Such measurement are used in particular-but not exclu- sively-within the fields of aviation and navigation, wherein icing can constitute a substantial safety hazard when it comes to wrecking.

The problem arises as a result of atmospheric precipita- tion, such as rain and mist, that has in its supercooled state a known propensity to freeze on to objects, such as hull and machine parts on vessels as well as aeroplanes.

Thus, in pactise critical weather conditions have often necessitated manual observations with a view to forming an impression of the acute risk of icing, in order to en- able warning of aeroplanes and vesses, if necessary.

It is a problem in this context that such manual observa- tion is based on a subjective discretion, and that conse- quently a standardised value for the risk of icing is not accomplished. Thus, a warning based on such subjective discretion will be associated with a good deal of insecu- rity, and the person who receives the warning cannot readily form a reliable picture of the risk of icing, ex- cept by relying on the recommendation of the issued warn- ing.

Accordingly, US patent No 4,730,485 and published NO pat- ent application No 151,060 teach apparatuses configure

for carrying out a more standardised measurement of the amount of atmospheric precipitation.

Thus, US patent No 4,730,485 teaches a stationary meas- urement device configure for measuring wind velocity as well as wind direction, but it is also suitable for meas- urement of the current icing.

Published NO patent application No 151,060 discloses a stationary weighing apparats for weighing an amount of atmospheric precipitation in the form of snow or ice that settles on a substantially horizontal weighing plate.

However, it is a problem in connection with these prior art devices that icing often occurs in situations when the air is relatively still, and that the icing factor measured by such devices are erroneous since only small amounts of ice are deposited on the devices.

It is a further problem in connection with the prior art device known from published NO patent application No 151,060 that atmospheric precipitation other than super- cooled water may deposit on the weighing plate and thus an erroneous weighing results in relation to the icing factor.

It is therefore the object of the present invention to provide a method and an apparats whereby it is possible, in almost all weather conditions, in particular also light winds and still air, to provide a standardised measurement result or a standardised value for the icing factor.

This is achieved with the present invention by the method according to claim 1, or by use of an apparats according to claim 7.

The method according to the present invention is thus characterised in comprising the following process steps: providing at least one surface element made of a material suitable for ice in atmospheric air to freeze there on, said element having a predetermined surface area; tempering the surface element (s) to a temperature that corresponds essentially to the temperature of the atmos- pheric air, following which a relative movement is pro- duced with a predetermined velocity between the atmos- pheric air and the surface element (s), preferably by mov- ing the surface element (s) through the atmospheric air, and at a predetermined period of time, and wherein the thickness or mass of the ice frozen fast onto the surface element is subsequently measured by means of a mesure- ment device intended therefor.

This means, on the one hand, that atmospheric precipita- tion other than supercooled raindrops or mist can only with difficulty settle on the surface elements and ad- versely influence the measurement results, and that it is hereby possible to perform relatively accurate mesure- ments of the icing factor, also in relatively still air.

In case the factor measured is the thickness of the ice layer, it is advantageous-to obtain a representative value therefor-to measure in a number of points, pref- erably in one or more points on each surface element, the

measurement results subsequently being summarised to a single value.

The value thus measured for the thickness of ice layer or weight increase will be a standardised factor that indi- cates a relative risk of icing of eg aeroplanes or ves- sels in the area in which measurement is performed. It goes without saying that the value can only be indicative of the risk since, obviously, it will vary more or less compare to the place where the measurement was per- formed.

The method can advantageously be exercised by use of an apparats as featured in claim 7, said apparats compris- ing at least a surface element made of a material suit- able for ice in atmospheric air to freeze there on, and said surface element having a predetermined surface area, and wherein the apparats further comprises means that are configure for moving the surface element through the atmospheric air at a predetermined velocity and for a predetermined period of time; and wherein means are also provided that are configure for measuring the thickness or the mass of the ice frozen fast onto the surface ele- ment after lapse of the predetermined period of time dur- ing which the surface element is moved through the atmos- pheric air.

According to a preferred embodiment of the method, it is ensured that frozen-on ice, if any, is removed prior to a first measurement, and likewise the frozen-on ice is re- moved from the individual surface element following meas- urement of its mass or thickness, whereupon a renewed measurement process can be performed. Advantageously, such removal of the ice can be accomplished by heating of

the individual surface elements either from the outside or from the inside.

Further advantageously, uniform measurement results are accomplished if a cover is provided that extends at least across the surface element, and covers and shields the surface element, and said cover being removed from the surface element at least for the predetermined period of time during which the surface element is moved through the atmospheric air at a predetermined velocity.

The accuracy of measurement is further enhanced if the surface element is moved through the atmospheric air at a velocity that ensures that atmospheric precipitation that does not freeze on to the surface element is to a sub- stantial extent thrown off the surface element.

In order to ensure that the inside of the cover is pro- tected against atmospheric precipitation settling thereon, it can advantageously be so arrange in its sec- ond position that its inside is protected against atmos- pheric precipitation. It is hereby ensured that atmos- pheric precipitation cannot drip from the inside of the cover and onto the surface elements when the cover is conveyed across same.

In order to ensure that the surface elements are essen- tially free of other atmospheric precipitation prior to the amount thereof being determined, they can advanta- geously be rotated for a predetermined period of time following return of the cover to its first position.

According to a particularly simple method, at least two surface elements are used that are rotatably arrange on

a rotor shaft whereby the movement of the two surface elements is effected by a rotation thereof about the ro- tor shaft.

According to a particularly simple embodiment, the appa- ratus comprises a weighing device configure for weighing and recording at least the weight of the surface element prior to and after movement of the surface element through the atmospheric air.

According to a particularly simple embodiment the appara- tus comprises a rotor with a rotor shaft, and at least two surface elements that extend from the rotor shaft and protrude there from, and wherein means are configure for rotating the rotor about its axis. Hereby it is obtained that the movement mechanisms that bring about the move- ment of the surface elements through the air can be ac- complished in a very simple manner that does not require maintenance.

Besides, with a view to also obtaining an increased accu- racy of measurement the apparats can also comprise a cover that is configure for assuming a first position in which it extends across the surface element, and thereby covers this upwardly, and a second position in which the cover has been removed from the surface element and does not cover same, and this cover is preferably configure such that in its first position, it forms a closed space around the surface element.

In order to be able to perform measurements in quick suc- cession, means are conveniently provided that are, on the one hand, able to heat the surface elements in order to melt the ice deposited thereon, and on the other, to cool

them to approximately ambient temperature. This can be obtained in that the surface elements are configure with passageways; and that the apparats comprises means whereby air can be conveyed through the passageways ei- ther in the form of heated air or air with approximately ambient temperature. Heating and cooling of the surface elements can also be accomplished by the closed space un- derneath the cover being heated and cooled.

It is desirable that the ice formation on the surface elements is as comprehensive as possible to ensure accu- racy and speed of measurement, and consequently the sur- face element will, in a first preferred embodiment, be in the form of a plate with a front and a back which have opposite orientations relative thereto; and wherein the plate is configure in such a manner that the front of the plate faces in the direction in which the surface element is moved through the atmospheric air; and wherein -through said plate-a plurality of passageways are provided from the front of the plate to the rear of the plate, whereby atmospheric air is able to flow through the passageways from the front of the plate to the back of the plate.

According to an alternative, preferred embodiment the ap- paratus comprises a system of surface elements mounted on a rotatable shaft configure for being arrange in a sub- stantially vertical position. The individual surface ele- ments are configure and arrange such that the individ- ual surface elements will, in correspondence with their projection on a face perpendicular to the rotatable axis, abut on or overlap other surface elements, which means that there is no space between the individual surface elements when the apparats is viewed from above. Hereby

it is obtained that all atmospheric precipitation within the expanse of the apparats hits the surface elements and thus can be deposited in the form of ice. The larger the overlap between the individual surface elements, the larger the deviation from vertically falling precipita- tion can be tolerated while ensuring this.

In correspondence with the above teachings, the surface elements can advantageously be configure and arrange such that the individual surface elements corresponding to their projection on a face parallel with the rotatable axis abuts on or overlaps other surface elements, so as to accomplis that there is no space between the individ- ual surface elements when the apparats is viewed from the side. Hereby it is obtained that the atmospheric air conveyed across the surface elements by the relative movement between the atmospheric air and the surface ele- ments hits a surface element and is thereby able to de- posit the water contained therein in the form of ice.

In case of embodiments like the ones described above, it is ensured that the apparats can be configure with the smallest possible physical dimensions.

The apparats according to the present invention is par- ticularly suitable for use in airports, where the appara- tus is preferably arrange at ground level in an air port, and whereby the apparats comprises means for re- cording the measured results of the thickness or mass of the ice deposited on the surface elements, and means for visually or auditively emitting a signal regarding the measurement results to the monitoring personnel of the airport.

The invention will now be described in further detail with reference to the drawings, wherein Figures 1 through 4 are explanatory sketches using a schematically represented apparats to illustrate various process steps according to the present invention; Figure 5 is a sectional view that illustrates a vertical, sectional view through a surface element for use in the apparats according to the present invention; Figures 6 through 8 show a first, preferred embodiment of an apparats according to the invention, wherein the cover is shown in different positions; Figure 9 shows an alternative, preferred embodiment of an apparats according to the invention, seen from the side; Figure 10 is a vertical, sectional view through the appa- ratus shown in Figure 9 corresponding to the plane indi- cated by B-B; Figure 11 illustrates a preferred embodiment of a rotor element for use in connection with the invention; Figure 12 is a top plan view of the rotor element corre- sponding Figure 11; and Figure 13 shows a further preferred embodiment of a rotor element for use in connection with the invention.

Thus, Figure 1 shows the constructive principles of an apparats according to the invention, said apparats com- prising a housing or a frame 1, in which a shaft or a ro-

tor 2 is arrange that supports two diametrically opposed surface elements 3, and that are rotated by a drive unit 4 in the direction of the arrow A. The rotor with one or more surface elements is also referred to as the rotor element.

Corresponding the normal operative state of the appara- tus, the shaft or the rotor is configure for being ar- ranged in a substantially vertical position. When, in the following, the terms vertical and horizontal are used, they refer to the apparats when arrange in such pre- ferred position.

Additionally the apparats comprises a weighing device 5 configure for weighing the surface elements 3, the rotor 2 and the drive unit 4, whereby a weight increase can be determined.

Besides, the apparats comprises a movable cover, in Fig- ures 1 through 4 shown as a dome-shaped shield consisting of two spherical quarter shells 6 that are shown in Fig- ure 1 in a first position in which they shield the sur- face elements 3 and the rotor 2 and form a substantially closed space 7 around the surface elements and the rotor.

Moreover, the apparats comprises a blower 8 configure for conveying atmospheric air towards the surface ele- ments 3.

In the process step shown in Figure 1, the rotor is thus rotated in the closed space 7, and as a consequence of the blower 8 generating circulation of air in that space, the surface elements 3 are caused to assume a temperature that corresponds essentially to the ambient temperature.

Now, Figure 2 illustrates a subsequent process step in which the two spherical quarter shells 6 have been with- drawn to a second position in which the surface elements 3 on the rotor 2 rotate in the open air, and wherein- provided supercooled water is present in the air-ice formations will settle on the surface elements 3. It will appear from the figure that the cover in its second posi- tion is situated within the housing that is advanta- geously configure such that inside of the cover is pro- tected against atmospheric precipitation settling thereon. In the embodiment shown, this could only be ac- complished by the spherical shells of the cover being conveyed down into the housing through a narrow opening between the top face and lateral walls of the housing.

Such configuration ensures that atmospheric precipitation cannot drip from the inside of the cover and down onto the surface elements when the cover is conveyed above them.

In accordance with the invention, the process step shown in Figure 2 is carried out for a predefined period of time, whereby a suitable amount of ice will deposit on the surface elements, and the rotor is rotated at a ve- locity that, on the one hand, takes into account that the ice is not to be thrown off the rotor, but wherein other precipitation, if any, in the form of rain and snow is thrown off to a suitable extent. As shown in the figure, it is of course to be ensured that the cover can be con- veyed past the various structures of the housing.

Advantageously, the weighing device can be configure with three weighing cells situated triangularly between the drive unit 4 and the lower part of the housing.

Hereby a stable determination of weight for the drive unit, the rotor, the surface elements and the ice frozen thereon is obtained.

Following the process step shown in Figure 2, a subse- quent step is shown in Figure 3 wherein the cover has been returned to its first position. In order to ensure that the surface elements are substantially free of at- mospheric precipitation other than ice before the amount thereof is determined, they can advantageously be rotated for a predetermined period of time after the cover has reverted to its first position.

Now the surface elements are brought to a halt, and the weight increase of the surface elements resulting from the ice deposited on its surfaces is recorde by means of the weighing device 5, and on the basis of the value measured, a signal can be generated for showing an icing factor; however, the drawing does not feature equipment for this use since it will be obvious to the person skilled in the art to configure such equipment on the ba- sis of the present description.

Now a subsequent process step is shown in Figure 4 wherein the two spherical quarter shells 6 have been moved across the surface elements 3 and shield them so as to form yet again the closed space 7. In this process step the rotor is caused to rotate, and a quick heating of the closed space 7 is carried out by means of the blower 8 and a heater element 9 whereby the ice deposited on the surface elements is melted and thrown off by the rotation of the rotor, whereby the combine weight of the rotor 2 and the surface elements 3 is caused to revert to the initial weight.

Now the process step shown in Figure 1 can proceed, and the apparats according to the invention is thus very suitable for carrying out repeated measurements with a very high degree of accuracy in standardised conditions.

In order to obtain the highest possible accuracy of meas- urement, the surface elements 3 should be configure with the largest possible surface for adhesion of ice. Figure 5 illustrates an embodiment wherein a surface element is constructed as a grid, as seen in a vertically sectional view through this, and from which it will appear that the surface element that is moved in the direction of the ar- row B has a front 13 and a back 14; and wherein walls 11,12 combine to form passageways 10 that extend from the front 13 to the back 14.

Hereby the surface element forms a relatively large sur- face compare to the indigenous weight of the surface element which means that a relatively quick formation of a suitable and mesurable amount of ice is accomplished on the surfaces of the surface element 3, and such that the surface element can quickly be caused to assume the desired temperatures by the heating as shown in Figure 4 and the cooling as shown in Figure 1.

Both walls 11,12 having a downwardly tapering course means that, on the one hand, atmospheric precipitation other than supercooled water or mist is very like to slide or flow off the surface element 3, but also that supercooled water droplets or mist are very like to set- tle on the surfaces of the surface element without having to pass all the way through the surface element.

The surface elements shown in Figures 1 through 4 are, for the sake of clarity, shown to be very small, but ac- cording to a preferred embodiment they are dimensioned to essentially fill the space 7, which means that the sur- face elements as shown in Figures 1 through 4 join to constitute an approximate semicircle. Hereby it is en- sured that the apparats can be configure with the smallest possible outer dimensions.

As described above, it should be ensured that the inside of the cover is protected against atmospheric precipita- tion in all process steps; and this is to ensure accurate determination of the amount of ice frozen fast there on.

Figures 6 through 8 show an embodiment in which an appa- ratus comprises a housing 1, a cover in the form of two spherical quarter shells 6, two storage units 41 for the two spherical quarter shells and a platform 40 on which the storage units have been arrange. Furthermore the ap- paratus comprises a rotor element, a drive unit and a (not shown) weighing device as described above.

In a first position the cover 6A covers the rotor element and forms a substantially closed space; in Figure 6 this is outlined with dotted lines. When it is desired to per- form a measurement, the elements of the cover are, as shown in Figures 6,7 and 8, moved to their second posi- tion where they are stored for protection in the storage units 41. Since it is in particular the inside of the cover that is to be protected against atmospheric pre- cipitation, it can be chosen to allow the storage units to be upwardly open, which would simplify the construc- tion. Once the first part of the measurement is accom- plished the cover reverts to its first position.

Above it has be outlined schematically how protection of the cover inside against the weather can be accomplished, but of course it is possible to select the configuration, shape and the mutual relations of the cover and the stor- age units on the basis of many considerations.

Figure 9 shows a further embodiment wherein the apparats comprises a housing 101 with a drive unit, a frame 110, a control unit 115, a cover 106, and a rotor element 103.

The housing 101 is configure as a closed and approxi- mately semicylindrical object cut-off in correspondence with the cylinder axis; the housing is mounted in a frame 110 such that the cylinder axis is substantially embedded horizontally. The cover 106 is also configure as ap- proximately as a semicylinder cut-off in correspondence with its cylinder axis and open in correspondence with the cut edge. The cover is mounted on the frame 110 in such a manner that the cylinder axis of the cover essen- tially coincides with the cylinder axis of the housing.

The cover is configure with a width that is wider (cor- responding to the length of the cylinder axis) and a cyl- inder radius that is larger than the housing, and pivo- tally mounted on the frame such that the cylinder axis of the cover also constitutes its axis of rotation. This configuration of the cover and housing makes it possible for the cover, upon a 180 degree rotation about its axis of rotation, to be conveyed from its first position as shown in Figure 9 to a second position underneath the housing, and such that the housing is essentially en- closed in the cover. In Figure 9, the end face of the cover towards the viewer has been removed such that the rotor element 103 arrange on top of the housing is visi- ble. When the cover is turned away as described above,

the rotor element will be uncovered and a measurement can be initiated. As also described above, this device will ensure that the inside of the cover is protected against atmospheric precipitation while in its second position.

Study of Figure 10 will now reveal a section through the apparats shown in Figure 9 corresponding to the plane indicated by B-B. As will appear, the housing is-by means of two fittings 112,113-mounted in a frame con- sisting of two posts 110,111. As described above, the housing as well as the cover are mounted with their re- spective cylinder axes about a common axis 102. The rotor element 103 comprises a rotor shaft 120 and a system of surface elements of which only the top 121 and bottom ones are shown. The overall cylindrical shape of the ro- tor element is outlined with dotted lines. In the space 107 between the cover and the housing, a sealing is ad- vantageously arrange whereby it is prevented both that atmospheric precipitation penetrates into the space be- tween the cover and the housing and that the atmospheric precipitation that has found its way to the space, if any, will be removed from the inside of the cover when it is conveyed from its second to its first position. As shown in Figures 9 and 10, the top face of the housing is configure as an upwardly conical face, whereby it is en- sured that eg melt water is, upon heating of the surface elements, conveyed away from the housing and in particu- lar away from the rotor shaft passage.

Between the posts a control unit 115 is arrange for con- trolling the drive unit 104, the weighing unit 105, the blower 108, and the heater element 109, and for collec- tion, storage and optionally transmission of measurement data. Such units are configure for functioning in a man-

ner similar to the one described above with reference to Figures 1 through 4. In Figure 10 it is indicated that air is, by means of the blower 8, blown into the rotor shaft and from there conveyed out through the surface elements as also described above. Between the top part of the housing and the rotor shaft, a (not shown) bearing device can advantageously be arrange for supporting and guiding the shaft. According to a preferred embodiment, the apparats further comprises (not shown) means for automatically shifting the cover between its first and second positions. Obviously, the apparats comprises a device for securing the cover in its first position; preferably also in its second position.

A preferred embodiment of a rotor element for use in an apparats according to the invention will now be de- scribed with reference to Figures 11,12 and 13.

In Figure 11, the rotor element comprises a shaft 20 on which four stacks are arrange that each consists of a number of surface elements arrange at a mutual distance opposite each other with the respective top surface ele- ments 21,22,23,24 arrange in an uppermost plane. Each surface element has a free outer end and an inner end se- cured to the shaft. The uppermost face elements are ar- ranged with a constant mutual angular distance that cor- responds to an angle of 90 degrees as far as four top surface elements are concerne.

As will appear from the figure, the surface elements in the individual stack are displaced relative to each other with the outer free ends arrange so as to generally form a helix. For each stack this helix extends at least over an angle corresponding to the angle between two succes-

sively arrange stacks. For an embodiment with four stacks a helix thus extends over at least 90 degrees. In a particular case where only one stack is used, such stack will be able to extend a full rotation about the shaft, ie 360 degrees.

The individual surface elements are configure and ar- ranged such that, in correspondence with their projection on a horizontal face, they overlap the surface element (s) that are adjacent to or arrange between, respectively, the individual surface elements, so as to eliminate spaces between the individual surface elements when the apparats is viewed from above. This is shown in Figure 12 that illustrates the apparats according to Figure 11, seen from above. Hereby it is obtained that atmospheric precipitation falling within the expanse of the apparats hits the surface elements and is thus able to settle in the form of ice. The larger the overlap between the indi- vidual surface elements, the larger a deviation from ver- tically falling atmospheric precipitation can be toler- ated, while ensuring this.

In correspondence with the above teachings, the surface elements in the embodiment shown can advantageously be configure and arrange such that the individual surface elements corresponding to their projection on a vertical face abut on or overlap the surface elements (5) that ad- join or surround, respectively, the individual surface element so as to eliminate a space, if any, between the individual surface elements when the apparats is seen from the side. Hereby it is obtained that the atmospheric air conveyed across the surface elements by the relative movement between the atmospheric air and the surface ele- ments hits a surface element and is thereby able to de-

posit the water contained therein as ice. This is in ac- cordance with the disclosures above with reference to Figure 5.

In an embodiment as shown in Figures 11 and 12 it is fur- ther ensured that the apparats can be configure with the smallest possible outer dimensions. For instance, an embodiment with four stacks of each eleven surface ele- ments and a diameter of 70 cm has proven to be conven- ient.

As will also appear from Figure 11, the individual sur- face elements are provided with a number of passageways 25 through which air can be blown, heated air to deice the surface elements and air with ambient temperature for tempering the surface elements prior to the next mesure- ment, respectively. According to a convenient embodiment the air is conveyed from the basis of the apparats to the surface elements through the shaft 20.

In accordance with the embodiment shown in Figure 11, the surface elements are attache only to the shaft 20 in correspondence with their one end, and this is why the individual surface element is dimensioned to support it- self and resist the forces that will occur during the in- tended use of the apparats. In an alternative embodiment shown in Figure 13, a large number of rather thin surface elements are used that will be secured partly in corre- spondence with their inner end to the shaft, partly se- cured with their outer end to a support structure. This support structure comprises an upper support element 30 secured to the shaft by means of upper connecting means 31 and a lower support member 32 secured to the shaft by means of lower connecting elements 33. Between the upper

and the lower support elements a number of outer support elements 34 are arrange, to which the outer end of the surface elements are secured. Corresponding to the above- described embodiment, four stacks of surface elements are also used herein that are in a corresponding manner sup- ported by four outer support elements 34.

Corresponding to the embodiment shown in Figure 11, the surface elements have equal lengths, which means that each helix extends in a manner that corresponds to the surface of a cylinder and, likewise, the overall shape of the rotor element will be cylindrical. In the alternative embodiment shown in Figure 13, for each stack surface elements are used that have decreasing length towards the top of the apparats; if the length decreases linearly the individual outer support element 34 will have a course corresponding to a helix on the surface of a cone, and-likewise-the overall shape of the rotor element will in that case be a cone. As stated above, the overall shape and dimensions of the rotor element and the cover will conveniently correspond to each other. For an em- bodiment of the apparats like the one shown in Figures 6 through 8, the rotor element should thus be semispheri- cal.

Of course, it is possible in case of both the described embodiments to arrange surface elements such that the he- lix-shape described is not a'perfect'geometrical helix but merely what the person skilled in the art describes as"spiral-shaped".

Obviously, on the basis of the above explanation of the principle underlying the invention, the person skilled in the art will readily be able to point to various embodi-

ments of the construction of an apparats that is able to perform said process steps as well as to identify process parameters that are suitable therefor with due regard to the configuration of the apparats, such as the period of time during which the surface elements are to be moved through the open air as shown in Figure 2, and the rate at which the surface elements 3 are to be moved through the air in order to obtain suitable measurement results that are not considerably influence in case atmospheric precipitation other than supercooled water and mist is deposited on the surface elements 3. Obviously, there is a correlation between the configuration of the apparats itself and the operation parameters that ensure that the desired measurement results are obtained.