DE2555817A1 - RF CONDUCTIVE MEASUREMENT METHOD AND DEVICE FOR DETERMINING THE LEVEL OF A CONDUCTIVE LIQUID - Google Patents

Description

The invention relates to a method and an apparatus for HF measurement of levels of conductive liquids in a container and especially for measuring flow velocities or mass flows through flow channels, the level of the conductive liquid in a flow channel, such as a channel or a weir, being measured.

A sensing element is already provided for measuring the flow velocity or the mass flow through a flow channel or a probe known (U.S. Patent 3,269,180). In order to correctly correlate the mass flow with the uppermost level of a liquid in a flow channel, draws the known probe electrode is characterized in that a connection of the probe with a suitable electronic device an output signal generated which is linear to the Mengens.trom or to the flow rate.

608826/0912

-In such probe electrodes, the accumulation is a Coating or the formation of deposits is a very serious problem. For example, if the coating is on a probe (Fig. Ib) forms where the conductive pad or the When the protective shield is connected to ground, the capacitance of the covering is resistively coupled around the sides of the Probe around with ground or with earth, creating a wrong Specification of the top level and thus the volume flow is generated.

Another very significant problem with probes of this type is that water or other conductive fluids flowing through the channel penetrate the insulation of the probe. Such penetration increases to a great extent with the temperature of the liquid when the adhesive bond between the probe electrode and the insulation is not solid, so that liquid penetrates the insulation and the probe electrode and isolation separates. This in turn creates voids or air gaps on the electrode, which the level measurements adversely affect and cause twisting and twisting of the probe.

In order to make the capacitance measuring probes insensitive to the influences of a deposit formation, are already "Systems known (US Pat. Nos. 3 781 672 and 3 7o6 98o) which have a protective shield that protects the materials to be measured exposed and brought to the same potential as the probe electrode in order to remove the accumulated deposit to hold essentially the same potential as the probe electrode and thereby influence any capacitance measurements to exclude. However, the known protective element (FIGS. 1b and 1f) according to US Pat. No. 3,269,180 cannot be brought to the same potential as the probe electrode when the probes are on the wall or on a otherwise earthed retaining element of the flow channel are attached, otherwise the protective element is earthed

6098287Ö912

or would be connected to ground. Even if it could be brought to the same potential as the probe electrode, this would not be able to eliminate the negative effects of the deposit, since the protective electrode brought to the potential, which is located at the back of the probe, not closely to the coating on the front of the probe as a result the presence of fairly strong insulation from the back to the front of the probe. this would lead to the fact that the capacity of the pavement would be resistively coupled to the wall of the flow channel, the is effectively coupled to the mass via the conductive liquid in the flow channel, and thereby in the capacitance measurement would come in.

The state of the art also includes a curved probe for measuring the mass flows. Flow velocity through a flow channel (U.S. Patent No. 3,729,994). However, this probe lacks conductive reinforcement or a protective electrode with a dielectric medium to protect the probe electrode against capacitance changes through the back to immunize the probe. The probe electrode is in front of the conductive liquid in the flow channel the probe by polytetrafluoroethylene (Teflon) in Insulated of sufficient strength to "strike through" materials and particles flowing in the flow channel to avoid. However, polytetrafluoroethylene has a relatively low dielectric constant of about 2.2, which is less than the optimal capacitive coupling of a covering with a protective electrode would be if a sufficient one Polytetrafluoroethylene starch would be used to avoid "bottoming out".

The probe electrode known from US Pat. No. 3,729,994 has a metallic woven wire mesh, which is in a polyester-reinforced fiberglass is embedded. the

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Probe electrode is embedded in the fiberglass while it is in a liquid state, which is for example can be achieved by spraying on. Heat curing of the probe is not necessary. This leads to, that the adhesive bond or the lack of adhesive bond between the mesh and the fiberglass the formation of minute Allows cavities to collect water. In the US patent mentioned there is no information regarding the peculiarities of the network, for example with regard to the mesh size and the opening size.

Another known probe (US Pat. No. 2,852,937), which can be attached to the wall of a container, is used to measure the Level of conductive liquid within the container. The probe has a probe electrode and a shield resp. Shielding electrode, which is arranged behind the probe electrode and extends a little laterally outwards over the side Ends of the probe electrode extends. However, the shield electrode is not closely capacitive with the conductive liquid ^ coupled. The insulation itself includes polytetrafluoroethylene, that in combination with the distance of the shield from the insulation surface is essentially any narrow Coupling of a coating or a covering with the shield excludes.

Finally, it is known to arrange a pair of insulator plates behind a probe electrode so that they are. Extend sideways a little outwards over the probe electrode (U.S. Patent 3,324,647). In this known arrangement, none of the insulator plates is at the same potential as the Probe electrode brought. In addition, there is no close coupling between a coating on the surface of the probe and the Isolator plates.

Other known methods include the use of a mesh or mesh embedded in a thermoplastic material. Grate for use as a conveyor belt.

According to the invention, an improved method and has provided an improved apparatus for measuring the level of a conductive liquid in a kettle or container will. With this method and the device, levels or volume flows of the conductive liquid are to be determined or another fluid in a container or in a flow channel, for example in a weir or in a Gutter, be determined. When measuring the level of the fluid in a container, the probe performing the measurement be arranged flush with the wall of the container, thus adversely affecting the flow or movement of the fluid in the container is excluded by the probe or vice versa. The flush arrangement of the Probe with respect to the wall of the container is to prevent an accumulation of fiber material on the probe, which is the Measurement or the flow of the fluid could adversely affect.

The probe should be attached to the wall of the container in such a way that an accumulated coating of the fluid or result in no adverse effects from a fluid layer on the probe. The probe should take into account the curvature correspond to the wall of the container or the flow channel. The probe should easily be in an existing container or flow channel can be installed. Changes in the dielectric constant of the insulation material in the measuring probe are intended to measure a level of a conductive liquid can not adversely affect. Furthermore, the probe should be able to detect the presence of an undesired to determine the insulating coating on the probe and to exclude the effects of this coating on the level measurement. The aforementioned measures are intended to

can be achieved without impairing the capability of the probe will resist abrasion from the materials flowing through the flow channel. Finally, the probe should be easy to calibrate.

Included in accordance with these and other goals the RF probe system according to the invention is a probe which is used to measure the level of an essentially conductive liquid is attachable to a surface in a container, the surface when covered with a coating of the liquid is coated or coated, through which the conductive liquid is effectively grounded. The probe has a conductive one A probe electrode extending longitudinally along the probe adjacent its front face, and a conductive one Protective electrode device which extends in the longitudinal direction along the probe. The protective electrode device has lateral sections that extend laterally outward beyond the lateral ends of the probe electrode. Inner solid insulation devices are arranged in between, which isolate the probe electrode and the rear portion of the guard electrode. External solid insulation devices cover the conductive protective electrode device and the conductive probe electrode in such a way that that the conductive liquid with the probe electrode on the lateral sections of the conductive protective electrode device is capacitively closely coupled. The coupling between the lateral sections of the protective electrode is preferred and the conductive liquid is achieved in that the lateral portions turn laterally outward can extend a distance which is at least six times greater than the thickness of the solid insulation device, which covers the protective electrode device, divided by the dielectric constant of the solid insulation device. The probe system furthermore has devices for the potential of the protective electrode device at substantially the same potential as the probe electrode.

809026/0912

In a preferred embodiment, the protective electrode has a rear portion disposed next to and behind the probe electrode.

So that the probe for measuring the mass flow or the flow velocity the liquid can be used through a flow channel, the probe electrode can be so be designed that it has a frontal lateral dimension, which with increasing distance starting from a The longitudinal end of the probe increases. The lateral sections d =; r Protective electrode devices then extend laterally outward over the lateral ends of the probe electrode a greater distance with decreasing distance from a longitudinal end of the probe.

The system further comprises track or guide devices with a longitudinal groove for receiving the probe, which the Allow the probe to move through the groove. The flexibly executable guide can be on the wall or on another Holding part of the container or the flow channel are attached. Alternatively, the guide can be inside the wall or be formed within the holding part. The leadership has a double function. On the one hand, it serves to hold a probe, which is preferably very thin, while on the other hand it also involves removing the probe from the container for replacement, repair purposes or for calibration enables.

In a particular form from the guide track or guide a .Strömungskanals extends along a curved portion such that _t the probe itself is curved to the curvature of the wall to correspond to the flow channel. For the assumption of this curvature , the probe can have a flexible layer structure which, by suitable etching of a conductive surface on one side of a

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ORIGINAL INSPECTED

insulating substrate can be formed such that the probe electrode and lateral protective electrodes while the conductive surface is on the opposite side of the insulating substrate as rear protective electrode is used. The outer insulation can comprise two sheets or foils, which run along the side Ends are attached by heat sealing.

The outer insulation device can be a vinylidene fluoride polymer have a high molecular weight whose dielectric constant exceeds four, so that one close capacitive coupling of a conductive coating on the lateral sections of the protective electrode device is ensured, while at the same time a resistance to it abrasion is created in a flow channel.

The system may include adjustable brackets which are used to mount a probe in various positions on a surface or wall of the container. The retaining means allow the removal of the probe of them for calibration purposes and replacement of the probe to the support means in a 'predetermined position. In addition, indices can be attached in the longitudinal direction along the probe under a transparent outer insulation, which facilitate the calibration.

The probe system can continue to have facilities for heating of the sample * in order to dissolve a deposit, for example fat, which can form on the outside of the probe. The facilities for Heating can include the protective electrode itself, which can be designed in a serpentine manner so as to be a resistance to serve. Alternatively, a separate heating element can be placed on the back of the probe adjacent to the

■■■ · ■■ OWQINAL INSPECTED

609826/0912

rear sections of the protective electrode device are used. When the probe is inserted into the guide the heating devices can be sandwiched between the base of the longitudinal groove in the guide and the probe will.

Additional electrode devices can be provided in the probe v / earths, which are covered by an outer insulation and changes in the dielectric constant of the outer Measure insulation device. Such additional electrode devices include in combination with suitable compensation devices the effects of any changes in the dielectric constant of the external insulation device based on the measurement of the liquid level.

According to the invention, undesired cavities or Air gaps between a probe electrode and the insulation of the probe are essentially eliminated, d. H. that any splitting into layers between a probe electrode and the probe insulation which form such air gaps would be essentially avoided. This split into layers between the probe electrode and the probe insulation should be essentially excluded even if the probe is immersed in hot water for a long time. The probe designed as a layered body should be uniform, and any twisting or twisting should also be avoided will.

To achieve this, the probe has a conductive probe electrode device, which extends in the longitudinal direction along the probe and has a plurality of openings, passing through the probe electrode means from side to side. On opposite sides of the probe electrode means, thermosetting insulating means extend in the longitudinal direction of these means. The isolating devices extend through

ORIGINAL JNSPECTED

80982670912

the openings and exert compressive forces on the electrode device via its surface. The compressive forces on the

Probe electrode devices should be larger than 7 kp / cm

(100 psi) and preferably exceed 35 kp / cm (500 psi).

To obtain the desired compressive forces, the mean minimum strength of the isolation device is measured by of the probe electrode means between adjacent openings and the outer surface of the insulating means is greater than 1o% of the mean minimum distance between the openings in the probe electrode. Preferably the middle one minimum strength greater than the mean minimum distance, with maximum compressive forces or compressive forces being reached when the mean minimum thickness is at least 1 1/2 times the mean minimum distance.

In order to ensure the desired compressive forces, the Probe electrode device must be surrounded by adequate insulation. This requires a certain minimum Thickness measured from the probe electrode assembly to the outer surface of the isolation assembly. Requires in the same way this is a certain minimum cross-sectional dimensioning of the openings in the probe electrode device. The middle however, the maximum cross-sectional dimension of the openings in the probe electrode device should be smaller than twice the mean minimum thickness of the insulation - to ensure the correct edge effect.

In a special embodiment, the probe electrode has various conductive threads. These filaments or threads can be woven into a network or lattice. In another embodiment, the probe electrode means a sheet of conductive material having a plurality of etched openings with the edges the openings are rounded.

To ensure that appropriate compressive forces are achieved it is essential that the temperature for thermosetting is greater than the working temperature of the probe. One would therefore like to have a heat setting temperature, which is above 38 ° C (100 ° F), preferably a temperature above 100 ° C (212 ° F).

In a further preferred embodiment, the insulating device has a thermoplastic material. That thermoplastic material can contain a fluorocarbon resin in the form of a crystalline vinylidene fluoride polymer high molecular weight, which is a dielectric constant of more than four has. When using such a thermoplastic material, the curing temperature is at least 188 ° C (37o ° F), which temperature constitutes the gel point of the material.

It has also proven advantageous to use the insulation material apply pressure before heating to the curing temperature. This pressure is preferably achieved by that any air between the isolating device and the probe electrode is evacuated. Then the isolating device a fluid pressure is applied.

The invention thus relates to numerous embodiments of probes for measuring the liquid level in a container, including the mass flow through a channel. The probes each include a conductive probe electrode and guard electrode means having a rear portion disposed between the wall of the container and the probe electrode, and a side portion extending outward from the side ends of the probe electrode. The probe electrode and the protective electrode device are separated from one another by an inner solid insulation, while an outer solid insulation covers the probe in this way; that d-le protective electrode device and the

6 Q SB 2 8/0 912 originally inspected

- The probe electrode is separated from the conductive liquid. Characterized in that the protective electrode device on im essentially the same potential as the probe electrode is driven, the section of a conductive coating, which has accumulated on the lateral sections of the protective electrode device, capacitively with the potential of the Protective electrode devices are coupled, whereby the disadvantageous effect of a conductive coating is reduced, that has accumulated on the probe electrode.

The invention is explained in more detail, for example, with the aid of the accompanying drawings.

1 is a plan view of a flow channel with a constriction and with probes arranged in the channel for recording the volume flow.

FIG. 2 shows a side view of the flow channel of FIG Fig. 1.

Fig. 3 is a cross section through an embodiment of a probe Eur for detecting the mass flow or the flow velocity. ■.

Pig. 4 is a view taken along line 4-4 of FIG. 3.

FIGS. 5a to 5g schematically show probes and probe potentials for explaining the advantages of a probe according to FIGS. 3 and

Fig. 6 is a sectional view of a second embodiment of a sensing probe.

FIG. 7 is a view taken along line 7-7 of FIG. 6.

8 is a sectional view of a guide for supporting the probe of FIGS. 6 and 7.

QRfGINAL INSPECTED

Figure 9 is a top plan view of the guide of Figure 8 attached to the wall of a flow channel.

Fig. 1o shows a further embodiment in a sectional view a sensor probe.

Figure 11 is a view taken along line 11-11 of Figure 10.

Figures 12a to 12e illustrate a method of manufacture a probe of Figures 1ο and 11.

FIG. 13 shows the probe of FIG. 1o in a sectional view and 11 in a guide attached to a flow channel.

FIG. 14 shows the probe from FIG. 1o in a sectional view and 11 in a guide which is in the wall of a flow channel is trained.

14a shows the probe from FIGS. 1o and 11 in a guide, which is designed to extend from the wall of the flow channel.

FIG. 15 shows a sectional view of the probe and guide from FIG. 13 on a mechanical holder in a flow skanal.

Fig. 16 shows the probe of Fig. Io in a sectional view and 11 ait integral with it Heating element.

FIG. 17 shows, in a sectional view, the probe from FIG. 16 in a guide for attachment to the wall of the flow channel.

18 shows an alternative embodiment in a sectional view a protective electrode for the probe of Figures Io and 11, which can be used as a heating element.

19 shows a sectional view of a probe similar to FIG Figures 1o and 11 with an additional electrode, which changes in the dielectric current of the external insulation measures. * ·

Fig. 2o shows in a sectional view devices for Holding a probe in a pre-calibrated position on the curved wall of a flow channel.

FIGS. 21a and 21b show in schematic representations the dual property of the probes that are attached along a curved wall of a flow channel.

22 and 23 show circuit diagrams as they can be used for the various designs of the probes.

Fig. 24 is a block diagram useful in conjunction with a probe of the embodiment of Fig. 19;

Fig. 25 shows schematically the meaning of the rear protective electrode.

26 shows a sectional view of a probe _f, with the aid of which a further important feature of the invention is explained.

27 shows the probe in an enlarged sectional view of FIG. 26 along line 27-27 of FIG. 28.

Fig. 28 shows in a partially broken away plan view a portion of the probe of FIG. 27.

603828/0912 originally inspected

29 shows a further embodiment in a sectional view a probe similar to that of FIG.

FIG. 30 is a sectional view of the probe of FIG. 29 taken along line 31-31 of FIG. 31.

Figure 31 is a top plan view, partially broken away, of a portion of the probe of Figure 30.

32 shows in a sectional view a pressing device for producing the embodiments of the probes of the figures 26 to 28.

FIG. 33 illustrates the first method stage of the device from FIG. 32.

34 illustrates the second process stage of the device of Fig. 32.

35 illustrates the third process stage of the device of Fig. 32.

FIG. 36 shows the relationship of the probe elements to one another in the process stage shown in FIG. 33.

37 shows the relationship of the elements to one another in the method stage according to FIG. 3.4.

Fig. 38 shows the relationship of the elements to each other after the application of heat.

39 schematically shows an insulated electrode thread.

Pig. 4o shows in a diagram the prints produced on the thread of FIG. 1 under different conditions,

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ORIGINAL INSPECTED

41 schematically shows an isolated portion of a plane-parallel electrode.

The Mengenstrom- or shown in the figures 1 and 2 flow velocity sensing probes 1o and 12 are arranged so that the probe longitudinal axis extends vertically in the grounded fluid 'that in a flow channel

14 with a constriction 16 flows. Since the mass flow of the -Liquid through the channel increases and decreases, the top level rises and falls within the flow channel.

A preferred embodiment of an HF conductivity sensor probe for use as a probe 12 attached to a grounded wall

15 of the flow channel 14 according to FIG. 1 can be attached, is is described below with reference to FIGS. 3 and 4. As shown in these figures, the probe has an insulating one Substrate 18 with a conductive electrode probe 2o, which is extends longitudinally across the front of the probe. The probe also has a conductive protective electrode 22, which is at the same potential as the probe electrode 2o

'is driftable and which extends lengthways over the back of the probe so that the substrate 18 lies between the probe electrode 2o and the protective electrode 22.

Extends according to an essential feature of the invention the conductive protective electrode 22 from the rear side of the probe electrode 2o to the opposite one lateral ends out laterally and around the front of the probe 12 so that each coating is made of conductive Liquid that collects on the probe 12 is completely coupled to the potential of the protective electrode 22 and a resistive coupling of the conductive coating around the sides of the probe with the wall 15 of the flow channel which is effectively grounded. The full Coupling of the coating on the sides of the probe 12 in the vicinity of the protective electrode 22 is ensured, that a

JNSPECTED

outer solid insulation device in the form of a can 24 is provided, which is produced by means of heat shrinkage, so that the capacitance C from the protective electrode to Surface of the probe with respect to the capacitance C of the insulating coating 24 from the front surface of the probe electrode 2o is essential to the front surface of the insulating coating 24, i.e.. H. is at least 5o% of the capacity C. As a result The uniform thickness of the sleeve 24 is the capacitance across the sleeve 24 per unit area on the guard electrode 24 equals the capacitance across the sleeve 24 per unit area of the probe electrode 2o.

By eliminating the resistive coupling around the probe is, the capacitance to earth or ground, as measured by the probe electrode 2o, can accordingly measured by the method according to US Pat. No. 3,746,975, so that the influences of the plaque which has accumulated on the probe has, are excluded. The basis for this known measurement is that a coating after a certain Length acts as an infinite transmission line, the characteristic final impedance of which is predictable. The resistance and capacitance components are measured. The effects of the pavement can be calculated and excluded will. This is true under the assumption that the resistance coupling extends in the longitudinal direction along the sensing element of the Probe extends to the conductive liquid to be measured, rather than around the sample to a grounded wall. Since the conductive protective electrode 24, which with its frontal section 26 is completely coupled to the coating, prevents that a resistive current flows around the probe, the coating occurs as a model of the infinite Line of transmission in appearance which enables the method of US Pat. No. 3,746,975 to be used.

The probe 2o according to the invention is characterized in that the lateral dimensions of the probe electrode decrease Distance from one longitudinal end of the probe, like

60SB28 / 0S12 ~ ^INSPECTED .

■ _.-.- ■ ■■. * ■■ - ■■■ - ■ ■ _ ■ "" "" * '"* sas *' * ?? *

this is shown in Fig. 4 decreases. The front section
26 of the probe is designed so that its lateral dimension increases as the distance from the longitudinal end of the probe decreases. As a result of the characteristic formation of the front portion of the guard electrode, the resistive coupling of the coating on the probe increases as the upper level of the liquid decreases, so that the effects of the resistance coating on the capacitance measurement are further reduced.

The probe electrode can be designed to accurately indicate the flow in the particular channel in which it is located. In this regard, the probe can according to the following
Equation can be interpreted:

b = k ^ H ^ " ¹⁾ CD

where b is the width of the probe,
k .. a constant
o <a constant that depends on the form of the

Flow channel depends, and
H is the amount of current above the zero flow level.

The flow through the channel can be expressed by the following equation
can be expressed:

Q =

For a full understanding of the importance of the protective electrode 22 with its front section 26 and the influences of the
Deposits on the probe measurement is shown in FIGS. 5a to
Reference is made to 5g, in which probes are shown with deposits
are. As can be seen from FIG. 5a, an uncharacterized probe electrode ρ with an insulated coating is arranged in a conductive liquid E. When the level of the

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conductive liquid t falls, a coating c remains on the probe electrode p. As shown in Fig. 5a, the probe electrode ρ is mounted at a distance from the conductive wall of the container or flow channel, i.e. h «the probe ρ is installed in the position of the probe 1o according to FIG.

As can be seen from Fig. 5b, the potential or the voltage of the coating c is shown in FIG. 5a, which is indicated by the line ν is shown, essentially constant across the width

or the lateral dimension of the probe ρ and is only slightly, namely by a potential drop d, below the potential or the voltage ν of the probe itself. Since the liquid is conductive and the liquid Z. is in a grounded container or flow channel, the Potential level of the liquid C represented by the line V £, which is held at ground or earth. From Fig. 5b it can be seen that the deposit itself has a very little influence on the probe measurement, since the potential, seen from the probe electrode ρ, over the liquid level C is essentially the same as the potential ν of the probe itself, so-

P.
do not place the probe on a grounded wall or on a

Support part is attached in the container or flow channel.

5c shows the attachment of the probe ρ to a wall w in such a way that a coating of the liquid extends over the probe electrode ρ and extends along the wall w. Since the lining c is again conductive, the lining c forms a resistance path to earth from the probe electrode ρ to the earthed liquid £.

As shown in FIG. 5d, the coating c according to FIG. 5c, which forms a path to earth _f which has a relatively low resistance , produces a very significant coating error, since the probe potential ν , as shown in FIG. 5d , the

■ r. · ■ -

\ . - . ; ORIGINAL WSPECTED

; 609826/0912

remains the same, but the coating potential ν is considerable falls to the earth at the lateral ends, namely by one Potential drop of 3d. This results in a coating failure when the probe is placed along the wall of the container which is very large compared to the case when the probe is attached away from the wall and the covering c the the same thickness and the probe ρ have the same width or lateral dimension.

From Fig. 5e it follows that a probe with infinite Width can be attached along the wall of the container or the flow channel without causing a significant flaw. As shown in FIG. 5e, the coating potential ν is essentially constant and is only slightly below the probe potential ν (a drop in d) along the entire width of the probe. From a practical point of view however, it is not possible to make the probe infinitely wide. This is particularly the case when the probe electrode, as shown in Fig. 3 and 4, must be designed to provide an indication of the mass flow through a flow channel to obtain. In this case, the probe electrode becomes very narrow at its lower end.

By providing a guard electrode g as shown in Fig. 5f at the lateral ends of the probe electrode ρ and the wall w, the advantages of a relatively wide probe electrode are obtained without making the probe electrode ρ itself excessively wide needs. Since the protective electrode g is brought to essentially the same potential as the probe electrode ρ, the potential ν, as shown in FIG. 5g, drops over the entire width of the probe electrode ρ plus the protective electrode g. However, the actual drop at the lateral ends of the probe electrode ρ is not great, ie the potential v_ at the lateral ends is not more than 25% of the potential drop between v · in the middle of the probe ρ and

OFUGiNAL INSPECTED

the potential ν of the probe electrode itself. As shown in Fig. 5g, the potential ν on the probe electrode is ρ essentially constant and is only slightly below the potential ν of the probe electrode ρ itself, whereby the deposit error is reduced to a minimum. Preferably the Lowering, d. H. the potential drop ν from the center of the probe electrode ρ to the side end, less than that Voltage drop between ν and ν at the center of the probe.

From this it can be concluded that initially the sensing probe or the probe electrode ρ should be as wide as possible, so that the capacitive coupling via the insulating cover of the probe electrode is as high as possible. In addition, should the probe electrode g extend between the lateral ends of the probe electrode ρ and any adjacent wall so that that it is possible with the covering as well as possible without any load or charge. According to the invention is now the protective electrode g is viewed as fully coupled with the conductive liquid when the capacitive coupling makes up at least 5o% of the capacitive coupling between the liquid and the probe electrode ρ. Overall has it has been shown that the lateral sections, which are laterally outwardly by a much larger distance than the minimum thickness of outer insulation, creating the required full coupling. The distance is greater than the distance between the lateral sections of the protective electrode and the probe electrode plus the thickness the protective electrode. The distance is preferably at least six times greater than the thickness of the outer insulation coating of the protective electrode divided by the dielectric constant of the external insulation. In the The probes shown in Figures 3 and 4 can vary the lateral extent as a function of the distance from the end of the probe. The distance by "six times" is about, the entire measuring length of the probe or at least a substantial portion thereof applicable.

ORIGINAL INSPECTED

609826./Od 12

- In the further embodiment of a probe, as shown in As shown in Figures 6 and 7, a backing or guard electrode 32 has a conductive substrate which is measured is relatively thick from front to back compared to a probe electrode 34 and an insulating material 36 therebetween. In the embodiment according to FIGS gives the thick protective electrode substrate 32 of the sample the mechanical strength that is required in the case of the probe according to FIGS. 3 and from the thick insulating substrate 18 is deposited. Any coating that is adjacent to the probe according to FIGS. 6 and 7 accumulates at the front sections 4o of the protective electrode, is completely with the potential of the protective electrode coupled in that the only insulation between the coating and the protective electrode 32 is a sleeve 38 and the front portions 4o of the protective electrode 32 are. This leads to the fact that the capacitance C over the front Sections 4o is not significantly smaller than the capacitance C of the probe electrode 34 through the coating 38 through. The guard electrode substrate 32 has a curved front side so that the use of a heat shrink tube for the sleeve 38 is possible, whereby the air spaces between the protective electrode 32 and the sleeve 38 on a To be reduced to a minimum.

The conductive protective electrode 32 has a heating coil 42 for Heating the entire probe structure to a temperature, in which the formation of a deposit, for example from fat, is prevented on the special. If the available Energy supply is limited, the heating element only needs to be activated if there is a Has accumulated a layer of fat of a predetermined thickness. This can be achieved by adding an additional Sense electrode 44, as shown in FIG. 7, is provided, which is covered by the sleeve 38. As a result of that the electrode 44 is placed below the longitudinal end of the probe electrode, the sensing electrode 44 is in a

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ORIGINAL INSPECTED

Position in which the build-up of a layer of fat can also be determined when the liquid level in the flow channel is relatively low. By periodically dissolving any accumulation of fat, the indices will remain on the probe visible.

FIG. 8 shows a guide 48 having a surface 46 for attachment to the wall 52 of a flow channel, as shown in FIG Fig. 9 is shown. The guide comprises a concave recess 5ο for receiving the probe of FIGS. 6 and 7. When the guide is installed so that the longitudinal axis of the concave recess 15 extends vertically across the wall 52 of the flow channel, the probe according to FIGS. 6 and 7 can be moved vertically over the guide so as to achieve the To facilitate calibration of the probe.

Another embodiment of the probe is shown in FIGS. This probe, which is relatively cheap to manufacture, has a layer structure with an inner insulating substrate 6o with internal adhesive layers 62 and 64, which have a probe electrode 66 and a front protective electrode 68 on the front side of the substrate 6o and a rear protective electrode 7o on the rear side of the substrate 6o hold in place. This structure is then sandwiched between two layers or foils of outer insulation 72 and 74 with outer adhesive layers 62 and 64 and held between them by heat sealing along the edges 78. As can be seen from FIG. 11, the probe electrode 66 is identified and separated from the front protective electrode 68 by a small distance 8o. A probe of this type can be made very thin, i. E. with a thickness of less than 9.5 mm (3/8 ") and preferably less than 1.6 mm (1/16 ¹ *) .

In the following, a method for producing a probe of FIGS. 10 and 11 will be described with reference to FIGS

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■ ORIGINAL INSPECTED

". The bare substrate 60 as shown in Fig. 1oa is first coated with the inner adhesive layers 62 and 64, for example with a polyester adhesive Im, as shown in Figure 12b. Thereafter, a copper foil 7o and a copper foil 67 are placed over the adhesive layers 62 and 64 as shown in Fig. 12c. At this time, the foil 67 can be etched to form the probe electrode 66 and the front guard electrode 68 as shown in Fig. 12d. Then the Layers or webs 72 and 74 applied over the outer adhesive layers 62 and 64 and the overall structure below Heat and pressure as shown in Figure 12e are laminated. The edges of the webs 12 and 74 are terminated with one another along the lateral ends for completion connected to the probe by heat sealing.

A particular advantage of a probe, as shown in Figures 1o and 11, is its flexibility, so that it can be attached in a curved guide, which corresponds to the curvature of the wall in a container or flow channel corresponds to, d. H. which extends vertically and horizontally. In this case, the substrate 60 can be made of Mylar, a polyester based on ethylene glycol and terephthalic acid. Mylar offers the flexibility you need and support for the probe assembly and at the same time has a sufficiently low dielectric constant to to insulate the probe electrode 66 from the rear protective electrode 7o.

Preferably, the outer insulating films or webs 7o and 72 have a high strength, so that they Resist abrasion and strikethrough from flowing particles. Preferably, the layers or webs 7o and 72 have a very high dielectric constant, so that the potential of the front protective electrode 68 is effective with the plaque accumulated on the adjacent probe

609828/0912

OHiGIN INSPECTED

capacitive coupling. In this case, the probe has proven to be particularly suitable for use as an external insulation a fluorocarbon resin, for example a crystalline one Vinylidene fluoride polymer with a high molecular weight and a dielectric constant greater than four is. A particularly favorable material for this purpose is also a high molecular weight vinylidene fluoride polymer with a dielectric constant of eight and high abrasion or puncture resistance values {Kynar).

The main advantage of using a high quality fluorocarbon such as Kynar in one Probe, as shown in Figures 10 and 11, results because the combination of mechanical and electrical properties enables the system to To ignore the formation of deposits on the probe. The extent to which plaque formation is neglected depends on the known measuring method (US Pat. No. 3,746,975) and on the capacity per unit area the probe isolation. The higher the capacitive coupling of the probe, the smaller the error due to deposits, which are deposited on the probe element. Overall, the capacitance across the insulation material can be as follows Can be expressed in the equation:

K.AK-c = - ^ i (3)

where K ^ is a constant

A the surface of the insulation

K _{3 is} the dielectric constant and

t are the strength of isolation.

Since Kynar is a very tough material, that is, it is resistant to abrasion and "cut through", it can be very thin. For example, the Kynar can do less than

609826/0912

ORIGINAL INSPECTED

OC

be half as strong as Teflon and still have the same resistance to "cutting through or puncturing" to have. Additionally, the high dielectric constant of eight allows for Kynar compared to about 2.2 for Teflon a capacity coupling at Kynar, which is 3.6 times larger than with the same Teflon thickness. The combined Effect of reduced strength in Kynar compared to that of Teflon and the higher dielectric constant at Kynar., compared to Teflon, gives a coupling capacitance for a probe coated with Kynar, which is at least seven to eight times higher than with a probe coated with Teflon. Since the Increased ability of the probe to ignore plaque formation, equal to the square root of the increase in coupling capacity, will be achieved with a probe, with v / elcher Kynar is used, the errors ■ due to the formation of deposits by more less than a third of the errors encountered with a probe using Teflon.

From the foregoing it can be seen that the probe itself should be particularly thin so that disturbances of the flow or the movement of liquid in a container are avoided. However, a thin probe is very difficult to install because it can be so flexible that it does not fit itself can support, d. H. has no resistance to bending when at right angles with respect to the flow or the Liquid movement is rotated in the container. This There is generally a disadvantage when the ratio of the probe width to the thickness is greater than 2o: 1. Additionally One usually wants to install the probe so that it can be removed for replacement, repair, and calibration is easy.

For installation requirements, the flexible probe of FIGS. 10 and 1.1 can be inserted into a track 82 as shown in FIG.

609828/0912

The guide has an opening 48 which generally corresponds to the shape of the removable probe. The guide 84 can then the wall 15 of the flow channel can also be attached if the wall 15 is curved, since the guide as well as the Probe can be flexible. The opening 84 in the probe 82 is essentially filled by the probe, where any Cracks and cracks, in which material can collect, are avoided.

It is also possible to form a recessed guide 86 in the wall 15, as shown in FIG. 14, wherein opening 88 through the guide corresponds to the shape of the removable probe. Alternatively, the wall 15 itself can be designed in this way or by molding to have an opening 88 which acts as a recessed guide for the Probe serves as shown in Fig. 14a. In the embodiments of FIGS. 14 and 14a, one particularly wishes limit the strength of the probe if the viand 15 is relatively thin. As shown in FIG. 15, the guide 82 is installed on a mechanical support element 9o in a boiler or container. As the removable probe protective electrodes would have, the support element 9o v / effective as in the case of the wall 15 in the embodiments of the figures 13 and 14 must be earthed. The mechanical support element 9o tapers at its ends, so that the influence of the Retaining element 9o is reduced to a minimum on the flow through a flow channel.

FIG. 16 shows a probe of the embodiment according to FIG and 11, with the exception that a separate heating element 92 in the layer structure behind the protective electrode 7o, however is sandwiched between the insulating layers 72 and 74. If the heating element 92, which is a suitable resistance heating element 16 is flexible, the entire structure shown in FIG. 16 can be incorporated into guides 82 and 86 according to FIG Figs. 13, 14 and 15 are introduced as in Fig. 17

609826/0912

ORIGINAL INSPECTED

is shown. Alternatively, the heating element 92 may be outside and behind the laminated probe assembly in the longitudinal opening 94 of a guide 96 can be arranged.

As a further variant, the rear protective electrode 7o of the probe according to FIGS. 1o and 11 can overall be serpentine be designed so that a protective electrode and heating element combination is obtained for the probe. Such Beat-shaped guard electrode 94 is connected in FIG shown with an alternating current source 96, which with the protective electrode 94 is coupled via an insulation converter 97 with a low capacitance coupling. the Protective electrode 94 is also connected to a source of protective potential shown. In this application, a low capacitive coupling means capacitive coupling with an impedance which is relative to the impedance of the Protective terminal to which the protective electrode is connected is high.

The capacitance across the external insulation of a probe according to the invention should correspond to the capacitance which is measured by the probe, since the liquid or the materials, the level of which is to be measured, are essentially conductive. Thus, any change in the dielectric constant of the insulation, depending on the temperature, creates an error. To avoid this, the probes shown in FIGS. 10 and 11 have a compensation electrode 98 which is arranged below the lower end of the probe electrode 66 and is isolated from the protective electrode by a suitable distance, which can be achieved by appropriate etching of the conductive foil which forms the front guard electrodes and the probe electrode 66 . By measuring the change in the dielectric constant of the outer insulation 72, which is described in Pig. 19n is not shown, and by using this result such that the measurement of the capacitance across the insulation 72 adjacent to the probe electrode 66 is below the level of the

60982S / 0912, _

. GRJGiNAL

conductive liquid is compensated and corrected, you can get accurate measurements of the liquid level obtain. The compensating probe electrode 98 is placed in a position that is always under the liquid remains in the container or flow channel.

A probe, as shown in Figures 10 and 11, can be pre-calibrated outside the flow channel and then in brought back the flow channel and easily mounted in the appropriate location. As can be seen from Fig. 2o is, an installation device on the wall of the flow channel has a base plate 1oo which has a retaining bracket Io2 carries on a threaded pin 1o4. The bracket 1o2, which by means of suitable means at the upper end of the Probe 1o6 is attached, can be easily removed from the pin 1o4 by removing a wing nut 1o8. if Once the probe 106 has been removed from the flow channel, it can be placed in any suitable calibration container that a suitable zero level is set. The probe 1o6 with the retaining bracket 1o2 can then be placed on the pin 1o4 returned and positioned at the appropriate zero level by inserting the nuts 11o into the corresponding Position on the pin 1o4 are brought. Then the wing nut 1o8 can be attached to the pin 1o4 so that that the bracket 1o2 is clamped in the corresponding position. About positioning the probe 1o6 in the zero level position To facilitate this, suitable indices such as those shown on the probe of Figures 4 and 7 may be used. The base plate 1oo of the mounting device can be attached to the wall 15 by suitable devices, for example by a threaded bolt 112 can be attached. The probe 1o6 extends into a guide 114 with a curved one Longitudinal groove. The probe 1o6 must therefore be flexible enough to be able to follow this groove when it is introduced into the guide will. To ensure that the probe 1o6 is not raised or lowered * with respect to the wall 15, a

609826/0912

ORiGiNAL INSPECTED

- 3ο -

-Wire fuse is provided, which extends between the bracket 1o2 and the lowermost nut 11o and through openings in the Bracket 1o2 extends.

As noted above, it is often necessary to mount a probe to match the curvature of a wall in a flow channel or other container. However, if the probe follows the curvature of the wall in a flow channel, the probe must be designed differently from a probe that extends vertically. For example, a special design of a probe is required which is attached flush to the wall of a circular tube, as shown in FIG. 21a. The probe 12o extends over half of the tube 122. The height H of the liquid in the tube corresponds to the submerged length H ₁ . The radius of the pipe is R. The mass flow through the pipe can be expressed by the following equation:

Q = K ₄ H * (4)

where K. is a constant and the width of the probe can be expressed by the following equation:

b = K ₅ H * "" ¹

where K _{5 is} a constant and the relationship between H and H. for a circular tube is:

• τ? —Tr

r Arc cos. C-

H ₁ = | ^ - I 2 TTR (5)

Similarly, in a so-called "Leopold Logco" flume, as shown in Fig. 21b, where H is the height of the flow above the zero level and H _{1 is} the length of the flow

809828/0912

. ORIGINAL INSPECTED ^rf '"

covered probe represents the mass flow through the following -Equation can be expressed:

Q = K ₆ H

1.547

(6)

where K, is a constant and is the width of the probe through ο

the following equation can be expressed:

b = K ₇ H ⁰ ' ⁵⁴⁷ .

where K- is a constant and the following applies to the height H ₁ under the straight walls of the channel:

Are cos

2TR

36o

(7)

Assume that the semicircular part of the flume has a radius of 7.5 cm (3 ") and the width b of the probe .2.5 cm (1") with a height H of 12.5 cm (5 "), so the following values result for the probe:

There ium W ₁ in (inch) mm (inch) O (Q) 0 (0) 3.61 (ο.142) 7.62 (o.3o) 6.91 (ο.272) 14.99 (or 59) 1o, 34 (o.4o7) 28.45 (U 12) 13.11 (ο.516) 41.66 (1.64) 14.78 (ο.582) 54.61 (2.15) 17.37 (ο.684) 67.31 (2.65) 19.23 (Ο.757) 8o, o1 (3.15) 21.59 (ο, 85) 1o5.41 (.4.15) 25.4o (1.O) 130.81 (5.15)

609826/0912

ORIGfNAL INSPECTED

This can be done by characterizing a straight probe in a so-called Leopold Logco channel can be compared based on the following values:

There mm (inch) mm W in (inch) 0 (O) O (O) 6.35 (O.25) 4.93 (O.194) 12.7o (O.5) 7.19 (O.283) 25.4o (1.O) Ίο, 52 (O.414) 38.1o (1.5) 13.14 (O.517) 5o, 8o (2.O) 15.37 (o.6o5) 63.5o (2.5) 17.37 (O.684) 76.2o (3.O) 19.22 (O.757) 1o1.60 (4.O) 21.59 (O.85) 127, oo (5.O) 25.4o (1.O)

To easily see that the characteristics are different, the relationship between H and W and H ₁ and W _{1 may be} normalized as shown below;

There . mm (inch) mm W in (inch) O (O) O (O) 1.27 (o.o5o) 4.91 (O.194) 2.54 (0.I00) 7.19 (O.283) 5, o8 (0.200) 1o, 52 (O.414) 7.62 (or 300) 13.14 (O.517) 1o, 16 (0.400) 15.37 (o.6o5) 12.7o (0.500 17.37 (O.684) 15.24 (0.600) 19.22 (O.757) 2o, 32 (o-83o) 21.59 (or 85o) 25.4o (Loo) 25.4o •
(1,000)

609826/0912

^H 1 mm in (inch) O (O) 1.47 (o.o58) 2.92 (Ο.115) 5.51 (Ο.217) 8.o8 (or 318) 1o, 59 (o.417) 13, o8 (o.515) 15.54 (Ο.612) 2o, 71 (0.806) 25.4o . (Loo)

2555817 in (inch) ^W 1 (0) R.A.M (Ο.142) 0 (Ο.272) 3.61 (o.4o7) 6.91 (Ο.516) 1o, 34 (Ο.582) 13.11 (Ο.684) 14.78 (Ο.757) 17.37 (or 85o) 19.23 (1,000) 21.59 25.4o

Fig. 22 shows a circuit in which the capacitance between the probe electrodes, for example between the Probe electrode 66 of Figures 10 and 11, and earth or ground is eaten. The circuit has a fixed frequency RF oscillator 13o that connects a bridge circuit 132 through a Transformer 134 drives or controls, the secondary winding of which forms one side of the bridge 132. The one from the probe electrode sensed capacitance is represented by a variable capacitor 136 connected between a capacitor 138 and ground or earth is connected. Any change in the capacitor 136 that is the change in the liquid level being measured represents, wert a signal in parallel to a voltage or bypass capacitor 14o. The signal in parallel with this capacitor 14o, an amplifier 142 for generating a protective potential and an output terminal 144 are supplied, this potential being the same is the potential of the probe electrode.

In some cases the protective electrode can be driven to a potential which is not the same at all times is the potential of the probe electrode. This can be done by

609828/0912

_ "54 -

be achieved that the connection öes bridging capacitor 14o and the secondary winding of the transformer 134 with the protective electrode at an output terminal 148 get connected. The potential at terminal 148 is equal to the potential at the probe electrode when the bridge is in place is in equilibrium. In the circuit shown in Fig. 23, the potential for the guard electrode is obtained at the output terminal 15o of an amplifier 152, the parallel is connected to the probe electrode 136.

If the probe has a compensating electrode 98 such as that shown in the probe of FIG additional circuitry can be provided so that a compensated output signal is obtained. One such circuit is 24, in which a probe unit 154 represents the circuit shown in FIG. The output signal from the probe unit 154 represents the signal in parallel with the bypass capacitor 14o. A similar circuit, at v / elcher the measured probe capacitance 136 by the capacitance between the compensating electrode 98 of FIG , Probe of FIG. 19 and ground is shown as compensating unit 156 in FIG. The output signal from the probe unit 154 and the output signal from the compensating unit 156 then become a divider 158 which generates a compensated output signal, which is not affected by changes in the dielectric constant of the outer probe insulation.

The foregoing has emphasized the importance of the front guard electrodes or frontal sections of the guard electrode exposed. The rear. However, the protective electrode or the rear section of the protective electrode is also of of considerable importance, as can be seen from the following numerical example for the probe according to FIG. The probe has an outer insulation 16o with a capacitance C. the

609828/0912

Insulation 16o covers the probe electrode 162. The inner insulation 164 separates the probe electrode 162 from a protective electrode 166, the capacitance C being the capacitance over the insulation 164. A rear insulation 168 covers the protective electrode 166. As in FIG. 25, too shown, the thickness is above the insulation

16o d and the thickness over the insulation 164 d,. away

The probe of Fig. 25 is intended to measure liquid levels in a Parshall flume. The probe has an active length of about 61o in (24 "). The probe is straight and has a 25.4mm (1 ") wide.

For such a probe there is a capacitance to

K ₈ AK _q AK _q

C = -2 - Ξ. = 6.97—- (Ο.235 ") (8)

where C is the capacity in pF

K ₀ a constant

A is the area in ram (sq inch)

d is the distance in mm (inch) Κ- the dielectric constant of the Isolation are.

The dielectric constant K _{g of} the material should be 2.5, the thickness d and d of the insulation 16o and 164 o.5o8 mm (o.o2o "). From the above, the capacitance C can be calculated by the following equation: a

C _a = 29.4 L (9)

where L is the length of the probe covered by the liquid in the flume.

609828/0912

The probe is intended to be used for a maximum level of 100 mm (4 "), which is a full scale reading of

C = (29.4) * (4) = 117.5 pF (1o)

el

is equivalent to. By similar calculations we get for the capacitance C,

η - (Q / 235 ) · ( 2.5) (1) - (24) ^b T7

C _b = 7o5 pF (12)

C, is the standing capacitance of the probe and is greater than C, as calculated above, since 61 ο mm (24 ") of the

Probe to C, while only 1oo mm (4 ") to C be Ιο a

wear. . ■

Assuming that the dielectric constant K _{g of} the insulation 164 changes 5% over a temperature range of 39 degrees (70 ° F), the change in C _fa is 35.3 pF, which is a 3o% shift in the zero- Level of the system. If you want to keep the error due to the standing capacitance at 3%, the insulation thickness d, would have to be ten times greater, so that C, = 70.5 pF. A 5% change in the dielectric constant K _g would result in an error of 3.5 pF, which would represent an error in standing capacitance of about 3%.

Therefore, when the guard electrode 166 is brought to ground potential, there is a limit to how thin the probe is can be made. In the numerical example above - the probe would be adjusted to a thickness of 6.35 mm (0.25 ")

609826/0912

be limited. In addition, if the active length of the probe were greater, the probe would also have to be thicker. An increase in strength However, the probe is undesirable if the probe is flush with the viand of a channel or container should be installed so as to reduce the disturbance of the flow through the container or the channel to a minimum. By driving the protective electrode 166 to the protective potential, however, the capacitance C. drops out of the measurement equation and the probe can be made as thin as the particular application requires. The use of a rear guard electrode is particularly important when the protection is removably arranged in a guide, as it is not possible is to prevent an accumulation of liquid behind the probe in such a duct.

Another embodiment of a probe according to the invention is shown in FIG. Again, this embodiment has a layer structure with a probe electrode 2oo, a front protective electrode 2o2 and a rear protective electrode 2o4. The electrodes are encapsulated within an insulation which comprises a thermosetting insulating material 2o8, which exerts pressure forces on the probe electrode 2oo.

The probe electrode 2oo and the protective electrodes 2o2 and 2o4 have a large number of openings, which are made of a wire mesh 2Io are formed, which is somewhat enlarged in FIG. 27 is shown. By using a thermosetting material for the insulation 2o8, which shrinks when it cools, and through the plurality of openings 212 in the mesh 21o, like it shown in Fig. 28 are over the surfaces of the probe electrode 2oo, 2o2 and 2o4 including the surface compressive forces or pressure forces exerted at the openings

2 practices. These compressive forces exceed 7 kgf / cm (100 psi) at the

2 surface and preferably 35 kp / cm (500 psi) below normal operating conditions.

ORIGINAL INSPECTED 609826/0912

In the probe structure shown in FIGS each wire mesh 21ο is surrounded by insulating material in such a way that that it mechanically grips every wire in the net 21o. That

in other words, that all spaces between the meshes 21 o are filled with the insulating material. This ensures that water or another liquid, its flow rate or depth are measured should not be able to collect in pockets or cavities near the probe electrode 2oo. JCede collection of Water adjacent to the probe electrode 2oo would change the calibration of the probe since the dielectric constant of water is 8o times the dielectric constant of air.

The mechanical engagement and the compressive forces around the wires of the meshes 21 o around is achieved when the thermosetting Material is tightening around the wires of the net 21 ο, when the probe is cooled after heat setting. In a special embodiment, the insulating material is a thermoplastic material, which through the openings 212, which are formed by the network 21 o, for Time of heat curing brings about a fusion bond. "The thermoplastic material is then cooled in order to achieve the compressive forces. For use as a Thermoplastic insulation 2o8 is particularly preferred as the thermoplastic material polyvinylidene fluoride (Kynar). However, other fluorocarbon resins can also be used, including, for example, FEP (fluorinated ethylene propylene) heard.

It has been shown that the clasping of the wires in the network 21 ο can be brought to a maximum in that a plurality of substantially equally spaced openings extend over the length and width of the Probe electrode 2oo and extends over the protective electrodes 2o2 and 2o4. It is essential that each thread or

6098 26/0912

ORIGINAL! NSPECTED

Wire is surrounded by an appropriate amount of insulation. It has been shown that the mean maximum Cross-sectional dimension d of the openings more than 1o% of the mean diameter of the minimum distance d of Wires should be between the openings in the probe electrode. In addition, it is essential that the distance d between adjacent openings is not too large in relation to the strength of the insulation. The strength t. the isolation, measured from the probe electrode to the outside of the probe, should therefore be more than Io% of the distance d. Preferably the strength is t. greater than d, the optimum being reached when t.i is 2d such that a good mechanical grip on the electrode is produced. To ensure the actual HF field on the electrode, the minimum cross-sectional dimension d of the openings should not be more than twice the thickness t. the Isolation. Finally, it has been shown that by avoiding sharp edges or corners at the openings in a better mechanical grip around the electrode is achieved. For this reason it is preferable to use a wire mesh as an electrode, as shown in FIGS. 26 to 28, since the openings of the strands or threads of the network are formed which have a substantially circular cross-section.

In FIGS. 29 to 31 there is a further embodiment in which a plurality of openings 214 are formed in a probe electrode 216 and in protective electrodes 218 are. The insulation 22o again forms a continuum extending through the openings 214, like this is shown in Fig. 3o. '

The openings in the probe electrode 216 and in the protective electrodes 218 are not formed by a wire mesh but by etching conductive foils, which the Probe electrode 216 and guard electrodes 218 form.

609826/0912

ORIGINAL INSPECTED

As can be seen from Fig. 3o, this etching leads to a natural rounding of the metal at the edges of the openings 214, V7o achieved by maximum mechanical tensioning will. The appropriate distance d, the strength t. and the opening dimension d are determined by known phototechnical ones Process as used in the manufacture of printed circuits, precisely adjusted. Preferably they are Dimension d and thickness t at least equal to 25% of the distance d, with no rounding assumed at the openings becomes, and preferably greater than d, the optimum being achieved when d and t. are greater than d.

The etching of the openings 214 can be carried out simultaneously with the shaping of electrodes 216 and 218 take place, as has been explained with reference to FIGS. 12a to 12e. The probe electrode 216 can therefore be constructed similarly to that shown in FIG. This also applies to the probe 2oo and the adjacent one Protective electrode 2o2 according to FIG. 26, although the properties of this electrode are obtained by mechanical cutting or Etching can also be achieved.

The device for producing the shaft structures according to FIGS. 26 and 29 will now be explained with reference to FIG. 32. the Fastening device comprises a base plate 222 with a channel 224 for receiving the elements 226 of the probe on. Cushions 228 are positioned in channel 224 above and below elements 226. The pillows preferably have one very heavily polished surface, which corresponds to a surface such as is created by FEP Teflon, and so on to create a smooth laminated surface, which will greatly reduce the build-up of any coating on the pad prevented. Immediately above the upper cushion 228, an insert 23o is arranged, which applies the pressure to the layer structure transmits.

609826/0912

ORJGINAL1N3PECTED ""

Over the length of the layer structure 226 in the chamber 222 a uniform pressure should be applied. This is achieved by a flexible seal 232 that extends over the Insert 23o extends so that a substantially airtight chamber is formed. The seal 232 is through Bolts 236 held in a sealing manner, which extend through pressure seals 234 and the seal 232 in openings in the Base 222 extend. Evacuation of the chamber under the seal 232 is via a vacuum port 238 in the base 222 reached.

In order to prevent the entrapment of any air bubbles in the layer structure 226, the chamber in which the Structure 226 is arranged, evacuated before each pressure is applied to the layer structure 226. This is done using a bridge element 24o which is attached to a support element 244 by bolts 242. The element 244 is in turn fastened to an insert 23o by means of bolts 245. The bridge element 24o is over the base 222 held by bolts 246 which come to rest against a pressure seal 236. If the chamber in which the Layer structure 226 is arranged, evacuated via the opening 238 and all air bubbles have been removed, For example, the bolts 242 can be removed so that the removal of the bridge 24o is possible while at atmospheric pressure uniformly applies appropriate lamination pressure to the elements of assembly 226. The entire device can then be placed in an oven for heating to the gel point of the thermoplastic insulation material, in order to achieve the desired fusion bond through the large number of openings in the electrodes of the probe.

Fig. 33 shows the elements of a probe assembly prior to Lamination sandwiched between pads 228 that sit in channel 224 of base 222. How one sees, channel 224 has not yet been evacuated «Besides, it is

609826/0912 _.:

ORiGfNAL iNSPECTED

so far no pressure has been exerted on the elements to be laminated been. In addition, there are air gaps between each wire mesh 21ο and the thermoplastic webs 28o that the Form isolation 2o8 of FIG. To ensure that the net 21o is in the correct position in the laminated Structure remains, the network 21 ο can be attached after the alignment, for example on the middle thermoplastic Slide 25o.

As shown in Fig. 34, the gasket 232 is sealingly seated on the top of the base 222 so that a substantially airtight chamber is formed in the channel 224. To prevent the formation of air bubbles between components 21o and 25o To prevent this, the bridge element 24o carries the insert 23o by means of the bolts 246. The device is in the manner shown in Fig. state shown until all the air has been withdrawn via the vacuum port 238.

When the air has been completely evacuated from the chamber in channel 224, bridge 24o is removed and atmospheric pressure pushes the elements of the probe into a compressed position as shown in FIG. The pressure exerted on the probe elements via the insert 23o occurs prior to any heating of the probe elements. It has been shown that it is particularly important that this pressure is applied before heating so that the subsequent release of internal stresses during heating does not lead to shrinkage or deformation of the plastic. It has also been found that the very uniform pressure applied to the insert as a result of atmospheric pressure ensures uniformity across the laminate by preventing any floating of the various grid electrodes 21 o. If the probe is very long, this uniform pressure would be very difficult to achieve by mechanical means. By using the fluid pressure as is offered by the atmosphere, the Gleichförmig-, pressure ness guarantees and gives a uniform laminate.

609826/0912

"The whole of the device shown in Fig. 35 in which atmospheric pressure pushes the insert 23o is then placed in a heated press or oven so that a fusion bond of the thermoplastic films occurs through the openings in the network electrodes 21ο. The temperature of the oven or the press should ensure that the thermoplastic materials or foils reach a temperature of 25o which is at least equal to the temperature of the gel point of the thermoplastic films. In the case of polyvinylidene fluoride films 25o (Kynar), a temperature of 188 C {37o ° F) is sufficient to melt a bond through the openings in the Mesh electrodes 21 ο to achieve. This temperature is below the gel point of FEP, which is 288 ° C (55o ° F), so that the use of FEP as a cushion 228 is guaranteed. However, when using FEP as a thermoplastic sheet material the temperature of the tracks must be 288 ° C or exceed this temperature (55o ° F) while the pads 228 have a highly polished surface of a different material, for example made of stainless steel.

In FIG. 36, the webs of thermoplastic material 25o and the mesh electrodes 21 o are separated from one another by air spaced as shown in FIG. In Fig. 37 the air is evacuated and the pressure is applied according to FIG. 35. In FIG. 38, heat is applied to the structure so that a fusion bond occurs the openings in the electrodes 21ο, which means that the mechanical attack on the strands in the wire mesh is guaranteed.

using the above measures for production Laminated probes show that they are particularly resistant to splitting into layers. Even if the probe is inserted into water at relatively high temperatures, the probe will withstand any splitting into

609826/0912

'ORJQfNAL INSPECTED "

2555517

Layers of what could otherwise cause water to collect in pockets of air near the probe electrodes. The liquid, into which the probe is inserted must have a temperature which is lower than the curing temperature of the Isolation. Therefore, it must be thermoset at temperatures not lower than 49 ° C (120 ° F), which is the temperature represents the maximum ambient temperature a probe is likely to be exposed to, and preferably above 100 ° C (212 ° F), the boiling point of water. That means with In other words, that the hardening temperature of the insulation material should be higher than the temperature of the liquid, into which the probe is immersed.

The way in which the compressive forces around the probe electrodes are developed around will be explained in more detail below with reference to FIG. 39. In this figure is. a single wire 3oo a wire mesh electrode is shown, which is surrounded by an insulation 3o2. a is the inner radius, b is the outer radius of the insulation 3o2. If P is the inner radial

2
Pressure in kp / cm (psi), where the longitudinal pressure is zero, Δ a is the change in the inner radius due to P, Δ b is the change in the outer radius due to P _f E is the modulus of elasticity and V is Poisson's ratio, applies to the model shown in Fig. 39:

+ V) Π ¹ )

b -a

= PI (-2 ^) (2 ¹ )

^(3f)

E b -aT

b -a 60982670912. -

ORIGINAL SNSPEOTBD

It is believed that the illustrated by the equation (4 ¹⁾ model represents the pressure applied to the wire 3oo when the insulation 3O2 shrinks around the individual wire around 3oo. The Poisson's ratio ν can be expressed by the following equation: v / earth:

where G is the shear modulus of elasticity. The Poisson's ratio v> however, it can also be expressed as follows:

V = (6)

where K is the spatial modulus of elasticity. The denominator of equation (4 ¹ J is a constant. The pressure exerted on wire 2o2 is therefore a function of the product of the shrinkage A a at the inner radius of insulation 3o2 and the modulus of elasticity of insulation E.

In FIG. 4o the pressure P is shown which is exerted on the wire 3oo by the polyvinylidene fluoride insulation 3o2 (Kynar) where a specific shrinkage of about 1.5% is assumed. The upper curve 3o4 of the diagram shows that the pressure increases almost linearly as the insulation increases, but begins to reach a limit value, when the ratio of b / a is about four. From the point of view of the pressure, this means that it would be of no use if the insulation is thicker than about three times the radius of the wire or than 1 1/2 times the wire diameter were. The lower curve 306 of the diagram clearly shows, however, that the increase in the ratio from b / a up to two results in a very substantial increase in the pressure exerted on the wire 3oo through the insulation 3o2.

609826/0912

ORIGINAL INSPECTED

255581?

The round wire model therefore shows that any thickness of insulation creates a compulsory pressure on the wire as long as there is a shrinkage of the insulation. This shrinkage can, as explained above as long as the insulation is cured at a temperature higher than that maximum operating temperature. However, since many thermoplastic materials that are suitable for use as insulation 3o2 Are particularly apt to relax after an initial tension, a pressure of sufficient height must be applied initially be applied to a corresponding pressure and a grip on the wire 3oo even after relaxation guarantee.

With reference to FIG. 41, reference is now made to sheet-like conductive electrodes which have etched openings so that an electrode section 3o8 remains which is essentially rectangular in cross section and is surrounded by the insulation material 31o. The pressure exerted on the electrode portion 3o8, which is a function of the electrode thickness, is different from the case where a round wire is used because of the rectangular nature of the electrode portion 3o8. In particular, the metal electrode 308 prevents any substantial movement at the corners 312 of the electrode. In addition, the insulation materials 31 o are held in lateral tension along surfaces 314 and 316, as shown by arrows 318 and 32o, respectively. Because of the lateral stress illustrated by arrows 318 and 32o, the insulation 31o withstands any deflection that would be required to apply pressure to the metal electrode surfaces 314 and 316. If the insulation is very thin, the pressure in the radial direction is not high enough to bend the insulation because of its lateral tension. This has the result that on the flat surfaces of the

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Electrode 3o8 essentially no pressure is applied. As the insulation strength increases, the radial pressure increases higher and possibly large enough to overcome the effects of the live insulation, whereby Pressure is applied to surfaces 315 and 316 of electrode 3o8.

The probes shown in FIGS. 26 and 29 can be used in conjunction with the circuits shown in FIGS. 22 and 23 will. The unknown capacitance 136 represents the capacitance from the probe electrode 2oo of that shown in FIG Probe and the ground or the capacitance between the probe electrode 216 of the probe shown in Fig. 29 and Earth.

A wide variety of thermosetting insulation materials can be used that tend to shrink after Distinguish heat curing. The thermosetting can take place by an exothermic reaction within the insulation material the application of external heat can be achieved.

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Claims (1)

PATENT CLAIMS RF probe assembly for measuring the level of a substantially conductive liquid in a container, characterized by a probe for attachment to a surface (15) of a container (14) so that it extends through the surface level of the liquid, with a conductive probe electrode (2o), which extends longitudinally along the probe adjacent its front and away from the surface, with a conductive protective electrode device (22), which extends in the longitudinal direction along the probe (12) extends and has lateral portions that extend laterally outward from the portion of the Probe electrode (2o) extend, with an inner solids insulating device (18), which the probe electrode (2o) and the protective electrode device (22) is supported, and with an outer solids isolating device (24), which covers the conductive probe electrode (2o) and the protective electrode devices (22), whereby the lateral sections extend laterally outwards over the section of the probe electrode (2o) extend beyond a distance that is at least six times greater than the thickness of the solids insulation device (24), which covers the protective electrode device (22), divided by the dielectric constant of the solid insulation means, and wherein means for holding the Potential of the protective electrode device (22) at essentially the same potential of the probe electrode (2o) are provided. 609826/0912 2. Arrangement according to claim 1, characterized in that the probe electrode (2o) has a front side Has dimension which increases with increasing distance from a longitudinal end of the probe. 3. Arrangement according to claim 2, characterized in that the lateral sections of the electrode device extend laterally outward beyond the section of the probe electrode by a distance, which increases with decreasing distance from the longitudinal end of the probe. 4. Arrangement according to claim 1, characterized by devices to warm the probe to dissolve a fat deposit on the probe. 5. Arrangement according to claim 4, characterized in that the protective electrode as a heating device for the Probe is used. 6. Arrangement according to claim 5, characterized in that the protective electrode is serpentine is. 7. Arrangement according to claim 4, characterized by a Heating control electrode for touching the capacity of a fat deposit on the probe. 8. A probe according to claim 7, characterized in that the heating control electrode under one end of the Probe electrode is arranged. 809826/0912 - 5ο - 9. Arrangement according to claim 1, characterized by a guide device with at least one longitudinal groove for receiving the probe, which a Movement of the probe in the recess in a direction parallel to the longitudinal dimension of the probe enabled. light. lo. Arrangement according to claim 9, characterized in that that the guide means is a recess within the surface of the container. 1t. Arrangement according to claim 9, characterized by means for heating the probe, wherein heating means are arranged on the back of the probe in the guide device. 12. Arrangement according to one of the preceding claims, characterized in that the protective electrode has a partial sleeve which is hollow Chamber forms the inner solids isolation device receives, with the lateral portions of the protective electrode a front wall of the sheath having an opening in the wall which is complementary in shape to the probe electrode, wherein the probe electrode is arranged in the opening and essentially fills them out. 13. Arrangement according to claim 12, characterized in that that the outer insulating device comprises a substantially tubular part. 14. Arrangement according to claim 1, characterized in that the protective electrode is a conductive substrate whose thickness from front to back is significantly greater than the probe electrode. 609826/0912 15. Arrangement according to claim 14, characterized in that the outer insulating device is a substantially having tubular part. 16. Arrangement according to claim 1, characterized in that that the protective electrode device furthermore has a rear section, which is next to and behind the probe electrode is arranged. 17. The arrangement according to claim 16, characterized in that the rear portion of the probe electrode device and the lateral portions of the protective electrode devices against each other by the internal pesticide isolation devices are insulated. _R that the outer longitudinal Feststoffisoliereinrichtung 18. A device according to claim 17, characterized in that a heat seal of their lateral ends. 19. The arrangement according to claim 18, characterized in that the outer solids isolation device Vinylidene fluoride polymer having a high molecular weight, which has a dielectric constant of over four has. 20. The arrangement according to claim 1, characterized in that the outer insulating device comprises a vinylidene fluoride polymer with a high molecular weight, the dielectric constant of which is greater than four . 21. The arrangement according to claim 1, characterized by a laminate structure, wherein lateral sections and the probe electrode are etched onto the inner solid insulation device. 609826/0912 22. The arrangement according to claim 1, characterized by an adjustable holding device for holding the Probe in various positions on the grounded surface of the grounded container, allowing removal the probe out of the holding device for calibration purposes and for replacing the probe on the holding device is possible in a predetermined position. 23. Arrangement according to claim 1, characterized by an additional electrode device for measuring of changes in the dielectric constant of the outer insulation device, this being additional Electrode device opposite the probe electrode and the protective electrode device is insulated, which are covered by the outer insulation. 24. The arrangement according to claim 1, characterized in that the longitudinal axis of the probe is in the vertical and extends in the horizontal direction. 25. Arrangement according to claim 24, characterized in that the probe electrode has an increasing lateral Has dimension with increasing distance from the lowermost end of the probe. 26. The arrangement according to claim 1, characterized in that the grounded holding surface is a wall of the container is and that a guide is provided which follows the contour of the wall, the wall in a extends vertically and in a horizontal direction and the probe is flexible so that it extends the guide, when it is inserted into this, adapts. 609826/0912 27. Arrangement according to claim 1, characterized in that that the probe is on the surface of the flow channel attachable and the probe electrode satisfies the equation: b = I ^ h (IK-I) where b is the lateral dimension of the probe electrode, Not a constant <X is a constant determined by the curvature of the Wall in the flow channel depends, and H is the height at which the probe electrode moves above the zero flow level in extends the flow channel. 28. Arrangement according to claim. 27, characterized in that the surface is a curved container wall, 29. Arrangement according to claim 28, characterized in that the container is a circular tube, 30. RF probe assembly for measuring the level of conductive Liquids, in particular according to one of the preceding claims, characterized by one Container with a conductive liquid and a holding surface that is at least slightly vertical extends such that the liquid rises along this surface with changes in the liquid level or falls through a probe attached to this surface in such a way that the longitudinal axis of the probe is extending at least somewhat vertically, the probe having a conductive probe electrode extending longitudinally extending along the probe, a conductive protective electrode device having a rear portion, which is arranged next to it between the Viand and the probe electrode, and with lateral 609326/0312 Portions extending laterally outwardly beyond the lateral ends of the probe electrode by a distance, the substantially greater _t having as the minimum distance between the side portions and the guard electrode plus the thickness of the protective electrode means, and an outer Feststoffisoliereinrichtung which the Surrounding the probe on the outside for isolating the protective electrode device and the probe electrode from the conductive liquid and the mounting surface, and the outer insulating device has an exposed surface in contact with the conductive liquid and a covered surface in contact with the holding surface, and by means for holding the potential of the protective electrode at substantially the same potential as the probe electrode. 31. Method of making a probe for measuring Fluid levels characterized in that conductive surfaces on opposite sides of a insulating substrate are applied that one of the surfaces is etched so that it is a longitudinally extending probe electrode between a pair of guard electrodes on one these sides of the substrate and that an insulation on the outside of the conductive surfaces is applied. 32. The method according to claim 31, characterized in that the application of the insulation by arranging of two insulating foils next to each other on the conductive surfaces and by heating the lateral ones Ends of the slides running. 609826/0912 33. The method according to claim 31, characterized in that that the insulation applied to the outside is a vinylidene fluoride polymer with a high molecular weight and a dielectric constant greater than four. 34. The method according to claim 31, characterized in that that the conductive surfaces on opposite sides of the insulating substrate by gluing be applied 35. The method according to claim 34, characterized in that the insulation applied to the outside of the surfaces is applied, applied to the outermost sides of the conductive surfaces by means of gluing will. 36. The method according to claim 34, characterized in that the conductive surfaces, the adhesive and the insulating substrate to be exposed to heat and pressure to form a layer structure. 37. A method for measuring the level of liquids in a container independently of an accumulated deposit, characterized in that a part of a probe with an insulated probe electrode and laterally outwardly arranged insulated protective electrodes is submerged in the conductive liquid in the vicinity of a holding element in the longitudinal direction is that any deposit accumulating on the probe extends over the protective electrodes before contact is made with the effectively grounded holding element, that the protective electrodes are driven to essentially the same potential as the probe electrode and that the potential of the protective electrode is also driven 809826/0912 the conductive covering over the insulation, which the Protective electrode covers, is capacitively coupled so that the potential drop of the coating between the side ends and the center of the probe electrode within 25% of this potential drop between the probe electrode and the coating in the Center of the probe electrode is maintained. 38. Probe for use in HF measuring systems for liquid levels, characterized by a conductive probe electrode, which extends in the longitudinal direction along the probe, through conductive protective electrode devices with side sections that extend laterally outwards over the side ends of the Probe extending out, and having a rear portion that extends behind the probe electrode assembly extends, through an inner insulating means, which is between the probe electrode and the rear Section of the protective electrode arranged is, and by an outer insulating device connected to the probe electrode and the lateral Sections of the guard electrode is in contact and forms an exposed front surface of the probe, which comes in direct contact with the liquids, with the side sections facing laterally extend outside of the lateral ends of the probe electrode by a distance which is substantially greater is as the minimum thickness of the outer insulator in contact with the probe electrode between the side ends. 609826/0912 39. RF probe assembly for measuring the level of a substantially conductive liquid in a container, characterized by a thin, flexible. Probe, which is removably attached to a surface of the container is attachable so that it extends above the surface level of the liquid, wherein the probe has a conductive probe electrode extending longitudinally along the length of the probe adjacent to it the front of which extends away from the surface, a conductive rear protective electrode device, extending longitudinally along the probe, an internal solids isolator interposed between the probe electrode and the rear section of the protective electrode, this is arranged in an insulating manner, and with an external solid insulation device in contact with the conductive probe electrode, and by means for maintaining the potential of the guard electrode means at substantially the same potential of the probe electrode, 40. Probe for use in RF measurement systems for one Liquid level characterized by a conductive probe electrode device extending lengthways extends along the probe, the probe electrode device having a plurality of openings, extending through the probe electrode assembly from side to side, and by thermosetting insulating means extending longitudinally along the probe electrode means extends on opposite sides thereof, the isolating means extending through the Extends openings and compressive forces on the probe electrode device exerts over their surface. 609826/0912 -41. Probe according to Claim 4o, characterized in that the insulating device is a thermoplastic Having material. 42. Probe according to claim 41, characterized in that the thermoplastic material is a fluorocarbon resin having. 43. Probe according to claim 42, characterized in that the fluorocarbon resin is a crystalline
High molecular weight vinylidene fluoride polymer with a dielectric constant greater than four. 44. A probe according to claim 4o, characterized in that the isolating device exerts pressure forces of over 7 kp / cm ² (loo psi) at 38 ° C (100 ° F). 45. A probe according to claim 44, characterized in that the isolating ^{device exerts compressive forces in excess of 35 kp / cm 2} (500 psi) at 38 ° C (loo ° F). 46. Probe according to claim 4o, characterized in that the probe electrode device has a plurality of conductive filaments. 47. Probe according to claim 46, characterized in that the probe electrode device is a network
made of conductive filaments, 48. Probe according to claim 46, characterized in that the minimum thickness of the insulation is measured
from the surface of a filament between adjacent openings and the outer surface of the
Isolation device is at least 1o% of the diameter of the filament. 609826/0912 255 * 581? 49. Probe according to claim 48, characterized in that the mean minimum cross-sectional dimension of the openings in the probe electrode device at least 10% of the diameter of the filament amounts to. 50. Probe according to claim 4o, characterized in that the probe electrode device is a conductive one Has film with a plurality of openings. 51. Probe according to claim 5o, characterized in that the mean minimum thickness of the insulating device measured by the probe electrode device between adjacent openings and the The outer surface of the isolating device is greater than 1o% of the mean minimum distance between openings in the probe electrode. 52. Probe according to claim 51, characterized in that the mean minimum strength is greater than the mean minimum distance. 53. Probe according to claim 52, characterized in that the mean minimum strength is at least equal 1 1/2 times the mean minimum distance. 54. Probe according to claim 4o, characterized in that the mean minimum cross-sectional dimension of the openings in the probe electrode device is smaller than twice the mean minimum Strength. 55. Probe according to claim 4o, characterized in that the probe electrode device has a multiplicity of etched openings. • « 809826/0912 - 6ο - 255581? 56. Probe according to claim 55, characterized in that the surface of the probe electrode device at the openings, which are available in a large number, is rounded. 57. Probe according to claim 4o, characterized by a protective electrode device which extends laterally extends outwardly beyond the probe electrode assembly and is insulated therefrom, wherein the protective electrode device likewise has a multiplicity of openings which are extend through the guard electrode from side to side, and the insulating device through the plurality of openings of the protective electrode device and compressive forces on the Protective electrode device exerts over the surface thereof. 58. Probe according to claim 4o, characterized by a conductive protective electrode device with lateral Sections that extend laterally outward over the lateral ends of the probe electrode device extend out, and having a rear portion extending behind the probe electrode means, wherein the protective electrode device has a plurality of openings which extend through the lateral section and the rear section extend from side to side, and the Isolation devices Pressure forces on the protective electrode device exercise over their surface. 59. A probe according to claim 4o, characterized in that the conductive probe electrode device has a front lateral dimension which increases with increasing Distance from one longitudinal end of the probe increases. 609826/0912 - ⁶¹ - 255581? 60. A method for producing an RF probe for measuring liquid levels, characterized in that a thermosetting insulating material on the outside of a probe electrode having a plurality of openings passing through the electrode is applied and that the insulating material is so heat-cured that a substantial compressive force is exerted on the probe electrode over its surface after Cooling is applied with the thermoset insulating material forming a continuum through the openings forms. 61. The method according to claim 60, characterized in that that the thermosetting is carried out at a temperature in excess of 38 ° C (100 ° F). 62. The method according to claim 60, characterized in that the heat curing at a temperature above 100 ° C (212 ° F) lying temperature is executed. 63. The method according to claim 60, characterized in that the insulation material is a pair of thermoplastic Has foils which are arranged on opposite sides of the probe electrode, the Foils are heated to the gel point during heat curing, so that a fusion bond occurs through the openings is formed. 64. The method according to claim 60, characterized in that pressure is exerted on the foils to the foils to press against the probe electrode. 609826/0912 65. The method according to claim 64, characterized in that that the application of the pressure on the insulating material takes place in that any air between the foils and evacuating the ground electrode and applying fluid pressure to the sides of the insulating material, pointing away from the electrode. 66. The method according to claim 64, characterized in that the air between the insulating material and the Probe electrode is evacuated before applying fluid pressure to the insulating material. 67. The method according to claim 65, characterized in that the pressure on the insulating material before heating is applied to the gel point. 68. Method of using an RF liquid level probe with electrode devices that a plurality of side-to-side extending through the probe electrode means Has openings and insulating means which are thermoset at a curing temperature so that Compressive forces are exerted on the probe electrode device via the surface thereof after cooling below the hardening temperature, characterized in that that the probe is placed in a flow channel and that liquid flow through the flow channel is left so that at least a portion of the probe is submerged with the liquid at a temperature has, which is substantially below the hardening temperature, so as to reduce the compressive forces on the probe electrode to maintain. 609826/0912 Blank page