NL8403475A - Capacitative liquid level or conductance measuring gauge - has compensation electrode of same length as and parallel to measuring electrode but of different shape or surface area - Google Patents

Abstract

The appts. includes measuring and reference electrodes provided in a liquid containing or flow tube, these electrodes cooperating with a wall or part of the vessel, acting as a counter-electrode, to form two capacitances (CM,CR), with the liquid acting as a dielectric. The quotient CM/CR is directly proportional to the liquid height. The reference electrode is constructed as a compensation electrode and is of the same length as and is parallel to the measuring electrode. The difference in shape or surface area w.r.t. the counter-electrode between the measuring and compensation electrodes is such that the result of the division of the capacitances CM and CR indicates a linear relationship of the liquid height or a relationship of higher order.

Description

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N 6127-2 Ned-M / LdB

Short designation: Level meter of the capacitive type.

The invention relates to a level meter of the capacitive type for capacitively measuring the liquid level in a vessel or flow tube, for which purpose in the vessel or the like. a measuring electrode (M) and a compensation electrode (R) are disposed, cooperating with a measuring tube acting as a counter electrode, the compensation electrode being disposed parallel to it by the same length as the measuring electrode.

An older proposal refers to a measuring electrode which cooperates with a wall part of the measuring tube. The measuring electrode is designed as a right-angled triangle and the compensation electrode as a straight narrow strip. With a level meter equipped with such a measuring electrode, level measurements can be performed with great precision.

The object of the invention is to indicate other combinations of measuring electrode and measuring tube, which are based on the same principle and with which thus the same great precision can be achieved. Hence, according to the invention, in a main embodiment of this principle, the measuring electrode (M) and the wall part of the measuring tube acting as a counter-electrode are arranged opposite each other such that the distance between them, seen horizontally, is variable - while the distance between the compensation is incidentally -electrode (R) and the wall part of the measuring tube arranged opposite to it is indeed constant, so that division of capacities (CM and CR) indicates a linear or higher order relationship with the liquid height to be measured.

In the older proposal, the distance from the measuring and compensation electrode to the associated wall of the measuring tube remains constant.

Only the surface of the measuring electrode increases quadratically, while in the invention it remains just constant.

In a first embodiment of this main idea, this leads to the wall part of the measuring tube lying opposite the measuring electrode (M) and / or the measuring electrode itself being inclined. The compensation electrode and the cooperating wall of the measuring tube are in principle straight. They can also slope, provided they remain parallel to each other.

In any case, this can be achieved in two different ways, firstly such that for use in a 'normal * oil-water system the wall part of the measuring tube co-operating with the measuring electrode tapers from top to bottom. A 'normal' two-fluid layer system, here oil-water, is understood to mean a system in which the useful liquid (oil) floats on a layer of contaminated liquid (water).

40 Secondly, this is possible because for use in a 'normal'

Vt, i *> / R

* i - 2 - oil leveler, the wall part of the measuring tube co-operating with the measuring electrode is straight, while the measuring electrode itself tapers from bottom to top. In these cases, measurement of the inverse quotient leads

from C ,, and C „, so C: c„ to an increasing linear relationship with the height M R R M

5 of the liquid level.

In the case of an 'inverted' fluid system, it must be ensured that, in order to measure the inverse quotient C ^ / C ^, the largest distance between the measuring electrode and the co-operating wall of the measuring tube is at the bottom and the smallest distance between them at the top .

10 Note .;

It will be clear, however, that in order to obtain a straight proportional relationship between the quotient and the liquid height, one can also start from the quotient Q = CM / CR (as in the earlier patent application), and that when using the meter in a normal liquid system it must be ensured that the distance between the measuring electrode and the co-operating wall of the measuring tube at the top is smaller than at the bottom, but when used in an 'inverted' liquid system it must be ensured that the distance at the top is greater. is then at the bottom.

For convenience, an electrode carrier body is fitted to which the 20 measuring and compensation electrodes are applied. A preferred embodiment is constructed such that in a symmetrical arrangement of a versatile electrode support body, the measuring tube walls on one side and on the other side, which cooperate with the measuring electrodes on one and on the other side and / or which measuring electrodes themselves run obliquely, while the compensation -25 electrodes are mounted on the support body opposite each other on two other sides and have a constant distance from the opposite wall parts of the measuring tube.

Another embodiment of the carrier body is constructed such that the carrier body is triangular in cross-section and that the measuring electrodes are arranged on two sides and the compensation electrode on the third side. The carrier body can also be designed as a body of revolution (cone, cylinder, etc.).

In addition to fixing the main electrodes relative to each other on a support body, it is also practical - in view of the close cooperation between the main electrodes and corresponding (electrode material-coated) wall parts of the measuring tube - to completely assemble these parts of the meter. to make. Hence, according to the invention, the main electrodes (measuring electrode and compensation electrode) and the counter-electrode measuring tube together form an integral unit which is galvanically insulated from this when placed in a liquid vessel.

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This results in a meter which can be introduced into a vessel or pipeline as a separate measuring unit, and that is galvanically separated therefrom. Galvanically separated means that the measuring tube with the electrodes inseparably connected therein is electrically separated from the vessel or pipe.

The above is in contrast to a conventional level meter of the standard type, where the (measuring) electrode arranged in the vessel forms a capacitive unit (capacitor) precisely with that vessel or line. The measurement therefore takes place there between the wall of the vessel and the electrode.

These meters can also be used in multi-fluid layer systems 10 with two or more interfaces *. One then places on resp. under the measuring tube section, the wall of which tapers at an angle from top to bottom, another section, from which the wall runs at an angle from top to bottom.

The total wall of the common measuring tube sections or measuring electrodes then shows a kink, namely a kink n-ar outside ("convex") resp. to 15 frines ("concave"). Of course, more than one of these kinks can be used, including combinations thereof. It is therefore recommended that in such situations a measuring tube is used, which is characterized in that the wall part cooperating with an electrode and / or the electrode itself exhibits one or more kinks.

20 Because the inclination of the wall or the measuring electrode can lead to an unacceptable size of the meters over great heights of the liquid meter, measures are proposed to avoid this, because the wall part cooperating with the measuring electrode is stepped and the measuring electrode itself is likewise divided into mutually separated partial electrodes. The bottom line is that the level meter is divided into a number of individual level meters, whereby the sloping wall of the measuring electrode or tube section jumps back each time. The actual measuring circuit therefore always switches to a higher measuring range.

The invention need not only relate to level meter equipment. It is quite conceivable that the construction forms can also be applied to other measuring situations, for example: in flow, pressure measurements, weighing techniques, wind tunnels, conductivity measurement etc.

The invention will be explained in more detail below with reference to some exemplary embodiments shown in Figures 35 of the accompanying drawings.

Fig. 1A to C show a first embodiment of the invention, in which one wall of the measuring tube tapers obliquely from top to bottom towards the measuring electrode; Fig. 40 2 A to C represent a variant of fig. 1, in which the 3 4 0 3 4 7 5 Ί * - 4 - measuring electrode, going from top to bottom, tapers obliquely to the co-operating wall of the measuring tube;

Fig. 3 A to C show another variant of fig. 1 for an "inverted" fluid system; FIG. 4 A to F illustrate the term 'inverted' fluid system;

Fig. 5 A to D and fig. 6 A to D show a second embodiment in which the support of the electrodes is provided with four side walls and two opposite walls thereof are made obliquely; Fig. 5 10 for a normal fluid system, Fig. 6 for an 'inverted' fluid system;

Fig. 7 A and B represent a variant of FIG. 5 in which the support of the electrodes is triangular in cross section;

Fig. 7C shows an embodiment in which the measuring tube or electrode is conical;

Fig. 8A to E show an embodiment in which two or more measuring tube sections, as shown in Figures 1-3, are combined, whereby the combination of measuring tube sections and / or electrodes has a kink at the transition site; FIG. 9 shows an embodiment in which the integral sections of the measuring tube and electrodes connect to each other in a stepped manner.

Fig. 1A shows a side view of a level meter according to the invention and also a top view (Fig. 1B) and a bottom view (Fig. 1C). Rather than - as in the earlier application êh intended for a normal bi-liquid system - the surface of the measuring electrode increases from the bottom upwards more than that of the compensation electrode, and the distance between the electrodes and the walls thereof the measuring tube placed around the electrodes remains constant, here the distance s between the measuring electrode 30 1 and cooperating wall part 6 of the measuring tube 10 increases and the ratio of the surfaces of the measuring electrodes 1 and the compensation electrode 3 remains constant.

The measuring electrode 1 forms with the inclined wall part 6 a capacitor CM with variable distance s. The compensation electrode 3 forms.

35 with the wall part 8 a capacitor C with constant distance s. The electrodes 1, 3 are mounted on a support 5. The measuring tube 10 is grounded at 11. At the top of the measuring tube 10 there is a measuring circuit 15, which contains two oscillating circuits 12, 13 and a sub-circuit 14. The oscillating circuit 12 resp. 13 is connected to the capacitor CM resp.

40 C, and provides a signal p resp. q to the sub chain 14. The capacity R

o i A I /, 7 v w ·· ’; *,» „j« * c .A - 5 - of CR is £ r _ s q o

that of C 't .A

M r

i- = EV

avg 5 where A - h ^ .r (for r, see fig. IB) = opp. of the electrode, and £ = dielectric constant of the measuring liquid. r

The distance s should be averaged from the distance s ^ • in the lowest point of the electrode and the distance in the highest point of the liquid at a given time.

10 Since the variable s is in the denominator of the capacity formula, one will have to determine the quotient Q = -, so that s = s =% (s + s.) P av o i appears in the numerator of the quotient.

This means that with increasing liquid height h ^, an increasing value of ΊΓ is associated.

15 It follows that the height to be determined is directly proportional to the measured quotient Q, which is a linear function of the distance.

In the standard version, the electrodes and the inner measuring tube are coated with PTFE to protect the electrodes and the measuring tube against any aggressive liquids.

FIG. 2 illustrates a variant of the embodiment of fig. 1, also with side view (fig. 2A9, top view (fig. 2B) and bottom view (fig. 2C) and with an electrical measuring circuit 15. Insofar as the same parts are used the same reference numerals are used as in Fig. 1. Parts which have a deviating constructional shape have been given a different reference numeral, as is the case with the measuring electrode, now 21, which is not straight, but inclined.

Furthermore, the measuring tube 30, which has a straight side 26 instead of the beveled side 6. The carrier 25, which was rectangular in cross section, is now a trapezium in cross section. Here, too, the distance between the measuring electrode portion of the measuring tube increases as the liquid rises.

In Fig. 3, another variant of the level meter of Fig. 1 is shown in side view (Fig. 3A), top view (Fig. 3B) and bottom view (Fig. 30, with like parts indicated with the same reference numerals). In this case, the wall 61 of the measuring tube 10 'cooperating with the measuring electrode 1 tapers obliquely from the bottom upwards, thus just the opposite of Figures 1 and 2.

This situation is the opposite of that of FIGS. 1 and 2. If one observes the distance that this arrangement is applied in a normal fluid system, then the quotient Q '- 1 must be determined to ensure that a linear relationship between the height h. and the distance s. measure.

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This case is shown in the measuring circuit 15.

The dielectric constant of the liquid 5 can be determined by means of a small dexterity with another sub-circuit 16, to which the signal q and the result of the division performed in the circuit 14, are applied, so that the possible presence of traces of water in the oil, which is located between the electrodes of the capacitor, can be detected. turn into.

If, on the other hand, the signals p and q are applied to the sub-circuit 14 in such a way that the quotient Q = is measured, then a]? 10 simple calculation that this construction form is suitable for an inverted liquid system, which will be elucidated with reference to figures 4A-F.

From all this it follows that a certain arrangement, which is suitable for a normal fluid system, does not necessarily have to be inverted in order to be made suitable for an inverted fluid system. It is sufficient to interchange the connection pins for the signals p and q in the sub-circuit 14.

Figures 4A and B show the level meter for use in a 'normal' two-fluid layer system. In Fig. 4A it is assumed that the vessel is full of oil, and Fig. 4B with water. At the interface 32 in Fig. 4A, the quotient of CR and Λ q const, const. ", .., Q = - = —-: —-- N1, for example = 1 P" S N «S J * O o

At the interface 33 in Fig. 4b, 25 = Q = N = Q, for example = 10

So rising water level becomes noticeable by an increasing value of N.

Figures 4C and D schematically show the case that the level meter according to the invention is used in an 'inverted' two-fluid layer system, the useful ECH being heavier than water and thus located below the interface.

In Fig. 4C it is assumed that the measuring vessel is almost completely filled with ECH, so that the interface 34 is located at the top of the vessel.

In Fig. 4D, on the other hand, the vessel is almost completely filled with water 35, and so the interface 35 is virtually at the bottom of the vessel.

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At the interface 34, a quotient Q = - with high

Jtr value, for example 10, while at the interface 35 Q has a low value, for example 1. So with increasing water level, the quotient Q decreases; that makes no sense. Therefore, in Fig. 4E and F5, the measuring tube is reversed.

In Fig. 4E now a small amount of H 2 O, so when the interface 36 is high in the vessel, a low value of Q, for example 1. In Fig. 4F, when the vessel is almost completely filled with water, the interface 37 is practically at the bottom, which means a high value of Q, for instance 10. Thus, an increasing amount of water is now again associated with a larger value of Q.

Fig. 5A to E show a second embodiment of the invention in front view (A), side view (B), top and bottom view (C, D). Here, the measuring electrode A or 41 and the compensation electrode B or 15 43 are doubled, ie on either side of a tetrahedral electrode carrier 45. Due to this symmetrical design of the electrodes on the carrier 45, the accuracy is not primarily , but the sensitivity to response improves; this can lead to higher accuracy. The like-minded electrodes are opposite each other and are electrically interconnected, as can be clearly seen in Fig. 5c.

A measuring tube 46 is placed around the whole, which is straight because the measuring electrodes 41 are arranged on the sloping sides of the support 45.

In Figures 6A through D, the electrode carrier 45 'is inverted from the electrode carrier 45 of Figure 5 and can therefore be used with an' inverted 'fluid system.

Figures 7A and B show a variant of the electrode carrier 45 of Figure 5, which is rectangular in cross-section there, while this variant is triangular in cross-section. Fig. 7A shows a top view and in Fig. 7B a perspective view. In this variant an electrical carrier: 50 is shown, with three sides 47, 48 and 49. The sides 47 and 48 are slanted and carry the measuring electrode M and M '. The third side 49 is straight and carries the compensation electrode R.

Not only in fig. 7B but also in the top view of fig.

7A, it can be clearly seen that the cross-section triangle 52 at the bottom has a larger surface area than the cross-section triangle 53 at the top. In Fig. 7A also a dashed line, around the triangular electrode carrier 50, shows the measuring tube 54, which has the shape of a rectangular, three-sided parallelepipid.

It will be clear that also a conical shape or other revolution-λ /. -λ 7. ·; “? s

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The loop body is very suitable for use in a level meter according to the invention. Fig. 7C shows such a conical level meter, at least as far as the measuring tube 54 is concerned. The electrode carrier 55 is only cylindrical. Where the compensation electrode 57 is arranged, the conical measuring tube 5 also has a straight descriptive 58. Again, the electrode carrier can be made conical, for example, such as the body 54, and then a straight measuring tube is arranged around it, as indicated by the dotted lines 59. .

Figures 8A through E show various possibilities to combine two different level meters, so that they are suitable for interface measurements in a combination of a 'normal' and an 'inverted' two-fluid layer system.

Thus, in Fig. 8A, the combination of a level meter 61 for a normal fluid system and a level meter 62 for an inverted fluid system is shown. Since the measuring electrode 63 is straight, the cooperating sides 66, 67 of the measuring tube sections 68, 69 are inclined and the measuring tube as a whole 70 has a (convex or protruding) kink.

Fig. 8B shows a combination of a level meter 71 for a normal fluid system and below it a level meter 72 for a reverse fluid system. As a result, the measuring tube as a whole 75 has an inward kink.

In figures 8C and D, the kink is located in the combined measuring electrode 77 resp. 78.

Fig. 8E shows that the compensation electrode 81 may also be kinked in such a combination, provided that the opposite wall 82 of the measuring tube 85 has the same slope and kink. Of course, the wall 83 must also be kinked opposite the measuring electrode 86.

If such a level meter has to bridge large height differences for only one fluid system, the dimensions in the transverse direction (due to the inclined slope of the sloping sides) can become unacceptably large. It is then recommended to let the capacitor plates jump in or out every few meters, for example. This is done in Fig. 9 for the total measuring tube 90 (i.e. the 'external' capacitor plate). In fact, this consists here of 7 individual measuring tube sections 91, 92, etc., each of which is 1.5 m long, for example, the measuring electrode 95 itself being correspondingly divided into mutually separated partial electrodes 96, 97, etc.

The measuring electrode 95 has thus become a particle measuring electrode, with each partial electrode providing part of the scale range. After every 40 particles on the electrode 95 the meter indicates 100%, then the 8403475 * 'f * - 9 - next particle starts again at 0% and increases to 100% etc. The particles are then digitally added.

Example; liquid cover by four particles, each 250 mm in length. The fifth particles are 50% covered. The clue is then; 5 4 x 250 mm = 1000 mm + h particle 5 (= 125 mm), the total content is then; 1000 + 125 = 1125 mm.

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Claims (10)

1. Level meter of the capacitive type for capacitively measuring the liquid level in a vessel or flow tube, for which purpose in the vessel or the like. a measuring electrode (M) and compensation electrode (R) are disposed cooperating with a measuring tube acting as a counter electrode, the compensation electrode being arranged parallel to it by the same length as the measuring electrode, characterized in that the measuring electrode (M) and the wall part of the measuring tube acting as a counter-electrode is arranged opposite each other such that the distance between them, seen horizontally, is variable - whereby the distance between the compensation electrode (R) and the wall part of the measuring tube arranged opposite it is, however, constant - whereby division of the capacities (C ^ and CR) indicates a linear or higher order relationship with the liquid height to be measured. Level meter according to claim 1, characterized in that the wall part of the measuring tube opposite the measuring electrode (M) and / or the measuring electrode itself is inclined. Level meter according to claim 2, characterized in that for use in a 'normal' oil-water system, the wall part of the measuring tube co-acting with the measuring electrode tapers from top to bottom. Level meter according to claim 2, characterized in that for use in a normal oil-water system the wall part of the measuring tube co-acting with the measuring electrode is straight, while the measuring electrode itself tapers from bottom to top. Level meter according to claim 3 or 4, characterized in that in a symmetrical arrangement of a versatile carrier body for the electrodes, the measuring tube wall parts on one side and on the other side, which co-act with the measuring electrodes on one side and on the other side, and / or which measuring electrodes themselves are inclined, while the compensation electrodes are arranged on the carrier body opposite each other: on the two other sides and at a constant distance from the opposite wall parts of the. 30 measuring tube. Level meter according to claim 3 or 4, characterized in that the carrier body is triangular in cross section and that the measuring electrodes are arranged on two sides and the compensation electrode on the third side. Level meter according to any one of the preceding claims, characterized in that the main electrode (measuring electrode and compensation electrode) and the measuring tube acting as counter-electrode together form an integral unit which, when placed in a liquid vessel, is galvanically q L η τ Al s; C "7 V V" i i% * - 11 -> 'is isolated therefrom. Level meter according to any one of claims 1-7, characterized in that the wall part cooperating with an electrode and / or the electrode itself exhibits one or more kinks. 5 Level meter according to one of the preceding claims, characterized in that the wall part cooperating with the measuring electrode is of step-shaped design and the measuring electrode itself is correspondingly divided into mutually separated partial electrodes. 10 8403475