SE523531C2 - Method and monitoring device for monitoring a corrosion protection capacity for a coolant in a cooling system - Google Patents

Abstract

The present invention relates to a method for in use determination of a corrosion protection capacity of a cooling liquid, comprising the steps of measuring an approximate proportion of anti-freezing solution in use, measuring, when applicable, a conductivity value of the cooling liquid in use and using said conductivity value together with a proportion of anti-freezing solution in the cooling liquid to determine the corrosion protection capacity. The method further comprises the steps of determining if the corrosion protection capacity is insufficient and, when applicable, providing a warning for a user of the cooling liquid if the corrosion protection is insufficient. The invention also relates to a monitoring device (100) comprising a conductivity meter (101) extending into the cooling liquid for measuring the ionic mobility in the cooling liquid and computer means (103) connected to the conductivity meter (101) and arranged to receive conductivity values from the conductivity meter (101).

Description

l5 20 25 30 523 531 2 merises on the surfaces of the cooling system and thus provides protection against corrosion. It is also known to use, for example, silicates or nitrates. The amount of corrosion inhibitors usually amounts to 5-10% by volume, a value which decreases with time due to various circumstances, such as leakage and aging of the inhibitors. Therefore, to avoid corrosion, more corrosion inhibitors must be added over time. This demonstrates the need for a careful procedure to determine the corrosion protection capacity as well as to determine the content of corrosion inhibitors and the content of antifreeze.

Coolant manufacturers usually provide an assay method for determining the corrosion protection capacity of the coolants provided by them.

Unfortunately, coolants from different manufacturers usually differ from each other in such a way that a procedure used by one manufacturer on its products cannot be applied to coolants from other manufacturers. Furthermore, these analysis procedures, as they are complicated, are usually performed by the manufacturers themselves, which means that the user of a coolant, for example a driver of a car, must send a sample to a manufacturer, which manufacturer performs the analysis and then informs the user of the result obtained. It would of course benefit the user if such a complex procedure, which is expensive as well as time consuming and thus sometimes not performed at all, could be replaced by a simple analysis procedure, which is performed automatically during operation of the cooling system.

The reliability of this assay procedure is of paramount importance, as incorrect results can either cause corrosion or lead to expensive overdose.

US 4,147,596 describes a process in which the content of corrosion inhibitors is determined by measuring the potential of the coolant, and from US 5,870,185 they are known to determine the degree of impurities in a coolant in an air conditioning system by measuring the refractive index of this agent. 10 15 20 25 30 523 531 3 Furthermore, SE 0102053 describes an analysis method, applicable to different types of coolants. However, this analysis cannot be performed during use.

OBJECT OF THE INVENTION It is therefore an object of the present invention to provide a method for determining and analyzing the corrosion protection capacity of a coolant as well as the level of corrosion inhibitors and the level of antifreeze in said liquid, which method is possible to carry out during operation of said cooling system. coolant, and without the assistance of a supervisor or mechanic.

Another object of the invention is to provide a monitoring device, which monitoring device utilizes the above-mentioned method and automatically measures and derives said variables, compares the obtained results with predetermined values and, when applicable, notifies a user, e.g. driver of a car, if more corrosion inhibitors or more antifreeze must be added to the coolant and preferably also the amount of the respective substance.

Finally, the device according to the present invention should also automatically measure the temperature on the outside and compare the value obtained with an estimated freezing point for the coolant and notify the user if there is a risk of freezing.

BRIEF DESCRIPTION OF THE INVENTION The above objects are achieved by the present invention with the features described in the independent claims 1 and 17, wherein claim 1 specifies a method for determining in use a corrosion protection capacity for a coolant in a coolant system, which coolant comprises at least one substance which acts as a corrosion inhibitor. The method comprises the measures of measuring an index value, which indicates an approximate level of antifreeze in use, to measure, where applicable, an electrical conductivity value of the coolant in use and to use the electrical conductivity value together. with a content of antifreeze in the coolant to determine the corrosion protection capacity. The procedure further comprises the measures of determining whether the corrosion protection capacity is insufficient and, where applicable, giving a warning to a coolant user if the corrosion protection is insufficient.

The advantages of using the conductivity to estimate the corrosion protection capacity are partly that this method can be used on different liquids, but all the more important that the analysis is quick and easy to perform. Thus, there is no need to send samples of the coolant to the manufacturer thereof and the time and cost savings are considerable.

Claim 17 describes a monitoring device, which device is connected to a cooling system, for example a cooling system of a car or a truck, for the purpose of determining a corrosion protection capacity of a coolant in the cooling system. The monitoring device automatically performs the method according to any one of claims 1-16 and comprises a conductivity meter, extending into the coolant to measure the ionic mobility of the coolant, an index meter, extending into the coolant to measure the index value, and computer means, connected to the conductivity meter and the index meter and arranged to receive electrical conductivity values and index values from the conductivity meter and the index meter, respectively.

It is obviously advantageous for the device to automatically perform the analysis during operation of the cooling system, as this means that no expensive and time-consuming service interruptions are required and that insufficient corrosion protection capacity is detected as soon as it occurs, which improves corrosion safety. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described in more detail by means of exemplary embodiments, in a non-limiting manner and with reference to the accompanying drawings, in which: in Figure 1 shows a fl schematic diagram of a the first preferred embodiment of a process according to the present invention in water; Figure 2 shows a flow chart of a second, preferred embodiment of a process according to the present invention in water; Figure 3 shows a calibration curve for a refractometer for a certain type of coolant in water; Figure 4 shows a calibration curve for a refractometer for a certain type of corrosion inhibitor in water; Figure 5 shows calibration curves for a conductivity meter, which curves describe the relationship between conductivity, volume percent coolant and volume percent corrosion inhibitors in water; Figure 6 shows calibration curves for a conductivity meter, which curves describe the relationship between conductivity, volume percentage of coolant and volume percentage of corrosion inhibitors in water; Figure 7 shows a diagram, which describes how the conductivity varies with the volume percentage of coolant in water; Figure 8 is a graph showing the corrosion protection capacity, expressed as volume percent coolant, relative to conductivity and volume percent coolant; and Figure 9 schematically shows a perspective view of an expansion tank, comprising a monitoring device, which constitutes a preferred embodiment according to the present invention. DETAILED DESCRIPTION OF THE INVENTION A coolant preferably comprises an antifreeze and a corrosion inhibitor. In order to determine the corrosion protection capacity of the liquid, in a preferred embodiment, two parameters must be measured: the conductivity of the liquid and the volume percentage of antifreeze. Preferably, a conductivity meter is used to measure the conductivity, while a density meter or a refractometer can be used to estimate the volume percentage of antifreeze.

Before measurements are performed, the density meter / refractometer is preferably calibrated according to the liquid-freezing agent and inhibitor specific in the liquid, which means that the density meter / refractometer must give the value zero when measurements are performed for distilled water. The conductivity meter is also calibrated against a solution of ordinary drinking water and the inhibitor, or an inhibitor with slightly higher conductivity. Calibration curves, which are used to obtain relevant test results, must also be produced before the measurements are performed.

When the measurements are performed, the temperature is preferably in a range of 0-50 ° C. If the temperature is outside the limits of said range, this must be taken into account when the measurements are performed, otherwise the results will be misleading. This is preferably done by correcting the measured results with a predetermined, temperature-dependent factor. The accompanying diagrams are reliable at a temperature of approximately 25 ° C.

The requirements refer to different levels of antifreeze and corrosion inhibitors. In the described embodiments, these measurement results are stated in a non-limiting manner in volume percent, unless otherwise stated. Hereinafter, a first preferred and a second preferred embodiment of the method according to the present invention will be described. These embodiments, which specify procedures for determining the corrosion protection capacity of a liquid, are performed automatically and repetitively by means of a monitoring device. Then follows, as an example, an embodiment of the preferred embodiment as well as a description of a preferred embodiment of the device.

Figure 1 shows a fate diagram, which describes the measures according to the first, preferred embodiment of a method according to the present invention for automatic determination of a liquid, such as a coolant in a car or a truck, corrosion protection capacity. Each of these measures will be fully described in the working example.

In this first preferred embodiment, a conductivity meter is used to measure the conductivity of the liquid and a density meter to determine the content of antifreeze.

Prior to the analysis of the liquid, a user thereof must specify 1 for the device what kind of liquid is used, as different curves have been developed for different antifreeze and inhibitors. Thereafter, 2, 4 a density value and an electrical conductivity value are measured by means of the density meter and the conductivity meter, respectively.

The density value relates to an approximate content of antifreeze 3, while the electrical conductivity value is compared 5 with a predetermined limit value for the conductivity, in this case 4 mS / cm, to determine whether the approximate content of antifreeze is a correct estimate of the actual level of antifreeze 6, hereinafter referred to as the correct level of antifreeze, or not. If the latter case exists, the correct content of antifreeze must be determined. Therefore, an estimate is made 7 of the present content of corrosion inhibitors, which is used together with the approximate content of antifreeze to obtain the correct content of antifreeze 8. When the correct content of antifreeze is known, the corrosion protection capacity can be derived 9. If the corrosion protection capacity meets certain criteria 10, the liquid is assumed to have adequate corrosion protection and no further measures need to be taken. If this is not the case, however, a lane device informs the user ll about the situation and preferably also about what measures must be performed.

It is of course possible to imagine a liquid, such as a coolant in a cooling system, essentially without antifreeze, especially in countries where the temperature never or rarely falls below 0 ° C. In these cases it may be sufficient to measure the conductivity of the liquid and use the values obtained to determine the corrosion protection capacity as well as the content of corrosion inhibitors.

According to the first preferred embodiment, a density meter is used to determine the approximate content of antifreeze. Other devices, such as a refractometer, can be used instead of measuring this parameter.

In order to avoid expensive overfilling of corrosion inhibitors and / or antifreeze agents, it is important that the user is informed in some way how much of said substances must be added to the liquid or that the method is used to indicate during filling when the corrosion protection capacity has reached an appropriate level. . The latter can be easily achieved, for example, by continuously controlling the system during filling and the amount of corrosion inhibitors and / or antifreeze agents that must be added can be quickly estimated by the device by performing the above-described, preferred embodiment of the process in reverse order, using the desired value of the corrosion protection capacity such as input data.

In a further embodiment, it is also possible to derive the freezing point of the liquid if the levels of water, antifreeze and corrosion inhibitors are known. The air temperature outside the liquid can furthermore be measured by means of a thermometer and thus it can be determined whether there is a risk of freezing by comparing the freezing point with the measured air temperature on the outside. If such a risk exists, the user is preferably informed of this. It is also possible to calculate the amount of antifreeze that must be added to avoid freezing and compare this necessary content with the correct content of antifreeze.

A second, preferred embodiment of the method is described in Figure 2. Again, the user must indicate the type of coolant used 12, before measuring the density 13.

As in the first, preferred embodiment, the density is used to estimate the approximate content of antifreeze 14. Tests have shown that if the approximate content of antifreeze exceeds a second, predetermined value 15, usually 30%, the corrosion protection capacity is sufficient 16. If the approximate level of antifreeze does not exceed 30%, the electrical conductivity value 17 is measured. To ensure that the liquid has good corrosion protection 16, the electrical conductivity value should preferably exceed a third, predetermined value 18, usually 9.5 mS / cm. If not, the present level of corrosion inhibitors 19 and the required level of corrosion inhibitors / the necessary level of antifreeze, which are required to obtain effective corrosion protection 20. Next, the amount of corrosion inhibitors or antifreeze agents to be added to the liquid 21 is calculated. measured values of the present content of corrosion inhibitors or antifreeze are subtracted from the necessary levels. A warning device is provided to inform the user that the corrosion protection capacity is insufficient and the amount of corrosion inhibitors or antifreeze must be added to the liquid.

The second embodiment is not as accurate as the first, preferred embodiment, but simpler and easier to perform.

It should be noted that the amount of corrosion inhibitors and / or antifreeze agents that must be added to the vest to obtain an effective corrosion protection capacity is determined in the second embodiment, although these measures may be omitted in another, simpler embodiment.

By way of example, an embodiment of the first, preferred embodiment of the method according to the present invention will now be described, with reference to the diagrams in Figs. 3-8. It should be noted that a refractometer was used instead of a density meter when this test was performed and that the antifreeze and inhibitor were BASF G 48-24 and BASF 93-94, respectively.

As mentioned above, the first measure according to the preferred embodiment is to estimate the approximate content of antifreeze in the liquid. This is done by means of the refractometer, which measures a refractive index, which represents an approximate content of antifreeze. The diagram according to Fig. 3 shows the calibration curve of the refractometer for BASF G 48-24, i.e. the ratio in distilled water between said refractive index and the content of antifreeze. From this diagram, the approximate content of antifreeze can be read, if said refractive index is known. As can be seen, the calibration curve is approximately linear within a range between a value of 0-55 Brix and the ratio can thus be expressed as: Bl a F 1> <G, (Equation 1) where B is a value of a first refractive index, G is the approximate content of antifreeze and F1 is a constant with a value of approximately 0.7. It should be noted that fl era of the references to the diagrams according to Fig. 3-8 can be replaced by relatively simple equations. However, the values referred to in this exemplary example according to the first, preferred embodiment have been read from the diagrams, with the exception of said measured refractive index value and the measured electrical conductivity value, and the equations are included only to show that it is possible to create such numerical conditions. In the present example, said refractive index was measured to a value of 18 Brix and G thus amounts to a value of 27%.

The corrosion inhibitors in the liquid also affect said refractive index, as shown in Fig. 4, which shows the ratio in water between said refractive index and the content of corrosion inhibitors. This ratio, which is approximately linear, can also be formulated as: B2 z F2 x I, (Equation 2) where B2 is a second refractive index, I is the present content of corrosion inhibitors and F2 is a constant factor with a value of about 0, 5.

However, this effect can be disregarded if the content of corrosion inhibitors is relatively low. It can be easily determined by measuring the conductivity if such a condition exists. Tests measuring the ratio of conductivity to BASF G 48-24 have shown that the conductivity varies with the coolant content, as shown in Fig. 7, with a maximum value of about 4 mS / cm for a BASF G 48-24 content of about 35%. Thus, it can be concluded that if the conductivity exceeds 4 mS / cm, corrosion inhibitors are present and that these must be taken into account. Other tests have shown that even if the opposite is not the case (a value obtained for the conductivity lower than 4 mS / cm does not mean that the coolant does not contain any corrosion inhibitors, only that the content of corrosion inhibitors is low), the presence of corrosion inhibitors can - torches are ignored if the electrical conductivity value is lower than 4 mS / cm.

In the present example, the electrical conductivity value is 7.5 mS / cm and consequently the present content of corrosion inhibitors must be determined. As shown in Fig. 5, the present level of corrosion inhibitors can be derived from the electrical conductivity value and the approximate level of antifreeze.

However, it has already been established that the present level of corrosion inhibitors affects the estimated level of antifreeze. Since the content of antifreeze in turn affects the conductivity used to determine the present level of corrosion inhibitors, this means that the present content of corrosion inhibitors thus estimated is only approximate. However, it has sufficient accuracy.

From Fig. 5 one can derive an equation 3 for determining the electrical conductivity value, assuming that the conductivity is linearly dependent on the present content of corrosion inhibitors within a certain range, for example 6-10 mS / cm. This gives that K s F3 x (1 - IB) + KB, (Equation 3) where K is the electrical conductivity value, In the present content of corrosion inhibitors to be calculated, KB is a base value of the conductivity from the diagram in Fig. 5, IB a base value for the present content of corrosion inhibitors, read from the diagram in Figs. 5 and F3 a constant factor. Factor F3 assumes, for the majority of corrosion inhibitors, a value between 0.6-0.8, often 0.7.

In this case, KB = 6 mS / cm, IB = 4% and K = 7.5 mS / cm and I can be read from the diagram in Fig. 4 as approximately 7.5%. If this value of I is used in the diagram according to Fig. 3, B2 can be estimated to a value of approximately 3.5 Brix. A new refractive index B3 can now be calculated according to equation 4.

B3 a B1 - B2 (equation 4) Since the refractive index B3, which relates to the correct content BASF G 48-24, is known, the corrosion protection capacity can be read from Fig. 3.

In the present example, B3 has a value of approximately 15 Brix and the correct content of antifreeze, G3, can be estimated at a value of approximately 21%.

Each level of anti-corrosion inhibitors corresponds to a certain level of antifreeze, with a ratio of 1 to 3-5 for the most anti-corrosion inhibitors. For BASF 93-94 and BASF 48-24, this ratio is 1 to 4, ie 1 percent BASF 93-94 has the same inhibitory effect as 4 percent BASF G 48-24, or IG1 z 4 x I, (Equation 5) where IG1 is the degree of inhibition, ie the estimated value of the corrosion protection provided by the corrosion inhibitors, expressed as an equivalent coolant content.

Eniequation, which describes the relationship between IG1 and the electrical conductivity value K, is obtained by a combination of equation 3 and equation 5.

K z F3 x (I - IB) + KB or I æ ((K - KB) / (F3)) + IB (equation 3) IGl ä 4 x I 1G1 = 4> <((1 <- Kim / Fa » + IB (equation 5) (equation 6) Since K has a value of 7.5 mS / cm, IG1 receives a value of 28.4%.

The total degree of inhibition IG3, expressed as a total percentage of BASF G 48-24, amounts to the sum of G3 and IG1, ie IG3 a G3 + IG1, or (equation 7) IG3 221% + 28% = 49% 10 15 20 25 30 523 531 14 Approximately the same result is obtained if one looks at the diagram in Figs. 8, where IG3 can be read if the total degree of inhibition G3 and the conductivity K are known.

Tests have shown that the area in the diagram according to F in g. 8, within which the liquid is said to have full corrosion protection, is defined by the lines IG4 = 30%, IG5 = 60% and the curve according to F in g. 7, which curve describes the relationship between the conductivity and the content of antifreeze. The liquid in the described example thus has adequate corrosion protection. In the event of an alternative result, where the corrosion protection capacity w proves to be insufficient, the user would have been landed by means of the warning device. However, the monitoring device may also be arranged to warn a user if the corrosion protection capacity is close to the limit of the area according to Figs. 8, to give the user an opportunity in time to replenish with corrosion inhibitors and / or chewing fluid.

Finally, a preferred embodiment of a monitoring device 100, attached to an expansion tank 110, will be described with reference to Fig. 9, which device 100 comprises a density meter 101, a conductivity meter 102, the computer means 103, a thermometer 104 and visual and / or acoustic warning devices 111. Again, the density meter 101 may be replaced by a refractometer.

The conductivity meter 102, the density meter 101 and the thermometer 104 are in the preferred embodiment preferably located in the vicinity of said computer means 103, in order to reduce the length of the connected cables 105. The said computer means 103 are preferably located in the vicinity of the dashboard, where according to the preferred embodiment said visual and / or acoustic warning means 111 are arranged.

To avoid coating thereon, the conductivity meter 102 and the density meter 101 are preferably located where a coolant fl decays rapidly. In all probability, however, coatings cannot be completely avoided. It is therefore proposed that this be taken into account when measuring the density and conductivity of the coolant, for example by correcting the measured values by a predetermined factor, which factor preferably varies logarithmically with time, according to empirical experience.

The method and a device according to the present invention incontonality are essentially from above. Thus, the conductivity meter 102 and the density meter 101 measure the conductivity and density of the coolant, respectively, and transmit these obtained values to said computer means 103, where the values are used to estimate the corrosion protection capacity of the liquid by the above-described method according to the present cooling point and preferably also cooling point. Said computer means 103 also receives temperature data from the thermometer 104, which temperature data is compared with the freezing point, in order to determine whether there is a risk of freezing of the coolant. If the temperature on the outside falls below the freezing point of the coolant, or is within a range around the freezing point, and / or if there is a risk of corrosion, the visual and / or acoustic warning means 11 are activated, to warn the user of the situation and preferably also inform the user about the measures that must be taken, such as the amount of corrosion inhibitors that should be added to the liquid.

Claims (27)

10 15 20 25 525 531 16 KRAV A method for determining during use a corrosion protection capacity for a coolant in a cooling system, which coolant comprises at least one substance which acts as a corrosion inhibitor, characterized in that the method comprises the measures: to measure an index value, which indicates an approximate content antifreeze in use; measuring, where applicable, an electrical conductivity value of the coolant in use; using the electrical conductivity value together with a content of antifreeze in the coolant to determine the corrosion protection capacity; to determine if the corrosion protection capacity is insufficient; and, where applicable, giving a warning to a coolant user if the corrosion protection is insufficient. Method according to Claim 1, characterized in that the approximate content of antifreeze is determined by the index value. Method according to Claim 2, characterized in that the index value is a refractive index value. Method according to claim 2, characterized in that the index value is a value of the density of the liquid. A method according to any one of the preceding claims, characterized by the measure of comparing the approximate content of antifreeze with a second, predetermined value, corresponding to a sufficient corrosion protection capacity. 10 15 20 25 523 531 17 Method according to any one of the preceding claims, characterized by the measure of using the electrical conductivity value and the index value to determine a correct content of corrosion inhibitors in the liquid. Method according to one of the preceding claims, characterized by the measure of comparing the electrical conductivity value with a first, predetermined value. Method according to claim 7, characterized in that the approximate content of antifreeze is assumed to be a correct estimate of a correct content of antifreeze, if the electrical conductivity value does not exceed the first, predetermined value. Method according to claim 8, characterized in that the electrical conductivity value is used together with the index value to determine the correct content of antifreeze, if the electrical conductivity value exceeds the first, predetermined value. Method according to one of the preceding claims, characterized by the measure of comparing the electrical conductivity value with a third, predetermined value, corresponding to a sufficient corrosion protection capacity. Method according to one of the preceding claims, characterized in that the corrosion protection capacity provided by the corrosion inhibitors as well as the correct content of antifreeze is expressed as an equivalent content of antifreeze. Method according to one of the preceding claims, characterized by the measures: determining the necessary content of corrosion inhibitors and / or the necessary content of antifreeze, necessary to obtain a sufficient corrosion protection capacity; and determining the amount of corrosion inhibitors and / or an amount of antifreeze that must be added to obtain a sufficient corrosion protection capacity by comparing the necessary levels of corrosion inhibitors and antifreeze with the present levels of corrosion inhibitors and antifreeze. - del. Method according to claim 12, characterized by the measure of informing the user of the amount of corrosion inhibitors and / or antifreeze, if the corrosion protection capacity is insufficient. Method according to one of the preceding claims, characterized in that the coating on the conductivity meter and / or the density meter / refractometer is taken into account by correcting the measured values by a predetermined, time-dependent factor. Method according to one of the preceding claims, characterized in that temperature deviations are taken into account by correcting the measured values by a predetermined, time-dependent factor, if the temperature is not within a predetermined range. Method according to one of the preceding claims, characterized by the measures: deriving the freezing point of the liquid from the present levels of antifreeze and / or corrosion inhibitors; measuring a temperature of the air outside the coolant; comparing the freezing point with the measured temperature; to inform the user if the temperature is lower than the measured freezing point or is within a certain range around the freezing point. Monitoring device (100) connected to a cooling system, for example a cooling system of a car or a truck, for the purpose of monitoring a corrosion protection capacity of a coolant in the cooling system, automatically carrying out the method according to any one of claims 1- 16, characterized by: a conductivity meter (101) extending into the coolant to measure the mobility of the coolant; an index gauge (102) extending into the coolant to measure the index value; and computer means (103), connected to the conductivity meter (101) and the index meter (102) and arranged to receive electrical conductivity values and index values from the conductivity meter (101) and the index meter (102), respectively. Monitoring device (100) according to claim 17, characterized in that the index meter is a density meter (102) and that the index values are density values. Monitoring device (100) according to claim 17, characterized in that the index meter is a refractometer and that the index values are refractive index values. Monitoring device (100) according to any one of claims 17-19, characterized in that said computer means (103) is arranged to process the received values and estimate the content of corrosion inhibitors. Monitoring device (100) according to any one of claims 17-20, characterized in that said computer means (103) is arranged to take into account coating on the conductivity meter and / or the density meter / refractometer by correcting the measured values with a predetermined , time-dependent factor. Monitoring device (100) according to any one of claims 17-21, characterized in that said computer means (103) is arranged to take into account temperature deviations, if the temperature is not within a predetermined range, by correcting the measured values with a predetermined, time-dependent factor. 10 15 523 531 20 Monitoring device (100) according to any one of claims 17-22, characterized in that said computer means (103) is arranged to estimate the freezing point of the coolant. Monitoring device (100) according to claim 23, characterized by a thermometer (104), exposed to the air outside the cooling system for measuring the temperature of said air, and in that said computer means (103) is connected to the thermometer (104) and is arranged to receive temperature values from the thermometer (104). Monitoring device (100) according to one of Claims 17 to 24, characterized by acoustic and / or visual warning means (111), arranged to indicate when there is a risk of corrosion and / or a risk of freezing. Monitoring device (100) according to one of Claims 17 to 25, characterized in that the conductivity meter (100) is attached to the cooling system. Monitoring device according to one of Claims 17 to 26, characterized in that the density meter (102) is attached to the cooling system.