Abstract:
In a fire sprinkler system, flow sensors are used having strain gauges mounted on supports which project into the sprinkler pipes. When water flow occurs, the supports bend, changing the strain gauge resistance and producing a signal which can be analyzed to indicate which sprinkler heads are open. Since there are no mechanical switches, the sensor units are much smaller and cheaper than previously, and provide more information. A strain gauge can also or alternatively be located outside the pipe to detect vibration caused by flowing water. As an alternative to strain gauges, piezo film can be used, with a vibration analyzer to analyze the signal from the film to determine whether water flow is occurring and which sprinkler heads are open. A piezo film can also be placed on the pipe exterior and the signals from the two piezo films can be applied to differential inputs of a differential amplifier, to cancel signals caused by external influences such as pipe vibration. A thermistor can also be used to sense water flow, using temperature changes when the water begins to flow.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to U.S. Provisional Application No. 60/649,579 filed on Feb. 4, 2005, which is incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to fire sprinkler systems, and more particularly to a system including water flow sensors used in fire sprinkler systems.  
       BACKGROUND OF THE INVENTION  
       [0003]     Fire sprinkler systems commonly include water flow sensors which are intended to provide some information about the activation of sprinkler heads within the system. The water flow sensors that are currently used throughout the industry are mechanical devices which contain a moving paddle (located within the pipe) and a microswitch. If water begins to flow within the pipe, the water flow displaces the paddle, which activates the microswitch, sending a signal to the building control panel.  
         [0004]     The mechanical sensors currently used are difficult to install, since they are large, and must be inserted from the top side of the pipe (which is not always accessible) in order to reduce clogging of the moving paddle from sediment in the water. In addition, the mechanical flow sensors must be installed in the proper direction with respect to the direction of water flow, since the microswitch used to trigger the device can only operate in one direction. The mechanical sensors can also operate only when there is a full flow of water in the pipe, and cannot detect lower water flow rates which may indicate leaks within the system. Further, the paddles sometimes break and impede water flow. In addition, the mechanical sensors used are very costly.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     In one aspect of the invention, an improved flow sensor is provided, which does not require a mechanical switch, and which is much less costly than the current mechanical flow sensors. Preferred forms of sensors according to the invention are smaller than the current mechanical flow sensors and can be installed in any orientation, so larger numbers of these sensors can be used to form a system which can provide more information to fire fighters and others than is feasible with the current system.  
         [0006]     In one aspect, the invention provides a fire sprinkler system having a water pipe and a sprinkler head connected to said water pipe, a water flow sensor unit mounted on the pipe upstream of the sprinkler head for detecting water flow to the sprinkler head, the sensor unit comprising a sensor support, the sensor support being adapted to experience movement when there is water flow in the pipe, a sensor mounted on the sensor support and adapted to sense movement of such sensor support, a detector circuit connected to the sensor and responsive to sensing by the sensor of movement of the sensor support caused by water flow in the pipe to produce a detector signal, and a processing circuit for processing the detector signal to produce an alarm signal when the detector signal meets selected criteria.  
         [0007]     In another aspect, the invention provides a sensor for sensing fluid flow in a conduit. The sensor includes a sensor base connected to the conduit, and a flexible stem connected to the sensor base. The stem experiences movement during fluid flow in the conduit. The stem includes a piece of piezo film adapted to produce a voltage upon movement of the stem, and a floater connected to a distal end of the stem. A counterweight is located at the tip of the floater.  
         [0008]     Further objects and advantages of the invention will appear from the following description, taken together with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     In the drawings:  
         [0010]      FIG. 1  is a diagrammatic perspective view of a flow sensor and accompanying electronics control box according to the invention;  
         [0011]      FIG. 2  is a perspective diagrammatic view of the flow sensor of  FIG. 1  mounted on a fire sprinkler pipe;  
         [0012]      FIG. 3  is a plan view of a strain gauge used with the sensor of  FIGS. 1 and 2 ;  
         [0013]      FIG. 4  is a schematic drawing of a full bridge employing strain gauges according to one embodiment of the invention;  
         [0014]      FIG. 5  is a schematic view of a half-bridge employing strain gauges according to one embodiment of the invention;  
         [0015]      FIG. 6  is a schematic view of a quarter-bridge employing strain gauges according to one embodiment of the invention;  
         [0016]      FIG. 7  is a side view of a sensor according to the invention using a single strain gauge;  
         [0017]      FIG. 8  is a view similar to that of  FIG. 7  but using a double strain gauge;  
         [0018]      FIG. 9  is a block diagram showing a system for processing strain gauge signals according to one embodiment of the invention;  
         [0019]      FIG. 10  is a diagrammatic view showing arrangement of sprinkler pipes, sprinkler heads and flow sensors in a building according to an embodiment of the invention;  
         [0020]      FIG. 11  is a diagrammatic view showing another embodiment of the invention with a strain gauge located on the outside of a pipe;  
         [0021]      FIG. 12  is a view similar to that of  FIG. 11  but showing the pipe pressurized and the strain gauge support warped outwardly;  
         [0022]      FIG. 13  is a view similar to that of  FIG. 12  but showing the pipe depressurized and the strain gauge support warped inwardly;  
         [0023]      FIG. 14  is a side view of a sensor employing a piezo film according to one embodiment of the invention;  
         [0024]      FIG. 15  is a block diagram showing a system for processing of a signal from the piezo film of  FIG. 14 ;  
         [0025]      FIG. 16A  is a perspective view of another embodiment of a flow sensor according to the present invention;  
         [0026]      FIG. 16B  is a plan view of the embodiment of  FIG. 16A ;  
         [0027]      FIG. 16C  is an elevation view of the embodiment of  FIG. 16A ;  
         [0028]      FIG. 17A  is a schematic view of the embodiment of  FIG. 16A  viewed in a longitudinal cross-section of pipe;  
         [0029]      FIG. 17B  is a schematic view of the embodiment of  FIG. 16A  viewed in a transverse cross-section of pipe; and  
         [0030]     FIGS.  17 C-E are schematic views of the embodiment of  FIG. 16A , viewed in a transverse cross-section of pipe, showing the oscillation of the sensor stem during flow conditions. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0031]     Reference is first made to FIGS.  1  to  3 , which show a flow sensor unit  10 . Sensor unit  10  includes a flexible sensing element support  12  mounted on a base  14  and supporting a sensing element  16 . In the embodiment being described, the sensing element  16  is a strain gauge. Strain gauges are readily available on the market and are made of a thin wire  18  arranged in a zigzag form (as shown in  FIG. 3 ) to form a long electrically conductive strip bonded to a flexible backing (the support  12 ). When the support  12  is stretched (e.g. when it is bent), the wire  18  is stretched and its electrical resistance increases. The increase in resistance is a measure of the strain (i.e. amount of bending) present in the support  12 . Leads  20  are typically connected to each end of the wire  18  which forms the strain gauge, and the leads are brought out to an appropriate amplifying and measuring circuit which detects and measures any change in resistance in the strain gauge.  
         [0032]     In the embodiment of FIGS.  1  to  3 , the support  12  is shown as projecting from a control box  22  into which the leads  20  extend. The control box  22  includes a sealing pad  24  (e.g. of a rubber material) surrounding the bottom of the support  12 . In use, a hole  26  is drilled in a sprinkler pipe  28  ( FIG. 2 ) and the control box  22  is pressed against the pipe  28  with the support  12  and strain gauge sensor  16  extending through the hole  26 , and with the sealing material  24  sealing the hole  26 . A suitable saddle or pipe clamp  30  connected to the control box  22  clamps and retains the control box  22  firmly in position on the pipe, with the strain gauge  16  positioned across the path of water flow in the pipe. Preferably, the sensor unit  10  is mounted upstream of one or more sprinkler heads  32 , so that the sensor unit  10  can signal which sprinkler head or sprinkler heads have opened.  
         [0033]     As is well-known, the change in resistance in most commercially available strain gauges is very small for practical deflections of the support  12 . In addition, the resistance of the strain gauge wire  18  is temperature dependent, and the resistance changes due to temperature changes can be greater than the resistance changes due to strain applied to the strain gauge. To deal with both these problems, strain gauges are commonly used in a bridge configuration.  FIG. 4  shows four strain gauges SG 1  to SG 4  arranged in a full bridge configuration  40 , with an excitation voltage of V in  applied across the bridge. When the bridge  40  is balanced, the output voltage V o  is zero. If there is a strain which changes the resistance in any arm of the bridge, V o  will become a non-zero voltage. The full bridge  40  shown in  FIG. 4  provides the best temperature stability (since resistance changes due to temperature are cancelled in opposite arms of the bridge) and the highest V o  reading when strain is applied to all four strain gauges simultaneously. However, the  FIG. 4  arrangement is costly since it requires four strain gauges.  
         [0034]      FIG. 5  shows a bridge  42  similar to that of  FIG. 4 , but with matched resistors R 1  and R 2  in two arms of the bridge, and strain gauges SG 1  and SG 2  in the other two arms. Applying strain (oppositely) to both gauges results in an unbalanced bridge and produces a non-zero V o  output voltage. The  FIG. 5  arrangement doubles the amplitude of the resistance change as compared with using a single strain gauge, and reduces sensitivity to temperature changes, since the temperature coefficients in the two strain gauges SG 1 , SG 2  cancel each other.  
         [0035]      FIG. 6  shows resistors R 1 , R 2 , R 3  in three arms of a bridge  44 , and a single strain gauge SG 1  in one arm. Applying strain to SG 1  unbalances the bridge, providing a non-zero output V o .  FIG. 6  represents the lowest cost solution, but the circuit is temperature sensitive and provides the lowest V o  reading in response to applied stress.  
         [0036]     Referring again to  FIGS. 1 and 2 , to compensate for temperature changes, a thermistor  50  can be mounted on the control box  22  to project into the pipe  28 . The thermistor  50  can sense temperature changes in the water flowing through the pipe  28 . Such temperature changes will commonly occur after a sprinkler head opens, since the standing water in the pipe (which may have been at or near room temperature) is rapidly replaced with flowing water, which may be much cooler. The temperature information sensed by the thermistor  50  can be processed in a control circuit (described below) to cancel changes in resistance of the strain gauge material resulting from temperature changes. The temperature information sensed by the thermistor can also be used to compensate for gradual temperature variations caused by changes in the weather and surrounding environment.  
         [0037]      FIG. 7  shows a single strain gauge SG 1  mounted on a flexible support  12  (used in the  FIG. 6  bridge configuration), while  FIG. 8  shows two strain gauges SG 1  and SG 2 , one mounted on each side of the support  12  (the  FIG. 5  half-bridge configuration). With respect to the four strain gauge full bridge configuration of  FIG. 4 , the arrangement of the strain gauges on the support  12  is similar to that shown in  FIG. 8 , except that two strain gauges are located on each face of the support in side-by-side orientation. It will be understood that in all configurations of the strain gauge, the strain gauge or gauges used will be encapsulated in plastic, rubber or any other substance that insulates the gauges&#39; wires from the water in the pipe.  
         [0038]     In  FIGS. 7 and 8 , the direction of water flow in the pipe is indicated by arrow  52 . For exemplary purposes, it is assumed that the strain gauge SG 1  can be mounted in the pipe facing in either direction, so the arrow  52  is shown as double-ended. It will be realized that the single strain gauge SG 1  shown in  FIG. 7  is largely direction independent, i.e. it will bend essentially the same amount whether it is on the upstream or downstream face of support  12  (assuming that the support  12  is sufficiently thin). The double strain gauge embodiment shown in  FIG. 8 , using gauges SG 1  and SG 2 , one on each side of support  12 , is entirely independent of flow direction and will produce the same results no matter which way it is oriented with respect to flow. It will be evident that this greatly facilitates installation and eliminates the possibility of non-functionality because of a mistake in the direction of installation.  
         [0039]     Reference is next made to  FIG. 9 , which shows a typical functional block diagram of a system for processing the strain gauge signals. It is assumed, for purposes of illustration, that a flow sensor unit  10  is installed upstream of the sprinkler heads  32  in each room of the building in question, as will be described.  
         [0040]     As indicated in  FIG. 9 , the two strain gauges SG 1  and SG 2  are connected in the half-bridge configuration  42  of  FIG. 5 . The output voltage V o  from the bridge is amplified in amplifier  60  and is then converted to digital form by A/D converter  62 . These components are, as shown, located in the control box  22 .  
         [0041]     The digital signal from the A/D converter  62  is processed in microprocessor  64 , which is equipped with a delay setting  66 , so that brief transients or pulses in the water in the pipe will not create a false alarm. The microprocessor  64  can output several types of signals, for example an alarm signal when it detects full water flow through the pipe  28 , and a different (e.g. leakage) signal when it detects leakage flow through the pipe  28 . If a thermister  50  (not shown in  FIG. 9 ) is used, its signal is also processed by microprocessor  64 , to provide temperature compensation.  
         [0042]     The output signal from the microprocessor  64  indicates whether or not full flow is occurring through flow sensor unit  10 , and preferably also indicates (when there is no full flow) whether leakage flow is or is not occurring through the sensor unit. This output signal is optionally directed to a communication interface  70 , which then outputs a signal on bus  72  to a building control panel  74 . The signals from other flow sensor units in the building are also carried on bus  72  to the control panel  74 . Thus, the control panel  74  will have (and can display) information showing each flow sensor unit which detects full flow, and showing in a different manner flow sensors which detect leakage flow. The communication interface  70  is not of course essential.  
         [0043]     While the strain gauge or strain gauges used have been described as connected in a bridge configuration, and while this facilitates reading the strain gauge signal, it will be understood that use of a bridge configuration is not essential. For example, the strain gauge may be read directly, e.g. by connecting it in series to one or more resistors and then reading the voltage across the strain gauge using a suitably sensitive amplifier.  
         [0044]     In one application, the information supplied to the control panel can be used to operate a building map, to indicate which sprinkler heads have been activated. An exemplary map is shown at  80  in  FIGS. 9 and 10 .  
         [0045]     In  FIG. 10 , three rooms indicated at  81 - 1 ,  81 - 2  and  81 - 3  are shown, with respective sprinkler heads  32 - 1 ,  32 - 2 ,  32 - 3  and  32 - 4 , and flow sensors  10 - 1 ,  10 - 2  and  10 - 3  upstream of the respective sprinkler heads in each room. The sprinkler heads are supplied by a main floor feeder pipe  82 , which is also equipped with a flow sensor indicated at  10 - 4 .  
         [0046]     In operation, if the sprinkler head in one room is open, causing water to flow, flow sensor  10 - 4  will indicate that there is an open sprinkler head. In addition, the flow sensor in the room where the open sprinkler head is located will also operate, showing that the sprinkler head in the room in question is open. This situation is displayed on the building map  80 .  
         [0047]     In some embodiments, it will not be necessary to indicate where on a floor a sprinkler head is open, but only to indicate that one or more sprinkler heads are operating on a floor. In that case, a simpler map can be displayed, or alternatively a multi-floor map can be displayed with all or several of the floors being shown at the same time, together with an indication of on which floors open sprinkler heads  32  are located.  
         [0048]     While the strain gauge sensing element  16  has been described and shown as being located inside the pipe  28 , it is also possible to locate sensing element  16  outside the pipe. Reference is next made to  FIG. 11 , which shows a sensor arrangement similar to that of  FIGS. 1 and 2  and in which corresponding numerals indicate corresponding parts. The major difference between the  FIG. 11  embodiment and that of  FIGS. 1 and 2  is that in the  FIG. 11  embodiment the strain gauge  16  is not located on the flexible paddle  12 , but instead is located on the outside surface of the sensor base  14  outside the pipe  28 . As shown, the paddle or support  12  is mounted on support  14  inside the pipe  28  (protruding into the pipe). The base  14  is made of plastic, thin stainless steel or other flexible material and is clamped and sealed to the pipe  28  in any desired known manner, e.g. by circular clamps, not shown).  
         [0049]     In use, when the pipe  28  is pressurized, the base  14  (depending on its flexibility) will typically warp or curve outwardly slightly, warping the strain gauge in a given position as shown in  FIG. 12 . (The curvature is exaggerated for purposes of illustration.) When a sprinkler head opens, the pressure inside the pipe drops and the base  14  and strain gauge  16  warp or curve inwardly, as shown in  FIG. 13 , resulting in a changed resistance for the strain gauge and producing a signal. In addition, it is found that the flow inside the pipe  28  is usually extremely turbulent, and indeed, depending on the size and design of the paddle or support  12 , the paddle may not bend in the direction of flow but may instead simply oscillate. The oscillations will be detected by the strain gauge  16  and will result in an alternative strain gauge signal which can be used to indicate that water flow is occurring inside the pipe  28 .  
         [0050]     One advantage of mounting the strain gauge  16  outside the pipe is that less rigorous measures are necessary to seal and encapsulate the strain gauge when it is outside the pipe.  
         [0051]     When the strain gauge  16  is used to detect vibrations of the paddle  14 , rather than steady bending of the paddle (or even if it is used to detect steady bending), it may be desirable to incorporate a time delay so that transient vibrations in the standing water in the pipe do not create a false signal that a sprinkler head has opened.  
         [0052]     The foregoing description has described the sensor element as a strain gauge. However, other sensing elements can alternatively be used. For example, and as shown in  FIG. 14 , the sensing element  16 ′ can be formed of piezo film  84  (also known as piezoelectric film) mounted on a support  12 ′ which, as before, projects into the sprinkler pipe  28 ′. Piezo film is a flexible, lightweight, strong engineering plastic widely available in a variety of thicknesses. Piezo film has the characteristic that when it is bent, it produces a pulse of electricity. Therefore, in its simplest form, a piezo film requires no external power source, and it is able to generate signals much larger than those available from conventional strain gauges. Again, the piezo film can be located inside the pipe on the support  12 ′, as shown, or alternatively, it can be mounted on the outside of the pipe where it can pick up vibrations from the support  12 ′, as described in connection with  FIG. 11  for the strain gauge.  
         [0053]     Since piezo film, when bent or otherwise strained, does not produce a continuous signal, the support  12 ′ is preferably designed so that the force and pressure of the flowing water cause the support  12 ′ to vibrate or oscillate, thus creating a pulsating signal (as also described in connection with the strain gauge located outside the pipe).  
         [0054]     As shown in  FIG. 15 , the pulsating signal from the film  84  is amplified by amplifier  60 ′. The amplified pulsating signal from amplifier  60 ′ is converted to a digital signal by A/D converter  62 ′, and is then processed by microprocessor  64 ′ which now contains a signal analyzer  86 . The signal analyzer  86  analyzes the signal from an analog/digital (A/D) converter  62 ′ to look for signal components which are characteristic of flowing water in the sprinkler pipe  28 ′, while filtering out signals resulting from transients, traffic vibrations and the like. If the microprocessor  64 ′ detects a signal indicative of flowing water in the sprinkler pipe  28 , it then sends a signal on the communication interface  70 ′ and bus  72 ′ to the building control panel  74 ′ as before.  
         [0055]     If desired, a thermister or other temperature sensing device can be used to provide temperature compensation for the piezo film.  
         [0056]     If desired, and to eliminate the influence of external vibrations on the piezo film  84  (i.e. vibrations produced by vibrations of the pipe  28 ), a second piezo film  100  can be mounted on the external wall of the pipe as shown at  100  in  FIG. 15 . The internal and external piezo films  84 ,  100  are then connected to the differential inputs of a differential operational amplifier (amplifier  60 ′ then being such an amplifier). This configuration cancels voltages produced by piezo film  84  as a result of vibrations of the pipe itself, while providing output generated by piezo film  84  from vibrations caused by the flowing water in pipe  28 . The output of amplifier  60 ′ will then indicate a water flow. With this arrangement, there will be less likelihood of false output signals due to external vibrations.  
         [0057]     Where a differential amplifier is used, the signal analyzer  86  may not be required, or may be very simple, since the differential amplifier cancels signals produced by pipe vibration, so that any remaining signal from piezo film  84  will normally be due to flowing water (since the support  12 ′ tends to vibrate in flowing water). Of course, some filtering may still be necessary, to eliminate voltages produced by pulses in the water.  
         [0058]      FIGS. 16A-16C  show another embodiment of a flow sensor  90 . The sensor  90  includes a flexible planar stem  92  connected at its proximate end to a sensor base  94 . The distal end of the stem  92  is connected to a floater  96  to urge the stem  92  away from the walls of the pipe  28  in the event the pipe  28  fills with water. The tip of the floater  96  includes a counterweight  98  which acts to center the stem  92  in the pipe  28 .  
         [0059]     The stem  92  is preferably composed of a piece of piezo film  84  encapsulated in a flexible plastic sheath. The encapsulated piezo film is commercially available from Measurement Specialties Inc. The encapsulated piezo film may be further coated by another compound in order to make it suitable for being submerged in water. One example of such a compound is rubberized silicone.  
         [0060]     Referring to FIGS.  17 A-E, the stem  92  is preferably oriented such that its planar surface is positioned longitudinally to the axis of the pipe  28 . The orientation and construction of the sensor  90  in this embodiment permits the stem  92  to oscillate transversely to the longitudinal axis of the pipe  28  when water is flowing in the pipe  28  (as best shown in FIGS.  17 C-E). The frequency and amplitude of the oscillations will depend on the flow rate of water through the pipe  28 . Higher flow rate creates higher frequency oscillations, which generates higher output voltage from the piezo film  8   b   4 .  
         [0061]     The output voltage from the piezo film  84  in this embodiment may processed in a similar fashion as illustrated and described for  FIG. 15  above. A predetermined threshold output voltage from the sensor  90  may be set to ignore low and random frequencies. This would increase the likelihood of avoiding false alarms and may obviate the need for the second piezo film sensor  100  (described above).  
         [0062]     Instead of the strain gauge or piezo film sensors described, in some cases a simple thermistor such as thermistor  50  shown in  FIG. 1  can be used as a flow detector, to indicate water flow. Normally when there is no flow, the temperature of the water in the pipe  28  stabilizes at a steady temperature, usually at or near room temperature. If a sprinkler head opens and water begins to flow, then the temperature of the water in the pipe flowing past the thermistor  50  tends to change rapidly. The rapid temperature change can occur for several reasons. For example, the water passing the thermistor has usually passed through several temperature zones as it travels through pipes in different parts of the building, resulting in temperature fluctuations. In addition, the water is often from a cool source (such as a lake or spring), so the temperature may drop as the cooler water reaches the thermistor. In this embodiment of the invention, a voltage or current is passed through the thermistor and the variation in this signal caused by a temperature change is detected and processed to provide a signal indicating that water flow is occurring. However, this method of detecting flow may be less reliable than using a strain gauge or piezo film, since it depends on variations of water temperature within the pipe, and such variations are not always well known or predictable.  
         [0063]     While preferred embodiments of the invention have been described, it will be realized that various changes can be made, and all such changes are intended to be within the scope of the invention.