252  are located at a predetermined distance from each other that corresponds to a distance of travel of bellows  250  when sensor tube  240  reaches a predetermined pressure. Bellows contact face  256  and integrity contact point  254  are located at a predetermined distance from each other that corresponds to a distance of travel of bellows  250  when sensor tube  240  reaches a predetermined pressure. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.