Patent Publication Number: US-2005128098-A1

Title: Device and method to detect the onset of fires

Description:
Priority is claimed to German Patent Application No. DE 103 58 531.1, filed on Dec. 13, 2003, the entire disclosure of which is incorporated by reference herein.  
      The invention relates to a device to detect an onset of a fire and to a method for cleaning the device.  
     BACKGROUND  
      Such devices can be utilized wherever the onset of fires is possible in rooms or in electronic equipment. The device can also be utilized wherever there are explosion zones according to ATEX95 and 137, for example, in dust-laden industries (lumber and mill industries). With the device, air samples from the room or from the equipment are continuously fed to a fire-parameter detector via a feed line that is installed in the room or else in the equipment to be monitored and that has several suction openings. When the detector senses a fire-recognition parameter, an evaluation unit that is electronically connected to the detector emits a signal according to specified criteria. The term “feed line” does not refer exclusively to pipes that have been installed for room-protection purposes and that lead to an air outlet in the housing of the detector and that draw in room air or equipment-cooling air through suction openings. Rather, the term “feed line” can also refer to a suction funnel, a collecting hood or a T-shaped pipe hood which, for instance, is placed onto the air-outlet vent of an electronic device, thus being arranged in the main cooling stream of the device. The term “fire-recognition parameter” refers to physical parameters—such as, for instance, the ambient temperature, the fraction of solids, liquids or gases in the ambient air or the ambient radiation—that undergo measurable changes in an area where the onset of a fire occurs.  
      German patent specification DE 196 05 638 C1 discloses a method and a device to detect the onset of fires in rooms or in electronic equipment, comprising a detector for recognizing a fire parameter, having at least one feed line installed in the room or else in the equipment to be monitored and several suction openings through which samples of room air or equipment-cooling air are continuously supplied. An evaluation unit is electronically connected to a detector and, according to specified criteria, it emits a signal if the detector senses a fire-recognition parameter. In order to adjust the effective diameter of the suction openings, a film is glued over them so as to reduce the effective diameter of the suction openings. This device has the drawback that dust tends to constantly accumulate in the holes of the suction opening. This increasingly impairs the proper functioning of the detection system. In a device of the above-mentioned type, which is designed for room protection and which has a feed line that preferably consists of one or more pipes, the suction openings in the pipes are distributed at regular intervals throughout the room. Such a method and such a device are known, for instance, from German utility model DE 295 18 042 U1 and from German patent specification DE 33 48 107 C2. However, it has been recognized that this entails the disadvantage that the reliability of the detection of a fire-recognition parameter diminishes as the distance from the intake fan increases due to the pressure drop in the pipes. When the above-mentioned method or device is employed for purposes of monitoring installations, that is to say, for example, for monitoring electronic equipment, the feed line can also consist of one pipe which, however, is then considerably shorter, so that all of the suction openings can be the same size. However, if a different number of suction openings is selected, then their diameters have to be adapted since the total suction surface area can only fall within a narrow range.  
      These dimensions have to be calculated on the basis of the laws of physics. These suction openings can be drilled into the feed line or lines at the construction site. In actual practice, due to the wall thickness of the feed line, dust is constantly accumulating in the hole of the suction opening. This increasingly impairs the proper functioning of the detection system. In order to prevent this, more frequent and extensive maintenance then becomes necessary.  
     SUMMARY OF THE INVENTION  
      It is an object of the invention to develop a device that displays a high level of effectiveness as well as long-lasting, high sensitivity in terms of detecting the onset of fires over the entire monitoring area while the maintenance requirements should be low.  
      The device according to the invention provides for the suction openings in the feed line—which can be of the same diameter and which can be created by drilling—to have a rubber-elastic part with an internal opening having a smaller diameter. The rubber-elastic part seals the opening of the feed line not only so that it is gas-tight but it also ensures that the film can be stressed on both sides, in other words, a gas stream can flow into the feed line through the hole in the film and a gas stream can flow out of the feed line without the rubber-elastic part exhibiting any leakage vis-à-vis the feed line.  
      According to the state of the art, in which there are suction bores with a film glued over them, it is not possible to direct the gas stream in the opposite direction without this causing the film that is glued on from the outside to start to peel off after a certain period of use. These glued-on films are only suitable to reliably limit a gas stream that is flowing into the device but not for a gas stream that is flowing out of the feed line.  
      It is advantageous to arrange the film on top of the rubber-elastic part. In order to clean the device, the dust particles that have accumulated in the film are removed by employing a fan to blow a gas stream through the opening in the film from the inside to the outside. It is advantageous to perform this reversing of the air stream at regular intervals. For this purpose, a timer can be employed so that the air stream is blown at prescribed time intervals from the inside against the film, thereby ensuring continuous cleaning.  
      It is advantageous for the film to be provided with a non-stick coating. Furthermore, it is advantageous for certain areas of the suction openings to be additionally fitted with a filter. In order to do so, a filter may be used in the area of the suction openings, for example at a ventilation extension disposed outside of the rubber-elastic part. This prevents dust from penetrating the feed line, so that no dust concentrations can be formed that could create an explosive mixture. The present invention offers two modalities for protecting the suction openings against dirt accumulation. Since the outer diameter of the insert with the elastic membrane is considerably larger than the suction bores, a dust filter can be installed on the outside over the suction opening. For this purpose, a dust filter is integrated into the elastic membrane. The air-stream monitoring system continuously monitors the state of this dust filter to see if it is functioning properly. The dust filter can also be placed at a region outside of the rubber-elastic part such as at a venitlation extension disposed outside of the rubber-elastic part an area of a suction opening so as to enlarge the surface area of the filter. The filter is either cleaned by countercurrent purging or by cleaning, or else it is replaced.  
      An advantage of this solution according to the invention is that all of the suction bores receive an insert that has a thin membrane having good sliding properties in the area of the suction borehole. According to the present invention, the accumulation of dust in the area of the bore is largely prevented. Another advantage of this invention lies in the fact that the thin membrane has a certain elasticity. Should dust accumulate in the area of the suction openings due to certain environmental conditions that would impair the proper functioning of the “device to detect the onset of fires”, the suction openings can be easily cleaned by introducing purging air into the feed line, since the increased pressure causes the membrane to bulge towards the outside, as a result of which the dust comes off easily.  
      The purging air can be introduced by means of the suction fan using compressed air at the air outlet or by means of a bypass between the fan and the first suction opening. Another possibility consists of reversing the rotational direction of the suction fan. In this manner, the feed line becomes a pressure line and the air flowing out cleans the suction openings. This can also be done automatically. In this case, however, it should be noted that the fire detection is interrupted during the purging phase. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention is described in greater detail below with reference to an example of an embodiment and to the drawings, in which:  
       FIG. 1  shows a sectional view of a feed line with a rubber-elastic part, venitlation extension and filter disposed at the ventilation extension;  
       FIG. 2  shows a sectional view of a rubber-elastic part, with a film on the inside;  
       FIG. 3  shows a feed line with a suction opening;  
       FIG. 4  shows a rubber-elastic part with filter and a film inserted into the center. 
    
    
     DETAILED DESCRIPTION  
       FIG. 3  shows a feed line  3  having a suction opening  5 . Dust particles can pass through this suction opening  5  without problems, so that dirt is continuously accumulating in the detectors. Moreover, under certain circumstances, the diameter of the opening  5  has to be adapted to the desired flow cross section.  
       FIG. 2  shows a rubber-elastic part  1  having a groove  8  for attachment purposes, whereby the internal diameter is provided with a film  2  that has an opening  4  for the air stream. The film  2  can be stressed equally on both sides. The rubber-elastic part  1  is inserted into the feed line  3 .  
       FIG. 1  shows a feed line  3  into which a rubber-elastic part  1  has been inserted which has a film  2  with an opening  4  on its upper edge. This is advantageous in that no corners are created between the rubber-elastic part  1  and the film  2  on the inside in which dirt particles could accumulate. A ventilation extension  9  is disposed outside of the rubber-elastic part to provide some protection to the rubber-elastic part while enabling air to flow to the rubber-elastic part. The opening  4  of the film  2  is protected against coarse particles by means of a filter  7  placed at an opening of the veniltation extension  9 .  
       FIG. 4  shows a rubber-elastic part  1  that is fitted with a filter  6  over the suction opening  4 . Severe dirt accumulation in all of the parts depicted in  FIG. 1, 2  and  4  is prevented since the air stream through the opening  4  can be easily reversed, which causes any dust deposits present to be carried to the outside. Moreover, the installation of the filter  6 ,  7  prevents coarse particles from penetrating the system.  
      The present invention opens up a wide range of application possibilities, particularly in dust-laden sectors.  
      In the execution according to the invention, the advantages of fire detection with multi-sensor suction detectors can be utilized in dust-laden sectors through the use of filters and through the convenient cleaning by means of membranes.