Safety circuit design

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Joined Feb 16, 2016
I need to design a truth table and safety circuit however im stuck on some aspects of the question

A powered guillotine uses a motor to position the cutter. The cutter must not operate while the motor is running. There is a guard which must be closed and locked before the cutter can operate but there is a maintenance facility which will allow the cutter to operate with the motor stopped but the guard open. A traffic light system must be incorporated to show when the Guillotine is unsafe (red), safe (green) and when in maintenance mode (amber). The guillotine can only operate once when in maintenance mode.

Draw the Karnaugh map and design the safety circuit using two input NOR gates (use as many as you require).

If each gate has a MTTF 1526173, calculate the MTBF for your circuit (in hours).

How could you redesign the circuit for an improved MTBF?

How could you achieve a MTBF of 1 × 109 hours?

What will the reliability be after 5 years?

That is the question. I designed a truth table but I dont know how you would include the cutter only working once in maintenance mode. I guess you have to put some way for it to remember. For my circuit I have made it using AND gates but I cant convert to NOR gates without effecting the truth table. I think I would need 3 NOR gates for 1 AND gate. For the redesign I think I will need less gates to improve MTBF. Any help is appreciated
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