Yes, there should be always a speed sensor but usually it goes directly to the console who decides to make the signal for speed control. As soon as you start console should send the lower speed signal to the MCB, then if console receives speed signal correctly and the user wants he can change to faster speed. I would say that is the logic behind.
In my case there is a PLD from Lattice at the MCB, that is the brain for all the logic. I have the datasheet but it´s difficult because it´s programmable.
I would like to know which type of signal or logic is sending console to MCB to change speed through the optocouplers.