^ 
^ Have a look on the example of my Monday 23.4.2007 lectures!
A sequence application controlling a process shown below is to be made.
| Step # | Step Name | Actions | Conditions |
|---|---|---|---|
| 1 | Sea water (SW) feed | Open V1 | V1 opened |
| 2 | Start P1 | P1 running | |
| 3 | Black water (BW) feed | Open V2, V3 | V2, V3 opened |
| 4 | Start P2, start 10 s delay | P2 running | |
| 5 | BW treatment ON | 10 s elapsed | |
| 6 | BW treatment OFF | Stop P2, start 20 s delay | P2 stopped |
| 7 | Close V2, V3 | V2, V3 closed | |
| 8 | 20 s elapsed | ||
| 9 | Start new cycle | Jump to step 3 | |
| 10 | Stopping of BW treatment | Stop P2 | P2 stopped |
| 11 | Close V2, V3 | V2, V3 closed | |
| 12 | Stop SW feed | Stop P1 | P1 stopped |
| 13 | Close V1 | V1 closed |
The inputs of the valves and pumps as well as the STOP input are simulated using PLC installation plate switches.
The valves have one control output (activated -> valve opens) and close and open limit switch inputs.
The pumps have one control output (activated -> pump runs) and one running feedback input.
First, draw an I/O table on paper.
The sequence starts from step 1 when START input is activated. STOP activation causes the sequence to immediatelly jump to step 10 ("Stopping of BW treatment").
Time permitting, implement running time discrepancy action: if any of the sequence conditions is not met in predefined time, an immediate jump to step 10 is activated.