Pre-study of new electrical coupling between train cars

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ISRN-UTH-INGUTB-EX-E-2011/06-SE

Examensarbete 15 hp

Augusti 2011

Pre-study of new electrical

coupling between train cars

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Teknisk- naturvetenskaplig fakultet UTH-enheten Besöksadress: Ångströmlaboratoriet Lägerhyddsvägen 1 Hus 4, Plan 0 Postadress: Box 536 751 21 Uppsala Telefon: 018 – 471 30 03 Telefax: 018 – 471 30 00 Hemsida: http://www.teknat.uu.se/student

Abstract

Pre-study of new electrical coupling between train cars

Emanuel Wahlqvist

This study is meant to be an initial study of the possibility to replace the discrete control signal wires over the electrical coupler between train cars with a data bus system. The reason for this is that the electrical coupler is large and heavy due to the high amount of contacts it contains. It is also a problem for manufacturers who are upgrading an existing fleet and need to transfer more signals through a coupler with no spare contacts to use. Except the control signals there are also Ethernet and power signals in the electrical coupler. Some trains also use a bus system for control signals and/or signals containing a large amount of data such as passenger information. This report gives a presentation of some common ways to distribute electrical signals throughout a train used by most manufacturers. It also presents some design

recommendations for a system that would collect existing signals to a bus system and two different design proposals that should be considered if such a system is to be developed.

The study shows that there are already systems on the market for transferring control signals over a bus but they are more aimed for trains under construction. For this reason a new bus system would only be suitable for upgrading existing couplers to free up space in the electrical coupler unit.

ISRN-UTH-INGUTB-EX-E-2011/06-SE Examinator: Nora Masszi

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Sammanfattning

Syftet med examensarbetet är att undersöka möjligheten att använda en databuss för överföring av diskreta styrsignaler över den elektriska kopplingen på ett tågkoppel. Detta skulle drastiskt minska ned storleken och således även vikten på kopplet. Dessutom skulle de bli mycket enklare att uppgradera ett befintligt elkoppel så att det kan bära flera

styrsignaler utan större modifieringar av kopplet.

I kopplet går inte bara de diskreta styrsignalerna utan även Ethernet trafik och

strömförsörjning. En del tåg har även någon form av bussystem för styrsignaler och/eller datakrävande signaler som till exempel passagerarinformation.

Rapporten ger en presentation av de vanligaste metoderna att överföra dessa signaler, några rekommendationer för hur ett nytt bussystem bör utformas samt två förslag på hur ett sådant system skulle kunna se ut hårdvarumässigt. Resultatet av examensarbetet är att ett bussystem är ett bra alternativ vid uppgradering av befintliga elkoppel, men vid

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Thesis work: Pre-study of new electrical coupling between train cars

I

Preface

This report gives a proposal for Dellner Couplers AB (DCAB) how to design an electrical coupler that is smaller than the ones used today. This is not so much for new designs but mostly for upgrading older couplers to carry more signals without replacing the whole electrical coupler unit.

The thesis was initiated and supervised by Lars Möttönen at DCAB. The approval and review was done by Professor Tadeusz Stepinski from Uppsala University.

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II

Table of figures

Figure 1-1: Arrangement of coupler contacts, every signal represented twice. ... 1

Figure 2-1: The CCU and the TCU ... 4

Figure 4-1: Schematic of the data flow in the units ... 9

Figure 4-2: Schematic of the integration of the units on a train... 10

Figure 4-3: Schematic of the integration of the units on a train... 11

Figure 7-1: Schematic of the linear logic converter ... 17

Figure 7-2: With calculated values according to the equations, R3=8.461kΩ, R4=7.857kΩ 18 Figure 7-3: With resistor values from E12 series, R3=8.4kΩ, R4=6.8kΩ ... 19

Figure 7-4: With calculated values according to the equations, R3=57.894kΩ, R4=10kΩ .. 19

Figure 7-5: With resistor values from E12 series, R3=56kΩ, R4=10kΩ ... 20

Figure 7-6: Schematic of non-linear logic converter ... 20

Figure 7-7: With calculated values according to the equations USWITCH=40V, R1=7.02kΩ, R2=180Ω, R3=125Ω ... 22

Figure 7-8: With resistor values from E12 series USWITCH=40V, R1=8.2kΩ, R2=180Ω, R3=120Ω ... 23

Figure 7-9: With calculated values according to the equations USWITCH=8V, R1=1.26kΩ, R2=180Ω, R3=88.7Ω ... 23

Figure 7-10: With resistor values from E12 series USWITCH=40V, R1=8.2kΩ, R2=180Ω, R3=120Ω ... 24

Figure 8-1: Schematic of the Input mux ... 25

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IV

Table of tables

Table 4-1: Risk analysis of multiplexer without microprocessors ... 12

Abbreviations

CRC – Cyclic Redundancy Check CTR – Current Transfer Ratio DEMUX - Demultiplexer

EMI – Electromagnetic Interference FPGA – Field Programmable Gate Array I/O – Input/Output

MSB – Most Significant Byte MUX – Multiplexer

MVB - Multifunction Vehicle Bus OP-amp – Operational amplifier PCB – Printed Circuit Board

PLC – Programmable Logic Controller SIL – Safety Integrity Level

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Thesis work: Pre-study of new electrical coupling

1 Introduction to train couplers

A train coupler is the mechanism

function of a coupler is uninteresting as it is irrelevant to the electr The electrical part of the coupler

shaped as a big rectangular contact

in a train set is identical and one half contains pins one, but with sleeves instead.

cable inside the coupler.

any direction. The coupler also transfers electrical power and Ethernet data traffic signals are not considered in this thesis

Figure 1-1: Arrangement of coupler contacts, every signal represented twice.

The size of the coupler varies with the application and depends on the amount and type of signals being transferred, and

not uncommon, they can get very big.

study of new electrical coupling between train cars

1

Introduction to train couplers

A train coupler is the mechanism that connects two train cars. In this thesis the mechanical function of a coupler is uninteresting as it is irrelevant to the electr

The electrical part of the coupler transfers all electrical signals that control big rectangular contact and mounted on the mechanical coupler

in a train set is identical and one half contains pins. The other half is a mirror of the first one, but with sleeves instead. The signals is wired to one half and linked to the

cable inside the coupler. This is to provide the functionality that any car can be coupled in The coupler also transfers electrical power and Ethernet data traffic

considered in this thesis, as they cannot be multiplexed

: Arrangement of coupler contacts, every signal represented twice.

The size of the coupler varies with the application and depends on the amount and type of signals being transferred, and since 140 or so signals with a four mm pin/sleeve

not uncommon, they can get very big.

between train cars

that connects two train cars. In this thesis the mechanical function of a coupler is uninteresting as it is irrelevant to the electrical coupling.

electrical signals that control the train. It is and mounted on the mechanical coupler. Every coupler

he other half is a mirror of the first The signals is wired to one half and linked to the other with a This is to provide the functionality that any car can be coupled in The coupler also transfers electrical power and Ethernet data traffic but these

multiplexed.

: Arrangement of coupler contacts, every signal represented twice.

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2 How signals are transferred today

Today there are several different ways of transferring an electrical signal throughout the train. The most common way is to combine two different types of signal transfer. One type is to use a dedicated wire that stretches throughout the train, and sometimes even back again. The other type is called Train Communication Network (TCN) and is a combination of two data buses and distributed I/O. Both the dedicated wires and the bus combination are used for control signals, however, some train manufacturers do not entirely trust the bus system for their critical control signals and therefore use the more service proven dedicated wires1.

2.1 Dedicated wires

This is, by some manufacturers, still considered the safest way of transmitting control signals. Some of the signals are even wired in a loop to get a confirmation that they have passed through the whole train. The discrete signals that are transferred by a dedicated wire often have a voltage level of 72 or 110 volts.

Advantages with the dedicated wire transfer type:

• A malfunction is easy to locate because the only ones possible are loss of electrical contact or short circuit.

• The signals have no common component which means that a malfunction in signal “A” does not affect the function of signal “B”.

• The risk that a malfunction occurs because of a failure of a contact in the electrical coupler is very small. Experience from the field says that the frequency of an occurred error is 8*10-9 errors per hour2.

Disadvantages with this transfer type:

• The electrical coupler expands in size, cost and weight.

2.2 Train Communication Network

The TCN is defined in IEC standard 61375-1 that was first published in 1999. The second edition, the one valid today, was published in 2007. The standard defines a combination of two different data buses for I/O management on a train. The names of these buses are MVB and WTB.

2.2.1 Functionality

The MVB is used in separate cars or a set of multiple cars that does not change their composition as they are configured with fixed addresses. In a complete train there will be

1

Nilsson Bo (2011) Customer Service Engineer DCAB (Verbal information)

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several separate buses and the purpose of WTB is to connect these segments with each other. The WTB doesn’t have fixed addresses but instead uses a negotiation called inauguration. The inauguration automatically numbers all units on the bus sequentially starting with the master as number 01, ascending in one direction and descending from 63 in the other. Each node on the bus has one of the following ranks:

• Strong node • Weak node • Slave node

In the inauguration process the ranking is used to decide which node is to become master of the bus. If there is only one strong node present on the bus it automatically becomes the master, but if there are more than one the bus is divided in individual segments with one segment per master. When this occurs the user is notified that a complete bus could not be configured and that he or she should degrade all but one strong master to weak masters as they then will act as slaves. In the case when several segments controlled by weak masters are connected the segment containing the most nodes renames the smaller segment. In the case when they consist of the same amount of nodes a randomized process decide which segment will rename the other. A slave node cannot act as master unless a user tells it to. The other differences is the speed, WTB operates at 1Mbit/s over a shielded twisted pair cable and MVB at 1.5Mbit/s3 over either cables that follow the RS-485 standard for distances up to 20m, a shielded twisted pair cable for connection distances up to 200m or optical fibers for longer distances up to 2km4.

Advantages of the TCN:

• The electrical coupler can be made small and light.

• Opens the possibility of upgrading the train in the future without redesign of the electrical coupler.

• Still operational if a contact fails as long as redundancy is applied. • Embedded functions for logging and diagnosis.

Disadvantages with this transfer type: • More difficult to debug than a wire.

• In case of a bus failure, many signals are affected. 2.2.2 Commercial product example

The Siemens SIBAS 32 control system is a complete solution for controlling a train based on modules, which communicates over the TCN. There are the Central Control Unit who

3

Kirrmann, H and Zuber, Pierre A. (2001) The IEC/IEEE Train Communications Network

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sends the control signals from the drivers cab to the doors, brakes, tracti

other functions. There is also the Traction Control Unit which receives information from the CCU and controls the traction motors. For interfacing to peripheral devices the SIBAS KLIP is used. It is a module for decentralized analog signals

Figure 2-1: The CCU and the TCU

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sends the control signals from the drivers cab to the doors, brakes, tracti

other functions. There is also the Traction Control Unit which receives information from the CCU and controls the traction motors. For interfacing to peripheral devices the SIBAS KLIP is used. It is a module for decentralized analog signals over the TCN.

: The CCU and the TCU

between train cars

sends the control signals from the drivers cab to the doors, brakes, traction control and other functions. There is also the Traction Control Unit which receives information from the CCU and controls the traction motors. For interfacing to peripheral devices the SIBAS

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3 Other transferring methods

An alternative bus system for distributing signals in a train is called distributed I/O. It consists of a PLC with its I/O units located on the other end of a bus. This bus can be configured with the Profisafe protocol which would mean that it meets the requirements of Safety Integrity Level (SIL) 3. SIL is a classification divided into 5 levels (0 is the lowest and 4 the highest) of functional safety in electrical and mechanical systems and is widely used on automation systems in the process industry and is starting to reach the railway industry as well5. The classification is meant to be for a complete system which in this case would mean the whole train but it can also be used for subsystems. To get a reference on how safe the transmission is today the value of contact errors per hour can be used. 8*10-9 errors per hour conform to the hardware requirements of SIL 3 systems6. If a Profisafe bus would be implemented on a train it would automatically reduce the size of the electrical coupler.

This, however, is not in DCAB’s business scope and the implementation of such a system is therefore a matter for the train manufacturers.

A possible solution for DCAB is to develop a similar system that takes use of the individual cables and transfer their logical values over the coupler on a data bus. As this is very much what TCN does it wouldn’t apply for newly developed trains but would be of great use on older ones in the process of being upgraded.

3.1 Standards

If a new bus system where to be accepted by the railway industry it would need to conform to some standard. The problem is which one to choose because it differs between countries which are applicable. To use all of them would be a very time demanding task and probably result in an unreasonably high cost. Based on the fact that DCAB from the beginning is a European company it seems logical to use a European standard and then adapt the system to the demands of other countries if the need arises. Applicable standards would then be EN-50126, EN-50128 and EN-501297. The main consequences for the development by these standards are that the whole development process is to be supervised by an independent firm. The product must then be analyzed and tested for its application according to the requirements of the standards to make sure that every possibility of a dangerous failure is taken care of.

5

Strandberg Per. (2011) Consultant at DCAB, RAMS/LCC-department (Verbal information)

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Siemens AB (2009) Simatic Safety Integrated Practical application of 62061, Kap9.2 Correlation: SIL and PFHD of a SCRF Available at:

http://www.nwe.siemens.com/sweden/internet/se/produkter/industry/automation/as-event/funktionssakerhet/Maskinsakerhet_2009/Documents/Maskinsakerhet_Simatic_Safety_Integrated_Practi cal_application_of_62061.pdf (2011-05-10).

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Before the initialization of such a project it would be a good idea to develop a system with the standards in mind but without the certification. This would work as a proof of concept to present to customers and get a better feeling if they are interested. Together with an extensive market research this would provide a base for the decision if a certified system should be developed or not. It also produces a great opportunity for the possible customers to express their opinions what functions or demands a system like this should have.

3.2 Design guidelines

Based on the three standards mentioned above and discussions with electrical engineers at DCAB the following guidelines should be considered when developing such a concept. One thing that also must be considered is the additional demands on a system that includes software and processors. The main guidelines for such a system are listed in a separate paragraph below.

3.2.1 Guidelines

• To be able to cope with the high voltage logic found on some trains:

o The outputs should be controlling the external components via a relay. The relay should be of solid state type to minimize fault probability and

maintenance as they do not include any mechanical parts.

o The inputs could also be equipped with relays to convert the voltage down to a level suitable for the controlling equipment. However a relay capable of handling about 110VDC control voltage is very large. Instead, a small circuit could be used for the conversion. A design proposal of such a circuit can be seen in annex A.

• A confirmation that the relays are working. • Dual contactors on all mechanical relays.

o This is a demand to reach SIL 3 and 4 because of the mechanical parts that can jam or be worn out.

• Any bus communication should be redundant and by being so the risk of a contact failure disrupting the communication is minimized.

• Cables used for bus communication should be shielded to reduce interference caused by electromagnetic interference (EMI).

• Bus communication shall be made with differential lines.

o The ground level can differ a lot between cars. In a logical system the highest common mode voltage allowed would be less than the smallest difference between:

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Otherwise a signal transferred over a coupler could be misinterpreted. Any differential receivers should therefore have a common mode rejection greater than this voltage.

• Bidirectional bus communication should be configured with full duplex to eliminate the risk of packet collisions.

• If there is a difference between units, they should be able to communicate between each other in every possible combination.

• In the case of an error in the communication the devices should try to reinitiate it. • The units in every car should be connected together with a bus that continues

throughout the train. This minimizes the signal delay between the ends of the train. • The front switch on the coupler could be used by the unit to sense if it is an end unit

or not.

• In the case where a synchronization process takes place:

o It should be continuous to make sure the units never are out of sync.

o The units shouldn’t change the state of any outputs until synchronization has taken place.

• If more than one unit with the ability to change the logical value of a signal is mounted on the same signal cable, it must be done in a manner that prevents short circuiting.

3.2.2 Additional guidelines for systems including software and processors • Redundant processors shall agree before changing the state of an output. • The information sent over the coupler should be checked for errors.

o This minimizes the risk of a bit error resulting in a misinterpreted signal value.

o The profisafe protocol uses a 24 bit cyclic redundancy check8 for a 96 bit transfer. As this is enough for SIL 3 it can be used as a good reference. • The software should be written in a way that makes it easy to understand and

maintain.

o The program should be divided in small sub-programs and then connected together in a main program.

o Every sub program should contain information of the author, version history and a description of its function.

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4 Concept design proposals

This chapter presents two designs made by the author that follow the previously stated guidelines. The main functionality is to compress the signals in the train and send them over the coupler via differential signaling. On the receiving end the signals are

decompressed via relays. The main difference between the designs is that one includes microprocessors.

4.1 Multiplexer with microprocessors

4.1.1 General description

Two units, one master and one slave, are to be mounted in every car. Both units are wired on to the already existing signal cables via a logic converter but only the master is equipped with output relays. This eliminates the risk of short circuiting. In case of a configuration where not only the train computer controls the signals but also switches in each car, the switches can be connected to the master’s inputs instead of the signal cables.

4.1.2 Communication

The units communicate with each other both in the car and over the coupler via redundant serial buses. The buses are identically configured and utilizes CRC to prevent that a signal value changes unintentionally due to a communication error. After every message, the sender will await an acknowledgement that it was received properly. If an error is detected, the unit will send the message again. Whether an error flag is to be set or not, and how a communication error should be affecting the signal outputs is implementation specific and is therefore handled separately in each case.

4.1.3 Change of a signal value

When the train computer changes the value of a signal the change is relayed through the train. The units are configured so that if it receives a message from the bus over the coupler it transmits it on the car-bus and vice versa. By sending the message as soon as it is

received the system makes sure that the delay is as short as possible. After receiving and transmitting of a message the master unit changes the values of the outputs to correspond to the ones stated in the message. Because the slave unit has received the same message as the master it knows what changes to expect and either sends an acknowledgement if the

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Figure 4-1: Schematic

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Schematic of the data flow in the units

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Figure 4-2: Schematic

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: Schematic of the integration of the units on a train

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4.2 Multiplexer

4.2.1 General description

This design is also separated in two different units. One unit called called Output mux. The

and therefore controls the train.

connected to the existing signal cables, the mux via output relays. The

via two separate differential lines.

user need to decide which of them should be active. Output mux can be found in annex B.

Figure 4-3: Schematic of the integration of the units on a train

4.2.2 Input sampling The Input mux consists of

multiplexers signal inputs are wired to the existing signal cables via Logic converter counter controlling the multiplexer

control bits on the multiplexer. This is because the MSB of the counter controls the RESET signal. As the counter value increases the multiplexer sequentially forward the signal values to the signal data line. When all signals have been transmitted, the counter resets and the sequence restart.

4.2.3 Clocks

All units have their own internal

however, the reference clock is divided by 16 before it is used by any components. The skew between the local clocks is therefore at most a sixteenth of a period of the clock after

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ultiplexer without microprocessors

General description

This design is also separated in two different units. One unit called

. The Input mux is mounted in the car that contains the train computer and therefore controls the train. In the other cars an Output mux is mounted. Both units are connected to the existing signal cables, the Input mux via a logic converter

ays. The Input mux transmits data and reset signals to the

separate differential lines. In the case where there are multiple Input muxes, the user need to decide which of them should be active. Schematics of both the

Output mux can be found in annex B.

: Schematic of the integration of the units on a train

Input sampling

consists of a multiplexer with a counter on the control inputs. The signal inputs are wired to the existing signal cables via Logic converter controlling the multiplexer, counter 1, has one more output bit than there are

multiplexer. This is because the MSB of the counter controls the RESET As the counter value increases the multiplexer sequentially forward the signal values to the signal data line. When all signals have been transmitted, the counter resets and the

All units have their own internal reference clock. They are all independent of each the reference clock is divided by 16 before it is used by any components. The skew between the local clocks is therefore at most a sixteenth of a period of the clock after

between train cars

This design is also separated in two different units. One unit called Input mux and another is mounted in the car that contains the train computer

is mounted. Both units are via a logic converter and the Output

signals to the Output muxes In the case where there are multiple Input muxes, the

Schematics of both the Input and

a multiplexer with a counter on the control inputs. The

signal inputs are wired to the existing signal cables via Logic converters. The output bit than there are multiplexer. This is because the MSB of the counter controls the RESET As the counter value increases the multiplexer sequentially forward the signal values to the signal data line. When all signals have been transmitted, the counter resets and the

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a RESET. This skew is small enough not to affect data acquisition. Before the clock is used in the Output muxes they are delayed a fourth of a period to make sure that the signal data from the Input mux has arrived.

4.2.4 RESET command

Every time the MSB of counter 1 goes high it sends a RESET command synchronized on a delayed clock to the Output muxes and resets itself. The clock is delayed a fourth of a period in relation to the clock controlling counter 1 to make sure that the right data from the counter is available to the D flip-flop when the triggering flank arrives. The RESET

command is received by the Output muxes asynchronously and therefore no timing errors will occur due to the delay. In the case of a contact error in the coupler the reset is wired via buffers and pull-resistors to ensure that it always has a specific value. Pull up or down resistors according to schematic is chosen to ensure that no outputs is changed when no reset signal is present. Also a watchdog timer, counter 5, disables the outputs if a RESET command hasn’t arrived one clock cycle after it is supposed to.

4.2.5 Output generation

Counter 4 controls the demultiplexer in the Output mux. The demultiplexer input is constantly logical high and as the counter increases, it is distributed to the different output flip-flops clock input. When a flip-flop senses a rising edge it reads the data signal from the Input mux and sets its output accordingly. The demultiplexer’s enable input is wired to counter 6 which together with an inverter and an AND gate enables it after a specified number of RESET commands has arrived.

4.2.6 Risk analysis

Identified risk Probability Counter action

Contact failure in coupler 8*10-9 failures per hour Watchdog timer on RESET.

Redundant transmission lines

possible for both RESET and DATA. Electromagnetic interference

(EMI)

Always present Shielded and twisted transmission

cables Different ground levels between

cars

Common Differential receivers capable of

handling a high common mode voltage (specific value depending on implementation)

Table 4-1: Risk analysis of multiplexer without microprocessors

4.3 Implementation

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5 Conclusion

It is definitively possible to develop a multiplexing system to replace the wires in an electrical coupler. Electrically it is not a very difficult task; the main obstacle is instead to get the system certified to current standards. Therefore, before any actual design work is done, it is recommended to conduct a thorough investigation of the intended applications and the specific demands on standards. The two main possible application categories are

• On an existing train under the progress of being updated • On a train currently under development

If the multiplexing system is to be applied to a train under development the

recommendation would be to look into TCN or another system with distributed I/O as it would further minimize the cabling throughout the whole train. On the other hand, if the multiplexing system is to be applied on an already existing train the development of a system similar to one of those mentioned above should be developed. This can drastically decrease the size of the coupler, in extreme cases, from 280 contacts to four at the same time as more signals can be transferred.

5.1 Continuing work

The next action to be taken is to decide if a prototype is to be built and in that case, which of the above proposals to follow. The one most suited for a concept is the one without microprocessor as it is a simpler design and the need of documentation is much smaller as it doesn’t contain any software. This shortens the development time and the elimination of software also makes it easy for any electrical engineer to maintain and operate the device. However, if the purpose of a concept is to show the full ability of a multiplexing system a system based on a microprocessor is more suited, as it can utilize a lot more functions, which also can be added after the concept is produced simply by changing the software. Even though wireless communication is not accepted as a safe transfer mode today, the research in that area will most probably come up with a method that can be accepted. This would completely minimize the need of signal pins in the coupler, and can be easily implemented in any of the proposals given in this thesis.

There is also a need to take the decision if a thorough market research should be conducted to utterly clarify the need of a new bus system and what standards it should conform to. Two standards that have been mentioned when the idea of a multiplexing system was first raised by Dellner Australia on behalf of a train manufacturer in Singapore are the

environmental conditions in the IEC standard 60077 and the EMC requirements in

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communication and one similar to the multiplexer with microprocessor presented in this thesis. However, the customer in Singapore dropped the issue after seeing the proposal, so there was no deeper research or development in this issue until this thesis.

At the end of the thesis, a very similar thesis report regarding this very issue was found in the archives at DCAB. That thesis report concludes in a multiplexing system with a single microprocessor, in and output relays, and the transmission over the couplers where

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6 Bibliography

Nilsson Bo (2011) Customer Service Engineer DCAB (Verbal information) Eriksson Conny (2011) RAMS/LCC Engineer DCAB (Verbal information)

Strandberg Per. (2011) Consultant at DCAB, RAMS/LCC-department (Verbal information) Kirrmann, H and Zuber, Pierre A. (2001) The IEC/IEEE Train Communications Network The International Electrotechnical Commission (2007). International standard IEC 61375-1:2007(E), Geneva

Siemens AB (2009) Simatic Safety Integrated Practical application of 62061, Kap9.2 Correlation: SIL and PFHD of a SCRF Available at:

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7 Annex A

7.1 Based on OP

Figure 7-1: Schematic of the

This Logic converter uses voltage division to scale down the input voltage level. The operational amplifier assures that

scales down the input signal to a level manageable for the subsequent electro

R4provide the operational amplifier with a voltage that act as reference for the switching

point between logical high and low. The resistance of R

equations below to suit the application. To eliminate the risk of calculations simpler the value of R

the power supply has the same voltage level as the subsequent electronics logical high level. Calculating R2

Calculating the reference voltage ∗ Calculating R4 →

Calculating the highest possible effect in

" ####

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A – Logic converter

Based on OP-amp

: Schematic of the linear logic converter

Logic converter uses voltage division to scale down the input voltage level. The operational amplifier assures that the output is a distinct discrete signal.

scales down the input signal to a level manageable for the subsequent electro

provide the operational amplifier with a voltage that act as reference for the switching point between logical high and low. The resistance of R2 and R4 is calculated with the

equations below to suit the application. To eliminate the risk of high currents and make the calculations simpler the value of R1 is set to 220kΩ and R3 to 10kΩ

the power supply has the same voltage level as the subsequent electronics logical high

→ $

∗ %

the reference voltage UREF to the operational amplifier

$&

∗ %

Calculating the highest possible effect in R1 at UIN = 135V and R2

614*+

between train cars

Logic converter uses voltage division to scale down the input voltage level. The signal. Resistors R1 and R2

scales down the input signal to a level manageable for the subsequent electronics. R3 and

provide the operational amplifier with a voltage that act as reference for the switching is calculated with the high currents and make the

Ω. It is also important that the power supply has the same voltage level as the subsequent electronics logical high

( 7-1 )

to the operational amplifier

( 7-2 )

( 7-3 )

2 = 0Ω

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, -.∗ 135 ∗ 0.000614 8345 ( 7-5 )

Calculating the highest possible effect in R3 at USUP=5V and R4=0Ω

#### 500*+ ( 7-6 ) , 67∗ 5 ∗ 0.000500 2,545 ( 7-7 ) 7.1.1 Simulations

All simulations where conducted with LTSpice IV

7.1.1.1 UIN=0-135V sweep, USWITCH=60V

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Figure 7-3: With resistor values from E12 series, R3=8.4kΩ, R4=6.8kΩ

7.1.1.2 UIN=0-24V sweep, USWITCH=12V

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Figure 7-5: With resistor values from E12 series,

7.2 Based on non

Figure 7-6: Schematic of non

This circuit uses an optocoupler for sensing the high voltage signal and converting it to low voltage logic. In this circuit the resistors R

application. R1 and R

levels, the desired voltage level for switching from 0 to 1 The logical levels of U

• U0,L – Lowest voltage for a logical 0

• U0,H – Highest voltage for a logical 0

• U1,L – Lowest voltage for a logical 1

0V 2V 4V 0V 1V 2V 3V 4V 5V 0V 4V 8V 12V 16V 20V 24V

20

With resistor values from E12 series, R3=56kΩ, R4=10k

n non-linear circuits

Schematic of non-linear logic converter

This circuit uses an optocoupler for sensing the high voltage signal and converting it to low is circuit the resistors R1, R2 and R3 needs to be matched for the

and R2 will depend on the input voltage UIN and its corresponding logical

, the desired voltage level for switching from 0 to 1, USWITCH

The logical levels of UIN are:

Lowest voltage for a logical 0 Highest voltage for a logical 0 Lowest voltage for a logical 1

6V 8V 10V 12V 14V 16V

V(uout) V(uin)

between train cars

=10kΩ

This circuit uses an optocoupler for sensing the high voltage signal and converting it to low needs to be matched for the

and its corresponding logical

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21 • U1,H – Highest voltage for a logical 1

The voltage required to make the optocoupler switch from 0 to 1,UF and IF the

corresponding current to hold a logical 1. R3 will depend on the CTR of the optocoupler

and the current that flows through the diode at U1,L, IT. A buffer is wired on the output of

the optocoupler to enable a high output current and a distinct output switch and thus R3 will

also be affected by the voltage when the buffer switches from low to high, UB.

To find the resistor values choose a value for R2, typically around 200Ω and set a value for

USWITCH so that U0,H <USWITCH<U1,L. Then calculate a value for R1

$

∗(% )

( 7-8 )

Calculate the current through R1 and R2 when representing a logical 1

= ,% ( 7-9 ) <= = ,>% ( 7-10 ) = ( 7-11 )

Make sure that the current through the optocoupler, IF, is within its recommended values

=

− ( 7-12 )

_<= =

<= − ( 7-13 )

If it fails, reiterate with different values on R2 and/or USWITCH until the demands are met.

Calculate IT _@ = AB$ ∗ ( 7-14 ) _@
<= = AB$ ∗ _<= ( 7-15 ) Calculate R3 $_" = -_<= ( 7-16 )

Make sure that the buffer can handle the voltage and current at _@ Calculating the effect produced in R1

, = _,C− ∗

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22 Calculating the effect produced in R2

, = ∗ ( 7-18 )

Calculating the effect produced in R3 (UT is the voltage drop over the transistor at @ and

IB is the current drawn by the buffer)

, = (₆₇− _@) ∗ (_@− _D) ( 7-19 )

7.2.1 Simulations

In simulations, IF is shown as Ix(Optocoupler:A).

7.2.1.1 UIN=0-135V sweep,U0,H=20V, U1,L=80V, UF=1V, CTR=75%, 5mA<IF<15mA

Figure 7-7: With calculated values according to the equations USWITCH=40V, R1=7.02kΩ,

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23

Figure 7-8: With resistor values from E12 series USWITCH=40V, R1=8.2kΩ, R2=180Ω,

R3=120Ω

7.2.1.2 UIN=0-24V sweep,U0,H=5V, U1,L=18V, UF=1V, CTR=71%, 5mA<IF<15mA

Figure 7-9: With calculated values according to the equations USWITCH=8V, R1=1.26kΩ,

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24

Figure 7-10: With resistor values from E12 series USWITCH=40V, R1=8.2kΩ, R2=180Ω,

R3=120Ω

7.3 Conclusions

7.3.1 Based on OP-amp

The simulations show that changing the calculated resistor values to values present in the E12 series has no significant impact on the system behavior. The biggest difference was noted when using UIN=24V where the USWITCH is changed from 12V to 13V.

7.3.2 Based on non-linear circuits

The simulations show that this design is sensitive to changes in the resistor values. The biggest difference is noted when using UIN=135V where the output does not change until

U1,L + 15V.

7.3.3 Comparison

The sensitivity of resistor values in combination with the trickier calculations is a con for the non-linear design. However, the advantage with galvanic isolation provided by the optocoupler makes it the better choice.

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25

8 Annex B – Schematics

8.1 Input mux

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26

Pre-study of new electrical coupling between train cars

Examensarbete 15 hp

Augusti 2011

Pre-study of new electrical

coupling between train cars

Abstract

Pre-study of new electrical coupling between train cars

Sammanfattning

Preface

Table of contents

Table of figures

Table of tables

Abbreviations

1 Introduction to train couplers

Introduction to train couplers

2 How signals are transferred today

2.1 Dedicated wires

2.2 Train Communication Network

3 Other transferring methods

3.1 Standards

3.2 Design guidelines

4 Concept design proposals

4.1 Multiplexer with microprocessors

4.2 Multiplexer

ultiplexer without microprocessors

4.3 Implementation

5 Conclusion

5.1 Continuing work

6 Bibliography

7 Annex A

7.1 Based on OP

A – Logic converter

Based on OP-amp

7.2 Based on non

n non-linear circuits

7.3 Conclusions

8 Annex B – Schematics

8.1 Input mux

8.2 Output mux