EP1858034A1 - Electric potentiometer - Google Patents

Abstract

The potentiometer (1) has a carrier plate (6) e.g. printed circuit board, carrying a resistance strip (3). The strip is formed from a resistor arrangement (4) of electrically interconnected discrete resistor units (30) e.g. surface mount device (SMD) components, with preset resistance values. A measuring tap (27) carries a sliding contact that is electrically connected with an electrical connection point (42) of the resistor arrangement along movement track of the strip by an electric connection device in an adjusting position of the tap. The sliding contact is formed as a ridge or brush.

Description

The invention relates to an electric potentiometer according to the preamble of claim 1. A generic electrical potentiometer has three potentiometer connections and a carrier plate which carries a resistance path. The free ends of the resistor track are connected to the first and second potentiometer terminals. Furthermore, a generic potentiometer has a tap, which carries a sliding contact and is connected to the third Potentiometeranschluss.

Generic electrical potentiometers are known as adjustable resistors in the prior art in principle. Their basic structure and their mode of use is, for example, in the textbook " Ekbert Hering, Klaus Bressler, Electronics for Engineers, VDI Verlag Düsseldorf, 1992, chapter 2.2.4 "described.

To produce generic electrical potentiometers, one or more resistance compounds are applied to a carrier element according to the hitherto known methods. These resistive masses form a continuous resistive layer. These are, for example, carbon layers or layers of CERMET, which are layers consisting of metal particles embedded in a ceramic or glass mass.

However, simple layer potentiometers are not very accurate. To increase the accuracy of known potentiometers in a subsequent operation, the resistance layers are aligned with a laser. The resistance layer also serves as a contact surface for the sliding contact, which forms the resistance tap.

Because of the required laser alignment, the previously known method is quite complex and inflexible. Known generic electrical potentiometer with high accuracy are therefore expensive.

It is therefore the object of the present invention to provide a generic electrical potentiometer with high accuracy, which can be produced in a simple and cost-effective manner.

The object is achieved by a generic electrical potentiometer with the characterizing features of claim 1.

According to the invention, therefore, the resistance path is formed from an arrangement of electrically interconnected, discrete resistance elements with predetermined resistance values, and there is a device with which the sliding contact can be electrically connected along its path of movement to predefinable parts of the resistance arrangement in the adjustment range of the tap.

The advantage of the novel electrical potentiometer according to the invention is that the discrete, ie isolated, resistance elements can be selected with predetermined resistance values such accuracy classes that their electrically interconnected arrangement results in a total of a potentiometer of the desired accuracy class. By selecting suitable tolerance classes for the individual resistance elements, the accuracy of the potentiometer can thus be determined and determined from the outset.

The resistance tap on the sliding contact is similar to the known in the prior art potentiometers. However, the change in resistance that occurs between the first or second and third potentiometer terminals when the wiper is moved along its trajectory is no longer continuous, as in the prior art. The resistance value changes rather stepwise. The amount of change from one stage to the next is determined by the resistance value between two contact points between two resistance elements.

A further advantage is that by varying the resistance values, different characteristics, for example linear or nonlinear or continuous or unsteady, etc., of the potentiometer can be realized. The type of characteristic of the potentiometer can also be selected by the type of interconnection of the individual resistive elements, that is, for example, in which type of network the individual resistive elements are connected, whether in series, or parallel or a mixed series and parallel circuit ,

In a particularly advantageous embodiment, the arrangement is a series circuit of resistive elements, and the predeterminable parts of the resistor arrangement, with which the sliding contact can be connected in the adjustment of the tap along its trajectory, are the electrical connection points between the individual resistance elements. An electrical series connection represents the simplest network and is thus one of the preferred possibilities for constructing an electrically interconnected arrangement of resistance elements according to the invention.

It is furthermore very advantageous if the device for electrically connecting the sliding contact with the predeterminable parts of the resistance arrangement comprises contact fields which extend between the electrical connection points of the resistance elements and the movement path of the sliding contact. In this way it is then possible to adapt the geometric arrangement of the series-connected resistance elements on the support plate to the respective space conditions. It is then in the arrangement on the support plate is not limited by the fact that the connection point between each two resistors itself must be in the range of the trajectory of the sliding contact.

The arrangement of electrically interconnected resistor elements may be mounted on the side opposite the sliding contact side of the carrier plate, so that the arrangement of electrically interconnected resistor elements and the sliding contact lie on different sides of the carrier plate. The advantage of such an arrangement is that a smaller and more compact design can be achieved.

The arrangement of electrically interconnected resistor elements according to another advantageous embodiment according to also on the same side of the carrier plate how the sliding contact be attached. The advantage of such an arrangement is that the resistor arrangement is protected by the free rear side of the carrier plate.

Advantageously, the tap is rotatably mounted about an axis of rotation, so that the path of movement of the sliding contact describes approximately a circular arc. This ensures a sufficiently long trajectory of the tap with a small absolute space requirement.

In particular, an embodiment in which the carrier plate is a printed circuit board is very advantageous. It can then be used from the printed circuit board technology and from the technology of the assembly of printed circuit boards known methods and machines for producing a potentiometer according to the invention

Particularly advantageous is in particular an embodiment in which the resistance elements are SMD components and applied in SMD technology on the circuit board. SMD stands for "Surface Mount Device", ie surface-mounted components. As is well known, SMD technology has proven to be a cost effective method in circuit board manufacturing for many years. The resistance components are designed in a special way, namely without connection wires, but with solder material-containing connection points directly at the ends of the example cuboid or cylindrical resistance elements formed.

When loading in the circuit board, the SMD components are placed in their predetermined place and held there. In a subsequent automated soldering process, for example after the so-called wave soldering, liquid solder is then rinsed over the components. At the connection points, the solder joint is made, in all other places the liquid solder rolls off again. The loading and soldering can be done on fully automated machines.

Resistor devices in SMD capable embodiment are available in a wide range of variation and in many accuracy classes. Thus, it is possible to implement arbitrary resistor arrangements with predetermined accuracy in this way cost-effectively.

A further advantage of such an embodiment is that the contact fields, which form the connection points between in each case two resistance elements and the movement path of the sliding contact, are formed as conductor tracks on the carrier plate. The production of such traces on a printed circuit board is one of the basic techniques in printed circuit board manufacturing and is therefore also easy and inexpensive to implement.

To reduce the contact resistance, and to minimize environmental influences, in a further advantageous embodiment, the contact surface of the sliding contact or the contact fields may be gold plated. This is particularly advantageous if it can not be ruled out that even moisture or dirt particles can get to the contact surface.

In a particularly simple and therefore advantageous embodiment of a potentiometer according to the invention, this comprises a potentiometer housing comprising a housing bottom and a housing top part. In this case, the support plate can simultaneously form the housing bottom of the Potentiometergehäuses with their functions as a carrier of the resistor assembly and the trajectory of the tap. This is particularly advantageous if the resistor arrangement and the tap are arranged on the same side of the carrier plate. Because then the back of the support plate is free of electrical components and can be fitted into the upper housing part so that it acts as a protective housing bottom.

The tap is mounted in an advantageous manner on a in the upper housing part about its axis of rotation rotatably mounted contact carrier part. It is then accessible from the side of the upper housing part for an operator, with or without tools, to set the desired resistance.

In an advantageous manner, the contact carrier part is sealed with a sealing means, for example an O-ring, against the upper housing part. In this way, in particular in combination with a sealing housing bottom, a dirt and moisture-proof housing of the potentiometer according to the invention can be achieved.

The sliding contact can advantageously comprise a metallic contact piece, which is held in the contact carrier part and the support plate resiliently applied. Due to the resilient loading a sufficient and temporally constant contact pressure is ensured.

In order to further minimize the effects of dirt particles, the sliding contact can consist of several partial contacts connected in parallel. It can therefore be designed, for example, as a comb or brush.

The production of an electrical potentiometer according to the invention is very cost-effective, in particular if, according to a further preferred embodiment, the contact carrier part and the upper housing part are prefabricated injection-molded parts. These can be manufactured consistently in large quantities and for different types of potentiometers. The distinction between the different types of potentiometers is then determined solely by the dimensioning of the resistor arrangement.

In a particularly simple and therefore preferred embodiment, an inventive electrical potentiometer is composed of only five individual components. These are the components: housing top, contact carrier part, contact piece, sealant and carrier plate.

During assembly, the sealant is inserted into the contact carrier part in a first step. According to one advantageous embodiment described above, an O-ring is inserted into a ring-shaped groove of the contact carrier part adapted to this as the sealing means. In a second step, the contact carrier part is then inserted in a suitable recess in the housing upper part, so that the O-ring between the inside of the housing upper part and the upper width of the contact carrier part causes a seal. In a third step, the contact piece is then inserted into a corresponding recess on the underside of the contact carrier part. In a fifth step, the printed circuit board is then placed and fastened on the still open housing bottom side. The fastening can be done either by locking or by gluing the circuit board to those outer walls of the housing top, or by casting with a sealing and filling compound, or in any other known manner.

Reference to the drawings, in which 2 embodiments of the invention are shown, the invention and further advantageous refinements and improvements of the invention will be explained and described in detail.

Figur 1:

einen Querschnitt (schematisch) durch ein erfindungsgemäßes Potentiometer,

Figur 2:

eine Aufsicht (schematisch) auf ein erfindungsgemäßes Potentiometer, bei dem die Widerstandsanordnung und der Abgriff auf derselben Seite der Trägerplatte angeordnet sind,

Figur 3:

einen Querschnitt (schematisch) durch ein erfindungsgemäßes Potentiometer, wobei die Trägerplatte gleichzeitig als Gehäuseboden dient,

Figur 4:

einen Querschnitt (schematisch) durch ein erfindungsgemäßes Potentiometer, wobei zusätzlich zur Trägerplatte ein Gehäuseboden vorgesehen ist,

Figur 5:

schematisch den Widerstandsverlauf eines erfindungsgemäßen Potentiometers gemäß Figur 2 bis 4 in Abhängigkeit des Drehwinkels, sowie

Figur 6:

einen Querschnitt (schematisch) durch ein erfindungsgemäßes Potentiometer, wobei die Trägerplatte mit einer Dicht- und Füllmasse mit dem Gehäuse verbunden ist.

Show it:

FIG. 1:

a cross section (schematically) by a potentiometer according to the invention,

FIG. 2:

a plan view (schematically) of a potentiometer according to the invention, in which the resistance arrangement and the tap are arranged on the same side of the support plate,

FIG. 3:

a cross section (schematically) by a potentiometer according to the invention, wherein the support plate also serves as a housing bottom,

FIG. 4:

a cross section (schematically) by a potentiometer according to the invention, wherein in addition to the support plate, a housing bottom is provided,

FIG. 5:

schematically the resistance profile of a potentiometer according to the invention according to Figure 2 to 4 as a function of the angle of rotation, and

FIG. 6:

a cross section (schematically) by a potentiometer according to the invention, wherein the carrier plate is connected to a sealing and filling compound with the housing.

1 shows an electric potentiometer 1 with a first potentiometer terminal 15, a second potentiometer terminal 18 and a third potentiometer terminal 21. On the underside of a support plate 6, an arrangement 4 of resistance elements 30 in the form of an electrical series circuit is mounted. The resistance elements 30 are designed as SMD components. They carry at the ends of the parallelepiped resistance body each connecting pieces 31 of solder material.

Of the connecting pieces 31 of each resistor element 30 lead electrically conductive bushings on the opposite side of the support plate 6. There are the conductive bushings each two adjacent resistance elements in one electrical connection point 42 electrically connected. Thus, the electrical feedthroughs provide a means for electrically connecting parts of the resistor assembly 3 to the sliding contact within the adjustment range of the tap 27. In this way, a series electrical connection of the resistance path 3 between the first free end 9 and the second free end 12th

The first free end 9 is also electrically connected to the opposite side of the carrier plate with the first potentiometer terminal 15 with a conductive passage, as well as the second free end 12 is electrically connected by an electrical feedthroughs with the second potentiometer terminal 18.

Connected to the third potentiometer terminal 21 is a tap 27 which terminates in a sliding contact 24. The sliding contact 24 presses resiliently against the resistance path 3 opposite side of the support plate 6. The tap 27 and thus the sliding contact 24 can be moved in the direction of arrow P along its trajectory B parallel to the surface of the support plate 6. The resistance between a free end of the resistance path 3 and the third Potentiometeranschluss 21 then adjusts itself as the value resulting from the series connection of those resistance elements 30 which lie between the respective free end of the resistance path 3 and the electrical connection point 42 through the sliding contact 24 is contacted.

FIG. 2 shows a plan view of a further embodiment of an electrical potentiometer according to the invention. The same or equivalent elements or functional groups bear the same reference numerals as in the figure 1. In the following, therefore, essentially only the differences from Figure 1 will be discussed.

The resistance elements 30, which form the resistor assembly 4 in the form of an electrical series connection of the resistor elements 30 are mounted in the embodiment of Figure 2 on the same side of the support plate 6 as the tap 27. They are circular about the axis of rotation 62 of the contact carrier member 60 around on the Applied top of the circuit board 6. In the contact support member 60 has approximately cylindrical shape, the tap 27 is approximately parallel to the surface of the circuit board 6 extending in the radial direction of this. It is about the axis of rotation 62 of the contact carrier part together with this by an angle of about 270 ° between the initial and the end position rotatable. The third potentiometer terminal 21 is led out laterally as a conductor track to the edges of the printed circuit board 6. Towards the center, the third potentiometer connection 21 widens to form a conductor circuit which surrounds the contact carrier part 60 in a ring shape.

The starting and end points of each two adjacent resistance elements 30 are connected by electrical conductor tracks in each case in an electrical connection point 42. The electrical connection point 42 are also arranged annularly around the axis of rotation 62 around. From each electrical connection point 42 extends radially to the axis of rotation 62 indicative of a contact pad 40, formed as a longitudinally extending rectangular conductor track piece.

At the bottom of the tap 27, hidden in the view of Figure 2 of this, is the sliding contact. This establishes the electrical connection between the contact pad 45 and the circular track in extensions of the third potentiometer terminal 21.

FIG. 5 shows schematically the course of the potentiometer resistance between the first or the second and the third potentiometer connection, plotted on the ordinate in the unit ohm, as a function of the angle of rotation of the contact carrier part 60. The step-shaped course of the resistance which arises when the contactor is clearly visible Sliding contact is moved from one to the next contact field on. The resistance values of the individual resistance elements 30 are predetermined so that a logarithmic curve of the resistance characteristic curve is established.

FIG. 3 shows a cross section through a further embodiment of an electrical potentiometer according to the invention. The same or equivalent elements or functional groups bear the same reference numerals as in the figures 1 and 2. In the following, therefore, essentially only the differences from Figures 1 and 2 will be discussed.

The support plate 6 is used in the embodiment of Figure 3 at the same time as the housing bottom 51 of the housing upper part 54 and the housing bottom 51 formed Potentiometergehäuses 57. The resistance elements 30 are mounted as SMD components on the underside of the support plate 6, corresponding to that shown in Figure 1 Arrangement. The tap 27 on the opposite side of the support plate 6 is part of the contact support member 60. The contact support member 60 has approximately the shape of a cylindrical body 64 with a centrally mounted thereon also cylindrical attachment 65. The attachment 65 is through an opening 61 in the upper housing part 54th performed and outwardly out of this. In the axis of rotation 62 of the contact carrier part 60 is a notch, suitable for engagement of a tool, such as a screwdriver.

At the top of the cylindrical body 64, an O-ring is inserted in an annular groove to know the cylindrical body against the inside of the housing top 54 minus. On the opposite underside of the cylindrical body 64 is a contact recess 28, arranged slightly eccentric. This serves to receive the sliding contact 24. The sliding contact 24 has approximately the shape of a metallic V-shaped expanding spring, which is resiliently acted upon in the opening direction.

At the free end of the sliding contact 24, this runs out into a flattened contact piece 66. To improve the electrical contact, the contact piece 66 is gold plated. In addition, even the contact pad 45 may be gold plated.

Due to the resilient loading of the sliding contact 24 in the opening direction on the one hand, the contact carrier member 60 is pressed with the O-ring 63 against the inside of the upper housing 54, on the other hand, thereby creating the necessary contact pressure on the contact piece 66. In this way, the contact carrier member 60 without additional aids in held the potentiometer 57 in the correct position. This makes the assembly of the potentiometer according to the invention in the embodiment of Figure 3 is very simple and inexpensive.

FIG. 4 shows a variant of the embodiment according to FIG. 3. The same or equivalent elements or functional groups carry the same reference numerals as in FIG. 3. In the following, therefore, essentially only the differences from FIG.

In the embodiment according to FIG. 4, the potentiometer housing 57 is closed by an additional housing bottom 51. The circuit board six is thus complete introduced inside the Potentiometergehäuses 57 and optimally protected from dirt and moisture. The potentiometer terminals are suitably performed and sealed by the potentiometer housing 57.

FIG. 6 shows a cross section through a further embodiment of an electric potentiometer according to the invention, in which the protection against dirt, moisture and other environmental influences is realized in a different way. The same or equivalent elements or functional groups bear the same reference numerals as in the preceding figures 1 to 4. In the following, therefore, essentially only the differences from the preceding figures will be discussed.

In the embodiment according to FIG. 6, the carrier plate 6 is inserted a little way into the upper housing part 54 from its open side, so that a free volume remains between the side of the carrier plate 6 equipped with the resistance elements 30 and the free edge of the upper housing part 54. This free volume is filled with a potting compound 67. On the one hand, it seals the interior of the potentiometer to the outside and serves as protection of the resistance elements 30 and the remaining internal space of the potentiometer from environmental influences, such. As dirt, moisture or mechanical shocks.

LIST OF REFERENCE NUMBERS

1

potentiometer

3

resistance path

4

resistor arrangement

6

support plate

9

first free end of the resistance track

12

second free end of the resistance track

15

first potentiometer connection

18

second potentiometer connection

21

third potentiometer connection

24

sliding contact

27

tap

28

contact recess

31

contact pads

30

resistive element

33

Adjustment range of the tap

36

Device for electrical connection

39

Trajectory of the tap

42

electrical connection point

45

Contact field

48

axis of rotation

51

caseback

54

Housing top

57

potentiometer

60

Contact carrier part

61

recess

62

axis of rotation

63

sealant

64

cylindrical body

65

essay

66

contact piece

67

potting compound

Claims (22)

Electric potentiometer (1) having a support plate (6) carrying a resistance track (3), the free ends (9, 12) of the resistance track (3) being connected to the first and second potentiometer terminals (15, 18), and having a Sliding contact (24) carrying tap (27) which is connected to the third Potentiometeranschluss (21), characterized in that the resistance track (3) of an assembly (4) of electrically interconnected, discrete resistance elements (30) is formed with predetermined resistance values , and in that there is a device (36) with which the sliding contact (24) can be electrically connected along its movement path (B) with predefinable parts (42) of the resistance arrangement (4) in the adjustment range of the tap. Electric potentiometer (1) according to claim 1, characterized in that the arrangement (4) is a series connection of resistance elements (30) and the predeterminable parts (42) of the resistance arrangement (4) are the electrical connection points between the individual resistance elements (30). Electric potentiometer (1) according to claim 1 or 2, characterized in that the means for electrically connecting (36) the sliding contact (24) with the predeterminable parts (42) of the resistor arrangement (4) in between the electrical connection points of the resistance elements (30). and the movement path (B) of the sliding contact (24) extending contact fields (45). Electric potentiometer (1) according to one of the preceding claims, characterized in that the arrangement (4) of electrically interconnected resistance elements (30) and the sliding contact (24) lie on different sides of the carrier plate (6). Electrical potentiometer (1) according to one of claims 1 to 3, characterized in that the arrangement (4) of electrically interconnected resistance elements (30) in and the sliding contact (24) lie on the same side of the support plate (6). Electric potentiometer (1) according to one of the preceding claims, characterized in that the tap (27) is rotatably mounted about a rotation axis, so that the movement path (B) of the sliding contact (24) describes approximately a circular arc. Electric potentiometer (1) according to one of the preceding claims, characterized in that the carrier plate (6) is a printed circuit board. Electric potentiometer (1) according to claim 7, characterized in that the resistance elements (30) SMD components and in SMD technology on the circuit board (6) are applied. Electric potentiometer (1) according to one of the preceding claims, characterized in that the contact fields (45) are formed as conductor tracks on the carrier plate (6). Electric potentiometer (1) according to one of the preceding claims, characterized in that the contact surface of the sliding contact (24) and / or the contact field (45) are gold plated. Electric potentiometer (1) according to one of the preceding claims, characterized in that different characteristics of the potentiometer (1) can be realized by varying the resistance values. Electric potentiometer (1) according to one of the preceding claims, characterized in that by selecting suitable tolerance classes for the resistance elements (30), the accuracy of the potentiometer (1) can be determined. Electric potentiometer (1) according to one of the preceding claims, characterized in that the carrier plate (6) forms the housing bottom of the housing bottom (51) and a housing top part (54) comprising potentiometer housing (57). Electric potentiometer (1) according to one of the preceding claims, characterized in that the carrier plate (6) on the open side of a housing upper part (45) inserted into the upper housing part (45) and sealed on the outside with a potting compound (67). Electric potentiometer (1) according to one of the preceding claims, characterized in that the tap (27) is mounted on a contact carrier part (60) rotatably mounted in the housing upper part (54). Electric potentiometer (1) according to one of the preceding claims, characterized in that the contact carrier part (60) with a sealing means on (63) against the upper housing part (54) is sealed. Electric potentiometer (1) according to one of the preceding claims, characterized in that the sliding contact (24) in the contact carrier part (60) held and the support plate (6) resiliently acting metallic contact piece (66). Electric potentiometer (1) according to one of the preceding claims, characterized in that the contact carrier part (60) and the upper housing part (54) are prefabricated injection molded parts. Electric potentiometer (1) according to one of the preceding claims, wherein the potentiometer (1) is composed of the five individual components housing upper part (54), contact carrier part (60), contact piece (66), sealing means (63) and carrier plate (6). Electric potentiometer (1) according to one of the preceding claims, characterized in that the distance between the individual segments of the contact field (45) is smaller than the width of the sliding contact (24). Electric potentiometer (1) according to one of the preceding claims, characterized in that the sliding contact (24) consists of several parallel connected partial contacts. Electric potentiometer (1) according to claim 21, characterized in that the sliding contact is designed as a comb or brush.

Images