Abstract:
A valve-position output apparatus capable of adequately detecting valve-positions on an optical basis. The valve-position output apparatus for a valve comprises an interlocking member arranged to move in sync with open and close operations of the valve, a position detecting aperture formed in said interlocking member, an optical encoder having a light-emitting section and a light-receiving section which are arranged opposed to each other with interposing the interlocking member therebetween, digital valve-position signal generating means for generating a digital valve-position signal on the basis of a signal from the optical encoder, and initial setting means for initializing the digital valve-position signal generating means so as to match the digital valve-position signal of the digital valve-position signal generating means with an actual valve position.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a valve-position output apparatus for outputting positions of a valve. 
     BACKGROUND OF THE INVENTION 
     With reference to FIG. 8, a conventional valve-position output apparatus will be described. FIG. 8 is a schematic explanatory view of the conventional valve-position output apparatus, wherein FIG.  8 ( a ) shows the state when a valve (not shown) is located at a fully closed valve-position and FIG.  8 ( b ) shows the state when the valve is located at a fully opened valve-position. A pair of first and second arms  02 ,  03  are attached to a valve shaft  01  of the valve. The valve shaft  01  and the arms  02 ,  03  are arranged to rotate together in sync with open and close operations of the valve. At the fully closed valve-position shown in FIG.  8 ( a ), the first arm  02  rotates a lever  07  of a limit switch unit  06  counterclockwise to turn on a first limit switch (not shown). On the other hand, at the fully opened valve-position shown in FIG.  8 ( b ), the second arm  03  rotates the lever  07  of the limit switch unit  06  clockwise to turn on a second limit switch (not shown). As described above, the limit switch unit  06  includes the pair of opened valve-position and closed valve-position limit switches. Thus, it is necessary to provide three or four wirings for externally outputting signals from the limit switches. 
     In the case that a valve-position output apparatus is constructed in such a mechanical structure, it is difficult to sufficiently process data of the valve positions and in particular, to adequately conduct an initial setting in order to accurately detect the valve positions. Further, during open and close operations of the valve, the conflict between the arms  02 ,  03  and the lever  07  causes an undesirable noise and the wear of the arms  02 ,  03  and the lever  07 . Furthermore, when the valve is moved between the fully opened valve-position and the fully closed valve-position which is spaced apart from the fully opened valve-position at an angle of about 90-degree, the conventional valve-position output apparatus may detect the fully opened and closed valve-positions, but may not detect any valve positions in a transition angle or intermediate angle where the valve is being moved between the fully opened and closed valve-positions. 
     SUMMARY OF THE INVENTION 
     In order to solve the aforementioned problems, it is an object of the present invention to provide a valve-position output apparatus capable of adequately detecting valve positions on an optical basis. 
     According to a first aspect of the present invention, there is provided a valve-position output apparatus comprising an interlocking member arranged to move in sync with the open and close operations of a valve, a position detecting aperture formed in the interlocking member, an optical encoder having a light-emitting section and a light-receiving section which are arranged opposed to each other with interposing the interlocking member therebetween, digital valve-position signal generating means for generating a digital valve-position signal on the basis of a signal from the optical encoder, and abnormality determining means for determining an abnormality to generate an alarm signal, by judging whether the valve is located in a transition angle defined between a fully opened valve-position and fully closed valve-position on the basis of the digital valve-position signal from the digital valve-position signal generating means and whether the time period in the transition angle exceeds a predetermined time. The abnormality determining means determines the abnormality when the valve is located in the transition angle for a period of time which exceeds the predetermined time. 
     In the first aspect of the present invention, the optical encoder is applied to the valve-position output apparatus. This provides reduced mechanical wear of parts and enhanced durability of the valve-position output apparatus. Further, noise arising from operations may be reduced and thereby undesirable noise of the valve-position output apparatus may be sufficiently reduced. Furthermore, contact points or the like may be reduced and thereby undesirable spark or the like may be prevented as least as possible. In addition, any valve positions including those in the transition angle defined between the fully opened and fully closed valve-positions may be readily detected. Since the encoder applied to the present invention is not a magnetic encoder, the valve-position output apparatus of the present invention may not be adversely affected by an external magnetic field and may not go against the external magnetic field. 
     The valve-position output apparatus of the first aspect of the present invention is also provided with the abnormality determining means. Thus, when the valve is stopped at the valve position in the transition angle, the alarm signal may be output. 
     According to a second aspect of the present invention, there is provided a valve-position output apparatus comprising an interlocking member adapted to move in sync with open and close operations of a valve, a position detecting aperture formed in the interlocking member, an optical encoder having a light-emitting section and a light-receiving section which are arranged opposed to each other with interposing the interlocking member therebetween, digital valve-position signal generating means for generating a digital valve-position signal on the basis of a signal of the optical encoder, and D/A converting means for converting the digital valve-position signal from the digital valve-position signal generating means into an analog signal. The D/A converting means is arranged to add a certain value to the digital valve-position signal so as not to make the analog signal have a zero value at a fully opened valve-position and fully closed valve-position. 
     In the second aspect of the present invention, the valve-position output apparatus is provided with the optical encoder. Thus, the effects yielded by the optical encoder are provided as with the valve-position output apparatus of the first aspect of the present invention. In addition, the valve-position output apparatus of the second aspect of the present invention includes the D/A converting means. This allows analog signals to be output despite of applying the optical encoder. Further, since the D/A converting means is arranged to add a certain value to the digital valve-position signal, the output analog signal does not become zero at the fully opened valve-position and fully closed valve-position in a normal state. Thus, when the output analog signal becomes zero, it may be judged as an abnormal state. 
     According to a third aspect of the present invention, there is provided a valve-position output apparatus comprising an interlocking member arranged to move in sync with open and close operations of a valve, a position detecting aperture formed in the interlocking member, an optical encoder having a light-emitting section and a light-receiving section which are arranged opposed to each other with interposing the interlocking member therebetween, digital valve-position signal generating means for generating a digital valve-position signal on the basis of a signal of the optical encoder, D/A converting means for converting the digital valve-position signal from the digital valve-position signal generating means into an analog signal, and ON-OFF signal generating means for generating ON and OFF signals. The ON-OFF signal generating means generates the ON signal at one of a fully opened valve-position and a fully closed valve-position and generates the OFF signal at the other of the fully opened valve-position and the fully closed valve-position. 
     In the third aspect of the present invention, the valve-position output apparatus is provided with the optical encoder. Thus, the effects yielded by the optical encoder are provided as with the valve-position output apparatus of the first aspect of the present invention. In addition, the valve-position output apparatus of the third aspect of the present invention includes the D/A converting means and the ON-OFF signal generating means. Thus, this valve-position output apparatus may output the digital valve-position signal, the analog signal and ON-OFF signal, and thereby may cope with various output forms by itself. 
     According to a fourth aspect of the present invention, there is provided a valve-position output apparatus for a valve arranged to stop at a fully opened valve-position and a fully closed valve-position which is spaced apart from the fully opened valve-position at an angle of about 90 degrees, and to move without any stop motion in a transition angle defined between the fully opened valve-position and the fully closed valve-position. This valve-position output apparatus comprises an interlocking member arranged to move in sync with open and close operations of the valve, a position detecting aperture formed in the interlocking member, an optical encoder having a light-emitting section and a light-receiving section which are arranged opposed to each other with interposing the interlocking member therebetween, digital valve-position signal generating means for generating a digital valve-position signal on the basis of a signal of the optical encoder, and ON-OFF signal generating means for generating ON and OFF signals. The ON-OFF signal generating means generates the ON signal at one of the fully opened valve-position and the fully closed valve-position and generates the OFF signal at the other of the fully opened valve-position and the fully closed valve-position. The valve-position output apparatus further comprises abnormality determining means for determining an abnormality to generate an alarm signal, by judging whether the valve is located in the transition angle defined between the fully opened valve-position and the fully closed valve-position on the basis of the digital valve-position signal from the digital valve-position signal generating means and whether the time period in the transition angle exceeds a predetermined time. The abnormality determining means determines the abnormality when the valve is located in the transition angle for a period of time which exceeds the predetermined time. 
     In the fourth aspect of the present invention, the valve-position output apparatus is provided with the optical encoder. Thus, the effects yielded by the optical encoder are provided as with the valve-position output apparatus of the first aspect of the present invention. In addition, the valve-position output apparatus of the fourth aspect of the present invention includes the ON-OFF signal generating means and the abnormality determining means. In the conventional valve-position output apparatus arranged to output either one of an ON signal and an OFF signal, when the ON signal or the OFF signal is output, the valve is not always located at the fully opened valve-position or fully closed valve-position, and there is the case that the valve is located at the valve position in the transition angle. However, in the valve-position output apparatus of the fourth aspect of the present invention, the alarm signal is output when the valve is located at the valve position in the transition angle for more than the predetermined time. Thus, when the ON signal or the OFF signal is output and the alarm signal is not output, it may be accurately judged that the valve is located at the fully opened valve-position or fully closed valve-position. 
     Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic sectional view of a valve-position output apparatus according to a first embodiment of the present invention. 
     FIG. 2 is a sectional view taken along the line II of FIG.  1 . 
     FIGS.  3 ( a )- 3 ( d ) are sectional views showing various types of valves, wherein 
     FIG.  3 ( a ) shows a butterfly valve located at a fully closed valve-position, 
     FIG.  3 ( b ) shows the butterfly valve located at a fully opened valve-position, 
     FIG.  3 ( c ) shows a ball valve located at a fully closed valve-position, and 
     FIG.  3 ( d ) shows the ball valve located at a fully opened valve-position; 
     FIGS.  4 ( a )- 4 ( d ) are explanatory views of an optical encoder, wherein 
     FIG.  4 ( a ) is a front view of a rotary plate of an incremental encoder, 
     FIG.  4 ( b ) is a sectional view taken along the line B—B of FIG.  4 ( a ), 
     FIG.  4 ( c ) is a front view of a rotary plate of an absolute encoder, and 
     FIG.  4 ( d ) is a sectional view taken along the line D—D of FIG.  4 ( c ), 
     FIGS.  5 ( a )- 5 ( b ) are explanatory views of a signal processing device of the optical encoder, wherein 
     FIG.  5 ( a ) is a schematic circuit diagram and 
     FIG.  5 ( b ) is a graph of an output of a D/A converter. 
     FIG. 6 is a flowchart of the operation of the valve-position output apparatus. 
     FIGS.  7 ( a )- 7 ( b ) are schematic explanatory views of a valve-position output apparatus according to a second embodiment of the present invention, wherein 
     FIG.  7 ( a ) is a sectional view and 
     FIG.  7 ( b ) is a partial view showing a substantial part of FIG.  7 ( a ) viewed from the arrow B of FIG.  7 ( a ). 
     FIGS.  8 ( a )- 8 ( b ) are schematic explanatory views of a conventional valve-position output apparatus, wherein 
     FIG.  8 ( a ) shows the state when a valve is located at a fully closed valve-position and 
     FIG.  8 ( b ) shows the state when the valve is located at a fully opened valve-position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIGS. 1 to  7 , embodiments of a valve-position output apparatus of the present invention will be described. 
     FIG. 1 is a schematic sectional view of a valve-position output apparatus according to a first embodiment of the present invention, and FIG. 2 is a sectional view taken along the line II of FIG.  1 . As shown in these figures, in the first embodiment, a valve  2  is rotatably provided in a duct or pipe  1 . This valve  2  is arranged to rotate between a fully opened valve-position and a fully closed valve-position which is spaced apart from the fully opened valve-position at an angle of about 90-degree. The valve  2  is typically used at either one of the fully opened and fully closed valve-positions. Specifically, the valve is not used at any valve position in a transition or intermediate angle between the fully opened and fully closed valve-positions, and is moved in succession or without any stop motion between the fully opened and fully closed valve-positions. 
     The valve  2  may include a butterfly valve  3  as shown in FIGS.  3 ( a ) and  3 ( b ), a ball valve  4  as shown in FIGS.  3 ( c ) and  3 ( d ) and the like. A valve body  5  of the butterfly valve  3  has a circular or disc shape. At the fully closed valve-position shown in FIG.  3 ( a ), the valve body  5  is located approximately perpendicular to a flow direction of a fluid in the pipe  1  to block off the fluid. At the fully opened valve-position shown in FIG.  3 ( b ), the valve body  5  is located approximately parallel to the flow direction of the fluid in the pipe  1  to allow the fluid to be flowed therethrough. On the other hand, a valve body  7  of the ball valve  4  has a spherical or globular shape and is formed with a through-hole  8  penetrating the valve body  7 . At the fully closed valve-position shown in FIG.  3 ( c ), the through-hole  8  is located approximately perpendicular to the flow direction of the fluid in the pipe  1  to block off the fluid. At the fully opened valve-position shown in FIG.  3 ( d ), the through-hole  8  is located approximately parallel to the flow direction of the fluid in the pipe  1  to allow the fluid to be flowed therethrough. 
     As shown in FIG. 1, a valve shaft  11  of the valve  2  extends outside the pipe  1 , and a pinion  12  (or a gear) is provided on the periphery of the extended section of the valve shaft  11 . This pinion  12  is arranged to rotate with the valve shaft  11  in one united body, and to engage with a rack  13 . Pistons  14  are provided at both ends of the rack  13 , respectively. Each of the pistons  14  is placed in a corresponding pneumatic cylinder  16 . Air is supplied to and discharged from each pneumatic cylinder  16  to drive the pistons  14 , as shown in FIG.  2 . When the pistons  14  are driven, the rack  13  is moved to rotate the pinion  12  and the valve shaft  11 . The pinion  12 , rack  13 , pistons  14 , pneumatic cylinders  16  and other make up a valve-driving device  17  for driving the valve  2 . This valve-driving device  17  and the valve  2  make up a valve unit. An end of the valve shaft  11  is formed in a rectangular column, and protrudes from the valve unit. A suitable tool, such as a wrench, may be fitted in the end of the valve shaft  11  to manually rotate the valve  2 . A valve-position output apparatus  31  for detecting a rotational position of the valve  2  and outputting a signal corresponding to the detected rotational position is attached to the end of the valve shaft  11 . Specifically, an interlocking shaft  32  of the valve-position output apparatus  31  is coupled with the end of the valve shaft  11  through an adapter  23 , such as a socket joint. 
     A circular rotary plate  33  is integrally provided in the interlocking shaft  32 . This interlocking shaft  32  and the rotary plate  33  make up an interlocking member which is moved in sync with the rotation of the valve shaft  11  (or the open and close operations of the valve  2 ). As best shown in FIG. 4A, a plurality of position-detecting apertures  34  are formed in the rotary plate  33 . Light-emitting diodes  36  serving as a light-emitting section and phototransistors  37  serving as a light-receiving section are located opposed to each other with interposing the rotary plate  33  therebetween. The interlocking shaft  32 , rotary plate  33 , position-detecting apertures  34 , light-emitting diodes  36  and phototransistors  37  make up an optical rotary encoder. The phototransistors  37  are arranged to receive light from the corresponding light-emitting diodes  36  through the position-detecting apertures  34 , and to generate a pulse signal in response to the rotation of the rotary plate  33 . Thus, the rotational position of the rotary plate  33  may be figured out by processing the pulse signal. The optical encoder may include an incremental type encoder shown in FIGS.  4 ( a ) and  4 ( b ), and an absolute type encoder shown in FIGS.  4 ( c ) and  4 ( d ). In the incremental type encoder, the position-detecting apertures  34  include A-phase slits  41  and B-phase slits  42 , and the phototransistors  37  are positioned to the slits  41 ,  42 , respectively. Each phase of the B-phase slits  42  is shifted by one-quarter pitch with respect to each phase of the A-phase slits. This phase shift makes it possible to detect whether the rotary plate  33  rotates in a normal rotational direction or in a reverse rotational direction. In the incremental type encoder, the rotational position of the rotary plate  33  may be figured out by counting pulse signals from one of the phototransistors  37  (more specifically, by adding the counted pulse signals during the normal rotation and subtracting the counted pulse signals from the previous total pulse signals during the reverse rotation). On the other hand, in the absolute type encoder, the position-detecting apertures  34  comprise a plurality of tracks  46  to  50 , and the phototransistors  37  are positioned to the tracks  46  to  50 , respectively. Thus, the rotational position of the rotary plate  33  may be figured out by identifying one or more of the phototransistors  37  which are one or more of the detecting the tracks  46  to  50 . 
     As shown in FIG. 5, in both types, the pulse signal from the phototransistors  37  is input to digital angle generating means  52  of a signal processor  51  composed of a microcomputer. The digital angle generating means  52  serving as digital valve-position signal generating means generates a digital signal corresponding to the rotational position of the rotary plate  33  on the basis of the pulse signal from the phototransistors  37 . In the incremental type encoder, the digital angle generating means  52  is initialized by closed valve-position setting means  53  of the signal processor  51  with locating the valve  2  at the fully closed valve-position. The closed valve-position setting means  53  serving as initial setting means is composed of a button switch or the like. The digital angle generating means  52  is set in its origin by pushing the button switch. After the initial setting, when the valve  2  is opened or closed to rotate the rotary plate  33 , the digital angle generating means  52  counts the pulse signal from the phototransistors  37 , and outputs the counted number in the form of a digital angle signal (digital valve-position signal). In the incremental type encoder, the digital angle generating means  52  appropriately stores a current digital angle signal in a nonvolatile memory, such as EPROM. When a power supply is cut off and then turned on, the stored digitals angle signal is read out from the nonvolatile memory and used as the digital angle  20  signal at that time. On the other hand, in the absolute type encoder, the rotational position of the rotary plate  33  may be figured out by the signal from the phototransistors  37 . However, the digital angle generating means  52  is initialized by the closed valve-position setting means  53  of the signal processor  51  with locating the valve  2  at the fully closed valve-position, because the valve  2  is not always located at the full closed valve-position with about zero degree. The digital angle generating means  52  is set in its origin by the closed valve-position setting means  53  and then generates the digital angle signal by subtracting an angel signal at the initial setting from the signal from the phototransistors  37 . 
     The digital angle signal from the digital angle generating means  52  may be externally output directly from an external output terminal  56 , or may otherwise be converted into an analog signal through a D/A converter  57  to externally output the converted analog signal. As shown in FIG.  5 ( b ), when converting into the analog signal, the current value of the analog signal or an output analog signal is not set in zero mA but set in about 4 mA at the fully closed valve-position. Thus, the state when the output of the D/A converter  57  becomes about zero may be judged as abnormality, or that a certain failure arises in the valve-position output apparatus, etc. 
     The digital angle signal of the digital angle generating means  52  is output to the closed valve-position determining means  58 . Then, the closed valve-position determining means  58  determines whether the valve  2  is located at the fully closed valve-position, on the basis of the digital angle signal. When determined that the valve  2  is locate at the fully closed valve-position, the closed valve-position determining means  58  outputs a closed valve-position signal to abnormality determining means  62  and an ON-OFF signal generator  61  serving as ON-OFF signal generating means. When determined that the valve  2  is not located at the fully closed valve-position, the closed valve-position determining means  58  outputs the digital angle signal received from the digital angle generating means  52  to opened valve-position determining means  63 . In response to the closed valve-position signal from the closed valve-position determining means  58 , the ON-OFF signal generator  61  externally outputs an ON signal (e.g. about 24 V) through an ON-OFF signal output section  64  being an amplifier composed of a transistor, etc. When receiving no closed valve-position signal from the closed valve-position determining means  58 , the ON-OFF signal generator  61  externally outputs an OFF signal (e.g. about 0 V) through the ON-OFF signal output section  64 . These ON and OFF signals are equivalent to a relay output of the conventional limit switch. 
     The opened valve-position determining means  63  determines whether the valve  2  is located it the fully opened valve-position, on the basis of the digital angle signal. When determined that the valve  2  is located at the fully opened valve-position, the opened valve-position determining means  63  outputs an opened valve-position signal to the abnormality determining means  62 . In response to the closed valve-position signal from the closed valve-position determining means  58  or the opened valve-position signal from the opened valve-position determining means  63 , the abnormality determining means  62  resets an abnormality determining timer  66 . The abnormality determining timer  66  is arranged to output a lapsed time after the abnormality determining timer  66  is reset, to the abnormality determining means  62 . The abnormality determining timer  66  has a specific abnormality determining time which is a predetermined reference time for determining the abnormality. When the lapsed time output from the abnormality determining timer  66  exceeds the abnormality determining time, the abnormality determining means  62  generates an alarm signal to an alarm device  67 . The alarm device  67  gives an alarm with light, sound or the like in response to the alarm signal. 
     With reference to the flowchart of FIG. 6, the operation of the valve-position output apparatus  31  will be described. 
     In Step  1 , for one of the initial setting after the valve-position output apparatus  31  is attached to the valve unit, the valve  2  is located at the fully closed valve-position being an original position of the valve  2 . In Step  2 , the light-emitting diodes  36  are activated to emit light, and the signal from the phototransistors  37  is input to the digital angle generating means  52  of the signal processor  51 . In Step  3 , the closed valve-position setting means  53  is operated by the button switch or the like as described above to set the origin of the digital angle generating means  52 . The initial setting is completed through Steps  1  to  3 . 
     In Step  4 , compressed air is supplied to one of the pneumatic cylinders  16 . Thus, the valve-driving device  17  is moved to rotate the valve  2 , and then the process proceeds to Step  5 . In Step  5 , the light-emitting diodes  36  emit light, and the signal from the phototransistors  37  is input to the signal processor  51 . Then, the process proceeds to Step  6 . In Step  6 , the digital angle generating means  52  generates the digital angle signal as a digital signal representing the rotational angle of the valve  2  on the basis of the signal from the optical rotary encoder or the light-emitting diodes  36  to externally output the digital angle signal from the external output terminal  56 , and then the process proceeds to Step  7 . In Step  7 , the digital angle signal is output to the D/A converter  57  and is externally output from the D/A converter  57 . Then, the process proceeds to Step  8 . In Step  8 , the closed valve-position determining means  58  determines whether the valve  2  is located at the fully closed valve-position, on the basis of the digital angle signal. When determined that the valve  2  is located at the fully closed valve-position, the process proceeds to Step  9 . When determined that the valve  2  is not located at the fully closed valve-position, the process proceeds to Step  11 . 
     In Step  9 , the closed valve-position determining means  58  outputs the closed valve-position signal to the ON-OFF signal generator  61  and the abnormality determining means  62 . In response to the closed valve-position signal, the ON-OFF signal generator  61  generates the ON signal, and the ON-OFF signal output section  64  amplifies the generated ON signal to externally output. In Step  10 , the abnormality determining means  62  resets the abnormality determining timer  66  in response to the closed valve-position signal, and the process returns to Step  5 . 
     As described above, when determined that the valve  2  is not located at the fully closed valve-position in Step  8 , the process proceeds to Step  11 . In Step  11 , since no closed valve-position signal is input to the ON-OFF signal generator  61 , the ON-OFF signal generator  61  generates the OFF signal to externally output it through the ON-OFF signal output section  64 . The closed valve-position determining means  58  also outputs the digital angle signal to the opened valve-position determining means  63 , and then the process proceeds to Step  12 . In Step  12 , the opened valve-position determining means  63  determines whether the valve  2  is located at the fully opened valve-position, on the basis of the digital angle signal from the closed valve-position determining means  58 . When determined that the valve  2  is located at the fully opened valve-position, the opened valve-position determining means  63  outputs the opened valve-position signal to the abnormality determining means  62 , and the process proceeds to Step  10 . In response to the opened valve-position signal, the abnormality determining means  62  resets an abnormality determining timer  66 , and then the process returns to Step  5 . 
     On the other hand, when determined that the valve  2  is not located at the fully opened valve-position in Step  12 , the process proceeds to Step  13 . In step  13 , the abnormality determining means  62  judges whether the lapsed time output from the abnormality determining timer  66  exceeds the predetermined abnormality determining time. When judged that the abnormality determining timer  66  does not exceed the predetermined abnormality determining time, the process returns to Step  5 . When judged that the abnormality determining timer  66  does exceed the predetermined abnormality determining time, the process proceeds to Step  14 . In Step  14 , the abnormality determining means  62  generates the alarm signal to output it to the alarm device  67 . In response to the alarm signal, the alarm device  67  gives the alarm, and then the process returns to Step  5 . 
     The external output from the valve-position output apparatus constructed as described above may be applied to display the valve position or control the valve. 
     With reference to FIG. 7, a valve-position output apparatus according to a second embodiment of the present invention will be described. 
     In FIG. 7, a flow-regulating valve  71  is provided in a pipe  1 . A valve body  72  of the flow-regulating valve  71  is linearly moved and is also reciprocated. The flow-regulating valve  71  is arranged to reciprocate between a fully closed valve-position where the flow-regulating valve  71  is almost fully closed (corresponding to the fully closed valve-position in the first embodiment) and a fully opened valve-position where the flow-regulating valve  71  is almost fully opened (corresponding to the fully opened valve-position in the first embodiment). The flow-regulating valve  71  is also arranged to stop at any position between the fully closed and fully opened valve-positions to regulate a flow rate of a fluid passing through the pipe  1 . A rack  74  is formed in a valve shaft  73  of the flow-regulating valve  71 , and a pinion  77  rotatably driven by a motor  76  is engaged with the rack  74 . The rack  74 , the motor  76  and the pinion  77  make up a valve-driving device. This valve-driving device and the flow-regulating valve  71  make up a valve unit. An interlocking shaft  79  of the valve-position output apparatus  80  is coupled with the end of the valve shaft  73  through an adapter  78 . A plate member  82  having position-detecting apertures  81  is connected to the interlocking shaft  79 . A light-emitting diode  83  and a phototransistor  84  are located opposed to each other with interposing the plate member  82  therebetween. The interlocking shaft  79  and the plate member  82  make up an interlocking member. The plate member  82 , the light-emitting diodes  83  and the phototransistors  84  make up an optical linear encoder. As with the optical rotary encoder, the optical linear encoder may include the incremental type encoder and absolute type encoder. A signal processor  86  has a similar structure as that of the signal processor  51 , but the valve-position output apparatus  80  does not include the alarm device  67 . 
     The invention has now been described in detail with reference to specific embodiments. However, it is not intended that the invention is limited to such embodiments, and various modifications may be made within the spirit and scope of the appended claims. Some modifications of the present invention will be described as follows. 
     (1) The ON-OFF signal output section, the D/A converter and the external output terminal for digital signals may be selectively provided and are not necessarily provided all together. In particular, in case of providing only either one of the D/A converter or the external output terminal for digital signals, wirings may be reduced as less as possible. The ON-OFF signal output section may be configured by a relay or the like. 
     (2) The structure or type of the valve and the optical encoder may be appropriately modified and selected. 
     (3) While the driving power of the valve-driving device is an air pressure in the above embodiments, any other type of driving power, such as electrical or hydraulic power, may be applied. The structure or type of the valve-driving device may also be appropriately modified and selected. 
     (4) The alarm device may be omitted. Further, the alarm signal may be externally output. 
     (5) While the origin is defined at the fully closed valve-position in the above embodiments, the fully opened valve-position may be used as the origin. 
     (6) While the analog signal is arranged to add a certain value to the output analog signal when converting the digital signal to the analog signal in the above embodiments, it is possible not to add such an additional value. However, it is preferable to add such an additional value for detecting the abnormality. 
     (7) While the ON-OFF signal generator and the ON-OFF signal output section are provided only to the fully closed valve-position in the above embodiments, they may also be provided to the fully opened valve-position. 
     (8) While the power source of the valve-position output apparatus is supplied from outside in the above embodiments, an internal power source, such as a battery, may be provided in the valve-position output apparatus, and an backup power source may be additionally provided. 
     (9) While the valve shaft is formed of a single member in the above embodiments, it may be constructed by a plurality of members. 
     (10) The ON-OFF signal may be switched to output the ON signal when the valve is moved to one of the fully opened and fully closed valve-positions, and to output the OFF signal when the valve is moved to the other of the fully opened and fully closed valve-positions. 
     (11) The digital signal may be output through an RS232C connector or any suitable connector, such as an RS 485 connector.