Abstract:
A flow sensor comprises a detection section and a main unit section. The detection section comprises a casing, a through water pipe line, a transmitter which transmits an ultrasonic wave, a receiver which receives the ultrasonic wave from the transmitter, and a flow indicator having light emission sections. The main unit section comprises a display section for displaying the flow quantity value. The casing and the through water pipe line have a width perpendicular to the longitudinal direction of the through water pipe line, and the width of the casing is approximately equal to the width of the through water pipe line. One of the faces of the casing consists of the light emitting sections and a planar face whereby the width of the casing can be minimized. The detection section further comprises an alarm detector and a compute unit performs different processing when the alarm signal is on.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a flow sensor for detecting the flow quantity of a fluid. 
   2. Description of the Related Art 
   Previously, various flow sensors have been used for detecting the flow quantity of a fluid. For example, an ultrasonic vortex flow sensor ultrasonically detects a flow quantity change in a noncontact manner. A Karman vortex regularly occurs downstream from a vertex generation pole placed in a flow. The ultrasonic vortex flow sensor can ultrasonically detect a change in the Karman vortex, and can thereby detect the flow quantity with a high accuracy over a wide flow quantity range. (For example, refer to JP-A-4-77620 and JP-A-8-304142) 
   Such flow sensors include an integral-type flow sensor and a separate flow sensor. The integral-type flow sensor, which has a flow quantity detection part and a flow quantity display part in one piece, becomes larger. On the other hand, the separate flow sensor is provided in a detection section for detecting the flow quantity. A display section displays the value of the detected flow quantity. Generally, in the separate flow sensor, the detection section does not have a display section and thus can be miniaturized. 
   However, by installing the detection section, the user cannot check whether or not the flow quantity exists and whether or not the flow sensor processes normally. 
     FIG. 13  is an external perspective view of the detection section of the flow sensor in the related art, and  FIG. 14  is an exploded perspective view of the detection section of the flow sensor in the related art. 
   As shown in  FIG. 13 , a detection section  900  has a casing  940  shaped like a rectangular parallelepiped and is provided with a through water pipe line  910  so as to pierce opposed sides of the casing  940 . A circuit board  950  is placed above the through water pipe line  910 . 
   As shown in  FIG. 14 , a cylindrical element storage part  920  is provided on both sides of the outer peripheral surface of the through water pipe line  910 , and a transmitter  911  and a receiver  912  are inserted into the element storage parts  920 . Each element storage part  920  is closed by a press member  930  having a convex part  9   a  in the central portion. Accordingly, the convex parts  9   a  of the press members  930  press the transmitter  911  and the receiver  912  against the outer peripheral surface of the through water pipe line  910 . A taking-out pipe  970  of a conductor KB of the transmitter  911  and the receiver  912  of the through water pipe line  910  is provided in the direction crossing the element storage parts  920 . Thus, the press members  930  each having the convex part  9   a  centrally press the transmitter  911  and the receiver  912  against the outer peripheral surface of the through water pipe line  910 . In this case, the size of the detection section  900  of the flow sensor in the related art becomes larger in the direction in which the transmitter  911  and the receiver  912  are aligned. Also, the size of the detection section  900  of the flow sensor becomes larger in the direction crossing the direction in which the transmitter  911  and the receiver  912  are aligned. Since such a structure is housed in the casing  940 , the detection section  900  is upsized as a whole. Recently, it has been desired to make the detection section  900  smaller. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide a flow sensor for enabling the user to easily check the detection state of the flow quantity in a detection section. 
   It is another object of the invention to provide a flow sensor for enabling the user to easily check the detection state of the flow quantity in a detection section that can be miniaturized and made smaller. 
   According to the invention, there is provided a flow sensor including a detection section for detecting a flow quantity of a fluid, the detection section having a display section for displaying information based on the detected flow quantity; and a main unit section being provided as a separate body from the detection section for displaying the flow quantity detected by the detection section. 
   In the flow sensor according to the invention, the detection section detects the flow quantity of a fluid. The detected flow quantity is displayed on the main unit section provided as a separate body from the detection section. The information based on the detected flow quantity is displayed on the display section of the detection section. 
   In this case, the detection section is provided with the display section for displaying the information based on the flow quantity, thus enabling the user to easily check the detection state of the flow quantity on the detection section. 
   The display section may includes a plurality of light emission sections; and a control section for turning on the plurality of light emission sections in order at speed responsive to the detected flow quantity. 
   In this case, the plurality of light emission sections are turned on in order at the speed responsive to the detected flow quantity, so that the user can easily recognize the flow of the fluid from a distance. The display section can be miniaturized and the detection section can also be miniaturized. 
   The detection section may further includes a Karman vortex detection section for ultrasonically detecting change in a Karman vortex of a fluid; and a pulse signal generation section for generating a pulse signal corresponding to the change in the Karman vortex detected by the Karman vortex detection section, and the control section may turn on the plurality of light emission sections in order based on the pulse signal generated by the pulse signal generation section. 
   In this case, change in a Karman vortex of a fluid is ultrasonically detected and a pulse signal corresponding to the detected change in the Karman vortex is generated. The plurality of light emission sections are tuned on in order based on the pulse signal. 
   Accordingly, the plurality of light emission sections are turned on in order at the speed corresponding to the flow quantity of the fluid, so that the user can visually recognize the flow of the fluid from a distance. 
   The display section may display a level responsive to the detected flow quantity. In this case, since the level responsive to the detected flow quantity is displayed, the user can visually recognize the flow of the fluid from a distance. 
   The detection section may include a pipe line through which a fluid passes; a vortex generation member being provided in the pipe line for generating a Karman vortex; a pair of ultrasonic devices being placed on an outer peripheral surface of the pipe line so as to be opposed to each other with the pipe line between; and a press member having a pair of press parts for pressing the pair of ultrasonic devices against the pipe line and a joint part for joining the pair of press parts. 
   In this case, the pair of ultrasonic devices is placed on the outer peripheral surface of the pipe line so as to be opposed to each other with the pipe line between, and is pressed against the pipe line by the pair of press parts joined by the joint part of the press member. 
   The detection section may include a casing having a width of a first length and a thickness of a second length smaller than the first length, and the pair of ultrasonic devices may be placed in the casing so as to be arranged in a width direction. 
   In this case, the pair of ultrasonic devices is provided in the casing so as to be arranged in the width direction, so that the detection section can be miniaturized and made slim. 
   The case may include a housing space for housing a circuit board connected to the display section provided so as to be adjacent to one of the ultrasonic devices in the width direction. 
   In this case, the housing space for housing the circuit board is provided so as to be adjacent to one of the ultrasonic devices in the width direction in the casing, so that the detection section can be miniaturized and made slim. 
   The case may include a hermetic seal space for hermetically sealing the pair of ultrasonic devices and a part of the pipe line. In this case, the hermetic seal space for hermetically sealing the pair of ultrasonic devices and a part of the pipe line is provided in the casing, so that the pair of ultrasonic devices and a part of the pipe line can be prevented from being contaminated by dust. 
   The housing space and the hermetic seal space may be put into one piece. In this case, the housing space and the hermetic seal space are put into one piece, whereby the pair of ultrasonic devices, a part of the pipe line, and the circuit board can be prevented from being contaminated by dust. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
       FIG. 1  is a schematic drawing to show the configuration of a flow sensor according to a first embodiment of the invention; 
       FIG. 2  is a block diagram to show the configuration of the flow sensor according to the first embodiment of the invention; 
       FIGS. 3A and 3B  are external perspective views of a detection section of the flow sensor according to the first embodiment of the invention; 
       FIG. 4  is an exploded perspective view of the detection section of the flow sensor according to the first embodiment of the invention; 
       FIG. 5A  is a plan view of the detection section of the flow sensor according to the first embodiment of the invention and  FIG. 5B  is an exploded side view of the detection section of the flow sensor according to the first embodiment of the invention; 
       FIG. 6  is a schematic drawing to show the flow quantity measurement principle of the flow sensor according to the first embodiment of the invention; 
       FIG. 7  is an exploded perspective view of a cabinet of the flow sensor according to the first embodiment of the invention; 
       FIGS. 8A to 8E  are schematic drawings to describe light emission patterns of a flow indicator of the flow sensor according to the first embodiment of the invention; 
       FIG. 9  is a drawing to show an application example of the detection sections of the flow sensor according to the first embodiment of the invention; 
       FIG. 10  is an external perspective view of a detection section of a flow sensor according to a second embodiment of the invention; 
       FIG. 11  is an exploded perspective view of the detection section of the flow sensor according to the second embodiment of the invention; 
       FIG. 12A  is a plan view of the detection section of the flow sensor according to the second embodiment of the invention and  FIG. 12B  is an exploded side view of the detection section of the flow sensor according to the second embodiment of the invention; 
       FIG. 13  is an external perspective view of a detection section of a flow sensor in a related art; and 
       FIG. 14  is an exploded perspective view of the detection section of the flow sensor in the related art. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the accompanying drawings ( FIGS. 1 to 12 ), flow sensors are shown according to first and second embodiments of the invention. 
   FIRST EMBODIMENT 
     FIG. 1  is a schematic drawing to show the configuration of a flow sensor according to a first embodiment of the invention. 
   In  FIG. 1 , the flow sensor is provided in a detection section (sensor head or sensor head section)  100  and a main unit section (sensor main unit section or sensor main section)  200 . The detection section  100  is connected to the main unit section  200  by a cable. The main unit section  200  has a display section  230 . 
     FIG. 2  is a block diagram to show the configuration of the flow sensor according to the first embodiment of the invention. As shown in  FIG. 2 , the flow sensor is provided in the detection section  100  and the main unit section  200 . 
   The detection section  100  includes a transmitter  111 , a receiver  112 , a high frequency signal oscillator  120 , a high frequency signal amplifier  130 , a phase comparator  140 , a low frequency amplifier  150 , a comparator  160 , a frequency divider  170 , a decoder  180 , a signal level determination unit  190 , and a flow indicator LU. This flow indicator LU includes light emission sections  81  to  84 . The light emission section  81  has a red LED (light emitting diode)  81 R and a green LED  81 G. Each of the light emission sections  82  to  84  has a green LED. For example, the transmitter  111  and the receiver  112  are implemented as ultrasonic devices. 
   The main unit section  200  includes a frequency measurement device  210 , a computing unit  220 , a display section  230 , a control output section  240 , and an analog output section  250 . For example, the frequency measurement device  210  and the computing unit  220  are implemented as a CPU (central processing unit). 
   The high frequency signal oscillator  120  generates a high frequency signal and gives the high frequency signal to the transmitter  111 , which then transmits an ultrasonic wave. The receiver  112  receives the ultrasonic wave from the transmitter  111 . In this case, the frequency of a Karman vortex occurring on a fluid changes due to the flow quantity of the fluid. The ultrasonic wave propagation time changes in proportion to the frequency of the Karman vortex. Therefore, change in the ultrasonic wave propagation time from the transmitter  111  to the receiver  112  is detected, whereby the flow quantity can be detected. 
   The high frequency signal amplifier  130  amplifies an output signal of the receiver  112 . The phase comparator  140  makes a phase comparison between the high frequency signal generated by the high frequency signal oscillator  120  and the output signal of the high frequency signal amplifier  130  and outputs a voltage corresponding to the phase difference. The low frequency amplifier  150  amplifies the output voltage of the phase comparator  140 . 
   The comparator  160  compares the output signal of the low frequency amplifier  150  with a reference voltage and outputs a pulse indicating the comparison result. The frequency divider  170  divides the pulse output from the comparator  160 . The decoder  180 , which is implemented as a shift register, decodes the output signal of the frequency divider  170 , thereby turning on the light emission sections  81  to  84  of the flow indicator LU in green in order. In this case, the speed at which the light emission sections  81  to  84  of the flow indicator LU are turned on in order changes in response to the flow quantity. The state in which the light emission sections  81  to  84  of the flow indicator LU are turned on is described later in detail. 
   The signal level determination unit  190  determines whether or not the level of the output signal of the high frequency signal amplifier  130  falls below a predetermined value. If the level of the output signal falls below the predetermined value, the signal level determination unit  190  turns on the red LED  81 R of the light emission section  81  and prohibits the decoder  180  from turning on the green LED  81 G of the light emission section  81  and the light emission sections  82  to  84  and further gives an alarm signal to the computing unit  220 . Accordingly, the computing unit  220  can recognize that the reception level falls. If the through water pipe line  10  through which a fluid flows is not filled with a fluid or if a bubble exists in a fluid, the reception level of the receiver  112  falls and the accurate flow quantity value cannot be detected. In this case, the signal level determination unit  190  outputs an alarm signal. 
   If the signal level determination unit  190  gives an alarm signal to the computing unit  220 , the computing unit  220  controls the display section  230 , the control output section  240 , and the analog output section  250  based on the given alarm signal. 
   If the given alarm signal is on (for example, high), the computing unit  220  causes the display section  230  to display an alarm and performs processing with a digital filter. For example, if the alarm signal is on, the computing unit  220  causes the display section  230  to display the flow quantity value applied before the alarm signal is turned on as many times as the preset number of times. The computing unit  220  also calculates moving average of the flow quantity values as many times as the preset number of times and causes the display section  230  to display the moving average. If the alarm signal is on, the control output section  240  turns on or off first output and second output using the flow quantity value applied before the alarm signal is turned on as many times as the preset number of times. The control output section  240  also turns on or off first output and second output based on the moving average of the flow quantity values as many times as the preset number of times. Further, the analog output section  250  outputs an analog alarm signal. 
   Thus, if the alarm signal is on, the computing unit  220  performs different processing from that if the alarm signal is off (for example, low), thereby performing processing based on the flow quantity value close to the accurate flow quantity value. Accordingly, processing based on an erroneous flow quantity value when the alarm signal is on can be prevented from being performed without decreasing the response speed when the alarm signal is off (in the normal mode). 
   The frequency measurement device  210  measures the frequency of the pulse output from the comparator  160 . The computing unit  220  converts the frequency measured by the frequency measurement device  210  into a flow quantity and controls the display section  230 , the control output section  240 , and the analog output section  250  based on the flow quantity value. 
   The control output section  240  turns on or off first output and second output based on the flow quantity value. The analog output section  250  outputs an analog signal indicating the flow quantity value. 
     FIGS. 3A and 3B  are external perspective views of the detection section of the flow sensor according to the first embodiment of the invention;  FIG. 3A  shows the detection section from one side and  FIG. 3B  shows the detection section from an opposite side. 
   In  FIG. 3 , the detection section  100  of the flow sensor includes a casing  20 . The casing  20  has an upper face  20   a , a lower face  20   b , an end face  20   c , an end face  20   d , a side face  20   e , and a side face  20   f.    
   A through water pipe line  10  made of a resin such as resin fluoride is provided so as to pierce the end faces  20   c  and  20   d  of the casing  20 . A fluid flows in the direction indicated by the arrow through the through water pipe line  10 . A cable  40  for transmitting the detected flow quantity value to the main unit section  200  is connected to the end face  20   c  of the casing  20 . Further, the above-described flow indicator LU is provided on the upper face  20   a  of the casing  20 . 
   As shown in  FIG. 3B , the casing  20  is formed on the side face  20   f  with a rectangular notch part  20 K. In the notch part  20 K, a lid  33  of a cabinet  30  integral with the through water pipe line  10  is flush with the side face  20   f  of the casing  20 , forming a part of the casing  20 . 
     FIG. 4  is an exploded perspective view of the detection section of the flow sensor according to the first embodiment of the invention.  FIG. 5A  is a plan view of the detection section of the flow sensor according to the first embodiment of the invention and  FIG. 5B  is an exploded side view of the detection section of the flow sensor according to the first embodiment of the invention. 
   In  FIG. 4 , the detection section  100  is provided with casing members  21  and  22 , the through water pipe line  10 , two circuit boards W, packing PK, and a plurality of screws  50 . The through water pipe line  10  is provided so as to pass through the cabinet  30  and is integral with the cabinet  30 . The casing members  21  and  22  are combined into the casing  20  in  FIG. 3 . 
   The casing member  21  has a circuit housing area AR in an internal upper portion. The circuit housing area AR is surrounded by the upper face  20   a  of the casing member  21  and a partition plane SI. The two circuit boards W are installed so as to overlap each other in the circuit housing area AR. 
   Installed on the circuit boards W are the high frequency signal oscillator  120 , the high frequency signal amplifier  130 , the phase comparator  140 , the low frequency amplifier  150 , the comparator  160 , the frequency divider  170 , the decoder  180 , the signal level determination unit  190 , and the flow indicator LU described above. 
   Four holes are made in the upper face  20   a  of the casing member  21 . The light emission sections  81  to  84  are placed on the circuit boards W in the circuit housing area AR corresponding to the four holes of the casing member  21 . 
   To assemble the detection section  100 , the through water pipe line  10  is attached to the inner lower side of the casing member  21 . The cabinet  30  is integral with the through water pipe line  10  as described above and is fitted into the notch part  20 K of the casing member  21  (see  FIG. 3B ). 
   A conductor taking-out part  31  is provided on an end face  30   a  of the cabinet  30 . A conductor introduction hole KH is made in the partition plane SI of the casing member  21 . To attach the cabinet  30  to the casing member  21 , the conductor taking-out part  31  of the cabinet  30  is fitted into the conductor introduction hole KH. Accordingly, conductors of the transmitter  111  and the receiver  112  implemented as ultrasonic devices (described later) in the cabinet  30  are introduced through the conductor taking-out part  31  and the conductor introduction hole KH into the circuit boards W in the circuit housing area AR. 
   A seal member (not shown) is previously mounted on the conductor introduction hole KH. Therefore, the conductor taking-out part  31  and the conductor introduction hole KH are fitted into each other, whereby the inside of the cabinet  30  and the circuit housing area AR communicate with each other and become a hermetically sealed space. 
   As shown in  FIG. 4 , the casing member  21  to which the two circuit boards W and the through water pipe line  10  are attached is joined to the casing member  22  by the plurality of screws  50  via the packing PK on a seal face GS. The packing PK is mounted on the seal face GS, whereby the internal space of the circuit housing area AR is reliably hermetically sealed. 
   In  FIG. 4 , the casing members  21  and  22  are attached to each other by the plurality of screws  50  as follows: The screws  50  are screwed through threaded holes a 1  to a 8  of the casing member  22  into threaded holes c 1  to c 8  of the casing member  21 , whereby the casing member  21  is attached to the casing member  22 . The through water pipe line  10  is formed with screw introduction holes b 4  to b 8 . To attach the casing members  21  and  22 , the screws  50  passing through the threaded holes a 4  to a 8  of the casing member  22  pass through the screw introduction holes b 4  to b 8 . 
   Thus, the casing members  21  and  22  are attached by the plurality of screws  50 , whereby the casing  20  can be easily made waterproof. 
   In the embodiment, the casing members  21  and  22  may be attached not only by the plurality of screws  50 , but also with an adhesive, etc. 
   The casing members  21  and  22  are attached as described above, whereby thickness t of the detection section  100  of the flow sensor in one direction of the detection section  100  is narrowed, as shown in  FIG. 5A . The thickness t is, for example, 20.0 mm. 
   The measurement principle of the flow quantity in the cabinet  30  will be discussed with  FIG. 6 .  FIG. 6  is a schematic drawing to show the flow quantity measurement principle of the flow sensor according to the first embodiment of the invention. In  FIG. 6 , arrow F indicates a flow of fluid in the through water pipe line  10 . A column PO for causing fluid to generate a Karman vortex is provided in the through water pipe line  10 . 
   In the cabinet  30 , the transmitter  111  is attached to the outer peripheral surface of the through water pipe line  10  downstream from the column PO in the through water pipe line  10 , and the receiver  112  is attached to the outer peripheral surface of the through water pipe line  10  so as to be opposed to the transmitter  111 . 
   To measure the flaw quantity of the fluid flowing through the through water pipe line  10 , the transmitter  111  transmits an ultrasonic wave. In contrast, the receiver  112  opposed to the transmitter  111  with the through water pipe line  10  between receives the ultrasonic wave transmitted through the through water pipe line  10  and the inside of the through water pipe line  10 . 
   The fluid flowing through the through water pipe line  10  generates a Karman vortex responsive to the flow quantity of the fluid in the presence of the column PO (arrows CU). Accordingly, the propagation time of the ultrasonic wave propagating in the fluid changes and therefore the flow quantity of the fluid flowing through the through water pipe line  10  is calculated based on the difference between the transmission point in time of the ultrasonic wave transmitted by the transmitter  111  and the reception point in time of the ultrasonic wave received by the receiver  112 . 
   The structure of the cabinet  30  will be discussed with  FIG. 7 .  FIG. 7  is an exploded perspective view of the cabinet of the flow sensor according to the first embodiment of the invention. 
   In  FIG. 7 , the cabinet  30  has end faces  30   a  and  30   b , side faces  30   c  and  30   d , and a bottom face  30   e . The through water pipe line  10  is provided so as to pierce the side faces  30   c  and  30   d . In the cabinet  30 , the transmitter  111  and the receiver  112  are attached to the outer peripheral surface of the through water pipe line  10  with the through water pipe line  10  between. 
   A press member  32  is provided with a pair of press parts  32   a  and  32   b  and a flat part  32   c . The pair of press parts  32   a  and  32   b  is formed integrally with both ends of the flat part  32   c  angular U-shaped in cross section so as to be opposed to each other. The press part  32   a  is formed with a notch shaped like a letter U. The press parts  32   a  and  32   b  of the press member  32  are inserted between the transmitter  111  and the receiver  112  and the end faces  30   a  and  30   b  of the cabinet  30 . Accordingly, the transmitter  111  and the receiver  112  are pressed against the outer peripheral surface of the through water pipe line  10  by the press parts  32   a  and  32   b  of the press member  32 . Consequently, the transmitter  111  and the receiver  112  are fixed in the cabinet  30 . 
   The conductors of the transmitter  111  and the receiver  112  are introduced through the notch of the press part  32   a  and the conductor taking-out part  31  of the cabinet  30  into the outside. In this state, the opening of the cabinet  30  is covered with the lid  33 , so that the cabinet  30  can be hermetically sealed. 
   Subsequently, light emission patterns of the light emission sections  81  to  84  of the flow indicator LU will be discussed in detail with  FIG. 8 .  FIGS. 8A to 8E  are schematic drawings to describe the light emission patterns of the flow indicator of the flow sensor according to the first embodiment of the invention. 
   When the flow quantity in the through water pipe line  10  is measured, if the fluid in the through water pipe line  10  flows, the light emission sections  81  to  84  of the flow indicator LU blink in green in order. 
   For example, first the green LED  81 G of the light emission section  81  goes on in green as shown in  FIG. 8A ; next, the light emission section  81  goes off and the light emission section  82  goes on in green as shown in  FIG. 8B ; subsequently the light emission section  82  goes off and the light emission section  83  goes on in green as shown in  FIG. 8C ; and further the light emission section  83  goes off and the light emission section  84  goes on in green as shown in  FIG. 8D . This operation is repeated in the order of  FIG. 8A  to  FIG. 8D . 
   In this case, the light emission sections are turned on in order at the speed responsive to the detected flow quantity, so that the user can easily recognize the flow of the fluid from a distance. The display section can be miniaturized and the detection section can also be miniaturized. 
   On the other hand, when the flow quantity in the through water pipe line  10  is measured, if there is no fluid in the through water pipe line  10  or if the fluid contains a large number of bubbles or the like, the light emission section  81  of the flow indicator LU goes on in red as shown in  FIG. 8E . 
   Here, assume that the light emission sections  81  to  84  of the flow indicator LU blink in order in a specific direction (for example, forward). In the embodiment, the limit emission operation of the flow indicator LU is performed based on the frequency of a Karman vortex as described above; for example, the frequency of a Karman vortex occurring in a flow sensor having a ½-inch bore is about 600 Hz at the maximum. If the limit emission operation is performed based on the frequency, it is too fast for human eyes to recognize the forward mode clearly. Then, 600-Hz pulse is divided by six ½ frequency dividers, whereby 9.4-Hz pulse at the maximum can be provided. In this case, forward display is produced at natural speed for human eyes. 
   Thus, the frequency dividing ratio can be determined appropriately by the bore of the flow sensor. The frequency dividing method can be realized by a logical circuit or microcomputer software. 
   In the embodiment, the light emission sections  81  to  84  of the flow indicator LU need not necessarily go on in green in order. For example, the light emission sections  81  to  84  may produce level display of the detected flow quantity rather than going on in green in order. Specifically, as many light emission sections as the number responsive to the flow quantity are turned on. 
     FIG. 9  is a drawing to show an application example of the detection sections of the flow sensor according to the first embodiment of the invention. The detection section of the flow sensor according to the embodiment has the small thick in the predetermined direction (t in  FIG. 9 ) as shown in  FIG. 5A , so that a plurality of detection sections  100  can be brought close into each other, as shown in  FIG. 9 . 
   The flow sensor according to the embodiment is formed of resin fluoride, etc. Therefore, the flow sensor is used suitably for a manufacturing line, etc., where fluid of chemicals, etc., flows. The flow sensor is also suited for measurement of the flow quantity of a fluid requiring cleanness. 
   SECOND EMBODIMENT 
   A flow sensor according to a second embodiment of the invention has a similar configuration and similar operation to those of the flow sensor according to the first embodiment except for the following points: 
     FIG. 10  is an external perspective view of a detection section of the flow sensor according to the second embodiment of the invention. 
   In  FIG. 10 , the detection section  500  of the flow sensor includes a casing  20 . The casing  20  has an upper face  20   a , a lower face  20   b , an end face  20   c , an end face  20   d , a side face  20   e , and a side face  20   f.    
   A through water pipe line  10  molded of the same material as the casing  20  is projected from the end faces  20   c  and  20   d  of the casing  20 . A fluid flows in the direction indicated by the arrow through the through water pipe line  10 . A cable  40  for transmitting the detected flow quantity value to a main unit section  200  is connected to the rear end part of the casing  20 . Further, a flow indicator LU similar to that in the first embodiment is provided on the upper face  20   a  of the casing  20 . 
     FIG. 11  is an exploded perspective view of the detection section of the flow sensor according to the second embodiment of the invention.  FIG. 12A  is a plan view of the detection section of the flow sensor according to the second embodiment of the invention and  FIG. 12B  is an exploded side view of the detection section of the flow sensor according to the second embodiment of the invention. 
   In  FIG. 11 , the detection section  500  is provided with casing members  21 ,  22 , and  23 , the through water pipe line  10 , two circuit boards W, packing PK, a plurality of screws  50 , and a press member  32 . The through water pipe line  10  is formed integrally with the casing member  22 . The casing members  21 ,  22 , and  23  are combined into the casing  20  in  FIG. 10 . 
   The casing member  22  has a circuit/sensor housing area AS in an internal portion. The circuit/sensor housing area AS is surrounded by the upper face  20   a  of the casing member  22  and a partition plane SI. The two circuit boards W are installed so as to overlap each other in an upper portion of the circuit/sensor housing area AS. 
   Installed on the circuit boards W are a high frequency signal oscillator  120 , a high frequency signal amplifier  130 , a phase comparator  140 , a low frequency amplifier  150 , a comparator  160 , a frequency divider  170 , a decoder  180 , a signal level determination unit  190 , and the above-mentioned flow indicator LU. 
   In a lower portion of the casing member  22 , a transmitter  111  and a receiver  112  are attached to the through water pipe line  10  as in the cabinet  30  of the detection section  100  according to the first embodiment. When the transmitter  111  and the receiver  112  are attached to the through water pipe line  10 , they are housed in a lower portion of the circuit/sensor housing area AS by the press member  32 . The press member  32  is provided with a pair of press parts  32   a  and  32   b  and a flat part  32   c . The pair of press parts  32   a  and  32   b  is formed at both ends of the flat part  32   c  so as to be opposed to each other. 
   Four holes are made in the upper face  20   a  of the casing member  21 . Light emission sections  81  to  84  are placed on the circuit boards W in the circuit/sensor housing area AS corresponding to the four holes of the casing member  21 . 
   As shown in  FIG. 11 , the two circuit boards W are attached and the transmitter  111  and the receiver  112  are attached to the through water pipe line  10  by the press member  32 . The casing member  22  is joined to the casing members  21  and  23  by the plurality of screws  50  via the packing PK on a seal face GS. The packing PK is mounted on the seal face GS, whereby the internal space of the circuit/sensor housing area AS is reliably hermetically sealed. 
   In  FIG. 11 , the casing members  21 ,  22 , and  23  are attached to each other by the plurality of screws  50  as follows: The screws  50  are screwed through threaded holes a 1  to a 8  of the casing member  22  into threaded holes C 1  to C 8  of the casing members  21  and  22 , whereby the casing members  21 ,  22 , and  23  are attached to each other. 
   Thus, the casing members  21 ,  22 , and  23  are attached by the plurality of screws  50 , whereby the casing  20  can be easily made waterproof. 
   In the embodiment, the casing members  21 ,  22 , and  23  may be attached not only by the plurality of screws  50 , but also with an adhesive, etc. 
   The detection section  500  of the flow sensor according to the embodiment can be molded of the same material in one piece and can be easily manufactured and cost reduction is made possible. In the structure of the detection section  500  of the flow sensor according to the embodiment, thickness t of the detection section  500  of the flow sensor in one direction of the detection section  500  ( FIG. 12 ) also lessens. The thickness t is, for example, 22.5 mm. 
   In the first and second embodiments described above, the flow indicator LU corresponds to the display section, the light emission sections  81  to  84  correspond to the light emission sections, the frequency divider  170  and the decoder  180  correspond to the control section, the transmitter  111  and the receiver  112  correspond to the Karman vortex detection section, and the high frequency signal oscillator  120  corresponds to the pulse generation means. The through water pipe line  10  corresponds to the pipe line, the column PO corresponds to the vortex generation member, the transmitter  111  and the receiver  112  correspond to the pair of ultrasonic devices, the pair of press parts  32   a  and  32   b  corresponds to the pair of press parts, the flat part  32   c  corresponds to the joint part, and the press member  32  corresponds to the press member. 
   Further, the circuit/sensor housing area AS corresponds to the housing space, the short side of the side face  20   e ,  20   f  of the detection section  100 ,  500  corresponds to the width of the first length, the thickness t in  FIG. 5A  and  FIG. 12A , the short side of the top face  20   a ,  20   b  of the detection section  100 ,  500 , corresponds to the thickness of the second length, and the cabinet  30  corresponds to the hermetic seal space.