The objective of the system shown in the figure is as follows:

• If push button 1 (PB1) is pushed, red light (RL) turns on. At the same time, the timer T1 is activated and it will provide 15 minutes duration for RL.
• After T1 completes counting time, RL turns off and the green light (GL) turns on and, at the same time, timer T2 is activated and it will provide 15 minutes duration for GL.
• After T2 completes counting time, GL turns off.
• If push button 2 (PB2) is pushed, a light that is currently tuned on will be off.

Note:

• PB1 is normally open contacts and its corresponding output will be energized if it is pressed. It will be open if it is not pressed. However, it is required that an operator should not keep pushing PB1 to keep a light on. PB2 is also a normally open contact.
• In this problem, the relay control C1 and C2 are external devices (external to the PLC) that have input through which they can be energized and have output to indicate that their input is energized (output signal turns ON immediately the input signal is ON).
• C1 is used to keep RL turned on, while its respective timer is counting. C2 does the same for GL.
• A timer is also an external devices that has input (to start counting time) and output (to signal when the counting of time is done after a pre-set value, 15 minutes in this problem)

Construct the ladder logic diagram for the system corresponding to the interface path provided. Assign input and output address (I1, I2, , I8, O1, O2, , O8) to the various elements in the ladder logic and also name each one of these elements in the ladder logic (as RL, GL, PB1, PB2, C1, C2, T1, T2).

Red Light (RL) Device PLC PBI Output Output Input RL Input O Q GL CI O PB1 O 3 Green Light (GL) C2 O4 TI QC20 5 T2 6 o O T2 o PB2 PB2 O Red Light (RL) Device PLC PBI Output Output Input RL Input O Q GL CI O PB1 O 3 Green Light (GL) C2 O4 TI QC20 5 T2 6 o O T2 o PB2 PB2 O