Question

There are 4 existing relays of 110V. Each relay controls a fan. Now when a fan has a fault the relay turns off. Each existing relay is now connected with a new relay that will output a signal to the (I.e PLC INPUT) to notify a Fan has turned off. Design the following:

1) a)Create a circuit with 4 relays in series with one output signal to a (I.e PLC INPUT).

b) what will happen when there is a fault on relay 2?

2) a)Create a circuit with the 4 new relays in parallel with one output signal.

b)What will happen when there is a fault on relay 2?

3) which type of circuit would be best to use and why?

Answer 1

1)

a)

All four relays are normally closed switches connected with fan as an output. When fan is running all relays are OFF i.e, closed when fan is ON the relays open and notifies PLC input.

b) When there is fault on relay 2 it will open and disconnect the circuit.

2) a)

b) When there is fault on relay 2 then R2 will open and disconnect that line. But other relays are connected the fan will be ON.

3) Series type of circuit is best so that if there is fault is any relay the circuit will and disconnect the PLC input.