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A Look at Solid State Interlocking

This is a pretty simple arrangement and can be realized by any computer suitably programmed to do the job. We only have to ensure that the equipment is constructed out of hardware which is reliable enough to work satisfactorily. Signaling gears are pretty simple electrical devices like a signal is simply a group of lamps, a point machine a motor , a track circuit as far as the computer is concerned will only be a potential free contact which is to be monitored whether its made or closed. The position of point as well as signals in its simplest form again can be simply fed to the computer as potential free contacts.

The next part is obviously the requirement of safety which is a logical analysis of the state of the points, track circuits and signals. The result of the analysis is to generate commands to operate points, signals as required. The logic of signal operation is also simple remembering that it can be implemented by relay logic or even mechanical logic so it’s a pretty simple job for the modern computers.

So if everything is so simple why don’t we just rig it up and start working it? Consider that while working with a computer we suddenly come across a printer printing garbage due to some mess up somewhere. Everybody using a computer has come across this scenario sometime or the other. The same thing can happen here. The result of this can  be a signal which was supposed to be red turns green allowing a train to come in when it is not supposed to as its route is occupied by something else. There will be accident and this is not what we want. The computer can similarly make a mistake in reading a input and again cause a accident.

To avoid this problem if we use computers we must ensure that this situation do not arise. The first step is to ensure that the hardware used at the last stage is fully fail safe. This a normal computer is not. Whatever is done the last stage driving conventional Railway signaling devices has to be failsafe. This is not a small job and economics of using a normal computer gets highly defeated as due to the complexity of this portion whether conventional computer is used or not becomes technically and economically of insignificant value. 

However, if the development of universal failsafe hardware is done then it can be used universally in such application. A very close example of such a hardware is Microlok equipment of Union Switch & Signal Inc. This equipment is very fundamental in nature in terms of the fact that given a set of logic input to it in a Boolean form it can ensure that the processing of the Boolean logic is done in safe manner and the integrity of the output is fully ensured.

However the hardware of this equipment is not dynamically programmable and the output follows a hardwired program (actually firmware). This or similarly engineered hardware can however be used for a more complete computer capable of processing Railway Signaling applications.

We now have to look at the next important area and the software which will ensure that the hardware is driven in line with the requirements of safety. If we were to use conventional computer software the job would be to write a program which will carry out the commands of the Railway controller and lit signals or move points ensuring basics of Railway Signaling. What it means in general sense 

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