For the dosing of liquids, especially of coolants, it has earlier been known to use external glass tubes which are arranged parallel with a container so that the level of the liquid for the tube can be read and indicate the amount of liquid in the container. Such a system suffers the disadvantage that the glass tube must be placed im- mediately at the side of the container and cannot be located in a place which is convenient for the user.

Moreover, the system naturally also places restrictions on the construction itself as a whole.

Systems are also known for the measurement of a medium deviation by measuring the pressure in the top and the bottom by means of measuring instruments and then calculating the difference in pressure, and also where incorporated in relation to the measuring instrument there are valves which must be opened in a quite definite sequence. Such systems are very sensitive to incorrect handling of the system, in that the measuring instruments can be damaged if, for example, the opening of the valves is not correct. Moreover, the systems must be seen to be relatively costly, the reason being that they not only comprise various components but also necessitate elec- tronic calculations.

A system for the measurement of the degree to which a re- actor container is filled is known from German Patent No.

41 31 086. The system cannot be used for dosing, in that the heating means which exist in the system are disposed in relation to both of the outgoing tubes. Consequently,

regulation of the temperature of- the coolant in the con- tainer is not ensured.

It is the object of the present invention to provide a dosing system which is not encumbered with the disad- vantages of the existing systems, and where it is pos- sible to establish a reliable dosing system whereby it is possible to continuously monitor the level of liquid in the container during the dosing, and where as a conse- quence of the mutual arrangement of the tubes and the heating means, which ensure that the liquid is converted to gas form, such monitoring is reliable and repro- ducible. Moreover, the actual reading can take place wherever it is considered to be most expedient, in that the measuring instrument can be placed in a position which is convenient for the reader.

This object is achieved with a dosing system of the kind disclosed in the preamble, and where the pipeline con- nection comprises a first pipe which extends from the lo- wermost end of the container, where that part of this first pipe which lies outside the container comprises a first pipe piece filled to a level with liquid from the container, said pipe piece comprising first means for the heating of the liquid in the first pipe piece, and where the system also comprises heating means disposed in the container.

It is hereby possible to measure how great an amount of liquid is dosed from the container over to the system.

Moreover, the measuring instrument can be placed wherever it is most suitable, and the components involved are par- ticularly inexpensive, in that costly and complicated electronic measurements are not necessary. Furthermore, a very precise indication of the weight is achieved which, moreover, is insensitive to vibrations and shock.

The way in which the system works is that the amount of liquid in the first pipe piece is converted to gas or vapour by being heated. When the liquid has been con- verted to vapour, a measurement is taken by means of a measuring instrument, preferably a differential mano- meter, of the difference in pressure on each side of this manometer. This pressure difference is a function of the liquid column in the pipe and thus also the level of the liquid in the container.

By measuring the pressure difference for two different liquid levels, a scale is achieved which is linear in its graduations, and which can be used to provide a reading of the weight dosed from the container. The scale is in- dependent of the relevant liquid, in that the scale indi- cates weight dosing and not volume dosing, which means that this is also independent of the temperature condi- tions of the actual liquid in the container.

It is thus essential for the invention that the system comprises two heating systems, where the one heating system carries out a heating in the container itself, and which functions partly to build up a pressure in the con- tainer and partly to ensure that condensate does not arise in the upper coupled pipe. The second heating ele- ment is coupled to that pipe part where the liquid must be converted to gas or vapour, and must consequently car- ry out a heating which exceeds that heating which takes place in the container. If no difference in temperature exists, the system will not function, since it is es- sential that the external pipe has a higher temperature than that of the coolant in the container. If not, the liquid would assume the same level in the pipe and the principle will not work.

By providing a dosing system according to the invention and as further disclosed in claim 2 and 3, it is achieved

that the construction itself is simplified and also that the measurement is correct within very small margins.

By providing a dosing system according to the invention and as further disclosed in claims 4-5, an expedient con- figuration of the system is achieved, so that this be- comes simple in its construction and makes it easy to ob- tain the conversion factor which is used in connection with the conversion from pressure difference to weight dosing.

By providing a dosing system according to the invention and as further disclosed in claim 6, a suitable heating of the liquid is achieved, so that this is converted to vapour/gas. The heating of the liquid is not critical in itself, in that a heating which results in a heating of the gas so that the gas pressure exceeds the pressure from the liquid, merely results in a bubbling of the gas through this in an equalization of the pressure, whereby the gas pressure in the first pipe system will always be a direct function of the pressure from the liquid in the container and herewith the weight which is remaining herein. The thermostat and the over-heating security de- vice are coupled to ensure that the temperature does not become so high that it has a damaging effect on the com- ponents of which the system is built up.

By providing a dosing system according to the invention and as further disclosed in claim 7, the possibility is achieved of carrying out a direct reading of the weight/amount remaining in the container and/or which is dosed.

By providing a dosing system according to the invention and as further disclosed in claim 8, a building-up of the filling pressure in the container is achieved, and also an adjustment of the temperature of the components so

that the formation of condensate is avoided.

The invention also concerns a method for the dosing of liquid and the use of the dosing system primarily for the filling and draining-off of coolants in cooling systems.

The invention will now be described in more detail with reference to the drawing.

The drawing shows an example embodiment of a dosing sy- stem comprising a container 4 for liquid, which in this case is coolant. In the bottom of the container 4 there is provided a heating element 13 which is controlled by thermostats 14 and 15. The heating element is used to build up a pressure in the container for the filling pro- cess, which takes place through a discharge pipe 16 and which is regulated by a valve 5 mounted in the discharge pipe 16. The heating element 13 is also used to heat com- ponents including the uppermost connection pipe 2 desig- nated second pipe piece.

Above the level of the liquid in the container there is gas from the coolant. Extending from the bottom of the container 4 there is a first connection pipe 12, and ex- tending from the top of the container there is a second connection pipe 2. After it leaves the container, the first connection pipe, also called the high-pressure pipe and, in its continuation outside the container, also called the first pipe piece, extends in such a manner that pockets of liquid are not formed. From the first connection pipe 12, this extends further to a measuring instrument, a differential manometer 1, and from the dif- ferential manometer 1 there is further connection to the container via the second connection pipe 2. The con- nection pipe 12 thus extends at an angle of approx. 90° and continues vertically approximately parallel with the container. The liquid column in the pipe 12 will thus be

on a level with the liquid lying in the container 4.

In order to measure the level of liquid in the container, the liquid column in the connection pipe 12 must be removed, which is effected by applying heat to the pipe 12. This can be done by connecting a heating element to the whole of the pipe 12 or, as indicated in the drawing, by simply applying heat to the lowermost part of the pipe 12 via a heating element 7 which is enclosed within a heat distribution jacket 6. When the heating element is activated, a heating of the pipe 12 will occur and here- with a heating of the coolant contained herein. The heating element 7 is provided with a thermostat 10 and a over-heating safety device 9, hereby ensuring that the temperature does not become so high that the system's components suffer consequent damage. The measurement of the liquid in the container is carried out by means of the differential manometer, which measures the dif- ferential pressure of the liquid column 11 in the contai- ner 4. Since the cross-sectional area of the container is known, the amount can be converted to a linear scale in the differential manometer, and via the connection pipes 2 and 12 the differential manometer can be placed wherever it is desired to be.

During the heating, the gas in the top of the pipes 2,12 condenses to liquid, and for this reason the connection pipes 2 and 12 must be of a certain size so that the ma- nometer reading is not disturbed, which would otherwise be the case if the condensate closed the clearance in the pipes. For example, at a heat transmission of 125 Watts the inside diameter must be approx. 10 mm or more.

Moreover, the system is independent of variations in the temperature of the surroundings, since while the volume of the liquid column will quite certainly be changed with the surrounding temperature, the weight of the column

will remain unchanged. Finally, it should be noted that the thermostats which regulate the heating element 13 in- side the container must be set at a temperature level which is lower than the thermostats which regulate the heating element 7 provided around the first connection pipe 12. If not, the system will not function.

During the functioning of the system, there will thus be effected an opening of the valve 5 after heating has been carried out and an evaporation of that liquid which exists in the pipe 12. This heating will give rise to a pressure indication at the manometer, which is again con- verted to an indication of the weight. During the drai- ning-off through the valve 5, the differential pressure will be changed, which is again converted to a new indi- cation of the weight on the scale of the dosing system.

The scale itself for the dosing by weight is independent of the liquid which is in the dosing system, in that the scale is produced by first measuring the pressure with one amount of liquid in the container, and then measuring the pressure with a second amount of liquid in the con- tainer. On this basis, a linear scale is produced which can be used regardless of the character of the medium, in that only the density of the liquid requires to be known.

It is essential for the system to be able to function that all of the liquid in the pipe 12 is converted to gas, in that the indication will otherwise be wrong and insufficient. It is thus essential for the invention that the liquid in the pipe is converted to vapour, which in this case is effected by placing a heating element around the first connection pipe.

The system is intended primarily for use for the dosing of coolants, but it can also be used for other liquids, e.g. water, oil etc.

The components which are chosen for the system will de- pend on the liquid which is required to be dosed. For example, for the dosing of coolants there is chosen a diffential manometer which can function at small dif- fences in pressure, while the system as such shall be able to withstand pressures in the container of up to 16 bar.