Ladder Diagram Design : Cascade Method
Automation
Cascade
Control System
Design
Electrical Engineering
Engineering
ITS
Ladder Diagram
Method
PLC
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Cascade method is a ladder diagram design method where various steps of the sequence are divided into groups. The rule of this method is "a new group must be started the moment it becomes necessary to shut off any output signal actuated during the presently active group".
Example 1, Suppose four cylinders, A, B, C, D,
START / A+ B+ C+ / C- A- D+ / A+ D- B- / A-
G1 G2 G3 G4
Each group allocated one control relay and connected as RS flip-flop. The switching functions are,
- Y1 = ((START && a1) || Y1) && !Y2
- Y2 = ((Y1 && c2) || Y2) && !Y3
- Y3 = ((Y2 && d2) || Y3) && !Y4
- Y4 = ((Y3 && b1) || Y4) && !a1
- A+ = Y1 || Y3
- A- = (Y2 && c1) || Y4
- B+ = Y1 && a2
- B- = Y3 && d1
- C+ = Y1 && b2
- C- = Y2
- D+ = Y2 && a1
- D- = Y3 && a2
 |
| source [1] |
Example 2,
START / A+ B+ / B- A-
G1 G2
- Y1 = ((START && a1) || Y1) && !Y2
- Y2 = ((Y1 && b2) || Y2) && !a1
- A+ = Y1
- A- = Y2 && b1
- B+ = Y1 && a2
- B- = Y2
 |
| source [2] |
information:
&& = and, || = or, ! = not.
reference:
[1] Industrial Automation: Circuit Design and Components by David W. Pessen
[2] PPT System Automation (M.Rameli & Eka Iskandar)
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