Proelec Feb 4, 2009:

"Bus Controller Unit" est tout aussi plausible. Il faudrait voir avec le reste du contexte.

Tony M Feb 4, 2009:

B = Brake? From that added bit of context, I can't help wondering if this isn't in fact Brake Control Unit? It seems to me that would be a pretty central and crucial device for a train!

Certianly looks like it, from a quick Google:

Design of the train network simulator based- on train ...

single BCU (Brake Control Unit). Simulator was constructed as 3 standard 19" racks. Each rack corresponds to one vehicle, and each one ...

ieeexplore.ieee.org/iel5/7417/20163/00931811.pdf

Christian Fournier Feb 4, 2009:

BCU peut aussi être "Bus Controller Unit" (dans l'optique de la remarque de Tony)

Jean-Paul ROSETO (asker) Feb 4, 2009:

context BCU CONTROL UNIT T4-T5 - failure mode “ failure of power supply”
Among these failures only the failure #2 is categorised as leading to “train mission not started/completed”. As explained in the remark column of the XX, this categorisation is due to contractual requirements of failure categorisation. From the technical point of view the train can be moved using the back-up brake as reported in “Compensating Prevision“ column and no limitation of speed less to 60 Km/h is necessary.

Tony M Feb 4, 2009:

BCU I strongly suspect that the 'CU' part already stands for 'control unit' — but what the 'B' might stand for is wide open to speculation, especially as you've given us hardly any context to go on: "railways"?

However, I suspect binary counter unit is pretty unlikely, unless there is something you already know about it that you're not telling us; it seems way too low down in the hardware architecture for what seems to be being discussed here (i.e. a pretty high level)