WO2002097313A1

WO2002097313A1 - Optical transducer for the detection and the remote indication of predetermined positions of a movable member, particularly of a valve member

Info

Publication number: WO2002097313A1
Application number: PCT/EP2002/005141
Authority: WO
Inventors: Lorenzo Bracco; Mario Desilani
Original assignee: A.P.S.S. S.R.L.; Rizzio Valvole S.P.A.
Priority date: 2001-05-28
Filing date: 2002-05-10
Publication date: 2002-12-05
Also published as: ITTO20010508A1; ITTO20010508A0

Abstract

The optical transducer includes a pair of fixed, rigid supports (18, 20), fast to each other and located respectively on one side and on the other side of a dimming plane along which a dimmer (32b), fixed to a movable member (10), moves. One of the supports carries at least two light-emitting diodes (PE1, PE2, PE3) and the other carries at least two corresponding light-receiving diodes (PR1, PR2, PR3), in such an arrangement as to form two pairs of diodes facing each other. Each of these pairs corresponds to a respective predetermined position of the movable member (10). The pairs of diodes are permanently secured to the respective supports (18, 20). For each pair of diodes, a DC voltage output is electrically connected or adapted to be connected to a load, such as a light indicator. For each pair of diodes, respective electrical circuit means are mounted in common at least in part on the two supports (18, 20). When the dimmer (32a, 32b) is located between the two diodes of the pair, a voltage is present to feed the corresponding load.

Description

OPTICAL TRANSDUCER FOR THE DETECTION AND THE REMOTE INDICATION OF PREDETERMINED POSITIONS OF A MONABLE MEMBER, PARTICULARLY OF A VALVE MEMBER

The present invention relates to an optical transducer for the detection and the remote indication of predetermined positions of a movable member, particularly of a valve member, according to the preamble of claim 1.

The invention has been developed in its application to fluid valves of the butterfly type and of the gate type in which the movable member whose position has to be detected and remotely indicated is, respectively, a turnable valve member and a slidable valve member, but is applicable to the detection and the remote indication of the position of any movable member which is adapted to angularly or linearly move between two end of stroke positions.

The optical transducers according to the preamble of claim 1, also called optical encoders, are known from many years.

They have the advantage of not being sensitive to electromagnetic fields.

In these known transducers each pair of diodes facing each other is a separate unit which is provided with its own support on which the diodes are first affixed in an approximate position, after which they are repositioned for calibration purposes.

The calibration must be carried out individually for each pair of diodes, with a complicated task which requires auxiliary equipment and specialized personnel.

The object of the invention is to provide an optical transducer of the type considered, which does not have the drawbacks of the known transducers and more particularly can be installed on a valve or other device even by a not very skilled person, without special equipment, and which can be calibrated by a very simple operation.

According to the invention this object is attained by means of an optical transducer as claimed.

As will be better understood from the description which follows, made with reference to the attached drawings, the main advantage of the invention consists of the fact that the pairs of diodes are preinstalled in predetermined fixed positions on respective fixed, rigid supports, and their positions do not have to be modified for calibration purposes.

Preferably, the supports are constituted by circuit boards which, in addition to the diodes, carry most of the electrical components. This allows to carry out the calibration of the transducer without disconnecting any wires.

As also will be better understood from the description made with reference to the drawings, in order to carry out the calibration in the application to a valve it is not necessary to open and close the valve, but it is sufficient to make sure that the valve is closed.

Since the positions of the pairs of diodes are fixed beforehand, it is possible to just carry out the calibration in the closed condition of the valve, because the open position is obtained automatically.

In a preferred embodiment, claimed in claim 5, the idle range for the calibration is not established in an approximate manner by the installer, but is detected with extreme accuracy by a third pair of diodes located in an overtravel position; once the operator has ascertained that the movable member is in this overtravel position, he must make sure that the light indicator, which is on the transducer, that is on the spot of installation, is lit. If it is not, that means that the transducer is not calibrated well and the dimmer is not located between the diodes of the third pair. Then, in order to perfect the calibration, the installer has just to unlock the dimmer with respect to the movable member (for example, by loosening a screw), move the dimmer by just the amount sufficient to switch on the light indicator, and then to lock the dimmer again in the new position with respect to the movable member (for example, by retightening the screw).

The invention also relates to fluid valves of the butterfly type and of the gate type, having a movable member, a rotary shaft or a sliding stem, respectively, equipped with a transducer according to the invention.

The invention will be better understood from the reading of the detailed description which follows, made with reference to the attached drawings, given by way of non-limiting example and in which:

Figure 1 is a perspective view of an optical transducer according to a first embodiment of the invention, of the angular type for a movable member constituted by the rotary shaft of a butterfly valve or the like,

Figure 2 is a perspective view which separately shows only the dimmer assembly of the embodiment of Figure 1,

Figure 3 is a perspective view of an optical transducer according to another embodiment of the invention, of the linear type for a movable member constituted by the sliding stem of a gate valve or the like,

Figure 4 is a perspective view which separately shows only the dimmer assembly of the embodiment of Figure 3, Figure 5 is a circuit diagram applicable to both the embodiments of Figures 1 and 3, and

Figures 6a, 6b, 6c are schematic representations which show three conditions of detection of the positions of the movable member and of calibration of the optical transducer, irrespective of the fact that the transducer is the one of Figure 1 or the one of Figure 2.

Referring to Figure 1, a movable member constituted by the rotary shaft of a butterfly valve (not shown) is indicated by 10.

A transducer of the angular type according to the invention, generally indicated by 12, which surrounds the shaft 10, is secured on an upper flange of the valve.

The transducer 12 comprises an annular base flange 14 which, in the installed condition, is bolted to the upper flange of the valve.

The flange 14 has upright threaded stud bolts 16 which support a pair of fixed, rigid discs, namely a lower disc 18 and an upper disc 20, which loosely and concentrically surround the shaft 10.

Three spacer bushings 22, 24, 26 are arranged around each of the stud bolts 16.

The lower disc 18 is interposed between the bushings 22 and 24 and the upper disc 20 is interposed between the bushings 24 and 26.

For each of the stud bolts 16, the "pack" which comprises the discs 18, 20 and the bushings 22, 24, 26 is tightly clamped by a respective nut 28.

The two discs 18, 20 are secured so as to be parallel to each other as well as to parallel to an intermediate dimming plane, whose trace is indicated by P in Figures 6a, 6b and 6c.

The dimming plane P is normal to the axis of rotation of the shaft 10 of the valve.

Three light-emitting diodes PEl, PE2, PE3 are affixed on the face of the lower disc 18 which is turned towards the upper disc 20 and emit respective light beams Bl , B2, B3 towards the upper disc.

Three light-receiving diodes PRl, PR2, PR3, which are affixed on the face of upper disc 20 which is turned towards the lower disc 18, are located exactly in front of the light-emitting diodes PEl, PE2, PE3 and receive the respective light beams Bl, B2, B3 from the latter.

Preferably, the light-emitting diodes PEl, PE2, PE3 are of the infrared light type and in any case they emit the light continuously.

A preferred light-emitter diode is of a type which emits a beam of infrared light with a maximum angle of 10 degrees and a wavelength of 950 nanometers.

The first pair of diodes PEl -PRl corresponds to a first predetermined end position of angular travel of the shaft 10, in which the valve is completely open; the second pair of diodes PE2-PR2 corresponds to a second predetermined end position of angular travel of the shaft 10, adjacent to the fist one, in which the valve is closed; the third pair of diodes PE3-PR3 corresponds to an angular overtravel position of the shaft 10, which is beyond, and opposite to, said second position.

The function of the third pair of diodes will be clarified below in the description referred to Figures 6b and 6c. A dimmer of an opaque material, which is associated to the three pairs of diodes PEl-PRl, PE2-PR2, PE3-PR3, is angularly movable with the shaft 10 and, when it is interposed between the diodes of one of the pairs, intercepts the corresponding light beam emitted by the light-emitting diode, masking thereby the light-receiving diode.

Referring to Figures 1 and 2, in the embodiment shown the shaft 10 has a ring 30 fastened thereto in an intermediate position between the two discs 18, 20, and the ring has two radially projecting wings 32a, 32b of an opaque material, having the function of a dimmer, which lay in the aforesaid dimming plane P.

The wing 32a is adapted to mask the light-receiving diode PR2 in order to signal, as will be seen, the fully closed position of the valve.

The wing 32b is disposed and dimensioned, along the dimming plane P, in such a manner that when it is in the position in which it masks the light-receiving diode PR3 which corresponds to the overtravel position, it also masks the light-receiving diode PRl which corresponds to the fully open position of the valve.

The arrangement is however such that when the wing 32a masks the light- receiving diode PR2, but the wing 32b has not exactly reached the overtravel position, it does not mask the light-receiving diode PR3.

The ring 30 is fastened to the shaft 10 in a loosenable manner. Preferably, as shown in Figures 1 and 2, the fastening is obtained by means of a set screw 34; by loosening the screw 34 by means of a simple wrench, the installer can rotate the ring 30, with its wings 32a, 32b, with respect to the shaft 10 in order to effect an accurate calibration, as will be described with reference to Figures 6a and 6b. Reference will now be made to Figures 3 and 4 to describe a linear embodiment of the optical transducer according to the invention.

In this description the pairs of diodes, some of which are not visible in Figure 3, are still indicated by PEl-PRl, PE2-PR2, PE3-PR3 and their light beams, which also in this case are preferably of the infrared type, are still indicated by Bl, B2, B3.

In Figures 3 and 4 the parts analogous to those of the angular embodiment of Figures 1 and 2 will be indicated as far as possible by the same reference numerals, increased by 100.

Referring to Figure 3, 110 indicates a movable member constituted by the sliding stem of a gate valve (not shown).

A transducer of the linear type according to the invention, generally indicated by 112, which is located next to the stem 110, is secured on a upper flange of the valve.

The transducer 112 has an annular flange 114 which, in the installed condition, is bolted to the upper flange of the valve.

The flange 114 supports a pair of opposed, fixed, rigid plates 118, 120.

The two plates 118, 120 are fixed in such a manner that they are parallel to each other as well as parallel to an intermediate dimming plane, whose trace is for example indicated by P in Figures 6a, 6b and 6c.

The dimming plane P is normal to the axis along which the stem 110 of the valve is slidable. On the face of the plate 118 which is turned towards the plate 120 there are secured three light-emitting diodes PEl, PE2, PE3 which emit respective light beams Bl, B2, B3 towards the plate 120.

On the face of the plate 120 which is turned towards the plate 118 there are secured three light-receiving diodes PRl, PR2, PR3 which are exactly in front of the respective light-emitting diodes PEl, PE2, PE3 and receive the respective light beams Bl, B2, B3 from the latter.

Also in this linear embodiment, preferably, the light-emitting diodes PEl, PE2, PE3 are of the infrared type and in any case they transmit the light continuously.

Also in this case, the preferred type of light-emitter-diode emits a beam of infrared light with a maximum angle of 10 degrees and a wavelength of 950 nanometers.

The first pair of diodes PEl-PRl corresponds to a first predetermined end position of the linear travel of the stem 110, in which the valve is fully open; the second pair of diodes PE2-PR2 corresponds to a second predetermined end position of the linear travel of the stem 110, opposite to the first one, in which the valve is closed; the third pair of diodes PE3-PR3 corresponds to a linear overtravel position of the stem 110, which is beyond, and adjacent to, said second position.

Also in this case the function of the third pair of diodes will clarified below in the description referred to Figures 6b and 6c.

A dimmer of an opaque material, which is linearly movable with the stem 110, is associated to the three pairs of diodes PEl-PRl, PE2-PR2, PE3-PR3 and, when it is interposed between the diodes of one of the pairs, it intercepts the corresponding light beam emitted by the light-emitting diode and masks therefore the light-receiving diode.

Referring to Figures 3 and 4, in the embodiment shown the stem 110 has a ring which is fastened thereto in an intermediate position between the two plates 118, 120 and which has a radially projecting wing or flag 132 of an opaque material, which lies in the aforesaid dimming plane P and acts as a dimmer.

The flag 132 is adapted to mask the light-receiving diode PRl (not visible in Figure 3) in order to signal the fully open position of the valve and moreover is disposed and dimensioned along the dimming plane P in such a manner that, when it is in the position in which it masks the light-receiving diode PR3 which corresponds to the overtravel position (not visible in Figure 3), it also masks the light-receiving diode PR2 which corresponds to the closed position of the valve.

Also in this case the arrangement is such that when the flag 132 masks the light- receiving diode PR2, but has not yet exactly reached the overtravel position, it does not mask the light-receiving diode PR3.

The ring 130 is fastened to the stem 110 in an loosenable manner. Preferably, as shown in Figure 3, the fastening is obtained by means of a set screw 134; by loosening the screw 134 with a simple wrench, the installer can slide the ring 130, with its flag 132, with respect to the stem 110 in order to carry out an accurate calibration, as will be described with reference to Figures 6a and 6b.

The linear transducer of Figures 3 and 4 is preferably adapted to be installed on gate valves of various diameters.

The requirement of adaptability of the angular transducer of Figures 1 and 2 to butterfly valves of various diameters was not strongly felt, since, regardless of its diameter, the valve member of a butterfly valve always accomplishes a rotation of approximately 90°. At the most, given that the diameter of the shaft increases with the diameter of the valve member, for the valve of Figures 1 and 2 one can foresee rings 30 of various inner diameters, or intermediate rings of various inner diameters to be interposed between the shaft 10 and a standard ring 30.

In a gate valve, instead, the stroke of the stem 110 varies in proportion to the diameter of the valve member and therefore the flag must have a longitudinal dimension which corresponds each time to the stroke of the stem 110.

The flag 132 of Figures 3 and 4 allows to use a single model of linear optical transducer on gate valves included in a whole range of sizes.

In order to obtain this, the flag is of an easily breakable or shearable plastic material and has parallel breaking notches 136 which delimit segments 138 on which the sizes of the valves in the range are indicated, namely the nominal diameters ND 40, ND 50... ND 150, ND 200 in the case shown

In order to adapt the transducer to a valve of a given diameter it will then be sufficient to break away the undesired segments, on the basis the indications provided on the segments.

Reference to Figure 5 will now be made to describe the preferred electrical circuitry of an optical transducer according to the invention, irrespective of the fact that the transducer is of the angular or of the linear type.

Preferably and advantageously, each of the aforesaid fixed supports 18, 20 (Figure 1) and 118, 120 (Figure 3) is constituted by a respective flat printed circuit board which includes, and/or which has affixed thereto, the majority of the various electrical/electronic components already mentioned above, plus those which will be mentioned below.

In Figure 5 a dotted line box 18 (118) indicates the board 18 or 118 which carries the light-emitting diodes PEl, PE2, PE3 and the corresponding feeding circuit, for example, at constant 24 V DC.

A dotted line box 20 (120) indicates a feeding circuit, for example, at constant 24 V DC, for the cathodes of the light-receiving diodes PRl, PR2, PR3.

This latter circuit, contained in the box 20 (120), can be carried by the board 20 or 120 rather than by the board 18 or 118.

The only requirement in this regard is that the two boards 18, 20 (or 118, 120) be interconnected by two feeding wires, for example, at 24 V.

Each pair of light-receiving diodes PRl, PR2, PR3, which are mounted on the board 20 or 120, is connected to a voltage comparator VC.

More particularly, the voltage comparator VC has respective inputs INP1, INP2, INP3 connected to the anodes of the respective light-receiving diodes PRl, PR2, PR3, and respective voltage outputs OUT1, OUT2, OUT3.

When the comparator VC detects the presence of a high signal (for example, 12 V) at one of its respective inputs INP1, INP2, INP3, it supplies a DC voltage, for example, of 12 V, to one of the respective outputs OUT1, OUT2, OUT3.

As regards the outputs OUT1 and OUT2, these are electrically connected or adapted to be connected to respective remote loads Ul, U2, such as light or acoustic indicators, servo controls, etc. As regards the output OUT3, this is directly connected to a light indicator LED, indicated by the latter reference in Figures 1 and 5, which, in the embodiment of Figure 1, is located on the upper face of the upper disc 20 and is clearly visible to the installer during the calibration step which will be described below.

The comparator VC is adapted to deliver, at one of the outputs OUT1, OUT2, OUT3, a respective DC signal only when a high signal, for example, at 12 V, is applied to the respective input INP1, INP2 INP3.

When a light-receiving diode PRl, PR2 or PR3 is masked by the dimmer 32a, 32b or 132, the predetermined voltage, for example, of 12 V, is applied to the input of the comparator VC, while, when the light-receiving diode is not masked, zero voltage, which corresponds to the masking of the respective light-receiving diode PRl, PR2, PR3, is applied to the input of the comparator VC.

The comparator VC is adapted to deliver, at one of its outputs OUT1, OUT2,

OUT3, a DC signal only when the predetermined voltage, for example, of 12 V, is applied to its corresponding input INP1, INP2, INP3.

As regards the light-receiving diodes PRl and PR2, the circuit means carried by the board 20 (or 120) comprise, for each of the diodes, a respectiye transistor TR1, TR2 of the n-p-n type and a respective power relay RL1, RL2, which can be mounted on same board 20 or 120.

The base of each transistor TR1, TR2 is connected to a corresponding output OUT1, OUT2 of the comparator, its emitter is connected to a zero voltage terminal of the feeder of the respective relay RL1, RL2 and its collector is connected to the other terminal of the feeder, in series with the coil of the relay. Therefore, the circuit of the corresponding load Ul or U2 is closed when the output voltage of the comparator VC is applied to the base of the corresponding transistor TR1 or TR2.

Each of the relays RLl, RL2 has a coil and power contacts which are inserted in a feed circuit for the corresponding load Ul, U2, and which are closed for feeding the load when the coil is energized.

The coil of each of the relays RLl, RL2 is fed by a constant voltage DC, which can be the same external source at 24 V mentioned above.

Preferably, each of the relays RLl, RL2 is of the reed type, that is with reed contacts sealed under vacuum in a tube, which close under the action of the magnetic attraction of the corresponding coil. The choice of this type of relay, among the other things, facilitates its installation on a circuit board such as the boards 20 and 120.

An optical transducer, be it angular or linear, thanks to its compactness, especially if its supports are constituted by circuit boards such as the boards 18, 20 or 118, 120, lends itself very well to being enclosed in a waterproof and airproof housing (not shown), which renders it particularly desirable in environments in which the valves or other equipment are at risk of being submerged by water or other liquids, such as oil, for example, in the hold of a ship, and which also in such conditions must be able to indicate in a distant place their open or closed condition.

Referring now to Figures 6a, 6b and 6c, the operation and the method of calibration of an optical transducer according to the invention will be briefly described, regardless of the fact that the transducer is an angular transducer like the one of Figures 1 and 2 or a linear transducer like the one of Figures 3 and 4. In Figures 6a, 6b, 6c the diodes are still indicated, respectively, by PEl, PE2, PE3 and PRl, PR2, PR3; P indicates the trace of the aforesaid dimming plane; 32 indicates the dimmer, regardless of the fact that it is constituted by the pair of wings 32a, 32b of Figures 1 and 2 or by the flag of Figures 3 and 4.

In Figure 6a the valve is completely open, and the dimmer 32 is located between the diodes PEl and PRl and intercepts the light beam Bl, whereby the load Ul (Figure 5), for example, a green light in a control room, is switched on to indicate this open condition of the valve.

In Figure 6b the valve is practically closed, but the dimmer 32 is located only between the diodes PE2 and PR2 and intercepts the light beam B2, but still does not intercept the light beam B3. The load U2 (Figure 5), for example, a red light in a control room, is fed in order to indicate this closed condition of the valve.

In the absence of other measures, the perfect closure of the valve could not be certain, also taking account of the fact that the light beam B2 is conical and is unable to supply a strictly accurate closed position signal.

At this stage, if the installer notices that the light indicator LED (Figures 1 and 5), which he sees in front of him while he works, is not lit, this indicates to him that the valve is in the incorrect condition of Figure 6b, that is that the transducer is not calibrated well.

After he has made sure that the valve is really closed to the hilt, the installer then ^' loosens the screw 34 (Figures 1 and 2) or 134 (Figure 3) and moves the dimmer 32 (to the left from the full line position of Figure 6b to the full line position of Figure 6c), until the dimmer intercepts also the light beam B3, whereby the indicator LED is lit and the installer is given the certainty that the correct calibration has been executed with the necessary overtravel of the valve member of the valve.

After that, the installer locks the dimmer 32 again by means of the screw 34 (Figures 1 and 2) or 134 (Figure 3) and the calibration is completed.

Claims

CLAIMS 1. An optical transducer for the detection and the remote indication of predetermined positions of a movable member (10; 110), more particularly a control member of a butterfly valve or a gate valve, of the type in which for the detection of each predetermined position of the movable member a pair of semiconductor diodes facing each other, one of which is a light-emitting diode (PEl, PE2, PE3) and the other of which is a light-receiving diode (PRl, PR2, PR3), and in which a dimmer (32; 32a, 32b; 132) of an opaque material is associated to the pair of diodes, which dimmer is movable with to movable member (10; 110) and, when it is interposed between the diodes of the pair, intercepts the light beam emitted by the light-emitting diode, thus masking the light-receiving diode with the consequent generation of an electrical position signal, characterized in that it includes:

- a pair of fixed, rigid supports (18, 20; 118, 120), fast to each other and located respectively on one side and on the other side of a dimming plane (P) along which the dimmer (32; 32a, 32b; 132) moves, one of which supports carries at least two light-emitting diodes (PEl, PE2, PE3) and the other of which carries at least two corresponding light-receiving diodes (PRl, PR2, PR3), according to an arrangement such as to form at least two pairs of diodes facing each other, each of which pairs corresponds to one of the said predetermined positions, the pairs of diodes being permanently affixed to the respective supports (18, 20; 118, 120);

- for each pair of diodes, a DC voltage output electrically connected or adapted to be connected to a load (Ul, U2, LED), such as a light indicator, and

- for each pair of diodes, respective electrical circuit means mounted in common at least in part on the two supports (18, 20; 118, 120) and arranged in such a manner that, when the dimmer (32; 3a, 32b; 132) is located between the two diodes of the pair, a feeding voltage for the corresponding load is present on the corresponding voltage output.

2. A transducer according to claim 1, characterized in that the, electrical circuit means include, for each pair of diodes (PEl-PRl, PE2-PR2, PE3-PR3):

- a voltage comparator (VC) having an input connected to the anode of the light- receiving diode and a voltage output, and

- a constant voltage DC feeder which applies a zero voltage to the cathode of the light-receiving diode and applies to its anode the said constant DC voltage, whereby, when the light-receiving diode is not masked by the dimmer, the said zero voltage is applied to the input of the comparator, while when the light- receiving diode is masked, the said predetermined voltage is applied to the input of the comparator (VC), and in that the comparator (VC) is adapted to emit an output DC voltage signal only when the predetermined voltage is applied to its input.

3. A transducer according to claim 2, characterized in that, at least for a pair of diodes, the circuit means include:

- a transistor of the n-p-n type (TR1, TR2),

- a power relay (RLl , RL2) having a coil and power contacts inserted in a feed circuit for the corresponding load (Ul, U2), which are closed for feeding the load when the coil is energised, and

- a constant voltage DC feeder for the coil of the relay (RLl, RL2), and in that the base of the transistor (TR1, TR2) is connected to the output of the comparator (VC), its emitter is connected to a zero voltage terminal of the feeder of the relay (RLl, RL2), and its collector is connected to the other terminal of the feeder in series with the coil of the relay, whereby the circuit of the load (Ul, U2) is closed when the output voltage of the comparator (VC) is applied to the base of the transistor (TR1, TR2).

4. A transducer according to claim 3, characterized in that the relay (RLl, RL2) is of the reed type.

5. A transducer according to any of the preceding claims, characterized in that it comprises three pairs of diodes, a first of which (PEl-PRl) corresponds to a first predetermined end-of-travel position of the movable member (10; 110), a second of which (PE2-PR2) corresponds to a second predetermined end-of-travel position of the movable member (10; 110), opposite to the first, and a third of which (PE3-PR3) corresponds to an overtravel position of the movable member (10; 110), located beyond said second position and adjacent thereto, in that a light indicator (LED) is associated to the third pair of diodes (PE3-PR3) and is adapted to be lit in order to indicate the overtravel position, in that the dimmer (32; 32a, 32b; 132) is so dimensioned, along the dimming plane (P), that, when it is in the position in which it masks the light-receiving diode (PR3) of the pair of diodes (PE3-PR3) corresponding to the overtravel position, it also masks the light-receiving diode (PR2) of the adjacent pair (PE2- PR2) which corresponds to the second position, the arrangement being such that when the dimmer masks the light-receiving diode (PR2) of the second pair, but has not exactly reached as yet the overtravel position, it does not mask the light- receiving diode (PR3) of the third pair, and in that the dimmer (32; 32a, 32b; 132) is materially connected to the movable member by mutual locking means (34; 134) which are manually adjustable in order to allow once for all the adjustment of the position in which the dimmer masks the light-receiving diode (PR3) of the third pair of diodes in the overtravel position.

6. A transducer according to any of claims 2 to 5, characterized in that the light indicator (LED) associated to the third pair of diodes (PE3-PR3) is in the form of a LED directly connected to the output of the corresponding comparator (VC).

7. A transducer according to any of the preceding claims, characterized in that each of the said fixed supports (18, 20; 118, 120) is constituted by a respective flat circuit board with printed circuits, which includes and/or which has affixed thereto, the majority of the various electrical/electronic components such as, on the one hand, the light-emitting diodes (PEl, PE2, PE3) with the corresponding feeding circuits, and, on the other hand, the light-receiving diodes (PRl, PR2, PR3) and the corresponding circuit means.

8. A transducer according to claim 7, for the application to a rotating movable member, such as a control shaft of (10) of a butterfly valve, characterized in that it is constituted by a unitary assembly adapted to be mounted around the rotating member (10), in that the said dimming plane (P) is normal to the axis of rotation of the rotating member (10), in that the said flat printed circuit boards are in the form of annular discs (18, 20) concentrically arranged around the rotating member (10), rigidly connected to each other and arranged on the two sides of the said one dimming plane (P), and in that the dimmer is in the form of at least a wing (32a, 32b) fast with a ring (30) which is secured in an angularly adjustable manner to the rotating member (10), is arranged between the discs (18, 20), and has a general plane which substantially coincides with the dimming plane (P).

9. A transducer according to claim 7, for the application to a slidable movable member, such as a control stem of (110) of a gate valve, characterized in that it is constituted by a unitary assembly adapted to be mounted around the slidable member (110), in that the said dimming plane (P) includes the sliding axis of the slidable member (110) or is parallel to said axis, in that the said flat printed circuit boards are in the form of parallel plates (118, 120) located on the two sides of the said dimming plane (P) and parallel to said plane, and in that the dimmer is in the form of a wing or flag (132) which is fast to a ring (130) secured in a longitudinally adjustable manner along the slidable member, arranged between the boards (118, 120) and whose general plane substantially coincides with the dimming plane (P).

10. A transducer according to claim 9, characterized in that the dimmer is in the form of a flag (132) of an easily breakable or shearable plastic material, which has parallel breaking notches (136) which delimit segments (138) on which the sizes of the gate valves included in a range of sizes are indicated.

11. A transducer according to any of the preceding claims, characterized in that it is enclosed in a hermetically sealed housing.

12. A transducer according to any of the preceding claims, characterized in that the light-emitting diodes (PEl, PE2, PE3) are of the infrared type and the light- receiving diodes (PRl, PR2, PR3) are correspondingly sensitive to infrared light.

13. A valve for fluids, of the butterfly type or of the gate type, including a movable member, respectively a rotary shaft (10) or a sliding stem (110), equipped with a transducer (12; 112) according to one of the preceding claims.