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Timo Heikkinen / My Courses / TL110103 PLC Control 3 cu / Exercise: Water Treatment Sequence /
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 NameActionsConditions
1Sea water (SW) feedOpen V1V1 opened
2 Start P1P1 running
3Black water (BW) feedOpen V2, V3V2, V3 opened
4 Start P2, start 10 s delayP2 running
5BW treatment ON 10 s elapsed
6BW treatment OFFStop P2, start 20 s delayP2 stopped
7 Close V2, V3V2, V3 closed
8  20 s elapsed
9Start new cycleJump to step 3 
10Stopping of BW treatmentStop P2P2 stopped
11 Close V2, V3V2, V3 closed
12Stop SW feedStop P1P1 stopped
13 Close V1V1 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.

Updated 23.4.2007


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