WO1994006032A1

WO1994006032A1 - A system for determining the interior structure of a glowing vessel

Info

Publication number: WO1994006032A1
Application number: PCT/SE1992/000616
Authority: WO
Inventors: Mats Lundqvist; Anders Melin
Original assignee: Geotronics Ab
Priority date: 1991-03-12
Filing date: 1992-09-08
Publication date: 1994-03-17
Also published as: SE9100746D0; SE9100746L; SE468109B

Abstract

A system for measuring the interior of a hot glowing vessel (1) in a metal works with the aid of an electric distance measuring device (200) which is protected against radiant heat from the vessel and which performs a measuring operation with the aid of a light beam which is emitted from a light beam source and reflected back from the measuring point in approximately the same direction as that in which it was emitted. The distance measuring device is provided with an angle indicator for at least two mutually different directions and also includes a calculating device (24) which is provided with a memory and which functions to calculate the position of the vessel in relation to the distance measuring device. All measurements are calculated in a coordinate system related to the vessel. The internal surface dimensions of the vessel are calculated with the aid of measurements made on selected parts of the internal surface. The distance measuring device (200) is placed on a stand (2; 6) which can be moved along a predetermined movement path (7). On the basis of information stored in the memory (32, 36) relating to the extension of the path in relation to the vessel and the position of the distance measuring device on the path, the calculating device (24) calculates the position of the distance measuring device in relation to the vessel at each point along the path.

Description

A System for Determining the Interior Structure of a Glowing Vessel

The present invention relates to a system of the kind set forth in the preamble of Claim 1.

Vessels of mutually different kinds and construction are used in the treatment and handling of molten metals in metal works. In order to enable the vessels to withstand the high temperatures that occur (in excess of 1000°C) , the vessels are lined with refractory material, such a dolomite or magnesite, for instance. The linings are initially several decimeters thick, but become eaten away and worn in time, some points of the vessel being subjected to greater wear than others, for instance in the region of the drainage hole, joints between lining bricks, pouring lips, etc. When the thickness of some part of the lining material in the vessel is reduced to a critical thickness value which may not be exceeded, owing to the risk of burning through the supporting shell or mantle, it is necessary to take the vessel out of operation and reline the vessel. Such relining is expensive, partly due to the actual cost of the repair and partly because the vessel must be taken out of operation for some length of time. Consequently, it is highly desirable to be able to measure the thickness of the lining continuously, to the greatest possible extent, so as to have constant access to relevant information relating to lining thickness. This enables the lining to be utilized optimally without risk of _burning through the lining and without relining the vessel unnecessarily when the lining still has some useful life. SE 7414531-9, with the same applicant as that of the present invention, teaches a system for measuring the distance to a point on the inner wall of a furnace. This system has a measuring accuracy of about 5 mm with respect to lining thickness, and also has a relatively short measuring time and is able to evaluate the mea¬ surement values rapidly. Thus, this system is able to provide a good picture of the vessel interior with a satisfactory degree of accuracy when a sufficient number of measuring points are determined within the vessel, so as to obtain a lining profile which can be compared with a corresponding profile of a newly lined vessel. As will be apparent from SE 7414531-9, it is essential that the configuration of the lining profile can be determined in an axial direction and also peripherally around the vessel (the furnace) . This is done with the intention of achieving the greatest uniformity possible in the wear on the lining, by controlling the process. Obviously, this will afford economic advantages. The measuring principle is based on the use of an electrooptical distance measuring instrument which operates in accord¬ ance with the phase comparison principle. The different components of the distance instrument and their individ¬ ual functions are described in detail in SE 7414531-9, and will therefore only be described briefly in this document. Electronic distance measuring devices of the phase comparison type operate to measure the distance to an object, by comparing the phase of a transmitted modulated light beam and the light signal that is re- ceived after having been reflected back by the object. The light source used is a low-power laser.

In one relevant application, the distance measuring device and the auxiliary devices associated therewith are incorporated to form a complete measuring unit which can be placed in positions appropriate for carrying out the measuring process. The distance measuring device is also protected in the unit against radiation heat from the object being measured.

By measuring at three points on the outside, for in¬ stance, of an ingot mould with the aid of the measuring unit, distance and angle deviations are obtained which are converted in a calculating device, which is provided with a memory, to a coordinate system which is related to the mould, using a mathematical method developed by Geotronics. In this regard, the measuring unit can be placed stationarily in any desired position in relation to the measured object (the mould) on the open side thereof. When the relative positions of the measuring unit and the measured object have been determined, the requisite number of selected parts of the interior of the mould are measured through the mould opening, the dimensions of the inner surface of the mould being calculated by the calculating device and stored in the memory.

One problem arising from the use of measuring equipment which is stationary during the measuring sequence, this problem becoming more and more acute, is that certain points in the vessel are unaccessible to the measuring equipment when so positioned. It has been found essen¬ tial to have access to and to be able to measure a sharply defined hollow in the vessel, e.g. a narrow gap or cavity between two brick sections, which means that the measuring unit must be capable of being positioned accurately in both the horizontal and the vertical planes. Although attempts have been made to move the measuring equipment to different positions, present-day equipment is found heavy and difficult to move. Such measures also involve a significant waste of time in determining the new position of the measuring unit in relation to the measured object after each movement of said unit, before the work of actually measuring the relevant area of the inner surface of the object can commence. If the vessel is allowed to cool excessively, energy is consumed in reheating the vessel, and energy, like time, is expensive. Furthermore, the radiation heat from the interior of the furnace or mould is intense and the surroundings are also noisy and dusty, which makes it unpleasant for the person who operates the measuring equipment and stands in front of the measured object.

Obviously, this will have a negative effect on measuring accuracy and also on the number of measuring processes that need to be carried out, so that the series of measured values necessary for optimal utilization of the vessel lining will not be sufficiently detailed. Too few measuring points and long time intervals between the measuring processes will increase the risk of burning through to the supporting shell, mentioned in the introduction.

Accordingly, the fundamental object of the invention is to enable the measuring unit to be positioned in front of the vessel opening so that the measuring unit, in each position, is related to the coordinates of the vessel and can be adjusted so as to be able to measure on each point of the inner surface of the vessel. The person who carries out the measuring processes shall also be protected against thermal radiation from the measured object and against other disturbing environ- mental factors.

This object is achieved in accordance with the invention by means of a system of the kind defined in the intro¬ duction and having the characteristic features set forth in the characterizing clause of Claim 1. Advantageous embodiments and further developments of the invention are defined in the dependent Claims.

The invention will now be described in more detail with reference to a number of preferred exemplifying embodi¬ ments thereof and also with reference to the accompany¬ ing drawings.

Figure 1 is a perspective view of a preferred embodiment in which the measuring unit is mounted on a stand which is mobile in a circular arc in front of the vessel;

Figure 2 is a top view of the arrangement shown in Figure 1 and illustrates an example of mounting the stand in front of the vessel on a circular arcuate path;

Figure 3 is an exploded view of the measuring unit and shows a part of a slide on which the measuring unit is placed, said view being in larger scale than Figure 1;

Figure 4 illustrates different arrangements for trans¬ porting a measuring unit to the measuring site, said unit having a cabin-like construction;

Figure 5 illustrates one embodiment of an angle indica¬ tor which indicates the rotational position of the slide;

Figure 6 is a block schematic of one embodiment of the calculating device forming part of the inventive system;

Figures 8 and 9 illustrate further embodiments of the path travelled by the stand;

Figure 10A is a perspective view of still another em¬ bodiment, in which the measuring unit is placed on a stand which is mobile in two planes in an arcuate path in front of the vessel; and Figure 10B illustrates movement of the stand in both the horizontal and the vertical plane.

Figures 1 and 2 illustrate a vessel 1, for instance a mould, which lies on one side on a supporting underlay in a metal works, said mould having just been emptied of its molten content. The hot, glowing interior 3 of the vessel is therewith accessible through the vessel open¬ ing. A measuring unit constructed in accordance with one preferred embodiment of the invention is housed in a cabin-like structure 2 which is positioned in front of the vessel so that the measuring components housed in the cabin, together with the operator, are protected against thermal radiation from the interior 3 of the vessel l and against dust and noise from the surround¬ ings.

According to one preferred embodiment, the cabin 2 is provided with an openable door 4 and a window 5, and houses the electronic measuring equipment, comprising a distance measuring device and associated calculating means. As will best be seen from Figure 3, the cabin 2 is placed on a stand which can be moved around a prede¬ termined path 7, which extends generally transversely to the vessel centre line.

One end 8 of the path 7, or track, may, for instance, constitute a fixed point in the room. In the case of the Figure 3 embodiment, the stand 6 has the form of a slide with wheels 9 which roll along the path as the slide is moved. The stand is rotatably attached to an attachment 12 in front of each vessel, with the aid of two attach- ment arms 10 and 11. In the illustrated embodiment, the attachment 12 is anchored to the supporting underlay. although it may, of course, be mounted in any desired manner in front of the vessel, e.g. hanging from a beam or the like.

The connection between the attachment and the attachment arms 10 and 11 is releasable, so that a slide 6 can be mounted in front of a measured object 1 when the object is to be measured and removed therefrom when not in use. As illustrated in Figure 4, empty moulds 1', 1" can be placed at a number of stations and there examined, prior to being taken back into use. It cannot be taken for granted that a mould whose internal dimensions need to be measured will be located at a particular station, and consequently it must be possible to move the inventive equipment to the station concerned. Figure 4 illustrates that a cabin, such as the cabin 2 ', can be moved into position with the aid of a truck or, such as cabin 2", with the aid of a traverse crane, the lifting hook of which is then attached to an eye A fitted to the cabin roof.

In the Figure 5 embodiment, the attachment has a posi¬ tion indicating element 13 which functions to disclose the angle at which the arms are rotated in relation to the attachment. This angle indicating device may have many different forms, the essential thing being that the device will indicate the angle of rotation of the arms around the attachment. In the Figure 5 embodiment, this device has the form of a number of promontories arranged in close relationship in a semi-circular arc around the attachment itself and a device on the attachment arm coupling which detects whether it is located over a promontory or not. In the illustrated case, the device produces pulses with each transition from one promontory to another and these signals are delivered to the calcu¬ lating unit of the distance measuring device for calculating said angular position so as to calculate the position of the cabin in relation to the vessel 1, as described in more detail here below.

Alternatively, as illustrated in Figure 3, a sensor 14 may be mounted on the stand 6 so as to indicate each movement of the stand around its movement path, either through the medium of one of the stand wheels 15 or through the medium of a roller (such as 16 in Figure 2) which is in direct abutment with the movement path 7. The path 7 may also be provided with abutments at a number of predetermined locations. In this case, the position of the measuring unit is determined with the knowledge of the position of the abutment concerned in relation to the aforesaid fixed point.

Figure 6 is a schematic illustration of the distance measuring device 200 and its electronics. The measuring unit is constructed in a manner similar to the measuring unit described in SE 7414531-9 and includes generally a transmitter unit 17 which emits a modulated light beam from a laser beam source. The beam is reflected back from the inner surface 3 of the vessel onto a receiver 18 in which a detector is mounted. The beam modulation is converted in the receiver to an electric signal. This signal is amplified in an amplifier 19, demodulated in a demodulator 20 to which a signal from an oscillator 20 is also delivered, this oscillator also sending a signal to the modulator 22 of the transmitter 17. A phase comparator 23 compares the phases between the demodulat¬ or 20 and the modulator 22 and the output signal of the phase comparator is delivered to a calculating unit 24.

The vertical and horizontal angles of the instrument, i.e. the vertical and horizontal rotation of the dis¬ tance measuring instrument in relation to a reference position of the instrument itself are also measured in a conventional manner, as illustrated in block 25. Block 26 symbolizes an external infeed unit for feeding data relating to the measured object into a memory unit 28 coupled to the calculating unit 24. The data stored in the memory comprises coordinates which denote the inner and the outer configuration of the vessel and which are specific for a given vessel. These coordinates are related to the intrinsic coordinate system of the vessel.

By initially placing the measuring unit in, for in¬ stance, one end position 8 of a circular arcuate path and, with the aid of the distance measuring device, measure this end position as a fixed point in relation to the vessel coordinate system, there is determined a starting position for the measuring processes to be carried out, this starting position being fed into the memory 32 via the block 36. Parameters which define the configuration of the movement path 7 are fed into the memory 32 via the block 30, said memory being coupled to the calculating unit in turn. Also coupled to the memory 32 is a sensor 34 which indicates the position of the measuring unit along said path, these values being fed into the calculating unit 24 via the memory 32. As mentioned above, the position of the measuring unit can be indicated in different ways, for instance with the aid of an angle indicator located at the fixed point 12 on the slide 6, or with the aid of roller device 16, or the like. The memory 32 contains information concerning the geometric data relating to slide and cabin, for instance the lengths of the attachment arms, this geo¬ metric is also beingsupplied to the calculating unit which, on the basis of this data, calculates the posi- tion of the distance measuring device in the coordinate system of the measured object. These calculations are carried out in accordance with geometrical principles which are well known to the person skilled in this art and therefore need not be described in detail here. Neither need the computer program particular to the calculating unit be described in great detail, since the manner in which such programs are constructed is consid¬ ered a matter of routine.

The specific features of the invention reside in the equipment which enables the position of the measuring unit in relation to the measured object to be updated continuously. These features enable a sequence of mea¬ suring operations to be carried out quickly and easily, by placing the measuring unit in selected positions along the movement path. The results of these measuring processes are stored in respective memories and are processed in the calculating unit, whereby an image, or picture, of the relevant internal profile of the vessel is displayed on a presentation unit 38, or is drawn on paper in said unit. Preferably, a profile of the highest internal measurement the measured object may have before needing to replace the lining is also presented at the same time, so as to provide a reference for comparison with the measurements actually obtained. The presenta- tion unit may be a terminal screen, a writer or some other type of presentation panel or unit. Obviously, it is not always necessary to carry out a complete series of measurements which would provide a complete picture of the inner profile of the vessel. The operator may choose to measure solely one particular point where the wear is greater than the wear in the remainder of the vessel, in order to quickly avoid catastrophic partial penetrative burning of the lining.

The calculating device 24 has at least two working modes, of which the first includes feeding information relating to the physical extension of the movement path into the memory of the calculating device prior to carrying out the measuring process concerned, by measur¬ ing the vessel from at least one position on the move- ment path with a known position on the path at the time of taking the measurement and calculating the position of the path in the vessel coordinate system, and the other working mode is measuring mode which involves measuring the measurement points and calculating their respective positions in relation to the vessel coordi¬ nate system.

The movement path need not necessarily be fixedly mount¬ ed in the room, but may well comprise, for instance, a loose rail 40, 41, 42 which is laid on an even support¬ ing surface, as illustrated in Figure 7. Since the rail will have a given weight, it need not be secured to the underlying support surface. The measuring unit is then able to travel backwards and forwards on this movement path, which when the measuring work has been completed can be moved to the next object to be measured.

To facilitate this movement of the movement path between different objects to be measured, the path is preferably made collapsible and capable of being attached to the cabin 2. Figure 7 shows a curved rail, although the embodiment which includes a loosely-placed straight rail affords greater security against unintentional movement of the rail.

Figure 8 illustrates an alternative embodiment of the invention in which a movement path 50 comprises a straight rail 51 which can be placed in any selected position on a flat support surface. The wheeled slide 52 carrying the measuring unit is placed on the rail and moved preferably to one end thereof, and a measuring process relative to the vessel coordinate system is carried out. The measurement values obtained and the values which represent the direction in which the rail extends and the shape of the rail, in this case straight, are inserted into the relevant memory unit 32 (Figure 6). A sensor 53 is connected to one of the wheels 54 and continuously delivers information to the memory unit 32 via the unit 34. This enables the unit 24 to calculate the position of the measuring unit in relation to the coordinate system of the measured object for each possible position of the measuring unit along said movement path.

Figure 9 illustrates a further alternative embodiment of the movement path 60. In this case, the path has a straight centre part and a curved part at each end of the straight part, these curved parts curving towards the measured object. Similarly to the embodiment illus¬ trated in Figure 8, values relating to one end point of the rail, the direction in which the rail extends and the configuration of the rail are fed into the memory unit 32. This embodiment also includes a sensor 63 which is connected to one wheel 64 of the slide 62 for con¬ tinuously feeding to the memory unit 32 information relating to the position of the slide along its movement path.

Figure 10A shows still another alternative embodiment in which the cabin 2 is mounted on a stand 6. The stand is mounted on a link-arm arrangement which enables the stand to be adjusted to selected positions and is pro¬ vided on its underside with an attachment 65 in the form of a universal joint. The cabin 2 is provided with an attachment 66 in the form of a ball-coupling on the upper part of respective side parts. Each of the attach¬ ments 66 is connected through a respective link-arm 67 to corresponding attachments 68 anchored in the under¬ lying supporting surface. The attachments 68 are com¬ prised of ball-couplings whereas the attachment 70 is comprised of an "active universal joint", which is described in more detail hereinafter. In the case of the Figure 10A embodiment, the supporting surface is a supporting wall but may also equally as well be a slab or plate lying on the ground or a holder device suspend¬ ed from the ceiling. The link-arms 67 have mutually the same length and each link-arms has a triangular cross- section and is comprised, for instance, of three round steels which are joined together by means of lattice¬ like spacers, so as to be able to withstand bending loads and breaking and tensile forces. The two upper ends of the link-arms are attached to the freely rotat- able part of respective ball-couplings with the aid of the attachments 66 and 68. The two ends of the bottom link-arms are attached to respective attachments 65 and 70. The attachment 70 also forms a means for driving and manoeuvering the link-arm arrangement and includes a holder 72 which is firmly anchored to the supporting surface. Mounted in the holder 72 is a servo-motor 74 having a vertically extending shaft 76 on which the horizontal part of a generally U-shaped fitting 78 is rotatably mounted. A pivot member 80 is pivotally mount¬ ed from the vertical legs of the U-shaped member and has a shaft pivot 82 which projects out through one of the vertical legs. The shaft pivot is non-rotatably connect¬ ed to the gear of a gearing 84 mounted on the shaft concerned. A further servo-motor 86 is mounted on the same leg, so that the output shaft of said motor extends vertically downwards. The shaft is herewith non-rotat¬ ably connected to the worm screw of the gearing 84. The servo-motor 86 and the worm gear 84 are hereby self- locking with regard to torque acting on the pivot member 80 from the relevant (rotatable) link arm 67. The two servo-motors 74 and 86 are connected by connecting devices, not shown, to a unit (also not shown) for manoeuvering and driving the motors.

The relative distance between the two upper attachments 66 corresponds to the relative distance between the attachments 68. The bottom attachment 65 is spaced at the same distance from the two upper attachments 66 as the attachment 70 is spaced from the upper attachment 68. Since the distance between the two pivot points of respective link arms is the same for all three link arms, the link arms will thus always be parallel with one another irrespective of the angular rotation of the link arms in relation to the supporting surface. Conse- quently, the cabin 2 will constantly maintain its atti¬ tude in which the front side of the cabin constantly faces towards the measured object with each possible angular deviation. Appropriate activation of the servo¬ motors 74 and 86 by means of the manoeuvering unit will cause the pivot shaft 76 and 82 to rotate through a given angle α and β respectively, as illustrated in Figure 10B. In turn, this means that the U-shaped member 78 and also the bottom arm 67 will be swung through an angle of - in the horizontal plane, while the same arm is swung through an angle of β° in the vertical plane by the pivot member 80. Because the upper link-arms accom¬ pany each rotational movement in both the horizontal and the vertical plane, as a result of the ball-coupling suspension, the measuring unit mounted in the cabin 2 can be brought to desired positions with free sight into the hot glowing vessel that is to be measured- up. The cabin 2 is herewith moved along a path x in the horizon¬ tal plane and along a path y in the vertical plane. The calculating unit calculates the position of the distance measuring device in relation to the vessel at each point on the two aforesaid paths, on the basis of information stored in the memory 32, 36 (see Figure 6) relating to the extension of the three paths in relation to the vessel and the position of the distance measuring device on each of said paths.

The ball-coupling attachment 66, 68 may also be replaced with universal joints which are mounted for free rota¬ tion, or by some other type of lift coupling that can be adjusted in all directions. If desired, the "inactive" universal joint 65 can be replaced with an "active" universal joint, similar to the universal joint included in the attachment 70, in order to obtain a driving force which is sufficiently powerful to manoeuver the cabin 2. It is also conceivable that one or more of the attach- ments 66, 68 may have a form similar to such an "active" university joint.

It will be understood that this embodiment is not restricted to its use in conjunction with a cabin, but that the link system can also be used to move a measur¬ ing head which then, in turn, is coupled to a stationary station through the medium of physical lines or through the medium of signals transmitted without the aid of physical lines. This measuring head may include a dis- tance measuring device and also a sighting device, so that an operator placed at the stationary station is able to see the area in which the measuring head is to perform a measuring operation. The measuring head may also be provided with a remotely controlled pivot ar- rangement which rotates in selected directions, prefera¬ bly in horizontal and vertical directions, and also includes a horizontal and vertical angle indicator.

The invention is not restricted to the illustrated and described embodiments thereof, since these embodiments can be modified and varied within the scope of the following Claims. Other combinations between the various embodiments are, of course, also conceivable. For in¬ stance, the movement path may be made collapsible and, in its collapsed state, carried on the measuring unit, irrespective of whether the path has an arcuate or straight configuration or has some other configuration suitable for a particular measured object. The cabin may also be equipped with vertical moveable devices (not shown) for raising and lowering the distance measuring device and, optionally, also the operator, so that the operator is able to move the position of his observation place also vertically in relation to the measured object 1. Data relating to this vertical shift in the observa¬ tion place is then, of course, delivered to the unit 34 (Figure 6) and from there to the memory unit 32.

Claims

1. A system for measuring the interior of a vessel (1) with the aid of an electronic distance measuring device (200) which measures with the aid of a light beam that is emitted by a light beam source, reflected from within the vessel with direct reflection on the measured point and reflected light is received in approximately the same direction as that in which it was emitted, said system including a calculating device (24) which is provided with a memory and which functions to calculate the position of the vessel in relation to the distance measuring device so that all measurements are calculated in a coordinate system related to the vessel, and which also functions to calculate the inner surface dimensions of the vessel with the aid of measurements carried out on selected parts of said inner surface, c h a r a c ¬ t e r i z e d by the following combination:

The distance measuring device (200) is mounted on a stand (2, 6; 52; 62) which can be moved to a selected position (7; 50; 60) in a predetermined fashion;

on the basis of information stored in the memory

(32, 36) relating to the movement pattern of the stand in relation to the vessel and the position of the dis¬ tance measuring device on the stand, the calculating device (24) calculates the position of the distance measuring device in relation to the vessel at each point on the path from which a measuring operation takes place and calculates each measurement in relation to the vessel coordinate system;

whereby even positions of those points which cannot be reached by a stationary distance measuring device during the whole of the measuring operation can also be mea¬ sured and calculated, and an operator is able to choose freely during a measuring operation to carry out the measuring operations from directions which will provide the best possible view, or sighting line, to the measur¬ ing point within the vessel relevant at that time.

2. A system according to Claim 1, c h a r a c ¬ t e r i z e d in that the stand can be moved along a predetermined path (7; 50; 60) with at least one move¬ ment component being transversal to the centre line of the vessel; and in that the predetermined movement path (7; 50; 60) is obtained by attaching the moveable stand (2, 6; 52; 62) with the aid of a non-elastic tie (10, 11) to an attachment (12) firmly mounted in front of the vessel, thereby enabling the stand to move around a circular arc in front of said vessel.

3. A system according to Claim 2, c h a r a c - t e r i z e d in that the stand (2, 6; 52; 62) carrying the distance measuring device (200) can be moved between different stations in which a hot glowing vessel may be located and can be detachably connected to said tie, of which one is found at each station.

4. A system according to Claim 1, c h a r a c ¬ t e r i z e d in that the stand carrying the distance measuring device is provided with a movement path (40-42) which is fixed to the stand and which can be placed in front of the hot glowing vessel to be mea¬ sured.

5. A system according to any one of the preceding Claims, c h a r a c t e r i z e d in that the calcu- lating device has at least two working modes, of which a first mode includes inserting into the memory of the calculating device information relating to the movement pattern of the positioning arrangement prior to carrying out a relevant operation, by measuring-up the vessel interior from at least one position in front of the vessel and using a position which is known at the mea¬ suring occasion, and calculating the position of the positioning arrangement in the vessel coordinate system, and the other measuring mode involves measuring points and calculating the positions of these points in rela- tion to the vessel coordinate system.

6. A system according to Claim 2 and 5, c h a r a c ¬ t e r i z e d in that movement of the distance measur¬ ing device along the movement path is measured with the aid of measuring wheels (16) which move in the direction of said path, wherein signals indicating movement of the measuring wheel are fed to the calculating device (24).

7. An arrangement according to any one of the preceding Claims, c h a r a c t e r i z e d in that the vessel is, e.g., an ingot and that the interior surface of the vessel glows with heat; and in that the stand carrying the distance measuring device has the form of a cabin (2) which houses the distance measuring device and an operator; and in that the cabin is provided with means which enables it to be moved readily to a measuring position in front of the vessel with the aid of a lift¬ ing device (Figure 4).

8. A system according to any one of Claims 1, 3-5, c h a r a c t e r i z e d in that the stand is mounted on a link-arm mechanism and can be adjusted to any selected position in front of the vessel through the guiding action of a joint means in the link-arm mecha- nism.

9. A system according to Claim 8, c h a r a c ¬ t e r i z e d in that the joint means includes a uni¬ versal joint whose two shafts are controllably motor driven.