DE3117279A1 - ARAEOMETER FOR DETERMINING THE DENSITY OF A LIQUID WITHIN A SPECIFIC AREA AND DENSITY MEASURING DEVICE WITH THESE ARAEOMETERS - Google Patents

Description

Patent attorney

Hubertusstrasse 83 ¹ A D-8035 Gauting

<sr Munich ^ 89) 8506036 * 4 BREVET

Telex 521707 lore d fax machine

? e? ds? r34 ³ ° ' ^{April 1981}

4000 Düsseldorf My files: c 12O-j, DE

Hydrometer for determining the density of a liquid within a predetermined Area and density measuring device with these hydrometers.

The invention relates to a hydrometer for determining the density of a liquid within a predetermined range Area according to the preamble of claim 1, and to a density measuring device with these hydrometers according to the Preamble of claim 4.

Due to the thermal expansion, density measurements at different temperatures are subject to a temperature error, ie the density measurement in a liquid at temperature T differs from a measurement in the same liquid at a different temperature 9.

Because the coefficient of thermal expansion of glass is much smaller As that of liquids, density measurements are made with glass hydrometers at different temperatures are subject to large temperature errors. This led to hydrometers - made of plastics, their thermal expansion coefficients are larger to manufacture. Plastic hydrometers are both with a weight - around the hydrometer to tare and to achieve an upright swimming -

/ 2

-2 -

as well as without weighting, whereby the hydrometer is held vertically in a narrow guide while it is in the liquid floats. In this context it is also known that the hydrometer is made of a material with approximately 'The same coefficient of thermal expansion as that of the liquid to make the temperature error small to keep.

A closer look at the thermal expansion of most liquids shows that they have different coefficients of expansion at different densities. Therefore, full temperature compensation (elimination of temperature errors) would be only possible with a single liquid density, namely where the expansion of the hydrometer coincides with the the liquid is identical. Other densities of the same liquid - with different coefficients of expansion - could only measured without errors at a single reference temperature, which was used as a basis for the calibration of the hydrometer will.

When considering materials whose coefficients of thermal expansion vary with temperature, the thermal expansion can be expressed as the ratio of a length L, measured at the reference temperature T, to the change in length a \> at another temperature 0. At temperature Θ each reference temperature length L and is therefore changed 1+ ^ h by a factor, the change in length Lq = L (1 + y ~ -) · Since "dL is small, it can be the appropriate volume change 3 Accept AL. The reference temperature volume V becomes a correspondingly changed volume V ^ = VCi + S · ^ - ^). This change in volume obviously causes an inverse change in density, so that ο - ·

The object of the invention is to correct this Temperature errors in the entire measuring range are based, especially if - as is often the case - the heat from coefficient of expansion of the liquid is a variable function of both density and temperature.

/ 3

According to the invention, this object is achieved by the features' m Characterizing part of claim 1 or 4 solved in conjunction with the respective preamble. Advantageous further training of the invention result from the features of claims 2 and 3 and 5 to 14, respectively.

The use of rotatable floats with weighting for measuring the density of a liquid Lst z.R. from US-PS 4,136,551 and US-PS 3,908,468, as well as from US Pat earlier US Pat. No. 3,908,468 to the applicant.

The invention generally makes the influencing the scale linearity and at the same time the enlargement of the scale is achieved, so that a more accurate reading is possible will. Furthermore, it achieves the avoidance of display errors due to the additional buoyancy more accidental Air bubbles, which in practice often falsify measurements with devices of the type mentioned.

Below are various preferred embodiments of the invention with reference to the drawings, for example described in more detail; show it:

1 shows typical thermal expansion curves, ver <- · i nl a ^ li t; Fig. 2 is a hydrometer with a volume graduation, which for

the invention is essential;

3 shows curves analogous to FIG. 1, but with reference to the invention;

Figures 4a and 4b show an embodiment of the invention;

Fig. 5 thermal expansion curves of the embodiment according to the Figures 4a and 4b;

6a shows a known device in an application example;

6b shows an embodiment of the invention analogous to FIG. 6a;

Fig. 7 the. actual temperature error of the device or embodiment according to FIG. 6a or 6b;

8 curves analogous to FIGS. 1 and 3, but for ο ine and or :; kind of liquid;

Figure 9 shows an embodiment of the invention for use with the liquid of Fig. 8;

10 schematically shows a float with weighting; Fig. 11 - the scale of the float of Fig. 10; 12 shows an example of the respective sideslip angles of two

Swimmers with equally large changes in density; 13 shows an embodiment of two floats and the resulting density scale;

14 and 15 details of the embodiment according to FIG. 13; 16 shows typical expansion curves in a simplified form; FIG. 17 shows the temperature error of known densitometers corresponding to FIG. 16; FIG.
18 for the invention expansion curves analogous to

Fig. 16;
19a and 19b show the corresponding temperature error for

one form of the invention;
Firj. 20 shows an alternative to FIG. 18; 31a and 21b show the corresponding temperature error for

a second form of the invention; 22 shows a further alternative to FIG. 18; 23a and 23b show the corresponding temperature error in

an ideal form of the invention; FIG. 24a shows an embodiment of a float similar to FIG. 15.

but with a low density weighting;

FIGS. 24b and 24c show embodiments analogous to FIG. 24a, but with a different attachment of the weighting lower Density;

25 shows the temperature error in an application with real Materials;

Figure 26 shows a portable densitometer.

To illustrate the temperature effects more clearly, simplistically assume that the thermal expansion of the materials is a linear function of temperature change. Accordingly, the thermal expansion curves become a typical one Liquid to straight lines - as shown in Fig. 1 - where the liquid density from a minimum ο. with a

Thermal expansion -y- (<? „·) Up to a maximum ο. with; a thermal expansion τ ^ (<?, -,,) is assumed. Di '- V.'irrn <> -

Li max

Expansion curves in between Lying liquids i t.:::.d i- ¹ Mt.en are distributed between these extremes. The thermal expansion curve of an aerometer material, which corresponds best to the expansion of the liquid and thus results in the best possible temperature compensation, is shown by curve 1. As can be seen from FIG. 1, a complete temperature compensation is only given in the middle of the density range, so that at extreme temperatures and densities, 2, 3, 4 and 5, a temperature error is unavoidable. The temperature error obviously results from the differences in expansion between the liquid and the hydrometer at a given temperature and density. Its size can significantly affect the reliability of the instrument. The invention enables these temperature errors to be corrected.

In Fig. 2 the total volume of the hydrometer is divided into three essential parts; the body volume Va that denotes the Includes hydrometer body to the lowest limit of the density scale; the scale volume Vb, between the lowest and the uppermost limit of the density scale; and the spindle volume Vc, the remaining volume above the uppermost limit of the density scale. If the hydrometer is in a liquid with of the highest density to be measured floats, only the volume Va is immersed in the liquid. If the hydrometer is in a liquid with the lowest density to be measured floats, both volume Va and volume Vb are immersed in the liquid. Volume Vc is required to enable reading of the scale at low densities and, as will be explained later, its size is used to determine the mass of the hydrometer so that the volumes Va and Vb can be measured precisely.

Obviously, the scale of such a device can be in different Units must be calibrated (e.g. in units of concentration, if the density of a solution depends on its concentration depends), but since this is only a design element, we are only talking about the density of the liquid.

because only this is measured with such devices.

According to the invention, the volume Va consists of a material or a combination of materials such that the thermal expansion of volume Va is essentially the same as that of the liquid with the greatest density to be measured. At the same time volume Vb consists of a material or a matorial combination such that the thermal expansion of the volumes Va and Vb taken together is essentially the same as that of the liquid with the smallest density to be measured. With the previously introduced expressions for thermal expansion, and if one writes the expansion of the volume Va simply = £ - and that of the volume Vb corresponding to τ-, the mentioned conditions are fulfilled if:

ν ~ + Vb ^Δ ^

Fig. 3 shows the corresponding thermal expansion curve 6 for Volume Va and curve 7 for the volumes Va and Vb together and, in comparison, the thermal expansion curves of the liquid as in Fig. 1. Due to the correspondence of the thermal expansion curves, Temperature errors are avoided at both the highest and lowest densities. ' In between Density results from the expansion of the hydrometer from the ratio between volume Va and that in the liquid submerged part of the volume Vb, so that the expansion of the hydrometer is proportional to the density of the liquid changes. Since the thermal expansion of the liquid also changes roughly proportionally with the density, is at all densities the expansion of the hydrometer is essentially the same as that of the liquid, so that in the entire measuring range temperature errors of the instrument can be avoided.

FIGS. 4a and 4b show, for example, an embodiment of the invention in the form of one made of two different plastics manufactured hydrometers. Volume Vb consists of

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a material 9, while volume Va is composed of the material 9 and a material 8 int. D <i fin ΛΚίοπκ · - they do not necessarily have a rice-shaped cross-section must, the cross-section of volume Va can be designed as in Fig. 4b, so that both materials the temperature can quickly accept a liquid surrounding the hydrometer.

In order to achieve complete temperature compensation in a liquid as previously described, the thermal expansion of material 8 should be greater than that of the largest liquid density to be measured, while the thermal expansion of material 9 should be smaller than that of the smallest liquid density to be measured. Dien is shown in Fig. 5, where curve 8 shows the thermal expansion of the; Material 8 represents and curve 9 shows the thermal expansion of material 9. At the highest liquid density to be measured, only volume Va is immersed, and it should consist of 65% material 8 and 35% material 9. The expansion of volume Va would thus lie in this relationship between curve 8 and curve 9, as curve 10 shows. At the smallest liquid density to be measured, both volume Va and volume Vb are immersed, and since Vb consists only of material 9, the immersed volume would now consist of 40% material 8 and 60% material 9. Here again the immersed volume would be a thermal expansion which corresponds to this ratio, as curve 11 shows. Obviously made use one ähnil cozy Ergebni if other materials with different thermal expansion coefficients are combined appropriately under other circumstances.

The linearized expansion curves of the examples have been said to simplify the properties of real materials represent. The conclusions from the examples are, however, independent of the linearity of the thermal expansion. In practice it has been found that the expansion curves of many areometer materials match the expansion curves of most aqueous solutions are similar. In both cases it shows

an increase in the expansion coefficient with increasing Temperature. Because of this correspondence, a variety of materials can be made according to the principles described herein can be combined for use with a wide variety of liquids.

It is obvious that in practical use According to the invention, the effective size of the volumes Va and Vb depends on the actual immersion depth of the hydrometer. Since the respective immersion depth is also determined by the mass of the hydrometer, this must be done in advance be precisely measured. At first it seems that the mass of the hydrometer is determined by a simple calculation of buoyancy could be, e.g .: M = Va * <? = (Va + Vb) · «> -.

IlLelΛ. JlL J_ II

In reality, however, the surface tension causes the Liquid an increase in the immersion depth, creating a non-negligible change in the volume ratio; e occurs .. For this reason, it is a further object of the invention to provide a sufficiently precise compensation for the capillarity effect to create so that the hydrometer swims with the predetermined immersion depths.

In a liquid with surface tension ϋ , the additional immersion of the hydrometer caused by capillarity can be calculated with a good approximation from ZId =, where C is the circumference and A is the area of the hydrometer cross-section on the surface of the liquid. Since Ad is a function of the (variable) liquid density, it would be more convenient to assume here that the additional immersion is based on an apparent increase in mass, and to calculate the apparent additional mass with AK - ^ίί ψ-. This can be thought of as the mass of liquid that is lifted by capillarity over the free surface of the liquid. For the purpose of the buoyancy calculation, the total mass of the hydrometer is then M = Ma + Mb + Mc + -, where Ma, Mb and Mc mean the masses of the volumes Va, "Vb and Vc. Thus the advantages of the invention in practical

Applications are fully effective, the hydrometer according to the invention also consists of a spindle volume Vc made of material of density qc, which is dimensioned so that

Va - [Va · ρ -Ma-Mb- -] · "- [3]

^v max g ' pe ^LJ

It has been said that such hydrometers are] with al: -; can also be without weighting. The former is the duty the materials are usually not critical, since the total mass of the hydrometer can be determined by the weight. In the case of the latter, the total mass would be due to the design of the volume Vc in accordance with equation (3). However, the scope of this remedy is limited by that if the volume Vc were increasingly increased, a hydrometer would become increasingly top-heavy without being weighed down and would experience an increasing frictional resistance in its guidance. (The volume Vc must have a certain minimum size so that in liquids of low density there are:; · hydrometers not accidentally immersed completely.)

In such cases the density of the hydrometer materials would be critical and it remains to be demonstrated that the principles set out under strict conditions - where the materials used meet the requirements for thermal expansion and density at the same time must meet - applicable with real fluency are.

A typical example would be the density measurement of aqueous sulfuric acid solutions, where because of the aggressiveness of the Liquid the use of a metallic weight would be avoided. Density measurements with glass hydrometers are subject large temperature errors, but carefree hydrometers made of polystyrene can be used because this material has greater thermal expansion, suitable density and sufficient chemical resistance. The most used Density ranges from 1100 kg / m up to 1300 kg / πΓ, and 6a shows, to scale, a hydrometer suitable for this purpose with a density of 1050 kg / m au π Po l.ynt yro]. } ·, ':; i:; l see! lent, that the volume Vc is just large enough to accommodate the hydrometer

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to function at the least liquid density; however, lighter materials (e.g. polyolefins) . need a much larger volume Vc - like contour 12 shows - and would not be useful for the above reason. . 6a thus shows an optimal one according to the prior art Hydrometers for this case.

Fig. 6b shows an embodiment according to on the same scale of the invention for this case, the volumes Va and Vb being identical to those of FIG. 6a. Here is volume Vb and Vc from SAN (styrene acrylonitrile) copolymer with density 1080 kg / m, while volume Va from 53% SAN and 47% polyethylene with a density of 917 kg / m. It can be seen that the volume Vc is of a suitable size and thus that dir · pe materials meet the requirements for density fully er-Cij I lon.

Ki <j. The temperature error of the two hydrometers Fig. 6d and 6b as a percentage of the indicated density, assuming liquid temperatures of 10 to 60 C. Although the temperature error of the hydrometer in Fig. 6a is less than that of a glass areometer, it extends from approx. -0.8% at 10 ° C (curve 13) to + 0.8% at 60 ° C (curve 14). The corresponding curves 15 and 16 for the hydrometer Fig. 6b show a temperature fault nowhere größep than - 0.2%, so an improvement of temperature compensation by a factor of

Fig. 6b shows the simplest embodiment according to the invention, namely a hydrometer without weight and consisting of only two materials. In cases where the requirements the temperature compensation are particularly strict, more than two materials are combined according to the invention in such a way that that the expansion of the hydrometer corresponds even better to the expansion of the liquid. For example Fig. 8 shows the thermal expansion curves of a liquid, the change in the coefficient of thermal expansion of the change is not proportional to the density, so that with decreasing density the decrease in thermal expansion is

accelerates. For this case, FIG. 9 shows an embodiment of the invention, where the volume Vb consists of a combination of a material 17 with a material 18. So that the thermal expansion of the hydrometer according to FIG. 9 corresponds to that of the liquid in FIG. 8, the expansion coefficient of the material 18 is smaller than that of the material 17,
so that the expansion of the submerged volume of the hydrometer also decreases with decreasing liquid density at-.

There are density measuring devices of the present type
there is hardly any literature and, since an understanding of its functional principle is assumed in the following description,
this principle is to be explained briefly with B'Szug on FIG

Such a density-sensitive swimmer consists of: -, a rotatably mounted buoyancy body with a weighting such that the following criteria within the entire measuring range are valid:

1. The radial connection between the fulcrum and the center of lift forms a higher angle with the horizontal as the radial connection between the pivot point and the center of gravity, i.e. the float is hydrostatically stable;

2. The density of the liquid (to be measured) i:; t greater than the density of the float and less than
the density of the loading, ie with a liquid density 9, a density of the float ς. and a density of the weight 9, the following inequality holds for all values

The geometry of such a float is shown in FIG. 10, where the radial connection between the center of rotation and the center of lift with the horizontal forms an angle <x and from the Connection between the pivot point and the center of gravity is separated by the angle ß. Is the volume of the buoyancy body V_ with the center of gravity in the radial distance A from the fulcrum, and the volume of the weight V, with the Center of gravity at the radial distance B from the pivot point, see above

is the torque of the float:

M = p [VA cos cc + VB cos (cc - 3)] - ρ VA cos et - pVB cos ία - β), fl)

α O 3 3 Ö Ö

If such a float is immersed in a liquid, it rotates until the torque is zero. The higher the relative Density of the liquid, the higher (more positive) is the angle «. This is a steady state where:

(p - P} VA cos <x = Cp, - p) VJB cos ία - a) [2.]

The slip angle for a given liquid density can be calculated with a rearrangement of (2), where the swimmers, geometry with the first expression, the ratio of the densities with the second expression and the corresponding angles with the third expression can be described:

V ₁ B p, - a
b _# ^v b ^v _ cos cc r, -

VA ρ - ρ cos (α - β)

3 3

The terms used for length, volume and density apply at a given reference temperature. The following will consider the effects on density measurements made at temperatures different from the reference temperature, and it will be apparent that these quantities are all affected by thermal expansion. When considering materials whose coefficients of thermal expansion vary with temperature, the thermal expansion can be expressed as the ratio between a length 1, measured at the reference temperature T, and the change in this length Jl at another temperature θ.

At the temperature θ, each reference temperature length is therefore changed by a factor of 1 + - , and the changed length is 1-, - 1 (1 + -). Since Δ1 is small, the corresponding change in volume can be assumed to be 3-41. The reference r-mper.i Iu r-Vo'l uraen V becomes a correspondingly changed volume V ₀ - V (1 ι; j 4 ^ ·)

borrowed an inverse change in density such that q _a ** "T ~ 2T '

The thermal expansion of the float is easy with

/ la.

- ~ - and the thermal expansion of the weight is correspondingly indicated by ^ ς ~, and if the aforementioned expressions for the changed lengths, volumes and densities are introduced into equation (i), then the float angle in a liquid with the density q _& at temperature 9 calculate with:

^V a ^A p _a (1 - 3 -) - ρ cos (et - ß)

9 3 3

This equation is similar to Equation (3), and the fact that the first "term" of both equations is the same is typical for swimmers, where - according to previous practice - the weight is attached to the float. In this case, the lengths A and B are determined solely by the thermal expansion of the float, so that their Change proportionally and on the Wa'riiHedUiJdcJinunrjij-ch.jrakteristik of the swimmer is without influence.

As an object of the invention, temperature errors better than To be corrected so far, new designs for influencing the thermal expansion characteristics of the float will be introduced suggested. For this it is necessary to introduce the concept of a "fastening radius"; this is the distance R.

between the pivot point of the float and the fixed point of attachment of the float, or the corresponding distance R for the weight. The introduction of these expressions removes the restriction made for equation (4), see above that thermal expansion effects in floats of all types are described with:

^{+ 1 n (1 +} V ^cos

T5 ""

^V a ^{A fl +} T ⁺ T ^[ τ ~ - -a ~ ^{]) 0} B ^{fl +} * r ^J " ^P a ^COS

IZ

At the reference temperature, equation (3) can be used to calculate the swimming angle Calculate a typical float for equal increments of the Klüsr.igkpj t density and record as in Fig. 11. Hüir · it is evident that soon «! Density increments very unequal Angle increments correspond, and that this lack of linearity the practically usable scale range to about 80 ° limited. This is a property of such devices, and so an acceptable linearity of the density scale can only be achieved through Limitation of the scale range - i.e. by reducing the Measuring range or the division distances - can be achieved.

As an example of a characteristic of the invention, Fig. 3 shows the angular scales 19 and 20, which correspond to equal liquid density increments (between 1020 and 1080 kg / m). Scale 19 applies to swimmers 19, who are obviously designed in such a way that they have relatively large angular increments in the lower part of the density range, while scale 20 applies to swimmers 20, which is designed the other way round. Since the area of the greatest angular increments is the area of greatest measurement accuracy, it can be said that the float 19 predominantly determines the measurement result in the lower density range, while the float 20 predominates in the upper density range. If half of the density range is assigned to each of the two floats in this way, it can be seen that each half corresponds to an angular range of approximately 80 ° (indicated by broken lines), in which the angular increments are relatively large. In a preferred embodiment of the invention, one of the floats carries a density scale and the other an index, the position of which can be read on the scale; a concept that is known per se from US-PS 4 136 55. ¹

13 shows an embodiment of float 10 FIG. 12 in the form of a scale part 21 and an embodiment of float 20 from FIG. 12 in the form of an index part 22. Both parts are rotatably mounted on a common axis. The scale part 21 carries a scale with angular increments

ments that show the relative positions of the two parts in the given densities, and these are obvious the sums of the angular increments of the individual parts, as in Fig. 12 shown. From FIG. 13 it can be seen that the linearity of the resulting scale is very good (also very much better than the linearity of the 80 ° scale halves of Fig. 12) and further that the scale circumference extends over 210 ° (and thus exceeds the sums of the 80 ° scale halves by 30%). the A combination of floats made in this way is therefore one simple "additive" combination of two swimmers clearly superior, both in terms of scales! inearity alu as well on scale range.

On closer inspection it becomes apparent that the scale division of FIG. 13 is symmetrical about the center of the scale, and that di-s follows from the mirror symmetry of the scales 19 and 20 of FIG. Obviously, the scale angles of FIG. 12 are not prescribed (by assigning a different angle range to the given density range, other angle increments result according to equation (3)), nor is a symmetry relationship required between the scales 19 and 20. A particular advantage can be seen in the fact that the angular range of each swimmer can be selected in such a way that the resulting scale division as a whole <x] ar is enlarged or reduced at any point, symmetrically or asymmetrically.

FIG. 14 shows the embodiment of the scale part 21 from FIG Fig. 1 3 in detail. If this part were a circular plate of uniform thickness, it would be around the center hydrostatically neutral. If the part consists of a buoyant material, a hydrostatic one can be used Create buoyancy volume (V) by moving the plate

thickened, e.g. within area 24.

The angle Qi then relates to the radial connection of the pivot point with the center of lift of the additional volume. Instead of the thickening within the surface . '■]

the plate thickness can be reduced - or the plate can be cut out completely - within the area 25, which is the area 24 diametrically opposite. A hydrostatically effective buoyancy volume can also be created by · that one Sector of the plate omits, or that in the case of a plate of uniform thickness, the axis 23 is arranged eccentrically. In In this example, the weight 26 on the float attached, as is customary in previous practice.

FIG. 15 shows the embodiment of the index part 22 of FIG. 1 '] in detail. An index part can be made according to the principles already described for the scale part (e.g. by using a smaller circular part so that the scale is not covered). However, every volume that is not symmetrical about the pivot point has a hydrostatic effect, so that in this example the buoyancy body is designed as a sector of a circle with an index 27. In this case, the index 27 can be arranged offset relative to the angle α (eg to make it easier to read the scale) if the scale is arranged offset by the same amount relative to the angle and the scale part 21 at the same time. In this example, the pivot point 28 is ring-shaped and rotatable about the axis 23 of the scale part 21, so that both parts have a common pivot point. The weighting 29 is here also attached to the float, as is customary in previous practice.

In Fig. 13, 14 and 15 the two floats are constructed so that the index part is arranged in front of the scale part. This arrangement can be reversed as long as the index remains visible so that its position can be derived from the scale; c-> ri can be. Here the scale part 21 is assigned to the angle scale 19 of FIG. 12 and the index part 13 is assigned to the angle scale 20 of Fig. 12, however, this assignment is arbitrary. Reversing the assignment changes neither the principles described nor the resulting scale.

/ 17

From what has been said it follows that in agreement it is irii.t Equation (3) every swimmer makes an angle oc with respect to the Horizontal occupies independently, so that the relative position of immersed swimmers only of d <.. * r · density dor Fluid depends. Another advantage is to be seen here in that the reading does not have any "artificial horizon" as is common in most previous devices (an example is in applicant's US Pat. No. 4,037,481 described).

Since density measurements often have to be made at different temperatures, the "temperature error" of devices of this type is important. The angular amount of the temperature error of a swimmer of conventional construction results from the difference between the angles ^, which are calculated from equation \ 3) and equation (4). In previous practice, weights made of metal were used. Because of their small volume (high density) and small thermal expansion coefficient, their influence on the temperature error is negligible. In such cases the temperature error is almost entirely due to the difference between the thermal expansion of the float and that of the liquid. Typical liquids (e.g. aqueous solutions) have different coefficients of expansion <> n at different densities (that these coefficients also vary with temperature, will be discussed later), so that complete temperature compensation could only be achieved with a single density. This would be the case if the expansion (U-; buoyancy body were identical to that of the liquid. Other densities of the same liquid, with different thermal expansion coefficients, would be subject to a terrestrial temperature error, provided that the measurement was made at a temperature other than the reference temperature for (For this reason, US Pat. No. 3,908,467 uses a plurality of floats and associated scales), and so the measuring range of the device is divided by the density range of each measuring mechanism to zoom out.) Under

/ 18th

In these circumstances, the temperature compensation consists simply in choosing a buoyancy material whose heat expansion an average thermal expansion of the Corresponds to liquid densities.

In order to illustrate the thermal expansion effects in this type of device, one can simplify the assumption that the thermal expansion of the materials is a linear function of the temperature change. Accordingly, the expansion curves of a typical liquid become straight lines - as shown in FIG. 16 - where the liquid density extends from 1020 to 1080 kg / m ³ and where - as is usually the case - the coefficient of thermal expansion of the liquid also increases with increasing density. The curve 30 then shows the expansion of a float, the expansion of which corresponds best to the average expansion of the liquid and therefore has the smallest temperature error.

Under the assumptions of FIG. 16, FIG. 17 shows the temperature errors of a typical swimmer with a scale angle of 80 ° for the given density range. The scale applies for the reference temperature shown in Fig. 16, and the temperature range ranges from 0 C to +70 C. For selected liquid densities, the temperature error is at

: i «3

0 C is shown as a broken line and that at +70 ⁰ C is shown as a dotted line. With a liquid density of 1100 kg / nr there is no temperature error, because here the expansion of the buoyancy material is identical to that of the liquid. The temperature errors are greatest at the density extremes, and the fact that the sign of the temperature error is reversed from one extreme to the other is a consequence of the relative expansions according to FIG. 16.

It should be noted here that the angle changes caused by thermal expansion are used to assess the temperature error are unsuitable insofar as this should actually be related to the displayed density. Where the Scale division is large, represents a given angle error

/ 19th

a smaller density error dar al :; where the:.; kaJ allocation is smaller. Thus, one inferred from the I · ¹ ig. 17, that (although the angular error in the density extrema are not large) of the display error is about - 5 kg / m amounts, and that this is the largest temperature error for the given temperature range.

This approach can be applied to the invention. by continuing to assume the liquid according to FIG. 16 and the sideslip angles shown in FIG. 12 at the reference temperature presupposes. Here the swimmer 19 iμ predominates the density range from 1020 to 1100 kg / nr, so that - analogously the previous example - a lift.smateria I ~ .u was to choose, whose thermal expansion would be roughly the same as that of the liquid at density 1060. For the swimmer 20 one chooses accordingly a buoyancy material with a thermal expansion roughly equal to that of the liquid at a density of 1140. Dir -: - Assumption is shown in Fig. 18, where the thermal expansions of the buoyancy bodies 19 and 20 are represented by curves 31 and 32.

19a shows the temperature errors of the respective swimmers, while FIG. 19b shows the resulting temperature errors in relation to the density scale. The latter are the sum of the angle changes caused by temperature effects. Here again the error at 0 C air is shown as a broken line and that at +70 ⁰ C as a dotted line. Here, too, the angular errors are greatest at the density extremes, but the display error is nowhere greater than: -. - 3 kg / m ³ .

The temperature errors of the individual swimmers add up according to a simple "sign rule" that can be found in FIG is easily recognizable: If the expansion of the liquid wedge lies between the expansion of the two swimmers, then have the angular errors of the swimmers have opposite signs, and their sum is smaller than the largest individual error; i: U.

-Stu

Expansion of the liquid, however, greater (smaller) than the largest (smallest) expansion of the swimmers, so have the angular errors of the individual swimmers have the same sign, and their sum is greater than the largest individual error. In the first case, the interaction of the swimmers causes an absolute reduction in the thermal expansion measurement errors caused; in the second case the opposite is effected.

With regard to the preceding sign rule, it is instructive to consider an extreme case. Fig. 20 shows an example where the curve 33 represents the thermal expansion of the float 19 and the curve 34 the thermal expansion of the swimmer 20. The expansion of the buoyancy materials do not correspond to the expansion of the liquid at any point, and FIG. 21a (analogous to FIG. 1Sa) shows that the angle errors of the individual swimmers are relatively large.

However, FIG. 21b shows that the sums of the individual errors (following the sign rule) are very much smaller than the individual errors themselves, so that the display errors nowhere is greater than - 2.5 kg / m. In addition, FIG. 21b shows an almost complete temperature compensation not only at. the mean density, but now also with the density extremes, where the almost equally large individual errors are opposite Have signs. The two examples show that the invention Use of buoyancy materials with very different thermal expansion in each case a better temperature compensation acts as the use of an "ideal" material in a conventional device.

If "ideal" materials are assumed for the invention (analogous to the assumption for FIGS. 16 and 17 ), the thermal expansions of the floats 19 and 20 would be roughly as shown by curves 35 and 36 in FIG. 22. FIG. 23a (analogous to Figure 19b and Figure I b..?) XfIfJl di ο resul L ierenden temperature error, the size of the entire measuring range anywhere r as - are 1 kg / m. Since the remaining angle errors are so small, they are

/ 21

Belle I listed where Δ <χ. the angular error of the individual float, ΣΔ <χ the sum of the angular errors at the respective temperature extreme and ^ T, A (X. denote the sums for the entire temperature range. Table I shows how the opposite signs of the individual errors ( Acx. ) Cause an absolute reduction of the display error (i'Zkx) at all densities and temperatures

Liquid (iicht at reference temp.

0 ⁰ C

Float 19 20

Δ -χ Δα

-70 ⁰ C

swimmer
19 20

ί, α Δ nc

0 ⁰ C

until

• 70 ¹

1020 j -0.7 - ¹ O ₁ I. -0.6 +1, 3 -0.2 + 1.1 ι 1 .7 ° 1060 -1.1 -1.7 +0.6 +1 9 -2.7 -0.8 I. 1.4 ° 1100 -1.7 + 1.6 -0.1 -3 .0 -2.8 -0.2 ι 0.3 " 1140 -1.8 +1.1 -0.7 +3 .2 -2.0 + 1.2 I. 1.9 ° 1180 0.0 +0.8 +0.8 +0 .2 -1.5 -1.3 I. 2.1 °

Table I.

If the sum of the display errors for each temperature extremum is related to the angles i π kremen l: en at the respective point on the density scale, then the maximum temperature error can be given as a percentage of the displayed density. Fig. 23b shows this data for the entire density range, wherein the temperature error at 0 ⁰ C as a broken line and is shown at + 7O ⁰ C as a dotted line. From Fig. 23b it can be seen that the "S" -shaped error curves, which are a property of the invention, greatly promote temperature compensation.

It has been said that the linearized expansion curves are a simplified representation of the real material properties. However, it is evident that the practical validity of the conclusions drawn from the previous examples does not depend on the linearity of the thermal expansion, but rather on the correspondence between

/ 22

IO

Curves of the real fluids and curves of the real ones Float materials. In practice it turns out that the thermal expansion curves, for example, a variety of Plastics (the density of which makes them suitable for use as a buoyancy material) are very similar to expansion curves a variety of aqueous solutions are. In both cases, the curves are not linear as there is an increase in the coefficient of thermal expansion show with increasing temperature. fjomj I- the designer can easily choose a material that for a given liquid sufficient temperature compensation within a certain density and temperature range guaranteed. It has been said that up to now the temperature compensation has primarily been achieved by choosing a suitable one Buoyancy material was achieved; in the case of the invention the requirements for the material properties are by no means stricter than with conventional devices the case is. On the contrary, the previous examples with three different material combinations (i.e. six different expansion coefficients) resulted in each Case a better temperature compensation than using an ideal material in a traditional device.

Thus di ^<3 advantages of the invention will be further exploited, the invention aims also to influence the temperature behavior of the swimmers with new constructive means. In previous practice, metallic loads, the influence of which on the temperature behavior is very slight, have been used. In contrast to this, weights with a relatively large volume and greater coefficients of thermal expansion are used according to the invention. The temperature behavior of swimmers is significantly influenced by such loads and is no longer determined almost exclusively by the thermal expansion of the buoyancy material. Obviously, such weightings must also satisfy the inequality ς><q for all values of ς>.

To what extent a weighting the thermal expansion of the swimmer as a whole can be determined by evaluating the first expression of equation (4) bourt ^ il ^ n. If one sets radius A - Radiu; B, the expression V. / V

D ti

and describes the volume ratio of weight and Floats. In conventional devices with metallic weights, this size is - depending on the given Densities and corresponding sideslip angles - approximately between 0.015 and 0.04; i.e. the volume of the float? is 25 to 70 times greater than that of the weight.

If the volumes are less unequal, the designer can determine the thermal expansion of the float as a whole through the Influence the thermal expansion of the weight. According to the invention this is achieved by using relatively low density weights in such a way that the The density of the loading is less than four times the density of the float, i.e .:

If, for example, the density of the weight is about one and a half times is the density of the float, the ratio V, / V would assume values of about 0.3 to 3. Thus can-D a

te the volume of the weight - depending on the density and angle range of the swimmer - be a third as large or three times as large as the volume of the float. So has the designer selected suitable materials, so he can also set the volume ratio of the materials and thus determine the thermal expansion of the float by setting the density and angle range accordingly right. Thus the orf'indr> according to <? use of Weightings of low di ^ hLe the advantage .girier. to ^ benefit "Degree of freedom" of the construction, because the temperature compensation is no longer due to the choice of material alone given.

As another new means of influencing temperature behavior the swimmer sees the invention swimmer "· truk t u-

SZ

ren before, in which the different expansion coefficients cause non-proportional changes in the hydrostatic radii A and B of the float and the weight. In conventional swimmers, the weight is attached to the float, so that the expansion of the buoyancy material the radii A and B changed proportionally and thus not influenced the temperature behavior of the float. However, weights of low density (i.e. with relatively large volumes) enable float constructions, where - while maintaining the relative angular position of the float and weighting - as a result of the unequal Extensions of the two materials a disproportionate change in the radii A and B takes place. In this case the behavior of the swimmer follows from equation (5) instead of, as before, from equation (4).

These means are used, for example, in the embodiments shown in FIGS. 24a, 24b and 24c. FIG. 24a shows an embodiment similar to that of the index part 22 from FIG. 13. Here, a float 37 is attached to a low density weight 38. This is a reversal of the previous one Practice, and since the thermal expansion of the weighting material would be relatively small, the swimmer would have a very much smaller coefficient of expansion than the buoyancy material alone. Here are the temperature-dependent changes of the two radii A and B determined by the thermal expansion of the loading; so that equation (4) for this Case still applies.

Fig. 24b shows a similar embodiment where a low density weight 39 and a buoyancy body 40 in the Pivot point by means of concentric rings 41 and 42 are attached to each other. A "dovetail" connection allows the temperature to change 43 a different radial extent while maintaining the relative angular position of the Parts. - Do the two materials have different heat levels:; dehriurig: »koof f icient, the change in temperature causes a non-proportional change in the radii A and B, which means

for this case equation (5) applies. Since both parts are fastened in the pivot point, both "fastening radii" are

R and R _K , equal to zero, and the first expression of Gleia D

chung (5) becomes:

VA fi -—j

Fig. 24 shows a similar embodiment, wherein the attachment 46 of the low density weighting 44 with the float 45 is at the edge of the swimmer, while the relative angular position of the toi. Le is ensured by d - n pancake tail 47. Here, as before, the float is attached to the pivot point so that the attachment radius R is equal to zero. The weighting is, however, attached at 46, so that the attachment radius R i assumes the value B + X. If these values are inserted into equation (5), the first expression becomes:

ι / (n j. rß ^ ri ^Äa v ^ft ^ i ν, {α -ι- (ΰ + Λ J— - Λ -, - J

VA il * f) aa

W.irf'H the materials and di <'Vo I i.jin i ni d'T An:. (iiht mi ·) ·; [Otmen according to FIGS. 24b and 24c are identical, the Ί'οπιρ'.τα-ture behavior of the two swimmers would nevertheless be different as a result of the inventive modification of the fastening radii.

Obviously, these means can be applied to one or both of the swimmers, and their effect on temperature compensation will depend on the density and angular ranges chosen for the swimmers. Since there are a large number of suitable materials and since these can be further modified by appropriate fillers, Ia:;:; en the advantage "(Ut Ρ! ΓΓ i mluriq without- K i iTvhrrnil- urin i π c | if l'r , ix j:; Ulli;,! · I / "ti.

To verify these advantages in an application, you can As an example, examine a precision densitometer for aqueous solutions of sulfuric acid. An essential one

The density range is from 1100 to 1300 kg / m and a common temperature range would be from + 10 ° C to + 45 ° C. In this example, the float of float 19 should consist of unmodified high-pressure polyethylene, the float of float 20 should consist of unmodified low-pressure polyethylene and the weights of both swimmers should consist of unmodified polyfluorocarbon. The attachment radii of the two parts of both floats are zero and dor:; calender circumference should], as before, be 210 °. l-'iij.X ¹ '/.(M(Ji dfi'i TcmpfTtiturfohler in percent of the indicated density for the measured temperatures +10 ⁰ C (broken line), + 25 ° C (continuous line) and + 45 ° C (dotted Fig. 25 confirms the conclusions drawn from the simplified assumptions and shows that application of the invention enables correction of temperature errors to an extent that is precluded in conventional devices.

In this regard, it should be noted that although one can use such a device by simply inserting it into a liquid is immersed - in most cases the swimmers in an at least partially transparent one Housing to be installed. The housing is filled - usually by means of a suction bellows - in such a way that the float enters the Immerse the liquid sample. In practice it has been shown that the density measurements made with such devices are often significantly falsified. This is because there are apparently inevitable air bubbles in the liquid sample cling to the swimmers and, due to insane additional buoyancy, change the sideslip angle significantly. The suction opening of such a housing must be small because of the surface tension within it The opening must counteract the leakage of the filled housing. Furthermore, a suction bellows, whose elastic

/ 27

did enable a sufficiently fast filling of the housing, especially at the beginning of the filling process (when the bellows is largely compressed) a steep pressure gradient generate at the suction point. Also at this point is the weight that is lifted by the pressure gradient The smallest column of liquid, so that the bellows can expand rapidly. A particularly high face velocity is the result, and flow velocities around 3 m / s are not uncommon. That is why it is common Impact surfaces of various shapes within dey To attach the housing so that the measuring mechanism is not directly is hit by this jet of liquid. At such speeds, however, it is inevitable that the Liquid jet atomized on impact, so that the liquid sample contains large numbers of air bubbles. the end For this reason, the user has been instructed to first knock off the air bubbles from the measuring mechanism and then the display read off. This was inevitable because a significant reduction in the inflow velocity (e.g. caused by a reduction in the elasticity of the suction bellows could be effected) would unduly increase the filling time. The user of such a device would then use the suction opening from the liquid to be examined before the bellows would have expanded completely. The further expansion of the bellows would then suck in air at the end of the process, although air bubbles may be at the beginning would have been avoided.

The falsification of the display by air bubbles is a difficult problem with devices of this type, and:; o it is fi Another purpose of the invention is to allow air bubbles to form in the liquid sample under all normal conditions impede. To do this, use the swimmers described above built into a known housing which is filled by means of a known suction device so that the float Immerse completely in the liquid sample. The small outer suction opening of the housing is according to the invention by means of a gradually evolving An.s.iuqk-Mnd 1 :,

connected to: the measuring chamber so that the channel cross-section at the point of entry to the measuring chamber much larger than is at the opening. Because the flow rate at the point of entry to the measuring chamber is equal in time to the flow rate at the suction opening, the flow velocity must be at these points be inversely proportional to the channel cross-section.

The possible delay within such a suction caria 1:; is limited by the fact that a pressure gradient that is too steep along dos canal to tear off the flow and turn would lead to the formation of air bubbles. The actual flow rate at the suction port is natural depends on the cross-sectional size and on the instantaneous pressure gradient, but typical conditions result REYNOLD's numbers not greater than 1 · 10. In these circumstances should - depending on the size of the openings and Arrangement of the measuring mechanism - the duct cross-section at the largest point should be four times as large as at the suction opening, and a conical suction duct should have an extension angle no greater than 5.

However , the cross-section of the intake duct does not have to be circular, and under certain circumstances a cross-section with a rectangular or other shape would be structurally advantageous. In such cases, the expansion of the channel can be related to its circumference C and corresponding cross-sectional area A. (This is done analogously to the "hydraulic radius" ^, a similarity criterion for the flow of liquid in straight pipes.) If dA is an increment of the cross-sectional area, corresponding to dl an increment of the length in the flow direction, ansdUijkanal extensions in the Sir.ne of the invention are then the same if the values of the expression -. . - ^ j are equal. Since the expansion angles in question are small, this expression is used for a kc-

dr
niche intake duct to -ry, where r means the cross-sectional radius. Thus, for a conical intake duct according to the invention:

O <~ <0.09
al

and for an intake duct of any cross-sectional shape:

If the advantages of an expanding intake duct are to be retained under all practical conditions, then is It must be taken into account that such devices are equipped with suction extensions for various purposes. For this a flexible hose of the appropriate length is pushed over the suction opening. Because a small hose diameter If the flow is delayed and thus the filling time is noticeably longer, the cross-sectional area of such hoses is usually much larger than that of the suction opening of the device. That's why (and because of the uncontrolled movements of the flexible hose) the hose usually runs empty as soon as it is open end emerges from the liquid level. This means that only a little fluid is lost, but it is because of the length of the hose is the change in the column of liquid compared to the total height of the GerciU; relatively large. Consequently the hydrostatic equilibrium existing at the end of the suction process is disturbed; the suction bellows can move further expand and thereby suck in air, although no liquid has leaked from the housing itself.

In the case of a very flexible suction bellows, a slight disturbance of the pressure equilibrium is sufficient to allow further expansion to trigger the bellows. This shortens the column of liquid inside the hose and becomes a process accelerates, drawing in liquid first, then air. The process can even do one assume an oscillatory character, the suction of air being repeated with the outflow of liquid alternates.

/ 30

ι *

For precise measurement it is essential that air bubbles and turbulence within the measuring channels are avoided will. For this reason, the invention further provides that the intake duct is arranged in the form of an inverted "U" is, wherein the highest point of the channel is significantly higher than the entry point of the channel into the measuring chamber lies. As a result, air that passes through the intake port after the intake process is completed becomes the highest Position of the channel. A hydrostatically stable state is thus created again, so that there is no air enters the measuring chamber and no liquid flows out of it.

In the housing, the space available for the intake duct will usually be limited. That is why the intake duct preferably designed so that in the ascending part (between the suction opening and the highest point) the expansion of the channel is relatively larger than in the descending one Part (between the highest point and the entry of the channel into the measuring chamber). Thus, by extension induced negative acceleration of the inflowing liquid where it is rectified by a Gravity acceleration is supported, greatest, and where gravity acceleration counteracts fluid delay, relatively smaller. This will reduce the risk of stalling the flow, and for a given one Length of the channel a maximum delay in flow velocity is achieved.

For example, Fig. 26 shows a densitometer according to the invention. The transparent housing 48 contains the floats 49 and 50 which are rotatably mounted about a common axis. The compressible volume of the suction bellows 51 is dimensioned so that the housing 48 with a liquid sample is filled so far that the floats 49 and 50 are completely immersed in the liquid. The liquid sample is taken from the Suction opening 52 through the widening suction channel 53

sucked in and enters the measuring chamber of the housing 48 at the point 54 with a reduced flow velocity.
The intake channel 53 runs approximately in the shape of an inverted "U", the highest point of which is significantly higher than the entry point 54. A hose 55 can be attached to the suction opening 52.

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Claims (14)

WILLY LORENZ patent attorney Hubertusstrasse 83 '/, D-8035 Gauting * Munich' (O89) 8506036 "H- BRHVET Telex 5 21707 bred Teiekopierer 4000 Düsseldorf My files: c 120-j, DE patent claims 1. hydrometer v, for determining the density of a liquid within a predetermined range, in which its coefficient of thermal expansion is variable, consisting of a lower body volume (Va) equal to the total mass of the hydrometer divided by the liquid density at the upper limit of said range, and a mean scale volume (Vb) which, together with the volume (Va), equals the total mass of the hydrometer divided by the liquid density at the lower limit of said range, and an upper spindle volume (Vc), characterized in that the volume (Va ) is made of one or more materials such that the coefficient of thermal expansion of the volume (Va) is substantially equal to that of the liquid at the upper limit of said range, and that da ;; Volume (Vb) of one or more materials is such that the coefficient of thermal expansion of the combined volumes (Va, Vb) is substantially equal to that of the liquid at the lower limit of the range. 2. Areometer according to claim 1, characterized in that the mass of the spindle volume (Vc), together with the masses of the Volumes (Va, Vb), equal to the product of said mass (Va; and the liquid density at the upper limit of said Area minus one due to surface tension the apparent increase in mass caused by the liquid is when the "apparent increase in mass is the product of the surface tension and the circumference of the hydrometer on the surface of the liquid, divided by the acceleration due to gravity. 3. hydrometer according to claim 1 for use with liquids whose coefficients of thermal expansion are not linear change with the liquid density, characterized in that the volume (Vb) consists of at least two materials with different There is a coefficient of thermal expansion that is unevenly distributed within the volume (Vb), such that the lower part of the volume (Vb) has a different coefficient of thermal expansion than the upper part of the volume (Vb). 4. Density measuring device with hydrometers according to claims 1 to 3, a housing for the liquid sample, a first float rotatably mounted about a horizontal axis in the housing and a second float rotatably mounted about the axis, both floats consisting of at least one float relatively low density, whose center of buoyancy is offset from the axis and whose density is smaller than that of the liquid to be measured, and at least one weighting body with a relatively high density, whose center of gravity is offset from the axis, and whose density is greater than that of the liquid to be measured Liquid is, each float is shaped so that the radial connecting line between the center of buoyancy and the axis is offset from the radial connecting line between the center of gravity and the axis and is higher, so that, due to the different buoyancy in liquids of different densities, the relative angle The swimmers' positions correspond to the density of the liquid surrounding them, with a change in the liquid density causing the swimmers to rotate in opposite directions, characterized in that the float and the weighting body of the first swimmer are designed and dimensioned in this way / 3 are that equally large changes in density within the predetermined Area cause relatively large changes in the angle of the first swimmer in the lower part of the area, and the The float and the weighting body of the second swimmer are designed and dimensioned so that they are the same large changes in density within the predetermined range, relatively large changes in angle in the upper part of the Cause area so that the relative angular positions of the two swimmers in the lower part of the area predominantly by the angular positions of the first swimmer, and in the upper part of the range mainly by the angular positions of the second swimmer. 5. Density measuring device according to claim 4 for measuring the density of a liquid whose density is within the predetermined Area varies with temperature and its thermal expansion with density within the area is variable, characterized in that the first float is designed and dimensioned so that its thermal expansion that of the liquid in the lower part of the range is substantially equal, and so constituted the second float and is dimensioned so that its thermal expansion is substantially that of the liquid in the upper part of the region is equal, so that the changes in the angular positions of the first due to changes in the liquid temperature Floats in the lower part of the range are comparatively small, and the angle changes caused by temperature changes of the second swimmer in the upper part of the range are comparatively small. 6. Density measuring device according to claim 5, characterized in that the floats are designed and dimensioned so that the difference between the mean thermal expansion of the liquid and the thermal expansion of the first float and the difference between the mean thermal expansion of the liquid and the thermal expansion · of the second Floats are about the same size but opposite, so that at any point within the predetermined Area the changes in angle of the first float caused by thermal expansion and the corresponding change in angle of the second swimmer are absolutely about the same size but in opposite directions, whereby the changes in the relative Angular positions of both swimmers are smaller than the angular changes of the individual swimmers. 7. Density measuring device according to claim 4 for measuring the Density of liquids, the thermal expansion of which is variable within the predetermined range, characterized in that that the two floats are designed and dimensioned so that the thermal expansion of the liquid within of the area is between the thermal expansions of the two swimmers in terms of size. 8. Density measuring device for measuring the density of a liquid having a density within a predetermined range; with a housing for the liquid sample, one rotatably mounted about a horizontal axis in the housing first float and a second float rotatably mounted about the axis, both floats consisting of at least a buoyancy body with a relatively low density, the center of gravity of which is offset from the axis and the density of which is smaller than that of the liquid to be measured, and at least one weighting body with a relatively high density, whose center of gravity is offset from the axis, and whose density is greater than that of the liquid to be measured, each float being shaped so that the radial connecting line between The center of the lift and the axis are offset from the radial connecting line between the center of gravity and the axis is and is higher, so that, due to the different buoyancy in liquids of different densities, the relative Angular positions of the float correspond to the density of the surrounding liquid, with a change in the Liquid density causes the float to rotate in opposite directions, " characterized in that at least one of the floats consists of a buoyancy body of relatively low density and a weight body of relatively high density, the density of the weight body being less than four times the density of the float body, so that due to the size ratio between the weighting body and the buoyancy body, the thermal expansion of the weighting body has a significant effect on the thermal expansion of the swimmer. 9. Density measuring device for measuring the density of a liquid with a density within a predetermined range, with a housing for the liquid sample, a first float rotatably mounted about a horizontal axis in the housing and a second float rotatably mounted about the axis, both floats Consists of at least one buoyancy body with a relatively low density, the center of gravity of which is offset from the axis and the density of which is smaller than that of the liquid to be measured, and at least one weighting body with a relatively high density, the center of gravity of which is offset from the axis, and its density is larger than that of the liquid to be measured, each float being shaped in such a way that the radial connecting line between the center of buoyancy and the axis is offset from the radial connecting line between the center of gravity and the axis and is higher, so that, due to the different buoyancy in F Liquids of different densities, the relative angular positions of the swimmers corresponding to the density of the surrounding liquid, a change in the liquid density causing the swimmers to rotate in opposite directions, characterized in that at least one of the swimmers, a center of gravity, its angular position in relation to the / 6 Is offset, is such that the float and the weight body have a common Have fastening concentric to the axis and against changing the relative angular position of the centers of gravity, however are not secured against radial expansion with respect to the axis, so that the angular distance between the centers of gravity remains unchanged remains, although the independent expansion of the body is an independent radial displacement of the center of lift caused compared to the center of gravity, the size of which is determined solely by the respective thermal expansion of the buoyancy body and the weighting body. 10. Density measuring device for measuring the density of a liquid with a density within a predetermined range, with a housing for the liquid sample, a first float rotatably mounted about a horizontal axis in the housing and a second float rotatably mounted about the axis, both floats Consists of at least one buoyancy body with a relatively low density, the center of gravity of which is offset from the axis and the density of which is smaller than that of the liquid to be measured, and at least one weighting body with a relatively high density, the center of gravity of which is offset from the axis, and its density is larger than that of the liquid to be measured, each float being shaped so that the radial connecting line between the center of buoyancy and the axis is offset from the radial connecting line between the center of gravity and the axis and is higher, so that, due to the different buoyancy in Liquids of different density, the relative angular positions of the swimmers correspond to the density of the surrounding liquid, a change in the liquid density causing the swimmers to rotate in opposite directions, characterized in that at least one of the swimmers, consisting of a buoyancy body with a buoyancy center and a weighting body with a / 7 Center of gravity, its angular position in relation to do.ii Center of lift is offset, is such that the one body is rotatably mounted about the axis while the other body is attached to the one body at a distance 'from the axis such that the other Body can expand radially independently of one body, so that the other body is indirectly on the axis is fixed in an unchangeable angular position to a body, with which temperature changes a radial displacement of the center of gravity of the other body, their size due to the thermal expansion of one body and is additionally determined by the thermal expansion of the other body relative to the attachment to the one body. 11. Density measuring device according to claim 4, wherein the housing is at least partially transparent and having a Suction device and a suction duct with a must-r atis. 'Eye opening is provided so that a sucked liquid sample fills the housing so far that the float is completely in immersing the liquid, characterized in that the cross section of the suction channel increases from a minimum value the location of the outer suction opening in the inflow direction gradually expanded by at least four times so that the increase in cross-sectional area per unit length is at no point greater than 0.09 times the start of the cross-section. 12. Density measuring device according to claim 11, characterized in that that the intake duct is in the shape of an inverted "U" and is arranged so that its highest Place is much higher than the entry point of the intake duct in the housing. 13. Density measuring device according to claim 12, characterized in that that the suction channel in the part between the outer suction opening and the highest point is relatively expanded more, and relatively less in the part between the highest point and the entry point in the housing expanded. M «* 14. Density measuring device according to claim 4, characterized in that that one of the floats is provided with a scale corresponding to the density of the liquid, and the other Float is provided with an index such that in all "relative angular positions of the two swimmers within of the predetermined range, the index indicates the corresponding density on the scale.