FIBER OPTIC SENSOR APPARATUS

Abstract: An optical apparatus for measuring physical quantities, comprising an optical transducer (33) for sensing position, outgoing and return optical fibers (20, 23), and an electronic sensor control module (43). Light is generated at the control module and transmitted by the outgoing optical fiber (20) to the optical transducer (33) which varies relative intensity of two colors in a dissimilar manner in response to location of a positionable device (34, 35) in the optical transducer. The modified intensity is transmitted back to the control module via the return optical fiber (23). The control module (43) measures the intensity of the two returning colors, and then outputs an electrical signal proportional to the intensity ratio for analog applications, or alternatively tests the intensity ratio against preselected constants and outputs discrete signals for digital applications. The control module can, in addition, incorporate self-testing of the optical components.

Description: DESCRIPTION FIBER OPTIC SENSOR APPARATUS TECHNICAL FIELD The present invention relates to the technical field of fiber op- tics, and more particularly to fiber optic sensor apparatus. BACKGROUND ART Factory automation requires extremely reliable limit switches and position sensors that are immune to electromagnetic induction. Also, cer¬ tain industries, such as in the petrochemical and energy fields, require intrinsi- cally safe switch devices in hazardous locations. Further, there is a major ef¬ fort to develop aircraft and ships with ah optical fiber control system. As well, the automotive industry is increasing the use of fiber optics. In the prior art, various measuring devices are known for measur¬ ing a physical parameter by measuring the intensity of light. In these devices, light from one or more light sources is transmitted via an outgoing optical fiber to an optical transducer which, in proportion to the sensed property, controls the amount of light transmitted back via a return optical fiber. Photodetection apparatus is used to convert the returned light intensity to suitable electrical signals. It is known that mechanical effects such as bending the fiber and re- mating connectors, as well as environmental effects such as temperature and pressure, can also affect the intensity of the light. Multiple light sources and detectors can be used to compensate for these undesirable effects. As described previously in United States Patent 4,356,396, light of two wavelengths is generated and two detectors monitor the outgoing light and two detectors monitor the returning light. One of the wavelengths of light is reflected back by a mirror between the optical fiber and optical transducer and provides a reference intensity for the compensation calculation. The trans¬ ducer acts only upon the second wavelength of light, thus it is not possible to make corrections for mechanical or environmental perturbations in the trans- ducer itself. Optical transducers acting on more than one wavelength of light are also known. For instance, United States Patents 4,514,860, 4,417,140 and 4,378,496 require two light emitting diodes and associated electronic compo¬ nents in the transducer assembly. A transducer operating without any electric current or voltage is desired to reduce the hazard associated with electrical devices. Further, multiple wavelengths of light have been used in trans¬ ducer assemblies in the prior art to make multiple measurements. The tech¬ nique, as described in United States Patent 4,523,092, does not compensate for environmental or mechanical perturbations in the transducer. Another example of using two wavelengths is described in United States Patent 4,492,860, but only a single fiber is used and polarization is em¬ ployed to control reflection of the outgoing light into detector apparatus. DISCLOSURE OF THE INVENTION Genericaily, the invention contemplates fiber optic sensor appa- ratus which provides a ratio of detected output light intensities of two different bands of light having spectral distributions centered at two different wave¬ lengths, the magnitude of the ratio corresponding to the position of an optical transducer and being utilized by an electronic signal processor. The light inten¬ sities of the two bands of light may be detected, either by a broadband detector from wavelength discriminant light sources, or by wavelength discriminant de¬ tectors from a broadband light source. In other words, equivalent results can be produced by a multiple light source cooperating with a single detector, or by a single light source cooperating with multiple detectors. It is an object of the present invention to provide fiber optic sen- sor apparatus for discrete or proportional sensing of a physical parameter, i.e., to provide digital operation such as for a switch, or to provide analog operation for position measurement or control. It is another object of this invention to provide such fiber optic sensor apparatus which is self-calibrating so that light sensitivity adjustment is not required. It is still another object of this invention to provide such fiber optic sensor apparatus which is self-monitoring to indicate malfunction when any of the optical components fau¬ lt is stiE another object of this invention to provide such fiber optic sensor apparatus which can be easily serviced in the field by visually checking the functionality of the optical circuit without requiring special test equipment. It is still another object of this invention to provide such fiber optic sensor apparatus which is intrinsically safe since no electrical current or voltage is supplied to or generated at the place of position sensing. Other objects and advantages of the present invention will be apparent from the ensuing detailed illustration and description of preferred em¬ bodiments which carry out the invention by a broadband detector detecting the light intensities of two bands of light generated by wavelength discriminant light sources. According to the present invention, a fiber optic sensor appara¬ tus contains an outgoing optical fiber having input and output ends, and a return optical fiber having input and output ends. The apparatus also contains a first light source for generating a first light having a spectral distribution centered at a first wavelength, and a second light source for generating a second light having a spectral distribution centered at a second wavelength. The first wave¬ length is different from the second wavelength. Both light sources may be part of a dual color light generating unit. These dual light sources may be operated alternately and include a suitable optical element for directing their respective light beams into the input end of the outgoing optical fiber. As a result, the first and second light beams will be transmitted from the input end to the out¬ put end of the outgoing optical fiber. The apparatus further contains an optical transducer operatively arranged between the output end of the outgoing optical fiber and the input end of the return optical fiber. This transducer includes a positionable device and an actuator for moving such device. The optical transducer modifies the inten¬ sity of the first and second lights, at the input end of the return optical fiber, in a dissimilar manner as a function of the change in position of the positionable device. The optical transducer may be of the transmissive type in which its positionable device includes a first optical filter that preferentially trans¬ mits the first light, and a second optical filter that preferentially transmits the second light, such filters acting in cooperation such that the relative amount of the first light and the second light transmitted into the return optical fiber changes with the position of the actuator. Instead, the optical transducer may be of the reflective type in which its positionable device includes a first reflector that preferentially re- flects the first light, and a second reflector that preferentially reflects the sec¬ ond light, such reflectors acting in cooperation such that the relative amount of the first light and the second light reflected into the return optical fiber changes with the position of the actuator. The actuator for moving the positionable device of the optical transducer is responsive to a command input, which may be controlled by any suitable parameter such as linear position, rotary position, temperature, pres¬ sure, flow, fluid level, electrical current or electrical voltage. The apparatus also contains a photodetector operatively arranged at the output end of the return optical fiber for measuring the intensity of light at such output end, and generating a voltage responsive to such light intensity, thereby to measure the return fiber output light intensities corresponding to the first light and the second light. The photodetector apparatus may utilize either wavelength dispersion or wavelength filters to produce a first detector voltage proportional to the intensity of the first light, and also to produce a second detector voltage proportional to the intensity of the second light. Another way of determining the light intensity is to alternately direct the first light and second light into the outgoing optical fiber, and the photodetector apparatus utilizes the time sequence to produce a first detector voltage proportional to the intensity of the first light and also to produce a sec¬ ond detector voltage proportional to the intensity of the second light. The apparatus also contains an electronic signal processor re¬ sponsive to detector voltages corresponding to the first light and second light. The electronic signal processor divides the first detector output voltage by the second detector output voltage to produce a first ratio, and also produces an output signal the magnitude of which is proportional to such first ratio for ana¬ log operation. This signal processor then tests this first ratio against a first constant and also against a second constant for digital operation, and if the ra¬ tio is greater than, or equal to, such first constant the signal output is activat- ed, and if the ratio is less than, or equal to, such second constant then the signal output is deactivated. The apparatus also contains an output controller having activated and deactivated states responsive to the controller signal output of the elec¬ tronic signal processor. If the aforementioned first ratio, as tested by this sig- nal processor, is less than the first constant and also greater than the second constant, then the actuator is considered to be in transition, whereupon the out¬ put controller is changed to the state opposite that which it had before the ac- tuator entered the transition zone, producing a snap action of the change of state. The apparatus also contains self-monitoring means having acti¬ vated and deactivated states responsive to a status signal output of the elec- tronic signal processor. The detector produces a third detector output voltage when neither of the first and second light generating means is operative. This third detector output voltage corresponds to the amount of stray light being returned through the detector fiber. The electronic signal processor divides the sum of the first and second detector output voltages by this third detector output voltage to produce a second ratio. Under normal operation of the appa¬ ratus, this second ratio will be much greater than 2. When one of the optical components of the apparatus is not functional this second ratio will be approxi¬ mately 2, and such ratio is then utilized by the signal processor to output the status signal indicating a fault in one of such optical components. Throughout the specification, the term "light" is used to denote electromagnetic radiation in the vicinity of the visible spectrum, but it should be understood that the term also includes electromagnetic radiation " in the in¬ frared and ultraviolet regions. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an abbreviated schematic of one embodiment of the op¬ tical transducer part of the inventive fiber optic sensor apparatus, and illustrat¬ ing a transmissive type of optical transducer. Fig. 2 is a graph illustrating the wavelengths of red and green light in relation to the intensity of each, employed in the practice of the pres- ent invention. Fig. 3 is a schematic of one preferred embodiment of the present invention and illustrating fiber optic sensor apparatus, the optical transducer part being of the transmissive type. Fig. 4 is a schematic of another preferred embodiment, and illus- trating the optical transducer part as being of the reflective type. Fig. 5 is an enlarged perspective view of a representative posi¬ tion sensing, optical fiber transducer of the reflective type. Fig. 6 is a vertical sectional view thereof, taken on line 6-6 of Fig. 5. Fig. 7 is a partial elevational, partial sectional view thereof, tak- en on line 7-7 of Fig. 6. Fig. 8 is a diagram comparing voltage waveforms produced at various times, under different representative conditions of operation of the in¬ ventive apparatus. Fig. 9 is a flow chart of the functions performed by the electron¬ ic signal processor part of the inventive apparatus, which illustrates implement¬ ing ratiometric time-multiplexed fiber optic discrete position measurement al¬ gorithm, including software snap-action. Fig. 10 is a first fragmentary schematic view of the inventive apparatus, illustrating its application as a reflective-type pressure sensor. Fig. 11 is a second fragmentary schematic view of the inventive apparatus, illustrating its application as a reflective-type liquid level switch. Fig. 12 is a third fragmentary schematic view of the inventive apparatus, illustrating its application as a reflective-type sensor for flow me- tering. Fig. 13 is an elevatlonal view of the dual color-coated disk shown in Fig. 12. ODE(S) OF CARRYING OUT THE INVENTION The first preferred embodiment of the inventive fiber optical apparatus, or mode of carrying out the invention, is illustrated in Figs. 1-3. Referring to Figs. 1 and 3, a light-source optical fiber or outgo¬ ing optical fiber 20 has a light receiving input end 21 and a light emitting output end 22. A light detector optical fiber or return optical fiber 23 has a light re¬ ceiving input end 24 and a light emitting output end 25. Suitable light genera- ting means are provided for generating a first light having a spectral distribu¬ tion centered at a first wavelength ^1, and a second light having a spectral dis¬ tribution centered at a second wavelength/tø. This is shown as a dual color light source 26 arranged to emit light alternately of two wavelengths *U and ^2. Typically, these may be light emitting diodes (LED) or LASERS, one for emit- ting a first light such as green, and the other emitting a second light such as red, or any other combination of two colors. As depicted in Fig. 2, which plots wavelength (< ) against relative light intensity, the curve 28 for the green color, when its LED is energized, has a spectral bandwidth centered about a wavelength ^ 1 of 560 nanometers (nm), and the curve 29 for the red color, when its LED is energized, has a spectral bandwidth centered about a wavelength fc_ of 655 nm. Means are shown for directing the first and second light beams generated by source 26 into the input end 21 of fiber 20, such means being represented by the arrow line 30 in Fig. 3. Light emitted by the output end 25 of fiber 23 is received, as represented by arrow line 31 in Fig. 3, by suitable detecting means 32 arranged to detect the intensity of light at such output end. Suitable optical transducer means, indicated generally at 33, is shown in Figs. 1 and 3 as operatively interposed between the output end 22 of fiber 20 and the input end 24 of fiber 23. Such transducer means includes a po- sitionable device and actuator means for moving such device. This device is shown as including a first or upper filter 34 and a second or lower filter 35 ar¬ ranged in line, with their opposing ends contacting each another. These filters as a unit are slidably arranged rectilinearly and reciprocally in a sensor body 36. This filter unit is constantly biased upwardly by a suitable spring means 38 shown arranged below such unit, with the lower end of the spring bearing against a suitable support surface 39 in body 36, and at its upper end bearing against the lower end of filter 35. The aforementioned actuator means is shown as a plunger 40 pro¬ jecting upwardly and outwardly from sensor body 36 through a suitable opening provided therein. The lower end of actuator plunger 40 is suitably connected to the upper end of the aforementioned filter unit, and its upper end is exposed and adapted to be engaged by a member (not shown) the position of which is to be sensed. Such unillustrated member is adapted to apply a downward force, represented by arrow line 41 in Fig. 3, against the upper end of actuator plunger 40 and push it further into sensor body 36, thereby moving the filter unit against the urging of the compressible spring 38. Upper filter 34 is selected such that its spectral bandwidth is centered about 560 nm, and hence will selectively pass green light, absorbing other colors. Lower filter 35 is selected such that its spectral bandwidth is cen- tered about 655 nm to selectively pass red light, absorbing other colors. When actuating force 41 does not exist, spring 38 holds the lower red filter 35 between the opposing ends 22 and 24 of fibers 20 and 23, respec¬ tively. However, when actuating force 41 exists, as depicted in Fig. 3, upper green filter 34 is positioned between fiber ends 22 and 24 so that a beam of light, represented by arrow line 42, passes through this filter 34. Obviously, when lower red filter 35 is positioned between fiber ends 22 and 24, as not illus¬ trated, the light beam 42 passes through this filter 35. Suitable electronic signal processor means, indicated generally at 43, are shown in Fig. 3 as operatively associated via arrow line 44 with dual light source 26; also via arrow line 45 with detector 32; further via arrow line 46 with digital control output state means 48, including output on/off relay means 49 and indicator 50; and still further via arrow line 51 with self-monitor¬ ing means 52, including on/off relay means 53 and indicator 54. Signal processor 43 comprises a single chip microcontroller, the functions of which are to be described later herein, capable of controlling the sequencing of the red and green light sources by a voltage Vout transmitted through conductor 44, and measuring the voltage Vin transmitted through con¬ ductor 45. Voltage Vin represents the resultant light amplitude for each wave¬ length in time sequence, and controlling the voltage outputs through conductors 46 and 51 to control the relays and indicators of the output state means 48 and the self-monitoring means 52. The control is accomplished by means of an in- ternally stored program, which conforms to the algorithm prepared for time multiplexed, ratiometric light measurement. The apparatus schematized in Fig. 3 thus includes a. discrete fi¬ ber optic position sensor of the transmissive type. The output state of the means 48 relies on the physical movement of switch actuator 40, which is me- ' chanically connected to the pair of optical filters unit 34,35 located in the path of bicolored light source fiber 20, and detector fiber 23, both of these fibers 20 and 23 being fixed. The displacement of actuator 40 causes either the green or red filter to be placed in the path of the light beam 30 emitted from source 26, which has the effect of filtering the light 31 returned to the signal proces- sor. Thus, the relative intensity of the first light and the second light returning from sensor 33 to detector 32 is dependent on the physical or "discrete" position of actuator 40. The second preferred embodiment of the inventive fiber optical apparatus, or mode of carrying out the invention, is illustrated in Figs. 4-7. Referring to Fig. 4, the apparatus there shown is similar to that shown in Fig. 3, except for a slightly different construction of optical trans¬ ducer 331 and the disposition of the adjacent end portions of the outgoing optical fiber 201 and return optical fiber 231. Otherwise, the balance of the apparatus is similar to that disclosed in Fig. 3, and hence the same reference numerals have been applied in Fig. 4 to corresponding parts. The positionable device of the optical transducer 331 is of the reflective type. Thus, the upper portion of a member 58 is coated with a layer 59 of a suitable color material to be reflective for the first light and absorptive for the second light. The lower portion of member 58 is similarly coated with a layer 60 of a suitable color material to be absorptive for the first light and reflective for the second light. The opposing ends of layers 59 and 60 are con- tiguous to each another. Assuming the first light and second light are the colors green and red, respectively, as considered in the example of 1?ig. 3, layer 59 is a green coating and layer 60 is a red coating. Member 58 with its color coatings 59 and 60 resembles the filter unit shown in Fig. 3, in that it is displaceable rectilinearly in opposite vertical directions by a lower spring 381 and an upper actuator plunger 401. When a downward force, represented by arrow line 411 in Fig. 4, is applied to the upper end of actuator plunger 401, and is sufficient to overcome yieldable spring 381, member 58 with its color coatings 59 and 60 can be displaced from its upper position (not illustrated) to its lower position as illustrated in Fig. 4. The end portion of outgoing optical fiber 201 adjacent its output end 221, and- the end portion of return optical fiber 231 adjacent its input end 241, are suitably fixed in close side-by-side relation so that both these ends of the fibers are facing toward member 58. An incident light beam, represented by the line 421, emitted from output end 221 of fiber 201, is arranged to be trained on a spot 61 on one of the coated surfaces on member 58. The input end 241 of fiber 231 is directed toward this spot 61 to receive a reflected or return light beam, represented by arrow line 422. As illustrated in Fig. 4, inci¬ dent light beam 421 is shown as impinging on the green coating 59 carried on member 58, from which coating the return light beam 422 is reflected. It is evident that if the light impingement spot 61 is located on the red coating 60, due to member 58 being in its upper position (not illustrated), the return light beam 422 will be reflected from this red coating 60. While optical transducer 331 of the reflective type may be of any suitable construction, a preferred construction of the same is illustrated in Figs. 5-7. As there shown, the transducer includes a block-like body member 62 having mounting holes 63 adjacent its corners, four such holes being shown. These holes 63 are adapted to receive suitable fasteners, such as screws or bolts (not shown), for mounting the body on some suitable support (not shown). Body 62 is shown as having an integral flat-surfaced boss 64 on its upper end, from which a vertically elongated cavity or recess 65 extends downwardly into the main portion of this body, terminating near its lower and closed end. Preferably this recess 65 is defined, in transverse section, by a cylindrical wall surface 66. Slidably arranged in this recess is a plunger 68 including a cylindrical stem 69 having a concentric, reduced cylindrical section 70 adjacent its lower end. Plunger 68 also includes a radially enlarged head 71, having a domed or rounded upper surface 72 and a downwardly facing annular flat shoulder 73. Operatively interposed between the opposing faces of body boss 64 and plunger shoulder 73, is a bellows type spring 74 having a compressible and expandable side wall 75 of generally cylindrical configuration, and inturned annular flat flanges 76 at opposite ends of this side wall. Side wall 75 is formed from flexible thin sheet metal, corrugated at vertically spaced intervals to pro- vide alternate annular folds and furrows. Flanges 76 are suitably sealingly con¬ nected to the flat surfaces of body boss 64 and plunger shoulder 73. The folds of side wall 75 flex or bend when the spring 74 is subjected to an axial load, of¬ fering return force when the load is removed. Spring 74 is shown in Fig. 8 in its fully expanded condition. The spring will yield resistively to shorten its axial length when the aforementioned load is applied by plunger head 71 being de¬ pressed. Applied to the cylindrical peripheral surface of the upper half of the plunger reduced section 70 'is a circumferential ring 78 of suitable red colored material. Contiguous to and below this red ring 78 is a circumferential ring 79 of suitable green colored material, which is applied to the cylindrical peripheral surface of the lower half of the plunger reduced section 70. These color rings 78 and 79 may be provided by painting the colored material on the surface of this plunger section 70. Body member 62 is also shown as having an integral externally threaded cylindrical projection 80 which extends horizontally outwardly from one side of this body. Projection 80 has a passage extending therethrough, in¬ cluding an inner cylindrical section 81 and an outer tapered section 82 which flares outwardly toward the outer end of the projection. Partially arranged in this projection passage is an elongated connector member 83 for holding optical fibers 201 and 231. This connector 83 includes an inner cylindrical portion 84, an adjacent tapered portion 85, an enlarged cylindrical intermediate portion 86, and a reduced cylindrical outer portion 88. A bore 89 extends longitudinally completely through connector 83. Body inner passage section 81 receives inner connector portion 84 which is shorter in axial length than section 81, so as to leave a gap 90 which opens to body recess 65. The surface of connector tapered portion 85 is complementary to the surface of body tapered passage section 82 and is adapted to be seated thereon. The annular step between connector por- tions 86 and 88 provides a shoulder 91 against which the inturned flange end 92 of a tubular nut 93 can bear when this nut is tightened. This nut has a threaded connection with body projection 80, as indicated at 94. Connector 83 is adapted to hold optical fibers 201 and 231 side- by-side, with their respective ends 221 and 241 substantially flush with the inner end face of this connector. Gap 90 allows the passage of light between these ends of the fibers and the reflective surface of the colored coatings 78,79. Bellows spring 74 is shown in Figs. 5-7 in its fully extended con¬ dition whereby the lower green colored coating 79 is positioned opposite and in spaced relation from ends 221 and 241 of fibers 201 and 231, respectively. If some object (not shown), the position of which is to be sensed, bears down¬ wardly against the domed surface 72 of plunger 68, spring 74 will be compressed, allowing the lower green ring 79 to be displaced from a position opposite fiber ends 221 and 241 and moving the upper red ring 78 into a position opposite these fiber ends. When such object backs away from plunger 68, spring 74 will expand and raise the plunger so that red ring 78 will move out of and green ring 79 will move into operative position. opposite fiber ends 221 and 241. Operation of the fiber optic sensor apparatus cati be best ex¬ plained and understood in connection with Figs. 8 and 9. Referring to Fig. 8, voltage is plotted against time. Time is in¬ dicated at zero time tO, and three successive times tl, t2 and t3. The time pe¬ riod during which the red LED is energized is indicated by the time interval tred. The time period during which the green LED is energized is indicated by the time interval tgreen. The time period during which neither LED is ener- gized is indicated by the time interval tdark. The condition of de-energized and energized for the LEDs is represented by 1 = energized and 0 = de-energized. Reading from top to bottom, the six voltage wave forms shown in Fig. 8 are designated I, II, III, IV, V and VI. Wave I represents when the red LED is de-energized and energized. Wave II represents when the green LED is de-energized and energized. Wave III represents detector voltage, at times tl, t2 and t3, when the optical transducer is positioned with the red element in the incident light path (42 or 421) emitted from the outgoing optical fiber (20 or 201). It will be seen that voltage Vtl is greater than voltage Vt2, and voltage Vt3 is zero since neither LED is energized. Wave IV represents the detector voltage, at times tl, t2 and t3, when the optical transducer is positioned with the green element in the light path (42 or 421) emitted from the outgoing optical fiber (20 or 201). It will be seen that voltage Vtl is less than voltage Vt2, and voltage Vt3 is zero since nei¬ ther LED is energized. Thus, at time tl, Vtl represents the magnitude of the voltage corresponding to the light transmitted to and measured at the detector (26) dur¬ ing the period when the red LED is energized. At time t2, Vt2 represents the magnitude of the voltage corresponding to the light transmitted to and mea¬ sured at the detector (26) during the period when the green LED is energized. 0 At time t3, Vt3 represents the magnitude of the voltage corresponding to the light transmitted to and measured at the detector (26) during the period when both the red and green LEDs are de-energized. Wave V represents the detector voltage, at times tl, t2 and t3, when the transducer sensor is in transition between red and green and some of 5 both the red and green elements are positioned in the incident light path (42 or 421) emitted from the outgoing optical fiber (20 or 201 * ). In this condition, * r voltage Vtl is equal to voltage Vt2, and greater than voltage Vt3 which is * zero. , Wave VI represents the detector voltage upon a failure in any one of the optical components comprising the -light source 26, either optical 0 fiber 20,201 or 23,231, connectors such as 83, optical transducer 33 or 331, and photodetector 32. The detector voltage varies over time, dependent on the amount of stray light that is incident to the detector, as in the case of a broken fiber that may be exposed to ambient light. Referring to Fig. 9, the flow chart there shown depicts the func- 5 tions performed by the signal processor 43 for controlling a species of discrete position instrumentality, and also for indicating the operative status or failure of the position sensing apparatus. Upon system power-up, diagnostic checks are first performed to determine that the microcontroller is capable of executing its program. Pro- 0 gram memory and input/output circuits are checked, and if functional, the switch failure bit is cleared, and the corresponding relay output 53 and status indicator 54 are turned on. The light source circuit is then enabled, and the red LED 26 is energized. After a short delay, the detector voltage, which corresponds direct- 5 ly to the amount of red light being transmitted through the detector or return optical fiber 231, is measured and stored as variable Vtl. The red LED is then de-energized. The green LED 26 is energized, and after a second delay, the detector voltage corresponding to the amount of green light being transmitted through the return optical fiber 231 is measured, and stored as Vt2. The green LED is now also de-energized. After a third delay, the detector voltage corresponding to the amount of stray light being transmitted through the return optical fiber 231 is measured and stored as Vt3. Under normal operation, this light amount is very small in relation to Vtl and Vt2, and is near zero volts. At this time, Vtl is divided by Vt2, and the result is stored as a variable RGRATIO, i.e., (RED/GREEN RATIO). This RGRATIO is now tested. If greater than or equal to a selected predetermined constant ONMIN, i.e., (minimum RED/GREEN RATIO allowed to consider the optical transducer "ON"), the sensor is considered ON, and the output relay 49 and on/off indicator 50 of the signal processor are energized. If the RGRATIO is less than or equal to constant OFFMAX, i.e., (maximum RED/GREEN RATIO allowed to consider the optical transducer "OFF"), the sensor is considered OFF, and the output re- -,lay 49 and on/off indicator 50 of the signal processor are de ' -energized. If RGRATIO is greater than OFFMAX but less than ONMIN, a second ratio must be calculated and tested to determine if a switch failure ex- ists, or if the switch is in a transitional state, midway between off and on. If midway between states, it is desirable to invert the then existing or present state immediately upon entering this transition zone. This then is considered as SNAP ACTION, and provides a distinct, repeatable switching point for each direction of actuator motion. If a failure exists due to a broken optical fiber, connector, actuator, light source, or other optical component, it is desirable to respond to this immediately by freezing or holding the present state output relay 49 and indicator 50, and de-energizing the status ok relay 53 and indicator 54. The difference between the two conditions is decided as follows. LDRATIO, i.e., (LIGHT/DARK RATIO), is calculated to be (Vtl + Vt2)/Vt3._ Under normal operation, the sum of Vtl and Vt2 will always be the same (a large number), with Vt3 near zero volts. Thus, the LDRATIO will be large, whether the switch is on, off or in transition, and will be a number greater than, say, 10. If a malfunction exists, such as a cut fiber, Vtl = Vt2 = Vt3, since the detector then sees only the ambient light level. Thus, the LDRATIO can never be more than (1 + 1)/1 = 2. A third selected predetermined constant LDMIN, i.e., (minimum LIGHT/DARK RATIO allowed to consider the optical transducer functional), is assigned a value, say, 10. If the LDRATIO is equal to or greater than 10, and the snap action has not taken place in the previous measurement cycle, the present output relay state is inverted, or "snapped". The program then returns to begin a new measurement cycle. If the snap action has taken place on the previous cycle, the present output state is held. If the LDRATIO is less than LDMIN, the switch is considered as having failed. The present output STATE relay 49 and indicator 50 are main¬ tained in their present state, and the STATUS OK relay 53 and indicator 54 are de-energized. The program then returns to begin a new measurement cycle. If the source of the failure is located and repaired, the failure condition will correct itself without requiring any operator action. Representative applications of the present invention are illus¬ trated in Figs. 10-13. In Fig. 10, a reflective type optical transducer 331a, similar to the one shown at 331 in Fig. 4, is illustrated in fragmentary fashion utilized as a pressure sensor. Similar reference numerals, except as distinguished by the suffix a, are employed in Fig. 10 to designate corresponding parts. The upper end of an actuator rod 401a is shown suitably con- nected to a flexible diaphragm 94 which is movable by the pressure of fluid con¬ fined above this diaphragm. Changes in pressure of this fluid move up or down the member 58a having a green coating 59a and a red coating 60a. As illustrat¬ ed in Fig. 10, this green coating is in operative position opposite fibers 201a and 231a, suggesting a high pressure above the diaphragm which has depressed the coated member and compressed spring 38a. If the fluid pressure decreases sufficiently, the red coating 60a will be shifted upwardly, by the return spring, into operative position. In this manner, transducer "331a serves as a pressure sensitive switch. In Fig. 11, a reflective type optical transducer 331b, similar to the one shown at 331 in Fig. 4, is illustrated in fragmentary fashion utilized as a liquid level switch. Similar reference numerals are employed in Fig. 11 as are used in Fig. 4, except for the addition of the suffix b, to designate corre¬ sponding parts. The upper end of an actuator rod 401b is shown as suitably pivot- ally connected to a lever 95, intermediate its length. One end of this rod is piv- otally mounted on a suitable support as indicated at 96, and the other end car¬ ries a float 98. This float determines the level of liquid 99 in a container or tank 100. As the liquid level falls below a predetermined level, the green coat¬ ing 59b will be positioned opposite the ends of fibers 201b and 231b to, say, open a valve (not shown) for filling tank 100 with more liquid. As the liquid level and float rises so as to position the red coating 60b opposite the ends of fibers 201b and 231b, the said valve will shut off. In Fig. 12, a reflective type optical transducer 331c, similar to the one shown at 331 in Fig. 4, except that green and red color coatings 59c and 60c, respectively, are mounted on a rotatable support member 58c, instead of the rectilinearly movable members 58,58a and 58b shown in Figs. 4, 10 and 11. Similar reference numerals, except as distinguished by the suffix c, are em¬ ployed in Figs. 12 and 13, to designate corresponding parts. Rotatable member 58c enables the transducer 331c to be used as a flow meter. To this end, member 58c is shown as a rotatable disk, one half of the face of which is covered with the green coating 59c, and the other half with the red coating 60c, as illustrated in Fig. 13. Disk 58c is shown as fast to a shaft 101 to which a paddle wheel • 102 is also secured, this shaft being suitably journaled in a housing 103 having a fluid inlet 104 and a fluid outlet 105. Fluid flowing into this housing through its inlet, and discharged through its outlet, causes the paddle wheel to rotate. This will alternately bring the red and green colored coatings into operative position for impingement by the light beam emitted from outgoing optical fiber 201c, to be reflected back through return optical fiber 231c. By counting the color changes in a given period of time, by suitable means (not shown) but which may be incorporated in the signal processor, flow rate can be determined. The electronic signal processor or sensor control module 43 can be arranged to handle several sensors, such as four sensors, and can be located remotely. Typical electrical outputs are +5 volts DC for transistor-transistor logic (TTL), and up to +40 volts DC for relay drives. Two electrical signals and two indicators are provided for each sensor. One signal and indicator match the position of the sensor actuator (tripped or released). The other signal and indicator remain on only as long as the optical circuit is functional. If optical continuity is lost, the "sensor opera¬ tional" indicator LED is de-energized and the status signal turns off. The microcontroller based sensor control module 43 permits ad- ditional features to be included, such as recording the number of sensor transi¬ tions which may be helpful in establishing the useful life of what is being con¬ trolled, logging the time of each transition, and providing modem interface. With multiple sensors, the microcontroller module permits Boolean logic output combining sensors. The measurement technique can be extended to more than two positions or parameters by increasing the number of colored zones on the actua- tor. The signal processing techniques can be applied to multiple light sources and their corresponding colored zones to resolve the position of the actuator within each of the colored zones. From the foregoing, it will be seen that the disclosed embodi¬ ments and applications of the inventive fiber optic sensor apparatus achieve the stated objects. Instead of the digital mode of operation of discrete position control, an analog mode of operation for position measurement may be obtained by overlapping dual colored wedge-shaped filters. Other modifications may oc¬ cur to those skilled in the art. The scope of the invention is intended to be measured by the appended claims.

Claims: CLAIMS 1. Fiber optic sensor apparatus, comprising in combination: (a) an outgoing optical fiber having input and output ends; (b) a return optical fiber having input and output ends; (c) first light generating means for generating a first light hav¬ ing a spectral distribution centered at a first wavelength; (d) second light generating means for generating a second light having a spectral distribution centered at a second wave¬ length; (e) means for directing beams of said first and second lights into said input end of said outgoing optical fiber; (f) optical transducer means, including a positionable device, operatively interposed between the output end of said outgo¬ ing optical fiber and the input end of said return optical fi- ber, operative to modify the light intensity of said first and second lights, at said input end of said return optical fiber, in a dissimilar manner as a function of change of position of said device; (g) detecting means for measuring the output light intensities at said output end of said return optical fiber; and (h) electronic signal processor means responsive to the ratio of said output light intensities. 2. Apparatus according to claim 1, wherein said optical transducer means also includes an actuator means for moving said positionable device and responsive to a command input. 3. Apparatus according to claim 2, wherein the optical transducer is of the transmissive type. 4. Apparatus according to claim 3, wherein said positionable device includes a first optical filter that preferentially transmits said first light and a second optical filter that preferentially transmits said second light, said opti¬ cal filters being arranged so that the relative amount of said first light and said second light transmitted into said input end of said return optical fiber changes with the position of the actuator. 5. Apparatus according to claim 3 or 4, wherein said detecting means utilizes wavelength filtering to produce a first detector voltage propor¬ tional to the intensity of said first light and also to produce a second detector voltage proportional to the intensity of said second light. 6. Apparatus according to claim 2, wherein the optical transducer is of the reflective type. 7. Apparatus according to claim 6, wherein said positionable device includes a first reflector that preferentially reflects said first light and a sec- ond reflector that preferentially reflects said second light, said reflectors being arranged so that the relative amount of said first light and said second light reflected Into said input end of said return optical fiber changes with the posi¬ tion of the actuator. 8. Apparatus according to claim 6 or 7, wherein said detecting means utilizes wavelength dispersion to produce a first detector voltage propor¬ tional to the Intensity of said first light and also to produce a second detector voltage proportional to the intensity of said second light. 9. Apparatus according to claim 2, wherein said first light and said second light are alternatively directed into said input end of said outgoing opti- cal fiber and said detecting means utilizes the time sequence to produce a first detector output voltage proportional to the intensity of said first light and also to produce a second detector output voltage proportional to the intensity of said second light. 10. Apparatus according to claim 4 or 7, wherein said signal proces- sor means divides said first detector output voltage by said second detector out¬ put voltage to produce a first ratio, and also produces an output signal the mag¬ nitude of which is proportional to said first ratio. 11. Apparatus according to claim 10, wherein said signal processor means tests said first ratio against a first constant and also against a second constant, and if said first ratio is greater than, or equal to, said first constant said signal output is activated, and if said first ratio is less than, or equal to said second constant then said signal output is deactivated. 12. Apparatus according to claim 11 and further comprising output control means having activated and deactivated states responsive to said signal output, wherein said signal processor means tests said first ratio and if it is less than said first constant and also greater than said second constant then said actuator is considered to be in transition and said output control means is changed to the state opposite that which it had before the actuator entered the transition zone, thereby producing a snap action of the change of state. 13. Apparatus according to claim 10 and further comprising self- monitoring means having activated and deactivated states responsive to a status signal, wherein said detecting means produces a third detector output voltage when neither of said first and second light generating means is operative, said third detector output voltage corresponding to the amount of stray light being returned through said return optical fiber; said signal processor means dividing the sum of said first and second detector output voltages by said third detector output voltage to produce a second ratio which, under normal operation, will be much greater than 2, and will be approximately 2 when any one of the optical components of the apparatus is not functional and said second ratio is utilized by said signal processor means to output said status signal indicating a fault in one of such optical components. 14. Apparatus according to claim 2, wherein more than two light sources are used to determine the location of the positionable device within multiple zones over the range of travel of said positionable device.

Inventors: POKORSKI JOSEPH D, RHODES GEOFFREY M, TREGAY GEORGE W, POKORSKI, JOSEPH, D., RHODES, GEOFFREY, M., TREGAY, GEORGE, W.
Applicants: CONAX BUFFALO CORP, CONAX BUFFALO CORPORATION
Application year: 1987
Main classification: H01J5
IPC codes: G01D5, G01F1, G01F23, G01L11, G02B6, G02B26