NO860026L - IMPROVED FIBEROPTICAL REMOVAL SENSOR. - Google Patents

Description

The present invention relates to the field of fibre-optic based communication and measuring devices, and more particularly light-stimulated, oscillating resonant element devices for measuring physical parameters.

Certain definitions are necessary to provide clarity and

facilitate the understanding of the present invention. As used herein, "radiation energy" includes both coherent and incoherent energy with a wavelength between 1000 and 100,000 Angstroms, and in particular includes infrared energy, ultra-violet energy and energy in the visible light range. Slijc radiant energy can be described as "shock" or "continuous wave"

("CW") to distinguish it from radiant energy signals that have been modified to carry information. "Modulation" is generally used here, and is intended to denote a process with regard to the modification of certain characteristics of a carrier so that it varies in step with the instantaneous value of another signal and in particular amplitude modulation. The "steady" radiation energy referred to here is radiation energy with essentially

equal constant intensity levels; i.e. without short-term variations in intensity and with an essentially unchanged spectral distribution. With regard to the light signal that carries information, the expressions "closed" and "interrupted" are used to refer to modulated light as well as the mechanism by which modulation takes place. "Fluid" includes gases and/or liquids. The term "silver plated" is used to describe species

a reflective metallization coating or its equivalent. "Partially silvered" is used to describe such a coating with transmission and reflection properties that can be high in relation to each other. The term "force" is used to describe any physical parameter or phenomenon capable of moving a body or modifying its motion, and in particular the term pressure includes any parameter or phenomenon capable of being converted into pressure. The term "motor" is used in a broad sense, i.e. describes a device that moves an object. The term "transducer" is used to describe a device for converting energy from one form to another, and as used here the terms "opto-electric transducer" and

"electro-optical transducer" more particularly the class of devices that can be used for the conversion of radiant energy into electrical energy, and electrical energy into radiant energy. "Cantilever beam" refers to the class of mechanical or other sensors where a beam element is attached at one of its ends and which can be brought into resonance. Such cantilever beam members may be hollow, in which case they are termed "resonant hollow beam" members or structures.

As the benefits of fiber-optic based communication and control of industrial processes become more widely known, increasing emphasis has been placed on various methods for simple, inexpensive, and reliable communication of low-level radiant energy via fiber optics to the sensor site to perform the desired measurement, and return of the measurement information on fiber optic paths to the control and measurement location. Among the many problems that designers face with such process control systems is the need for few, low-light optical paths and methods for accurately and reliably carrying out the measurements in such a way that the derived measurement information can be accurately communicated using fiber optic signals.

It is well known that the resonant frequency of a tight

thread is a function of the tension on the thread. It is also recognized that a force measuring instrument can be based on this relationship by causing the wire to vibrate while it is stretched by means of an unknown force applied thereto and measuring the frequency of vibration, such as in US Patent No. 4,329,775 Similarly, it is known that by subjecting the interior of a vibrating hollow beam structure to pressure variations, its resonance frequency will be caused to vary in accordance with or in the same ratio as the pressure variations. In the field of fiber optic technology, it is known that a vibrating element that partially blocks the light path in a periodic manner between two aligned fiber optic elements will "close" the light passing along the other fiber optic element.

It is also known that a steady light beam can be directed along a first fiber optic element, modulated (e.g. acoustically) and returned to a point near its source via a second fiber optic element (US patents no. 4,343,482 and 4,275 295). It has recently been claimed that a vibrating wire element can be driven by sending a pulsating light down a first fiber optic element, guiding a steady beam of light down a second fiber optic element to a point where the vibrations modulate the steady light,

and the frequency of the vibrations is measured by reflection of the modulated light back along a third fiber optic element path. The modulation frequency can then be measured. Changing the tension on the vibrating wire can cause the returned light energy to vary regularly with the tension on the wire (Jones, B. E. and G. S. Philp, "A Vibrating Wire Sensor with Optical Fiber Links for Force Measurement", Paper No. 05.1, Sensors and Their Applications , UMIST Manchester (UK)

20.-22. September 1983).

The proposal of Jones and Philp is illustrated in fig.

2. In the apparatus they propose, a thin thread is stretched between an anchoring post and a pressure diaphragm. The wire is placed between the poles of a permanent magnet and its two attachment points are electrically connected, via a suitable converter, to the photodiode 1. If light of alternating intensity is fed via an optical fiber to the photodiode and an alternating current is passed through the wire, it will move in a plane perpendicular to that defined by the current and the magnetic field with a frequency equal to that of the intensity variations. The movement of the thread is sensed by two optical fibers which are placed parallel and adjacent in the plane of movement. The first of these two fibers is fed with light of nominally constant intensity from LED 2

in the control unit, and this light, when it leaves the fiber at the sensor head, will illuminate the thread. Some light is reflected back to the other fiber and returned to the control unit. The intensity of this returned light is a function of the position of the thread in relation to the fiber ends. When the thread vibrates,

alternating light intensity in phase with the oscillation will therefore be returned to the control unit by the other fiber. This signal is electrically amplified in the control unit, and part of the electrical output is used to drive LED 1 in phase and resonance with the wire; a third optical fiber leads this in-phase light signal to the sensor head where it is converted into

oscillating driving force to support the oscillation.

These and the previous methods of remote sensing and communication with fiber optic devices generally require multiple light paths, complex circuits and/or independent sources of oscillation energy for the resonant part.

The invention relates to the discovery that a simple stable radiant energy beam can be simultaneously blocked and reflected by a vibrating or resonant element.

The present invention includes directing a stable beam of radiant energy along a first communication path to a radiant energy detector-transducer element which is placed adjacent to a vibrating resonant element so that the resonant element periodically at least partially blocks the path of radiant energy that strikes the resonant element, reflects a part of the steady radiant energy back along the same communication path in the opposite direction when the resonant element obstructs or blocks the radiant energy path, and uses the detected radiant energy to cause the resonant element to support the oscillation. It is during periods when the resonant element does not block the source radiation energy,

that the energy is allowed to reach a light energy to electrical energy transducer, which forms an electrical current at the transducer output.

The electric current is phase-shifted in accordance with known principles and is used to initiate and support vibration for the resonant element. In a vibrating wire or tape version of the oscillator part of the invention, the phase-altered electric current is applied in accordance with the known electromagnetic laws to the ends of a tensioned wire or tape element suspended in a magnetic field and causes the wire or tape to begin to oscillate and continue to oscillate at the resonant frequency of the wire or ribbon.

In an alternative resonant hollow beam version, the transducer output is phase-shifted and fed to an electrical-to-mechanical energy transducer to initiate and support oscillation.

The periodically reflected radiant energy varies in intensity and in synchrony with the oscillating frequency of the resonant element. By including means for deflecting a detectable portion of the oscillatory reflected radiant energy from the first stable radiant energy path along the second path to a remote detector, the frequency of the oscillatory radiant energy (and thus of the resonant element frequency) can be determined using conventional facilities. The application of a force to the resonant element to vary its frequency in accordance with the magnitude of the force enables remote measurements of the force.

Of course, different physical phenomena can thus be measured by transforming the physical phenomenon or parameter into a force which is exerted as stated above. Examples of elongate devices suitable for use as resonant elements include tensioned wires or ribbon elements, double or single tuning forks, bells, other cantilevered structures and double cantilevered devices.

To recode and communicate more information it can

stable radiation (or light) energy input to the fiber optic path can be either broad-spectrum or particularly limited spectrum, and the light returned from the vibrating element can also be either broad-spectrum or a particularly limited spectrum and thus provides great flexibility when communicating information along the simple path. Other embodiments of the invention further include e.g. at least one pair of separate resonators which are placed in a defined space where each resonant element is designed for measuring a different physical parameter. With two resonators and a single fiber optic path, it becomes

steady energy communicated to both oscillating resonators and each reflected part of the light is filtered at a different wavelength and then combined to be returned to a encoder along the same single fiber optic path. This filtering can be carried out with ordinary filters or with reflective elements coated with multiple layers which are attached to the resonant element and positioned for reflection of wavelength-limited light energy back along the fiber optic path.

"Coating of multiple layers" as used here, is a coating built up of multiple layers of dielectric material with special refractive indices. Such coatings can be (spectrally) high-pass, band-pass or low-pass, depending on the device

of the layers, as the choice of this is within what can be expected of an ordinary professional in the field of optics. At the encoder, a beam splitter (or an equivalent) can be used to separate energy with a shorter wavelength from energy with a longer wavelength. The oscillation frequencies can then be measured to indicate the sensed physical parameters. A multitude of similar multiple-use designs may be employed, limited in combinations only by the different types of physical parameters to be measured and in number only by the ability to differentiate and discriminate among the radiant energy wavelengths. Some combination applications of a single optical fiber path in accordance with the present invention include indication of frequency and of "out of range", position and limit stops, local or remote temperature and pressure, pressure and/or differential pressure and other variables, such as temperature, etc. as desired by the particular device.

It is therefore an advantageous purpose of the present invention to provide a method for measuring one or more physical phenomena at a location remote from the location where the signal is used or observed, and where the measurement signal is immune or resistant to virtually all common environmental disturbances.

It is an advantage of the present invention that a single fiber optic path can be used to carry both oscillator source energy and the oscillating resonance signal.

Another advantage of the invention is that numerous types of physical parameters can be easily and accurately measured.

A further advantage of the invention is the possibility

to carry a plurality of signal information energies and the oscillator source energy on a single fiber optic path.

There is a further advantage of the present invention

that since the recoded communication carried by the optical fiber is not particularly dependent on the radiation energy level, the provision of at least minimal suitable energy levels will enable a successful measurement even where optical amplitude noise of wide bandwidth is present.

Yet another advantage of the present invention is effective total isolation and freedom from radio frequency interference (RFI).

A further advantage is the elimination of electrically conductive paths between the sensor location and the control room that result in earth-loop currents.

A further advantage of the present invention

is significantly reduced taking into account electrical conductors that carry strong electromagnetic pulse energy into the electronic and control parts of the control system.

Another advantage of the invention described here is freedom from the danger of explosion associated with electric currents in critical environments.

A further advantage of the present invention

is freedom from lightning-induced hazards.

An advantage of an embodiment of the present invention is that it is very easy to adapt both to optical and electrical connection, which enables even greater variation when adapting new technology to old control equipment and/or integration or combination of electrical technology and light energy technology.

A further advantage of the invention is that the light signals can easily be multiplexed for multiple signal transmission on very few paths.

A further advantage of the invention described herein lies in the fact that the oscillating resonant element part is reliably self-starting.

And a further feature of this invention is that

it is easily adaptable to operation under difficult environmental conditions, such as corrosive environments.

Another advantage of the invention relates to its simple methodology and design features in that expensive, complex, inherently less reliable circuit elements can be replaced with cheap, simple and reliable ones.

A further advantage of this invention is that measurement errors introduced due to path loss (such as fiber optic bending loss) are avoided, as the measurement is frequency based.

Another particularly advantageous feature of the invention

is that no local energy source is required at the remote location

measuring point to initiate or maintain the oscillations.

Another advantage of the invention is that it can be easily and economically manufactured, calibrated and installed and put into routine operation.

And another advantage of the present invention is

that as it is optically based, the field sensor has minimal electronic content, i.e. the sensor unit does not require any silicon-based amplification devices.

Further features and advantages of the invention are self-evident from the following detailed description of preferred and different embodiments seen in connection with the attached drawings.

Numerous features of the invention described here will become apparent upon examination of the various drawings which form part of this description. Solid line arrows indicate steady or CW light energy propagation direction, while dashed line arrows indicate a pulsed or modulated light direction. In all drawings, like reference numbers indicate corresponding parts: Fig. 1 is a simplified block diagram of the invention. Fig. 2 is a base diagram illustrating the level of relevant work carried out in the area near the invention. Fig. 3 is a simplified schematic diagram of the base resonant wire oscillator sensor portion of the invention. Fig. 4 is a simplified diagram of the basic resonant hollow beam oscillator sensor embodiment of the invention. Fig. 5 is a simplified schematic view of a dual resonator sensor according to another embodiment of the applicants' invention. Fig. 6 shows the spectral distribution of a part of the radiation energy that can be used in the present invention and shows two discrete usable bandpass curves. Fig. 7 is a simplified schematic view of a pressure cell design in the present invention. Fig. 8 is a simplified view of a temperature-compensated pressure sensor design in the present invention. Fig. 9 is a simplified schematic diagram of a temperature sensor according to the present invention. Fig. 10 is a simple load cell design of the present invention in a schematic view. Fig. 11 illustrates a resonant hollow beam temperature sensor.

Fig. 12 is a simplified view of another embodiment

of the invention where an electric switch is inserted in combination with the sensor.

Fig. 13 is a simplified diagram of an embodiment in which either an optical or electrical drive device can be used, and

fig. 14 is a timing diagram showing the correct and incorrect relationship between signal and feedback current in the preferred embodiment of the invention.

Reference is now made to the drawing, especially fig. 1, where it

is shown an improved fiber optic remote sensing apparatus 10, which includes radiant energy supply source devices 19,

static (or CW) radiation energy path 11, radiation deflection device 12, including e.g. reverse beam deflection/splitting device 13, two-way radiation energy path 14, deflected radiation energy path 15, power conversion device 16 and communication devices 17 for transmitting the power to an oscillator device 20 and signal detection device 18.

For the purpose of this description, the energy supply source device 19 is a steady supply of radiant energy, including coherent and non-coherent light that is generally within the wavelength range from approx. 1000 to approx. 100,000 Angstroms. The term "light" may be used in this description to indicate the more general form of "radiant energy" within the particular wavelength range indicated above. This steady energy is identified for the purpose of this description as steady or continuous wave (CW) energy to distinguish it from on/off modulated, pulsed or closed energy. On

fig. 1, this CW energy is connected into the steady radiation energy path 11 which can be a single fiber optic light conductor or the like. A beam deflection device 12, which will be described below, is placed in the path 11 at a suitable control location remote from the physical location of size measurement

the place. The path 11 enters the deflection device 12 at a first location to direct light energy into it, and a bidirectional radiant energy path directs the light energy away from the deflection device 12 from another location therein. Again, the path 14 is a simple fiber optic light guide or the like. The path 14 conducts CW light energy into the oscillator device 20 which contains a resonant frequency element which is described more fully below. A force conversion device 16 effectively converts the physical quantity to be measured into a mechanical force that is exerted on the resonant frequency element of the oscillator device 20. The choice of force conversion device of the many types known in the field lies within the choice of the person skilled in the art and will vary depending on the physical phenomena to be measured. Generally speaking, CW light received via the successive paths 11 and 14 is reflected as light whose intensity varies with a frequency dependent on the measured physical parameter and is fed back along the path 14 to the inverse beam splitter 13 located in the deflection- the device 12. The beam splitter 13 can be any known device for guiding light when it is advanced through it from a first direction and deflects part of the light that is guided through in the opposite direction. The deflected light with variable intensity (or pulsating) is guided along the path 15 to the signal detection device 18. The detector sensor 18,

a light energy to electrical energy transducer, may be any of several photosensors, including a photodiode,

a photovoltage cell or element, or equivalents thereof.

In operation, CW light is then conducted along a simple sequential path (11, 14) to an oscillator 20 which is driven by CW light.

A detailed description of this circuit is included here in connection with fig. 3 and 4. A force related to the physical parameter to be measured is exerted by the force conversion and communication devices (16, 17) on the resonant element of the oscillator 20 to cause a light to pulsate at a variable frequency (related to the force) which is reflected along the path 14 to a distant location where it is deflected (12, 13) to a detector 18 via a light path 15. The detector thus provides an output signal which is related to the physical parameter being measured.

Reference should now be made to fig. 3, where a simplified diagram of a basic embodiment of the oscillator device 20 as part of the remote measuring device is shown. It should be noted that while all the necessary elements of the oscillator device

20 are included, they are shown and described in schematic form to give a general description instead of specifying particular features, details and devices. This is done to allow those skilled in the art to make use of the invention in accordance with their own needs. x

The oscillator device 20 includes a first end support structure 21, the resonant element 22, the fiber optic path end piece 23, radiant energy to electrical energy transducer 24, isolator 25, converter 26 or an equivalent thereof, phase switching device 27, an electrical connection device 28, a second end support structure 29 , magnetic field source device 30, 31 and frame 32.

The frame 32 is arranged for assembly of the components and is rigidly constructed. The end supports 21, 29 for the resonance element 22 are attached to the frame 32. In this example, a ribbon element is used as resonance element 22. Alternatively, other shapes or profiles can be used, including wires, ribbons or beam structures that require another physical device which to be described later. A reflective surface is included to reflect light when the resonant element 22 "closes" the light. An end support structure 29 includes isolation devices 25 for electrically isolating one end of the resonance element 22 from the frame 32. The light path 14 ends at the end point 23 adjacent to the resonance element

22. A radiant energy to electrical energy transducer 24

is located on the opposite side of and is partially blocked by the resonant element 22. The transducer 24 is electrically connected to the transducer 26 via connecting wires or leads 28. Other windings on the transducer 26 include connections with a phase change device 27, and with the ends of the resonant element 22 via the insulated end thereof and the frame 32 and the opposite support 21. Magnets 30, 31 are equally distributed

parallel to and on opposite sides of the resonance element 22. In this example, magnet 30 is north and magnet 31 is south. The field can be reversed if desired, provided that the electromagnetic laws are properly taken into account. They are positioned so as to produce a magnetic field perpendicular to the resonant element 22 and also perpendicular to the direction of the current carried in the resonant element 22 to cause the resonant element 22 to move back and forth, located between the radiant energy source (the end point

23) and the transducer 24. In this form, converter 26, phase stabilizer 27, connecting wires 28 and magnets 30, 31

in a general sense form an apparatus which causes vibration of the resonant element 22.

This mechanism is explained as follows. Radiant energy arriving at endpoint 23 illuminates opto-electric transducer 24, forming a voltage that is changed to a low level by converter 26. A phase shifter circuit 27 shifts the phase angle of the driving current so that it exceeds 0° and remains less than 180° above vibration frequency range for element 22 (see also fig. 14). The phase change circuit 27 is an impedance formed by at least one of the following reactances: capacitive, inductive and/or resistance. The alternating current supplied to the ends of the band element 22 forms an electromagnetic field around the resonant element 22. Due to the interaction between the electric field and the fixed magnetic field around the band from the magnets 30 and 31, the resonant element 22 is moved in the field, perpendicular to the light beam from the end point 23 When the resonant element is moved to block the radiant energy path between the end point 23 and the opto-electric transducer 24, the current generated by the photocell will be reduced, and when the resonant element 22 obstructs the radiant energy path, the radiant energy is reflected back along the same source path as the arriving energy.

When the resonant element 22 sufficiently blocks the radiant energy path to substantially stop the generation of current, the resonant element, which is under tension, will return to its rest position, exposing the radiant energy path, and the same action is repeated, resulting in undamped oscillation.

Fig. 4 shows a cantilevered beam fiber optic remote sensing device 40, which includes an alternative embodiment of the oscillator device 20, shown within the dashed line box. This resonant cavity sensor includes the continuous (CW) radiant energy path 11, the opposite beam deflection splitter 13, the bidirectional radiant energy path 14, the deflected pulsating radiant energy path 15, the power conversion device 16, the power conversion communication device 17, the signal detection device 18, the radiation energy source supply device 19, the end of the optical fiber path 23, the radiation energy to electrical energy- the transducer 24, the electrical connection device 28, the interrupter 41, the phase switching circuit 42, the (hollow beam) resonant element 43 and the vibrator device 44.

In the present design, the power conversion device 16 is inherent in the resonant hollow beam element 43 when used to measure pressure, as the pressure applied by the power conversion communication device 17 stiffens (and therefore changes the resonant frequency of) the resonant hollow beam element 43. The details of the design of the oscillator device 20 are somewhat different from those in Fig. . 3. Oscillation of the hollow beam 43 is provided by the vibrator device 44

which is an electromechanical device such as a piezoelectric crystal element, a bimorph cell (two crystal elements such as Rochelle salts in fixed combination and arranged to act

such as a mechanical transducer) or the like. The alternating current or pulsating electrical energy for operating the vibrator is derived from the opto-electric transducer 24, which may be a photocell, photodiode or the like. At the endpoint 23

for the fiber optic path, radiation energy is directed towards the adjacent transducer 24. Placed between the end point 23

and the transducer 24, and at least partially blocking the light path therebetween, is a specular or reflective interrupter 41 attached to the end of the hollow beam resonant element 43. To maintain the correct phase relationship for reliable oscillation, the output of the transducer 24 is under the influence of a common phase shifter circuit 42 prior to the connection with the vibrator 3 via electrical connection line devices 28. The phase shifter circuit 42 includes at least one of the following

impedances: capacitive, inductive and/or resistive, as required to change the phase angle of the driving current so that it exceeds 0° and remains less than 180° throughout the frequency range of element 43.

The physical arrangement of the oscillator elements 23, 41, 24, 43 and 44 is such that CW radiation energy is directed towards the transducer 24 from the end point 23, and an electrical signal is generated, which is phase-shifted as required (see above) and supplied to the vibrator device 44 which electromechanically brings resonance helps the jel element 43 to move from its stable position. Attached to the end of the resonant element 43 is an interrupter 41 which is positioned to interrupt the radiant energy path by electromechanical deflection of the resonant element 43. When interrupting the radiant energy, a specular or reflective part of the interrupter will reflect the radiant energy back along the path 14. During this period of reduced driving force the resonant element 43 will return in the direction of its stable position until sufficient radiant energy is allowed to pass by the interrupter and again strike the transducer to form the driving force of the vibrator.

The oscillation is thus initiated and maintained at the natural resonant frequency of the resonant hollow beam element. A pressure (P-j) change introduced via the communication device 17 in the hollow beam cavity will vary the stiffness of the hollow beam and thereby change the oscillation frequency.

Still referring to fig. 4, the input power in the form of CW radiation energy is supplied from the supply source device 19 via successive paths 11

and 14 to the end point 23. The interrupter 41 includes reflection means to effectively reflect at least a portion of the radiant energy back along the path 14 (as described) to turn the beam deflection mirror 13, which redirects the pulsed radiant energy reflected by the interrupter 41 to the signal detector 18 via the path 15, for determining the frequency of the oscillator 20.

An embodiment of the present invention comprises the use of a number of signals on the individual fiber optic path on

the way shown by the double resonator sensor 50 in fig. 5.

The elements of such a dual resonator sensor 50 include power source devices 19, the continuous (CW) radiation energy path 11, an inverted beam deflection mirror 13, a first bidirectional radiation energy path 14, a first deflected pulsed radiation energy path 15, sensor beam splitter/combiner 51, a second bidirectional radiation energy path 52, a third bidirectional radiant energy path 53, a first sensor 54 and second sensor 55, detector beam slits 56, second and third pulsed radiant energy paths 57, 58, first and second detector wavelength filters 59 and 60, first and second detectors 61 and 62 and their respective first and other output signals 63

and 64, and first and second sensor wavelength filters 65 and

66.

In the dual sensor unit of fig. 5, the sensor splitter/combiner 51 will split the incoming, steady CW radiant energy at port A into two (or more) radiant energy signals that follow separate output paths. (The sensor splitter/combiner 51 is discussed in more detail below). The output ports B and C of the splitter/combiner are thus separated from each other. The two-way paths 52 and 53 conduct the radiation energy to the sensors 54

and 55. In each sensor 54, 55, a separate wavelength filter 65, 66 is shown which is placed between the end of the fiber optic path (52, 53) and the reflected or reflective surface.

(Examples of dual-wavelength filtering are shown in Fig.

7 and described below in connection with fig. 7). As an alternative to discrete filters, the specular or reflective areas of the resonant element/interrupter can be coated with one or more extremely thin coatings that are sensitive to a particular wavelength to limit the wavelength of the reflected signal. Each separate filter element 65, 66 (or coated mirror surface) is specific to a different wavelength and limits the wavelength of the returned radiant energy. The sensors 54 and 55 are similar to the oscillator devices 20 previously described, except that the filters 65 and 66 (or the coated mirror surfaces) limit the wavelength of the radiant energy that is returned, so that a particular (and different) wavelength is associated with each sensor 54 , 55. The exit

63, 64 on each respective detector 61, 62 is related to the physical quantity being measured.

The beam splitter 51 forms an optical device for splitting a beam into two or more separate beams. Examples of simple beam splitters include: 1) a thin plate of light-transmitting glass, often with a special reflective coating, such as in metallization, inserted into a beam at an angle to divide part of the beam in another direction; and 2) two right-angled prisms glued together at their hypotenuse faces, where one of the hypotenuse faces may be partially reflective coated. When a beam is passed through, parts of the beam energy will be deflected at angles determined by the position of the prism floats and the direction of the indicator light. Alternatively, more than one smaller optical fiber can receive energy from at least one larger optical fiber and split the energy from the larger fiber into the smaller fibers. Any known light or radiant energy splitter and/or splitter/combiner equivalent in function to the above may be used instead; the example described here is for illustration purposes only.

Reference should now be made to fig. 6, where is shown a spectral distribution curve 70 for an IR (infrared) LED (light emitting diode), with which are superimposed separate bandpass response curves 71, 72 for two discrete wavelengths of radiant energy within the spectral output of the LED. The bandpass curves 71, 72 shown are the product of multilayer radiant energy reflections or transmission coatings. The use of reflective coatings is preferred, as it is more radiant energy efficient.

In the present case, the curves 71, 72 are written from radiation energy which has been passed through filters such as the type shown in fig. 5 (59, 60, 65, 66). Further selectivity (eg, a narrower response curve) can be achieved by equipping the resonant element with multi-layer radiant energy reflecting mirror coatings or elements and thus allowing multiple sensor return signals on a single fiber optic path.

Fig. 7 illustrates an embodiment of the invention for carrying out the function of a pressure sensor 80 and includes the two-way radiant energy path 14, power conversion communication device 17, which in this case is a pressure communication device such as a hose or tube, the resonant element 22, the fiber optic path end part 23, radiant energy to the electrical energy transducer 24, isolator 25, converter 26, phase changer device 27, electrical connection device 28, end support structure 29, magnetic field source device (north) 30 and (south) 31, frame 32, diaphragm 81 with a reinforced and/or reinforced central region 83, the preloaded spring 82, the first chamber 83, the pressure chamber 85, the separator 86 and the port 88.

In the embodiment in fig. 7, the resonant element 22 is a

thread or a band stretched between the end support structure 29 and the diaphragm 81 which seals the first chamber 84

from the pressure chamber 85. The central area 83 of the diaphragm 81 is reinforced for attachment of the resonant element 22 which is held under tension by the preloaded spring 82 which forces the diaphragm away from the partition wall 86. The resonant element 22

is placed between the end part 23 of the optical path and the transducer 24 to at least partially block the path between these two. Pressure (P-j) is communicated to the pressure chamber 85 via the communication device 17. Magnets 30, 31 form a magnetic field which, when the resonant element 22 is electrically energized, causes the resonant element 22 to move back and forth between the permanent magnet pole surfaces in a direction perpendicular to to both the direction of the current in the resonant element and the magnetic field.

When fitting into a system during operation, the diaphragm 81 of the pressure sensor 80 is exposed to a pressure P which represents the physical quantity that can be measured. presses against the diaphragm

81 and its control area 83 will, in relation to the pressure P^, cause a change in the tension of the resonant element- 22

and therefore its resonant frequency will vary in proportion to the pressure P^. The resonant element is caused to oscillate or vibrate at a determinable frequency by an electrical signal derived from radiant energy conducted via path 14 from a remote radiant energy supply source (not shown) to path end point 23. When radiant energy (which may be in the form of light energy) strikes the transducer 24, receives resonance-

the element 22 an electrical signal via the converter 26 which causes the resonant element 22 to move (under the influence of the magnetic field provided by the magnets 30, 31)

in and out of the light path between the end points 23 and the transducer 24, closes the light reaching the transducer 24 at a regular rate, the frequency of which depends on the tension exerted on the resonant element 22 by the diaphragm 81. The resonant element 22 is a metallic band with a reflective surface or the like. To feed back the band's resonant frequency, the light is reflected in a modulated form during the closure back along the same path 14 on which it arrived and is detected remotely in accordance with the description previously given above. An outer port 88 is required if gauge pressure is to be measured; the unit may be evacuated and the port 88 sealed if an absolute pressure is to be measured.

The device according to the invention can also measure temperature. This can be done in different ways, and the choice of these options often depends on the application for which the temperature measurement is intended. For example, a gas-filled flask (e.g. 121 in Fig. 11) can be connected to the apparatus as described above in connection with Fig. 4 and the pressure variations are measured as described there. The same gas-filled flask apparatus can be used to pressurize the interior of a cavity, as described in fig. 8, to measure temperatures. It is often particularly advantageous to know the degree to which the temperature affects the resonant frequency of the resonant element 22, in order to identify the accuracy of the measurement. Fig. 8 illustrates a common such situation, where the pressure is measured remotely; the temperature at the pressure sensor location must be measured to identify the presence and degree of temperature that caused variations in the determination of the pressure measurement accuracy.

Measurement of temperature and pressure in fig. 8 is carried out

with a dual sensor design of a temperature compensated pressure sensor 90, including radiant energy delivery devices 19, continuous (CW) radiant energy path 11, reverse beam deflection slits 13, first bidirectional radiant energy path 14, first deflected pulsed radiant energy path 15, sensor

beam splitter/combiner 51 (see discussion of Fig. 5), second two-way radiation energy path 52, third two-way radiation energy path 53, detector beam slits 56, second pulsed radiation energy path 57, third pulsed radiation energy path 58,

first detector wavelength filter 59, second detector wavelength filter 60, first sensor wavelength filter 65, second sensor wavelength filter 66, pressure sensor 80 (see above discussion in connection with Fig. 7), temperature detector 93 and its output signal 91 (Fig. 8), pressure detector 94 and its pressure output signal 92 and temperature sensor 100 (discussion to fig. 9).

The temperature compensated pressure sensor 90 is essentially the same as the double resonator sensor 50 of FIG. 5, except for the use of special temperature and pressure sensors 100, 80. Pressure sensor 80 is described above; temperature sensor 100 (essentially the same as the oscillator device 20, which has been described earlier) is illustrated in fig. 9 and described below.

As in fig. 5, two separate signals representing physical parameters in the sensors 80 and 100 respectively are developed using a single radiant energy source device (not shown) as an energy supply source and are conducted along a single path. The two signals, here pressure and local temperature at the pressure sensor location, are developed as two signals with different wavelengths and fed back along the same individual fiber optic path 14 to be separately detected, and provide a temperature related signal which can be electronically related to the pressure signal and used to reduce the temperature that causes pressure signal errors.

Fig. 9 schematically shows a simple temperature sensor 100 particularly suitable for use for measuring ambient temperature within an enclosure that contains one or more other sensors that measure temperature-affected physical quantities, such as pressure. Included elements are: two-way radiant energy path 14, end support structure 21, resonant element 22, fiber optic path end part 23, radiant energy to electrical energy transducer 24, converter 26, phase change device (resistor) 27, electrical connection device 28, magnetic field source device 30 (N) and 31 (S ), frame 32, reflector 101, bypass 102 and mounting 103, electrical insulator 104 and end support structure 105.

The resonance element 22 is suspended under tension between the first and second end support structures 21, 105 and is electrically isolated by the insulation 104 at the end support 105. A connection to the end assembly 103 enables the attachment of the resonance element 22 to the insulator 104 and the end support 105. The phase changer device

27 is inserted to set the phase for the driving force within

for the desired range (0°-180°). A flexible electrical conductor connects the insulated end of the resonant element 22

to the converter's 26 secondary winding. The reflector element 101 is optional; it is arranged to improve the reflectivity of the resonant element 22 if this does not have sufficient light reflectivity or if greater light efficiency is required. By choosing resonant element 22 and frame (base or housing) 32 of materials with different temperature coefficients, local temperature can be accurately measured. The resonance band 22

itself remains frequency independent of temperature. In case of multiple sensor use as discussed above in connection with fig. 5, the mirror surface can be coated with one or more radiation energy frequency selective coatings to limit the frequency response of the returned, closed energy. The remaining parts and elements work exactly like the essentially corresponding apparatus in fig. 3 (described above), with the exception of the above differences.

The improved fiber optic remote sensor is ideally adaptable to the design of a load cell sensor 110

as shown in fig. 10, which sensor includes two-way radiant energy path 14, power conversion communication device 17, resonant element 22, fiber optic path end member 23, radiant energy to electric energy transducer 24, electric isolator 25, converter 26, phase changer device 27, electric connection device 28, magnetic field (north) device 30 and (south) 31, load 111, load cell housing 112, first end wall 113, second end wall 114, chamber 115 and end assembly 116.

With this design, the sensor essentially works

in the same way as previously described in connection with fig. 3,

except that the physical quantity being measured is a pressure exerted directly on the entire load cell housing 112 (and supplied to the housing 112 as a whole instead of to the end wall 113) by the power conversion device 17, which is a collar or lip 17. In this drawing, the load 11

shown schematically as a mass affected by gravity. The collar or lip 17 of the load cell 110 can be

an integral part of the housing 112 or a completely separate piece. Its function is to transmit the load force exerted

to the side walls of the house 112 instead of to the end wall. 113,

which could result in a false or uncalibrated output reading. It should be noted that since the sensor measures the force exerted by the load as a frequency change rather than as an absolute frequency measurement per se, the load cell can be arranged at any setting or position and still accurately measure the force exerted with little or no discrepancy on due to this position or setting.

Fig. 11 is a simplified schematic diagram of a resonant cavity temperature sensor 120 for a fluid-filled flask in accordance with another embodiment of the present invention, and which sensor includes bidirectional radiant energy path 14, power communication device 17 (shown in section) as in this case is a pressure communication device, fiber optic path end member 23, radiant energy to electrical energy transducer 24, electrical connection device 28, reflective interrupter 41, phase shifter circuit 42, resonant hollow beam element 43 (shown in partial section), vibrator device 44 and the fluid-filled, temperature-sensitive container 121,. containing a temperature-sensitive fluid 122. Conventional filled vapor pressure techniques may be used to avoid temperature effects on the fill fluid.

The use of this embodiment is substantially similar to that described for the base sensor oscillator device 40

in connection with fig. 4, apart from the particular power conversion device, a fluid-filled, temperature-sensitive fluid container 121 which may contain any suitable temperature-sensitive fluid 122, either gas or liquid. By this one

device, the power conversion communication device may be a tube or a capillary tube, which is connected to the hollow beam resonant element 43 and the temperature-sensitive fluid container 121, which may be flask-shaped as desired. Temperature changes affecting the container 121 expand or contract the fluid contained therein. Fluid expansion is communicated to the cavity of the hollow beam resonance element 43

and causes the resonance frequency for this to change.

Although the invention has been described in that it

has optically supplied useful energy and is optically sensed, it is clear that the electromechanical drive part of the oscillator can be interrupted if desired to stop the oscillation.

Fig. 12 is a simplified schematic drawing illustrating an embodiment of the invention intended for certain applications in which low-level electrical signals are available for further electrical signal communication and includes bidirectional radiant energy path 14, end support structure 21, resonant element 22, fiber optic path end portion 23, radiant energy to electrical energy- transducer 24, converter 26, phase stabilizer device 27, electrical connection device 28, end support structure 29, switch 131, end assembly 132 and insulator 133.

The end assembly 132 and the insulator 133 are as previously described in connection with points 25 and 87 (fig. 3 and 7). With the exception of switch 131, the remaining elements are described in connection with fig. 3. Switch 131 (SW^) is capable of interrupting the feedback signal of the electrical signals, and as such is an excellent device for starting and stopping these signals. As a sealed magnetically responsive reed switch, it makes an ideal limit switch or other oscillation interrupter. Two or more normally closed devices may be connected in series with switch 131, or two or more normally open switch devices may be connected in parallel with switch 131 to provide multiple interrupt functions. Additional switches located at other locations may be useful in different area identification or position location and reference uses. Alternatively, an electrical signal can be derived directly from the end parts 134, 135, as in fig. 13, and used for further electrical communication; this is usually a low-level signal.

The embodiment in fig. 13 is substantially similar to that on

fig. 12, except for the elimination of the switch (S1) 131

on fig. 12 and the introduction of electrical contacts 134, 135

on fig. 13 to enable direct electrical and/or optical power supply/sensing for the apparatus. These electrical contacts can also be used for detection, local indication and/or calibration purposes. The same is the case in many of the other embodiments of the invention described here. If used in the electrical operating condition, the hoop 140 between the end parts 141 and 135 can be cut to avoid stressing the transducer. A switch can be inserted instead of the bracket 1 40 .

Finally, reference should be made to fig. 14, where two drawings

of wire position and driving current is shown, where the relative phase of the currents is correct in fig. 14B and alternated by 90° (incorrectly in fig. 14A). Stable operation is illustrated by fig. 14B. Drive current is only available when the reflective part of the resonant element does not prevent light from reaching the transducer.

Claims (38)

1. Optically driven oscillating resonant element apparatus, characterized in that it comprises: a) a resonant element subjected to a loading force, b) a radiant energy source device for providing radiant energy, c) a simple communication path device for channeling the radiant energy in a first direction to an end point adjacent to the resonant element; d) a transducer device, capable of converting radiant energy into electrical energy, adjacent to the resonant element and opposite to said end point, for the generation of an electric current derived from the magnitude of the radiant energy coming from the end point, e) an electrical drive device electrically connected to the transducer to induce motion of the resonant element transversely between the transducer and the endpoint at a frequency related to the resonant frequency of the resonant element, and f) a reflective device, connected to the resonant element and placed between the end point and the transducer device during movement of the resonant element, for reflection of at least part of the radiation energy along at least part of the communication path in a second direction opposite to the first direction. 2. Oscillating resonance element device according to claim 1, characterized in that the resonance element which is subjected to a loading force is a band. 3. Oscillating resonant element device according to claim 1, characterized in that the resonant element which is subjected to a loading force is a resonant hollow beam construction. 4. Oscillating resonant element device according to claim 3, characterized in that the resonant hollow beam construction is a cantilever device. 5. Oscillating resonant element device according to claim 1, characterized in that the radiation energy provided by the radiation energy source device has a wavelength between 10 3 and 10 <5> Angstroms. 6. Oscillating resonant element device according to claim 5, characterized in that the radiation energy provided by the radiation energy source device preferably has a wavelength between approx. 1000 and approx. 4000 Ang-current . 7. Oscillating resonant element device according to claim 5, characterized in that the radiation energy provided by the radiation energy source device preferably has a wavelength between approx. 4000 and approx. 7000 Angstroms. 8. Oscillating resonant element device according to claim 5, characterized in that the radiation energy provided by the radiation energy source device has a wavelength between approx. 7,000 and 100,000 Angstroms. 9. Oscillating resonant element device according to claim 1, characterized in that the radiation energy provided by the radiation energy source device is incoherent. 10. Oscillating resonant element device according to claim 1, characterized in that the radiation energy provided by the radiation energy source device is coherent. 11. Oscillating resonant element device according to claim 1, characterized in that the communicating path devices comprise a simple fiber optic radiation energy passage. 12. Oscillating resonant element apparatus according to claim 1, characterized in that the communication path comprises a sequential series of radiation energy passage elements along a uniform path. 13. Oscillating resonant element apparatus according to claim 1, characterized in that the radiation energy provided by the radiation energy source device is essentially steady and unmodulated. 14. Oscillating resonant element device according to claim 1, characterized in that the reflective device further includes a separate, reflective element device which is connected to the resonant element, which reflective element is placed at least partially between the radiation energy endpoint and the transducer device to reflect at least a part of the radiation energy back up the communication path device in the opposite direction and synchronously with the oscillating resonant element. 15. Oscillating resonant element apparatus according to claim 1, characterized in that it further includes a converter impedance matched device with at least first and second windings, where the transducer output current is connected to the first winding and the resonant element's drive device is connected to the second winding. 16. Oscillating resonant element apparatus according to claim 15, characterized in that it further comprises phase changer devices to effect a phase delay for the drive current and be between 0° and 180°. 17. Oscillating resonant element device according to claim 1, characterized in that the electrical drive device therein comprises: a) a magnetic force biasing device for the formation of a magnetic field around the resonant element, b) a device for communicating between the transducer electrical energy output and the respective ends of the resonant element and conducting the transducer output current therethrough to form an electromagnetic field, and c) a device for inducing movement of the resonant element between the transducer device and the end point of the radiant energy by interaction between the magnetic force biasing device and the electromagnetic field. 18. Oscillating resonant element device according to claim 3, characterized in that the electrical drive device therein comprises: a) a piezoelectric vibrator device for converting electrical energy into mechanical motion for the resonant element, and b) a device for communication between the transducer's electrical energy output and the piezoelectric vibrator. 19. Force measurement method in an optically driven oscillating resonant element device comprising a resonant element which is subjected to a load force, with radiation energy drive source and devices for returning a signal value which is related to the load force, characterized in that the method comprises: a) exposing a source end of a radiant energy path device to a solid beam of such radiant energy, b) communicating the steady radiant energy along the path in a first direction to a remote resonant element device, and c) alternatively using the communicated radiant energy to intermittently drive the resonant element in an oscillating state and to reflect at least a portion of the radiant energy partially along the path in a second, opposite direction, where the electrical energy is derived from the radiant energy during periods when the radiant energy is not reflected and is used to support the oscillation for the resonant element. 20. Method according to claim 19, characterized in that the resonant element is caused to oscillate due to the influence of an electromagnetic field in an essentially fixed magnetic field. 21. Method according to claim 19, characterized in that the resonant element is brought to oscillate by subjecting it to mechanical stress which is caused by the direct application of an electric field on a piezoelectric element. 22. Method according to claim 19, characterized in that the frequency of reflected radiation energy pulses is related to the value of the load force exerted on the resonant element and further includes the step of detecting the reflected radiation energy to indicate the value of the load force. 23. In an optically driven oscillating resonant element apparatus comprising a resonant element subjected to a loading force, with a radiant energy drive source and means for returning a number of signal values related to the loading force, the method comprises: a) exposing a source end of a radiant energy path device to a steady beam of radiant energy comprising a number of wavelengths comprising at least first and second wavelengths; b) communicating the steady beam of radiant energy along the path in a first direction to a splitter, which splitter splits the radiant energy into a number of separate paths, c) communicating the radiant energy from at least one of the plurality of spaced paths to a remote resonant element device, and d) alternatively using the communicated radiant energy to intermittently operate at least one resonant element in an oscillating state and to reflect energy of a wavelength selected from at least part of the radiant energy along at least part of the path in a second, opposite direction in which the electrical energy is derived from the radiant energy during periods when the radiant energy is not reflected and is used to amplify oscillation for the resonant element. 24. Method according to claim 23, characterized in that the resonant element is caused to oscillate by the influence of an electromagnetic field in an essentially fixed magnetic field. 25. Method according to claim 23, characterized in that the resonant element is caused to oscillate by subjecting it to mechanical stress caused by the direct application of an electric field on a piezoelectric element. 26. Method according to claim 23, characterized in that the reflected radiation energy is selectively separated by wavelength and detected to indicate the load force value. 27. Optically driven sensor for remote measurement of a number of load forces which are related to at least one physical parameter, characterized in that it comprises: a) a radiant energy source device for providing radiant energy, b) a number of oscillating resonant elements subjected to at least two loading forces related to at least one physical parameter, located remote from the radiant energy source device, c) a single communication path device for channeling the radiation energy in a first direction from the source device, d) a device for dividing the individual communication path into a number of communication paths, e) several communication path devices for communicating radiation energy along each of said communicating paths to corresponding individual end part devices adjacent to each of the resonant elements, f) individual transducer devices associated with each path and each endpoint, adjacent to each of the resonant elements and opposite to the respective corresponding endpoints, for the generation of an electrical voltage from the radiant energy emanating from the respective corresponding endpoints; g) individual electrical actuators to induce movement for each resonant element transversely between its corresponding transducer and respective endpoint to block radiant energy reaching the transducer; h) a reflective surface on each of the resonant elements for modulating the radiant energy by reflecting at least part of the radiant energy along at least part of the communicating path in a second direction opposite to the first direction, i) a device for selectively separating the radiant energy returned from each of the resonant elements at the wavelength, and j) a device for detecting the modulation frequency of the returned radiant energy belonging to each of the resonant elements. 28. Apparatus according to claim 27, characterized in that the device for selectively separating the radiation energy about the wavelength comprises a wavelength-selective filter element by means of which the radiation energy from the respective resonance element passes. 29. Apparatus according to claim 27, characterized in that the device for selectively separating radiation energy by wavelength comprises another wavelength-selective coating on the reflective surface of each respective resonant element. 30. Apparatus according to claim 2, for measuring a fluid pressure force, where the resonant band element includes first and second ends, and further includes: g) a housing device which forms a rigid enclosure with at least one end wall in an enclosing enclosure which has at least one side wall perpendicular to and connected to said end wall, h) a pressure diaphragm spaced from the end wall, which diaphragm includes mounting devices attached to a first end of said resonant band element, and which in the enclosure defines first and second cavities so that the first cavity is essentially sealed and includes said end wall, an atmospheric outflow opening , and at least part of the side wall, and where the second cavity is sealed from the first cavity, and i) fluid pressure source devices for communication of the compressive force to the second cavity and to the diaphragm, characterized in that the other end of the resonant band element is attached to the inner surface of the end wall of the enclosure in the first cavity, and whereby the longitudinal stretch of the resonant band is varied in relation to the pulling force exerted on the diaphragm. 31. Apparatus according to claim 30, for measuring absolute pressure, characterized in that the first cavity is evacuated and sealed tightly. 32. Apparatus according to claim 30, for measuring manometer pressure, characterized in that the first cavity is ventilated to the atmosphere. 33. Apparatus according to claim 2, for measuring temperature, further including a casing with opposite first and second ends to which the ends of the resonant band element are attached, further characterized in that the casing construction has a different expansion temperature coefficient than that of the band element. 34. Apparatus according to claim 2, for measuring mechanical compressive force, where the resonant band element includes first and second ends, characterized in that it further includes: g) first and second end walls and at least one adjacent side wall surrounding a longitudinal axis perpendicular to and between the ends and forming an enclosure having internal surfaces, h) fastening devices for fastening the first and second ends of the resonance band element under tension to the interior of these first and second end walls, and i) spacing devices placed between the adjacent side walls and the mechanical pressure force, for separating the mechanical pressure force from the respective end wall and to communicate only the mechanical pressure force to said side walls, which force is communicated coaxially with the longitudinal axis. 32 35. Apparatus according to claim 3, characterized in that it includes a resonant hollow beam construction with an inner cavity for measuring a fluid pressure force by communicating with the fluid pressure force and further including a vapor in equilibrium which separates the fluid pressure force source from the resonance hollow beam's inner cavity. 36. Apparatus according to claim 1, characterized in that it further includes devices for interrupting the electrical connection between the transducer and the electrical drive device. 37. Apparatus according to claim 2, characterized in that it further includes end devices for electrical connection to the electrical drive device, for remotely controlled electrical signaling and isolation of the oscillating resonant element apparatus. 38. Apparatus according to claim 37, characterized in that it further includes devices for interrupting the electrical connection between the transducer and the electrical drive device.