DE102023201094A1 - Determining wear of a contact strip - Google Patents

Abstract

The invention relates to an arrangement and a method for determining the wear of a used contact strip of a rail vehicle current collector. Three areas (MB, TB1, TB2) of a contact strip (SL) are monitored by magnetic field sensors (SEN, SEN1, SEN2). A contact wire (FD) contacts the contact strip (SL) to feed in a contact wire current (I). The contact wire current (I) is divided into two partial currents (I1, I2) that flow in assigned partial areas (TB1, TB2) of the contact strip (SL). A central magnetic field sensor (SEN) is provided to monitor a middle area (MB) of the contact strip (SL), so that a central magnetic field (B) caused by the contact wire current (I) is measured at a distance that includes a thickness of the contact strip (SL) in the middle area (MB). Two further magnetic field sensors (SEN1) are provided to monitor the two partial areas (TB1, TB2). During calibration, the magnetic field sensors (SEN, SEN1, SEN2) are arranged on an unused contact strip (SL) in such a way that the electrical signals (S, S1, S2) formed from the magnetic fields (B, B1, B2) add up to a total signal value of zero. When a contact strip is in use, the electrical signals (S, S1, S2) add up to a total signal value that is not equal to zero. This value is used to determine the current thickness of the contact strip (SL) in use in the middle area (MB).

Description

The invention relates to an arrangement and a method for determining the wear of a used contact strip of a rail vehicle pantograph.

A pantograph on a rail vehicle is equipped with one or two pairs of contact strips. The contact strips wear out as the rail vehicle moves when they come into contact with an overhead electric line. The contact strips need to be replaced as soon as a predetermined limit value, such as a minimum thickness or strength of the contact strip, is reached on at least one of the pairs of contact strips.

If the minimum thickness or strength as the required limit is significantly undercut, there is a risk of energy transmission failure via the contact strip and thus a failure of the rail vehicle.

Pantographs are often equipped with a so-called “automatic drop down” system, which automatically lowers the loop bar pairs when the minimum thickness is reached or exceeded.

A worn contact strip is particularly critical in so-called multi-system vehicles, which use different energy supply systems (AC overhead line, DC overhead line, ...) to alternately drive the rail vehicle.

Due to the limited installation space on these rail vehicles, often only one pantograph is provided on board the rail vehicle for an energy supply system, for which there is no additional pantograph for conceivable redundancy.

During periodic maintenance of the current collector or its contact strips, the current condition or the current thickness of the contact strips is determined by measurements (e.g. using a caliper, measuring template, or similar).

• - die zurückgelegte Fahrtstrecke,
• - die durchschnittliche Geschwindigkeit des Schienenfahrzeugs,
• - die Reibung zwischen Oberleitung und Schleifleiste,
• - die thermische Beanspruchung der Schleifleiste während der Stromübertragung,
• - die Kontaktsituation zwischen Schleifleiste und Oberleitung, die durch Eisbildung, Verschleißzustand, Oberflächenstruktur, Funkenbildung, etc., bedingt und beeinflusst wird,
• - usw.

The current condition of the grinding strips is determined by:

• - the distance travelled,
• - the average speed of the rail vehicle,
• - the friction between the overhead line and the contact strip,
• - the thermal stress on the contact strip during current transmission,
• - the contact situation between the contact strip and the overhead line, which is caused and influenced by ice formation, wear, surface structure, sparking, etc.,
• - etc.

After the measurement has been carried out, maintenance specialists will make a rather rough estimate based on their experience as to whether the contact strip in question can continue to be used for an intended future range or whether it needs to be replaced.

If the subsequent operating conditions for the maintained rail vehicle are more stressful than expected, the estimated range does not correspond to reality, so that the probability of failure of the maintained rail vehicle increases.

To address this problem, maintenance professionals tend to estimate future service life conservatively, resulting in contact strips being disposed of preventively, even if they are still capable of remaining in service for a longer period.

Apart from maintenance, the remaining strength or thickness of a used contact strip and the associated remaining range of the rail vehicle at a desired point in time cannot currently be determined or estimated.

It is therefore the object of the present invention to provide an improved method and a suitable arrangement for determining the wear of contact strips in a rail vehicle pantograph in order to determine at any time the remaining strength or thickness of the contact strips used.

This object is achieved by the features of patent claim 1. Advantageous further developments are specified in the dependent patent claims.

The invention relates to an arrangement and a method for determining the wear of a contact strip (SL) of a rail vehicle current collector.

A contact strip has a middle section, a first section and a second section along its length. The middle section is arranged (preferably in the middle) between the two sections.

A contact wire contacts the contact strip in order to feed a contact wire current into the contact strip. The contact wire current is then split into a first partial current that flows in the first partial area and a second partial current that flows in the second partial area.

The two partial streams are essentially equal in size.

A central magnetic field sensor is provided to monitor the central area, so that the central magnetic field sensor measures a central magnetic field caused by the contact wire current at a distance that includes a thickness of the contact strip in the central area.

A first magnetic field sensor is provided for monitoring the first partial area, so that the first magnetic field sensor measures a first magnetic field caused by the first partial current at a distance that includes a thickness of the contact strip in the first partial area. A second magnetic field sensor is provided for monitoring the second partial area, so that the second magnetic field sensor measures a second magnetic field caused by the second partial current at a distance that includes a thickness of the contact strip in the second partial area.

During calibration, the magnetic field sensors are arranged on an unused contact strip for area monitoring in such a way that electrical signals formed from the measured magnetic fields have a total signal value of zero.

When a contact strip is subsequently used, the electrical signals generated from the measured magnetic fields add up to a total signal value that is not equal to zero.

The total signal value of the contact strip used is fed to a vehicle diagnostic device, which, based on this and in comparison to the calibration, determines a current thickness of the contact strip used in the middle range.

In an advantageous further development, the contact wire contacts the contact strip on a first side of the contact strip in a back and forth movement.

In an advantageous development, the central magnetic field sensor is arranged on a second side of the contact strip opposite the first side.

In an advantageous development, the first magnetic field sensor is arranged on a second side of the contact strip opposite the first side.

In an advantageous development, the second magnetic field sensor is arranged on a second side of the contact strip opposite the first side.

In an advantageous development, the contact strip is connected to a contact strip holder. At least one of the magnetic field sensors is preferably attached to the contact strip holder.

In an advantageous further development, the contact wire and the contact strip are preferably aligned with each other in the contact area and are essentially perpendicular to each other in order to form a system geometry.

In an advantageous further development, the system geometry arranges the first and the second magnetic field in respective parallel planes that are orthogonal to the plane of the central magnetic field, so that the magnetic fields are decoupled from each other via their distance and via the orthogonality for the magnetic field measurement.

In an advantageous further development, the sums of the signals of the magnetic field sensors are processed based on their mean values, preferably at predetermined time intervals.

In an advantageous further development, calibration is carried out every time an unused contact strip is installed on the rail vehicle.

In an advantageous further development, the calibration is carried out at the room temperature of the pantograph.

The present invention makes it possible to determine the actual strength or thickness of the grinding strip used at any time.

This enables an improved estimation of the future or remaining range of the rail vehicle over the contact strip under consideration.

The present invention enables an improved or extended use of the contact strip, which is based on actual wear and is free from estimates.

The present invention makes it possible to determine the strength or thickness of the grinding strip used with high precision and without the need for manual measurements.

This saves time, effort and ultimately costs both in maintenance and in replacing contact strips.

• 1 eine Betrachtung von Strömen und Magnetfeldern bei einer Schleifleiste als Basis für die vorliegende Erfindung,
• 2 mit Bezug auf 1 erfindungsgemäß verwendete Magnetfeldsensoren,
• 3 mit Bezug auf 1 und 2 eine Übersicht der Magnetfeldsensoren, Magnetfelder und Ströme bei einer unverbrauchten Schleifleiste,
• 4 mit Bezug auf 3 eine Draufsicht der Schleifleiste, und
• 5 mit Bezug auf die vorstehenden Figuren eine Übersicht der Magnetfeldsensoren, Magnetfelder und Ströme bei einer abgenutzten Schleifleiste.

The invention is explained in more detail below with the help of a drawing. It shows:

• 1 a consideration of currents and magnetic fields in a contact strip as a basis for the present invention,
• 2 with reference to 1 Magnetic field sensors used according to the invention,
• 3 with reference to 1 and 2 an overview of the magnetic field sensors, magnetic fields and currents in an unused contact strip,
• 4 with reference to 3 a top view of the contact strip, and
• 5 With reference to the above figures, an overview of the magnetic field sensors, magnetic fields and currents in a worn contact strip.

1 shows, as a basis for the present invention, a consideration of currents I, I1, I2 and magnetic fields B, B1, B2 in a contact strip SL which is in contact with a contact wire FD.

A contact wire current I flows from the contact wire FD into the contact strip SL and branches there into a first partial current I1 and a second partial current I2 in order to reach further components inside the rail vehicle via associated strands LI, which are provided at both ends of the contact strip SL.

The first partial flow I1 flows through a first partial area TB1 of the contact strip SL, while the second partial flow I2 flows through a second partial area TB2 of the contact strip SL.

The two partial currents I1, I2 are approximately equal, but oppositely aligned to each other.

This means that the following applies to their amounts: $$\text{I}=\text{I1}+\text{I2}.$$

The contact wire current I flowing in the contact wire FD generates a magnetic field referred to as the central magnetic field B. Its approximately circular and closed induction lines lie in a plane that is orthogonal to the longitudinal axis of the contact wire FD.

According to the well-known “Biot-Savart law”, a magnetic field strength of the central magnetic field B is inversely or indirectly proportional to a considered distance r from the contact wire FD. $$\text{So it applies}:\text{B}\sim \text{1}/\text{r}$$

The first partial current I1 generates a first magnetic field B1, whose approximately circular and closed induction lines lie in a plane that is orthogonal to the longitudinal axis of the contact strip SL.

A magnetic field strength of the first magnetic field B1 is inversely or indirectly proportional to a considered distance from the contact strip SL, so that: $$\text{B1}\sim \text{1}/\text{Distance}.$$

The second partial current I2 generates a second magnetic field B2, whose approximately circular and closed induction lines lie in a plane that is orthogonal to the longitudinal axis of the contact strip SL.

A magnetic field strength of the second magnetic field B2 is inversely or indirectly proportional to a considered distance from the contact strip SL, so that $$\text{B2}\sim \text{1}/\text{Distance}.$$

2 shows with reference to 1 Magnetic field sensors SEN, SEN1 and SEN2 of the contact strip SL and their signals S, S1 and S2 used according to the invention.

• - Stromabnehmer sind im Allgemeinen mit zwei Schleifleisten ausgestattet. Eine Energiezuführung vom Fahrdraht einer Oberleitung über die beiden Schleifleisten erfolgt häufig von zwei Unterwerken aus, die sich jeweils vor und hinter einer zugehörigen Kontaktstelle befinden.
• - Da die beiden Schleifleisten auf dem gleichen elektrischen Potential liegen, kann davon ausgegangen werden, dass der Strom, der in einem Drahtabschnitt zwischen den beiden Schleifleisten fließt, vernachlässigbar klein ist im Vergleich zu dem Strom, der von jeder einzelnen Schleifleiste abgenommen wird.
• - Dies ermöglicht es, bei der vorliegenden Erfindung lediglich einen vereinfachten Fall zu analysieren, bei dem nur eine Schleifleiste SL den Fahrdrahtstrom I aus dem Fahrdraht FD entnimmt.

In advance, the following consideration is made for the two contact strips of a pantograph shown here:

• - Pantographs are generally equipped with two contact strips. Energy is often supplied from the contact wire of an overhead line via the two contact strips from two substations, each of which is located in front of and behind a corresponding contact point.
• - Since the two contact strips are at the same electrical potential, it can be assumed that the current flowing in a section of wire between the two contact strips is negligible compared to the current drawn by each individual contact strip.
• - This makes it possible to analyse in the present invention only a simplified case in which only one contact strip SL takes the contact wire current I from the contact wire FD.

• - die Magnetfelder B1 und B2 liegen in jeweiligen parallelen Ebenen,
• - diese Ebenen sind jeweils orthogonal zu der Ebene, in denen das zentrale Magnetfeld B liegt.

The contact wire FD and the contact strip SL are aligned perpendicular to each other, so that a special system geometry is formed:

• - the magnetic fields B1 and B2 lie in respective parallel planes,
• - these planes are each orthogonal to the plane in which the central magnetic field B lies.

In the area of the contact strip SL, preferably on an associated contact strip holder, magnetic field sensors SEN, SEN1 and SEN2 are attached, which detect the respective magnetic field strengths of the magnetic fields B, B1, B2 at the mounting points and convert them into electrical signals S, S1 or S2.

A central magnetic field sensor SEN is arranged below and in a middle or central area MB of the contact strip SL.

Preferably, the central sensor SEN is attached to a contact strip holder that supports the contact strip SL.

The central magnetic field sensor SEN is positioned at a distance from the contact wire FD in the middle area MB of the contact strip SL due to its mounting position and the thickness of the contact strip SL and detects the magnetic field strength of the central magnetic field B at this position. The central magnetic field sensor SEN converts this magnetic field strength into an electrical (central) signal S from the central sensor SEN.

A first magnetic field sensor SEN1 is arranged below and in the first partial area TB1 of the contact strip SL. Preferably, the first sensor SEN1 is also attached to the contact strip holder.

The first magnetic field sensor SEN1 has a predetermined distance from the central magnetic field sensor SEN.

In the first partial area TB1, the first magnetic field sensor SEN1 has a distance to the contact strip SL due to its mounting situation and the thickness of the contact strip SL.

The first magnetic field sensor SEN1 detects the magnetic field strength of the first magnetic field B1 at this position and converts this magnetic field strength into an electrical first signal S1 of the first sensor SEN1.

A second magnetic field sensor SEN2 is arranged below and in the second partial area TB2 of the contact strip SL. Preferably, it is also attached to the contact strip holder.

The second magnetic field sensor SEN2 has the same predetermined distance from the central magnetic field sensor SEN as the first magnetic field sensor SEN1 has from the central sensor SEN. The two magnetic field sensors are thus arranged mirror-symmetrically to the central magnetic field sensor SEN.

In the second partial area TB2, the second magnetic field sensor SEN2 has a distance to the contact strip SL due to its mounting situation and the thickness of the contact strip SL.

The second magnetic field sensor SEN2 detects the magnetic field strength of the second magnetic field B2 at this position and converts this magnetic field strength into a second electrical signal S2 of the second sensor SEN2.

• - dass der zentrale Magnetfeldsensor SEN, der das zentrale Magnetfeld B erfasst, unempfindlich gegenüber den beiden Magnetfeldern B1 und B2 ist,
• - dass der erste Magnetfeldsensor SEN1, der das erste Magnetfeld B1 erfasst, unempfindlich gegenüber dem zentralen Magnetfeld B ist,
• - dass der zweite Magnetfeldsensor SEN2, der das zweite Magnetfeld B2 erfasst, unempfindlich gegenüber dem zentralen Magnetfeld B ist,
• - dass durch den räumlichen Abstand des ersten Magnetfeldsensors SEN1 zum zweiten Magnetfeldsensor SEN2 der erste Magnetfeldsensor SEN1 unempfindlich gegenüber dem zweiten Magnetfeld B2 ist, und
• - dass durch den räumlichen Abstand des ersten Magnetfeldsensors SEN1 zum zweiten Magnetfeldsensor SEN2 der zweite Magnetfeldsensor SEN2 unempfindlich gegenüber dem ersten Magnetfeld B1 ist.

Due to the special system geometry and the positions of the sensors SEN, SEN1 and SEN2 described above,

• - that the central magnetic field sensor SEN, which detects the central magnetic field B, is insensitive to the two magnetic fields B1 and B2,
• - that the first magnetic field sensor SEN1, which detects the first magnetic field B1, is insensitive to the central magnetic field B,
• - that the second magnetic field sensor SEN2, which detects the second magnetic field B2, is insensitive to the central magnetic field B,
• - that due to the spatial distance between the first magnetic field sensor SEN1 and the second magnetic field sensor SEN2, the first magnetic field sensor SEN1 is insensitive to the second magnetic field B2, and
• - that due to the spatial distance between the first magnetic field sensor SEN1 and the second magnetic field sensor SEN2, the second magnetic field sensor SEN2 is insensitive to the first magnetic field B1.

3 shows in a side view and with reference to 1 and 2 an overview of the magnetic field sensors or sensors SEN, SEN1, SEN2, the magnetic fields B, B1, B2 and the currents I, I1, I2 for an unused or unworn SL contact strip.

Due to the unused contact strip SL, the central magnetic field sensor SEN is located rather far away from the contact wire FD, so there is typically a distance of ≥ 40 mm between the two.

The special system geometry described above makes it possible to use the magnetic field sensor ren SEN, SEN1 and SEN2 via their respective positioning.

The calibration is carried out in such a way that the electrical signals S, S1 and S2 assume a signal value of “0” when the contact strip SL is unused or not worn and a contact point of the contact wire FD with the contact strip SL is in the middle of the contact strip SL.

This leads to the following equation with a signal S0 as the resulting signal from the sensors SEN, SEN1 and SEN2: $$\text{S0}=\text{S1}+\text{S2}-\text{S}=0$$

This configuration corresponds to an equilibrium state in which the effects of the magnetic fields B, B1 and B2 generated by the currents I, I1 and I2 cancel each other out.

During the operational operation of the rail vehicle, the contact wire FD is actively guided back and forth via the contact strip SL, whereby this active guidance is realized by a suspension of the contact wire FD along the route traveled by the rail vehicle.

This means that in the middle area MB of the grinding list SL there is a higher material removal on the surface of the grinding strip SL than is the case on the surface of the grinding strip (SL) in the two partial areas TB1, TB2 of the grinding strip SL.

As shown above, the magnetic field sensors SEN1 and SEN2 are positioned laterally in the sub-areas TB1, TB2 and below the contact strip SL or at corresponding locations on the contact strip holder.

The central magnetic field sensor SEN is positioned in the central or middle area and below the contact strip SL or at a corresponding point on the contact strip holder.

The central magnetic field sensor SEN monitors the thickness of the contact strip SL in the middle area MB.

The sensors SEN1 and SEN2 monitor the thickness of the contact strip SL in the corresponding sub-areas TB1, TB2 of the contact strip SL.

4 shows with reference to 3 a top view of the SL contact strip.

5 shows with reference to the previous figures 1 until 4 an overview of the magnetic field sensors SEN, SEN1, SEN2, the magnetic fields B, B1, B2 and the currents I, I1, I2 for a worn contact strip SL.

Compared to 3 The central magnetic field sensor SEN, which is located in the middle area MB of the contact strip SL, is now closer to the contact wire FD due to the increased material removal there.

Typically, there is now a distance of well under 40 mm between the two, for example 25 mm. The value of 25 mm is often assumed to be the operating limit and represents a minimum thickness for the SL contact strip.

Due to the increased material removal in the middle area MB, the corresponding signal S of the central magnetic field sensor SEN changes compared to the calibration described above, while the signals S1 and S2 of the two associated magnetic field sensors SEN1 and SEN2 remain essentially the same.

Due to the Biot-Savart law, this is due to the fact that the sensors SEN1 and SEN2 maintain their distance from the source of the magnetic fields B1 and B2 almost unchanged (because they are installed below less stressed parts of the contact strip), while the central magnetic field sensor SEN continuously reduces its distance from the source of the magnetic field B (contact wire FD, current I) due to material removal.

The increased material removal in the middle area MB of the grinding strip SL leads to a change in the geometry and thus to a change in the equilibrium set during calibration.

The following now applies to the worn SL contact strip shown: $$\text{S0}=\text{S1}+\text{S2}-\text{S}\ne \text{0}\text{.}$$

The electrical signal S0 is processed accordingly and transmitted to a receiving device of a vehicle diagnostic device.

The vehicle diagnostic device is preferably designed as part of the rail vehicle or is part of a remote monitoring system with which the rail vehicle is monitored via a fixed control point, which is referred to as the land side.

The vehicle diagnostic device is used to monitor the wear condition of the SL contact strip, whereby this monitoring can be carried out at any time with regard to the wear condition is up to date and monitoring can be carried out continuously.

Despite the generally high system voltages, the sensors SEN, SEN1 and SEN2 require only a small amount of energy to generate signals.

This makes it possible to power the sensors SEN, SEN1, SEN2 via a rechargeable and/or replaceable battery, the battery being provided in the sensor.

This avoids additional cabling of the magnetic field sensors on the rail vehicle with all its disadvantages.

Preferably, the magnetic field sensors are protected from temperature fluctuations that occur during operation of the rail vehicle. This ensures that the signal measurements can be carried out reliably at any temperature.

Preferably, the signals S, S1 and S2, which contribute to the formation of S0, are processed not based on their instantaneous value, but on their average value. This reduces the influence of deviations that arise in particular due to temperature fluctuations.

Preferably, the mean values are calculated at predetermined time intervals.

The described calibration for specifying or setting S0 = 0 is preferably carried out each time a new, i.e. unused, contact strip is installed on the rail vehicle.

Calibration is preferably carried out at room temperature and under resting conditions of the pantograph.

Claims (10)

Arrangement for determining the wear of a contact strip (SL) of a rail vehicle current collector, - with a contact strip (SL) which has a middle area (MB), a first partial area (TB1) and a second partial area (TB2) in its length, the middle area (MB) being arranged between the two partial areas (TB1, TB2), - with a contact wire (FD) which contacts the contact strip (SL) in order to feed a contact wire current (I) into the contact strip (SL), which is divided there into a first partial current (I1) which flows in the first partial area (TB1) and a second partial current (I2) which flows in the second partial area (TB2), - in which a central magnetic field sensor (SEN) is provided for monitoring the middle area (MB), so that the central magnetic field sensor (SEN) measures a central magnetic field (B) caused by the contact wire current (I) at a distance which determines a thickness of the contact strip (SL) in the middle area (MB) includes, - in which a first magnetic field sensor (SEN1) is provided for monitoring the first partial area (TB1), so that the first magnetic field sensor (SEN1) measures a first magnetic field (B1) caused by the first partial current (I1) at a distance that includes a thickness of the contact strip (SL) in the first partial area (TB1), - in which a second magnetic field sensor (SEN2) is provided for monitoring the second partial area (TB2), so that the second magnetic field sensor (SEN2) measures a second magnetic field (B2) caused by the second partial current (I2) at a distance that includes a thickness of the contact strip (SL) in the second partial area (TB2), - in which during calibration the magnetic field sensors (SEN, SEN1, SEN2) are arranged on an unused contact strip (SL) for area monitoring in such a way that electrical signals (S, S1, S2) formed from the measured magnetic fields (B, B1, B2) add up to a Have a total signal value of zero, - in which, in a subsequently used contact strip, electrical signals (S,S1,S2) formed from the measured magnetic fields (B,B1,B2) summed up have a total signal value of not equal to zero, which is fed to a vehicle diagnostic device (FDV) in order to determine, based on this and in comparison to the calibration, a current thickness of the contact strip used (SL) in the middle area (MB). Arrangement according to Claim 1 , - in which the contact wire (FD) contacts the contact strip (SL) on a first side in a back and forth movement, - in which the central magnetic field sensor (SEN) is arranged on a second side of the contact strip (SL) opposite the first side, and/or - in which the first magnetic field sensor (SEN1) is arranged on a second side of the contact strip (SL) opposite the first side, and/or - in which the second magnetic field sensor (SEN2) is arranged on a second side of the contact strip (SL) opposite the first side. Arrangement according to one of the preceding claims, in which the contact strip (SL) is connected to a contact strip holder and at least one of the magnetic field sensors (SEN, SEN1, SEN2) is attached to the contact strip holder. Arrangement according to one of the preceding claims, in which the contact wire (FD) and the contact strip (SL) are in the contact area with each other in Essentially aligned vertically to form a system geometry. Arrangement according to Claim 4 , in which the system geometry arranges the first and the second magnetic field (B1,B2) in respective parallel planes which are orthogonal to the plane of the central magnetic field (B), so that the magnetic fields (B0,B1,B2) are decoupled from one another via their distance and via the orthogonality for the magnetic field measurement. Method for determining the wear of a contact strip (SL) of a rail vehicle pantograph, - in which a contact strip (SL) is divided in its length into a middle area (MB), a first partial area (TB1) and a second partial area (TB2), the middle area (MB) being arranged between the two partial areas (TB1, TB2), - in which a contact wire (FD) contacts the contact strip (SL) in order to feed a contact wire current (I) into the contact strip (SL), which is divided there into a first partial current (I1) that flows in the first partial area (TB1) and a second partial current (I2) that flows in the second partial area (TB2), - in which a central magnetic field sensor (SEN) is used to monitor the middle area (MB) in order to measure a central magnetic field (B) caused by the contact wire current (I) at a distance, the distance including a thickness of the contact strip (SL) in the middle area (MB), - in which a first magnetic field sensor (SEN1) is used to monitor the first partial area (TB1) in order to measure a first magnetic field (B1) caused by the first partial current (I1) at a distance, the distance including a thickness of the contact strip (SL) in the first partial area (TB1), - in which a second magnetic field sensor (SEN2) is used to monitor the second partial area (TB2) in order to measure a second magnetic field (B2) caused by the second partial current (I2) at a distance, the distance including a thickness of the contact strip (SL) in the second partial area (TB2), - in which, during a calibration, the magnetic field sensors (SEN, SEN1, SEN2) are arranged on an unused contact strip (SL) for area monitoring in such a way that electrical signals (S, S1, S2) formed from the measured magnetic fields (B, B1, B2) add up to form a total signal value of zero, - in which, during a subsequent Electrical signals (S,S1,S2) formed from the measured magnetic fields (B,B1,B2) of the contact strip used are summed to form a total signal value that is not equal to zero and is fed to a vehicle diagnostic device (FDV) which, based on this and in comparison to the calibration, determines a current thickness of the contact strip used (SL) in the middle region (MB). Procedure according to Claim 6 , in which a system geometry is formed by the contact wire (FD), which is aligned essentially perpendicular to the contact strip (SL) in the contact area with the contact strip (SL). Procedure according to Claim 7 , in which the system geometry decouples the first and the second magnetic field (B1,B2), which are arranged in respective parallel planes and which are both orthogonal to the plane of the central magnetic field (B), via their distance and via the orthogonality for the magnetic field measurement. Method according to one of the Claims 6 until 8 , in which the sum of the signals (S,S1,S2) of the magnetic field sensors (SEN,SEN1,SEN2) are processed based on their mean values, preferably at predetermined time intervals. Method according to one of the Claims 6 until 9 where calibration is performed each time a fresh contact strip is installed on the rail vehicle and/or where calibration is performed at room temperature of the pantograph.

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