Patent Publication Number: US-2009236205-A1

Title: Pneumatic fire detector

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit as a continuation-in-part of PCT/US08/75321, filed Sep. 5, 2008; which claims benefit to U.S. Provisional Application No. 60/970,609, filed Sep. 7, 2007, the entire content of both applications which are incorporated by reference herein in its entirety for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to pneumatic fire detectors. 
     BACKGROUND OF THE INVENTION 
     Reliable fire detection is critical for any aircraft used for cargo or passenger operations. There are several fire detectors available on the market which use diverse technologies to achieve detection. Some of the most common are point thermocouple, continuous thermocouple, resistance wire, and pneumatic tube. 
     A fire alarm system well known in the prior art incorporates a titanium or vanadium wire inserted into a capillary sensor tube. The wire is exposed to high temperature and pressurized hydrogen gas and absorbs the gas and stores it as the wire cools. This saturated wire is inserted into a sensor tube, pressurized with an inert gas, and sealed at both ends forming a pressure vessel, which can be used as a pneumatic detector. 
     The pressurized background gas expands in accordance to the physical gas laws. One of the ends is incorporated into a housing that comprises a plenum, where the alarm and integrity switches are located. 
     When the sensor tube portion of the pneumatic detector in its final form is exposed to high temperature, the pressure inside will rise. Pneumatic fire detectors in the prior art also utilize diaphragms that are pre-formed prior to assembly and have its edges typically brazed and which comprise part of the gas seal for the device. The purpose of pre-forming the diaphragm is to operatively position the diaphragm to form initially either: a) an open switch (alarm switch) condition requiring the background pressure to increase to create a closed or alarm condition, or, b) or a maintained closed switch (integrity switch) condition with the background pressure. 
     For an alarm switch configuration, the diaphragm is deformed: a) so that the diaphragm, responsive to a pre-determined background pressure, will further deform sufficiently outward and create a closed switch; and, b) 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 would rise. If a pre-determined 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 creating a closed switch. 
     Conversely, for an integrity switch configuration, the diaphragm is deformed: a) so that the diaphragm, responsive to a pre-determined drop in background pressure, will deform sufficiently inward and lose electrical contact creating an open switch; and, b) 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 would open if a loss of pressure occurs in the sensor tube or plenum. If a pre-determined pressure loss occurs, the pressure within the plenum will decrease to such an extent that the diaphragm will lose electrical contact creating an open switch. 
     Description of the background art is generally disclosed in U.S. Pat. No. 5,691,702 issued to Hay and U.S. Pat. No. 3,122,728 issued to Lindberg, Jr. 
     The &#39;702 patent discloses an improvement in pneumatic pressure detector design by using only a single wire constituting a signal wire between the control electronics and the switch assembly. A second circuit path between the two major components of the system is provided by way of the ground path established by a ground connection at the control electronics block and another ground connection at the sensor assembly block. Completion of this circuit path is effected by way of the common grounding path in the aircraft. 
     The &#39;702 patent also discloses a set of resistors in the sensor circuit module. This arrangement eliminates the need for a second wire, which would constitute a return wire, extending between the control electronics block and the sensor assembly and also provides an additional capability of detecting a ground fault anywhere along the wire extending between the two remote sections of the sensor circuit. 
     Another prior art reference worth noting is U.S. Pat. No. 5,136,278 issued to Watson et al. The &#39;278 patent is directed to a pneumatic pressure detector which comprises a substantially cylindrical container having a gastight plenum with a first end carrying an alarm means and a second end carrying an integrity means. The alarm means comprises a deformable diaphragm normally spaced from an electrical contact. The integrity means comprises a deformable diaphragm normally in contact with a second electrical contact. The integrity means diaphragm and alarm means diaphragm are juxtaposed in a back-to-back relationship and form between them the gastight plenum which is connected to a sensor tube at the same gas pressure. The integrity means diaphragm is responsive to less gas pressure to move away from the second contact to provide fault indication. This configuration was directed to space savings and weight reduction. 
     In order to assemble the pneumatic fire detector, it is first necessary for the customer to provide the specific temperatures for each alarm to become activated. The manufacturer then determines the pressure level that corresponds to the desired threshold temperature and can thereafter construct the necessary diaphragm shape, braze the edges to form the gas-tight seal and assemble the detector. 
     Well known in the prior art, these metallic diaphragms are stamped from metal sheets; typically flat discs which are thereafter manipulated or deformed prior to installation into the pressure detector assembly. 
     The degree of necessary deformation is dependent on the thickness and diameter of the diaphragm metallic disc as well as its material of construction. The diaphragm is thereafter pressure tested to insure electrical contact will be made with the switch upon a threshold pressure being reached inside the sensor tube. The fire detector is thereafter assembled with appropriate wiring, resistor(s) and electric connectors for communicating alarm and integrity signals. 
     SUMMARY OF THE INVENTION 
     A pneumatic pressure detector is disclosed having a unique switch module design. The design allows the metallic discs or diaphragms that comprise a portion of the switch module to be deformed subsequent to assembly of the switch module. This pneumatic detector is suitable for aircraft as well as other demanding applications. 
     The pneumatic fire detector of the present invention, and in particular, the switch module design, can be manufactured in various configurations to suit the end-user&#39;s specific requirements. 
     Configurations include: a) a dual switch, which incorporates one alarm switch and one integrity switch; b) a multi-switch, which has at least two alarm switches and at least one integrity switch connected to a respective downstream outlet from a common manifold; and c) most preferably, a tri-switch, which has two alarm switches juxtaposed from one another in a generally back-to-back relationship, with at least one integrity switch spaced apart from, but operably connected to the manifold formed between the alarm switches by an outlet. The tri-switch configuration is also capable of supporting additional alarm or integrity switches if the outlet line is branched. 
     In this disclosure, the term “comprising” means including the elements or steps that are identified following that term, but any such elements or steps are not exhaustive, and an embodiment may include other elements or steps. 
     In this specification, the term “deformed” means the altering of the surface contour of a diaphragm. 
     As is typical in the prior art, the pneumatic fire detector presently disclosed includes a sensor tube that is operably connected to a switch module. The switch module comprises a manifold having a first opening, defined as the inlet, operably connected to the sensor tube. The manifold can be designed with at least two other openings, termed outlets, for operable connection to respective integrity and alarm switches. At least one integrity switch and at least one alarm switch comprise the switch module. 
     The inventions of this application incorporate the use of a substantially flat deformable metallic diaphragm disc permanently secured into position along its circumference either by brazing or welding to form a gas-tight seal between the manifold and each respective header assembly. Inside the switch module, facing a respective deformable diaphragm is an electrical contact pin. 
     As mentioned earlier, the switch module can be designed in many configurations and to accommodate additional switches. For example, in order to accommodate a third switch, an additional outlet could be designed directly opposite the manifold inlet. As shown in FIG.  2 , two alarm switches, B &amp; C, are juxtaposed to one another for space economy with the third switch, an integrity switch A, spaced apart from, but operably connected to the third outlet by a connecting tube  16 . The distal end of the third outlet is connected to a switch housing  34  which is designed to maintain a gas-tight seal after the diaphragm has been welded into position. The connecting tube could also be in a T configuration to accommodate a fourth switch. As will be appreciated by those having skill in the art, the connecting tube can be designed having a plurality of outlets to accommodate respective switches. 
     For purposes of this specification, the term “manifold” comprises that portion of the switch module which is exposed to the background pressure from the sensor tube when the unit is operational. For clarity, the manifold includes any additional outlets and respective connector tubes and switch housings  34 . 
     The switch module is installed within the detector along with electrical circuitry to provide an alarm signal whenever the integrity switch opens or the alarm switch closes. 
     A key inventive step for the disclosed pneumatic fire detector is the ability to assemble the switch module, which incorporates at least one integrity switch and at least one alarm switch, prior to the diaphragms being deformed into either an alarm switch or integrity switch operative configuration described earlier. 
     The circumferential edges of each metallic disc are welded in place forming a gas-tight seal. In a preferred embodiment, electron beam welding per AMS 2681 is used. The housing is constructed of a suitable material, such as molybdenum. The material for construction of the diaphragm is of a suitable material, such as a TZM alloy. 
     With each of the aforementioned configurations, the switches are qualified to TSO C11 E or MIL-F-7872. Overheat settings can be designed from 150 Deg F. to 900 Deg F. (±5%). Flame response testing indicates the alarm can activate within 5 seconds, when inserted directly into 2000° F. (1100° C.) using a six-inch diameter burner. 
     The switch module incorporates a respective forming tube for each switch header assembly. For purposes of this specification, the term “forming tube” incorporates any design capable of delivering fluid pressure to the outer surface of a respective diaphragm. 
     Preferably, each forming tube has a first or proximal end opening into an enclosed gas-tight space located behind a respective metallic disc. The forming tube and contact pin are preferred to be both in perpendicular relationship to the metallic disc. The forming tube extends through the switch module and can be temporarily connected on the distal end to a controllable pressure source. 
     The advantageous effect is the ability to secure by a suitable technique, such as welding the metallic discs in place, forming a gas-tight seal, and thereafter completely assemble the switch module without requiring the temperature settings for each alarm switch from the customer. Thus, the switch module can be produced in quantity. 
     The inventions disclosed herein provide a mechanism and method for deforming a diaphragm which has been secured into position along its circumference to form a gas-tight seal. The mechanism for deforming comprises the application of a first pre-determined pressure applied through the forming tube sufficient to deform the diaphragm inward into a concave contour relative to the electrical contact pin and the subsequent application of a second pre-determined pressure through the manifold to check the responsiveness of the diaphragm. 
     The fire detector can be designed for any exterior shape but preferably is constructed having a generally cylindrical configuration. Operative connection to an electronic control unit can be accomplished by any suitable arrangement known by those skilled in the art. Preferable connections are the use of a pin connector operatively attached to the back end of housing  11  as shown in  FIG. 1  or alternatively, the use of at least one terminal stud  320  as shown in  FIG. 7 . 
     Diaphragm Deforming Procedure 
     The procedure for deforming a diaphragm is as follows: 
     a. The respective switch is electrically connected for testing whether the diaphragm will close the switch at a second pre-determined pressure. 
     b. A first pre-determined pressure is applied through the forming tube to the diaphragm. This forming tube pressure is sufficient to deform the diaphragm inward in a substantially concave contour relative to the electrical contact. The severity of the deformation is dependent upon the thickness, diameter and type of metallic disc used as well as the pressure being applied. 
     c. The pressure in the forming tube is bled-off. 
     d. Next, pressure is applied through the manifold inlet to the convex surface of the diaphragm. This manifold pressure is sufficient to deform the diaphragm outward and toward electrical contact. The manifold pressure is gradually increased to a second pre-determined pressure that corresponds to the threshold temperature for the alarm. If the alarm switch closes within an acceptable range about the desired pressure, for example ±2 psig, and more preferably ±1 psig, the diaphragm is operatively configured. If the alarm switch closes at a pressure below the acceptable range, the diaphragm will not function correctly. 
     e. The manifold pressure is bled-off. 
     f. Steps a-e are repeated with incrementally more pressure if electrical contact in d was not made at the desired pressure. 
     It is necessary that the forming tube pressure be of a sufficiently low pressure so as not to excessively deform the diaphragm inward. If this were to occur, diaphragm contact with the switch would occur at a much lower manifold pressure making the diaphragm unacceptable for use. It is for this reason that an incremental forming tube pressure increase procedure be applied for determining the correct forming tube pressure to use upon a metallic diaphragm taking into account the diaphragm&#39;s specific thickness, diameter and physical properties. In one method of this application, each diaphragm assembled within the fire detector is deformed separately rather than all being deformed at the same time. 
     Thereafter, once all diaphragms have been appropriately deformed to function properly at a respective desired background pressure, each forming tube is sealed. The sensor tube is operatively connected to the switch module and pressurized with an inert gas to the desired pressure and sealed. The diaphragms subjected to the deforming procedure mentioned above will, in response to the sensor tube pressure, respond to the background pressure; namely, the integrity switch diaphragm will respond to the pressure and close, and the alarm switch will remain open until a pre-determined overheat condition occurs for which the diaphragm will contact and make it respective switch close. 
     Thus, at least one alarm switch is provided for indicating a first or overheat condition, the alarm switch comprising a deformable diaphragm having an outer surface normally spaced from a first electrical contact located outside of the manifold, the deformable diaphragm responsive to greater pressure from within the manifold to move toward the first contact for indicating the first or overheat condition. 
     Additionally, at least one integrity switch is provided for indicating a fault condition of a decrease in gas pressure in the sensor tube, the integrity switch comprising a deformable diaphragm having an outer surface normally in contact with a second electrical contact located outside of the manifold, with the deformable diaphragm being responsive to less gas pressure to move away from the second contact for indicating said fault condition. 
     As mentioned earlier, the switch modules can be made and assembled without knowledge of the temperature alarm settings desired by a customer. As an order is received, the procedure defined by the above steps a-f are used and after the diaphragms have been properly deformed to achieve electrical contact at the desired sensor tube pressure, the switch module can be installed within the detector housing and electrically connected. 
     The time to complete a fire detector following receipt of a customer&#39;s order and specifications is reduced since subsequent labor to deform the already installed flat diaphragms require only the deforming procedure mentioned earlier. This allows a final product to leave the manufacturing facility in less time; thus making the overall method of manufacture extremely efficient. 
     Operable connection of the alarm and integrity switches to an electronic control unit is accomplished via a signal wire and a return wire to the switches as is well known to those having skill in the art. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective side view of a tri-switch embodiment for a pneumatic fire detector. 
         FIG. 2  is an illustrative side view of the switch module for the tri-switch embodiment of  FIG. 1  showing the alarm switches in juxta position relative to each other, and the integrity switch spaced apart from the alarm switches. 
         FIG. 3   a  is an illustrative view of a diaphragm electron beam welded into place. 
         FIG. 3   b  is an illustrative view of pressure being applied thru a forming tube and displacing the diaphragm inward. 
         FIG. 3   c  is an illustrative view of pressure being applied thru the manifold and displacing the diaphragm outward and into contact with its respective switch. 
         FIG. 4A  is a side view of a dual-switch embodiment for a pneumatic fire detector. 
         FIG. 4B  is an electrical wiring diagram for the dual-switch embodiment of  FIG. 4A . 
         FIG. 5A  is a side view of a multi-switch embodiment for a pneumatic fire detector. 
         FIG. 5B  is an electrical wiring diagram for the multi-switch embodiment of  FIG. 5A . 
         FIG. 6  is a diagram illustrating the pneumatic fire detector connected to an electronic control unit. 
         FIG. 7  is an alternative embodiment of the pneumatic fire detector illustrating the use of terminal studs. 
         FIG. 8  is an cut away view of the alternative embodiment of  FIG. 7 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Tri-Switch Embodiment 
     The tri-switch embodiment pneumatic fire detector  10  is generally shown in  FIG. 1 . The tri-switch detector incorporates a switch module  12  having a manifold  14 , shown in more detail in  FIG. 2  and  FIG. 3 . The switches are depicted by A, B, and C. It is to be noted the illustrations are not drawn to scale and are presented for ease of understanding. Additionally, for ease of illustration, Switch A, depicted in  FIGS. 1 ,  4 A, and  5 A is an integrity switch while Switches B &amp; C are alarm switches. 
     The diaphragms  22  are made of flat metallic discs stamped out of TZM alloy sheet having an approximate thickness of 0.003″±0.0005″. The diameter of the discs are appropriately sized to form a gas-tight seal between either manifold  14  or switch housing  34  and the respective header assembly  32  when the metallic discs are correctly positioned and electron beam welded per AMS 2681 along its edge with the weld illustrated by W. 
     Each respective header assembly  32  incorporates a forming tube  30 . Each forming tube  30  has a first end opening into an enclosed gas-tight space located behind the outer surface of each diaphragm  22  and extends through respective header assembly  32 . The distal end is configured to be temporarily connected to a controllable pressure source. 
     Integrity switch A, and alarm switches B and C each have an electrical contact pin  26  and a contact pin insulator  28 . A configuration of connecting signal wires  18   a ,  18   b , and including return wire  18   c  and resistor(s)  21 , well known in the prior art, are used for transmitting a respective alarm or integrity signal via connector  20 . 
     Manifold  14  is designed with four openings; one inlet for operably connecting to one end of the sensor tube  24  and three outlets for operative contact with a respective diaphragm  22 . 
     The first switch, denoted in  FIG. 1  as A, is a dedicated pressure integrity switch that is used to monitor the hermeticity of the pneumatic element that makes up the detector. Switch A is operably connected to manifold  14  by use of connecting tube  16 . Connecting tube  16  is necessary because alarm switches B and C are juxtaposed to one another about manifold  14 . For the same reason, a connecting tube  17  operably connects an isolator assembly  19  to manifold  14 . 
     Isolator assembly  19  serves a dual function. Initially, it is used for connecting to a controlled pressure source and applying pressure through manifold  14  onto diaphragms  22  which is necessary for obtaining the desired operative configuration for each diaphragm. In a final assembled condition, isolator assembly  19  connects to sensor tube  24  with strain relief  25  used for support through housing  11 . 
     What follows is the procedure by which diaphragms  22  are operably deformed after switch module  12  has been assembled and electrically connected for testing purposes. 
     As mentioned earlier, each diaphragm  22  has been electron welded into place as illustrated in  FIG. 2 , forming a respective gas-tight seal. A controllable pressure source (not shown) is temporarily connected to the distal end of forming tube  30 . Referring to  FIG. 3   b , a first pre-determined pressure P 1  is applied through forming tube  30  to diaphragm  22  creating a concave contour relative to header assembly  32 . 
     By way of example, for a TZM alloy having a thickness of 0.003″ and an alarm requirement for signaling a 450° F. overheat condition, the switch must close at about 61 psig. In order to achieve this condition, the following steps are taken:
         1. Approximately 1200 psig is applied through forming tube  30  to diaphragm  22  and maintained for at least one minute to permit maximum diaphragm deformation for this pressure. The pressure is thereafter bled-off.   2. Thereafter, approximately 61 psig is applied through manifold  14  from the controllable pressure source connected to isolator assembly  19 . Pressure, represented by P 2 , is gradually increased from 0 psig to a second pre-determined pressure, in this case 61 psig. The pressure is thereafter bled-off.       

     At this point, three situations may be applicable. 
     First, if diaphragm  22  makes contact with contact pin  26  before the pressure reaches the desired pressure of 61 psig, steps 1 and 2 are repeated except that the forming tube pressure is incrementally increased by a pre-determined amount, such as between 5-50 psig. These steps are repeated until one of the other following conditions occur. 
     Second, if diaphragm  22  makes contact with contact pin  26  within a pre-determined range, in this case 61 psig±1 psig, the diaphragm is considered to be in its operative configuration. Thereafter, the respective forming tube  30  is sealed. Once all diaphragms  22  have been deformed to operative configuration, sensor tube  24  is connected to isolator assembly  19  and pressurized. 
     Third, if diaphragm  22  makes contact with contact pin  26  above 61 psig±1 psig is reached, the switch module cannot be used for those temperature conditions and is a result of excessive forming tube pressure being applied to the outer surface of diaphragm  22 . 
     By this technique, each switch can be tailored to open at a specific operational pressure by varying the forming tube pressure used to create the shape of each diaphragm. 
     Once each diaphragm  22  has been pressured into its operable configuration, the functionality of the pressure detector is the same as available in the prior art. 
     The diaphragm associated with integrity Switch A moves into electrical contact with contact pin  26  when the calculated background pressure is introduced within sensor tube  24  and manifold  14  and remains closed for the life of the detector. However, the diaphragm is responsive to less gas pressure and designed to displace inward and break electrical contact in the event that the hermetic background pressure is lost from within the sensor tube  24 . 
     The second and third switches, Switches B and C, are alarm switches that warn of a high temperature or fire condition. 
     Switch B is a normally open switch that remains open until an event occurs which causes the pressure to increase to a preset level within sensor tube  24  which in turn causes the diaphragm to deform outward and close an electrical circuit to Switch B. 
     Switch C also functions as an alarm switch in the same manner as Switch B and can either be a redundant switch if it is calibrated to make contact at the same pressure of Switch B or it can be set to make contact at a different temperature. 
     Dual Switch Embodiment 
       FIG. 4A  illustrates a dual-switch embodiment pneumatic fire detector  110 . Isolator assembly  119  connects to sensor tube  24  with strain relief  25  used for support through housing  11 . The primary difference from the tri-switch embodiment is that manifold  114  is not welded to a switch header assembly. Rather, two connecting tubes  116  are operably connected from manifold  114  to a respective switch housing  34 ; similar in construction to that of tube  16  of Switch A of  FIG. 2 . The dual switch embodiment utilizes one integrity switch and one alarm switch.  FIG. 4B  illustrates a wiring diagram  130  for the dual-switch embodiment. The procedure for deforming diaphragms  22  is the same as for the Tri-Switch embodiment. Although manifold  114  has 3 connecting tubes, only two are operably connected to respective switch housings. The third is plugged and not used in this embodiment but is used in the multi-switch embodiment discussed below. This allows the same manifold  114  to be used for either dual or multi-switch embodiment. 
     Multi-Switch Embodiment 
       FIG. 5A  illustrates a multi-switch embodiment pneumatic fire detector  210 . Isolator assembly  119  connects to sensor tube  24  with strain relief  25  used for support through housing  11 . The primary difference from the dual-switch embodiment is that multiple connecting tubes  116  are operably connected from manifold  114  to a respective switch housing  34 ; similar in construction to that of Switch A of  FIG. 2 . The multi-switch embodiment utilizes one integrity switch and two alarm switches.  FIG. 5B  illustrates a wiring diagram  230  for the multi-switch embodiment. The procedure for deforming diaphragms  22  is the same as for the Tri-Switch embodiment. 
       FIG. 6  is a diagram illustrates one embodiment for electronically connecting pneumatic fire detector  10  to an electronic control unit  50 . 
     As with the fire detector of  FIG. 1 , for the fire detector embodiments of  FIGS. 4   a  and  5   a , a signal wire and a second return wire are provided to each switch. 
     Finally,  FIGS. 7 and 8  illustrate an alternative detector housing  310 . Illustrated here is the multi switch design; although any of the aforementioned designs are herein applicable. Detector housing  310 , rather than using a pin connector  20 , utilizes at least one terminal stud  320  which is welded to housing body  311 . Terminal stud  320  is used as an outlet for electronic wiring (not shown) to operatively connect from the respective alarm and integrity switches to electronic control unit  50 . The housing body  311  is substantially cylindrical but having a sealed end portion  319  and a corresponding aperture for a respective terminal stud to be welded about. Mounting plates  322  each have holes for mounting the housing body  311  onto a suitable structure. The terminal stud housing design is useful in situations where it may not be possible or practicable to use an end pin connector terminal.