GB2238382A

GB2238382A - Level detecting device

Info

Publication number: GB2238382A
Application number: GB9024006A
Authority: GB
Inventors: Colin Webb; Trevor Smith
Original assignee: SURE RIGHT WEBB Ltd
Current assignee: SURE RIGHT WEBB Ltd
Priority date: 1989-11-03
Filing date: 1990-11-05
Publication date: 1991-05-29
Anticipated expiration: 2010-11-05
Also published as: GB2238382B; GB9024006D0

Abstract

The device is based on a spirit level system where a bubble 6 is housed within a reservoir 7 of liquid. One side of the reservoir 7 acts to reflect light, from a source 2 disposed on a side of the reservoir remote therefrom, towards a pair of light sensors 1 and 3 disposed one each side of the source 2. Presence of the bubble 6 at a central zone of the reservoir increases reflectance of the light and the device detects a level condition when signals from both sensors 1, 3 are equal. <IMAGE>

Description

LEVEL DETECTING DEVICES This invention relates to level detector devices and more particularly to spirit levels. More particularly, to a device Which may determine level automatically.

Spirit levels currently use a bubble in a fluid contained in a curved reservoir. The bubble has to be aligned between two lines marked on the reservoir. This is not very accurate anL can also be difficult t use in poor lit and if the spirit level has become dirty which is frequently the case in the building trade, where such levels are commonly used.

It Is knowr to detect tne position of a bubble in a spirit level reservoir by means of light sources and receivers. One such disclosure is in EP 349074 where light is directed from a light scurce towards the reservoir and is received by a detector on the opposite side of the reservoir. Where the central portion of the reservoir is filled with liquid, ie. non-level, the light is focused by the liquid, acting as a lens, on the detector. When the central porticn of the reservoir contains the air bubbie, ie. level, the light is diverged at the liquid/air interface and less light is received at the detector. Thus automatic detection is possible, level being indicated by a minimum in light detected.However determination of an absolute minimum is not always easy.

It is an object of the present invention to provide a level detection system which overcomes the above disadvantages and enables accurate measurements to be obtained more easily.

According to the present invention there is provided a level detecting device comprising a reservoir containing liquid and a gas bubble, said gas bubble being adapted to assume a central position in the reservoir when the device is level, means to illuminate a central zone of said reservoir, reflective means on a side of the reservoir remote from said illuminating source, two light sensors disposed substantially equidistantly either side of said illuminating source to sense light from said illumination source reflected by said reflective means and by a surface of said gas bubble, and comparator means input by outputs from said light sensors to determine when said bubble is substantially central and thereby giving increased reflected light equally to both said sensors.

An embodiment of the invention wll ow be more particularly described by way of example and with reference to the accompanying drawings, in which: FIGURE 1 shows schemattcally a level detecting device embodying the invention, in level condition; FIGUR- 2 shows diagrammatically the device of Figure 1 in an unlevel condition; FIGURE 3 shows diagrammatically the device of Figure 1 at a cut-off unlevel condition: FIGURE 4A and 4B show circuit diagrams of an emitter/detector head; FIGURE 5 is a circuit diagram of one of tw identical circuits showing a plurality of LEDs to indicate degree of level when connected to the circuits of Figure 4; and FIGURE 6 is a circuit diagram showing an audible means to indicate degree of level, when connected to the circuit of Figure 5.

Referring now to the drawings, particularly to Figures 1 to 3, a level detection device is shown in which light is radiated from an emission source 2 towards a liquid reservoir 7. Most of the light reaching the reservoir 7 and the liquid mass 4 passes through arriving at a reflective surface 5. This liyht is then reflected back through the liquid to arrive at left and right sensors 1 and 3 in equal amounts. These left and right sensors are disposed equidistantly from the emitter 2 and on the sarge side of the reservoir 7 as the emitter 2.

A low proportion only of the light is normally reflected back to the sensors and is distributed equally between them. When the device is level, r.- is reflected frorr. the lower surface of t-he bubble 6 additiQnally and equally to both sensors 1 and 3. Thus, at level condition the sensors eacn receive an equal amount of reflected light, which is less than the maximum but greater than the minimum.

As the device is tilted away from level on either end, d, the position of the bubble 6 changes relative to end points of the reservoir. As the bubble 6 moves towards one end, it will disrupt reflections from surface 5 towards t sensor at that end, reducing the light input thereto. Initially a greater proportion of light will be reflected from an end of the bubble 6 towards the other sensor, increasing its light input. However, beyond a certain point, the bubble 6 so interferes with normal reflection from surface 5 that a minimum occurs in the input to the sensor at that end. At this point sensing may be discontinued.

Sensitivity of this system can be modified, depending on the required application, by the alteration of the distances of the emitter 2 from the reservoir 7, and the sensors 1 and 3. Also the distances of sensors 3 from the reservoir may be varied. Other modifications possibie are alteration of the angle of reservoir 7 relative to the emitter 2 and sensors 1 and 3. Also alteration of the relationship between emitter 2 and sensors 1, 3 is possible Referring now to Figure 4, 5 and 6, a sensing head, as shown in Figures 1 to 4, comprise a level indicator and d plumb indicator. Mercury switches select which of the indicators is connected to the remainder of the circuit.

Components D1 TR1 TR2 R2-R7 receive a statilized supply from R1/ZD2 junction. As the voltage increases from photo transist@rs TR1 and TR2 to levels beyond that set by the values of R2-R7 each Op Amp switches on or off in sequence, in turn switching on or off LED's D3-D6 and D11.

The values or R2-R7 can be changed or made variable to aiter the switching threshcld or sensitivity of the device, depending on the chosen application. The LED's D3-D6 and D11 are arranged in a sequence, preferably using di@terent colour LED's so that a central one is illuminated when the devic is leve, and progressively outer ones are illuminated is the device tilts further of @ level. As shown, Dll is a central LED. D7 and D6 protect the output of the Quad Op Amp from damage caused by back voltage from any other circuits which control the common VCO stage.

R8-R12 limit the current to the LED's an therefore their brightness.

The circuit shown in Figure 5 is duplicated, once for level and once for plumb.

Mercury switch MSl (Fig 6) switches the -V supply via (H) to a level display and to a level sensing system.

Mercury switch MS2 (Fig 6) switches the -V supply via (I) to a level display and to a level sensing system.

The voltage controlled oscillator (VCO) (Fig 6) frequency is set by the value of R13, R14, C1 and controlled from (F) and (G) plumb and level displays, so that the frequency of the speaker changes stepwisely as level is approached.

A further embodiment of the invention includes a 'level with a magnetized body to facilitate hands free operation when working with metal surfaces.

The measuring head may be set at any desired angle with respect to a levelling edge whereby the device may be used to detetmined whether components are assembled or retain a correct angle. For convenience this correct angle is referred to herein as "level".

The device is sufficiently sensitive to enable it to be use to detect vibration, for example that caused by heavy traffic.

Due to surface tension effects, InitIally the bubble changes shape but does not move. This change ot shape may be utilized to effect the amount of light raflected to the pair of sensors and thereby give highly sensitive results.

Claims

AIMS

1. A level detecting device comprising a reservoir containing liquid and a gas bubble, said gas bubble being adapted to assume a central position in the reservoir when the device is level, means to illuminate a central zone of said reservoir, reflective means on a side of the reservoir remote from said illuminating source, two light sensors disposed substantially equidistantly either side of said illuminating source to sense light from said illuminaLion source reflected by said reflective means and by a surface of said gas bubble, and comparator means input by outputs from said light sensors to determine When saId bubble is substantially central and thereby giving increased reflected light equally to both said sensors.

2. A device as claimed in claim 1, wherein said illuminating source comprises an LED.

3. A device as claimed in either claim 1 or claim 2, wherein said device may be adapted to detect r5 level or a plumb level.

4. A device as claimed in claim 3, wherein mercury switch means are provided to determine whether level or plumb level is to be sensed.

5. A device as claimed in any one of the preceding claims, further comprising means to provide an audible signal when said device is level.

6. A device as claimed in any one of the preceding claims, further comprising illuminable signal means to indicate when said device is level.

7. A device as claimed in claim 6, wherein a plurality of said illuminable signal means are provided, each illuminable in response to a predetermined degree of level.

8. A level detecting device substantially as described herein with reference to the accompanying drawings.