A Simple Electronic Circuit for an Automatic Train Safety Stop System

A particular safety system known as “dead man’s circuit” detects the presence of human command in the conduction of the trains operated by the Brazilian Company of Urban Trains (CBTU) in Recife, Brazil, thus consisting a security mechanism that makes automatic braking of any train composition circulating in the transportation system of the city feasible in incidents of loss or apparent loss of driving. Originally, the electrical signal indicating human control in the conduction of the vehicles came from the descent of the traction lever in the driving cabins, which caused the switching of a pair of electrical contacts. Given the importance of the system and the need to avoid repetitive strain injuries to drivers, the need to push the traction knob was eliminated by the use of an electronic device developed by an outsourced company and deployed in the trains of the older fleet. However, the high failure and downtime rates associated with the circuit acquired from the referred contracted company caused the need to develop a more robust and maintenance-friendly design for the dead man’s system. In fact, despite the good performance of the purchased system, the strength of the resin coating that accommodated the capacitive touch sensor assembly at the end of the traction lever prevented the corresponding electronic circuit from any access for research or corrective interventions. Thus, the content of this paper essentially presents the specifications and the description of operation of the alternative electronic circuit designed for the dead man’s system, which is operating normally without electrical defects in 4 old trains for almost a year. Keywords-urban trains; safety system; touch sensor; automatic braking


INTRODUCTION
A large number of techniques based on different maintenance approaches have been proposed to solve various types of maintenance problems [1].These techniques and approaches must be adequate to specific situations and must be adapted to the singular needs of a company [2].Obviously, in any approach, reliability assessments play a key role in determining whether or not a critical system or equipment should be replaced.The older fleet of the metropolitan trains operated by the Brazilian Company of Urban Trains (CBTU) in Recife, Brazil, is composed by vehicles from a Brazilian company, namely CISM.A particular system of these trains, known as dead man's circuit detects the presence of human command in the conduction of the trains, thus consisting of a security mechanism that makes feasible in incidents of loss or apparent loss of driving, automatic braking of any train composition circulating in the transportation system of the city.The high failure and downtime rates associated to the dead man system developed by an outsourced company for the old fleet caused the need to deploy another design of this system.Thus, the current paper essentially presents the specifications and the description of operation of the alternative electronic circuit designed for the dead man's system, which is operating normally without electrical defects in 4 trains since August 2017.

II. HISTORY OF THE SYSTEM
Originally, the electrical signal indicating human control in the conduction of the old railway vehicles of CISM came from the descent of the traction lever in the driving cabins, which caused the switching of a pair of electrical contacts, being continuously necessary for the driver to be with a hand supported on the traction knob to get or keep any train moving.Given the importance of the system and the need to avoid repetitive strain injuries to drivers, the need to push the traction lever to conduct the trains of the old fleet was eliminated by the use of a set consisting of two devices: a touch sensor, installed at the end of the traction handles, and an electronic main module, both shown in Figure 1, developed and installed by an outsourced company admitted by CBTU.Despite the ergonomic advantage, the implemented modification did not increase the reliability of the system and the maintenance quality.The strength of the resin coating that accommodated the touch sensor assembly at the end of the traction lever prevented the corresponding electronic circuit from any access for research or corrective interventions.Due to the lack of technical documentation of the circuits implemented by the outsourced company and the impossibility of accessing the sensor assembly without damaging it, the initial solution adopted to reduce the time of unavailability of trains for commercial operation due to failures in the dead man system was the acquisition of adjustable sensitivity capacitive given the parti capacitive sen the main con pany, did not s stem.The hig the old trains r ve touch senso r to adjust the the old fleet.As the 555 tr agnitude of th gh level when ceiver, which lays K1 and K erminal 2) is q ceiver, the lev ntact occurs, duced voltage low level.Th pidly, only sub pacitor C1.T ghtly different osed metal str ough to activa the traction h ry small electr ( (2) es satisfactoril on region, sinc

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VI. CONCLUSION
The decision about replacing a critical system is sometimes controversial within the planning of the maintenance processes of a company.In fact, resolutions such as these consume time, resources, manpower, and should be carried out by objective considerations about the costs and benefits of the change.Therefore, its effects should also be revised so that new actions can be taken after the disclosure of any unwelcome unrolling.So far, no incident has exposed any relevant vulnerability of the new dead man's system, which is operating normally in four trains for almost a year.There are no electronic components damaged in these vehicles and no complaints from drivers regarding the new traction levers.Although no unexpected event has happened, the operation of the new system continues to be monitored to evaluate the durability and the reliability of the system.In the path between the dead man's system and the programmable logic controller of the brake control circuit, there is a device that can have its timing function incorporated through the CI 555 of the touch sensor.Future developments of the project include this modification.
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TABLE I .
ELECTRICAL CONNECTIONS IN THE MAIN MODULE BOX.Scheme of connections in the main module board.. a