DE8705399U1 - Measuring conductor for a level sensor - Google Patents

Description

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The invention relates to a measuring conductor for a level sensor with a flexible, elongated, flat* strip-shaped insulating carrier with elongated electrical resistors of equal length that are lined up on the insulating carrier, with elongated electrical switches of equal length that can be magnetically actuated, the contacts of which are in closed tubes filled with protective gas and which are individually assigned to the individual resistors and lined up on the insulating carrier, with the resistors and switches being arranged axially parallel to one another on the insulating carrier with respect to their longitudinal axis, and with a support tube made of magnetically inactive material into which the insulating carrier equipped with the resistors and switches fits tightly and is inserted.

In such a level sensor, a permanent magnet designed as a float or moved in another way runs along the measuring conductor and activates switches depending on its position. This short-circuits individual resistors connected in series, causing the resistance value of the entire arrangement as a measured variable to change according to the position of the permanent magnet.

In a known measuring conductor, the switches and resistors are arranged in a staggered manner with their longitudinal axis at an angle to the longitudinal axis of the insulating support. The staggered arrangement leads to a close sequence of switches along the measuring section and thus to a high level of measuring accuracy, but on the other hand leads to a disadvantageous stiffening of the equipped insulating support.

In a known measuring conductor of the type mentioned above, the support tube has a circular cross-section.

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The task of the [Drfiridurig is to design a measuring conductor of the type mentioned above in such a way that as many switches as possible are arranged on the long section of the measuring conductor and that the measuring conductor is bendable.

The invention is characterized in that the resistors and the switches are arranged perpendicular to the longitudinal axis of the insulating carrier with respect to their longitudinal axis and that the question tube has a rectangular cross-section and closely surrounds the cross-sectional contour of the equipped insulating carrier.

By arranging the switches and resistors perpendicular to the longitudinal axis of the insulating support, a large number of them can be accommodated on the length section. The insulating support is only minimally stiffened by the inclusion of resistors and switches, so it essentially retains its flexibility, which allows deflection on both sides to the transverse axis of the insulating support.

This arrangement of the switches and resistors results in a cross-section of the equipped insulating support in the form of an elongated rectangle. To save space and therefore advantageously, the support tube should be designed with a correspondingly rectangular cross-section. Such a support tube is easier to bend across the transverse axis than an otherwise comparable support tube with a circular cross-section, so that not only the equipped insulating support but also the finished measuring conductor is bendable and can therefore be rolled up for transport and storage and can be laid curved. The invention therefore opens up completely new application possibilities.

For reasons of space, it is desirable to make the measuring conductor as narrow as possible. To do this, the insulating support must be as narrow as possible and this is achieved by making the insulating support only a minimal amount of insulation material wider on both sides than the length of the individual switches and by making the resistors shorter than the switches.

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You can arrange the resistors and switches alternately next to each other, but you can also arrange the resistors and switches in pairs one above the other.

Preferably, only one resistor is associated with a switch, although circuits are also conceivable in which several resistors are associated with a switch. In circuits with only one resistor for each switch, assembly can be made easier by combining the pair and then assembling them together. This is achieved according to an expedient development of the invention by integrating a resistor with the associated switch next to each other, parallel to the axis, into a common plastic housing made of electrically insulating material, which closely surrounds the switch with the resistor and from which connection pins for the switch and the resistor are led out.

Such a plastic housing for a switch with two associated resistors is already known from US Patent 4,284,409. However, according to this patent specification, these plastic housings are mounted on the insulating support in the longitudinal direction of the insulating support with their longitudinal extension, which corresponds to the longitudinal extension of the switches and resistors, which impairs flexibility and means that the number of switches that can be accommodated on a unit length is very small.

In order to keep the external dimensions of the measuring conductor as small as possible, the insulating support is only about as wide as the plastic housing is long. The connecting pins are conveniently arranged on one long side of the plastic housing, protruding perpendicular to it. In the US patent specification cited, the corresponding connecting pins protrude from the front sides of the plastic housing and would require additional space in width if the plastic housing were arranged transversely to the longitudinal axis of the insulating support.

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According to the cited US patent, the switch and the J

Resistors inside the plastic housing next to each other j

arranged so that the plastic housing is also wide enough *

So that as many switches as possible are set to the unit of length |

to be accommodated, you need a very narrow plastic |

fabric housing and this is achieved by the resistance and the |

Switch within the plastic housing, related to the |

Insulating supports, arranged one above the other. 1

In general, the resistor is shorter than the switch and then | ₍ for reasons of space it is recommended that the resistor is arranged in the longitudinal center of the switch on the side of the switch facing the insulating support.

Such plastic housings equipped with resistors and switches can be manufactured very easily in mass production. This makes fitting the insulating support much easier than fitting the switches and resistors separately, because you only need to handle one element for each pair, which is also less easily damaged than the unprotected switch or resistor. To assemble, all you have to do is insert the connecting pins into prepared holes in the insulating support. The insulating support is conveniently provided with an electrically conductive coating that is part of a circuit diagram and that extends immediately adjacent to these holes and adheres firmly to the insulating support. The connecting pins can then be soldered to this coating, and the soldering can be carried out very easily by pulling the support slightly bent through a bath of liquid solder. As soon as the soldered connections have hardened, they form electrical contact and also hold the plastic housing on the insulating support.

The invention will now be explained in more detail with reference to the attached drawing. I

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In the drawing shows:

Figure 1

figure 2 figure 3 figure 4 figure 5 figure 6 figure 7 figure 3 figure 9 figure 10 figure 11 figure 12

Figure 13

Figure 14

Figure 15

the section of a measuring conductor, partly in section, with a parallel tube in which a float slides, · the section II axis Figure 1,
the insulating support from Figure 1 seen from the side facing away from the viewer of Figure 1, an electrical equivalent circuit diagram for Figure &igr;, a plastic housing with a switch and a resistor in section, the plastic housing from Figure 5 in perspective,

the section VII of Figure 5» in section another embodiment of a circuit element,
section IX of Figure 8,
another embodiment of a circuit element in perspective, fully assembled but not yet filled with casting compound, section XI from Figure 10, another embodiment of a populated insulating carrier,
another embodiment of a populated insulating carrier,

another embodiment of a measuring sensor which is equipped with an additional, visually visible level indicator, and the view according to the arrow XV in Figure 4.

In the drawing, 1 designates a support tube 1 made of aluminum, which has the shape of an elongated rectangle in cross-section. In the support tube 1 there is an elongated, band-shaped, flexible insulating support 2, on the support side of which 3 cuboid-shaped, elongated, equally sized plastic housings 4 to 7 are lined up closely next to one another. The plastic housing 4 is shown in Figures 5 and 6 , has the shape of an elongated cuboid, the longitudinal axis of which is designated 8.

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An elongated switch 9 and an elongated resistor 10 are housed within the plastic housing. The switch 9 and the resistor 10 are cast into the plastic of the housing 4. The switch 9 can be actuated magnetically, its contacts 11 and 12 are housed in a closed _tube 13 filled with protective gas. The longitudinal axis 14 of the switch is parallel to the longitudinal axis 15 of the resistor and to the longitudinal axis 8 of the plastic housing 4.

16, 17, 18 and 19 denote contact pins that protrude from the plastic housing 4. These contact pins 16 to 19 are, as can be seen from Figure 6, lined up along a straight line 20 and penetrate the housing wall on one long side, the so-called connection side 21, of the plastic housing 4 and extend perpendicular to the connection side. The connection side 21 is the long side of the plastic housing that, when assembled, faces the insulating support 2, i.e., in Figure 1, faces away from the viewer.

The electrical connection lines 25 to 28 extend from the ends of the switch and the resistor and are angled as contact pins.

The resistor 10 is shorter than the switch 9 and is arranged below the switch in the longitudinal center of the switch and fits into the space between the connection pins 30, 31 of the switch formed by the contact pins 16 and the connection lines 25 and 27. The corresponding connection pins of the resistor are designated 32 and 33. The resistor is therefore adjacent to the connection side 21 and the switch 9 is on the side of the resistor 10 opposite the connection side 21.

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Two spacer ribs 40, 41 extend across the connection side 21 transversely to the longitudinal axis 8. The plastic housing 4 sits on the support side 3 of the insulating support 2 with these spacer ribs. The connection pins 30 to 33 are inserted into holes in the insulating support 2, for example holes 44, 45, -46, 47. In order to show these holes, some plastic housings are not shown in Figure 1.

As can be seen from Figure 3, a conductor pattern 49 is applied to the back of the insulating carrier 2, the so-called connection side 48, by means of a coating of electrically conductive metal. The holes, for example the holes

44 to 47 are closely surrounded by the coating of the conductor pattern 49. The ends of the connection pins inserted through the holes are soldered to the conductor pattern or the coating. The coating of the conductor pattern 49 is electrically conductive and is provided directly adjacent to the holes 44 to 47 and firmly adheres to the insulating carrier 2.

The plastic housings are individually lined up close to one another with their longitudinal axis 15 transverse to the longitudinal axis 8 of the insulating support 2. The plastic housings 4 to 7 are approximately as long as the insulating support 2 is wide, so that the minimum required insulation distance 70, 71 to the edge remains, but no unnecessary space is required by the insulating support 2, so that the entire arrangement, as can be seen from Figure 2, including the support tube 1 closely surrounding the equipped insulating support, is built as compactly as possible and takes up little space in cross-section.

The insulating bracket 2, which is fitted with plastic housings, can be bent on both sides with a radius of 0.5 to five metres.

This results in the circuit diagram shown in Figure 4, in which the resistors of all plastic housings are connected in series and this series arrangement is tapped off step by step by the associated switches. The resistance value between the output lines 51» 52, 53 of the insulating support 2, which is delimited in Figure 4 by the dot-dash line 50, changes depending on which of the switches is closed.

A guide tube 55 is arranged parallel to the axis next to the support tube 1. It is made of magnetically inactive material and a float 56 can slide within it. The tube 55 communicates with an external liquid level, so that a liquid level 57 is established within the tube 55, which constantly changes and raises and lowers the float 56 - when the support tube 1 and the guide tube 55 are arranged upright.

A permanent magnet 58 is arranged inside the float 56, which closes one or two switches located at the same height*. This switch closure changes the resistance values between the output lines 51 to 53 according to the height of the float and thus according to the height of the liquid level 57 and is displayed in a level indicator.

The plastic housing 60 shown in Figure 8 is equipped with a switch 61 and a resistor 62, which are embedded in the plastic of the plastic housing. The electrical connection lines 63, 64 of the resistor 62 are led out on one long side 65 and the electrical connection lines 66, 67 of the switch 61 are led out on the opposite long side 68. The parts of the connection lines protruding from the plastic housing are angled in a direction perpendicular to the plane of the drawing to the side facing away from the viewer in Figure 8, as can be seen in Figure 9. The long side 69 located between the long sides 68 and 65 is the connection side.

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Figure 10 shows a plastic housing 75» in the form of a tub that is open at the top, into which the contact pins 76 to 79 corresponding to the contact pins 16 to 19 are inserted. They protrude vertically from the bottom of the tub along a straight line from the connection surface 80 formed by the bottom of the tub. During mass production, the switch 82 and the resistor 83 are inserted into the filling space 81 and are electrically connected to the contact pins 76 to 79 with their connection leads 85, 86, 87, 88, which are angled downwards. The switch 82 and the resistor 83 are thereby also held in place, at least provisionally.* Once this has been done, the filling space of the tub is filled to the top with flowable, insulating casting compound, which then hardens. The now finished plastic housing can, according to the example, be used in many different ways. Figures 1 to 4 can be used.

Instead of arranging the plastic housings as in Figure 1 with their longitudinal axis 8 transverse to the longitudinal axis 90 of the insulating support, they can also be arranged axially parallel to the longitudinal axis 91 of the insulating support 92, as shown in Figure 12. According to Figure 12, two rows of plastic housings 93, 94 are arranged offset next to one another. In Figure 13, plastic housings 97, 98, 99 are arranged in a row on the insulating support 95, axially parallel to the axis 96 of the insulating support. In addition, the insulating supports 92 and 95 equipped in this way are wired according to the equivalent circuit diagram in Figure 4 and can be designed accordingly as described in the text for Figures 1 to 4.

Figure 14 shows a circular float tube ₁₀₀ in which a float 101 is guided. The tube 100, like the tube 55, is mounted upright during operation. Axially parallel to the float tube 100 is a support tube 102 corresponding to the support tube 1, within which a fitted insulating support 103 is arranged, which is designed in the same way as the insulating support 2 from Figures 1 to 4. In this respect, the embodiment according to Figure 14 is designed in the same way as the

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Example of implementation according to Figure 1. The mode of operation is the same as described in the text for Figures 1 to 4.

In addition to the embodiment according to Figures 1 to 4, however, a second rectangular, magnetically inactive tube 104 is provided, within which rollers 105, 106, 107 are lined up parallel to the axis, which extend with their axis perpendicular to the longitudinal axis 109 of the rectangular tube 104 and are mounted so as to be rotatable about their axes. These rollers are partially magnetized and colored differently on the circumference in different sectors. They are visible through a window 110 in the direction of arrow 111 and, depending on whether the permanent magnet of the float 101 is above or below the rollers, take on different rotational positions, so that for all rollers below the permanent magnet one color segment and for all rollers above the permanent magnet the other color segment is visible from the direction of arrow 111. The border between these different color segments visibly marks the height of the permanent magnet and this can be read on the centimeter scale 115 located next to the window 110.

The rectangular design of the support tube 102, which is advantageous and space-saving for reasons as explained above, proves to be advantageous in combination with the tube 104, because these tubes can easily be made the same size, in such a way that the rollers do not end up too far away from the permanent magnet of the float 101.

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To equip an elongated, flexible, strip ^- shaped insulating support, for example the insulating support 2, with plastic housings, such as the plastic housings 4 to 7, one advantageously proceeds as follows.

First, a plate coated with holes 44 to 47 ... for the connection pins and with a wiring diagram 49 is

Insulation carrier 2 kept ready* The plastic housings 4 to 7 equipped with switches and resistors are then lined up on the support side 3 of the insulation carrier 2, with the connection pins being inserted through the prepared holes.

The insulating support is then bent with the center of curvature on the support side and its connecting side is pulled through liquid solder. The resulting solder joints are then hardened and electrically and mechanically connected to the wiring diagram via the connection pins.

Claims (9)

&bull; · · · * · · &eegr;&igr;&lgr;&ggr;« Af -&igr; ANS PROVERBS 1. Measuring conductor for a level sensor with a flexible, elongated, flat, band-shaped insulating carrier, with elongated electrical resistors of equal length, which are lined up on the insulating support, with elongated, electrical switches of equal length, which can be operated magnetically, whose contacts are in closed tubes filled with protective gas and which are individually assigned to the individual resistors and arranged in a row on the insulated carrier, the resistors and switches are arranged axially parallel to each other on the insulating support with respect to their longitudinal axis, and with a support tube made of magnetically inactive material, into which the insulating support equipped with the resistors and switches is tightly inserted and plugged, characterized in that that the resistors (10) and the switches (9) are arranged with respect to their longitudinal axis (15, 14) perpendicular to the longitudinal axis (8) of the insulating support, and that the support tube (1) has a rectangular cross-section and closely surrounds the cross-sectional contour of the equipped insulating support. 2. Measuring conductor according to claim 1, characterized in that the insulating support ( 2 ) is only wider by minimal insulation material thicknesses on both sides than the individual switches ( 9 ) are long and that the resistors ( 10 ) are shorter than the switches ( 9 ). _ 2 3. Measuring conductor according to one of the preceding claims, characterized in that a resistor (10) with the associated switch (9) is embedded axially parallel next to one another in a common plastic housing (4) made of electrically insulating material, which closely surrounds the switch with the resistor and from which connection pins (30-33) for the switch and the resistor are led out. 4. Measuring conductor according to claim 3, characterized in that the plastic housing (4) has the shape of a* cuboid elongated to the longitudinal axis (14) of the recessed switch (9). 5. Measuring conductor according to one of claims 3 and 4, characterized in that that the insulating support ( 2 ) is approximately as wide as the plastic housing ( 4 ) is long and that the connecting pins (30-33) protrude perpendicularly to one long side (21) of the plastic housing. 6. Measuring conductor according to one of the addresses 3 to 5» characterized by that the resistor ( 10 ) and the switch ( 9 ) are arranged one above the other within the plastic housing, relative to the insulating carrier. 7· Measuring conductor according to one of the preceding claims, characterized in that the resistor (10) is shorter than the switch (9) and is arranged in the longitudinal center of the switch on the side of the switch facing the insulating support (2). ·· ·<« &igr;&igr; iait i * · · « ti a < » » · · I it &igr; 8. Measuring conductor according to one of the preceding claims, characterized in that the plastic housing (4) is arranged on the insulating support with the connection pins (30-33) facing the insulating support (2). 9. Measuring conductor according to one of the preceding claims, characterized in that that the connecting pins (30 - 33) are inserted into prepared holes (44-47) of the insulating support ( 2 ), that an electrically conductive coating (49)> belonging to a circuit is provided immediately adjacent to these holes on the insulating support, that the connection pins are soldered with this coating, and that these solder connections form an electrical contact and the holder of the plastic housing on the insulating carrier