- A push button is used to start a supply fan (controller 1).
- A return fan (controller 2) is interlocked to start automatically with the supply fan.
- In the event of a smoke condition the fans shutdown automatically.
- The supply and return fans cannot be restarted until the smoke detector system is reset (a latching relay is going to be used).
- In the case of excessive smoke, an exhaust fan (controller 3) can be started but only if the smoke detector system has not been reset.
You mention that you have to create a ladder and wire diagram.
Are you going to use a PLC programmed in ladder logic or are you going to do the assignment with relays, hence the need for wire diagram?
If using a PLC, surely there should be some SR (Set/Reset) flip flop software elements in the application? If using relays, latching relays are available (relays with a Set coil and a Reset coil)