To eliminate expensive cables along the track, the natural solution is to use a computer network. But to collect SIL4 safety information along the whole track (points – position, track circuits – free/busy), many often very expensive SIL4 input/output modules (or “object controllers”) are needed. To optimize their economic performance, these modules usually offer a large number of inputs/outputs, which raises the problem of cables if the sensors are distributed over the entire distance of the track. For example, this is the case with track circuits.
The low-cost input module from CLEARSY offers a solution to this problem. It allows the networking of each input individually, with the simple safety principle that the power supply of the CLEARSY module is driven by the sensor in the track and constitutes the input of the module. Thus, when the sensor is in a restrictive state (i.e., in the example of the track circuit: the busy state) or in failure, the input module is not powered, which allows to guarantee safety (absence of wrongly permissive information) in SIL4. This approach allows CLEARSY to offer a secure product at a lower cost for each input.
The network protocol allows to keep this security whatever the physical communication medium used along the channel. The CLEARSY module is made of two separate parts, the security part in the track close to the sensor and a part for the network communication, adaptable to any type of network and protocol along the track (optical fiber, radio networks, TCP/IP protocol, RS485, etc.). The network safety information reception system, typically in signaling cabinets, can be realized from safety PLCs, proprietary SIL4 safety computers or those based on the CLEARSY Safety Platform SIL4.
SIL4 safe control of remote equipment
We also propose a module integrating a safety output, to control some remote equipment like a switch. This safety module is close to the equipment to be controlled, and communicates in an open network (specific protocol but implementable on all media) with a safety computer (based on the CLEARSY Safety Platform computer) in the cabinet.
Thus, on the same network, the remote safety computer can control safety outputs: lights, switches, alarms etc… and acquire, if necessary, the information delivered by the equipment thanks to the input modules described above (acquisition of the switch position for example).
Thus, the use of our simple and inexpensive input/output system allows the operation on a single network without the need to run a cable through a signal/cdv/ or other