GB2074325A

GB2074325A - Level Indicators for Electrically Conductive Liquids or Loose Materials

Info

Publication number: GB2074325A
Application number: GB8112371A
Authority: GB
Original assignee: Politechnika Wroclawska
Current assignee: Politechnika Wroclawska
Priority date: 1980-04-17
Filing date: 1981-04-21
Publication date: 1981-10-28
Also published as: PL223607A1; DE3114678C2; GB2074325B; PL126453B1; DE3114678A1

Abstract

An indicator for determining the level of a conductive liquid or loose material comprises at least one section of contact elements mounted on an insulating bracket 8. The contact elements comprise measuring electrodes 1 cooperating with an auxiliary electrode 5. The measuring electrodes 1 are connected to the first plates of capacitors 2 whose other plates in each section are connected together. Between the individual sections of measuring electrodes 1 there are disposed control electrodes 4. As the liquid rises this causes electrode 5 to come into electrical contact with the measuring electrodes 1 at the liquid level with the result that the capacitors 2 below the level are connected in parallel, the resultant capacitance being measured at 6. In an alternative arrangement the electrodes 1 are covered with a dielectric layer and connected together, the capacitance being measured between electrode 5 and the connection point. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Level Indicators for Electrically Conductive Liquids or Loose Materials This invention relates to a level indicator for an electrically conductive or loose material, and may be used for the measurement of level and variations of level of water and wastes, for instance in hydrometeorology, navigation, or water economy.

U. S. Patent Specification No. 4,003,259 discloses a liquid level indicator consisting of capacitance elements and a plurality of contact elements. Metal annular electrodes of the capacitance elements are arranged in pairs, one above another, at a predetermined distance from each other, in the wall of an insulating bracket.

Each pair of electrodes represents a capacitor with air dieelectric. Some plates of the capacitors are connected to each other, whiie the remaining ones are connected to the contact elements, that is contactrons. The gauge includes an additional magnetic moving member causing the successive contact elements to operate and connect the capacitor co-operating with the said part to the measuring system. The capacitance at the liquidair phase boundary changes rapidly according to the liquid level because of the considerable difference between the dielectric constants of the liquid and air. The measuring system determines the number of capacitors with identical capacitance and, in consequence, the liquid level.

However, electromechanical contact elements used in the known gauge impair reliable operation thereof, particularly in the case of continuous operation of the gauge and of considerable numbers of contactrons. The contractrons used require a magnetic or electric control ensuring the switching on of the successive contractrons at each liquid level variation. The contactrons used must be electrically or magnetically controlled; in consequence the successive contactrons are switched on at each liquid level variation.

In the case of magnetic control of contactrons, the indicator (gauge) must be provided with a mechanism for moving the magnet. In this case, a magnet moving system must be used, whereas in the case of electromechanical control of contactrons a special system for sequential switching on of the contactrons must be used.

Moreover, irrespective of the method of control of the contactrons used, the measuring system coacting with the gauge must include an electronic detecting system for detection of the capacitance variations, as well as a counter with memory. This leads in effect to a complicated design of the gauge itself and of the measuring system cooperating with the gauge. An additional disadvantage of the known liquid level indicator is the dynamic character of its operation leading to vulnerability to electrical interference, as well as a relatively long measurement time because of the limited working speed of contactrons and their control systems.

According to one aspect of the invention, there is provided a level indicator for determining the level of a conductive liquid or loose material, comprising an insulating bracket accommodating at least one section of contact elements connected to capacitors, the contact elements comprising measuring electrodes co-operating with an auxiliary electrode, each of the measuring electrodes being connected to one plate of a respective capacitor, the other plates of the capacitors of the or each section being connected to each other, there being provided control electrodes disposed between the successive sections of the measuring electrodes.

According to another aspect of the invention, there is provided an indicator for determining the level of a conductive liquid or loose material, comprising a column of measuring electrodes and an auxiliary electrode, each of the measuring electrodes being effectively in series with a capacitor to form a series circuit, first ends of the series circuits being connected together to provide a first output terminal and the auxiliary electrodes providing a second output terminal.

It is thus possible to provide a gauge made in the form of an insulation bracket accommodating one section of contact elements connected to capacitors. The contact elements are made in the form of measuring electrodes cooperating with an auxiliary electrode, each of the measuring electrodes being connected to one of the plates of a separate capacitor, the remaining plates of the capacitors belonging to the given section being connected to each other. Moreover, in the case of a considerable number of sections of measuring electrodes, between the individual sections there are control electrodes. The gauge may be designed so that the measuring electrodes serve as one of capacitor plates.In such a case the measuring electrodes are covered with a dielectric layer and all the electrodes in one section are connected to each other, whereas the remaining capacitor plates are formed of a liquid or loose material the level of which is being measured. In this design, the need to use capacitors in the form of separate structural members is eliminated.

An indicator may thus be provided having a relatively simple design compared with known indicators, easy manufacture and reliable operation because it has no moving parts. The contact elements in the form of the measuring electrodes, as well as the auxiliary.electrnde are short-circuited by the liquid or loose material the level of which is being measured. When electrodes with a dielectic layer are used, the liquid or loose material the level of which is being measured constitutes a movable capacitor plate providing a resultant capacitance variation substantially proportional to the level being measured. The indicator can co-operate with a measuring system including a converter for converting capacitance into an electric current or voltage signal, or into the frequency of an electric signal. Such systems are characterized by a simple design.The output signal of the indicator is proportional to the total value of the level being measured. Owing to this, the indicator is substantially insensitive to any electrical interference, especially of pulse type. The indicator may comprise several sections and, in consequence, can provide measurement of considerable level variations of liquid and loose materials with great accuracy and resolution.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic illustration of a water level indicator connected to an electrical capacitance measuring system; and Figure 2 is a diagrammatic illustration of a onesection water level indicator provided with measuring electrodes covered with a dielectric.

As shown in Figure 1, an indicator constituting a preferred embodiment of the invention comprises three sections of measuring electrodes 1, wherein each section includes 99 electrodes.

Each of the electrodes is connected to one of the plates of a respective capacitor 2, whereas the other plates of the capacitors 2 of each section are connected to each other and to a switch 3.

Between the successive sections of measuring electrodes 1 there are provided additional control elements 4. The indicator is further provided with an auxiliary electrode 5 which, together with all the common points of the connections of capacitors 2 provides the indicator output. The output signal is transmitted to a capacitance measuring system 6. The control electrodes 4 serve for controlling the switching over of the sections of the measuring electrodes 1 by a control element 7, which simultaneously indicates the total number of sections of the completely immersed measuring electrodes. In the illustrated embodiment of the invention, all the electrodes 1 and 4 are situated on an insulating bracket 8 and are made of acid-resistant steel, whereas the auxiliary electrode 5 has the shpae of a flat iron.

The spacing between adjacent measuring electrodes 1, as well as the spacing between the control electrodes 4 and adjacent measuring electrodes 1, is 1 cm, the diameters of electrodes 1 and 4 are also 1 cm, and the capacitance of the capacitors 2 is 1 nF.

The water in which the indicator is immersed causes the auxiliary electrode 5 to come into electrical contact with the measuring electrode 1 situated at the water level. Owing to this, the capacitors 2 situated below the water level are connected in parallel. The resultant capacitance of the capacitors 2 proportional to the level being measured is transmitted to the measuring system 6. When the water level has reached the level of the control electrode 4, the control element 7 connects the next section of the measuring electrodes 1 to the output of the measuring system 6. The indicator makes possible the measurement of water level up to 3 m height wiht 1 cm resolution.

As shown in Figure 2, another indicator constituting a preferred embodiment of the invention comprises one section of measuring electrodes 1 situated one above another on an insulating bracket 8, and an auxiliary electrode 5.

The measuring electrodes 1 are connected to each other, the common point of the connections of the measuring electrodes 1 and accessory electrode 5 constituting the indicator output. The output signal is measured by a measuring system.

Each of the measuring electrodes 1 is covered with a dielectric layer 9.

In this indicator, the liquid being measured and the measuring electrodes 1 covered with a dielectric layer 9 represents a parallel capacitor system. The liquid level is measured as the resultant capacitance of the capacitors situated below the liquid level.

Claims

1. A level indicator for determining the level of a conductive liquid or loose material, comprising an insulating bracket accommodating at least one section of contact elements connected to capacitors, the contact elements comprising measuring electrodes co-operating with an auxiliary electrode, each of the measuring electrodes being connected to one plate of a respective capacitor, the other plates of the capacitors of the or each section being connected to each other, there being provided control electrodes disposed between the successive sections of the measuring electrodes.

2. An indicator as claimed in claim 1, in which the plates of the capacitors connected to each other are constituted by the measuring electrodes which are covered by a dielectric layer, the other capacitor plates being constituted by the liquid or the loose material, the level of which is to be measured, when the indicator is in use.

3. An indicator for determining the level of a conductive liquid or loose material, comprising a column of measuring electrodes and an auxiliary electrode, each of the measuring electrodes being effectively in series with a capacitor to form a series circuit, first ends of the series circuits being connected together to provide a first output terminal and the auxiliary electrode providing a second output terminal.

4. An indicator as claimed in claim 3, in which the series circuits are arranged in groups, each group having the first ends connected together and to a respective contact of a selector switch, a respective control electrode being disposed between each adjacent pair of groups and being connected to a device for controlling the selector switch.

5. An indicator as claimed in claim 3 or 4, in which each series circuit comprises a respective one of the measuring electrodes connected to a first plate of a respective capacitor whose other plate constitutes the first end of the series circuit.

6. An indicator as claimed in claim 3 or 4, in which each series circuit comprises a respective one of the measuring electrodes connected to the first end of the series circuit and covered by a dielectric layer arranged to form a capacitor with the liquid or loose material when contacted thereby.

7. A level indicator substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

8. A combination of an indicator as claimed in any one of the preceding claims, and a capacitance measuring circuit connected to the indicator output.