GB2074315A

GB2074315A - Inclinometer

Info

Publication number: GB2074315A
Application number: GB8111160A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-04-22
Filing date: 1981-04-09
Publication date: 1981-10-28
Also published as: DK176281A; NO156544B; FI811026L; DE3115838A1; DE3115838C2; CA1156828A; NO811242L; AU537772B2; DK150079C; GB2074315B; FR2480934A1; DK150079B; AU6937281A; NO156544C; FR2480934B1

Abstract

An inclinometer includes a resilient optic fibre (9) which is firmly held at the top (10) in a holder (8). The held end (10) of the fibre is arranged to co-act with an LED light source (7) and its free end lies close to the surface of a quadrant detector (12) and shines a point of light onto the surface of the detector. The coordinates of the light point and hence the inclination are determined from the outputs of the detector quadrants. Vibrations may also be measured. An additional LED (22) and a lens 25 may shine a second point of light onto the underside of the detector (12) to measure the degree of bending of a bore into which the device is inserted. The LED's (7) and (22) are illuminated alternately to distinguish the measurements. <IMAGE>

Description

SPECIFICATION A Device for the Measurement of Inclinations The present invention relates to a device for the measurement particularly the dynamic measurement of inclinations.

A device of the general kind comprising a resilient thread which is firmly held at one end in a holder and the other, free end of which is arranged to co-act with a light source adapted to irradiate a light-sensitive detector means, can be constructed from the teachings of Swedish Patent Specification No. 141 501 and the US Patent Specification No. 3,324,564. The Swedish Specification No. 141 501 refers to a device having a flexible thread or rod whose free end is loaded with a weight which when the device is inclined causes the thread or rod to bend. The bending stresses and strains occurring in the rod are detected by means of a strain gauge.The US Patent Specification No. 3,324,564 relates to a device having a pendulum whose free end carries an incandescent lamp which is arranged to co-act with a light-sensitive detector in a manner to indicate the angle at which the pendulum is inclined to the vertical. Even though the rigid pendulum of the device according to the US Patent Specification No. 3,324,564 should be replaced with a flexible, loaded rod according to the Swedish Patent Specification No. 141 501, it would still not be possible to provide an inclinometer which is sensitive and which reacts quickly, owing substantially to the relatively high mass of the part which indicates the angle of inclination.

One object of the invention is to provide an inclinometer which is very precise and reacts extremely rapidly, thereby enabling it to be used for indicating those settlements and subsidences which occur even with slight earth tremors.

Hereinafter the inclinometer according to the invention is stated as being used mainly for measuring the inclination of a bore or drilled hole or the like.

Another object of the invention is to provide an inclinometer which will not only indicate any deviation from the vertical, but will also indicate the bend in a drilled hole or bore which is not straight.

According to this invention, I propose a device for measuring inclinations comprising a light source, a light-sensitive detector and an optic fibre suspended by one end adjacent the light source to receive light therefrom, the other, free end being so disposed adjacent the light sensitive surface of the detector, to project thereon a spot of light.

In preferred embodiment for the dynamic measurement of inclinations from the vertical, the device comprises a resilient thread which is firmly held at one end in a holder and the other free end of which is arranged to co-act with the light source arranged to irradiate the light-sensitive detector means. The thread comprises an optic fibre which is unloaded and the free end of the fibre is located close to the light-sensitive surface of the detector means.

The preferred embodiment will now be described in detail by way of example with reference to the accompanying drawings, in which Figure 1 is a simplified axial sectional view of an inclinomter according to the invention having a schematically illustrated inclination indicating means, Figure 2 illustrates a suitable, fundamental detector means for use in the inclinometer according to the invention, Figure 3 is a simplified view of an inclinometer according to the invention for the simultaneous measurement of the curvature of a bore.

Figures 4a, 4b and 4c illustrate the positions oF the measuring points on the detector of the inclinometer when simultaneously measuring the inclination and curvature of a bore from a given line, and Figures 5a and 5b illustrate the inclination and the curvature of the device which gives rise to measuring point positions illustrated in Figures 4a-4c.

Figure 1 is a simplified axial sectional view of a device according to the invention intended for determining deviations from the vertical. When the device of the illustrated embodiment is fully vertical, deviation from the vertical is zero. The device illustrated in Figure 1 includes a housing 1, which in the shown embodiment is assumed to be cylindrical but which may have any crosssectional configuration suitable for the use to which the device is to be put. The housing 1 has an upper cap 2 provided with an opening 3 for a cable 4 having two electrical conductors 5 and 6 for supplying voltage to a light-emitting diode 7, or some other source of light radiation which produces infra-red, ultraviolet or visible light.

Hereinafter it is assumed that the light source has the form of a light-emitting diode and that said diode is supplied with an alternating voltage having a frequency of, for example, 1000 Hz. It will be understood, however, that any suitable frequency may be used and that the diode 7 may be supplied with a direct-current voltage. In the illustrated embodiment, the light-emitting diode 7 is mounted on the upper side of a plug 8, which form a holder for an optic fibre 9. The fibre 9 is firmly held at one end 10 thereof in the holder 8 while the remainder of the fibre is freely movable and is free of any load. The upper end 10 of the fibre 9 is arranged to co-act with the diode 7, and light from the diode will thus be transmitted to the free end 11 of the fibre 9.The free end 11 lies above a detector 12 and is located so close to the surface of the detector that a well defined, small spot of light is projected onto said surface.

The fundamental principle of a suitable detector 12 is illustrated in Figure 2. The detector 12 of the illustrated embodiment has the form of a known, so-called lateral photo detector which constructed about a square plate comprising a semi conductor material. The upper side of the plate is covered with a light-permeable gold layer, while the underside has a thin homogeneous layer of resistive material. Arranged along the periphery of the resistive layer (not shown), adjacent the edges of the plate, are two pairs of mutually opposite discharge electrodes 13,13 and 14,14.

When a point 15 is illuminated, the light flow gives rise to a voltage/current source across the p--n-transition zone present in the doped plate.

This voltage/current source is able to form a closed circuit via said gold layer and the resistive layer with the electrodes 13,13 and 14,14 and thus four part current-flows, one for each electrode, can be registered. The magnitude of these part current-flows is dependent upon the distance of the light spot 1 5 from the origin 1 6 of the co-ordinates in the incorporated XY-system.

The four current-flows taken out through the electrodes 13,13 and 14,14 are supplied, via electrical conductors 17,18,19 and 20, to an analyser 21 which discloses the position of the light spot in the co-ordinate system, either directly or indirectly. The location of the light-spot 15 is identical with the position of the end 11 of the fibre 9, and having knowledge of the bending characteristics of the fibre 9 and its length it is possible to give the inclination of the housing 1 relative to the vertical both directly and precisely.

The maximum outward bending of the fibre 9 with an inclination of 900 can be given any desired value by selection of fibre material, fibre length and cross-sectional area. The crosssectional area need not be constant along the whole length of the fibre, although there is preferably used a fibre of uniform thickness and of circular cross-section. As will be understood, the measuring accuracy of the device depends upon the characteristics of the fibre and upon the detector. A detector of the kind described above gives the position of the centre of the light spot with an accuracy of 10-6 metres, or higher.

Depending upon the length and cross-sectional area of the flexible, resilient fibre 9, it is possible when using such a detector to obtain a measuring accuracy of 1 (one) microradian. When the demand for measuring accuracy is not so high, it can be mentioned that an accuracy of 0.010 can be obtained with a glass fibre having a length of about 10 cm and a diameter of about 50 micrometers within a measuring range of +900.

The described device can be used within a multiplicity of technical fields. Thus it can be used as a conventional plumb-bob and as a sensor in the automatic alignment of objects at a certain angle of inclination, for example in the remote horizontalization of underwater apparatus. The device illustrated in Figure 1 can also be used for continuously measuring extremely small movements in the earth's crust, thereby functioning as an avalanche early-warning system, and in loose deposits, thereby to act as an early warning system in the event of land slides, etc. The short reaction time of the fibre, and similarly the short rise time of the described detector, about one microsecond, enables the device to be used as a vibration meter for determining vibration frequencies and amplitudes.

It should be noted that the described electrode is only one of various kinds of photodetectors which can be used to detect the position of the free end of tip 11 of the fibre 9 relative to the vertical. In certain cases it may be suitable, and desirable, to arrange a system of lenses between the tip 11 of the fibre 9 and the detector 12.

It will be apparent that the device illustrated in Figure 1 is only intended to indicate angles of inclination, i.e. a function of the distance from the origin 1 6 and the light spot 15, and that it cannot be used in its illustrated state to show, for example, the presence of a bend in a bore in which the device is inserted.

In order for the device to indicate a crooked bore, it is provided with an optical system of the kind shown in Figure 3 for example. In this embodiment the housing 1 is extended with a cylindrical part 1'. Arranged in the lower end of the part 1' is a light source 22, for example a light-emitting diode of the same kind as the lightemitting diode 7, said diode 22 being supplied with a voltage over two electrical conductors 23 and 24. The light from the light-emitting diode 22 is focused onto the underside of the detector 12 by means of a lens or a system of lenses 25. As will be seen from the drawings, the detector 12 of the Figure 3 embodiment has been exposed by removing the bottom 26 in Figure 1.When the housing 1, 1' is free from all bends, the light spot 27 generated by the lens arrangement 25 will lie on the origin 16 (Figure 2), but if the device is inserted into a bore which is somewhat crooked, the housing 1, 1' will bend slightly, causing the light spot 27 generated by the fixed lens arrangement 25 and the fixed light source 22 to move across the undersurface of the detector 12.

It will be noted that if, as before described only one detector 12 is used for two light spots 15 (Figure 2) and 27 (Figure 3) it is necessary to alternately extinguish and illuminate the two light-emitting diodes, in order for the detector 12 to give the correct values. To this end there is provided a voltage source 28 which alternately supplies an ignition voltage to the diode 7 and the diode 22, whereby only one light spot is projected onto the detector 12 at any given time. The X-Ysignals generated by the detector 12 are sent to a recorder 29, a data processor or some other like apparatus and the signals generated by the lightemitting diode 7 and the light-emitting diode 22 respectively are separated by synchronising pulses from the voltage source 28 over a line 30.

It is also possible, of course, to use two mutually independent detectors superimposed one upon the other, of which one is arranged to co-act with the light-emitting diode 7, in the manner described with reference to Figure 1, and the other is arranged to co-act with the lightemitting diode 22.

For a closer explanation of the device according to Figure 3, reference is made to Figures 4a-4c and Figures 5a to 5b. Figure 5a illustrates a bore in a horizontal X-Y-plane, and it will be seen that the bore is slightly curved in a clockwise direction. Figure 5b shows the same bore in an X-Z-plane, which is vertical and in which the bore extends rectilinearly. In the Figure 3 embodiment the housing 1, 1' is assumed to be enclosed in a long tube, for example a liner tube, which is successively fed into the bore as the bore is being drilled.The housing 1, ' will therewith bend in a manner corresponding to that illustrated in Figure 5a, meaning that the light spot 27 will obtain a position relative to the origin 1 6 of the detector according to Figure 4a. It will be equally apparent that rotation of the housing 1, 1' about its long axis, which is unavoidable, will not alter the distance of the light spot 27 from the origin 16, and neither will the light spot 27 be moved relative to the point 1 5 which indicates the inclination according to Figure 5.The angular position in the co-ordinate system will, of course, be changed with rotation of the co-ordinate system, as evident from Figures 4a 4c. The light spot 1 5 will also take a specific position in the coordinate system, irrespective of the rotation of the housing 1, 1' about its longitudinal axis.

The radius of the bend in the bore at each separate measuring point is a function of the distance between the light spot 27 and the origin 16, since the housing 1, 1' exhibits the same bend and has, of course, a diameter substantially corresponding to the diameter of the bore. The centre of the bend is calculated trigonometrically with aid of the co-ordinates of the light spot 15, which always lie in a vertical plane through the origin 1 6. Thus, irrespective of the position of rotation of the housing 1, 1' about its longitudinal axis, there can be obtained all of the values required for drawing up curves which show precisely the inclination and curvature of the bore, either directly or with the aid of a data processor.

The requisite voltage can be supplied to the equipment either from the ground surface or from a voltage source incorporated in the housing 1, 1'.

Similarly, the position signals can be sent to the ground surface, via a cable, or the requisite circuits for successively storing and calculating positional information can be incorporated in the housing 1, '. The housing 1, 1' should be relatively readily bendable, to allow it to pass bends of small radius. The length of the housing, 1, 1' is decisive in enabling the bend to be registered, and if great precision is desired, the housing should thus be long. Of course, the accuracy of the device depends upon the signal/noise ratio of the electronic circuits receiving the signals from the detector or detectors. The resolution power of a detector of the kind described is of the order of 10-6 metres.

With the aid of relatively simple electronic devices, it should be possible to determine the inclination of about rut0.01 0, and the bend radius up to about 100 km. This means that in the worst of cases it is possible to determine the configuration of a bore having a length of 1000 metres with an error in the order of 5 metres, since with continuous measurement errors constantly accumulate with the same sign.

Claims

1. A device for measuring inclinations comprising a light source, a light-sensitive detector and an optic fibre suspended by one end adjacent the light source to receive light therefrom, the other free end being so disposed adjacent the light sensitive surface of the detector, to project thereon a spot of light.

2. A device according to claim 1, wherein the detector is arranged to produce signals disclosing the position of said light-spot relative to a given reference position.

3. A device according to claim 1, wherein the detector, the light source and the optic fibre are incorporated in an elongate, flexible housing in which a lens is also arranged in the said housing beneath the detector means to project onto the detector a punctiform image of a further light source.

4. A device according to any one of claims 13, comprising circuits for processing signals from the detector means.

5. A device according to any one of claims 14, wherein the light source or light sources each comprise a light-emitting diode.

6. A device according to claim 5, wherein the light source or the light sources is or are arranged to be supplied with an alternating voltage.

7. A device for measuring inclinations constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.