Internal lock and external lock for point machines

[Peter]

Dear PJW

Could u please help explain the function of the point machines for internal lock and external lock?

It would be really good to see how it is different in a picture.

Thanks
Arnut

The internal and external just refers to whether the Facing Point Lock Function is done in the machine (and is part of the motion of the machine) or externally (separate to the machine mechanism. This link shows a mechanical FPL if you are not familiar with it. I do not have a diagram of a machine that has the FPL inside, but the principle is the same - when the motor has moved the switches over, a bar moves through a port to lock the switches in position.

Peter