GB2074316A - Opto-electric Transducer - Google Patents

Opto-electric Transducer Download PDF

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GB2074316A
GB2074316A GB8111362A GB8111362A GB2074316A GB 2074316 A GB2074316 A GB 2074316A GB 8111362 A GB8111362 A GB 8111362A GB 8111362 A GB8111362 A GB 8111362A GB 2074316 A GB2074316 A GB 2074316A
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liquid
tube
system
pressure
detection
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Revell D
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01FMEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00Indicating or measuring liquid level, or level of fluent solid material, e.g. indicating in terms of volume, indicating by means of an alarm
    • G01F23/22Indicating or measuring liquid level, or level of fluent solid material, e.g. indicating in terms of volume, indicating by means of an alarm by measurement of physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/28Indicating or measuring liquid level, or level of fluent solid material, e.g. indicating in terms of volume, indicating by means of an alarm by measurement of physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electric or acoustic waves applied directly to the liquid or fluent solid material
    • G01F23/284Electromagnetic waves
    • G01F23/292Light, e.g. infra-red or ultra-violet
    • G01F23/2921Light, e.g. infra-red or ultra-violet for discrete levels
    • G01F23/2922Light, e.g. infra-red or ultra-violet for discrete levels with light-conducting sensing elements, e.g. prisms
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01LMEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material by electric or magnetic means
    • G01L9/0091Transmitting or indicating the displacement of liquid mediums by electrical, electro-mechanical, magnetic or electro-magnetic means
    • G01L9/0097Transmitting or indicating the displacement of liquid mediums by electrical, electro-mechanical, magnetic or electro-magnetic means using photoelectric means
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using infra-red, visible or ultra-violet light
    • G01N21/17Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/41Refractivity; Phase-affecting properties, e.g. optical path length

Abstract

The invention utilises changes in the image forming properties of an appropriate transparent chamber 9, a cylindrical tube being on example of such a chamber, with changes of the medium 8 contained in the said chamber, to give an electronic signal indicative, in simpler embodiments, of the presence or absence of a certain type of medium within the chamber, such embodiments being of use in level detecting; and in more complex embodiments, a signal indicative of the refractive index of the medium, such embodiments being of use, for example, in the control of liquid mixing. The desired image forming property of the chamber and any contents will vary according to the application, but in general is detected by means of an appropriately positioned source of electromagnetic radiation at O, an appropriately positioned detector of said radiation at O', and associated electronics comprised as to the particular requirements. <IMAGE>

Description

SPECIFICATION Liquid Refractive Index Transducer I, Dennis Revell, a British citizen, born in Lancashire, England, on the 11th. May 1950, and presently residing at 8, Thames Avenue, Reading, Berkshire, England, on the 1 ooth. April 1981, and for an indefinite period thereafter, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:: The invention relates to systems utilising the change in image forming properties of an appropriate transparent chamber (in particular, cylindrical to tube-shaped) due to changes of the medium contained in the chamber, to give an electronic signal indicative, in simple embodiments, of the presence or absence of certain types of medium within the chamber (level-detecting); and in more complex embodiments, of the refractive index of the particular medium within the chamber.

Systems utilising liquid-level detection transducers are well-known, being of value in process control, leakage detection, and numerous other areas. These devices vary widely in form, mechanical (hydraulic), ultrasonic and opto-electronic techniques being known, the degree of non-invasiveness into the particular medium varying from device type to device type.

In particular, one group of embodiments is concerned with systems for detecting liquid levels in transparent portions of cylindrical tubing. As an extension, variously shaped said portions, if describable sensibly as optical lens systems, may be convenient in certain applications. In contrast to known systems, in those applications where a liquid level in transparent tubing already existing as part of some equipment is of interest, or can easily be incorporated therein, the invention will, in one embodiment, constitute only a suitable radiation emitter and radiation detector, mounting for said emitter and detector, and suitable conditioning electronics, according to the desired indicating or control requirements, without collimating means or addition of other optical component.A second group of embodiments is concerned with systems for the rapid and accurate measurement of the refractive index of liquids, known methods being accurate, but not very rapid.

In the drawings: Figure 1 is a cross-sectional view of opposing portions of transparent cylindrical tubing (or a spherical portion thereof), depicted and considered as an optical system, and annotated as such, used to illustrate subsequent optical results.

Figure 2 is a cross-sectional view of said tubing indicating conjugate planes with a suitable transparent liquid present in said tubing.

Figure 3 is as Figure 2 with said liquid absent.

Figure 4 is used in a simple consideration of relative intensities obtained with configurations as in Figures 2 and 3, at a suitable detector position, on the one hand in the presence of said transparent liquid, and on the other in its absence.

Figure 5 is a graph giving an indication of the variation of an optical quantity L', giving the position of focus, with liquid refractive index; with a known source (object) position fixed in relation to the tube, given tube radial dimensions, and tube material refractive index.

Figure 6 is a diagram used to deduce the form of the intensity distribution at out of focus planes on the opposite side of a transparent tube to a source of light giving rise to the intensity distribution.

Figure 7 is a diagram illustrating the general form of the intensity distribution at the said out of focus planes.

Figure 8 is used to show how calculated expressions pertaining to the intensity distributions at out of focus positions need to change in form as the liquid refractive index of interest passes through certain values.

Figure 9 is a flowchart showing how the calculated expressions pertaining to the intensity distributions at out of focus positions are correctly assigned according as to whether certain relationships involving optical quantities (not the liquid refractive index directly) are true or false.

Figure 10 illustrates in detail imagery occurring for an optical system comprising a transparent tube (though the diagram applies to spherical symmetry as well), with an object of finite size, and with the entrance pupil of the optical system fixed in position at the first refracting surface of the optical system, by means of a stop.

Figure 11 is a graph depicting the variation of quantities of length associated with the intensity distribution with liquid refractive index, at a given detector position, for-a system with given transparent tube radial dimensions and material, a given size and position of light source, and a given entrance pupil size.

Figure 12 is a graph depicting the variation of certain intensity quantities of interest with liquid refractive index, at a given detector position, for a system with given transparent tube radial dimensions and material, a given size and position of light source, and a given entrance pupil size.

Figure 1 3 illustrates various cross-sectional views of optical geometries other than the cylindrical tube geometry.

Figure 14 illustrates a basic "d.c." electronic conditioning system for use in liquid level limit detecting applications.

Figure 1 5 is a block diagram for a mainly pulsed electronic circuit comprised so that operation in high ambient lighting conditions is possible, without special shielding from said conditions, again for use in said applications.

Figure 1 6 is a block diagram for an analogue electronic circuit comprised for said operating conditions as for Figure 1 5.

Figure 1 7 is a block flow diagram detailing operations required to be executed by appropriate calculating or logic circuitry, for one method of liquid refractive index measurement.

Figure 1 8 is another block flow diagram detailing operations required to be executed by appropriate calculating or logic circuitry, for a somewhat different method of liquid refractive index measurement.

Figure 1 9 is a block flow diagram detailing operations required to be executed by appropriate calculating or logic circuitry, for a simpler system than those for which Figures 1 7 and 18 are drawn.

Figure 20 is a circuit representation for a low supply voltage alarm system, mainly having relevance to those applications where battery operation may be convenient.

Figure 21 illustrates one embodiment of the invention, for use in level detection, where transparent tubing already exists as part of some equipment, or can easily be incorporated therein.

Figure 22 illustrates a second embodiment, for use in level detection, applicable as an immersion device, for example in tanks of various types; or as a leakage detecting device, wherein, for example, it would be positioned in a drip-chamber under a tank.

Figure 23 illustrates a third embodiment, used to measure gas pressure if the temperature is known, or vice-versa.

Figure 24 illustrates a fourth embodiment, for the simultaneous measurement of gas pressure and temperature. (Pressure/temperature transducer).

Figure 25 illustrates a fifth embodiment, a schematic of a liquid pressure and temperature transducer. The transducer is shown in the Figure attached to the base of a tank containing liquid, whose pressure and temperature in the vicinity of the tank base are being monitored.

Figure 26 illustrates a sixth embodiment whereby small differential pressures may be monitored and/or controlled.

Figure 27 illustrates a seventh embodiment whereby flow rates in tubes may be monitored and/or controlled.

Figure 28 illustrates a schematic of a part system utilising a linear array detector device, with suitable sourcing arrangements, in effect constituting a plurality of source detector pairs, for use in linear liquid level measurement Figure 29 is a schematic of another linear liquid level measurement system utilising only one source-detector pair.

Figure 30 is a schematic of a transducer head, illustrating the essential parts thereof, for the rapid and accurate measurement or monitoring of liquid refractive indices.

Figure 31 is a plot of the general form of signal detected by a linear photodiode array comprised as part of a system for measuring liquid refractive indices, in a transducer head as depicted in Figure 30, over the length of the active elements of the said array, taking into account the leakage or dark signal inherently associated with such array devices.

Figure 32 comprises plots of the maximum plus or minus errors in parts per thousand as functions of the refractive index of the liquid concerned, for a system devised to measure liquid refractive indices having a transducer head as depicted in Figure 30, for given transducer head geometry, given transducer head tube refractive index, and electronic processing of signals from the transducer head according to the block flow diagram of Figure 17, on the one hand taking into account photodiode array fixed pattern noise and dark signal effects, and on the other with these effects eliminated.

Figure 33 is essentially as Figure 32 but with the electronic processing of signals from the transducer head according to the block flow diagram of Figure 18.

Following is a brief description giving the source of origin of the invention and its basic principles; and a detailed description comprising detailed optical principles, suggested electronic signal conditioning systems, and some examples of embodiments of the invention.

Brief Description Expensive infusion-drip combined control and alarm systems are in use in hospital intensive care units. It seemed likely that a requirement would exist in less critical circumstances for a device which merely caused an alarm to operate at the exhaustion or near exhaustion of an infusion set. These considerations led to the ideas embodied in this specification.

A transparent liquid within a transparent tube, for all reasonable refractive index values, comprises a system having image forming properties analogous to those of a bi-convex ("positive power" or "converging") lens in the direction perpendicular to the tube axis. Thereby a suitable source of illumination may be focussed to lie within a small area of an image plane, where a photodetector is placed. In the absence of the transparent liquid, and with a suitably small ratio of tube-wall thickness to total diameter, image forming properties analogous to those of a bi-concave ("negative power" or "diverging") lens are produced, again in the direction perpendicular to the tube axis.

A large difference in intensities is thus produced at the detector for the two conditions described above; and this can be detected by using an appropriate opto-electronic transducer, comprising, for example, a light emitting diode (L.E.D.), and photodiode or phototransistor, the source and detector being disposed on opposite sides of the tube, or for linear monitoring applications an effective plurality of such combinations, possibly comprised as a part of one of the solid state detector array devices which are available, and suitable electronic techniques.

Further, for opaque or substantially opaque liquids an "inverted" mode of operation is possible. In these cases the illumination level difference to be detected is that between the nominally zero level with the liquid present, and that finite level obtained with the liquid absent.

The mode of operation for transparent liquids, utilising the imaging properties of transparent tubes either containing or devoid of liquid, is in contrast to known systems.

It is apparent that the intensity produced or the size of the illuminated pattern, at a suitable detector, for a fixed geometry system, comprising as a central part a chamber enclosed by surfaces, said central part constituting a sensible optical lens system, transparent cylindrical tubes thus far considered being special cases of this, and as outer parts suitably positioned source and said detector, or an effective plurality of such source-detector pairs, will be a function of the refractive index of the material present in the said chamber. Systems for detecting boundaries between immiscible liquids, similar, in principle, to those for detecting liquid-gas boundaries, and systems for measuring liquid refractive indices are therefore implied.

Detailed Description The following detailed description is expounded under appropriate sub-titles: Optical Basis With reference to Figure 1, a cross-section of opposing parts of a transparent tube, considered as as optical system, comprising concentric surfaces 1 to 4, the principal planes H, H' of an optically concentric system as under consideration here lie at the geometric centre of the system 5, perpendicular to any optical axis 6, under consideration.Gaussian optics shows that for the system shown in Figure 1, the equivalent focal length F (defined as the distance from H' to the image or focus plane for a collimated incoming light beam parallel to the said optical axis 6), in terms of the notation of Figure 1, wherein the relevant refractive indices Been5, of the optical spaces, and the surface radii r, and r2, are marked, for the system in air, such that n1=n5=1, and noting that n4=n2, is given by: <img class="EMIRef" id="027300730-00030001" />

equation (1).

With reference to Figures 2 and 3, 0 and 0' specify conjugate object and image points in crosssection, for the system 5; Figure 2 depicting geometrical light ray paths, 7, with a liquid 8, present in the tube 9, giving rise to 0' on the opposite side of the centre of the system 5, as 0; Figure 3 depicting said path types 7, with no liquid present in the tube 9, giving rise to 0' on the same side of the centre of the system 5, as 0. The points 0 in Figures 2 and 3 are taken to have the same position relative to the system 5. In Figures 2 and 3, the conjugate lengths, depicted L and L' are defined by: L=(HO); L'=(H'O').

These lengths are measured from the coincident principal planes, specified by H and H', and the sign convention used here is to take distances leftwards of this plane as negative, rightwards as positive.

Gaussian optics further shows the geometrical image forming properties of such a system 5, to be described by: 1/L'-1/L=1/F equation (2) This is known as the "conjugate equation". Evidently, variation of centre index n3, notated in Figure 1, gives the required variation in image forming behaviour. A numerical example will be found illustrative: Let: rut=4 mm., r2=2.5 mm., n2=1 .5.

Examine the two conditions: (i) n3=1.333, corresponding to the refractive index of water.

This gives, from equation (1): F=+ O mm.

For minimum system throw, and from equation (2): L=-20 mm., L'=+20 mm.

Thus, a real image 0' is produced 20 mm. to the right of the system centre (H, H'), as Figure 2 illustrates.

(ii) n3=1, corresponding to no liquid present in the radiation path.

This gives, again via equation (1): F=-10 O mm.

For the same object position as in (i), i.e.: L=-20 mm., equation (2) gives: L'=6.67 mm.

Thus a virtual image, 0', is produced 6.67 mm. to the left of the system centre (H, H'), as Figure 3 illustrates. This corresponds in Figure 3 to a diverging cylindrical wave 10, in the detection space.

Hence a large difference in the intensities produced in the image plane 11, specified under (i), i.e.: for L'=+20 mm., is indicated, for cases (i) and (ii) respectively.

Simple Relative Intensity Considerations With the tube 9, full or empty, the same amount of light is incident on it and refracted by it. With reference to Figure 4, the outer surfaces 1,4 only of the tube are shown, as straight lines, and a point source at 0' assumed, for simplicity. Entrance and exit pupil centres of symmetry are denoted E, E' and the heights of these pupils denoted hE, hÉ repsectively. The plane P", of a centrally located detector (not shown) of half-width W is located generally at a distance D from the centre of symmetry (H, H'), of the optical system.

From Figure 4, similar triangles PclO"O', AE'O', the substitution HÉ=MEhE, where ME is the magnification for pupil imagery, given by ME=LE/'LE, and applying the conjugate equation (2) to this pupil imagery gives: <img class="EMIRef" id="027300730-00040001" />

equation (3) where d', LE, L and L' are as marked in the Figure.

For the one-dimensional imaging properties of a cylindrical tube, using the data given in the previous numerical example, and noting that LE=4 mm.; letting D=20 mm., h E=2 mm. (which can be arranged by the use of a "slit" stop at the first surface 1), and W=1 mm., gives the ratio of the intensities detected by the detector with water and air present to be: R=dÁ,R/W=10 equation (4) where d,,IR is that value of d' obtained with air in the tube. This value of R is of high enough value for certain discrimination.The exercise may be repeated for any value of liquid refractive index via equations (1), (2), (3), and the following equations: R=d,,IR/W if W > d:,, equation (5) or: R=d,,IWdL'IQ if W < d,lQ equation (6) where d',lQ=d' obtained for the particular liquid index of concern; and the symbols " > " and " < " are to be read as "greater than" and "less than" respectively.

Finally in this section it is pointed out that nominally an infinite intensity ratio may be obtained for the two cases, (liquid present and liquid absent), if a detector is positioned non-centrally in the detector plane, denoted by the axis P" in Figure 4, if d,lQ < X+W, where X is the displacement of the detector from the centre of symmetry 0". Nominally zero intensity at such points is obtained with transparent or opaque liquids present.

Liquid Refractive Index Considerations For the fixed data given in the previous numerical example, Figure 5 is a plot 12, of the variation of image distance L' with liquid index n3 the object (source) distance L being kept constant at -20 mm., as in the said example. The tube position 13, and points on the graph corresponding to the air present 14, and liquid (water) of index n3=1 .333 present 1 5, are marked in the Figure, as are the asymptote L'=+oo (infinity) 16, and the point on the n3 axis corresponding to F=oe,17.

The slope at any point on these curves is given from equations (1) and (2) by: <img class="EMIRef" id="027300730-00050001" />

equation (7) For the point were n3=1.333, dL'/dn3=-1 80 mm. so for the case of a level detecting system to be utilized with various clear liquids, only a restricted range of refractive indices may be allowed, depending on the values of R occuring for the various refractive indices of interest, and the sensitivity of the associated electronics, or alternatively the source and/or detector must be movable along their line, over an appropriate range. In general, the geometry of a particular system may, if necessary, be tailored to suit a particular liquid, or the sensitivity of the appropriate associated electronics adjusted.

The above variations of L' and d' with n3, the latter implying a variation also of detected intensity 1, at the centre 0", of the detector plane P", in Figure 4, suggests, on the one hand analogous leveldetecting systems for the detection of boundaries between immiscible liquids, with the optical theory of operation being just the same as previously given, and on the other hand, systems to rapidity measure the refractive indices of liquids, which, in principle, may utilize any of the parameters varying with n3 and for which the theory is developed in the next section in some detail, with the eventual purpose of establishing, in a later section, the likely accuracies that will be obtainable with such systems.

Form of Intensity Distribution in the Detector Space In the following, points marked on the Figures (e.g.: point P,' in Figure 6), are to be understood to also represent the co-ordinate of that point with respect to the optical axis 6, when this is convenient.

In Figure 6, showing the exit pupil E' and the image position 0', for an object (source) of finite size, it is seen that the image points along the P' axis are the convergence points of triangular ray pencils 1 8, (or conical ray pencils for two dimensional imaging); each such pencil being contributed by the appropriate object point, and bounded by outermost light-rays 19, from the exit pupil edges A.

Examination of the Figure reveals that all points between P'1, and P'3, along the P" axis, receive light from all the pencils 18, and that therefore there is constant intensity within this region. Examination of the regions between P:', P2' and P3', P4' shows that as points nearer and nearer to the axis of symmetry 6, are considered, successively more and more of the pencils contributing to the image will contribute their light to these points. There is, therefore, a linear fall off in intensity from the inner to the outer edges of these regions in the Figure.The intensity variation 20, along the P" axis is illustrated in Figure 7, the intensity and length of the uniform central region denoted 1c and 1 c respectively, and the lengths of the two outer regions of linear intensity fall-off by ls.

This form of the intensity distribution, is, in fact, quite general, whatever the position of the P" axis along the optical axis (plane) 6. This is more difficult to visualize for some other of the regions above and below the P' axis in Figure 6, but can be shown mathematically for all regions (eg: for the region defined by: P' < P1" < 0 the symbol " < " to be read as "less than"). Referring to Figure 8, at some locations 21, along the central axis 6, lc will be zero, and at others 22, is will be zero, the same general form 20, as in Figure 7, however, always being maintained.

In Figure 9, diamond shaped boxes 23, contain conditions which control the assignments of the lengths lc and iS of the central constant and sloping edge regions respectively, of the intensity distribution, (as depicted in Figure 7), anywhere in the detector space and/or for any liquid refractive index under consideration, these assignments appearing in the rectangular boxes 24. In the Figure, symbol S gives the starting point for the procedure, symbols T and F denote condition true and false respectively, and the symbol " > " is to be read as "greater than or equal to".These conditions can be deduced by drawing diagrams, such as Figures 8 or 10, for varying imaging possibilities, all the conditions and assignments possible, as appearing in Figure 9, being comprehensively revealed when the liquid index and source (object) position are such that a real image and a real exit pupil are formed.

Figure 10 illustrates in detail imagery occurring for a finite sized object of size 2PM centred at O, giving rise to a real image of size 12PMI centred at 0', and such that a virtual exit pupil of size 2hue' centred at E' is formed, this being the image of the entrance pupil of size 2hE centred at E, located at the first surface 1, of the optical system. This Figure allows calculation of P1,,, P2' occurring in Figure 9, and which are intimately linked with the intensity distribution, in terms of quantities known for a given system.

From Figure 10, similar triangles A.C.PM', Pl".Q.PM' and similar triangles A.B.(PM'), P2,,.N.(PM') give: (P"1-P'M)/(L'-D)=(h'E-P'M)/(L'-L'E) equation (8) (P:'+P)/(L'-D)=(h:+P)/(L'-L:) equation (9) Using the conjugate equation (2), for source and pupil imagery, and substituting in: hE'=hELE/'LE, and PM=PME1L, equations (8) and (9) eventually give:: <img class="EMIRef" id="027300730-00060001" />

equation (10) <img class="EMIRef" id="027300730-00060002" />

equation (11) wherein 1/L' is given by equations (1) and (2) for a particular liquid index n3, in the tube, which with equations (10) and (11) above, can be used in conjuction with Figure 9 to calculate the quantities of interest Ic and 1S as a function of n3 for a fixed detector plane position (P").With the tube radial dimensions, tube material and source (object) distance the same as in the previous numerical example, a fixed detector plane (P") 20 mm. from the system centre (H, H'), and on the opposite side of the tube as a radiating source of half-width 1 mm. (=PM), and an entrance pupil at the first refracting surface 1, of the tube, of half-width 1 mm. (=hE), the variations of it/2, Is, and half the width of the whole illuminated pattern (=ld2+1,), at the detector plane P", as functions of n3 are given by the hatched 25, dotted-hatched 26, and full 27, curves respectively in Figure 1 These curves illustrate a marked dependence of the lengths of interest on n3, angering well for refractive index measuring devices detecting any of these length parameters, especially in view of the fact that data from a previous numerical example were used, and additional data chosen, without regard to maximising sensitivity.

Attention is now turned to consideration of intensity variations with liquid refractive index n3.

With the entrance pupil at the first refracting surface, and a stable source, the intensity over the entrance pupil will be uniform and constant, (ignoring obliquity effects, which is reasonable, as the refracting system is considered to be a sensible optical system). Denoting the intensity over the entrance pupil by IE, than Ic (defined before), and IA, the average intensity of the whole pattern illuminated at the detector plane (P"), are given by: Ic=2hEIE/(Ic+ls) equation (12) lA=2hEIE/(lc+2ls) equation (13) these assuming that the transmissivities of liquids used does not vary from unity.Using system data as before (hE=PM=l etc.), Figure 12 shows the variation of 1, 28 and IA 29, with n3, where the intensity over the entrance pupil has been normalised to unity (-IE=1 ). Similar comments as with the lengths varying with n3 apply also to these variations.

The above theory fixes the entrance pupil position at the first surface 1 of the refracting system (by means of a stop, such as aperture limiting opaque material applied to this first surface). Alternatively the exit pupil position can be fixed by means of a stop at the final refracting surface 4, of the system.

The theory when this is the case can be developed along lines similar to that developed with the entrance pupil fixed at the first surface, and the two theories are very similar, though for brevity this is not done. Fixing the exit pupil in this way may be advantageous in some embodiments, in particular those for measuring refractive indices of liquids varying in transmissivity, from the intensity modulation occurring through index change. Errors due to transmissivity variations may be eliminated by the use of a (secondary) small light detector, located close to, or against the exit pupil, which is now the final surface 4, of the optical system, to vary the light output of the radiating object appropriately, the detector and light source being arranged in a feedback circuit to maintain the intensity detected by the said detector, at the exit pupil, constant.

Optical aberrations are also not considered in the theory given, it is assumed throughout this specification that these are capable of being made arbitrarily small, and contribute negligible error in any system.

Analogous System Geometries Some possible alternative optical system geometries are indicated in cross-section in Figure 13, parts (i) to (iv) inclusive, others being possible. These may be of use in various specialised applications.

Gaussian optical characteristics may be worked out as before, such details not being given. The source, or sources 30, and detector or detectors 31, on opposite sides of the chambers 32, enclosed by transparent material 33, may be placed according to the said calculated Gaussian characteristics, and particular requirements.

Embodiments incorporating parts (i), (ii) and (iii) of Figure 13, will be of use in those applications where it is desirable to have the source and detector encapsulated from the external environment, wherein material 33, for example, may be a moulded transparent epoxy resin.

Geometry as part (i) of the Figure can be achieved by drilling a hole 32, followed by polishing of the internal wall thereof, in the case of cylindrical symmetry. Geometry as in part (ii) of the Figure may be achieved by introducing two suitable pieces of material to each other, said pieces being made by slicing a piece of material, drilled and polished as in part (i) of the Figure, at lines 34, the slices on the extreme left and right being chosen.

Embodiments utilising geometries such as parts (ii), (iii) and (iv) of Figure 6 will enable larger intensity differences from liquid to liquid or liquid to gas to be achieved, than optical systems of comparable external dimensions utilising continuous surfaces (as in part (i) of the Figure), as heretofore considered. This corresponds, roughly speaking, to an allowed increase in hE in equation (3) (and thus equation (4) as weli), and thus an increase in R, the intensity ratio of interest. Such characteristics may be advantageous in more accurate liquid refractive index measurement.

Electronic Basis One set of requirements is that a light, audible alarm, control system or combinations of all of these, should be triggered by the intensity change over a suitably placed photodetector occurring when a liquid level falls below the level of the detector, or by the reverse occurrence, according to the needs of the particular system in which the invention is implemented.

In one class of linear level monitoring systems, which in effect would utilise a plurality of emitterdetector dual combinations thus far considered, the detectors, for example, comprising one of the linear self-scanned array devices available, arranged parallel with the tube axis, or indeed for increased range, a further plurality of such arrays similarly arranged, with appropriate radiation sourcing and electronic arrangements, the requirement is that a signal, indicative of the location of the intensity change, over a small region of the detector sensory elements is produced, the level of this region in the vertical plane corresponding to the liquid level.In passing, it may be noted that for extended linear sources and detectors arranged to be parallel to a transparent cylindrical tube, specular reflection of light impinging on the liquid surface from above the said surface and total internal reflection of light impinging on the said surface from below the said surface, both serve to keep the level of maximum contrast produced in the detector plane in very close correspondence with the liquid level, in spite of the stigmatic imaging qualities caused by the cylindrical symmetry.

Electronic arrangements for the second of the two requirements expounded above are not given, but would involve, where solid-state sensor arrays are used, electronically counting the scanning pulses up (or down) to the level of the region of maximum contrast and converting this count digitally to give, for example, a suitable seven-segment or dot-matrix display, such techniques being known.

Some examples of arrangements for the first of the two requirements expounded above are given however, and comprise the material of the next three sections. The circuit philosophies presented in these sections are restricted to the use of the photodiodes as the detector, for brevity, and as the selfgenerating e.m.f.s. of photo-voltaic cells (photodiodes of a kind anyway), and the built-in gain of phototransistors are not seen as vital requirements. A linear self-scanned detector array, would seem to present certain advantages as far as overcoming possible effects of source and detector misalignment, and allowing the further possibility of providing a digital output for subsequent processing, in the case of simple level limit detecting, in which embodiments the array would be mounted with the line of its' sensing elements perpendicular to the tube axis.As an aside, the use of a self-scanned area array in embodiments requiring linear level measurement could also provide the first of the two advantages above, the second being implicit.

Further, the philosophies presented in the next three sections assume that levels of transparent and opaque liquids are of interest, and that the forms of the source emitting area and the detector sensitive area are appropriate to the application. It is further assumed that the source and detector are symmetricaliy positioned with respect to the tube, in which case two reference comparator voltages are required in the circuit schemes presented, and also that an alarm condition may be required for either of the two conditions, liquid present or absent, accomplished by means of a switchable inverter.

The said two comparator voltages correspond respectively to the two possible cases of transparent and opaque liquid level limits being of interest. Circuit simplification results, if, as mentioned earlier in this specification, the detector is positioned non-centrally in the detector plane, in that only one comparison voltage is required, and consequently no switching to distinguish between opaque and transparent liquid level limits being of interest.

It being in the nature of modern electronics that a required function may possess a multiplicity of electronic solutions, only outlines of possible schemes are proposed, generally in the form of block diagrams, though a circuit is given for the case of the simple d.c. system dealt with first, no component manufacturers types or values being specified. In particular, only block flow diagrams are given, detailing operations required to be executed by appropriate calculating or logic circuitry, for a number of ways, these possibly not being exhaustive, of liquid refractive index measurement.

D.C. System The meaning and intended operation of the scheme detailed in Figure 14 are considered to be readily understandable to those skilled in the art. Part (i) is a block diagram of a d.c. system, with component implementation given in part (ii). With reference to the Figure, a current-to-voltage converter plus amplifier 35, implemented in the circuit by resistors 36, 37, and by operational amplifier, (Op. Amp. for short) 38, produces a voltage V01, proportional to the light induced reverse photocurrent produced in the reverse biassed photodiode 39, the light source being light emitting diode (L.E.D. for short) 40, supplied so as to give nominally constant light output, constant current supplied in the circuit via resistors 41, 42 and operational amplifier 43.With the switches 44, 45 in the positions shown, the circuit is primed to indicate when transparent liquid in the transparent cylindrical tubing, implicitly understood to be positioned between L.E.D. 40, and detector 39, no longer lies in the path between said L.E.D. and detector. V01 is then compared to a reference voltage Vc1 via comparator 46, Vc1 implemented in the circuit by resistors 47, 48,49, and a tapping on resistor 48, said comparator implemented by resistors 50, 51, and Op. Amp. 52, giving a comparator output V02 nominally equal to the positive supply rail voltage Vcc, for Vci more positive than Vo1, and nominally equal to the negative supply rail voltage Vcc, for Vci less positive than VO,. The circuit is arranged so that as the liquid-air boundary falls below the opto-electronic transducer level, Vc1 is of such a value that a change of state occurs in the output V02 of the comparator from +Vcc to Vcc, and thereby in the output V03 of the inverter 53, implemented in the circuit by resistors 54, 55, 56, and Op. Amp. 57, from Vcc to +Vcc respectively.Required alarm functions represented in parts (i) and (ii) of the Figure by an L.E.D. in series with a resistor denoted together 58, a sound emitting device in series with a resistor denoted together 59, and required control functions, represented by a solenoid activated switch 60, are caused to be activated by this change of state in V03, via the current amplifying emitter-follower transistor 61. Similar interpretation of operation is possible in the cases of opaque liquids and/or reversal of the alarm condition (liquid present or liquid absent).

The system shown in Figure 14 will not latch in the alarm condition once this has occurred and desisted. A simple modification to the circuit, almost involving no more than replacing transistor 61, with a suitably connected silicon-controlled rectifier will enable latching to the alarm condition.

The major disadvantage with such a D.C. system is that the enclosure for the opto-electronic transducer (39, 40), would have to be substantially lightproof; which could be inconvenient in certain embodiments. This leads to the consideration of "digital" pulsed or "analogue" filtering techniques to eliminate the effects of what may be a large, unwanted background of radiation.

Pulsed System The meaning and intended operation of the scheme detailed in the block diagram of Figure 1 5 are considered to be readily understandable to those skilled in the art. Waveforms at various points in the circuit are illustrated for clarity of exposition. Symbol B represents background signal level output from the current-to-voltage converter plus amplifier 78, this block producing an output voltage proportional to the light intensity incident on the photodiode 39; symbol S representing signal level output from the block 78 due to the excited radiation emitter 40.

A square wave generator 65, drives the radiation emitter 40, via means of current amplifying transistor 66, and resistor 76; and two identical transmission gates 67, 68, the latter via logic inverter 69, said gates being low impedance between terminals I, I' with a high voltage, denoted H, from said generator, applied at the terminals G, and high impedance with a low voltage L applied at the said terminals G.Output from gate 67, at terminal 1', can thus be represented by a square wave with a peak of magnitude (B+S), whilst the output from terminal I' of the other gate 68, represented as a square wave with a peak of magnitude (B), these peaks being one square-wave half-cycle phase shifted with respect to those of the square wave from gate 67, the output from which is inverted via inverter 70, to give an inverted square-wave, of peak value -(B+S), this being added to the output from gate 68 via suitable Op. Amp. 71, and resistors 72,73, 74, 75 connected in association with said Op. Amp. in a summation mode, the output from the Op. Amp. thus being as indicated.This output is then averaged via averaging circuit 77, and it is seen that the output from the averaging circuit will be a voltage proportional to (B+S)-(B), that is, proportional to the desired signal S. Thus the effect of the background radiation, B being proportional to this, is eliminated. Further signal processing may be as in the D.C. System already discussed, from the point designated V01 in Figure 14.

Effects of ripple at twice the mains frequency, from mains operated light sources will not be completely eliminated by the system described, unless the square generator period contains many such ripples, or the square-wave frequency is derived from the mains frequency such that it equals said mains frequency, or is a whole submultiple thereof.

A.C. Filtering System The meaning and intended operation of the scheme detailed in Figure 1 6 are considered to be readily understandable to those skilled in the art. In such systems, the supply to the radiation emitter 40, from electronic unit 79, is frequency-modulated, or "chopped". Thus, the signal produced by the detector due to ths emitter is also frequency modulated or chopped, but not that part of the signal produced by the detector due to background radiation. The output from current-to-voltage converter plus amplifier 78, is then passed through an a.c. amplifier with a passband 80, whereby only the modulated or chopped part of the (composite) signal received by the detector is amplified. The nominally d.c. background and ripple from mains powered lights are thus excluded.The output from the a.c. amplifier may be processed into a more convenient form, for example by averaging rectifier 81, or a peak detector with reset, also 81, to give the required alarm/control outputs 58, 59, 60, via comparator 46, switches 44, 45 and inverter 53, as detailed previously for the D.C. system.

Immiscible Liquid Boundary Electronics In principle, the probe of immiscible liquid boundary detection is the same as liquid level detection in air; the liquid-air interface comprising a boundary between two immiscible fluids.

Reference is therefore made to the last three sections, and the systems described therein. Greater circuit sensitivity will be required for the detection of liquid-liquid boundaries, than liquid-gas boundaries, liquids having closer indices of refraction, and greater control of source and detector characteristics may have to be exercised.

Liquid Refractive Index Electronics The meaning and intended operation of the schemes outlined in Figures 1 7 and 1 8 are considered to be readily understandable to those skilled in the art. Figures 1 7 and 1 8 are block flow diagrams detailing operations required to be executed by appropriate calculating or logic circuitry, in systems comprised to measure liquid refractive index by detecting length variables, dependent on n3, and by detecting intensity variables, dependent on n3, respectively.In both cases, the detector is considered to be a linear photosensor (eg: photodiode) array, whose line of sensory elements is perpendicular to the axis of a transparent tube containing liquid whose refractive index is of interest, and positioned at an appropriate distance from the axis of the said tube, a suitable light source being disposed on the opposite side of the said tube.

The principles of measurement assumed are the dependency of n3 (liquid index) on the full width (it+215 in Figure 7), of the illuminated pattern produced over the photodiode array elements in Figure 17, and the dependency on n3 of the average intensity (IA in equation (13)), detected by the photodiode sensory elements, of the full illuminated pattern falling thereon, in Figure 1 8.

In the methodologies of both Figures 1 7 and 18, the number of sensory elements illuminated are counted. This count cannot be an exact representation of the length of interest (it+215), as there will be an uncertainty of plus or minus (+) one sensory element on either side of the illuminated region, furthermore photosensor arrays suffer from "Fixed Pattern Noise" (F.P.N.) and leakage or dark signal effects, (though these last two can, in principle, be eliminated).Thus the locations of zero intensity on the edges of the illuminated region in Figure 7 cannot be precisely detected, and associated electronics must be comprised to detect the approximate edges of the said illuminated area by counting the number of sensory elements which fall within an illuminated area, nowhere in which the intensity falls below a certain small value, denoted 1M in Figure 1 7 and Figure 1 8. Effects on accuracy of these factors associated with photosensor arrays is considered in a later section, for the two electronic schemes being described.

In the Figures n denotes the sensory element of concern, the element on which the array scan begins being given by n=1 (one). J in the Figures is a dummy variable, which after one complete scan of the array becomes nominally equal to the number of array sensory elements illuminated by the whole pattern of illumination. The nomenclature used for the diamond and rectangular shaped boxes is the same as that previously used for Figure 9, the symbol "" is to be read as "less than or equal to", and the symbol "=:" as "becomes", rather than "equals", for example, as the box containing the statement JJ+ 1 is passed through, the last value of J is incremented by 1 (one), and that value re-assigned to J.

The symbols J, n, X are to be regarded as identifying storage locations for the appropriate quantities (which change), rather than the quantities themselves.

Following the block flow chart in Figure 1 7 through from the uppermost rectangular box shows that after one array scan (or more accurately part of a scan), that the variable J is correctly set to the number of array sensory elements illuminated (or more accurately the number having an intensity > 1M impinging on them).The assignment box 82, merits further comment in that if it required to display a value for n3 (which will not be required in control applications), this may be done, and probably most easily, assuming J is in binary form, as it almost certainly will be, by means of a "lock-up table", in the form of an electronic "Read-Only Memory" (R.O.M.), whereby J in binary form is applied to the address bus of such a device, the address locations of which are pre-programmed with the appropriate values of n3 in binary form, which are then outputted from the R.O.M., and can be displayed, via an appropriate character generator, on one of the commonly available seven-segment or other numeric displays.The comparison InAlM for each sensory element in turn may be done either in analog or digital form, the latter being preferable in that 1M can be stored more accurately in digital form, though involving an analogue-to-digital converter (A/D converter) to convert In from analogue to digital form.

In the methodology of Figure 1 8 the average intensity 1A is built up sensory element by sensory element, in each array scan, via the expression, appearing in the box 83, in the dummy variable X: X=(In+(J1)X)/i equation (14) wherein the X on the left hand side of this expression represents the average intensity over the first J sensory elements for which In > lM, and the X on the right hand side represents the (less accurate) average intensity over the first (J-1) sensory elements for which 1n > IM before the intensity contribution In of the n th. sensory element in the array (which is the J th. element sensed to be illuminated) has been taken into account.As with the "length" methodology of Figure 17, the comparison In6lM may be done in digital or analogue form, and similar comments apply to the assignment box 82, as were made for the same numbered box in Figure 17. As F.P.N. tends to be random (though fixed) from sensory element to sensory element, this method of averaging over what may be a large number of elements will largely eliminate the effects of F.P.N., (though not of dark signal).

Finally on this time of refractive index measuring electronics, Figure 19 is a block flow diagram for a simpler and less accurate system than those heretofore considered. In this case, a single detector with a small sensory area is considered to be located appropriately and centrally on the opposite side of a transparent tube to a source of light, and the measured quantity dependent on n3 is lc the central intensity (see Figures 7 and 12). As noted before, for liquids with varying transmissivities it will be advantageous, for systems detecting n3 through intensity variables, to fix the exit pupil at the final surface of the refracting system, by means of a stop, and maintaining the intensity at the exit pupil constant by means of a feedback system.The box 84, is again to be understood to be implemented as an electronic "iook-up table", as before not required in control applications.

Safety and Failsafe Considerations It is expected to be necessary in some embodiments of the invention, that failsafe alarm, or operation in the case of control loop usage, will be required on transducer failure or accidental disconnection. No great difficulty electronically is envisaged in the implementation of such schemes. In the case of critical applications, extra circuit complexity will allow periodic dynamic self-checking, giving constant assurance of correct device operation.

For some applications battery operation may be convenient, and a low battery alarm and/or safety action would be desirable. Again, no difficulty is envisaged here, a simple scheme being illustrated in Figure 20, comprising resistors 85, 87, 88, zener diode 86, comparator 90, and a system 91, which implements the required low battery alarm and/or safety action. The battery 89, is also indicated in the Figure. In relation to these applications, some battery saving circuitry would also perhaps not go amiss.

In electrically hazardous environments, for example explosive atmospheres, light emitter and detector lead-in and lead-out can be comprised of non-coherent fibre-optic bundles, with all electrical equipment completely isolated from the hazard. Alternatively, electrical isolation techniques are known.

Comments on Opto-electronic Transducer Due to the property of photodetectors that they integrate the light falling on their sensitive areas, previously implicitly assumed, and the nature of the embodiments simply detecting liquid level limits, it is essential that the detector sensitive width perpendicular to the tube axis be restricted (see equations (5) and (6)). A slit aperture placed over the detector will prevent signal integration outside the slit, or one of the small detectors available may simply be used.

As the light output from L.E.D.s diminishes with age, differential detector circuitry may be considered. Thus the intensities detected by adjacent photodetectors would be compared electronically. Alternatively the light output could be monitored and used as feedback to maintain itself constant. An additional advantage of such arrangements would be that intensity reductions due to moderate dirt or dust accumulation would automatically be taken account of. In simple level detecting embodiments, because of the significant intensity differences to be detected, the precautions suggested in this paragraph will not be necessary, as system failure is considered far more likely to occur for reasons other than variations caused by component ageing.

Embodiments Due to the fairly large number of embodiments presented, others quite conceivably being possible, detailed and exact mechanics are generally not given, rather schematic arrangements are indicated, in which single rather than multiple source-detector pairs are assumed for simplicity, unless otherwise stated.

Clip-on Device Figure 21 illustrates the type of scheme intended, comprising part of some transparent tubing 92, comprised as part of some other system (not shown), source 93, detector 94, each supported in some way (not shown) at appropriate positions within the casing 95, this casing being secured on the said transparent tubing by retaining clips 96, appropriate electrical cabling 97, connected at one end within the said casing to the said source and detector, and at the other end within a control box 98, containing an appropriate electronic conditioning system, and whereon is indicated an on-off switch 99, a switch 100, selected as to whether transparent or opaque liquids are being monitored, an audible alarm (bleeper) 101, a visual alarm means 102, probably an L.E.D., and a low supply voltage alarm 103. A control output 104, from the control box 98, is also indicated.Such an embodiment will be suitable for use where liquid level limit is required in any system where transparent tubing already exists as part of said other system, or can easily be incorporated therein.

Circuit schemes as illustrated in Figures 14, 1 5, and 1 6 discussed previously, will be suitable for use as part of this particular embodiment, such part being contained in the control box 98, in Figure 21.

An example of use is as an infusion drip alarm, for use with those infusion liquid containers which exhibit a liquid surface in the feed-tubing leading from them, on exhaustion of liquid from the said containers. A control output 104, indicated in Figure 1 2 can be used to activate or de-activate a solenoid valve positioned downstream in the tubing from the infusion liquid container, to cut off the liquid flow, when the liquid level as fallen in the tubing to the device level thereby giving a further safeguard against air embollism, over and above that provided by aural and visual alarms. A reservoir of given volume may be interposed "downstream" of the device head, to give an alarm and/or cut-off with a predetermined volume of liquid still remaining.

Immersion Device Figure 22 illustrates a vertical cross-section of the type of scheme intended, comprising an appropriately drilled, and in some locations, threaded cylindrical block of material 105, with a locating shoulder 106, enabling a seal, if required, to be formed between said shoulder and part of the top of a tank or other container 107, possibly with the aid of a suitable grommet 108, a transparent cylindrical part 109, source 110 and detector 111, both disposed suitably on opposite sides of said cylindrical part 109, suitable electrical leads 112, leaving the block 105, to electrical cabling 113, leading to a control box, not shown, but for example being. of the same type described in the last section (98 in Figure 21).A threaded part 114, is indicated shaded, the use of such part in the construction of the illustrated transducer head enabling the head to be made by drilling and thread cutting techniques alone. A liquid 11 5, at a level just below the level of the line of the source and detector, is also indicated in Figure 22. Such embodiments will be suitable where liquid level limit detecting is required in a tank or other container, used for holding liquids.

Circuit schemes as illustrated previously, Figures 14, 1 5, 1 6, will be suitable as part of this embodiment. As all background radiation may in some cases be easy to exclude from such devices, the simpler circuit scheme illustrated in Figure 14, may be particularly appropriate.

Examples of use are in monitoring or controlling tank-to-tank transfer, detecting leakage or overfilling, by mounting the sensor in a drip-pan under a tank; for pump control, for example controlling the pumping of inflammable liquid to a burner in a boiler room, or to some kind of heat engine; and for giving a convenient dashboard indication of low radiator water or other vehicle fluids, (wherein the use of integrating circuitry will be appropriate).

The embodiments described in this and the last section may be used to detect boundaries between immiscible liquids and arranged to behave appropriately to requirements.

Pressure/Temperature Transducer In the cross-sectional schematic depicted by Figure 23, a source of gas is allowed to transmit its pressure P, in a flexible tube 116, to a transparent U-tube 117, the right hand limb of which contains a fixed quantity of gas 11 8, at a pressure Pc, trapped by a liquid 119, of density PT' the levels of liquid in the two limbs of the tube being detected by a linear photosensor array 120 (in association with appropriate electronics, not shown), and two appropriately-shaped and disposed light sources 121, the leftmost one included to account for liquid loss by evaporation down the tube 11 6, a part plan view of the situation depicted in part (b) of the Figure.In the notation given, and of the Figure: P=Pc+PT(llI2) equation (15) By the Gas-law, for a fixed mass of gas: (virial relationship better) PCI21T=k equation (16) where k is a fixed known quantity, for a fixed mass of gas; T is the gas temperature (or). Substituting equation (16) into equation (15) gives: P=kT/12+PT( 2) equation (17) The liquid density PT in general depends on temperature: PT=PO/( 1 +g(T-T0)) equation (18) where p0 is a (known) reference liquid density at a (known) reference liquid temperature T,, PT is the liquid density at the temperature T, and g is the (known) coefficient of cubic expansivity of the liquid.

Thus if one of T or P are known, the unknown one can be calculated by appropriate electronics comprised to calculate the quantity required.

The cross-sectional schematic depicted by Figure 24 essentially consists of two U-tubes 11 7, each as depicted in Figure 23, and already described. The two U-tubes are connected, each by one of their limbs to a source of gas pressure, of magnitude P, the other limbs containing different fixed amounts of gas trapped by liquid 119, the levels of which are again detected by an appropriate sensor array 120, together with an appropriate sourcing arrangement 121, extending for the length of the Utubes.

Denoting appropriate quantities pertaining to the right-most U-tube, corresponding to those pertaining to the left-most U-tube, by primed (') quantities, and noting that all equations derived before in this section apply to the left-most U-tube, or generally to both tubes: P PC+PT(I1 12) PC+PT(I1 12) equation (19) The Gas-law gives, additionally to equation (16), which still remains true: PC12/T=k' equation (20) wherein again k' is known for a fixed mass of gas. Substituting equation (20) into equation (19) gives: P=k'T/I:+p,(l:--l:) equation (21) Equating equations (17) and (21), and substituting in equation (18) for PT' gives an expression for Tin terms of known quantities k, k', p0, g, To and measured quantities I2, I'2, I1, and I'1.Thus the value of T can be calculated. Substitution of this calculated value into equations (17) or (21) gives the value of P, the applied gas pressure. Hence with appropriately comprised calculating electronics, such a system behaves as a pressure and temperature transducer, where isothermal (long-term) changes are of interest.

An approximate idea of the likely order of accuracy of pressure measurement obtainable with systems as considered here can be obtained as follows: Assume in Figure 23 that when the liquid levels in the two limbs of the U-tube are the same, that l2=l1=L/2. Thus, whatever the positions of the two liquid levels, I 1=L-l2. Substituting this into equation (17) and differentiating with respect to dP/dl 2= (kTA22+2PT) equation (22) The accuracy in measuring P, in parts per thousand (p.p.t.) is given by: Accuracy <img class="EMIRef" id="027300730-00120001" />

equation (23) where e2 represents the accuracy with which 12 can be measured.If the detector 120, is a typical linear photodiode array with 1,024 sensory elements in one inch, then e2 is sensibly ascribed as equal to the distance between adjacent sensory elements in the array, or the "array pitch", this being 0.025 mm.

Furthermore, if the area of the inner section of the tube is 100 mm2., L=50 mm., and the trapped gas 118 is helium, which is at Standard Temperature and Pressure (S.T.P.) when the liquid levels in the two limbs of the U-tube 117, are the same, then k=9.3 kg 0K-1 s-2. If, for convenience, the pressure P is chosen such that 12=20 mm., and if the density of the liquid in the U-tube is 1 ,000 kg m-3, then the accuracy in p.p.t. comes out as + 1.25. This appears to be reasonably good as the data substituted into equations (22) and (23) was chosen pretty much at random, though effects such as the solubility of the trapped gas in the liquid, and the presence of liquid vapour in the trapped gas have not been taken into account Liquid Pressure/Temperature Transducer Figure 25 is a cross-sectional schematic of the type of system intended.It comprises two transparent vertical U-tubes 122, containing different but fixed amounts of gas 11 8, trapped by liquid 1.1 9, the bases of these tubes being connected to a source of, ostensibly liquid pressure (but may be hybrid, i.e.: gas plus liquid pressure, see later), said source being depicted in the diagram by liquid 123, obtained in a tank 124, only part of which is shown, any gas 125, above the liquid 123 in the tank being at a pressure P, as depicted in the diagram. As before in this specification, the levels of liquid, the lengths 1g' Ig in the diagram being representative of these levels, in the said tubes 122, are detected by means of a photosensor array 120, an appropriate light-source arrangement 121 (and appropriate electronics, not shown), the dispositions of these being more clearly seen in plan form, in part (b) of the Figure. The liquid 11 9, in the tubes 122, may be the same liquid 123 that is in the tank 124, in which case hatched parts 126,127 in the Figure should be ignored. Alternatively, the liquid 11 9, in the tubes 122 may be different from the liquid 123, in the tank 124.In this case, pressure is transmitted from the liquid 123, in the tank 124, to the liquid 11 9, in the tubes 122, via a light-weight plunger 126, designed to move smoothly within the widened flange 128, connecting to the said tubes 122. A sealing membrane 127, of flexible material (e.g.: silicone rubber) may be used to provide extra security against the mixing of the liquid 11 9, in the tubes 122, with the liquid 123, in the tank 124.

Denoting the average density of the liquid 123, over its depth H, in the tank 124, as PA' the density of the liquid 119 in the transparent tubes 122, both of length L, as PT' the gas pressure in the left-most of these tubes as P,, and in the right-most as P ', the fixed amounts of gas occupying lengths 1g and Ig in the tubes respectively, as indicated in the Figure (generally, analogous quantities pertaining to the gas in the rightmost tube are given the same symbols as for the left-most tube, but are primed (')),then: P+PAH PC+PT(L 19) PC+PT(L Ig) equations (24) By the Gas-law, for the two fixed masses of gas: (virial relationships better) Pclg/T=k; and PclglT=k' equations (25) where as previously k, k' are known constants for the fixed masses of gas. Substituting equations (25) into equations (24) gives: P+PAH=kT/Ig+PT(LIg)=k'T/lg+pT(LIg) equations (26) From equations (26):: T=PT(l glg')Ak/lgk'Ag') equation (27) As before, for greater accuracy, the temperature dependence of PT' as in equation (18) should be taken into account, but for brevity the density of'the liquid 11 9, in the tubes 122, will be left as PT Substitution of equation (27) into equations (26) then gives the quantity P+pAH in terms of the known quantities k, k', L, PT' and the measured quantities Ig/ Ig. For simplicity, this known calculated quantity, equal to P+pAH, will be denoted D. Thus: H=(DP)/PA equation (28) The height H of the liquid 1 23, in the tank 1 24, can therefore be derived if Pa and P are known.P can be measured by device types as described in the last section (Figure 24 refers), as well as the temperature in the vicinity of the top of the tank, by applying such a device at a location 129, indicated by the dotted hatched lines in Figure 25. Furthermore, if the average, known area A, of the tank 124, iooking vertically downwards onto the tank, does not change under operational conditions, then pAH=M/A, where M is the total weight of liquid 123, in the tank 124. Thus: M=A(D-P) equation (29) Thus the weight (quantity) M, of liquid 123, in a tank 124, can be monitored by a combination of systems as proposed in this and the last section, given the appropriate electronic calculating means.In passing, if such influences as high winds etc. deform, say, a nominally circular section (in plan) tank into an elliptical section tank with an eccentricity of 0.9, along the whole of the liquid depth H, which seems unlikely, then the error caused in the average area A, of the tank, from the circular case, is less than 6 parts in 1,000.

In summary of this and the last section, the two device types proposed have one of their applications as the measurement of liquids in tanks, additionally providing, in the schemes described, temperature and pressure measurements in the vicinities of the top of the tank and the bottom of the tank, which may be advantageous. If the temperatures and pressures in these vicinities, inside the tank are required, mechanical means may be devised to mount the sensing heads of the device types proposed, internal to, rather than external to the tank.

Small Differential Pressure Transducer Figure 26 illustrates the type of scheme intended, comprising two vertically oriented transparent cylindrical tube sections 130, and an interconnecting piece 131 of flexible tubing, comprising together, in essence, a U-tube arrangement, said arrangement containing a suitable quantity of liquid 132, the scheme further comprising a transducer head 133, not dissimilar to the casing (and contents) depicted in Figure 21, and similarly containing a suitably positioned source-detector arrangement (not shown), associated cabling 134, connected internally at one end in the said head 133 to the said sourcedetector arrangement, and at the other end to a control box, not shown, but for example, again possibly being of the type described in the last but three sections (98 in Figure 21), a wall 135, for example the wall of a box containing other components, said transparent tube sections and transducer head being shown secured to said wall by screws 136, and clips 137, other means being possible. Interconnecting flexible tubing 131, is shown passing through the wall 135, via hole 138; also shown is a plug 139, which may be one of the sintered bronze types available, and flexible tubing 140, connected at the end not shown to a system whereof the gas pressure (relative positive or negative), is to be monitored.

Such embodiments utilise the fact that pressure, which is small for most liquids, is required to displace the liquid in a U-shaped tube, and that the resulting difference in levels of the liquid surfaces in the two limbs 130, is representative of the difference in gas pressure above the liquid in the two limbs.

Again, in some applications circuit schemes as described previously are suitable for use as part of this embodiment.

An example of use of such a differential pressure transducer, as described, is as part of a fan control system in electrical and other units which are to be used in explosive atmospheres, whereby a known technique is to ensure that a slight continuos positive pressure of air, or inert gas, relative to the outside pressure, is always maintained within the unit, explosive constituents of the outside atmosphere thereby being excluded.

In cases where the end of one of the tubes is open to the atmosphere, a plug 1 39, of material, such as sintered bronze, may be used, inhibiting liquid loss by evaporation or spilling, as well as an effort made to use non-volatile liquids. According to the application, it may be possible to use plugs in both limbs of the U-tube, pressure drops across these being zero in equilibrium, (steady pressure differential). Additionally, or alternatively, the levels of the liquid in both limbs of the U-tube may be monitored, to account for any liquid loss.

Flow-rate Device Figure 27 illustrates the type of scheme intended, comprised in the Figure of vertically oriented transparent tube sections 141, connected in a U-tube arrangement containing a suitable quantity of liquid 142, by flexible tubing 143, with a transducer head 144, with its associated cabling 145, as described in the last section, said cabling again terminating in some kind of monitoring or control apparatus (not shown), the U-tube arrangement connected across a constriction 146, in a tube 147, through which gas is supplied from some source (not shown).

It is well-known that the difference in gas pressure across a constriction in a tube is a wellbehaved function of the flow rate of the said gas. This differential pressure may be used for control or to activate an alarm, as in previous sections, thereby controlling a flow-rate and/or activating an alarm if said flow-rate falls outside certain bounds.

As has been noted before, liquid level differences are representative of relatively low pressure differentials for most liquids, implying that in such devices as here described, wide constrictions will be possible, thereby offering minimal resistance to gas flow.

Liquid flow-rates may also be monitored or controlled with liquid pressure measuring devices incorporating trapped masses of gases, as described in an earlier section (last but one).

Applications may be found where gas and liquid fiow-rate limits have to be detected or controlled.

Linear Liquid Level Measuring Devices As intimated previously, a system which in effect constitutes a plurality of source-detector pairs, said pairs arranged parallel to a transparent tube under consideration, can be used as part of a continuous liquid level measuring and level display device. With reference to Figure 28, a continuous strip radiation source 148, and one of the array detectors 149, which are available, comprising sensing elements 150, as a part, these parts 148, 149, as usual disposed suitably relative to the transparent tube 1 51, shown containing a liquid 152, suggest themselves for use in such embodiments. For convenience, and as mentioned before, a plurality of such detector arrays, arranged longitudinally to the tube, with appropriate light-sourcing arrangements, may be used to give increased range.

Sourcing and detection arrangements as just described may be used with the embodiments illustrated in Figures 21,22, 26, and 27, previously described, and thus, by implication, linear level measurement with clip-on devices (Figure 21), immersion devices (Figure 22), continuous small differential pressure measurement (Figure 26), and continuous gas flow-rate measurement become possible, and may be considered to comprise further embodiments.

In some applications, it will be possible to use a single source-detector pair as part of a linear liquid level measuring device, with the implications for measurement of related quantities as summarised in the last paragraph. For example, with reference to Figure 29, a feedback signal Sf, from source-detector electronics 153, is used to activate means, such as a motor M, to maintain the sourcedetector pair 154, at the liquid level 155, in transparent tubing 1 56, rotation of said motor in response to the error signal Sf, causing rotation of a leadscrew 157, held in fixed bearings (not shown) at each of its ends, thereby moving vertically the light-weight casing 158, in which said source-detector pair 154, are mounted, to keep their line at the liquid level. A pin 159, located in fixed slot 1 60 prevents rotation of said casing 1 58, about the leadscrew axis, said pin being fixed in hole 1 61, in the casing 1 58, and constrained to move linearly along the said slot, and in the Figure also serving the purpose of locating in the helical groove of the leadscrew, giving the required transference of motion from the leadscrew to the casing 158, thereby avoiding the complication of having the hole 162, in the casing 158, through which the leadscrew 157, passes, conform to the leadscrew contours (as a thread in a nut conforms to the thread on a screw). Thus the said hole 1 62, is merely drilled out to the outer diameter of the leadscrew, 1 57.The angle and sense of rotation of the motor M, as the liquid level varies, is monitored by some means, for example photoelectrically, by counting graduations 163, in the plate 164, carrying the slot 1 60, with a photocell (not shown) suitably mounted in the back face of the casing 1 68, and suitable electronic processing of the counts used to give a convenient display and/or control of the liquid level.

Refractive Index Transducers Figure 30 is a schematic of a detector head to be used for liquid refractive index measurement. It comprises a short section of transparent tube 1 65, of higher optical quality than tubing used in liquid level detecting, disposed appropriately on the centre line 170, of a source of light 166, and a horizontally mounted linear photosensor array 1 67, all of which are suitably mounted in and enclosed by casing 168, shown hatched. The section of the said tube 165, facing the source 1 66, within the casing 168, has an aperture limiting stop 169, which limits the angle in the horizontal plane of light rays from the source 166, passing through the tube 1 65.This stop merely consists of opaque material applied symmetrically onto the face of the tube 165, when looking from the source, that is on either side of the centre line 1 70, between the source 1 66 and detector 167, as indicated in the Figure, the gap in the stop 1 69, then forming the entrance pupil of the optical system comprised of the tube 165 and any contents thereof.

The principle of measurement of the liquid index n3 has been expounded in the section entitled "Form of Intensity Distribution in Detector Space", wherefrom any of the parameters, such as certain lengths along the line of sensory elements 171, associated with the intensity distribution thereon, or certain quantities of intensity impinging on the line of sensory elements 1 71, that depend on n3, may be measured and subsequently processed to yield the value of n3 (see Figures 7, 11, and 12).

For brevity, attention will be confined to measurement of n3 by detecting the width of the full illuminated pattern, lc+21s, in the notation of the earlier section mentioned in the last paragraph and of Figures 7 and 11; and by measurement of the average intensity IA' again in the notation of the earlier section and of Figure 12. Outlines of electronic requirements for these two particular methods have already been given in the section entitled "Liquid Refractive Index Electronics", so consideration will be confined herefrom to a consideration of the accuracies that these two methods can be expected to yield.

If f is taken as a detected parameter dependent on the parameter of interest, namely n3, the refractive index of the liquid in the tube 165, in Figure 30, then the accuracy of measurement of n3, in parts per thousand (p.p.t.), is given by: <img class="EMIRef" id="027300730-00150001" />

equation (30) where Ef is the inaccuracy in the measurement of the detected parameter f, df/dn3 is the differential coefficient off with respect to n3, or the rate of change off with n3, and En3 is the expected error in the measurement of n3. Consideration must therefore be given as to the causes of Ef in order to calculate a value for it, in general for each value of n3 in turn, as Ef will be a function of this. Consider first the accuracy of the system detecting the parameter 1,+21,.

A photosensor array will contribute to Ef in that there will be an uncertainty of + two sensory element pitches in the measurement of the length of any pattern of illumination falling on the line of the sensory elements 171, in Figure 30, or an uncertainty of +p, p being the distance between adjacent sensory elements on the array, in the quantity f=-(iC+215), this half-width turning out to be a more convenient quantity to consider in these calculations. Secondly, as mentioned in an earlier section, photosensor arrays suffer from leakage or dark signal effects, and Fixed Pattern Noise (F.P.N.). The former is equivalent to saying that even in complete darkness, an array sensory element still produces a small signal as though a small intensity of light were still being detected by it.The maximum value of the intensity that would be needed to produce this said small signal, if the array did not suffer from this dark signal effect, will be denoted 1,, (a "dark signal equivalent intensity").

The maximum error F in the intensity I, detected by an array element, in an array, due to F.P.N.

can be expressed: F=+(e,l/l 00+ e21S /100) equation (31) where e1 is the maximum percentage error in the nominal responsivity to light intensity of the array, and is normally quoted for a given array; is is that light intensity which saturates the array elements, that is above which no larger signal can be obtained from any of the array elements, and the term e21S /100 in equation (31) represents the contribution to F.P.N. of variations in breakthrough from sensory element to sensory element of the "clocking" pulses used to scan such arrays, expressed as the maximum percentage e2, also normally quoted for a given array, of the saturation intensity Is.

Figure (31) is a plot 1 72, of the distribution of signal level detected by the linear array over the line, denoted by the axis P" as used in the relevant earlier section of this specification, of the array sensory elements, the "dark signal equivalent intensity" 1L being marked in the Figure, for the type of intensity distribution obtained with arrangements such as that depicted in Figure 30 (see earlier relevant section, and Figure 7).As mentioned in the section entitled "Liquid Refractive index Electronics", the true width (it+215 in Figure 7), of the illuminated pattern over the line of array sensory elements can not be detected due to the existence of dark signal, the equivalent light intensity to this being 1L. Thus, instead of detecting the edges of the region where the intensity theoretically falls to zero, edges of a region where the intensity is a certain amount larger than the dark signal equivalent intensity 1L, and including the effect of F.P.N., must be detected. The intensity at the edges of this smaller, detected region is denoted IMT as in the section entitled "Liquid Refractive Index Electronics", and Figures 17 and 18 pertaining to that section.To ensure the approximate edges of the illuminated region are detected, it is reasonable to choose the fixed value of 1M in the following form: IM=ml,+e,(lMIL)/100+e21s /1 00 equation (32) where m is a constant greater than unity. Hence: <img class="EMIRef" id="027300730-00160001" />

equation (33) It is easy to show from Figure (31) that the half-width PM of the region actualiy detected is given by: <img class="EMIRef" id="027300730-00160002" />

equation (34) Substituting equation (33) into equation (34), and taking into account the effect of the finite sensory element array pitch p:: <img class="EMIRef" id="027300730-00160003" />

equation (35) in which IG is given by equation (12) for a uniform intensity over the entrance pupil of 1E For a system nominally measuring the parameter 1c+21S as the quantity dependent on n3, and for which suitable electronic operating requirements are given in the block flow chart, Figure 1 7, choosing the fin equation (30) as f=-(lc+21s), gives for EF in that equation: Ef=2(1C+21S)PM equation (36) The quantities I,, 15 and thus any quantities dependent only thereon, are known as a function of n3 for given optical system parameters, as illustrated in Figure 11; furthermore, the expression df/dn3 in equation (30) can, again for given optical system parameters, be deduced, for each value of n3 of interest, via Figure 9, differentiation of equations (10) and (11) with respect to the quantity L' appearing in those equations, and equation (7). Using the same fixed optical system data as were used in the derivation of Figures 11 and 12, and which to re-cap were: Light-source to transparent tube axis distance =20 mm.

Tube-axis to detector distance =20 mm.

Source half-width, perpendicular to tube-axis =1 mm.

Entrance pupil half-width, perpendicular to tube-axis =1 mm.

Outer radius of transparent tube =4 mm.

Inner radius of transparent tube =2.5 mm.

Refractive index of material of tube =1.5 Uniform intensity at entrance pupil, normalised to unity, IE =1.

Additionally, choosing (reasonable) values for e, and e2 in equation (35) as 5% and 0.5% respectively, a saturation intensity, is=0.5, (as this application is not readily concerned with an imaging use of the photosensor array, it does not matter if some of the array elements are saturated), m=3, I=0.00001 (implying a dynamic intensity range for the photosensor array of 1,:1,=50,000, which is not untypical of such devices), and a value for p in equation (35) of 0.025 mm. (corresponding to a typical photodiode array with 1,024 photodiodes over a length of one inch), then the full curve 1 73 in Figure 32 is a plot of the maximum plus or minus (+) error in p.p.t., of n3, as a function of n3, calculated from equation (30).The hatched curve 174, in Figure 32, gives the maximum + error in n3, again as a function of n3, in the absence of dark current and F.P.N., which in principle can be accounted for electronically; whereby the multiplicative responsivity variations and the additive clock breakthrough variations comprising F.P.N., and quantities representative of the individual sensory element dark signals are stored in electronic memory locations, these being clocked in synchronism with the sensory elements in the array.

The curve 175 in Figure 33, gives the maximum + error inn3, again in p.p.t., as a function of n3, for a system comprised to measure n3 by detecting the average intensity 1A (see Figure 12), of the whole illumination pattern falling along the array sensory elements, with the same optical system data used to derive the curve 1 73 in Figure 32, with one exception, and whose calculating electronics is comprised to operate as in the block flow diagram of Figure 1 8. As the average intensity over the array sensory elements is required, the liberty of making its=0.5 cannot be taken, as this must now be greater than or equal to unity, and for the curve 175 in the Figure, ls was taken to equal unity.The curve for which F.P.N. and dark signal effects are eliminated (analogous to the curve 174 in Figure 32) hardly differs from the one shown, which includes the effects of F.P.N. and dark signal, as these effects are averaged out for a particular index, over the number of sensory elements at which an intensity is detected.

The results of transducer accuracy calculations in this section are very promising as far as rapid and accurate liquid refractive index determination is concerned, as usual in this specification, no particular attention has been paid to choosing system data with a view to maximising calculated accuracies; yet Figure 5, for example, indicates that rapid index measurement to better than l5 p.p.t.

can be expected to be routine, with a system comprising a transducer head as schematically depicted in Figure 30, and electronics comprised to operate as in the block flow diagram of Figure 1 7. The method will be rapid due to the electronic involvement in the embodiment, and, with relevance to some uses, tubing sections (165 in Figure 30), can be rapidly filled and subsequently exhausted, of liquids of interest.

Apart from the accurate and rapid measurement of a series of liquids of interest, one after the other, for which appropriate techniques may be used to ensure that traces of the last measured liquid are removed, other applications that suggest themselves are the control of liquid mixing, wherein the refractive index of a mixture is a function of the proportion of mixing, and quality control or purity monitoring, wherein the refractive index of a liquid as it flows out of some plant would be continuously monitored to be within certain set limits. These latter two applications will not, of course, require any electronic means to calculate the refractive index directly.

Greater accuracy still in refractive index monitoring should be achieved by the use of certain of the alternative optical system geometries depicted in Figure 13, especially in those utilising two dimensional symmetry, such as a chamber, the inner surfaces of which are concave spherical and opposing, the outer surfaces being convex spherical and opposing, and two dimensional or area arrays, (illuminated areas and intensities will be "squared" the analogous quantities measured with one dimensional symmetry).

Finally, photosensor arrays as described, may be used in another embodiment of a liquid refractive index measuring device, said array being movable by means such as a motor, along the optical axis, used to locate the position along the said axis of maximum contrast, said position then corresponding to the best image plane for a given liquid refractive index. Means are included to monitor this position, and calculating means to convert this positional information into a displayed value for n3.

Some liquid index value may make the object position, specified previously by the length L, (Figures 2, 3, 4, etc.), coincident with, or almost coincident with, the first focal plane of the current optical system (including liquid), in which case parallel emergent light results, in the detector space. A position of maximum contrast will then not be found and means depending on the lack of contrast change over a distance along the optical axis will have to be incorporated to prevent the array searching the detector space uselessly, as well as means for displaying the particular liquid refractive index for which this occurs. In the even more unlikely event of liquid indices giving virtual images in the detector space, further means to detect this, and to act accordingly will need to be included, intensity ratios between two known planes perpendicularly to the optical axis then possibly being of use as the inputs to further calculating means to deliver a value for n3. Indeed, such a process may have to be resorted to with liquids giving real image locations far from the optical system surfaces, to keep a reasonable overall system size.

Claims (36)

Claims
1. A system comprising, as a part, an effective inner chamber effectively enclosed by two or more transparent walls, with effective openings into the chamber whereby liquids or gases may be introduced into the said chamber, the shape of the said walls being such that the resulting system of surfaces can be considered as a sensible image forming system in at least one dimension, wherein variables of the image forming and/or electromagnetic radiation transmission behaviour may be detected using an appropriate electromagnetic radiation sourcing arrangement, disposed at an appropriate position relative to the said chamber, and an appropriate electromagnetic radiation detection arrangement suitably disposed on the opposite side of the said chamber as the said sourcing arrangement, detection thereby of the said variables, in combination with other measured variables, or not, according to requirements, allowing a conclusion or conclusions regarding the nature of the medium, or the position, or regarding the value of any parameter dependent thereon, of an interface between media, contained in the said chamber, to be drawn, via suitable electronic processing and/or display means.
2. A system as claimed in claim 1, wherefrom the conclusion that is drawn is the existence or not of a liquid surface, or interface between immiscible liquids at, above or below some level in a system part or all of which is used to contain a liquid or liquids, via electromagnetic sourcing and detection arrangements, as claimed in claim 1, which detect electromagnetic radiation intensity or the size of the illuminated region impinging on the detection arrangement as variables of the image forming behaviour, also as claimed in claim 1, such systems as here claimed thereby comprising liquid level limit detection systems.
3. A linear liquid level measuring system, comprising as parts, an effective chamber, as claimed in claim 1, this being in the form of transparent cylindrical tube, the effective inner chamber claimed in claim 1 being that region enclosed by the continuous inner wall of the said tube, sourcing and detection means as claimed in claim 1, said sourcing means comprising an emitter or emitters of radiation, extending over a distance parallel to the said tube, said detector arrangement comprising a plurality of individual localised detectors disposed appropriately on the opposite side of the said tube as the said emitter or emitters, and for a similar distance along the direction parallel to the said emitter or line of the said emitters, and an appropriate electronic processing arrangement used to give a signal and/or display indicative of the location of the boundary between immiscible fluids between the said sourcing and detection means, this boundary being perpendicular to the axis of the said vertically oriented tube, the location of the said boundary being a function of the position of maximum contrast on the said detection means, said position also being perpendicular to the axis of the said tube.
4. A linear liquid level measuring system comprising a carrier supporting a source of electromagnetic radiation and a localised detector of said radiation, said carrier being mounted to move vertically with the said source and detector positioned on opposite sides of a column of liquid contained in transparent cylindrical tube, a motor connected to move the carrier vertically, for example by means of a leadscrew held at its ends in fixed bearings, and whereon the said carrier is constrained to move, via a hole in the said carrier through which the leadscrew passes, a pin protruding towards the centre of the said hole engaging with the leadscrew threads, and fixed in the carrier, means to hold the carrier against rotation, for example by allowing the said pin to pass through the outer carrier wall and engage in a fixed vertically running slot; means activated by the variation in the detected radiation to control the said motor such that the carrier follows changes in the liquid level in the said column, and means to detect carrier movement in response to said changes, such as a graduated scale mounted vertically on a plate in which the said slot, used to hold the carrier against rotation, is cut, and a second electromagnetic radiation detector fixed in the carrier and disposed suitably relative to the said scale.
5. Systems for liquid refractive index measurement or detection comprising as parts, an effective chamber, appropriate sourcing and detection arrangement, and appropriate electronic processing means all as claimed in claim 1, whereby radiation intensity or the size of the illuminated region, or parts of this region impinging on the said detection arrangement are detected as variables of the image forming behaviour, said variables being dependent on the refractive index of any ostensibly transparent liquid within the said chamber, a conclusion thereby being drawn via an electronic signal produced indicative of the refractive index of the said liquid in the said chamber, said signal being derived from one of the said variables in combination with another measured variable, or not, according to application.
6. A liquid level limit detecting system as claimed in claim 1 and 2, wherein the detection arrangement is in the form of a displaced single, localised sensor, appropriate electronic processing means comprised to be variable in sensitivity according to the transmissivity of the liquid whose level limit is of interest or not, if only ostensibly transparent or ostensibly opaque liquids are of interest, without the need for electronically switching between modes to account for, on the one hand transparent liquids being of interest, and on the other, opaque liquids being of interest.
7. A liquid level limit detecting system, as claimed in claims 1 and 2, wherein the detection arrangement is characterised by being a single localised detector of radiation, symmetrically positioned on the opposite side of a transparent chamber, this being as claimed in claim 1 , wherein the variable of the image forming behaviour that is detected is the radiation intensity impinging on the said detector, whereby the conclusion that is drawn is the existence of a liquid surface, or interface between immiscible liquids at, above, or below the line between the said detector and an appropriate source of radiation. Associated electronic processing means may or may not be comprised to be variable in sensitivity according as to whether or not liquids varying in transmissivity are of interest.Furthermore, if ostensibly transparent and opaque liquids are of interest, electronic switching between modes to account for these two cases will be required, this being in contrast to the type of system claimed in claim 6.
8. A liquid level limit detection system as claimed in claim 2, characterised by the detection arrangement being comprised of a plurality of individual localised detectors, such as one of the electronic photosensor arrays that are available, whereby any effects associated with accuracy of relative positioning between the source and said detector are obviated, and whereby the resulting electronic signal made available for further processing may be of digital form, for example representative of the number of said localised detectors illuminated, or not, according to requirements.
9. A liquid level limit detection system as claimed in any of claims 1, 2, 6, 7, or 8, characterised by the transparent chamber being in the form of a transparent cylindrical tube, the effective inner chamber, as claimed in claim 1 being that region enclosed by the continuous inner wall of the said tube.
10. A liquid level limit detecting system as claimed in any of claims 1,2, 6, 7, 8, or 9, characterised by the sourcing and detection arrangements being mounted in an ostensibly portable casing, and wherein the effective transparent chamber may be part of claimed system or effectively part of some second system, according to application; means such as a suitably sized slot in said casing, and securing clips attached to said casing enabling attachement of said casing to said effective transparent chamber, mainly for use, for example, where transparent cylindrical tubing already exists as part of said second system, or can easily be incorporated therein, said liquid level detecting system essentially constituting a "ciip-on" device, substantially as described in the specification.
11. A liquid level limit detecting system, as claimed in any of claims 1,2, 6, 7, 8, or 9, characterised by the sourcing, detection and effective image forming transparent chamber arrangements being mounted suitably in an appropriate casing, part of which is worked, for example by threading beneath a shoulder, enabling said casing with its contents to be mounted in the top of a tank or other container, said transparent chamber probably most conveniently, but not necessarily, comprising a short length of transparent cylindrical tubing mounted in an appropriately shaped inner cavity in the casing, said cavity being open at both ends, to allow unrestricted movement of liquid therein, this occurring with change of liquid level in the said tank or container, said liquid level limit detecting system essentially constituting an immersion device substantially as described in the specification.
12. A differential pressure level limit detecting system, comprising, in essence, a U-tube containing a suitable quantity of liquid, with a system substantially as claimed in claim 10, the casing of which is permanently or otherwise attached to one or other of the arms of the said U-tube, it being known that the difference in height of the liquid columns in the respective arms of the said U-tube is representative of the difference between the pressures applied to the spaces above the liquid in the said two arms of the U-tube.
13. A gas flow-rate level limit detecting system essentially comprising a U-tube and attached casing and contents, as claimed in claim 10, and wherein the pressure drop across a constriction in a tube through which gas is flowing is manifested as a difference in the heights of the liquid in the arms of the said tube, it being known that the pressure difference across a constriction in a tube through which gas is flowing is a well-behaved function of the flow-rate of the said gas.
14. A gas pressure/temperature level limit detection system comprising a liquid in a transparent U-tube closed at one end, said liquid trapping a fixed mass of gas in the said end, the other end of said tube being connected to a source of gas whose pressure or temperature is of interest; an appropriate source of electromagnetic radiation disposed suitably relative to the said tube, and a suitable radiation detection arrangement, having the form of any of the detection arrangements as claimed in claims 6, 7, or 8, whereby the occurrence of the pressure at, above, or below a certain value, if the temperature remains constant, or the occurrence of a temperature at, above, or below a certain value, if the gas pressure remains constant, may be detected via detection of the radiation intensity or size of region of illumination impinging on the said detection arrangement, and appropriate electronic processing means the liquid level in either arm of the said U-tube being a function of the said pressure or temperature.
1 5. A liquid pressurejemperature level limit detection system comprising a liquid in a transparent U-tube closed at one end, said liquid trapping a fixed mass of gas in the said end, the other end of the said tube being connected to a source of liquid pressure, the pressure of the said liquid or other liquid transmitting its pressure to the liquid in the U-tube, or the liquid temperature in the vicinity of the said U-tube being of interest. The claimed system also comprises, as parts, as appropriate source or sources of radiation disposed suitably relative to the said tube, and a suitable radiation detection arrangement, having the form of any of the detection arrangements as claimed in 6, 7, or 8, whereby the occurrence of a liquid pressure at, above, or below a certain value, if the temperature remains constant, or the occurrence of a liquid temperature at, above, or below a certain value, if the liquid pressure remains constant, may be detected via detection of the radiation intensity or size of region of illumination impinging on the said detection arrangement, and appropriate electronic processing means, the liquid level in the arm of the U-tube containing the fixed mass of gas being a function of the said pressure or temperature.
1 6. A linear liquid level measuring system, as claimed in claim 3, characterised by the detection arrangement being comprised of one of the linear photosensor array devices which are available, the line of the array sensors being parallel to the axis of the transparent tube, said tube being claimed in claim 3.
1 7. A linear gas pressure/temperature measuring system comprising as parts a liquid in a transparent U-tube closed at one end, said liquid trapping a fixed mass of gas in the said end, the other end of said tube being connected to a source of gas whose pressure or temperature is of interest; a detection arrangement characterised by being comprised of a plurality of individual localised detectors disposed appropriately relative to the said tube, a sourcing arrangement comprising an emitter or emitters of radiation, disposed appropriately on the opposite side of the said tube as the said detection arrangement, and extending for a similar distance along the direction parallel to the axis of the said tube as the said detection arrangement, substantially as claimed in claims 3 or 16, whereby the pressure of the said gas if the temperature remains constant or is measured by other means, or the temperature of the said gas if its pressure remains constant or is measured by other means, may be deduced by detection of the location of the line of maximum intensity contrast on the said detection arrangement, this being in close correspondence with the liquid level in the said U-tube, the liquid level in either arm of the said U-tube being a function of the said pressure or temperature.
1 8. A liquid pressure/temperature measuring system comprising as parts a liquid in a transparent U-tube closed at one end, said liquid trapping a fixed mass of gas in the said end, the other end of the said tube being connected to a source of liquid pressure, the pressure of the said liquid or other liquid allowed to transmit its pressure to the liquid in the U-tube, or the liquid temperature in the vicinity of the said U-tube being of interest.The claimed system also comprises, as parts, an appropriate source or sources of radiation disposed suitably relative to the said tube, characterised by extending over a distance parallel to the axis of the said U-tube; a detection arrangement characterised by being comprised of a plurality of individual localised detectors disposed on the opposite side of the appropriate arm or arms of the said U-tube as the said emitter or emitters, and extending for a similar distance along the direction parallel to the said emitter or line of the said emitters, this source detection arrangement being as claimed in any of claims 3 or 1 6; whereby the pressure of the said liquid if the temperature remains constant or is measured by other means, or the temperature of the said liquid if its pressure remains constant or is measured by other means, may be deduced electronically by the detection of the line of maximum intensity contrast on the said detection arrangement, this being in close correspondence with the liquid level in either arm of the said U-tube, the liquid level in either arm of the said U-tube being a function of the said pressure or temperature.
1 9. A gas pressure and temperature measuring system comprising in essence two adjacent U tube arrangements, each one having a different but fixed mass of gas trapped in an appropriate arm by a liquid, the other arms of the said U-tubes being connected to the same source of gas pressure; an appropriate source or sources of radiation disposed suitably relative to the said tubes, characterised by extending over a distance parallel to the axes of the said U-tubes, a detection arrangement characterised by being comprised of a plurality of individual localised detectors disposed on the opposite side of the appropriate arms of the said U-tubes as the said emitter or emitters, and extending for a similar distance along the direction parallel to the said emitter or line of the said emitters as said emitter or line of emitters, whereby the pressure and temperature of the said gas in the vicinity of the said U-tubes may be deduced electronically by the detection of the lines of maximum intensity contrast on the said detection arrangement, these being in close correspondence with the liquid levels in the arms of the U-tubes, according to the particular arrangement, the liquid levels in the U-tube arms with the trapped masses of gases, for example, being simultaneous functions of the pressure and temperature of the gas whose source is applied to the other two U-tube arms.
20. A liquid pressure and temperature measuring system in essence comprising as parts two adjacent U-tube arrangements, each one having a different but fixed mass of gas trapped in as appropriate arm by a liquid, the other effective arms of the said effective U-tubes being connected to a source of liquid pressure, the pressure and temperature of the said liquid or other liquid allowed to transmit its pressure to the liquid in the effective U-tubes being of interest.The claimed system also comprises as parts an appropriate source or sources of radiation disposed suitably relative to the said effective U-tubes, characterised by extending over a distance parallel to the axes of the said effective U-tubes, a detection arrangement characterised by being comprised of a plurality of individual localised detectors disposed on the opposite side of the appropriate arms of the said effective U-tubes as the said emitter or emitters, and extending for a similar distance along the direction parallel to the said emitter or line of the said emitters as said emitter or line of emitters, whereby the pressure and temperature of a liquid allowed to transmit its pressure to the effective arms of the effective U-tubes not containing the fixed masses of trapped gas, may be deduced electronically by the detection of the lines of maximum intensity contrast on the said detection arrangement, the locations of these being closely related to the liquid levels in the arms of the said effective U-tubes containing the trapped masses of gas, these liquid levels in turn themselves being simultaneous functions of the pressure and temperature of the liquid of interest that is allowed to transmit its pressure to the effective U-tube arrangement.
21. A system to measure the weight of liquid contained in a tank or other container, comprising, in essence a system as claimed in claim 1 9 to measure the pressure of any gas above the liquid in the said container, in combination with a system as claimed in claim 20 to measure the liquid pressure and temperature at the bottom of the said container, in combination with appropriate electronic means to calculate the weight of liquid from the parameters measured by the systems as claimed in claims 1 9 and 20, and suitable display means to give an indication of said weight.
22. A liquid level measuring system characterised by having a sourcing arrangement in the form of an emitter or emitters of radiation and having a detection arrangement comprising a plurality of individual localised detectors, as claimed in claim 3, and an appropriate electronic processing arrangement also as claim 3, the system being characterised by having the line of the said individual localised detectors displaced to one side of the line of symmetry joining the centre of the said extended emitter or line of emitters and the axis of a transparent cylindrical tube the inner walls of which enclose an effective inner chamber as claimed in claims 1 or 3, said electronic processing means being comprised to be variable in sensitivity according to the transmissivity of the liquid whose level is of interest or not, if only ostensibly transparent or ostensibly opaque liquids are of interest, without the need for electronically switching between modes to account for, on the one hand transparent liquids being of interest, and on the other, opaque liquids being of interest.
23. A liquid level measuring system as claimed in any of claims 3, 1 6, or 22, characterised by the sourcing and detection arrangements being mounted in an ostensibly portable casing, and wherein the transparent cylindrical tube may be part of claimed system or effectively part of some second system, according to application; said casing having means such as a suitably sized slot and attached securing clips enabling attachment of said casing and contents to the said transparent cylindrical tube, mainly for use, for example, where transparent cylindrical tubing already exists as part of some second system or can easily be incorporated therein, said liquid level detecting system essentially constituting a "clipon" device, substantially as described in the specification.
24. A liquid level measuring system as claimed in any of claims 3, 1 6, or 22, characterised by the sourcing, detection and transparent cylindrical tubing arrangements being mounted suitably in an appropriate casing, part of which is worked, for example by threading beneath a shoulder, enabling said casing with its contents to be mounted in the top of a tank or other container, said transparent cylindrical tubing arrangement comprising a convenient length of tubing mounted in an appropriately shaped inner cavity in the casing, said cavity being open at both ends, to allow unrestricted movement of liquid therein, this occuring with change of liquid level in the said tank or container, said liquid level measuring system essentially constituting an immersion device substantially as described in the specification.
25. A differential pressure measuring system, comprising, in essence, a U-tube containing a suitable quantity of liqud, with a system substantially as claimed in claim 23, the casing of which is permanently or otherwise attached to one or other of the arms of the said U-tube, it being known that the difference in height of the liquid columns in the respective arms of the said U-tube is representative of the difference between the pressures applied to the spaces above the liquid in the said two arms of the U-tube.
26. A gas flow-rate measuring system essentially comprising a U-tube and attached casing and contents as claimed in claim 23, and wherein the pressure drop across a constriction in a tube through which gas is flowing is manifested as a difference in the heights of the liquid levels in the arms of the said U-tube, it being known that the pressure difference across a constriction in a tube through which gas is flowing is a well-behaved function of the flow-rate of the said gas.
27. A liquid refractive index measuring system as claimed in claim 5, characterised by being comprised of, as parts, a convenient length of transparent cylindrical tubing the continuous inner surface of which encloses an effective chamber into which liquids whose refractive indices are of interest can be introduced, an appropriately disposed source of radiation of convenient dimensions, a detection arrangement disposed on the opposite side of the said tubing as the said source, said detection arrangement comprising a plurality of individual localised detectors in a linear array, the line of the said detectors being perpendicular to the axis of the said transparent cylindrical tubing.
28. A liquid refractive index measuring system as claimed in claim 5, characterised by the detection arrangement being in the form of a plurality of individual localised detectors, in a linear array as claimed in claim 27, or in an area array, said array being movable by means such as a motor, toward or away from an effective transparent chamber into which liquids whose refractive indices are of interest may be introduced, said array and motor being comprised in a feedback arrangement such that the array locates and stops at the position of maximum contrast, said position then corresponding to the best image plane for a given liquid refractive index. Means are included to monitor this position, and calculating means to convert this positional information into a displayed value for the liquid refractive index, or not according to requirements. If some liquid refractive index value results in parallel or almost parallel emergent radiation impinging on the detection arrangement, means dependent on the lack of contrast change over a distance along the line that the detection arrangement is permitted to move will have to be incorporated to prevent the array trying to search the detection space for a position of maximum contrast over what may be large distances, in order to keep a reasonable overall system size; as well as means to calculate liquid refractive indices for which this occurs, from an input or inputs other than the position of maximum contrast, such as, for example, intensity ratios at two planes perpendicular to the allowed line of movement, at known positions along the said line.
29. Systems as claimed in any preceding or following claims wherein the sourcing and detection arrangements are mounted in some location remote from the effective transparent chamber or chambers implicit or explicit in the said claims, lead-in of radiation from the said sourcing arrangement being via fibre-optic cable to a position in the vicinity of said chamber or chambers, lead-out of detected radiation being accomplished similarly.
30. Level limit detecting systems as claimed in any of claims 2, 6, 7, 9, 10, 11, 12, 13, 14, or 15, characterised by the detection arrangement comprising a single localised detector of radiation, and by the electronic signal processing arrangements being comprised of a "D.C. System", or a "Pulsed System", or an "A.C. Filtering System", substantially as described in the specification.
31. Parameter level limit detecting systems, said parameter being capable of manifesting itself as a liquid level, substantially as hereinbefore described with reference, or not, to the accompanying drawings.
32. Parameter level measuring systems, said parameter being capable of manifesting itself as a liquid level, substantially as hereinbefore described with reference, or not, to the accompanying drawings.
33. Parameter level measuring systems, said parameter being a function of the refractive index of a liquid, substantially as hereinbefore described with reference, or not, to the accompanying drawings.
34. Liquid level limit detecting systems substantially as hereinbefore described with reference, or not, to the accompanying drawings.
35. Liquid level measuring systems substantially as hereinbefore described with reference, or not, to the accompanying drawings.
36. Liquid refractive index measuring systems substantially as hereinbefore described with reference, or not, to the accompanying drawings.
GB8111362A 1980-04-10 1981-04-10 Opto-electric Transducer Withdrawn GB2074316A (en)

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GB8111362A GB2074316A (en) 1980-04-10 1981-04-10 Opto-electric Transducer

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2201772A (en) * 1986-10-16 1988-09-07 Papirind Forskningsinst An opto-electronic method for determining by length-measurement the quality of cultured fish and a device for implementing the method
GB2298481A (en) * 1995-03-01 1996-09-04 Caradon Mira Ltd Fluid detector device
WO2007012607A1 (en) * 2005-07-26 2007-02-01 Groupe Des Ecoles Des Telecommunications / Ecole Nationale Superieure Des Telecommunications De Bretagne Optical refractometer for measuring seawater salinity and corresponding salinity sensor
EP2041527A2 (en) * 2006-07-18 2009-04-01 Insitu, Inc. Fluid sensing system and methods, including vehicle fuel sensors
CN102095473A (en) * 2010-12-26 2011-06-15 河海大学常州校区 Transmission type photoelectric liquid level meter
DE102010052870A1 (en) * 2010-12-01 2012-06-06 Baumer Innotec Ag Arrangement for detecting level of medium, particularly fluid in container, has area for receiving container with medium introduced in interior of container

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2201772A (en) * 1986-10-16 1988-09-07 Papirind Forskningsinst An opto-electronic method for determining by length-measurement the quality of cultured fish and a device for implementing the method
GB2298481A (en) * 1995-03-01 1996-09-04 Caradon Mira Ltd Fluid detector device
GB2298481B (en) * 1995-03-01 1998-12-23 Caradon Mira Ltd Instantaneous water heaters
WO2007012607A1 (en) * 2005-07-26 2007-02-01 Groupe Des Ecoles Des Telecommunications / Ecole Nationale Superieure Des Telecommunications De Bretagne Optical refractometer for measuring seawater salinity and corresponding salinity sensor
FR2889312A1 (en) * 2005-07-26 2007-02-02 Groupe Ecoles Telecomm Optical refractometer for measuring the salinity of the sea water salinity sensor and corresponding
US7821622B2 (en) 2005-07-26 2010-10-26 Get/Enst Betagne Optical refractometer for measuring seawater salinity and corresponding salinity sensor
EP2041527A2 (en) * 2006-07-18 2009-04-01 Insitu, Inc. Fluid sensing system and methods, including vehicle fuel sensors
EP2041527A4 (en) * 2006-07-18 2010-11-03 Insitu Inc Fluid sensing system and methods, including vehicle fuel sensors
DE102010052870A1 (en) * 2010-12-01 2012-06-06 Baumer Innotec Ag Arrangement for detecting level of medium, particularly fluid in container, has area for receiving container with medium introduced in interior of container
CN102095473A (en) * 2010-12-26 2011-06-15 河海大学常州校区 Transmission type photoelectric liquid level meter
CN102095473B (en) 2010-12-26 2012-06-13 河海大学常州校区 Transmission type photoelectric liquid level meter

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