DE4037927A1 - Stepwise level measurement arrangement - uses simple circuit contg. groups of capacitors with subgroups of parallel capacitors and digital comparison unit - Google Patents

Abstract

The arrangement for stepwise level measurement contains capacitors (71-1..72-4,81-1..82-2) arrranged along a fill section with capacitance values affected by a dielectric formed by the fill material. The capacitors are arranged in one or two groups (70,80), each with two sub-groups (71,72;81,82) of parallel capacitors. Each two capacitors of a group in succession in the vertical direction and in the same dielectric have approximately the same capacitance and belong to different sub-groups. The sub-groups of a group are connected to a common comparator unit which forms a digital comparison signal according to the difference in the sub-group capacitances. At least some capacitors of one group are arranged for interpolation between those of the other. The group-wise digital signals form binary locations of an output signal. ADVANTAGE - Contains simple circuitry and exhibits long-term output signal stability.

Description

The invention relates to a device for steps indicate level measurement along a filling path arranged capacitors, the capacities of which by a a dielectric formed can be influenced.

In such a known (DE-OS 37 20 473) device are along a filling line - which is at a vertical the cylindrical vessel corresponds to the filling level - individual Capacitors arranged. The capacitance of each capacitor varies depending on the dielectric that is between electrodes forming the capacitors (capacitor surfaces). Each capacitor is its own Line connected to an evaluation circuit, the one Contains demodulation stage, the output signal by the Ratio of the capacitance of the respective capacitor to one externally set reference value is determined. By a The individual output signals of the demo are mixed Dulators composed to a measurement signal. For example brought a filling between the electrodes, the one has a significantly higher dielectric constant than air Changes in capacities detected by the evaluation circuit. With an increasing fill level, a measurement signal also results stepped course as a function of the fill level.

In the known device are also in proportion low resolution of the filling distance one because of the individually Capacitors to be evaluated are relatively complex Wiring and evaluation circuit required. By change the capacitor properties - for example by Aging or due to the effects of the filling material - is with the known device the risk of falsification of the  Given measurement. The capacitor properties must therefore be on Changes are monitored. Furthermore, the external Reference value or that of the filling material compared to the unfilled one Condition caused size of the change in capacity accordingly the contents are adjusted; is such an adjustment especially often necessary when the Dielek Tricity number of the product in the filling at the same time medium (e.g. air) is only insignificant differs.

The invention is therefore based on the object To create a device for gradual level measurement, the is simple in terms of circuitry and is nevertheless due to the high long-term stability of their output signals distinguished.

According to the invention, this object is achieved when the initially specified type solved in that the capacitors to form a first and at least one further group are summarized that each group two sub-groups of parallelge switched capacitors that contain two each in fill direction of successive capacitors of the same Group with approximately the same dielectric for the same dielectric have and are assigned to different subgroups that each the subgroups of a group to one in common same comparison unit are connected, depending the difference in the resulting capacities of the sub-groups a digital comparison signal that forms at least part the capacitors of one group interpolating between the Capacitors of each further group are arranged and that the comparison signals formed in groups are binary digits form an output signal. A major advantage of the inventive device is that for reference size for the resulting capacity of a subgroup the resulting capacity of the other subgroup serves a group. Because the comparison signal from the difference  of the resulting capacities are compensated same age and environmental influences on the capacitors a group. By comparing the resulting capaci activities of the respective subgroups and their group exits evaluation is a high-resolution level measurement in scarf given technically simple way. Another advantage is that to check the resulting Kapa abilities of the subgroups of a group on equal or Inequality only two measuring lines and one connection each to a reference potential are required.

An advantageous development of the A according to the invention direction is that the capacitors are arranged in this way are that during the transition of the product from a level only one binary digit of the next level Output signal changes. This changes the output signal gradually z. B. in the so-called Gray Code (see. Lexicon of Data processing, publishing house modern industry, 9th edition, pages 754 ff.). This embodiment of the invention is in view of dynamic processes in level measurement are particularly advantageous liable because of measurement or transmission errors at sufficiently high Sampling rate at the simultaneous change of two or more Binary digits of the output signal can be recognized.

Regarding the compensation of aging and environment flows on the capacitance of the capacitors is according to one further advanced training of the device according to the invention see that each one of the electrodes of the capacitors at least one group on a common substrate are arranged.

A particularly space-saving, for example cylindrical, Arrangement of the capacitors is according to a further advantage adhere to the invention by enabling that Substrate is a flexible conductor film.  

A particularly compact and trouble-free construction of the The device according to the invention can be achieved in that the each other electrodes of the capacitors of a group of one common to each of the electrodes same reference electrode are formed. In this regard and out manufacturing reasons, it is particularly advantageous Reference electrode from a tube made of conductive material put.

A further reduction in the space requirement of the invention ßen device can be according to another advantageous Training of the invention achieve that each an electrodes from capacitors assigned to a group at least partially in between each Electrodes of the capacitors of at least one other group are arranged.

A in terms of circuit technology and in terms of Reliability of the measurement results particularly advantageous fort education of the device according to the invention provides that each Comparison unit contains two monostable multivibrators that the resulting capacities of the subgroups of a group in Implement pulse widths that a comparator to the pulse widths Reset time of one of the monostable multivibrators compares and that the comparator depending on equality or Inequality of pulse widths a first or second digital Outputs signal.

An embodiment of the invention is described below a drawing explained in more detail; show it:

Fig. 1A, 1B and 1C, the basic construction of the device according to the Invention;

Figs. 2 and 3 possible arrangements of capacitors in the inventive device for generating an output signal having four binary digits;

FIG. 4 shows an arrangement of capacitors corresponding to FIG. 3, in principle, for generating an output signal with seven binary digits;

Fig. 5 shows an arrangement of capacitor areas;

Fig. 6 is a level sensor;

Fig. 7 shows the basic structure of the device according to the invention for generating an output signal with seven binary and

Fig. 8 during operation of the device according to the invention occurring pulses in a comparison unit shown in FIG. 7.

Fig. 1A shows in basic representation in a container 1 arranged capacitors 2 and 3 of a first group with respect to a filling line. 4 The filling section 4 coincides in the present example with the height of the container 1 , but can also have a different orientation with a different orientation of the container 1 and a corresponding filling material (e.g. bulk material). The capacitors 2 and 3 have a common connection to a reference potential 5 and are connected with their respective other connections 6 to a comparison unit 7 for comparing their capacitances. The capacitances of capacitors 2 and 3 are approximately the same for the same dielectric located between their electrodes. The comparison unit 7 supplies a digital comparison signal 8 which assumes the value "1" if the capacities are identical and assumes the value "0" if there is a minimum deviation of the capacities. Referring to FIG. 1A, the container 1 is unfilled so that 2 and 3 air as a dielectric is present between the electrodes of the capacitors; the capacitors 2 and 3 are therefore approximately the same; the comparison signal 8 thus has the value "1".

According to FIG. 1B, water is let into the container 1 up to a filling level 10 as the filling material 9 . The water serves as a dielectric for the capacitor 2 , which leads to unequal capacitance values of the capacitors 2 and 3 . The comparison signal 8 therefore has the value "0".

Referring to FIG. 1C, the filling material has 9 (water) is now a filling level 11 so that both capacitors 2 and 3 are equally influenced by the water 9 as a dielectric. The comparison unit delivers a comparison signal with the value "1" because of the approximately the same capacities. Further capacitors (not shown) connect in the direction of the filling section 4 , as will be explained below.

The measurement results of the group of capacitors 2 and 3 are largely free of signs of aging of the capacitors 2 and 3 and of environmental influences, since these are compensated for by the difference in capacitance. Since no absolute determination of the capacitances, but only a capacity comparison is required, the device according to the invention is extremely simple in terms of circuitry and is therefore unaffected by interference.

FIG. 2 shows a group 20 of capacitors 21-1 to 22-8 constructed according to FIG. 1. The capacitors 21-1 to 21-8 are each led with their one electrode connection together to a reference line 23 with ground potential. Their respective other electrode connections are on a bus 24 ge leads, so that the capacitors 21-1 to 21-8 form a first sub-group 25 of group 20 . A second subgroup 26 is formed in the same way by the capacitors 22-1 to 22-8 , which are also connected with their respective electrode connection to the reference line 23 and with their respective other electrical connection to a further collecting line 27 . Seen in the filling path direction 4 ( FIG. 1A), at least two successive, alternately different subgroups 25 and 26 assigned capacitors (for example 21-1 and 22-1 ) each have approximately the same capacitance with the same dielectric.

A further group 30 is formed in the same way, in that capacitors 31-1 to 32-4 are alternately assigned to subgroups 33 and 34 . The subgroups 33 and 34 also have connecting lines 35 and 36 , which lead to a comparison device not shown in FIG. 2. Another group 40 consists in the same way of capacitors 41-1 to 42-2 , the subgroups 43 and 44 with lines 45 and 46 form. Another group 50 finally consists of capacitors 51 and 52 formed sub-groups 53 and 54 with connecting lines 55 and 56 .

The capacitors 21-1 to 22-8 of one group 20 are arranged with respect to the capacitors 31-1 to 32-4 of the other group 30 in such a way that they are used to interpolate the distances formed between the capacitors 31-1 to 32-4 serve in the filling direction 4 . For example, the capacitors 21-1 to 21-2 interpolate the distance between the capacitors 31-1 and 32-1 of the further group 30 . The capacitors 31-1 to 32-4 in turn serve to interpolate the distances in the filling path direction 4 of the capacitors 41-1 to 42-2 of the group 40 . The same applies to the capacitors 41-1 to 42-2 with regard to the capacitors 51 and 52 of the group 50 .

As will be explained in more detail below, the resulting capacities of subgroups 25 and 26 , 33 and 34 , 43 and 44 and 53 and 54 are each fed to a comparison unit which, if the capacities of the subgroups are identical, has a first digital state (e.g. the value "1") and in the case of inequality of the subgroups each assumes the second digital state (eg the value "0") as a comparison signal. The comparison signals of the respective comparison units form binary digits of an output signal.

In Fig. 2, the output signals formed in this way for 16 different fill levels 60-1 to 60-16 are Darge. At the fill level 60-1 , which corresponds to an empty container, the respective subgroups of groups 20 , 30 , 40 and 50 each have a corresponding resulting capacity. Therefore, all comparison signals have the value "1". As the combination of the binary digits shows, with increasing fill level, capacitors of the different groups 20 to 50 are supplied with the fill material as a dielectric and change their capacitance accordingly. For example, at level 60-6, capacitors 22-8, 21-8, 22-7, 21-7 and 22-6 of group 20 , capacitors 32-4 and 32-4 of group 30 and capacitor 42 -2 of group 40 is acted upon by a dielectric which differs from the other capacitors. Since in group 20 only two capacitors 21-7 and 21-8 of subgroup 25 , but three capacitors 22-6 , 22-7 and 22-8 of subgroup 26 are charged with the filling material as a dielectric, these are also resulting capacities of subgroups 25 and 26 differ, so that the comparison unit assigned to group 20 outputs a comparison signal with the value "0". In group 30 , the capacitors 31-4 and 32-4 are each charged with the filling material as a dielectric. Since these successive capacitors of group 30 each, as explained in detail at the beginning, have approximately the same capacitances with the same dielectric and the other capacitors of group 30 are also subjected to the same dielectric (e.g. air), there is a total of one Equality of the resulting capacitances of subgroups 33 and 34 and thus the value 1 as a comparison signal for group 30. Accordingly, for group 40 with a capacitor 42-2 charged with the filling material, a comparison signal has the value "0" and for Group 50 a comparison signal with the value 1. Upon reaching the maximum level level 60-16 to be recognized, all subgroups of a group 20 to 50 have different capacities compared to one another, so that the output signal formed from the comparison signals is finally excluded is composed of the values "0".

Fig. 3 shows a further arrangement possibility of capacitors in the device according to the invention. A first group 70 consists of two subgroups 71 and 72 , which in turn each consist of capacitors 71-1 to 71-4 or 72-1 to 72-4 connected in parallel. Connecting lines 73 and 74 of subgroups 71 and 72 lead to a comparison unit, not shown. In the same way, a group 80 is formed from subgroups 81 and 82 with capacitors 81-1 to 82-2 ; a group 90 consists of capacitors 91-1 and 92-1 , each of which forms a subgroup 91 and 92, respectively. A last group 100 consists of capacitors 101-1 and 102-1 , which form subgroups 101 and 102 . As explained in detail above, are seen in Füllstreckenrichtung 4 consecutive capacitors of a group (eg., 70) alternately (z. B. 71 and 72) the sub-groups assigned to, wherein at least capacitors each weils two successive in Füllstreckenrichtung 4 following Kon (e.g. B. 71-4 and 72-4 ) of the same group 70 with the same chemical dielectric have approximately the same capacitances. The capacitors 71-3 and 72-3 can, for example, also have the same capacitance with one another with the same dielectric, but this capacitance can differ from the capacitances of the capacitors 71-4 and 72-4 with the same dielectric. However, all capacitors preferably have at least one group with the same capacitances with the same dielectric.

Groups 70 to 100 of FIG. 3 are also configured with regard to the arrangement of their capacitors in such a way that the capacitors (e.g. 72-1 and 71-2 ) of one group 70 for interpolating the distances between the capacitors (e.g. 81-1 and 82-1 ) of group 80 are used. Another capacitor (e.g. 91-1 ) from the further group 90 in turn serves to interpolate the distance between the capacitors 81-1 and 82-1 .

Fig. 3 also shows the in a group comparison of the resulting capacities of the respective subgroups 71 and 72 , 81 and 82 , 91 and 92 and 101 and 102 in dependence on different fill levels 110-1 to 110-16 from the comparison signals the groups 70 to 20 formed binary represent an output signal. The fill level 110-1 corresponds to an air-filled container. As the filling level of the filling material rises , the further filling level heights 110-2 , 110-3 etc. are reached in stages , whereby the specified binary positions of the output signal occur in each case. Only one binary position, ie one of the comparison signals formed by groups 70 to 100 , changes its value (level code) from level level to level level; in the transition from the fill level 110-2 to the fill level 110-3 , for example, only the comparison signal formed by the group 80 changes its value from "1" to "0".

The arrangement of the capacitors according to FIG. 3 offers the advantage in comparison with the arrangement according to FIG. 2 that also 16 different fill levels ( 110-1 to 110-16 ) can be measured with a comparatively considerably smaller number of capacitors. Furthermore, even with a relatively rapid change in the fill level, the measured values are reliably checked because only one binary position of the output signal changes from fill level to fill level. With sufficiently fast scanning, a measurement error can therefore be inferred if more than one binary position of the output signal is changed between the measurement of two successive fill level heights.

Fig. 4 shows an arrangement 300 of capacitors 301-1 to 301-n .. 307-1 to 307-n, which in the in connection with FIG 3 described manner. Each in subgroups 301 a, 301 b ... 307 a , 307 b of groups 301 to 307 are arranged. As stated above, e.g. B. the capacitors 301-1 to 301 -n alternately assigned to subgroups 301 a and 301 b of group 301 . Each group 301 to 307 is connected to a comparison unit (not shown). The output signals from the comparison units form an output signal with 7 binary digits (7 bits), so that a level measurement with 128 stages is possible. Here too, when changing from one level to the next, the output signal changes only in a single binary position.

FIG. 5 shows electrodes (conductive surfaces) 401-1 to 401 -n arranged on a common substrate 400 designed as a flexible conductor foil, each of which has the one capacitor surface of the capacitors 301-1 to 301 -n shown in FIG. 4 the one Form group 301 . In the same way, conductive surfaces 402-1 to 402 -n are arranged on the substrate 400 , which in each case form the one electrode of the capacitors of the group 302 ( FIG. 4). Further conductive surfaces 403-1 to 403 -n, which each form the one electrode of the capacitors of group 303 ( FIG. 4), are partially in the spaces between the electrodes or conductive surfaces 402-1 to 402 -n of the capacitors of the Group 302 arranged. Similarly, electrodes 404-1 to 404 -n, 405-1 to 405 -n, 406-1 to 406 -n and 407-1 to 407 -n of groups 304 , 305 , 306 and 307 ( FIG. 4) arranged in the respective spaces formed by the electrodes of the other groups to save space. It can be seen that the electrodes 401 -1 to 401 -n of the group 301 ( FIG. 4) arranged in the filling path direction are alternately connected to form the two subgroups of connecting lines 410 and 411 which lead to connecting points 412 and 413 . In the same way, the electrodes of the other groups are alternately connected to corresponding connecting lines or connecting points.

FIG. 6 shows the structural design of a level sensor 420 of the device according to the invention, which contains the substrate 400 ( FIG. 5) applied to a tubular support body 421 . A reference electrode 422 formed by a conductive tube is arranged on the outside concentrically with the supporting body 421 .

Through a carrier plate 423 the connections (z. B. 412 and 413 / Fig. 5) of the sub-groups and a reference potential 425 circuit. The reference electrode 422 forms a common counter electrode to the electrodes (conductive surfaces) of the substrate 400 , so that a multiplicity of capacitors are arranged along a filling path 426 in the pattern shown in FIG. 5.

Fig. 7 shows the overall structure of the Einrich device according to the invention with the level sensor 420 of FIG. 6 with the connection points 412 and 413 shown in play , which are connected to a first comparison unit 500 . The connection point 412 is connected to an input of a first monostable multivibrator 501 and the connection point 413 to an input of a second monostable multivibrator 502 . The multivibrators 501 and 502 are synchronized by a common clock via clock inputs 503 and 504 . The capacities of the sub-groups 301 a and 301 b assigned to the connection points 412 and 413 of the group 301 ( FIG. 4) determine the holding time of the multivibrators 501 and 502 . The pulse width of the multivibrator 502 is increased by an additional capacitor 505 . An output of the first multivibrator 501 is connected to a data input 506 of a memory 507 serving as a comparator. An inverting output of the second multivibrator 502 is connected to a takeover input of the memory 507 . The memory 507 can be formed, for example, by a D flip-flop. If the multivibrator 502 drops , the signal present on the output side of the multivibrator 501 is transferred to the memory 507 . The repetition frequency of this scanning is essentially limited by the pulse widths of the monostable Mul tivibrators 501 and 502 , but in practice also sufficient for fast filling processes.

Fig. 8 shows, in addition to the multivibrators 501 and 502 (Fig. 7) the input clock signals 600 having a pulse width of 0.1 ms the output signals 601 of the multivibrator 501 and the inver formatted output signals 602 of the monoflop 502. The left part of Fig. 8 shows the situation with an empty container, the sub-groups z. B. 301 a and 301 b of parallel capacitors ( Fig. 4) have the same resulting capacitances. The multivibrator 501 therefore already falls back into the stable state before the multivibrator 502 falls back due to the additional capacitor 505, and thus by the time t 2- t 1 later a scanning edge 610 for taking over the output signal "0" of the multivibrator 501 into the memory 507 generated.

If, on the other hand, the container is filled with a filling material (e.g. water) in such a way that a capacitor of one sub-group 301 a is more than capacitors in the other sub-group of group 301 b with the filling material as a dielectric, the resulting capacitance is the one Sub-group 301 a larger than that of the other sub-group 301 b. Provided as shown in Fig. 8 on the right is, then a sampling edge 611 of the multivibrator 502 b of the sub-group 301 is associated with the lower capacity at a time when the multivibrator 501 (FIG. 7) due to the greater capacity of the other Under group 301 a is still in the raised state, so that a value "1" is transferred to memory 507 . In the same way, the other groups or their subgroups are evaluated by similar comparison units, only the comparison unit 500 for group 407 (corresponding to group 307 of FIG. 4) being shown in FIG. 7 for the sake of clarity. The outputs of the memories 507 of the comparison units 500 according to FIG. 7 are then fed to a commercially available decoder module, which generates a value for the respective fill level from the respective values formed in this way.

Claims (8)

1. Device for stepwise level measurement with capacitors ( 71-1 ... 72-4; 81-1 ... 82-2 ) arranged along a filling section ( 4 ), whose capacities can be influenced by a dielectric formed by a filling material ( 9 ) are characterized by
that the capacitors ( 71-1 ... 72-4; 81-1 ... 82-2 ) are combined to form a first ( 70 ) and at least one further ( 80 ) group,
that each group ( 70 ; 80 ) has two sub-groups ( 71, 72; 81, 82 ) of capacitors connected in parallel ( 71-1 ... 71-4; 72-1 ... 72-4; 81-1 ... 81 -2; 82-1 ... 82-2 ) contains
that in each case two capacitors ( 71-1; 72-1 ) of the same group ( 70 ) following one another in the filling path direction ( 4 ) have approximately the same capacitances with the same dielectric and are assigned to different subgroups ( 71 ; 72 ),
that in each case the subgroups ( 71 ; 72 ) of a group ( 70 ) are connected to a common comparison unit ( 500 ) which forms a digital comparison signal as a function of the difference in the resulting capacities of the subgroups ( 71 ; 72 ),
that at least some of the capacitors ( 71-1 ... 71-4; 72-1 ... 72-4 ) of the one group ( 70 ) interpolate between the capacitors ( 81-1, 82-1; 81-2, 82-2 ) of each further group ( 80 ) are arranged and
that the comparison signals formed in groups form binary digits of an output signal. 2. Device according to claim 1, characterized in that the capacitors ( 71-1 ... 72-4; 81-1 ... 82-2; 91-1, 92-1; 101-1, 102-1 ) are arranged such that only one binary position of the output signal changes during the transition of the filling material from one filling level ( 110-2 ) to the next filling level ( 110-3 ). 3. Device according to claim 1 or 2, characterized in that in each case the one electrodes ( 401-1 ... 401 -n) of the capacitors ( 301-1 ... 301 -n) at least one group ( 301 ) on a common Substrate ( 400 ) are arranged. 4. Device according to claim 3, characterized in that the substrate ( 400 ) is a flexible conductor foil. 5. Device according to claim 3 or 4, characterized in that the respective other electrodes of the capacitors ( 301-1 ... 301 -n) of a group ( 301 ) of one each of the electrodes ( 401-1 ... 401 - n) opposite common reference electrode ( 422 ) are formed. 6. Device according to claim 5, characterized in that the reference electrode ( 422 ) is a tube made of conductive material. 7. Device according to one of claims 3 to 6, characterized in that the respective one electrodes ( 403-1 ... 403 -n) from a group ( 303 ) associated capacitors ( 303-1 ... 303 -n) at least partly in spaces between the one electrodes ( 402-1 ... 402 -n) of the capacitors ( 302-1 ... 302- n) of at least one further group ( 302 ). 8. Device according to one of the preceding claims, characterized in that each comparison unit ( 500 ) contains two monostable multivibra gates ( 501 , 502 ) which implement the resulting capacities of the subgroups ( 301 a, 302 b) of a group ( 301 ) in pulse widths that a comparator ( 507 ) compares the pulse widths at the time of reset of one of the monostable multivibrators ( 501 , 502 ) and that the comparator ( 507 ) outputs a first or second digital signal depending on the equality or inequality of the pulse widths.