WO2000033035A2

WO2000033035A2 - Liquid level gauge

Info

Publication number: WO2000033035A2
Application number: PCT/US1999/022154
Authority: WO
Inventors: Willy M. Sander; Donald Mattis
Original assignee: Casco Products Corporation
Priority date: 1998-12-03
Filing date: 1999-09-24
Publication date: 2000-06-08
Also published as: WO2000033035A3

Abstract

A liquid level gauge for a tank or vessel, consists of a p-c board (22) having electrical circuitry thereon, a light source (66) mounted on and connected to the p-c board to direct light laterally thereof, and a light-responsive device (68) mounted on and connected to the p-c board to receive light which is directed to the board laterally thereof. There is a tubular probe (54, 56) connected with the p-c board (22), providing a path for light from the source to travel to the tip of the probe. The probe tip (70) is conical and as such, provides a similar path for light reflected therefrom, to travel back to the light-responsive device, depending on whether or not the tip is immersed in liquid. The tip (70) of the probe (54, 56) is provided with an extension (72) which functions to break any drops that might otherwise form due to capillarity or surface tension of the liquid. Thus, when the liquid level in the tank falls below the tip, for the most part, residual liquid is substantially completely drawn off from the area around the cone of the tip. There is thus encountered no interference from erroneous reflections arising from liquid drops at the tip.

Description

LIQUID LEVEL GAUGE GG

TECHNICAL FIELD

This invention relates to liquid level gauges, and more specifically to gauges of the electronic type, which utilize no moving parts.

BACKGROUND ART

The following patents constitute a sampling of prior U. S. Patents that are considered representative of the state of the art to which the present invention pertains.

U. S. Patents Nos . :

2,368,705 3,299,770 3,543,581 3,553,666 3,589,191 3,751,672 3,776,395 3,818,470 3,834,235 3,850,528 3,887,836 3,932,038 3,939,470 3,995,169 4,037,967 4,107,661 4,134,022 4,155,013 4,242,590 4,306,805 4,354,180 4,440,022 4,468,567 4,503,419 4,513,277 4,631,529 4,644,177 4,711,126 4,713,552 4,998,022

More particularly, the invention relates to improvements in the gauge disclosed in U. S. Patent No. 4,840,137 dated June 20, 1989, entitled LIQUID LEVEL GAUGING APPARATUS, and having common ownership with the present application. The entire disclosure of U. S. Patent No. 4,840,137 is incorporated into the present application, by specific reference .

U. S. Patent No. 4,840,137 above identified illustrates and describes a liquid level gauge having a semi- transparent cup-shaped housing with a closed end, the end having a configuration which forms a light-ref acting prism. Mounted inside the housing are a light source and a light sensor. In the disclosed embodiment, both the source and the sensor are secured in operative positions by a carrier block (72) . The latter has seats for the source and sensor, such that they are positioned so as to be slightly convergent with respect to one another. Essentially, the gauge detects variations in the light that is reflected interiorly of the lens when the latter becomes immersed in liquid. Changes in the light arriving at the sensor are converted to measurements of liquid level in the area exterior of the lens.

Relatively high-resolution measurements are possible with the disclosed arrangement. Due to space requirements and automotive vehicle manufacturers' constraints, following the filing of the patent application which matured into this patent, the disclosed design was modified to incorporate an elongate internal printed circuit board that contained the various elec- trical circuitry which was necessary in order to power the light source, as well as processing the output from the light sensor.

As a consequence of such modifications, one proposal was the mounting of the light source and light sensor on a miniature p-c board that itself was disposed perpendicular to the main p-c board.

However, a distinct drawback resided in the assembly of the miniature p-c board, and establishment of electrical connections between the miniature board and the main, elongate p-c board.

Furthermore, where the gauge was subjected to vibration, as in automotive applications, it had to be capable of reliable operation and over extended periods of use. A fairly concise explanation of the theory of operation of gauges of the type to which this invention relates is given in U. S. Patent No. 4,998,022 issued March 5, 1991, entitled OPTICAL LIQUID LEVEL SENSOR USING A POLYTETRAFLUOROETHYLENE PERFLUOROALKOXY MATERIAL, assigned to Conax Buffalo Corporation, Buffalo, New York. Specific reference is made to the first sheet of drawings of this patent, and the description beginning at line 10 of col. 6 thereof. The entire disclosure of U. S. Patent No. 4,998,022 is also incorporated into the present application, by specific reference. Additionally, a similar, graphic illustration is illustrated in Fig. 1 of U. S. Patent No. 4,713,552, issued to Electricite de France (Service National) , of Paris.

Briefly addressing the subjects matter of the remaining patents listed above:

U. S. Patent No. 2,368,705 involves a liquid level gauge utilizing a total of five vertically mounted, coextensive solid transparent rods, each having a different length, corresponding to different levels of liquid in a tank on which the gauge is mounted. The bottoms of the rods are conical in shape, and depending on the level detected, one, two, three, four or all five of the rods can reflect light beams that travel down each rod. Each rod is secured at its uppermost portion, to a transparent block, which permits light rays to pass through it and to the respective rod.

U. S. Patent No. 3,299,770 illustrates an apparatus for determining the index of refraction of a liquid in a conduit. It employs a light source, light- conducting rod, reflecting surface on the end of the rod which is immersed, a photo-detector, and electronic circuit comprising a bridge, servo amplifier and motor, and a pointer indicator. The position of the latter indicates the index of refraction/density of the liquid, Patent No. 3,543,581 relates to a liquid level indicator having in one embodiment, a hollow tubular component with a conical tip constituting a prism. The inner surface of the prism is hollow, and a series of annular steps is incorporated therein. The arrangement is such that an observer viewing the component from the top will see either no reflection, or alternately reflective circular patterns of different diameters corresponding to different depths of liquid in the vessel being verified.

Patent No. 3,553,666 relates to a liquid probe utilizing solid rod-like elements that are intended to be immersed in a liquid to be monitored. The device utilizes light sources and light detectors, in a variety of configurations. In each instance, the end of the rod-like element is conical, whereby alteration of the internally reflected light in the rod-like element varies according to whether or not the conical end of the element is immersed in the liquid being checked.

Patent No. 3,589,191 involves a liquid level indicator of the photo-detector kind, which utilizes a semi- cylindrical transparent member. The bottom end of the member is formed with a plurality of step-like lens elements, each element being located at a different axial point along the length of the member. A digital-type output is thus attainable according to the number of lens elements used.

U. S. Patent No. 3,751,672 relates to an optical sensor for detecting changes in the concentrations of various solutions. The device incorporates a probe having a light source, light receiver, and probe tip in the form of a prism. The prism is immersed in the liquid to be tested, and light reflected internally within the prism strikes a phototransistor , which in turn is connected to an amplifier and indicator/relay device.

U. S. Patent No. 3,776,395 shows diagrammatically a probe for measuring liquid levels, incorporating a transparent rod having a conical tip intended for immer- sion in a liquid to be monitored, a light source, and photo-detector. Various forms of electronic amplifiers arranged to drive suitable light-emitting indicators are disclosed, for use with the probe. U. S. Patent No. 3,818,470 illustrates a liquid level detector employing a transparent rod having a conical lower end, a light source, and a light-detector. In the various circuits that are disclosed, a single stage transistor amplifier is employed to drive a visual indicator.

U. S. Patent No. 3,834,235 discloses a liquid and solid sensor incorporating a transparent rod having a conical lower tip, light source and sensor, and associated amplifier circuitry, for selectively measuring liquid levels, or alternately for determining the proximity of the end of the probe to a solid substance.

U. S. Patent No. 3,850,528 shows a refractometer gauge which measures the specific gravity of a fluid. It employs an angled transparent rod, light source and light-sensor. Changes in the specific gravity cause corresponding changes in the light transmission through the rod, these in turn giving rise to variation in the light-sensor response. The light-sensor is incorporated in one leg of a bridge circuit, and a meter in the bridge circuit reads changes in the resistance of the light-sensor.

U. S. Patent No. 3,887,836 relates to an electrical circuit for driving an LED, particularly by means of a short-duration pulse which results in a higher-than- normal burst of light being emitted by the device, during the application of the pulse, and without burning out or over-stressing the LED.

U. S. Patent No. 3,932,038 illustrates an apparatus for measuring the density of a liquid, particularly acid concentrations in the electrolyte of a storage battery. The device utilizes a light source and light- detector, and two reflecting surfaces on the tip of a rod-like prism. The output of the light-detector is fed to an operational amplifier, which in turn drives an indicator . U. S. Patent No. 3,939,470 relates to a liquid level gauging system employing two temperature-responsive variable resistance elements mounted in adjacent walls of a motor vehicle oil pan. The elements are arranged to drive various types of logic circuits, which in turn operate indicator lamps.

U. S. Patent No. 3,995,169 shows an optical liquid level gauge employing multiple U-shaped rods of different length, adapted to extend downwardly into a tank or vessel. Light rays travelling through each rod are refracted by different amounts, according to whether or not the yoke portion of each rod is immersed in liquid. The refracted rays are detected by multiple photosensitive cells, which in turn drive transistor amplifier circuitry to trigger suitable indicator/alarm devices. U. S. Patent No. 4,037,967 illustrates another device for measuring the density of a liquid, employing a housing or body carrying a light source, a light- detector, and having a chamber between the source and detector, to receive the liquid being measured. Patent No. 4,107,661 relates to an LED-phototran- sistor pair which is used to sense the presence or absence of a meter pointer at a particular region or over a particular range of the meter scale. The circuitry utilizes a pulse generator for applying one or more pulses to the LED, and the phototransistor response is determined according to whether or not the pointer of the meter is in a position wherein it can reflect light to the phototransistor.

U. S. Patent No. 4,134,022 discloses a liquid level sensor incorporating a transparent rod, light source, and light-detector. The rod has a conical tip which is intended to be immersed in the liquid being gauged. The light-detector drives logic circuitry which in turn powers an indicator/alarm device.

U. S. Patent No. 4,155,013 shows a liquid gauge for measuring oil levels, incorporating a transparent rod having a conical tip constituting a prism. A phototransistor drives amplifier circuitry which in turn controls a visual indicator.

U. S. Patent No. 4,242,590 relates to a liquid level detector incorporating a transparent rod, light source and light-detector. The latter is connected to a single stage operational amplifier having an output terminal arranged to drive an indicator.

U. S. Patent No. 4,306,805 involves a refractive index monitor employing a prismatic body having a curvilinear measuring surface on an immersible tip. A phototransistor in the body is arranged to control an indicator through suitable amplifier circuits.

U. S. Patent No. 4,354,180 shows another type of optical sensor, incorporating a prism having a conical tip at its lower end, and a recess at its upper end, employing a light source and light-detector, for making liquid level measurements. Amplifier and logic circuitry sense the response of the detector, and are connected to an alarm/indicator means.

Patent No. 4,440,022 is directed to a liquid gauge that is applied to the outer surface of a sight-glass or window in a tank or vessel. Suitable light pipes carry light to and from the sight glass. Depending on the presence or absence of liquid on the other side or face of the sight glass, varying degrees of light from the one light pipe will be reflected off the outer surface of the sight glass. With the arrangement shown, only a single level in the tank can be checked, and accordingly only a binary-type reading obtained, corresponding to the presence of liquid above or below a critical point on the sight glass, and thus in the tank. U. S. Patent No. 4,468,567 illustrates a liquid level detector incorporating various types of probes having light-conducting paths, and wherein the intensity of light arriving at a light-detector varies according to changes in the level of liquid being monitored. Gen- erally conventional amplifier/logic circuits are employed with the detector.

Patent No. 4,503,419 discloses a level indicator for the crankcase of an automotive vehicle. An oil level measurement is read simultaneously with operation of the ignition switch. A number of circuits are provided to monitor other parameters, such as vehicle inclination and engine temperature, to minimize false readings that might arise from manual cycling of the ignition switch, or where the vehicle was parked on a hill, for example. U. S. Patent No. 4,513,277 is concerned with a fuel level monitor that utilizes a liquid level sensor, the details of which are not illustrated, and corresponding electrical circuitry that is mounted on a p-c board having an indicator light, or in another embodiment, an LED. The LED becomes illuminated by the electrical circuitry in response to a low level condition in the fuel tank, which condition is sensed by the circuitry.

U. S. Patent No. 4,631,529 discloses a detector circuit for determining whether or not a transparent tube contains a liquid. A conventional LED and phototransistor are employed, together with electrical circuitry that is driven by the phototransistor in order to assure that the latter is prevented from being driven into saturation, which is desirable from the standpoint of accuracy and reliability in operation. Automatic circuitry connected with the LED adjust the output there- from, in a manner to maintain the operation of the phototransistor in an unsaturated or "linear" area of operation.

U. S. Patent No. 4,711,126 relates to a combination refractive-index monitor and liquid level gauge. The device utilizes a hollow, Y-shaped tubular probe, having at one leg of the "Y" , a light source, and at the other leg of the "Y", a light detector. The exterior of the probe has both coated and non-coated reflective areas defining transparent windows, as well as a reflective coating at the end of the body of the "Y" . Generally, multiple windows are incorporated in the "Y" probe where measurements of the index of refraction of a liquid are being made. The window configuration is modified for liquid level measurements.

Patent No. 4,713,552 discloses an optical probe utilizing a light source, a light sensor, and a pair of light-transmitting members having their bottom ends connected with a conical prism. The reflection of light which takes place in the prism is dependent on whether or not the prism is immersed in the liquid being gauged, in an arrangement which is quite similar to other probelike systems that exist in the prior art.

U. S. Patent No. 4,644,177 relates to a combina- tion liquid level indicator and condition sensor incorporating a transparent rod for immersion in the liquid being monitored, and a light source and light detector, and wherein changes in either the level of liquid or the characteristics thereof cause changes in the inten- sity of light rays travelling within the rod. Various forms of amplifier/logic circuitry are disclosed, for processing signals from the detector.

Swiss Patent No. 615,995 discloses a number of different forms of liquid gauges, at least one of which illustrates a cylindrical extension that is disposed at the end of a conical prism, for breaking "drips" that might otherwise form and possibly lead to erroneous measurements .

For reasons which are not readily apparent, few of the gauge constructions described in the preceding paragraphs have met with any significant commercial success. Nevertheless, improvements in this general type of optical gauge are still being sought, particularly from the the standpoint of simplifying manufacture and reducing cost, but without sacrificing long life and reliability.

DISCLOSURE OF THE INVENTION Accordingly, it is an object of the present invention to provide a liquid gauge which is simple in its structure, and rugged and reliable over extended periods of use. A related object of the invention is to provide a novel and improved liquid gauge in accordance with the foregoing, which overcomes potential problems of erroneous readings resulting from liquid capillarity and surface tension. Still another object of the invention is to provide a novel and improved liquid gauge as above set forth, which can be used in a wide variety of installations, and under harsh operating conditions.

Yet another object of the invention is to provide a novel and improved liquid gauge as above characterized, wherein the components are physically small, and manufacturing and assembly costs are reduced to an absolute minimum.

The above objects are accomplished by an improved liquid gauge comprising in combination, a p-c board having electrical circuitry thereon, a light source mounted on the p-c board to direct light laterally thereof, said light source being connected with circuitry of the board, and a light-responsive means mounted on the p-c board to receive light which is directed to the board laterally thereof. The light- responsive means is also connected with circuitry of the board. There is further provided an enclosure attached to the p-c board, and lens means carried by the enclosure for providing a partially solid, reflective path for a light beam which emanates at the source and is to be received at the light-responsive means. The lens means is capable of aiding in the establishment, at the exterior of the enclosure, of an auxiliary, influencing light path which diverges from the solid reflective path when the exterior of the enclosure is surrounded by liquid which has an index of refraction that is different from the index of refraction of the lens means. The gauge further comprises means on the enclosure at an exterior location adjacent the lens means, for dripping off excess liquid from the lens means so as to minimize the influence of any such excess liquid on the light beam.

Other features and advantages will hereinafter appear .

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, illustrating a preferred embodiment of the invention:

Figure 1 is an axial sectional view of the gauge of the present invention, shown as mounted in a tank or vessel, such as an automotive vehicle engine coolant reservoir .

Fig. 2 is a fragmentary right side elevation of the gauge of Fig. 1. Fig. 3 is a fragmentary bottom plan view of the gauge of Figs. 1 and 2 per se.

Fig. 4 is a top plan view of the gauge per se, with a portion of the top cover broken away to reveal part of the underlying p-c board showing a light-emit- ting diode and phototransistor, and light intercepting means disposed therebetween, comprising a plated-through hole in the p-c board, and

Fig. 5 is a fragmentary right side elevation of the gauge of Fig. 1 per se.

MODE FOR CARRYING OUT THE INVENTION

Referring first to Fig. 1 there is illustrated a tank or vessel generally designated by the numeral 10, having an opening defined by a depending nipple 12 in which there is mounted a liquid level gauge 14, for monitoring the depth of liquid contained in the tank.

The top wall of the vessel 10 has two threaded bosses 18 which receive screws by which the gauge is secured to the top wall in the position shown. The gauge comprises a low flat housing 20 disposed exteriorly of the tank, the housing containing a p-c board 22 that carries electrical circuitry associated with the gauge. The p-c board is disposed in a compartment 24 formed by the housing, which is arranged to be air- tight so as to minimize water entering the area surrounding the p-c board. The housing 20 has an upper wall 26 and a lower wall 28, with the p-c board 22 sandwiched therebetween and supported at its left end in Fig. 1, by a ledge or foot 30, and at its rear in Fig. 1, by a foot 32 on the lower housing wall. The upper and lower housing walls are provided with sealing members 34 and 36. The housing, Figs. 3 and 4, is provided with mounting holes 38 and 40, which in turn are aligned respectively with corresponding mounting holes in the top wall 16 of the tank 10, as shown.

Three contact prongs 42, 44 and 46 extend through the right end of the housing, Figs. 1 and 5, and are adapted for connection to an electrical connector receptacle (not shown) that in turn, extends to indicator circuitry associated with the gauge. Where the gauge is utilized in an automotive environment, as for example, the coolant reservoir of the engine, the connector receptacle is connected to the automotive wiring harness (not shown) . The housing 20 has a snorkel 48 that sur- rounds the prongs, and is adapted to mate with the connector receptacle of the wiring harness.

As noted, the three prongs 42, 44 and 46 are connected with the circuitry on the p-c board. An epoxy sealant is preferably applied around the prongs where they exit the compartment, as shown.

The gauge is of the general type illustrated and described in U. S. Patent 4,840,137 above identified. The operation of gauges of this kind is clearly set forth in U. S. Patent No. 4,998,022 issued March 5, 1991, entitled OPTICAL LIQUID LEVEL SENSOR USING A POLYTETRAFLUOROETHYLENE PERFLUOROALKOXY MATERIAL, assigned to Conax Buffalo Corporation, Buffalo, New York.

Depending from the lower housing wall 28 is a tubular skirt 50, which telescopically receives an elongate outer tube 52 of the gauge. The tube 52 is fastened to the housing wall by suitable means, preferably an ultrasonic weld. Referring to Fig. 1 again, there is disposed within the outer tube an inner tube that is generally concentric therewith, and preferably constituted of two tubular sections, a lowermost tubular section 54 having an enlarged upper end portion, to telescopically receive the adjacent lower end of an uppermost tubular section, 56 with some play purposely included, so as to constitute a sliding fit. The bottom end of the lower tubular section 54 is joined to the outer tube 52, preferably by ultrasonic welding, and the joint at this location is air tight, constituting an hermetic seal. The nipple 12 of the tank 10 is substantially cylindrical at the bottom opening thereof. The outer tube 52 is provided with a hub 58 containing an annular groove which receives a sealing ring as shown in Fig. 1. Preferably a ring of the type known as a "quad seal" is employed, so as to prevent liquid at the interior of the tank from escaping at the juncture of the outer tube 52 and the nipple 12.

Where the tank 10 is utilized in an environment characterized by wide fluctuations in temperature, it has been found that effectively isolating the interior of the outer tube from the exterior area surrounding the tank is extremely difficult to achieve in practice, regardless of the number and configuration of sealing arrangements that are employed.

In order to minimize collection of water in the outer tube 52, which would interfere with the operation of the gauge, it has been discovered that one or more vent openings establishing communication between the inside of the outer tube and the ambient area around the tank exterior was desirable. The inside of the outer tube is thus kept at atmospheric pressure. In accomplishing the venting, and referring to Fig. 1, there are provided vent passages 60 and 62 between the skirt 50 of the flat housing 20 and the upper end of the outer tube 52, which latter telescopically fits into the skirt. A sealing gasket 64 is utilized between the lower wall 28 of the flat housing 20 and the top surface of the tank 10 at the tank opening, as shown. The vent passages 60 and 62 actually form a by-pass of the seal provided by this gasket 64. By utilizing openings 60 and 62, venting occurs as described above, and it has been found that this is effective in avoiding excessive condensation inside the outer tube. Such condensation would adversely affect the operation of the gauge, as will be described further hereinbelow. Fig. 1 shows two sets of vent openings; additional sets can be provided, if desired. Mounted on the p-c board are a light source 66, preferably in the form of a light-emitting diode, and a light sensor 68, preferably in the form of a phototransistor. These components are physically small, and are particularly illustrated in Fig. 4. The light-emitting diode 66 is also shown in Fig. 1, and the phototransistor is mounted on the p-c board directly behind the light-emitting diode in this view.

The bottom end of the tubular section 54 terminates in a conical lens or prism 70. In operation, light rays from the light-emitting diode 66 are directed downwardly through the two end-to-end tubular sections 54 and 56, and strike the flat, rear face of the prism 70. Depending on whether or not the conical portion of the prism 70 is immersed in liquid of the tank, the nature of the reflection of light within the prism will correspondingly be different. If the prism 70 is not immersed in liquid, the rays of light are reflected transversely of the prism and directed back through the tubular sec- tions 54 and 56, so as to strike the phototransistor

68. The phototransistor is rendered conducting in response to reception of light, and in conjunction with the electrical circuitry on the p-c board, provides an output signal on one of the prongs 42, 44 or 46 in the connec- tor housing 48.

In contrast, when liquid surrounds the prism 70, the light rays are refracted in such a way as to, for the most part, escape into the liquid in the tank, with the result that substantially no light travels back through the tubular sections. A second signal is thus produced by the phototransistor 68, and this in turn results in a different output signal on one prong in the connector housing 48.

With certain liquids, where a conical prism has been utilized in a gauge having a vertically disposed tubular housing as in the present case, there is a ten- dency for liquid to adhere to the tip of the prism at certain times, mostly in the form of a droplet or drip, even when the overall level of liquid in the vessel has fallen a substantial distance so as to be below the prism.

In accordance with the present invention there is provided a novel wafer-like, drip-dispersing blade 72 in combination with the conical tip of the prism 70, the blade 72 extending below the lowermost portion of the prism, and under the force of gravity effectively drawing away any water from the prism, that would tend to accumulate at the prism itself. In accomplishing this new combination, the blade 72 is constructed to be of substantially rectangular configuration, being slight- ly longer than it is wide.

It has been discovered that the blade construction as specified, effectively breaks the surface tension of any liquid drop that might otherwise form at the tip of the prism 70, and instead draws the liquid away from the prism.

Further, in accordance with the invention it has been discovered that the angular disposition of the blade 72 is critical in assuring that it does not interfere with the light refraction that takes place in the prism 70. As particularly shown in Fig. 4, and in accordance with the invention, the blade 72 preferably lies in a plane that, if extended to the p-c board 22, bisects the path between the light-emitting diode 66 and the phototransistor 68. In effect, the blade 72 is disposed in a position with respect to the prism 70, where the blade does not interfere with light rays that impinge on the prism 70, and similarly does not interfere with light rays that are either within the prism itself, or being reflected back to the phototransistor 68. Stated differently, the blade 72 can be molded integral with the prism 70, and the junction of the blade and prism is formed or molded on a portion of the prism that is normally not involved with receiving or transmitting light associated with the gauge measurements.

As shown, the width of the blade 72 slightly exceeds the dimension of the base of the conical prism 70, as shown in Fig. 1, and as a consequence, the entire conical surface of the prism is rendered free of drops that might otherwise form.

In order that the blade 72 be maintained at a fixed, predetermined orientation with respect to the light-emitting diode 66 and the phototransistor 68, keying means are provided between outer tube 52 and the housing 20 that carries the p-c board 22. In a preferred form, the keying means comprises the joint between the outer tube 52 and housing 20, this being an ultrasonic weld as noted above.

As shown in Fig. 4 and as noted above, the blade 72 is circumferentially oriented on the prism 70 so as to not cover that part of the prism which receives light from the light-emitting diode 66 and which reflects light back to the phototransistor 68. The disposition of the blade 72 is thus considered an important feature of the present invention.

Further in accordance with the invention there are provided on the p-c board 22, plated-through means 74 for intercepting and dissipating or dispersing stray light that originates at the light-emitting diode 66 and which would otherwise travel through the p-c board to illuminate the phototransistor 68, in the manner of a leakage path that would by-pass completely the prism 70. The phototransistors 68 that are utilized in the present gauge are remarkably sensitive, to the end that they tend to respond to stray light, as well as directed rays that have been reflected by the prism 70. In its simplest form, the intercepting means 74 comprises what is known as a "plated-through hole" in the p-c board. In practice, the hole is incorporated in the board at the time of manufacture. With double sided (foil) p-c boards, often it is necessary to connect two tracks on opposite sides of the board. During the plating-through procedure, copper is electro-deposited on the walls of the hole (in the fiberglass p-c board) and forms a junction with and electrical connection between one or more tracks on opposite sides of the p-c board. In accordance with the invention, by providing the plated-through hole 74, the simplest possible solution to the problem of stray light is achieved. No additional cost is involved, and the need for separate opaque light shields that are glued or otherwise fastened to the p-c board is completely eliminated.

From the above it can be seen that there has been provided a novel and improved liquid gauge featuring high accuracy and resistance to capillarity effects of the liquid being gauged. The drip-dispersing blade 72 is useable with virtually any shape of prism cone 70, and is not dependent on the mounting position of the tank or vessel. In effect, the blade 72 renders the conical surface of the prism 70 essentially dry under conditions of low liquid level, while at the same time not interfering with the level measurements that are being made, and which rely on an unobstructed path between opposing surfaces of the conical prism in order to operate properly.

The disclosed device is thus seen to represent a distinct advance and improvement in the field of liquid gauges .

Variations and modifications are possible without departing from the spirit of the invention.

Each and every one of the appended claims defines an aspect of the invention which is separate and distinct from all others, and accordingly it is intended that each claim be treated in this manner when examined in the light of the prior art devices in any determination of novelty or validity.

Claims

What is claimed is:

1. A device which responds to the attainment of a predetermined height of liquid in a vessel, comprising in combination: a) a p-c board having electrical circuitry thereon, b) a light source mounted on the p-c board to direct light laterally thereof, said light source being connected with circuitry of the board, c) light-responsive means mounted on the p-c board to receive light which is directed to the board laterally thereof, said light-responsive means being also connected with circuitry of the board, d) an enclosure for the p-c board, e) lens means carried by said enclosure for pro- viding a partially solid, reflective path for a light beam which emanates at said source and is to be received at said light-responsive means, f) said lens means being capable of aiding in the establishment, at the exterior of said enclosure, of an auxiliary, influencing light path which diverges from said solid reflective path when said exterior of the enclosure is surrounded by liquid which has an index of refraction that is different from the index of refraction of the lens means, and g) means on said enclosure at an exterior location adjacent said lens means, for dripping off excess liquid from the lens means to minimize the influence of any such excess liquid on the light beam.

2. A device as set forth in claim 1, wherein: a) said means for dripping off excess liquid comprises a projection.

3. A device as set forth in claim 2, wherein said projection comprises a substantially flat blade that depends from the lens means, and is integrally molded therewith.

4. A device as set forth in claim 1, wherein said projection bisects the lens means, and lies in a plane that passes between the light-source and the light- responsive means.

5. A device as set forth in claim 1, wherein: a) the enclosure is elongate, and the lens means is disposed at a remote end of the enclosure, and the means for dripping off excess liquid is disposed at the end of the enclosure, and b) the means for dripping off excess liquid is disposed in a plane that passes between the light-source and the light-responsive means.

6. A device as set forth in claim 1, and wherein the enclosure comprises a tube, said lens means being disposed at the end of the tube.

7. A device as set forth in claim 1, and further including a light-barrier on the circuit board, disposed between the light-source and light-responsive means, for intercepting stray light that would otherwise directly impinge upon the light-responsive means from the light-source.

8. A device as set forth in claim 7, wherein said intercepting means comprises a plated-through hole in the p-c board.

9. An optical liquid level gauge, comprising in combination: a) a prism and means mounting the prism in a vessel containing liquid to be measured, b) a p-c board having a light source mounted there- on and a light sensor mounted thereon, said light sensor being disposed in spaced relation to said light source, c) said light source and light sensor being located on the same side of the p-c board, such that stray light from the light source would normally strike the light sensor, d) means mounting the p-c board so that the light source and the light sensor both face the prism whereby light emitted by the light source can strike the prism and be reflected back to strike the light sensor, and e) means comprising a plated through-hole in the p-c board, for intercepting said stray light and for dispersing it so as to block it from striking the light sensor, whereby the latter responds substantially solely to light rays that have been reflected by the prism.

10. In an optical liquid level gauge, the method of reducing the influence of stray light from a light source striking a light sensor, and wherein both the light source and light sensor are mounted in spaced relation on a p-c board, the method comprising the step of providing a plated-through hole in the p-c board at a location between the light source and the light sensor, whereby said stray light is intercepted by the plating on the said plated-through hole, and dispersed thereby.