Designing a car wash

So you have a tunnel 100 ft long
holds up to four cars with staging
four different recipes
1 prewinse/soap tower
2 under carriage wash and rinse
3 rinse and or wax stage
4 stage one of the air blowers
5 stage two of the air blowers

up to four cars can be in the tunnel at once

cars are locked and move at same speed on a conveyor
distance between vehicles can vary based on length of vehicle
each vehicle cycle is started when vehicle rolls over a pressure plate on the track. The recipe is set by operator
as vehicle stages so recipes can also be stages.

So how would you approach this problem

asterof said:

So how would you approach this problem

Click to expand...

Define all my Inputs and Outputs.
Determine the sequence and write it out on paper. Including all inputs necessary to activate a step and what outputs occur during that step.
Convert it to logic that my chosen PLC can use.

Do what Tharon said, then add 4 bit-shift registers (1 bit-shift register for each possible recipe option).

Bit-Shift Register 1: Soap & Prerinse (1) or Not (0)?
Bit-Shift Register 2: Undercarriage Wash (1), or Not (0)?
Bit-Shift Register 3: Wax (1), or Only Rinse (0)?
Bit-Shift Register 4: Air-Dry (1), or Not (0)?

Your instructor wants you to set up your PLC program so that all 4 bits for each car move in PLC memory proportionaly as the car moves down the conveyor.