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Exercise: Water Treatment Sequence
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.