herman116 wrote:
Maybe it also has to do with the safety. I can imagine that the coaster won't work in automatic mode if something like this happened. They can probably give the train a little push and manually stop the train pretty safely but normally a themepark will never use the manual mode when there's a train full of visitors (except for maybe Alton Towers
Normally when something gets stuck or valleys, the PLC doesn't throw an error unless the train is trapped on a PX switch. Even then sometimes nothing happens. You just get a block cascade as logically all it knows is that a unit has not cleared the block and its going to wait until it does. I was one of the first process controls folks to start implementing time based blocking safety checks in ride control systems.
Essentially all we do is monitor X input and Y input, and have a separate piece of logic that says if X input does not trigger by Y input after X amount of seconds, this is a process fault trigger the STOP function.
Most modern control systems have three modes, Automatic, Maintenance, and Maintenance Over Ride. Which breaks down to, does not let you do anything stupid, requires thinking but still will only let you clear errors (ESR) and clear blocks, and Maintenance Over Ride. The last one just so happens to remove all the safeties and does not give a damn if your input results in some catastrophic event happening.
It was never acceptable to go into MO while the ride was loaded, it was semi-acceptable to use ME to fix silly problems, and AUTO was so dumbed down the squirrels could make run it safely.