DE102007033647B4 - Plain bearing and method for transmitting a measuring current - Google Patents

Abstract

bearings for a Swivel joint, in particular plain bearing (1) of a movable roof area a vehicle, for transmission a measuring current, wherein the sliding bearing (1) has a bearing pin (4) and a bearing bush (4) slidably at least partially enclosing the bearing pin (4) (5) and wherein the bearing bush (5) at least one electrically conductive contact spring tongue (6), the bearing pin (5) electrically conductively connected to the bearing bush (5), characterized in that the bearing bush (5) with the contact spring tongue (6) is a one-piece component (8).

Description

The The invention relates to a slide bearing for a rotary joint and method for transmission a measuring current. In particular, the invention relates to a plain bearing a moveable roof area over which measuring currents of a metrological monitoring system of entrapment hazard areas of the movable roof area can be transmitted low impedance. The Sliding bearing has a bearing pin and a bearing bolt at least slidable partially enclosing Bearing bush, wherein the position sleeve at least one electrically having conductive contact spring tongue, the bearing pin electrically conductively connects to the bearing bush.

The Method of transmission a measuring current over a plain bearing of a kinematic joint, in particular a kinematic joint a movable roof area of a vehicle, has the following Method steps, wherein the kinematic joint is a swivel joint is. First is a bushing with a contact spring tongue in a cylindrical Section of the bearing bush equipped. Subsequently, an assembly takes place of the plain bearing under introduction a bearing pin in the bearing bush, wherein the contact spring tongue contacted the bearing pin low impedance. Subsequently, measuring currents of a metrological monitoring system of entrapment hazard areas over the Sliding bearing from the bearing pin to the bearing bush on the Contact spring tongue and / or transferred in the opposite direction become.

such Slide bearings are usually used for mechanical transmission of forces and moments of hinge joints. Your electrical conductivity is unreliable and accordingly is exposed to contact resistance fluctuations of several ohms. This unreliability Mechanical plain bearing results from the bearing tolerances, the an undefined contact pressure between bearing pin and bearing bush of the sliding bearing. Associated with this is the possibility that, for example, random occurring air gaps the line and thus the conductivity deteriorate. Thus, such plain bearings provide no process reliability, in particular in plain bearings of a movable roof area of a Vehicle, the measuring currents in the microampere range for metrological monitoring of pinch hazard areas of Folding and folding roofs transmitted low impedance of a vehicle should.

From the publication DE 10 2005 006 095 A1 For example, an electrically conductive, self-lubricating bearing system and method of using the system is known. For this purpose, the storage system has an electrically conductive carrier, wherein the carrier surface has electrically conductive ribs with recesses or valleys arranged therebetween. These recesses are filled with a self lubricating lubrication material, so that the electrically conductive ribs together with the lubrication material, which consists for example of a plastic compound, the bearing gap to form a bearing bush or a bearing pin. As already stated above, such bearing gaps have tolerances which permit a high fluctuation of the contact resistance of such an electrically conductive, self-lubricating bearing system and offer no process reliability in the transmission of measuring currents.

The DE 1 119 415 B describes a bearing of a shaft (axis) of a movable part of a rotary capacitor. The shaft is supported by four symmetrically arranged leaf springs. Because of the risk of self-induction due to looping, direct contact with the edge of the bore by the shaft is expressly undesirable. The axis diameter is therefore aware only almost as large, so not quite as large as the diameter of the hole 3 chosen by which the shaft is guided.

Erk, A. et al .: Grundlagen der Schaltgerätetechnik, 1974 (3) connector ferrules of appliance sockets. The plug sleeves have contact sleeves with spring-loaded contact parts and act with unsprung massive Pins together.

The DE 198 17 796 C2 describes a device for contact-transmitting electrical signals and energy between at least two relatively movable units, wherein a first of the two units is formed as a wire-shaped brush.

The WO 00/69341 A1 describes a tubular medical instrument for applications within the human body. Extending in an axial direction is an inner tubular housing which receives two slip rings spaced apart from each other in the axial direction. The slip rings each have a cylindrical shape and have a cylindrical support, which rests with its outer surface over the inner wall of the inner housing. Through the two successive slip rings extends a drive shaft which is arranged coaxially with the slip rings and also the inner housing. Cut out of the cylindrical support are inwardly curved contact springs which are integrally connected at one end to the cylindrical support and abut with its other end approximately tangentially on the circumference of the shaft.

The DE 28 36 410 C2 describes a rotary joint. The rotary joint has a coupling housing in which an insert is rotatably arranged. The coupling housing can be inserted and latched into a housing of an electrical hand-held device. On the clutch housing contact springs are attached. The contact springs connect an electrical lead of the handset with slip rings attached to the rotatable insert, which are connected to leads of a power cord attached to the insert.

From pamphlet DE 28 36 410 C2 Starting from an object of the present invention to provide a sliding bearing with a reliable electrical contact, which is inexpensive to produce.

These The object is achieved with the subject matter of the independent claims. advantageous Further developments of the invention will become apparent from the dependent claims.

The Invention builds on a generic plain bearing thereby, that the bearing bush with the contact spring tongue a one-piece component is. This feature has the advantage that the plain bearing with spring contact from a strip material by means of roll production and cutting punches can be easily made.

A Another object of the invention is to provide a sliding bearing and a method for transmission a measuring current to create, regardless of the gap tolerances a sliding bearing a reliable and low-resistance contact resistance and ensures the mechanical Properties of the sliding bearing despite wear on bearing pins and bearing bushing maintains

According to the invention is a Slide bearing created, in particular a plain bearing of a mobile Roof area of a vehicle, and a method of transmission a measuring current over the plain bearing. The plain bearing has a bearing pin and a sliding the bearing pin at least partially enclosing Bushing on. The bushing has at least one electrical conductive contact spring tongue, the bearing pin electrically conductive contacted.

A preferred embodiment provides that the electrical connection between the bearing bush and the contact spring tongue is low impedance.

This Slide bearing has the advantage that the contact spring tongue a permanent high conductivity is also ensured if with the beginning of wear of the bearing the sliding bearing gap changes. Due to the spring force of the contact spring tongue, which is on the bearing pin rests, is constantly a metallic and thus electrically conductive connection low resistance maintained.

In an embodiment invention, the bearing bush has a cylindrical section, the sliding of the bearing bolt at least partially encloses, wherein the contact spring tongue in the cylindrical portion of the bearing bush is arranged. As a result, the contacting takes place in an advantageous manner inside the bearing, so that subsequent processing steps for the Swivel does not affect the function of the contact spring tongue. Even high temperatures of almost 180 ° C, as in a subsequent Corrosion coating processes can occur, the function of the inside the bearing point on the cylindrical portion of the bearing bush arranged contact spring clip does not affect. The bearing bush forms with the contact spring tongue in a further embodiment of the invention one-piece Component. This means that the contact spring tongue the material having the bearing bush and worked out of the bearing bush material has been.

In a further embodiment the invention, the cylindrical portion of the bearing bush a Dividing joint, which is arranged parallel to an axis of a joint is, wherein a freely resilient contact end of the contact spring tongue ends at this parting line. This has a manufacturing advantage, because exactly the contact spring tongue end coincides with the parting line and consequently facilitating the production. Alternatively, the contact spring tongue also opposite be arranged to the parting line, indicating the stability of the bearing bush can improve, since the contact spring tongue is not in the weakened place the parting line of the bearing bush is arranged.

there For example, the contact spring tongue in the cylindrical portion may be radial be aligned. In an alternative embodiment, the contact spring tongue aligned axially parallel in the cylindrical section. In the radial alignment of the contact spring tongue corresponds to the shape of the Contact spring tongue of the cylindrical shape of the cylindrical Section of the sliding bearing. With an axis-parallel alignment however, the contact spring tongue is aligned in a straight line like the axis. Only a pre-stamped Contact area to contact the bearing pin. stands out the cylindrical portion resiliently inwardly out.

As a result of this arrangement and shaping, the slide bearing can have an electrical contact resistance in ohms of less than 1 Ω, and preferably less than 100 mΩ. Decisive here is not only the magnitude of contact resistance but also the constancy of the contact resistance, which is for the metrological monitoring of Einklemmbereichen in kinematics of sliding roof areas of a vehicle is of crucial importance.

Around the self-lubrication of the sliding bearing and the dimensional stability of its To ensure components the bearing bush has a carrier layer and a sliding layer, wherein the carrier layer is a solid metal and the sliding layer is a porous one Sintered metal with Gleitstoffeinlagerungen have. This will guaranteed that the self-lubricating effect is ensured by the Gleitstoffeinlagerungen and through the porous Sintered metal layer is achieved mechanical strength, which the permissible Gap widths of the sliding gap of the sliding bearing guaranteed. The can Gleitstoffeinlagerungen solid lubricants on a polytetrafluoroethylene (PTFE) base exhibit.

The Contact spring tongue can in a further embodiment of the invention only the material of the carrier layer have the bearing bush. In this case, the sliding layer becomes in the area of the future Contact spring tongue removed from the multilayer bearing bush material. Experiments have shown that at a correspondingly high contact pressure the contact spring tongue these both the carrier layer and the sliding layer may have the bearing bush, without significant contact resistance fluctuations occur. This has the advantage that the contact spring tongue on the bearing pin through the support the sliding layer can slide without the bearing pin or the contact area wear the contact spring tongue. To this end, measurements have shown that the contact resistance by maintaining the sliding layer does not differ significantly from a contact resistance at a sliding zone of carrier layer material the bearing bush is provided.

Furthermore it is also possible to realize the contact spring tongue by a wear-resistant spring bronze. In the case, if not coincidentally, also the carrier material the bearing bush consists of a spring bronze, then is the contact spring tongue made of spring bronze with the cylindrical portion of the bearing bush electrically conductive and cohesive connected. The cohesive connection can by spot welding, Diffusion soldering, Hartlotlöten or by gluing. When gluing is on it though to ensure that a conductive adhesive is used.

Further has such a bearing bush at least on one end face of the cylindrical portion on a disc-shaped collar, which has a fixation on an articulated arm of the rotary joint joint allows. Such a sliding bearing described above is preferably for joint linkage a Kinematics of a folding or folding roof of a vehicle with metrological monitoring of Einklemmgefährdungsbereichen used.

The Invention is based on the generic method for transmission a measuring current characterized in that the bearing bush with the contact spring tongue a one-piece Component forms. An easy manufacturability is given.

This Procedure has as well the advantage that during insertion of the bearing pin in the bearing bush, a contact pressure of the contact spring tongue is exerted on the jacket of the bearing pin. This contact pressure makes sure that the contact resistance remains low, or the electrical conductivity of such a sliding bearing constant, independent of the angle of rotation and on the Life of the plain bearing is consistent. It can when inserting the Bearing in the bearing bush a contact resistance through the Contact spring tongue smaller than 1 Ω, preferably even less than 100 mΩ can be achieved.

One Method for producing an electrically conductive plain bearing for a Rotary joint, in particular a sliding bearing of a movable roof area a vehicle, for transmission a measuring current has the following method steps. First a metal strip is provided which comprises a carrier layer and a sintered metallic layer Sliding layer with Gleitmitteleinlagerungen for a bearing bush has. Subsequently a cutting punching a contact spring tongue with pre-stamping of a Contact area of the contact spring tongue in the metal band in areas, which are to be formed into a cylindrical portion of the bearing bush. Thereafter, the metal strip is separated into sections for bearing bushes.

Finally done the deformation of the sections to bushings with contact spring tongue and with a one-sided collar. In this condition, the bearing bush with its unilateral collar on one of two components of a Swivel joint to be mounted to a bearing point. After that is the bearing with the molding of an opposite Federal and the manufacture of tolerances and / or fits the Bearing point to the bearing pin by means of a calibration mandrel or a calibration tool calibrated.

Finally, a positive and non-positive connection of the bearing pin takes place in a second component of the swivel joint to produce an electrically conductive connection. Finally, it is then possible to apply a nationwide corrosion protection on the finished hinge joint. At this Aufbrin gen is already the contact spring tongue protected by its location in the interior of the bearing from interference with such a coating. Because such a coating can be done at about 180 ° C, for example in a powder coating, the contact point or the contact spring tongue must survive such a temperature without damage.

in the Interior of the bearings at the arranged the contact spring tongue is, there is good protection against corrosion. At the shown here Production of the contact spring tongue from the material of the bearing bush the area of the contact spring tongue only has to be made of the material the bushing be unlatched and then bent or embossed. It can these processing steps of a manufacturing process for rolled Sockets are provided. Likewise, it is also conceivable during the Manufacturing process, the area of the spring contact, for example to harden with a laser beam. However, the for the forming process of the rest of the bush, to a cylindrical section with covenant and for the calibration during assembly the softer properties needed maintain.

One The second collar can be calibrated by calibrating the bearing bush on an opposite Formed end face of the cylindrical portion of the bearing bush become. The Anformung has the advantage that the inner region of the bearing bush with the contact spring tongue is not affected and the function the contact spring tongue during calibration of the bearing bush and the Formation of the second covenant is preserved.

Furthermore It is envisaged that the positive and non-positive connection of the bearing pin in the second component of the swivel joint by means of wobble rivets he follows. After assembly of such a plain bearing can the application of a nationwide Corrosion protection by means of a powder coating on the finished Assembly performed become. In this case, preferably a cathodic dip coating used. For this purpose, the cathodic dip painting can be done on a hood frame, its entrapment hazard areas monitored metrologically by means of smallest measuring currents in the microampere range should be.

The The invention will now be described with reference to the accompanying figures.

1 shows a schematic perspective view of a sliding bearing of a first embodiment of the invention;

2 shows different schematic views A, B and C of the bearing bush of the sliding bearing according to 1 ;

3 shows different schematic views A, B and C of a bearing bush of a sliding bearing of a second embodiment of the invention;

4 shows different schematic views A and B of a bearing bush of a sliding bearing of a third embodiment of the invention.

1 shows a schematic perspective view of a sliding bearing 1 a first embodiment of the invention. This slide bearing 1 has a plain bearing bush 5 and a bearing pin 4 on, with bearing bush 5 and the bearing pin 4 coaxial with an axis 10 a rotary joint connection are arranged. The bearing bush 5 slides with a cylindrical section 7 made of a backing layer 12 and a sliding layer 13 exists on the mantle surface 18 of the bearing bolt 4 , At the front ends 14 and 15 is each a covenant 16 and 17 arranged, which fix the bearing bush in an articulated arm, not shown.

The bearing bolt 4 acting cooperates with a second articulated arm of a rotary joint joint. In this first embodiment of the invention is a contact spring tongue 6 radially aligned from the material of the cylindrical portion 7 the bearing bush 5 elaborated. The contact tongue 6 has a free-spring contact spring end 11 on, in which a contact spring area 19 the contact spring tongue 6 is impressed and a contact pressure on the lateral surface 18 of the bearing bolt 4 exercises.

Such a depository 20 has the advantage that not only mechanical forces can be transmitted through the rotary joint connection, but also that low impedance minimum measuring currents in the microampere range from a first articulated arm not shown here to a second articulated arm not shown here via the bearing pin 4 , the contact spring tongue 6 and the bearing bush 5 can be transmitted.

2 shows different schematic views A, B and C of the bearing bush 5 of the plain bearing 1 according to 1 , The view A is a side view, in which a parting line 9 can be seen, which results from the rolling production of the plain bearing bush made of a strip material. The contact spring tongue became preparatory from the strip material by means of cutting punches 6 with her contact spring area 19 produced. Here is the contact spring tongue 6 opposite to the parting line 9 arranged and forms with the bearing bush 5 a one-piece component 8th ,

The view B of the 2 shows a plan view on the bearing bush shown in view A. 5 , where clearly the free spring end 11 the contact spring tongue 6 you can see.

The view C of 2 is a left side view of the view A and shows the contact spring 6 in its almost complete length with the contact area 19 , With the contact spring tongue 6 a pressure can be exerted on a lateral surface of a bearing pin.

3 shows different schematic views A, B and C of a bearing bush 5 a plain bearing 2 a second embodiment of the invention. For this purpose, the view A shows a side view of the parting line 9 , In this embodiment of the invention, the free-resilient contact end 11 at the parting line 9 is arranged, which is technically feasible.

The view B of the 3 shows a perspective view of the bearing bush 5 , which is made here of two materials, namely a carrier layer 12 and a sliding layer 13 , wherein the sliding layer 13 consists of a porous sintered metal, while the carrier layer 12 has a solid metal. In the cylindrical section 7 the bearing bush 5 For example, the pores of the sliding layer or of the sintered metal are filled with a solid lubricant based on a polytetrafluoroethylene, which ensures self-lubrication of the sliding bearing 2 provides.

The view C of 3 is a plan view of the bearing bush 5 as shown in view A. In the cylindrical section 7 the bearing bush 5 is in turn the contact area 19 the contact spring tongue 6 clearly visible, extending from the inner surface of the cylindrical section 7 takes off.

4 shows different schematic views A and B of a bearing bush 5 a plain bearing 3 a third embodiment of the invention. Components having the same functions as in the previous figures are identified by the same reference numerals and will not be discussed separately.

Both the view A and the view B are arranged in perspective and allow a view of an axially parallel arranged contact spring tongue 6 , in contrast to the radially symmetrically arranged contact spring tongues of the embodiments according to 1 to 3 , Such an axially parallel aligned contact spring tongue 6 assumes that they are not adjacent to the parting line 9 is provided. In this third embodiment of the invention, the contact spring tongue 6 opposite to the parting line 9 arranged, but this is not absolutely necessary, as long as the first fret 16 the bearing bush 5 holds together.

1

bearings (1st embodiment)

2

bearings (2nd embodiment)

3

bearings (3rd embodiment)

4

bearing bolt

5

bearing bush

6

Contact spring tongue

7

cylindrical Section of the bearing bush

8th

one-piece component

9

parting line

10

axis of a joint

11

free resilient contact spring end

12

backing the bearing bush

13

Overlay

14

front

15

front

16

Federation

17

Federation

18

coat of the bearing bolt

19

contact area the contact spring tongue

20

depository

Claims (26)

Sliding bearing for a rotary joint, in particular plain bearings ( 1 ) of a movable roof area of a vehicle, for transmitting a measuring current, wherein the plain bearing ( 1 ) a bearing pin ( 4 ) and a bearing pin ( 4 ) sliding at least partially enclosing bearing bush ( 5 ) and wherein the bearing bush ( 5 ) at least one electrically conductive contact spring tongue ( 6 ), which the bearing pin ( 5 ) electrically conductive with the bearing bush ( 5 ), characterized in that the bearing bush ( 5 ) with the contact spring tongue ( 6 ) an integral component ( 8th ). Sliding bearing according to claim 1, characterized in that the bearing bush ( 5 ) a cylindrical section ( 7 ), the bearing bolt ( 4 ) at least partially encloses, and wherein the contact spring tongue ( 6 ) in the cylindrical section ( 7 ) is arranged. Sliding bearing according to claim 1 or claim 2, characterized in that the electrical connection between bearing bush ( 5 ) and contact spring tongue ( 6 ) is low impedance. Slide bearing according to one of the preceding claims, characterized in that the contact spring tongue ( 6 ) the material of the bearing bush ( 5 ) having. Slide bearing according to claim 2, characterized in that the cylindrical portion ( 6 ) a parting line ( 9 ) parallel to an axis ( 10 ) of a joint, and a free-springing contact end ( 11 ) of the contact spring tongue ( 6 ) ends at this parting line. Slide bearing according to claim 2, characterized in that the cylindrical portion ( 7 ) a parting line ( 9 ), which is arranged axially parallel, and the contact spring tongue ( 6 ) opposite to the parting line ( 9 ) is arranged. Slide bearing according to claim 2, characterized in that the contact spring tongue ( 6 ) in the cylindrical section ( 7 ) is radially aligned. Slide bearing according to claim 2, characterized in that the contact spring tongue ( 6 ) in the cylindrical section ( 7 ) is aligned parallel to the axis. Plain bearing according to one of the preceding claims, characterized in that the plain bearing ( 1 ) has an electrical contact resistance in ohms less than 1 Ω, preferably less than 100 mΩ. Sliding bearing according to one of the preceding claims, characterized in that the bearing bush ( 5 ) a carrier layer ( 12 ) and a sliding layer ( 13 ), wherein the carrier layer ( 12 ) a massive metal and the sliding layer ( 13 ) has a porous sintered metal with Gleitstoffeinlagerungen. Slide bearing according to claim 10, characterized that the lubricant deposits are solid lubricants based on PTFE exhibit. Slide bearing according to claim 10 or claim 11, characterized in that the contact spring tongue ( 6 ) the material of the carrier layer ( 12 ) of the bearing bush ( 5 ) having. Slide bearing according to one of claims 10 to 12, characterized in that the contact spring tongue ( 6 ) the carrier layer ( 12 ) and the sliding layer ( 13 ) of the bearing bush ( 5 ) having. Slide bearing according to one of the preceding claims, characterized in that the contact spring tongue ( 6 ) has a wear-resistant spring bronze and with the cylindrical portion ( 7 ) of the bearing bush ( 5 ) is electrically conductively and materially connected. Sliding bearing according to one of the preceding claims, characterized in that the bearing bush ( 5 ) on end faces ( 14 . 15 ) of the cylindrical section ( 7 ) at least one disc-shaped collar ( 16 ) having. Use of plain bearing ( 1 ) according to one of the preceding claims for linkage kinematics of a folding or folding roof of a vehicle with metrological monitoring of Einklemmgefährdungsbereichen. Method for transmitting a measuring current via a plain bearing ( 1 ) of a kinematic joint, in particular of a kinematic joint of a movable roof area of a vehicle, the method having the following method steps and the kinematic joint being a swivel joint, equipping a bearing bush ( 5 ) with a contact spring tongue ( 6 ) in a cylindrical section ( 7 ) of the bearing bush ( 5 ); characterized in that the bearing bush ( 5 ) with the contact spring tongue ( 6 ) an integral component ( 8th ) forms; - Assembly of the sliding bearing ( 1 ) while inserting a bearing bolt ( 49 into the bearing bush ( 5 ), wherein the contact spring tongue ( 6 ) the bearing pin ( 4 ) contacted with low resistance; - Transmission of measurement currents of a metrological monitoring system of Einklemmgefährdungsbereichen on the slide bearing ( 1 ) from the bearing pin ( 4 ) to the bushing ( 5 ) via the contact spring tongue ( 6 ) and / or in the opposite direction. A method according to claim 17, characterized in that the contact spring tongue ( 5 ) during insertion of the bearing pin ( 4 ) in the bushing ( 5 ) a contact pressure on the jacket ( 18 ) of the bearing pin ( 4 ) exercises. A method according to claim 17 or claim 18, characterized in that during insertion of the bearing pin ( 4 ) in the bushing ( 5 ) sets a contact resistance in ohms smaller than 1 Ω, preferably smaller than 100 mΩ. Method for producing an electrically conductive plain bearing ( 1 ) for a rotary joint, in particular a sliding bearing of a movable roof area of a vehicle, for transmitting a measuring current, the method comprising the following method steps, - providing a metal strip from a carrier layer ( 12 ) and a sintered metallic sliding layer ( 13 ) with lubricant storage for a bearing bush ( 5 ); - Cutting punches of a contact spring tongue ( 6 ) with preprinting of a contact area ( 19 ) of the contact spring tongue ( 6 ) in the metal strip in areas that form a cylindrical section ( 7 ) of the bearing bush ( 5 ) are formed; - separating the metal strip into sections ( 7 ) for bushings ( 5 ); - deforming the sections ( 7 ) to bushings ( 5 ) with contact spring tongue ( 6 ) and unilateral collar ( 16 ); - mounting the bearing bush ( 5 ) in one of 2 components of a hinge connection to a La workstation ( 20 ); - Calibrating the bearing ( 20 ) with molding of an opposite federal ( 17 ) and the tolerances and / or fits of the bearing ( 20 ) to the bearing pin ( 4 ) by means of a calibration mandrel or tool; - positive and non-positive connection of the bearing pin ( 4 ) in the second structural member of the hinge joint to form an electrically conductive connection; - Application of a comprehensive corrosion protection on the finished hinge joint. A method according to claim 20, characterized in that the deformation of the sections into cylindrical sections ( 7 ) of bushings ( 5 ) is achieved by means of a rolling process. Method according to claim 20 or 21, characterized in that the opposite collar ( 17 ) is positively formed Method according to one of claims 20 to 22, characterized in that the positive and non-positive connection of the bearing pin ( 4 ) takes place in the second component of the swivel joint by means of wobble rivets. Method according to one of claims 20 to 23, characterized that applying a nationwide Corrosion protection by means. a powder coating on the finished Assembly takes place. Method according to one of claims 20 to 24, characterized that applying a nationwide Corrosion protection by means of a cathodic dip coating (cathodic dip painting) the finished assembly takes place. Method according to one of claims 20 to 25, characterized that applying a nationwide Corrosion protection on a hood frame is done, its Einklemmgefährdungsbereiche monitored metrologically by means of smallest measuring currents in the microampere range become.