The document outlines a 5-step process for developing a PLC program for a paint spray application system. The steps are: 1) define the task, 2) define inputs and outputs, 3) develop a logical sequence of operation using a flowchart, 4) develop the PLC program, and 5) test the program. It then provides details for each step as applied to a conveyor system that feeds boxes through a spray nozzle, with inputs like start/stop buttons and outputs like conveyor motor and spray valve control.

1. Five Steps to PLC Program
Development
Paint Spray
Application

2. 1. Define the task:
 What has to happen?

3. 1. Define the task:
Paint spraying system where boxes are fed by gravity through a
feeder magazine one at a time on to a moving conveyor belt.
Upon the start signal, boxes are pushed towards the conveyor by
cylinder A which extend and retract operation is controlled by switch S1
and S2.
A spraying nozzle paints each box as it passes by and a detector D1
counts each box being sprayed.
When 20 boxes have been painted the valve V2 shuts off and cylinder
A stops operating.
Eight seconds later the conveyor stops moving and the hopper with its
load now moves to the B+ position where it is emptied.
Thirty seconds later the hopper returns to the original B- position.
End of cycle of operation.

4. 2. Define the Inputs and
Outputs:
 Inputs:
Start Pushbutton – Normally Open – On/Off
Stop Pushbutton – Normally Closed – On/Off
S1 – Valve 1 (cylinder retract) On/Off - NO
S2 – Valve 1 (cylinder extend) On/Off – NO
S3 – Box Detected- On/Off - NO
Outputs:
Motor – On/Off (Conveyor Run)
Valve 1- Cylinder to feed boxes – On/Off
Valve 2- Paint Spray – On/Off
Valve 3- Cylinder to move hopper – On/Off

5. 3. Develop a logical sequence of
operation:
Use a flow chart or sequence table.
Fully understanding the logic before starting to program
can save you time and frustration.
What happens when electrical power and/or pneumatic
air is lost? What happens when the input /
output devices fail? Do we need redundancy?

6. 3. Develop a logical sequence of
operation:

7. 3. Develop a logical sequence of
operation:
Review this sequence with the person with the
most knowledge of the machine. This can be the
designer and / or the machine operator.

8. 4. Develop the PLC program:

9. 4. Develop the PLC program:

10. 4. Develop the PLC program:

11. 4. Develop the PLC program:

12. 4. Develop the PLC program:

13. 4. Develop the PLC program:

14. 4. Develop the PLC program:

15. 4. Develop the PLC program:
Document, Document, Document!
This save you time and money when you have to
return to the program years later.

16. 5. Test the program:

17. 5. Test the program:
Test the program with a simulator or actual
machine. Make modifications as necessary.

18. 5. Test the program:
Check with the people most knowledgeable on
the machine, to see if it is doing what they
expect.

19. 5. Test the program:
Follow up after a time frame to see if any
problems arise that need to be addressed in the
PLC program.

20. PLC Program Development
The five steps form the basis of all PLC
development. You will notice that the actual
programming does not occur until the second
last step. Usually more time is spent on clearly
understanding the task and sequence of
operation.

21. ACC Automation
Practical Tips and Techniques
Spray Paint Application – More information can
be found on our website
More PLC Programming Examples